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Artigos de revistas sobre o assunto "Membrane receptor-Ligand interactions"
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Langelaan, David N., e Jan K. Rainey. "Membrane catalysis of peptide–receptor bindingThis paper is one of a selection of papers published in this special issue entitled “Canadian Society of Biochemistry, Molecular & Cellular Biology 52nd Annual Meeting — Protein Folding: Principles and Diseases” and has undergone the Journal's usual peer review process." Biochemistry and Cell Biology 88, n.º 2 (abril de 2010): 203–10. http://dx.doi.org/10.1139/o09-129.
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The membrane catalysis hypothesis states that a peptide ligand activates its target receptor after an initial interaction with the surrounding membrane. Upon membrane binding and interaction, the ligand is structured such that receptor binding and activation is encouraged. As evidence for this hypothesis, there are numerous studies concerning the conformation that peptides adopt in membrane mimetic environments. This mini-review analyzes the features of ligand peptides with an available high-resolution membrane-induced structure and a characterized membrane-binding region. At the peptide–membrane interface, both amphipathic helices and turn structures are commonly formed in peptide ligands and both hydrophobic and electrostatic interactions can be responsible for membrane binding. Apelin is the ligand to the G-protein coupled receptor (GPCR) named APJ, with various important physiological effects, which we have recently characterized both in solution and bound to anionic micelles. The structural changes that apelin undergoes when binding to micelles provide strong evidence for membrane catalysis of apelin–APJ interactions.
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Ledig, Matthias M., Fawaz Haj, John L. Bixby, Andrew W. Stoker e Bernhard K. Mueller. "The Receptor Tyrosine Phosphatase Crypα Promotes Intraretinal Axon Growth". Journal of Cell Biology 147, n.º 2 (18 de outubro de 1999): 375–88. http://dx.doi.org/10.1083/jcb.147.2.375.
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Retinal ganglion cell axons grow towards the optic fissure in close contact with the basal membrane, an excellent growth substratum. One of the ligands of receptor tyrosine phosphatase CRYPα is located on the retinal and tectal basal membranes. To analyze the role of this RPTP and its ligand in intraretinal growth and guidance of ganglion cell axons, we disrupted ligand- receptor interactions on the retinal basal membrane in culture. Antibodies against CRYPα strongly reduced retinal axon growth on the basal membrane, and induced a dramatic change in morphology of retinal growth cones, reducing the size of growth cone lamellipodia. A similar effect was observed by blocking the ligand with a CRYPα ectodomain fusion protein. These effects did not occur, or were much reduced, when axons were grown either on laminin-1, on matrigel or on basal membranes with glial endfeet removed. This indicates that a ligand for CRYPα is located on glial endfeet. These results show for the first time in vertebrates that the interaction of a receptor tyrosine phosphatase with its ligand is crucial not only for promotion of retinal axon growth but also for maintenance of retinal growth cone lamellipodia on basal membranes.
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Behling, Ronald W., e Lynn W. Jelinski. "Importance of the membrane in ligand-receptor interactions". Biochemical Pharmacology 40, n.º 1 (julho de 1990): 49–54. http://dx.doi.org/10.1016/0006-2952(90)90177-m.
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KATZ, A., D. RHODES e L. HERBETTE. "Role of the membrane bilayer in ligand-receptor interactions". Journal of Molecular and Cellular Cardiology 18 (1986): 12. http://dx.doi.org/10.1016/s0022-2828(86)80522-3.
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Wang, Li, Xin-Pu Hou, Angelica Ottova e H. Ti Tien. "Receptor–ligand interactions in a reconstituted bilayer lipid membrane". Electrochemistry Communications 2, n.º 5 (maio de 2000): 287–89. http://dx.doi.org/10.1016/s1388-2481(00)00008-4.
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Torres, Manuel, Catalina Ana Rosselló, Paula Fernández-García, Victoria Lladó, Or Kakhlon e Pablo Vicente Escribá. "The Implications for Cells of the Lipid Switches Driven by Protein–Membrane Interactions and the Development of Membrane Lipid Therapy". International Journal of Molecular Sciences 21, n.º 7 (27 de março de 2020): 2322. http://dx.doi.org/10.3390/ijms21072322.
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The cell membrane contains a variety of receptors that interact with signaling molecules. However, agonist–receptor interactions not always activate a signaling cascade. Amphitropic membrane proteins are required for signal propagation upon ligand-induced receptor activation. These proteins localize to the plasma membrane or internal compartments; however, they are only activated by ligand-receptor complexes when both come into physical contact in membranes. These interactions enable signal propagation. Thus, signals may not propagate into the cell if peripheral proteins do not co-localize with receptors even in the presence of messengers. As the translocation of an amphitropic protein greatly depends on the membrane’s lipid composition, regulation of the lipid bilayer emerges as a novel therapeutic strategy. Some of the signals controlled by proteins non-permanently bound to membranes produce dramatic changes in the cell’s physiology. Indeed, changes in membrane lipids induce translocation of dozens of peripheral signaling proteins from or to the plasma membrane, which controls how cells behave. We called these changes “lipid switches”, as they alter the cell’s status (e.g., proliferation, differentiation, death, etc.) in response to the modulation of membrane lipids. Indeed, this discovery enables therapeutic interventions that modify the bilayer’s lipids, an approach known as membrane-lipid therapy (MLT) or melitherapy.
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Cao, Shengya, Sean M. Peterson, Sören Müller, Mike Reichelt, Christian McRoberts Amador e Nadia Martinez-Martin. "A membrane protein display platform for receptor interactome discovery". Proceedings of the National Academy of Sciences 118, n.º 39 (16 de setembro de 2021): e2025451118. http://dx.doi.org/10.1073/pnas.2025451118.
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Cell surface receptors are critical for cell signaling and constitute a quarter of all human genes. Despite their importance and abundance, receptor interaction networks remain understudied because of difficulties associated with maintaining membrane proteins in their native conformation and their typically weak interactions. To overcome these challenges, we developed an extracellular vesicle-based method for membrane protein display that enables purification-free and high-throughput detection of receptor–ligand interactions in membranes. We demonstrate that this platform is broadly applicable to a variety of membrane proteins, enabling enhanced detection of extracellular interactions over a wide range of binding affinities. We were able to recapitulate and expand the interactome for prominent members of the B7 family of immunoregulatory proteins such as PD-L1/CD274 and B7-H3/CD276. Moreover, when applied to the orphan cancer-associated fibroblast protein, LRRC15, we identified a membrane-dependent interaction with the tumor stroma marker TEM1/CD248. Furthermore, this platform enabled profiling of cellular receptors for target-expressing as well as endogenous extracellular vesicles. Overall, this study presents a sensitive and easy to use screening platform that bypasses membrane protein purification and enables characterization of interactomes for any cell surface–expressed target of interest in its native state.
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Scheel, Andreas A., Bettina Funsch, Michael Busch, Gabriele Gradl, Johannes Pschorr e Martin J. Lohse. "Receptor-Ligand Interactions Studied with Homogeneous Fluorescence-Based Assays Suitable for Miniaturized Screening". Journal of Biomolecular Screening 6, n.º 1 (fevereiro de 2001): 11–18. http://dx.doi.org/10.1177/108705710100600103.
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Cell membrane receptors play a central role in controlling cellular functions, making them the target of drugs for a wide variety of diseases. This report describes how a recently developed method, fluorescence intensity distribution analysis (FIDA), can be used to develop homogeneous, nonradioactive high throughput screening assays for membrane receptors. With FIDA, free ligand and ligand accumulated on receptor-bearing membrane vesicles can be distinguished on the basis of their particle brightness. This allows the concentration of both bound and free ligand to be determined reliably from a single measurement, without any separation. We demonstrate that ligand affinity, receptor expression level, and potency of inhibitors can be determined using the epidermal growth factor and β2-adrenergic receptors as model systems. Highly focused confocal optics enable single-molecule sensitivity, and sample volumes can thus be reduced to 1,IL without affecting the quality of the fluorescence signal. Our results demonstrate that FIDA is an ideal method for membrane receptor assays offering substantial benefits for assay development and high throughput pharmaceutical screening.
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Yang, Yun-Hee, e Jwa-Min Nam. "Single Nanoparticle Tracking-Based Detection of Membrane Receptor−Ligand Interactions". Analytical Chemistry 81, n.º 7 (abril de 2009): 2564–68. http://dx.doi.org/10.1021/ac802477h.
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Valenzano, Kenneth J., Wendy Miller, Jared N. Kravitz, Philippe Samama, Dan Fitzpatrick e Kevin Seeley. "Development of a Fluorescent Ligand-Binding Assay Using the AcroWell Filter Plate". Journal of Biomolecular Screening 5, n.º 6 (dezembro de 2000): 455–61. http://dx.doi.org/10.1177/108705710000500608.
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One of the most powerful tools for receptor research and drug discovery is the use of receptor-ligand affinity screening of combinatorial libraries. Early work involved the use of radioactive ligands to identify a binding event; however, there are numerous limitations involved in the use of radioactivity for high throughput screening. These limitations have led to the creation of highly sensitive, nonradioactive alternatives to investigate receptor-ligand interactions. Pall Gelman Laboratory has introduced the AcroWell, a patented low-fluorescent-background membrane and sealing process together with a filter plate design that is compatible with robotic systems. Taken together, these allow the AcroWell 96-well filter plate to detect trace quantities of lanthanide-labeled ligands for cell-, bead-, or membrane-based assays using time-resolved fluorescence. Using europium-labeled galanin, we have demonstrated that saturation binding experiments can be performed with low-background fluorescence and signal-to-noise ratios that rival traditional radioisotopic techniques while maintaining biological integrity of the receptor-ligand interaction. In addition, the ability to discriminate between active and inactive compounds in a mock galanin screen is demonstrated with low well-to-well variability, allowing reliable determination of positive hits even for low-affinity interactions.
