Auswahl der wissenschaftlichen Literatur zum Thema „PDZ domain proteins“

PDZ domains are highly abundant protein–protein interaction modules and are often found in multidomain scaffold proteins. PDZ-domain-containing scaffold proteins regulate multiple biological processes, including trafficking and clustering receptors and ion channels at defined membrane regions, organizing and targeting signalling complexes at specific cellular compartments, interfacing cytoskeletal structures with membranes, and maintaining various cellular structures. PDZ domains, each with ~90-amino-acid residues folding into a highly similar structure, are best known to bind to short C-terminal tail peptides of their target proteins. A series of recent studies have revealed that, in addition to the canonical target-binding mode, many PDZ–target interactions involve amino acid residues beyond the regular PDZ domain fold, which we refer to as extensions. Such extension sequences often form an integral structural and functional unit with the attached PDZ domain, which is defined as a PDZ supramodule. Correspondingly, PDZ-domain-binding sequences from target proteins are frequently found to require extension sequences beyond canonical short C-terminal tail peptides. Formation of PDZ supramodules not only affords necessary binding specificities and affinities demanded by physiological functions of PDZ domain targets, but also provides regulatory switches to be built in the PDZ–target interactions. At the 20th anniversary of the discovery of PDZ domain proteins, we try to summarize structural features and target-binding properties of such PDZ supramodules emerging from studies in recent years.

Over 250 PDZ (PSD95/Dlg/ZO-1) domain-containing proteins have been described in the human proteome. As many of these possess multiple PDZ domains, the potential combinations of associations with proteins that possess PBMs (PDZ-binding motifs) are vast. However, PDZ domain recognition is a highly specific process, and much less promiscuous than originally thought. Furthermore, a large number of PDZ domain-containing proteins have been linked directly to the control of processes whose loss, or inappropriate activation, contribute to the development of human malignancies. These regulate processes as diverse as cytoskeletal organization, cell polarity, cell proliferation and many signal transduction pathways. In the present review, we discuss how PBM–PDZ recognition and imbalances therein can perturb cellular homoeostasis and ultimately contribute to malignant progression.

PDZ/LIM genes encode a group of proteins that play very important, but diverse, biological roles. They have been implicated in numerous vital processes, e.g., cytoskeleton organization, neuronal signaling, cell lineage specification, organ development, and oncogenesis.In mammals, there are ten genes that encode for both a PDZ domain, and one or several LIM domains: four genes of the ALP subfamily (ALP, Elfin, Mystique, and RIL), three of the Enigma subfamily (Enigma, Enigma Homolog, and ZASP), the two LIM kinases (LIMK1 and LIMK2), and the LIM only protein 7 (LMO7). Functionally, all PDZ and LIM domain proteins share an important trait, i.e., they can associate with and/or influence the actin cytoskeleton.We review here the PDZ and LIM domain—encoding genes and their different gene structures, their binding partners, and their role in development and disease. Emphasis is laid on the important questions: why the combination of a PDZ domain with one or more LIM domains is found in such a diverse group of proteins, and what role the PDZ/LIM module could have in signaling complex assembly and localization.Furthermore, the current knowledge on splice form specific expression and the function of these alternative transcripts during vertebrate development will be discussed, since another source of complexity for the PDZ and LIM domain—encoding proteins is introduced by alternative splicing, which often creates different domain combinations.

Sorting nexin 27 (SNX27) contains a PDZ domain that is phylogenetically related to the PDZ domains of the NHERF proteins. Studies on nonepithelial cells have shown that this protein is located in endosomes, where it regulates trafficking of cargo proteins in a PDZ domain–dependent manner. However, the role of SNX27 in trafficking of cargo proteins in epithelial cells has not been adequately explored. Here we show that SNX27 directly interacts with NHE3 (C-terminus) primarily through the SNX27 PDZ domain. A combination of knockdown and reconstitution experiments with wild type and a PDZ domain mutant (GYGF → GAGA) of SNX27 demonstrate that the PDZ domain of SNX27 is required to maintain basal NHE3 activity and surface expression of NHE3 in polarized epithelial cells. Biotinylation-based recycling and degradation studies in intestinal epithelial cells show that SNX27 is required for the exocytosis (not endocytosis) of NHE3 from early endosome to plasma membrane. SNX27 is also required to regulate the retention of NHE3 on the plasma membrane. The findings of the present study extend our understanding of PDZ-mediated recycling of cargo proteins from endosome to plasma membrane in epithelial cells.

PDZ and LIM domains are modular protein interaction motifs present in proteins with diverse functions. Enigma is representative of a family of proteins composed of a series of conserved PDZ and LIM domains. The LIM domains of Enigma and its most related family member, Enigma homology protein, bind to protein kinases, whereas the PDZ domains of Enigma and family member actin-associated LIM protein bind to actin filaments. Enigma localizes to actin filaments in fibroblasts via its PDZ domain, and actin-associated LIM protein binds to and colocalizes with the actin-binding protein α-actinin