Teses / dissertações sobre o assunto "Membrane receptor-Ligand interactions"
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Dogra, Navneet. "INVESTIGATING PROTEIN - BILAYER COMPLEXES: A STUDY OF LIGAND - RECEPTOR INTERACTIONS AT MODEL MEMBRANE SURFACE BY USING ELECTRONIC ABSORPTION SPECTROSCOPY AND FLUORESCENCE RESONANCE ENERGY TRANSFER". OpenSIUC, 2014. https://opensiuc.lib.siu.edu/dissertations/812.
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The main aim of work presented here is to design, develop and characterize a colorimetric model membrane (liposome) systems, which can bind with proteins, enzymes, bacteria, virus and other biomolecules. PDA molecules are utilized as a scaffold for the bilayer membrane, and a colorimetric assay is carried out. The holy grail of present work contributes towards the better understanding of protein interactions with the cell bilayer surface. Chapter 1 introduces a brief history on the advent of bilayer systems for cellular research exploration. We presented a literature survey about how liposome systems are used as a complementary technique to understand the fundamental principles of cellular membrane functions. Furthermore, we describe about membrane protein functions and recent findings on how proteins interact with the cell membrane. Finally, we explain conjugated systems and their exploration in bilayer membrane as a colorimetric scaffold. We also touch bases with major fluorescence techniques used in our experiments. Chapter 2 provides details on the preparation protocols of liposome and liposome-protein complexes. We confirmed protein-bilayer interactions by monitoring FRET between PDA and rhodamine molecules. Furthermore, we performed streptavidin-biotin binding studies on the PDA bilayer. Protein binding changed the spectral overlap (J) between PDA and rhodamine, which ultimately increased the fluorescence emission of rhodamine. The goal of performing these studies was to present a complete protocol for the preparation of liposome and protein-liposome complex. In chapter 3, we investigate how proteins bind on the cell membrane. Additionally, we propose a model of protein-bilayer complex. We reported that, by harnessing cell bilayer with specific bio-molecules, we monitored protein--bilayer, protein--protein and enzyme--substrate signal transduction. We have developed a colorimetric system for monitoring vital stimulations occur on the liposomal membrane surface. Bilayer was modified to covalently bind the amino group of lysine residues present on protein molecules. These bio-molecular interactions on bilayer surface provide differential stimulus, which turned out to be the major cause of differential spectroscopic signals depending upon size and shape of the protein bounded to the bilayer. Polydiacetylene (PDA) liposomes are the core of our color based system. These liposomes are used to monitor subtle interactions on the bilayer surface. We have also developed a semi-quantitative method based on the colorimetric response of PDA liposomes; we were able to detect protein molecules at sub-nanomolar concentrations in the solution. It's capability of distinguishing protein molecules based on their chemical and physical interactions to bilayer contributes towards the identity of our system. Interestingly, our mass spectroscopic data suggested non-specific enzymatic cleavage of membrane-bound proteins. These fragments were not present in bulk protein cleavage. We also proposed a model that depicts the covalent binding of protein at the bilayer of liposomes. These studies are intended to investigate protein-bilayer and enzyme-protein interaction occurring on the cell surface. In chapter 4, we focus on the kinetics of protein interaction on bilayer surface and we also attempt to visualize these interactions by exploring fluorescence microscopy. A self-assembled cell membrane is consisted of various lipids, which cluster themselves in their preferred phase separated regions. Lipid clusters are very important for lipid specific protein interactions. We investigated protein binding on such phase separated regions under a fluorescence microscope. Furthermore, we enzymatically catalyzed proteins, which were covalently bonded on the bilayer surface. This catalytic reaction was monitored both spectroscopically and under a fluorescence microscope. These studies were performed to help us in the better understanding of biological interactions at cell surface. Chapter 5, describes the encapsulation and controlled delivery of antimicrobial compounds from liposomes. Use of antimicrobial coatings on food packaging is one of the important technologies of active packaging for improving food safety. There is growing demand for natural antimicrobials because of fear of adverse health effects of synthetic preservatives. The main objective of this study is to compare antimicrobial activity of free versus encapsulated curcumin. Glass surfaces coated with nano-encapsulated curcumin may be used as an active packaging material in preserving liquid foods; however, further study is required to improve antimicrobial activities of polylactic acid PLA surfaces. In chapter 6, we investigate interactions between receptors and ligands at bilayer surface of polydiacetylene (PDA) liposomal nanoparticles using changes in electronic absorption spectroscopy and fluorescence resonance energy transfer (FRET). We study the effect of mode of linkage (covalent versus noncovalent) between the receptor and liposome bilayer. We also examine the effect of size-dependent interactions between liposome and analyte through electronic absorption and FRET responses. Glucose (receptor) molecules were either covalently or noncovalently attached at the bilayer of nanoparticles, and they provided selectivity for molecular interactions between glucose and glycoprotein ligands of E. coli. These interactions induced stress on conjugated PDA chain which resulted in changes (blue to red) in the absorption spectrum of PDA. The changes in electronic absorbance also led to changes in FRET efficiency between conjugated PDA chains (acceptor) and fluorophores (Sulphorhodamine-101) (donor) attached to the bilayer surface. Interestingly, we did not find significant differences in UV−Vis and FRET responses for covalently and noncovalently bound glucose to liposomes following their interactions with E. coli. We attributed these results to close proximity of glucose receptor molecules to the liposome bilayer surface such that induced stress were similar in both the cases. We also found that PDA emission from direct excitation mechanism was ∼2−10 times larger than that of the FRET-based response. These differences in emission signals were attributed to three major reasons: nonspecific interactions between E. coli and liposomes, size differences between analyte and liposomes, and a much higher PDA concentration with respect to sulforhodamine (SR-101). We have proposed a model to explain our experimental observations. Our fundamental studies reported here will help in enhancing our knowledge regarding interactions involved between soft particles at molecular levels. In chapter 7, we conclude the summary of all work carried out in previous chapters.
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Sahai, Michelle Asha. "Computational studies of ligand-water mediated interactions in ionotropic glutamate receptors". Thesis, University of Oxford, 2011. http://ora.ox.ac.uk/objects/uuid:b86d2f5a-3554-44c0-b985-5693241369ec.
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Careful treatment of water molecules in ligand-protein interactions is required in many cases if the correct binding pose is to be identified for molecular docking. Water can form complex bridging networks and can play a critical role in dictating the binding mode of ligands. A particularly striking example of this can be found in the ionotropic glutamate receptors (iGluRs), a family of ligand gated ion channels that are responsible for a majority of the fast synaptic neurotransmission in the central nervous system that are thought to be essential in memory and learning. Thus, pharmacological intervention at these neuronal receptors is a valuable therapeutic strategy. This thesis relies on various computational studies and X-ray crystallography to investigate the role of ligand-water mediated interactions in iGluRs bound to glutamate and α-amino-3-hydroxy-5-methyl-4- isoxazole-propionic acid (AMPA). Comparative molecular dynamics (MD) simulations of each subtype of iGluRs bound to glutamate revealed that crystal water positions were reproduced and that all but one water molecule, W5, in the binding site can be rearranged or replaced with water molecules from the bulk. Further density functional theory calculations (DFT) have been used to confirm the MD results and characterize the energetics of W5 and another water molecule implicated in influencing the dynamics of a proposed switch in these receptors. Additional comparative studies on the AMPA subtypes of iGluRs show that each step of the calculation must be considered carefully if the results are to be meaningful. Crystal structures of two ligands, glutamate and AMPA revealed two distinct modes of binding when bound to an AMPA subtype of iGluRs, GluA2. The difference is related to the position of water molecules within the binding pocket. DFT calculations investigated the interaction energies and polarisation effects resulting in a prediction of the correct binding mode for glutamate. For AMPA alternative modes of binding have similar interaction energies as a result of a higher internal energy than glutamate. A combined MD and X-ray crystallographic study investigated the binding of the ligand AMPA in the AMPA receptor subtypes. Analysis of the binding pocket show that AMPA is not preserved in the crystal bound mode and can instead adopt an alternative mode of binding. This involves a displacement of a key water molecule followed by AMPA adopting the pose seen by glutamate. Thus, this thesis makes use of various studies to assess the energetics and dynamics of water molecules in iGluRs. The resulting data provides additional information on the importance of water molecules in mediating ligand interactions as well as identifying key water molecules that can be useful in the de novo design of new selective drugs against iGluRs.
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Piguet, Joachim. "Advanced Fluorescence Microscopy to Study Plasma Membrane Protein Dynamics". Doctoral thesis, Ecole Polytechnique Fédérale de Lausanne (EPFL), Switzerland, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-178147.
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Membrane protein dynamics is of great importance for living organisms. The precise localization of proteins composing a synapse on the membrane facing a nerve terminus is essential for proper functioning of the nervous system. In muscle fibers, the nicotinic acetylcholine is densely packed under the motor nerve termini. A receptor associated protein, rapsyn, acts as a linker between the receptor and the other components of the synaptic suramolecular assembly. Advances in fluorescence microscopy have allowed to measure the behavior of a single receptor in the cell membrane. In this work single-molecule microscopy was used to track the motion of ionotropic acetylcholine (nAChR) and serotonin (5HT3R) receptors in the plasma membrane of cells. We present methods for measuring single-molecule diffusion and their analysis. Single molecule tracking has shown a high dependence of acetylcholine receptors diffusion on its associated protein rapsyn. Comparing muscle cells that either express rapsyn or are devoid of it, we found that rapsyn plays an important role on receptor immobilization. A three-fold increase of receptor mobility was observed in muscle cells devoid of rapsyn. However, in these cells, a certain fraction of immobilized receptors was also found immobile. Furthermore, nAChR were strongly confined in membrane domains of few tens of nanometers. This showed that membrane composition and membrane associated proteins influence on receptor localization. During muscle cell differentiation, the fraction of immobile nAChR diminished along with the decreasing nAChR and stable rapsyn expression levels. The importance of rapsyn in nAChR immobilization has been further confirmed by measurements in HEK 293 cells, where co-expression of rapsyn increased immobilization of the receptor. nAChR is a ligand-gated ion-channel of the Cys-loop family. In mammals, members of this receptor family share general structural and functional features. They are homo- or hetero-pentamers and form a membrane-spanning ion channel. Subunits have three major regions, an extracellular ligand binding domain, a transmembrane channel and a large intracellular loop. 5HT3R was used as a model to study the effect of this loop on receptor mobility. Single-molecule tracking experiments on receptors with progressively larger deletions in the intracellular loop did not show a dependence of the size of the loop on the diffusion coefficient of mobile receptors. However, two regions were identified to play a role in receptor mobility by changing the fractions of immobile and directed receptors. Interestingly, a prokaryotic homologue of cys-loop receptors, ELIC, devoid of a large cytoplasmic loop was found to be immobile or to show directed diffusion similar as the wild-type 5HT3R. The scaffolding protein rapsyn stabilizes nAChR clusters in a concentration dependent manner. We have measured the density and self-interactions of rapsyn using FRET microscopy. Point-mutations of rapsyn, known to provoke myopathies, destabilized rapsyn self-interactions. Rapsyn-N88K, and R91L were found at high concentration in the cytoplasm suggesting that this modification disturbs membrane association of rapsyn. A25V was found to accumulate in the endoplasmic reticulum. Fluorescent tools to measure intracellular concentration of calcium ions are of great value to study the function of neurons. Rapsyn is highly abundant at the neuromuscular junction and thus is a genuine synaptic marker. A fusion protein of rapsyn with a genetically encoded ratiometric calcium sensor has been made to probe synapse activity. This thesis has shown that the combined use of biologically relevant system and modern fluorescence microscopy techniques deliver important information on pLGIC behaviour in the cell membrane.QC 20151217
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Cinier, Justine. "Importance et potentiel thérapeutique d'un nouveau couple récepteur-ligand dans l'inhibition des lymphocytes T CD8 par les lymphocytes T régulateurs dans les tumeurs". Electronic Thesis or Diss., Lyon 1, 2024. http://www.theses.fr/2024LYO10336.
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La présence de lymphocytes T (LT) CD8 dans le microenvironnement tumoral (TME) corrèle avec un bon pronostic dans de nombreux types de cancers solides. En périphérie, les LT régulateurs (Treg) jouent un rôle majeur dans le maintien d’une homéostasie immunitaire et empêchent le développement de pathologies auto-immunes. Néanmoins, dans le TME, les Treg (TA-Treg) ont un impact pronostic défavorable en inhibant la réponse immunitaire antitumorale. Sur le plan thérapeutique, il est indispensable d’éliminer ces TA-Treg ou leur fonction pour restaurer une réponse immunitaire antitumorale efficace. Pour cela, il reste important d’identifier des molécules membranaires permettant le ciblage sélectif de ces TA-Treg sans affecter les Treg périphériques pour éviter toute réaction auto-immune. L’analyse de données publiques de scRNA-seq comparant les LT (Treg, CD8, CD4) de tumeur, tissu sain et sang, a permis d’identifier l’expression sélective de CD177 par une population de TA-Treg dans plusieurs tumeurs solides. Si cette glycoprotéine est impliquée dans l’extravasation et la survie des neutrophiles, son rôle sur les Treg n’a été que peu décrit hormis dans quelques études confirmant l’expression de CD177 sur les TA-Treg dans plusieurs types tumoraux et montrant un effet suppresseur de ces TA-Treg CD177+ dans des cocultures avec des LT CD4 naïfs. Néanmoins, la caractérisation phénotypique et fonctionnelle de ces Treg reste peu explorée. CD177 interagit avec PECAM-1 qui est impliqué dans la transmigration des LT par interaction homophilique des domaines extracellulaires distaux immunoglobuline-like (IgD1/D2) avec les cellules endothéliales. De plus, il a été décrit que l’interaction avec le IgD6 extracellulaire de PECAM-1, zone de liaison de CD177, transmet un signal négatif via les motifs intracellulaires inhibiteurs (ITIM) et le recrutement de SHP2 qui bloque la signalisation TCR et la prolifération des LT. La réanalyse de données publiques de scRNA-seq de LT intra-tumoraux montre la restriction de l’expression de PECAM1 à des clusters de LT CD8 effecteurs mémoires suggérant qu’ils pourraient être la cible de la fonction immunosuppressive des Treg CD177+ dans le TME. Ainsi, dans l’objectif d’identifier un mécanisme de suppression des Treg spécifique des LT CD8 effecteurs dans l’environnement tumoral il est important de caractériser de manière approfondie ces TA-Treg CD177+ et d’identifier leurs interactions avec les LT CD8 PECAM-1+ dans le TME et leur impact sur la fonction de ces LT CD8. Ce travail de thèse a permis de démontrer, dans plusieurs types tumoraux, que CD177 identifie une population de Treg spécifiques de la tumeur, avec un phénotype activé. PECAM-1, la cible de CD177, est exprimé dans le TME par des LT CD8 effecteurs polyfonctionnels (GzmK, IFNү, TNFα), à forte capacité de prolifération. In situ sur coupe de tumeurs, des analyses de multi-immunofluorescence ont montré la colocalisation des Treg CD177+ et des LT CD8 PECAM-1+ au niveau du stroma tumoral, suggérant un lien entre ces deux populations. Par ailleurs, l’engagement de PECAM-1 IgD6, domaine de liaison de CD177, réduit l’activation et les fonctions des LT CD8 PECAM-1+ induites par le signal TCR en diminuant pZAP-70 et la sécrétion d’IFNү. Enfin, des premiers résultats sur tumeur ont montré que la culture de LT CD8 avec des TA-Treg CD177+ diminue la prolifération et la sécrétion d’IFNγ par les LT CD8 PECAM-1+ et l’ajout d’un anti-CD177 permet de lever en partie cette inhibition, suggérant le rôle de l’axe [CD177/PECAM-1] dans l’inhibition des LT CD8 PECAM-1+ par les TA-Treg CD177+. L’interaction [CD177/PECAM-1] représente la première mise en évidence d’un couple récepteur/ligand membranaire impliqué dans l’inhibition sélective des LT CD8 effecteurs par les TA-Treg dans le TME et CD177 apparait comme une cible prometteuse pour lever spécifiquement la suppression médiée par les Treg dans le TME sans altérer ceux de la périphérieThe presence of CD8 T cells in the tumor microenvironment (TME) correlates with good prognosis in many types of solid cancers. In the periphery, regulatory T cells (Treg) play a major role in maintaining immune homeostasis and preventing the development of autoimmune pathologies. However, in the TME, Treg (TA-Treg) have an unfavorable prognostic impact by inhibiting the anti-tumor immune response. Therapeutically, it is essential to eliminate these TA-Treg or their function to restore an effective anti-tumor immune response. For this, it remains important to identify membrane molecules allowing the selective targeting of these TA-Treg without affecting the Treg present in the periphery to avoid any autoimmune reaction. The analysis of public scRNA-seq data comparing T cells (Treg, CD8, CD4) from tumor, healthy tissue and blood, made it possible to identify the selective expression of CD177 by a subpopulation of TA-Treg in different solid tumors. If this glycoprotein is known for its involvement in the extravasation and survival of neutrophils, its role on Treg has been little described except in a few studies confirming the expression of CD177 on TA-Treg of several types of tumors and showing a suppressive impact of CD177+ TA-Treg in cocultures with naïve CD4 T cells. However, the phenotypic and functional characterization of these Treg remains little explored. CD177 interacts with PECAM-1 which is involved in T cells transmigration through homophilic interaction of distal extracellular immunoglobulin-like domains (IgD1/D2) with endothelial cells. Furthermore, it has been described that interaction with extracellular PECAM-1 IgD6, CD177 binding site, transmits a negative signal via inhibitory intracellular motifs (ITIM) and recruitment of SHP2 which blocks TCR signaling and the proliferation of T cells. Reanalysis of public scRNA-seq data from intra-tumoral T cells shows the restriction of PECAM1 expression to clusters of memory effector CD8 T cells suggesting that they could be the target of the immunosuppressive function of CD177+ Treg in the TME. Thus, with the aim of identifying a Treg suppression mechanism specific to effector CD8 T cells in the TME, it is important to characterize in depth these CD177+ TA-Treg and to identify their interactions with PECAM-1+ CD8 T cells in the TME and their impact on the function of these CD8 T cells. This thesis work demonstrated, in several tumor types, that CD177 identifies a population of TA- Treg, with an activated phenotype. PECAM-1, the target of CD177, is expressed in the TME by polyfunctional effector CD8 T cells (GzmK, IFNγ, TNFα) with a high proliferation capacity. In situ on tumor sections, multi-immunofluorescence analyses showed the colocalization of CD177+ Treg and PECAM-1+ CD8 T cells in the tumor stroma, suggesting a link between these two populations. Furthermore, engagement of PECAM-1 IgD6, CD177 binding domain, reduces the activation and functions of PECAM-1+ CD8 T cells induced by the TCR signal by decreasing pZAP-70 and IFNү secretion. Finally, initial results on tumors have shown that the culture of CD8 T cells with CD177+ TA-Treg reduces the proliferation and secretion of IFNγ by PECAM-1+ CD8 T cells and the addition of an anti-CD177 makes it possible to partly rescue this inhibition, suggesting the role of the [CD177/PECAM-1] axis in the inhibition of PECAM-1+ CD8 T cells by CD177+ TA-Treg. The [CD177/PECAM-1] interaction represents the first demonstration of a membrane receptor/ligand pair involved in the selective inhibition of CD8 T cells effectors by TA-Treg in the TME and CD177 appears as a promising target to specifically raise suppression mediated by TA-Treg in the TME without altering those in the periphery
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Mahlberg, Florence. "Les sites membranaires de liaison specifiques des hdl : caracterisation du ligand, aspects fonctionnels". Paris 7, 1987. http://www.theses.fr/1987PA077223.
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Les lipoproteines de haute densite (hdl) jouent un role protecteur contre l'atherosclerose, en partie en captant le cholesterol des tissus peripheriques, est ensuite catabolise dans le foie ou dans les tissus steroidrogenes. L'existence de sites membranaire de liaison specifique des hdl, distincts des recepteurs apob/e et apoe, pourraient etre impliques dans les echanges de cholesterol entre hdl et les tissus hepatiques et peripheriques. Ces sites ne sont pas regules, et leur intervention au niveau des tissus peripheriques dans l'efflux du cholesterol cellulaire en presence de hdl n'est pas limitante
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Hénault, Camille. "The Role of the M4 α-Helix in Lipid Sensing by a Pentameric Ligand-Gated Ion Channel". Thesis, Université d'Ottawa / University of Ottawa, 2021. http://hdl.handle.net/10393/42519.
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Pentameric ligand-gated ion channels (pLGICs) are membrane-embedded receptors found extensively in pre- and post-synaptic membranes throughout the nervous system where they play an important role in neurotransmission. The function of the prototypic pLGIC, the nicotinic acetylcholine receptor (nAChR) is highly sensitive to changes in its lipid environment, while other pLGICs display varying lipid sensitivities. This thesis presents a multidisciplinary investigation into the features of the transmembrane domain (TMD) that determine the unique functional and physical traits of different pLGICs. Using two prokaryotic homologues of the nAChR, ELIC and GLIC, as models, I focus on the outermost, lipid-exposed α-helix, M4, which, despite being distant from the primary allosteric pathway coupling agonist binding to channel gating, exercises significant control over channel function. Here, I present evidence that M4 acts as a lipid sensor, detecting changes in the surrounding lipids and transmitting these changes to the channel pore via contacts with the adjacent TMD α-helices, M1 and M3, and/or with structures in the extracellular domain. Using ELIC and GLIC chimeras, I first show that the TMD is the main driver of pLGIC thermal stability. I then demonstrate that the M4 α-helices in each channel play different roles in channel maturation and function, which suggests a divergent evolutionary path. Following this, I show that the M4 C-terminus is essential to both maturation and function in GLIC, while in ELIC its role is less defined, again showcasing possible evolutionary differences. Building on these findings, I examined the role of aromatic residues at the M4 – M1/M3 interface, and found that they predictably determine the interactions between M4 and M1/M3. Notably, the addition of aromatic residues to enhance M4-M1/M3 interactions in ELIC promotes channel function, while the elimination of aromatic residues at the M4-M1/M3 interface in GLIC is detrimental to channel function. Furthermore, I show that these same aromatics alter the strength of pLGIC lipid sensing and the sensitivity to certain disease-causing mutations, both indicating that aromatic residues are key players in channel function, stability and modulation. Finally, I and my collaborators identified and characterized a novel desensitization-linked lipid binding site in ELIC. Extensive mutagenesis studies coupled with biophysical measurements allowed us to develop a model describing how lipid binding influences the rates of ELIC desensitization to shape the agonist-induced response.
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López, Muñoz Laura. "Homology modeling and structural analysis of the antipsychotic drugs receptorome". Doctoral thesis, Universitat Pompeu Fabra, 2010. http://hdl.handle.net/10803/7228.
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Classically it was assumed that the compounds with therapeutic effect exert their action interacting with a single receptor. Nowadays it is widely recognized that the pharmacological effect of most drugs is more complex and involves a set of receptors, some associated to their positive effects and some others to the side effects and toxicity. Antipsychotic drugs are an example of effective compounds characterized by a complex pharmacological profile binding to several receptors (mainly G protein-coupled-receptors, GPCR). In this work we will present a detailed study of known antipsychotic drugs and the receptors potentially involved in their binding profile, in order to understand the molecular mechanisms of the antipsychotic pharmacologic effects.The study started with obtaining homology models for all the receptors putatively involved in the antipsychotic drugs receptorome, suitable for building consistent drug-receptor complexes. These complexes were structurally analyzed and compared using multivariate statistical methods, which in turn allowed the identification of the relationship between the pharmacological properties of the antipsychotic drugs and the structural differences in the receptor targets. The results can be exploited for the design of safer and more effective antipsychotic drugs with an optimum binding profile.
Tradicionalmente se asumía que los fármacos terapéuticamente efectivos actuaban interaccionando con un único receptor. Actualmente está ampliamente reconocido que el efecto farmacológico de la mayoría de los fármacos es más complejo y abarca a un conjunto de receptores, algunos asociados a los efectos terapéuticos y otros a los secundarios y toxicidad. Los fármacos antipsicóticos son un ejemplo de compuestos eficaces que se caracterizan por unirse a varios receptores simultáneamente (principalmente a receptores unidos a proteína G, GPCR). El trabajo de la presente tesis se ha centrado en el estudio de los mecanismos moleculares que determinan el perfil de afinidad de unión por múltiples receptores de los fármacos antipsicóticos.
En primer lugar se construyeron modelos de homología para todos los receptores potencialmente implicados en la actividad farmacológica de dichos fármacos, usando una metodología adecuada para construir complejos fármaco-receptor consistentes. La estructura de estos complejos fue analizada y se llevó a cabo una comparación mediante métodos estadísticos multivariantes, que permitió la identificación de asociaciones entre la actividad farmacológica de los fármacos antipsicóticos y diferencias estructurales de los receptores diana. Los resultados obtenidos tienen interés para ser explotados en el diseño de fármacos antipsicóticos con un perfil farmacológico óptimo, más seguros y eficaces.
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Dunand, Christophe. "Perception d'un signal xyloglucane par des protéines membranaires et mise en évidence d'activité xyloglucane endotransglycosylane induite". Université Joseph Fourier (Grenoble ; 1971-2015), 1997. http://www.theses.fr/1997GRE10111.
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Afin de relier l'activite biologique du motif actif des xyloglucanes a la reconnaissance par des proteines membranaires, nous avons adopte une approche biochimique de detection basee sur l'utilisation de tests immunoenzymatiques. Nous avons utilise le dimere -l-fuc (12), d-gal marque avec de la digoxigenine ou de la biotine et des proteines solubilisees provenant de fractions enrichies en plasmalemme isolees de protoplastes de rubus, pour modeliser les interactions ligand-recepteur. Les resultats obtenus ont montre qu'une proteine membranaire de 62 kda est capable de fixer le dimere fuc-gal et que cette fixation est saturable et reversible. Par ailleurs, le deplacement competitif de la fixation montre une inhibition de l'activite de liaison a la fois par des analogues structuraux (xxfg, fuc-gal-glc, fuc-gal-xyl) et par des phytohormones (2,4-d, kinetine, ga#3, acide abscissique). Cependant, a ce stade de nos travaux, il n'est a pas encore etabli que ces structures proteiques correspondent a des recepteurs de xyloglucane. Une technique de determination de l'activite xyloglucane endotransglycosylase par tests immunoenzymatiques a ete mise au point et a permis de mettre en evidence une activite induite par differents signaux. Le polymere de xyloglucane marque avec de la digoxigenine et l'oligomere xxlgbsa sont utilises comme substrats pour la reaction enzymatique. Les solutions enzymatiques testees sont extraites a partir de fractions microsomales provenant de protoplastes de rubus temoins ou traites. Grace a une sequence d'anticorps (primaire, secondaire et tertiaire), l'activite transferase est suivie en mesurant l'activite peroxydase. Les avantages de cette nouvelle methode sont la sensibilite de la detection et la possibilite d'analyser plusieurs echantillons simultanement.
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Ma, Haijun. "Single molecule force spectroscopy of membrane receptor-ligand interactions : a model study". 2005. http://link.library.utoronto.ca/eir/EIRdetail.cfm?Resources__ID=370104&T=F.
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Baradji, Issa. "The Role of Apical Membrane Antigen-1 in Erythrocyte Invasion by the Zoonotic Apicomplexan Babesia microti". 2008. http://hdl.handle.net/1969.1/ETD-TAMU-2008-08-68.
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Babesia microti is a tickborne hemoprotozoan parasite that causes the disease
babesiosis in humans. Babesia microti Apical Membrane Antigen-1 (AMA-1) is a
micronemal protein suspected to play a role in erythrocyte invasion. To investigate
interaction between AMA-1 and the host cell, the ectodomain region of the B. microti
ama-1 gene was cloned into an expression vector, expressed as a histidine-tagged fusion
protein, and used to probe red blood cell membrane proteins in far Western blot assays.
The B. microti ama-1 ectodomain, which excludes the signal peptide and the
transmembrane region of the open reading frame, was amplified from a cloned gene
sequence. The AMA-1 ectodomain is a membrane bound polypeptide that extends into
the extracellular space and is most likely to interact or initiate interaction with the host
red blood cell surface receptor(s). The amplicon was ligated into a protein expression
vector to produce a 58.1 kDa recombinant His-tagged fusion protein, which was
confirmed by Western blot analysis. The recombinant B. microti AMA-1 fusion protein was enriched on nickel
affinity columns and then used to probe mouse, human and horse red blood cell
membrane proteins in far Western blot assays. Babesia microti AMA-1 consistently
reacted strongly with a protein migrating at 49 kDa. A similar reaction occurred between
the B. microti AMA-1 and horse red blood cell membrane proteins, suggesting that
similar interacting proteins of this size are shared by red blood cells from the three
species.
The B. microti AMA-1 may bind to red blood cell membrane sialic-acid groups,
as shown for other Babesia spp. This may explain the signal at the 49 kDa position
observed between B. microti AMA-1 and red blood cell membrane proteins from three
different species. Further studies may determine if the binding epitopes of the red blood
cell binding partner at this position vary and contribute to the specificity of each parasite
AMA-1 for their respective host cells.
Livros sobre o assunto "Membrane receptor-Ligand interactions"
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Tax, Frans. Receptor-like Kinases in Plants: From Development to Defense. Berlin, Heidelberg: Springer Berlin Heidelberg, 2012.
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2
Ma, Haijun. Single molecule force spectroscopy of membrane receptor-ligand interactions: A model study. 2005.
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3
Kemmerling, Birgit, e Frans Tax. Receptor-like Kinases in Plants: From Development to Defense. Springer, 2014.
Encontre o texto completo da fonteCapítulos de livros sobre o assunto "Membrane receptor-Ligand interactions"
1
Lei, Li, M. Page Haynes e Jeffrey R. Bender. "Estrogen-Stimulated, Membrane-Initiated Receptor-Ligand Interactions in Vascular Cells". In The Identities of Membrane Steroid Receptors, 37–45. Boston, MA: Springer US, 2003. http://dx.doi.org/10.1007/978-1-4615-0339-2_5.
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Israelachvili, J., D. Leckband, F. J. Schmitt, J. Zasadzinski, S. Walker e S. Chiruvolu. "Direct Measurements of Specific Ligand-Receptor Interactions Between Model Membrane Surfaces". In Studying Cell Adhesion, 37–49. Berlin, Heidelberg: Springer Berlin Heidelberg, 1994. http://dx.doi.org/10.1007/978-3-662-03008-0_3.
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Jung, Seung-Yong, Edward T. Castellana, Matthew A. Holden, Tinglu Yang e Paul S. Cremer. "Multivalent Ligand-Receptor Interactions on Planar Supported Membranes An On-Chip Approach". In Nanoscale Assembly, 99–117. Boston, MA: Springer US, 2005. http://dx.doi.org/10.1007/0-387-25656-3_6.
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Orgovan, Norbert, Beatrix Peter, Szilvia Bősze, Jeremy J. Ramsden, Bálint Szabó e Robert Horvath. "Label-Free Profiling of Cell Adhesion: Determination of the Dissociation Constant for Native Cell Membrane Adhesion Receptor-Ligand Interaction". In Methods in Pharmacology and Toxicology, 327–38. New York, NY: Springer New York, 2015. http://dx.doi.org/10.1007/978-1-4939-2617-6_18.
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Strange, Philip G. "Charcoal Adsorption for Separating Bound and Free Radioligand in Radioligand Binding Assays". In Receptor-Ligand Interactions, 247–54. Oxford University PressOxford, 1992. http://dx.doi.org/10.1093/oso/9780199630905.003.0008.
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Abstract As discussed extensively in this book, there is a requirement for accurate, reproducible, rapid, and cheap methods for separating bound and free radioligand in radioligand receptor binding assays. In other chapters (Chapters 6, 7) methods have been described for the assay of membrane bound receptors based on collection of the bound radioligand by filtration or centrifugation of the membranes. When studying a soluble receptor (either a naturally soluble cytosolic receptor, such as a steroid hormone receptor, or a detergent solubilized receptor, formerly membrane bound) these methods are not applicable. A popular technique in such studies is the charcoal adsorption assay which relies on the ability of charcoal to selectively remove the free radioligand from the mixture of bound and free radioligand.
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Hulme, E. C. "Centrifugation Binding Assays". In Receptor-Ligand Interactions, 235–46. Oxford University PressOxford, 1992. http://dx.doi.org/10.1093/oso/9780199630905.003.0007.
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Abstract Centrifugation assays are best applied to assaying the labelling of receptors in membrane preparations using radioligands. The principle is elementary. At the end of the assay period, the membranes bearing the labelled receptors are sedimented, and thus physically removed from the supernatant, containing the bulk of the unbound radioligand. After pouring off the supernatant, and subjecting the pellet to washing procedures of greater or less rigour, the amount of bound ligand is assayed, typically by liquid scintillation spectroscopy, or γ-counting.
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Hulme, E. C., e N. J. Buckley. "Receptor Preparations for Binding Studies". In Receptor-Ligand Interactions, 177–212. Oxford University PressOxford, 1992. http://dx.doi.org/10.1093/oso/9780199630905.003.0005.
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Abstract From the point of view of technique in binding studies, receptor preparations fall into two major categories: First preparations in which the cell surface membrane remains locally or globally intact. These include: whole tissues, in particular thin slices whole cells membrane preparations Secondly, preparations in which the cell surface membrane is disrupted by the me of a solubilizing agent.
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Dolly, J. Oliver. "Polypeptide Neurotoxins as Probes for Certain Voltage-Dependent K+ Channels". In Receptor-Ligand Interactions, 37–61. Oxford University PressOxford, 1992. http://dx.doi.org/10.1093/oso/9780199630905.003.0003.
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Abstract A paucity of specific probes for membrane-bound, neuronal proteins has restricted their molecular characterization, particularly where functional assays applicable to broken cell preparations are not available. Thus, the discovery of toxins acting electively on nicotinic acetylcholine receptor or Na+ channel proteins, for example, has resulted in the elucidation of their detailed structural and functional properties.
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Hulme, E. C., e N. J. m. Birdsall. "Strategy and Tactics in Receptor Binding Studies". In Receptor-Ligand Interactions, 63–176. Oxford University PressOxford, 1992. http://dx.doi.org/10.1093/oso/9780199630905.003.0004.
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Abstract The questions answerable by receptor-binding studies fall into two major categories: Firstly, there are fundamental questions which one may ask about: the molecular pharmacology of receptors, the mechanism of ligand binding, and the nature and mechanism of receptor-effector in1eractions. Secondly, there are applied questions which concern the cell biology and anatomical distribution of receptors, particularly: their concentrations in different tissues, their distribution on different eel! types, their ontogenetic development, and how their synthesis, membrane insertion, coupling, degradation. and re cycling are regulated in a given cell! type.
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Wang, Jian-xin, Henry I. Yamamura, Wan Wang e william R. Roeske. "The use of the Filtration Technique in in Vitro Radioligand Binding Assays for Membrane-Bound and Solubilized Receptors". In Receptor-Ligand Interactions, 213–34. Oxford University PressOxford, 1992. http://dx.doi.org/10.1093/oso/9780199630905.003.0006.
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Abstract It has been nearly a century since the receptor hypothesis was first proposed for the mechanism of the effects of drug and toxins on biosystems (1,2). In 1926, A. J. Clark established his receptor occupation theory (3) describing a quantitative interaction between drugs and their receptors. For a period of almost 40 years putative drug receptors were detected by measuring the functional response elicited by drugs. This method must make assumptions that relate the drug-receptor binding properties to the function measured. The first attempt to directly measure the receptors with radiolabelled ligand can be traced back to the 1960s when [3H]atropine (4) and [3H]propranolol (5) were used to label the muscarinic uptake sites in the intestinal smooth muscle and the adrenergic uptake site in atria, respectively. In 1970, radioiso tope labelled adrenocorticotropic hormone (ACTH) (6), angiotensin (7) and o.-bungarotoxin (8) were used to measure ACTH, angiotensin, and nicotinic cholinergic receptors, respectively. These pioneering experiments demon strated that radioisotopically labelled hormones or toxins could be used to study directly the interaction of hormones or toxins with their specific membrane sites. However, some of these studies were limited by technical difficulties such as a low signal-to-noise ratio.
Trabalhos de conferências sobre o assunto "Membrane receptor-Ligand interactions"
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Zhu, Cheng, e Scott E. Chesla. "Dissociation of Individual Molecular Bonds Under Force". In ASME 1997 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 1997. http://dx.doi.org/10.1115/imece1997-0286.
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Abstract Specific interactions between receptors on cell surfaces are essential for living organisms to sense and adapt to their environment. For example, CD16A (Feγ receptor IIIA) signals a variety of immune functions upon binding of immunoglobulin (Ig) G. While receptor-ligand binding has been extensively studied in chemical terms, only until very recently has direct measurement of individual bond forces become possible. Evans et al. [1] pioneered the use of the micropipet technique to measure detachment forces between two red blood cells (RBC) crosslinked by antibodies. While these authors achieved the sensitivity necessary to detect individual bonds (in piconewton range), the forces they measured appeared to be those of uprooting the molecules from the cell membrane (cohesive detachment mode) instead of dissociating the antibody-antigen bonds (adhesive detachment mode).
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Sarvestani, Alireza. "Kinetics of Membrane Spreading on Compliant Bio-Adhesive Substrates". In ASME 2010 First Global Congress on NanoEngineering for Medicine and Biology. ASMEDC, 2010. http://dx.doi.org/10.1115/nemb2010-13321.
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The contact formation between cell membrane and a bio-adhesive substrate is driven by binding between transmembrane mobile receptors (e.g., integrin) and complementary ligand molecules on the substrate (fibronectin, collagen, etc.) This short range specific adhesion is alleviated by a phalanx of interfacial non-specific forces. In addition to cell-substrate interfacial interactions, cell adhesion can be mediated by a wide range of substrate physiochemical properties. In particular, mechanical stiffness of the substrate has been recognized as one of the major regulators for bio-adhesion. Cells in general, exhibit an apparent adhesion preference for stiffer substrates and switch from a round to spread morphology as the substrate stiffness increases. Understanding the mechano-chemical pathways mediating the interplay between the substrate properties and cell behavior could be critical for effective performance of synthetic biomaterials in tissue engineering applications. In this study, we consider the effect of substrate elasticity on the dynamics of membrane spreading and growth of focal adhesion zone. The formation and growth of the focal adhesion points during the early stage of adhesion process is a result of spontaneous spreading of membrane on the substrate. This can be considered as a non-equilibrium kinetic process which is controlled by the diffusibility of receptor molecules. In order to study the effect of substrate elasticity on the kinetics of membrane-substrate association, receptors are assumed as ideal solute particles laterally diffusing within the plane of the membrane until they are stabilized through association with their complementary ligands which are immobilized on the surface of a compliant substrate. Considering different mechanical stiffness for the substrates, the displacement and speed of spreading at the edge of adhesion zone are predicted as a function of time. Results show that decreasing the stiffness of bio-adhesive substrates reduces the rate of membrane spreading, due to a weaker thermodynamic force which drives the membrane-substrate association. This mechanism restrains the growth of focal adhesion zones on compliant substrates and can be considered as a reason for smaller spread area of the cells after stabilization of adhesion.
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Chesla, Scott E., Bryan T. Marshall e Cheng Zhu. "Measuring the Probability of Receptor Extraction From the Cell Membrane". In ASME 1997 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 1997. http://dx.doi.org/10.1115/imece1997-0262.
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Abstract Recently, there has been an increasing interest in measuring the interaction forces between cell adhesion receptors and their ligands [1–3]. These molecules are either anchored on the membrane of a cell or coated on the surface of a substratum. The two surfaces are joined together as a result of the formation of non-covalent bonds between the receptors and ligands. The forces are measured when the two surfaces are separated. In a theoretical paper published nineteen years ago, George Bell estimated the force required to break a receptor-ligand bond and that required to uproot the receptor from the cell membrane to be of the same order of magnitude [4]. The interpretation of the force data therefore requires the knowledge of detachment mode, i.e., via adhesive mechanism if the receptor-ligand bond is dissociated or via cohesive mechanism if the receptor-membrane anchor is disrupted.
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Authi, K. S., B. J. Evenden e N. Crawford. "ACTION OF GTPγS [GUANOSINE 5∲-0-(3-THIOPHOSPHATE)] ON SAPONIN-PERMEABILISED PLATELETS: INVOLVEMENT OF 'G' PROTEINS IN PLATELET ACTIVATION". In XIth International Congress on Thrombosis and Haemostasis. Schattauer GmbH, 1987. http://dx.doi.org/10.1055/s-0038-1644514.
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Certain ligand-receptor interactions at cell surfaces lead to the phospholipase-C (PLC) hydrolysis of phosphatidyl inositol (4.5) bisphosphate (PIP2). The products serve as intracellular second messengers, e.g. inositol (1.4.5) trisphosphate (IP3) releases Ca2+ from intracellular stores and diacylglycerol activates protein kinase-C. From studies using GTP and analogues (e.g. GTPγS) there is evidence of a key role for a guanine nucleotide binding protein(s) as a link between receptors and PIP2 hydrolysis. We report the actions of GTPγS on washed human platelets permeabilised with saponin (12-14 μg/ml) to allow penetration of low MWt polar substances. The responses to GTPγS are dose dependent (range 9-60 μM) and at 60 μM the agent induces shape change, aggregation and the secretion of 50% of previously incorporated [14C]-5HT. No effect of GTPγS is seen with intact cells. Shape change occurs 25-30 sec after GTPγS; aggregation and secretion is complete after 3 min. When GTP was used (up to 135 μM) with similarly permeabilised platelets no responses were initiated. Phosphatidylinositol turnover was monitored using 32P-labelling before permeabilisation. The addition of 90 μM GTPγS resulted in a 143 ± 23% (n=4) increase in 32P-phosphatidic acid (PA) with respect to the basal levels of “saponised control” cells. These findings suggest that GTPγS stimulates PLC activity through a ‘G’ protein interaction. The GDP analogue (GDPβS) produced no activation responses in saponised platelets but inhibited responses induced by GTPγS in a dose dependent manner (0-480 μM, max inhibition 480 μM). At 960 μM, GDPβS totally inhibited aggregation and secretion initiated by low doses of thrombin (0.1 U/ml) and collagen (1 μg/ml). Identical inhibition by GDPβS of thrombin and collagen-induced activation of intact platelets was observed indicating membrane penetration of this analogue. Shape change effects were not inhibited by GDPSS. The inhibitory effects of GDPSS towards thrombin and collagen induced secretion could be progressively overcome at higher doses of thrombin (0.2 U/ml - 2 U/ml) and collagen (5 μg/ml - 60 μg/ml) suggesting that at higher concentrations these agonists may exert effects through 'G' protein-independent mechanisms.
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Gupta, Vijay K., e Charles D. Eggleton. "A 3-D Computational Model of L-Selectin-PSGL-1 Dependent Homotypic Leukocyte Binding and Rupture in Shear Flow". In ASME 2012 Summer Bioengineering Conference. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/sbc2012-80862.
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Cell adhesion plays a pivotal role in diverse biological processes, including inflammation, tumor metastasis, arteriosclerosis, and thrombosis. Changes in cell adhesion can be the defining event in a wide range of diseases, including cancer, atherosclerosis, osteoporosis, and arthritis. Cells are exposed constantly to hemodynamic/hydrodynamic forces and the balance between the dispersive hydrodynamic forces and the adhesive forces generated by the interactions of membrane-bound receptors and their ligands determines cell adhesion. Therefore to develop novel tissue engineering based approaches for therapeutic interventions in thrombotic disorders, inflammatory, and a wide range of other diseases, it is crucial to understand the complex interplay among blood flow, cell adhesion, and vascular biology at the molecular level. In response to tissue injury or infection, polymorphonuclear (PMN) leukocytes are recruited from the bloodstream to the site of inflammation through interactions between cell surface receptors and complementary ligands expressed on the surface of the endothelium [1]. PMN-PMN interactions also contribute to the process of recruitment. It has been shown that PMNs rolling on activated endothelium cells can mediate secondary capture of PMNs flowing in the free blood stream through homotypic interactions [2]. This is mediated by L-selectin (ligand) binding to PSGL-1 (receptor) between a free-stream PMN and one already adherent to the endothelium cells [3]. Both PSGL-1 and L-selectin adhesion molecules are concentrated on tips of PMN microvilli [4]. Homotypic PMN aggregation in vivo or in vitro is supported by multiple L-selectin–PSGL-1 bondings between pairs of microvilli. The ultimate objective of our work is to develop software that can simulate the adhesion of cells colliding under hydrodynamic forces that can be used to investigate the complex interplay among the physical mechanisms and scales involved in the adhesion process. However, cell-cell adhesion is a complex phenomenon involving the interplay of bond kinetics and hydrodynamics. Hence, as a first step we recently developed a 3-D computational model based on the Immersed Boundary Method to simulate adhesion-detachment of two PMN cells in quiescent conditions and the exposing the cells to external pulling forces and shear flow in order to investigate the behavior of the nano-scale molecular bonds to forces applied at the cellular scale [5]. Our simulations predicted that the total number of bonds formed is dependent on the number of available receptors (PSGL-1) when ligands (L-selectin) are in excess, while the excess amount of ligands controls the rate of bond formation [5]. Increasing equilibrium bond length causes an increased intercellular contact area hence results in a higher number of receptor-ligand bonds [5]. Off-rates control the average number of bonds by modulating bond lifetimes while On-rate constants determine the rate of bond formation [5]. An applied external pulling force leads to time-dependent on- and off-rates and causes bond rupture [5]. It was shown that the time required for bond rupture in response to an applied external force is inversely proportional to the applied external force and decreases with increasing offrate [5]. Fig. 1 shows the time evolution of the total number of bonds formed for various values of NRmv (number of receptor) and NLmv (number of ligand). As expected, the total number of bonds formed at equilibrium is dependent on NRmv when NLmv is in excess. In this particular case study since two pairs (or four) microvilli each with NRmv are involved in adhesion hence the equilibrium bond number is approximately 4NRmv. It is noticed that for NRmv = 50, as we vary NLmv the mean value of the total number of bonds at equilibrium does not change appreciably. However, it can be noticed from Fig. 1 that for NRmv = 50, as the excess number of ligands (NLmv) increases there is a slight increase in the rate of bond formation due to the increase in probability of bond formation. Having developed confidence in the ability of the numerical method to simulate the adhesion of two cells that can form up to 200 bonds, we apply the method to study the effect of shear rate on the detachment of two cells. In particular, we first would like to establish the minimum shear rate needed for the two cells to detach for a given number of bonds between them. Fig. 2 shows the variation of force per bond at no rupture with number of bonds for various shear rates indicated. It is seen that at a given shear rate as the number of bonds increases the force per bond at no rupture decreases. This is attributed to the fact that force caused by shear flow is shared equally among the existing bonds. Further, it is seen that a given number of bonds as the shear rate increases the force per bond at no rupture increases. This is due to the fact that at a given number of bonds between the cells as we increase the shear rate the force caused by the flow increases hence the force per bond increases. We further notice that at shear rate = 3000 s−1 cells attached either by a single bond or by two bonds detach while they don’t for higher (> 2) number of bonds. This clearly demonstrate that there is a minimum shear rate needed to detach cells adhered by a given number of bonds. The higher the number of bonds, the higher the minimum shear rate for complete detachment of cells. For example, from Fig. 2 is it clear that for the cells adhered by two and five bonds the minimum shear rate needed for complete detachment of these two cells are 3000 s−1 and 6000 s−1, respectively.
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N’dri, Narcisse, Wei Shyy, Roger Tran-Son-Tay e H. S. Udaykumar. "A Multi-Scale Model for Cell Adhesion and Deformation". In ASME 2000 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2000. http://dx.doi.org/10.1115/imece2000-2069.
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Abstract A multi-scale computational approach for studying the adhesion kinetics and deformation of a cell on a substrate is presented. This method breaks the computational work into two separate but interrelated domains. At the cellular level, a continuum model satisfying the field equations for momentum transfer and mass continuity is adopted. At the receptor-ligand or molecular level, the bond force is mechanically represented by a spring, and the formation and dissociation of bonds are characterized by a reversible two-body kinetic model. The model demonstrates that as the reverse reaction rate increases, the receptor-ligand bonds break faster, and the opposite is observed when the forward reaction rate increases. As expected, the cell peeling time increases as the number of ligands increases until it equals the number of receptors. The peeling time becomes shorter when the spring constant or slippage constant is larger. Furthermore, as the cell velocity increases during the peeling process, the maximum bond length increases while the total peeling time decreases. Based on the information from the two modeling levels, dynamics of membrane movement can be computed, illustrating that the cell mechanical properties and surrounding fluid dynamics affect the receptor-ligand kinetics, and that these effects need to be included in any realistic cell-surface interaction models.
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Murgasova, Renata, Jan Sabo, Angelica L. Ottova e H. Ti Tien. "Ligand-receptor contact interactions using supported bilayer lipid membranes: cyclic voltammetry studies with electron mediators". In Smart Structures & Materials '95, editado por A. Peter Jardine. SPIE, 1995. http://dx.doi.org/10.1117/12.209816.
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Li, Jianrong, Tianle Cheng e Martin Y. M. Chiang. "Finite Element Modelling of Cell Adhesion Mediated by Receptor-Ligand Binding". In ASME 2009 Summer Bioengineering Conference. American Society of Mechanical Engineers, 2009. http://dx.doi.org/10.1115/sbc2009-206297.
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The process of cell adhesion and spreading on the extracellular matrix (ECM) protein layer is mediated by the interaction of cell receptors and ECM ligands [1]. Receptors diffuse along the cell membrane surface and interact with ligands in ECM to form bonds. Cells spread and the adhesion zone grows as bond formation at the adhesion front increases to a critical level. This process involves coupling of reaction-diffusion and mechanical contact between cells and ECM. In this study, a novel numerical algorithm is developed to implement this coupling into the finite element method for modeling the process of cell adhesion and spreading. By taking the mass diffusion and the user-defined gap conductance features provided in a commercial FEM code, Abaqus [2], the process has been solved in an integrated and fully coupled manner. Preliminary results have been obtained from the simulation of cell spreading on a rigid substrate. The influence of glycocalyx layer (present at cell surface) on the adhesion development has also been incorporated into the modeling.
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Goldsmith, Harry L. "Observing Human Blood Cells in Flow Through Microchannels". In ASME 2010 8th International Conference on Nanochannels, Microchannels, and Minichannels collocated with 3rd Joint US-European Fluids Engineering Summer Meeting. ASMEDC, 2010. http://dx.doi.org/10.1115/fedsm-icnmm2010-31330.
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For the rheologist, blood is essentially a concentrated suspension of biconcave 8-μm diameter red cells (40–45% by volume) that circulates within the body in vessels from 25 mm down to 5 μm diameter. Here, we describe in vitro tracking of blood cells in a traveling microtube apparatus and in a counter-rotating micro cone-plate device at low Reynolds numbers, Re. Observations of the flow behavior of individual red cells reveal a marked and continuously changing deformation and interaction of the cells in shear, and this, together with their migration away from the vessel wall accounts for the low whole blood overall viscosity compared to other concentrated suspensions and emulsions. Red cells also strongly affect the flow behavior and interactions of platelets and of white cells, which although present at much lower concentrations (0.3% by volume), play key roles in thrombosis, hemostasis, and inflammation. Studies of the kinetics of the formation and break-up of receptor-ligand bonds between membranes of platelets and of white cells in shear flow revealed single bond strengths of 50 −200 nN. Such micro particle image velocimetry (μPIV) studies have recently been considerably refined and extended to in vivo vessels such as postcapillary venules. Using submicron fluorescent latex spheres, the existence of an impermeable and hydrodynamically effective surface layer (< 0.5 μm thick) extending out from the vessel endothelium has been confirmed. The lecture is illustrated by movies of blood flow in vitro and in vivo.
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Hawiger, J. "PLATELET RECEPTOR RECOGNITION DOMAINS AND THEIR SYNTHETIC PEPTIDE ANALOGS". In XIth International Congress on Thrombosis and Haemostasis. Schattauer GmbH, 1987. http://dx.doi.org/10.1055/s-0038-1643726.
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Adhesive molecules and their receptorsplay an essential role in hemostasis and thrombosis. Platelet thrombi are formed through the interaction of cell adhesion molecules (CAMs) with intercellular adhesion molecules (IAMs)and substrate adhesion molecules (SAMs). Platelet CAMs encompass membrane glycoproteins lb, lib, Ilia,and possibly la and IV, which constitutemembrane receptors for IAMs(e.g., fibrinogen) and for SAMs encompassingvon Willebrand Factor (vWF), fibronectin, vitronectin, collagen, and thrcmbospondin. Receptorfunction of platelet CAMs can be specific,i.e., only one adhesive protein among IAMs and SAMs is selected forbinding as exemplified by GPIb and vWF. Alternatively,more than one adhesive protein can interact with platelet CAMs comprising the GPIIb/IIIa complex.This common adhesive receptor mechanism switched on by thrombin, ADP, phorbol ester or ionophore A23187 is turned off by a rise in intraplatelet cyclic AMP which provides a negative control.Fibrinogen, the most abundant adhesiveprotein in plasma, interacts with platelet CAMs via receptor recognition domains on gamma and alpha chains. Pinpointing platelet receptor recognition domain to a carboxy-terminal segment of the gamma chain encompassing residues 400-411gave rise to a series of synthetic peptide analogs which do not interfere with themetabolic pathways of platelets but blockbinding of I fibrinogen to its receptors on stimulated platelets, inhibit their aggregation in vitro, and formation of a platelet thrombus in vivo. The alpha chain of human fibrinogen contains the sequenceRGD (residues 95-97 and 572-574). Synthetpeptide analogs of the RGD sequence, which constitute the "cell adhesion site" of fibronectin, also inhibit binding of 125I-fibrinogen to stimulated platelets. However, these synthetic peptides are not "specific" for fibrinogen chains because thealpha chain of human fibrinogen which hasnosequence homology with gamma 400-411 is prevented by a peptide gamma 400-411 from interaction with platelet receptors. Viceversa, the human gamma chain is blocked by tetrapeptide RGDS not expressed in the human gamma chain. Interaction of human vWF with human platelets is blocked by synthetic peptide analogs of gamma 400-411 (not present in vWF)and of RGD sequence (present in vWF).These synthetic peptides inhibite "common" receptor pathwaystimulated with ADP, thrombin, or phorbolester, but they do not interfere with binding of 125I-vWF via a "specific" pathvoy induced with ristocetin and involving GPIb.The design of synthetic peptide analogs which inhibit platelet receptors for adhesive molecules includes the following considerations: ligand specificity (is thepeptide inhibitory toward binding of one or more adhesive molecules?),cell speciicity (is the peptide specific for platelets or does it perturb the adhesive properties of other cells, e.g.,endothelium?);the hydrophilic character; protection against degradation by peptidases; and a sufficiently long half-life to achieve platelet inhibitory potency in vivo without overloading the blood with excessive amounts of peptide.This is accomplished by constructing a peptide-albumin conjugate with ahalf-life extended at least 30 times.Whenpeptides are modeled with predominantly hydrophilic or hydrophobic residues, only the hydrophilic peptide remained active to block the platelet receptor. This agreed with the general observation that sequences on adhesive molecules that are knownto interact with cellular receptors have a hydrophilic rather than a hydrophobic character. Furthermore, changing the charge of synthetic peptides toward the negative reduced the reactivity, whereas introducing additional arginine residues enhanced the reactivity toward platelet receptors. Localization of the functionally important binding domain in the flexible segment of an adhesive protein increases the likelihood that the synthetic peptide will assume the conformation mimicking such a domain in the native adhesive protein. Structure-function studies of the receptor recognition domains on adhesive molecules led to development of a new class of platelet inhibitors acting at the membranereceptors responsible for anchoring of platelets to the vessel wall and linking them to each other.
Relatórios de organizações sobre o assunto "Membrane receptor-Ligand interactions"
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Rafaeli, Ada, Russell Jurenka e Chris Sander. Molecular characterisation of PBAN-receptors: a basis for the development and screening of antagonists against Pheromone biosynthesis in moth pest species. United States Department of Agriculture, janeiro de 2008. http://dx.doi.org/10.32747/2008.7695862.bard.
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The original objectives of the approved proposal included: (a) The determination of species- and tissue-specificity of the PBAN-R; (b) the elucidation of the role of juvenile hormone in gene regulation of the PBAN-R; (c) the identificationof the ligand binding domains in the PBAN-R and (d) the development of efficient screening assays in order to screen potential antagonists that will block the PBAN-R. Background to the topic: Moths constitute one of the major groups of pest insects in agriculture and their reproductive behavior is dependent on chemical communication. Sex-pheromone blends are utilised by a variety of moth species to attract conspecific mates. In most of the moth species sex-pheromone biosynthesis is under circadian control by the neurohormone, PBAN (pheromone-biosynthesis-activating neuropeptide). In order to devise ideal strategies for mating disruption/prevention, we proposed to study the interactions between PBAN and its membrane-bound receptor in order to devise potential antagonists. Major conclusions: Within the framework of the planned objectives we have confirmed the similarities between the two Helicoverpa species: armigera and zea. Receptor sequences of the two Helicoverpa spp. are 98% identical with most changes taking place in the C-terminal. Our findings indicate that PBAN or PBAN-like receptors are also present in the neural tissues and may represent a neurotransmitter-like function for PBAN-like peptides. Surprisingly the gene encoding the PBAN-receptor was also present in the male homologous tissue, but it is absent at the protein level. The presence of the receptor (at the gene- and protein-levels), and the subsequent pheromonotropic activity are age-dependent and up-regulated by Juvenile Hormone in pharate females but down-regulated by Juvenile Hormone in adult females. Lower levels of pheromonotropic activity were observed when challenged with pyrokinin-like peptides than with HezPBAN as ligand. A model of the 3D structure of the receptor was created using the X-ray structure of rhodopsin as a template after sequence alignment of the HezPBAN-R with several other GPCRs and computer simulated docking with the model predicted putative binding sites. Using in silico mutagenesis the predicted docking model was validated with experimental data obtained from expressed chimera receptors in Sf9 cells created by exchanging between the three extracellular loops of the HezPBAN-R and the Drosophila Pyrokinin-R (CG9918). The chimera receptors also indicated that the 3ʳᵈ extracellular loop is important for recognition of PBAN or Diapause hormone ligands. Implications: The project has successfully completed all the objectives and we are now in a position to be able to design and screen potential antagonists for pheromone production. The successful docking simulation-experiments encourage the use of in silico experiments for initial (high-throughput) screening of potential antagonists. However, the differential responses between the expressed receptor (Sf9 cells) and the endogenous receptor (pheromone glands) emphasize the importance of assaying lead compounds using several alternative bioassays (at the cellular, tissue and organism levels). The surprising discovery of the presence of the gene encoding the PBAN-R in the male homologous tissue, but its absence at the protein level, launches opportunities for studying molecular regulation pathways and the evolution of these GPCRs. Overall this research will advance research towards the goal of finding antagonists for this important class of receptors that might encompass a variety of essential insect functions.
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Altstein, Miriam, e Ronald J. Nachman. Rational Design of Insect Control Agent Prototypes Based on Pyrokinin/PBAN Neuropeptide Antagonists. United States Department of Agriculture, agosto de 2013. http://dx.doi.org/10.32747/2013.7593398.bard.
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The general objective of this study was to develop rationally designed mimetic antagonists (and agonists) of the PK/PBAN Np class with enhanced bio-stability and bioavailability as prototypes for effective and environmentally friendly pest insect management agents. The PK/PBAN family is a multifunctional group of Nps that mediates key functions in insects (sex pheromone biosynthesis, cuticular melanization, myotropic activity, diapause and pupal development) and is, therefore, of high scientific and applied interest. The objectives of the current study were: (i) to identify an antagonist biophores (ii) to develop an arsenal of amphiphilic topically active PK/PBAN antagonists with an array of different time-release profiles based on the previously developed prototype analog; (iii) to develop rationally designed non-peptide SMLs based on the antagonist biophore determined in (i) and evaluate them in cloned receptor microplate binding assays and by pheromonotropic, melanotropic and pupariation in vivo assays. (iv) to clone PK/PBAN receptors (PK/PBAN-Rs) for further understanding of receptor-ligand interactions; (v) to develop microplate binding assays for screening the above SMLs. In the course of the granting period A series of amphiphilic PK/PBAN analogs based on a linear lead antagonist from the previous BARD grant was synthesized that incorporated a diverse array of hydrophobic groups (HR-Suc-A[dF]PRLa). Others were synthesized via the attachment of polyethylene glycol (PEG) polymers. A hydrophobic, biostablePK/PBAN/DH analog DH-2Abf-K prevented the onset of the protective state of diapause in H. zea pupae [EC50=7 pmol/larva] following injection into the preceding larval stage. It effectively induces the crop pest to commit a form of ‘ecological suicide’. Evaluation of a set of amphiphilic PK analogs with a diverse array of hydrophobic groups of the formula HR-Suc-FTPRLa led to the identification of analog T-63 (HR=Decyl) that increased the extent of diapause termination by a factor of 70% when applied topically to newly emerged pupae. Another biostablePK analog PK-Oic-1 featured anti-feedant and aphicidal properties that matched the potency of some commercial aphicides. Native PK showed no significant activity. The aphicidal effects were blocked by a new PEGylated PK antagonist analog PK-dF-PEG4, suggesting that the activity is mediated by a PK/PBAN receptor and therefore indicative of a novel and selective mode-of-action. Using a novel transPro mimetic motif (dihydroimidazole; ‘Jones’) developed in previous BARD-sponsored work, the first antagonist for the diapause hormone (DH), DH-Jo, was developed and shown to block over 50% of H. zea pupal diapause termination activity of native DH. This novel antagonist development strategy may be applicable to other invertebrate and vertebrate hormones that feature a transPro in the active core. The research identifies a critical component of the antagonist biophore for this PK/PBAN receptor subtype, i.e. a trans-oriented Pro. Additional work led to the molecular cloning and functional characterization of the DH receptor from H. zea, allowing for the discovery of three other DH antagonist analogs: Drosophila ETH, a β-AA analog, and a dF analog. The receptor experiments identified an agonist (DH-2Abf-dA) with a maximal response greater than native DH. ‘Deconvolution’ of a rationally-designed nonpeptide heterocyclic combinatorial library with a cyclic bis-guanidino (BG) scaffold led to discovery of several members that elicited activity in a pupariation acceleration assay, and one that also showed activity in an H. zea diapause termination assay, eliciting a maximal response of 90%. Molecular cloning and functional characterization of a CAP2b antidiuretic receptor from the kissing bug (R. prolixus) as well as the first CAP2b and PK receptors from a tick was also achieved. Notably, the PK/PBAN-like receptor from the cattle fever tick is unique among known PK/PBAN and CAP2b receptors in that it can interact with both ligand types, providing further evidence for an evolutionary relationship between these two NP families. In the course of the granting period we also managed to clone the PK/PBAN-R of H. peltigera, to express it and the S. littoralis-R Sf-9 cells and to evaluate their interaction with a variety of PK/PBAN ligands. In addition, three functional microplate assays in a HTS format have been developed: a cell-membrane competitive ligand binding assay; a Ca flux assay and a whole cell cAMP ELISA. The Ca flux assay has been used for receptor characterization due to its extremely high sensitivity. Computer homology studies were carried out to predict both receptor’s SAR and based on this analysis 8 mutants have been generated. The bioavailability of small linear antagonistic peptides has been evaluated and was found to be highly effective as sex pheromone biosynthesis inhibitors. The activity of 11 new amphiphilic analogs has also been evaluated. Unfortunately, due to a problem with the Heliothis moth colony we were unable to select those with pheromonotropic antagonistic activity and further check their bioavailability. Six peptides exhibited some melanotropic antagonistic activity but due to the low inhibitory effect the peptides were not further tested for bioavailability in S. littoralis larvae. Despite the fact that no new antagonistic peptides were discovered in the course of this granting period the results contribute to a better understanding of the interaction of the PK/PBAN family of Nps with their receptors, provided several HT assays for screening of libraries of various origin for presence of PK/PBAN-Ragonists and antagonists and provided important practical information for the further design of new, peptide-based insecticide prototypes aimed at the disruption of key neuroendocrine physiological functions in pest insects.
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Eyal, Yoram, e Sheila McCormick. Molecular Mechanisms of Pollen-Pistil Interactions in Interspecific Crossing Barriers in the Tomato Family. United States Department of Agriculture, maio de 2000. http://dx.doi.org/10.32747/2000.7573076.bard.
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During the evolutionary process of speciation in plants, naturally occurring barriers to reproduction have developed that affect the transfer of genes within and between related species. These barriers can occur at several different levels beginning with pollination-barriers and ending with hybrid-breakdown. The interaction between pollen and pistils presents one of the major barriers to intra- and inter-specific crosses and is the focus of this research project. Our long-term goal in this research proposal was defined to resolve questions on recognition and communication during pollen-pistil interactions in the extended tomato family. In this context, this work was initiated and planned to study the potential involvement of tomato pollen-specific receptor-like kinases (RLK's) in the interaction between pollen and pistils. By special permission from BARD the objectives of this research were extended to include studies on pollen-pistil interactions and pollination barriers in horticultural crops with an emphasis on citrus. Functional characterization of 2 pollen-specific RLK's from tomato was carried out. The data shows that both encode functional kinases that were active as recombinant proteins. One of the kinases was shown to accumulate mainly after pollen germination and to be phosphorylated in-vitro in pollen membranes as well as in-vivo. The presence of style extract resulted in dephosphorylation of the RLK, although no species specificity was observed. This data implies a role for at least one RLK in pollination events following pollen germination. However, a transgenic plant analysis of the RLK's comprising overexpression, dominant-negative and anti-sense constructs failed to provide answers on their role in pollination. While genetic effects on some of the plants were observed in both the Israeli and American labs, no clear functional answers were obtained. An alternative approach to addressing function was pursued by screening for an artificial ligand for the receptor domain using a peptide phage display library. An enriched peptide sequence was obtained and will be used to design a peptide-ligand to be tested for its effect o pollen germination and tube growth. Self-incompatibility (SI) in citrus was studied on 3 varieties of pummelo. SI was observed using fluorescence microscopy in each of the 3 varieties and compatibility relations between varieties was determined. An initial screen for an S-RNase SI mechanism yielded only a cDNA homologous to the group of S-like RNases, suggesting that SI results from an as yet unknown mechanism. 2D gel electrophoresis was applied to compare pollen and style profiles of different compatibility groups. A "polymorphic" protein band from style extracts was observed, isolated and micro-sequenced. Degenerate primers designed based on the peptide sequence date will be used to isolate the relevant genes i order to study their potential involvement in SI. A study on SI in the apple cultivar Top red was initiated. SI was found, as previously shown, to be complete thus requiring a compatible pollinator variety. A new S-RNase allele was discovered fro Top red styles and was found to be highly homologous to pear S-RNases, suggesting that evolution of these genes pre-dated speciation into apples and pears but not to other Rosaceae species. The new allele provides molecular-genetic tools to determine potential pollinators for the variety Top red as well as a tool to break-down SI in this important variety.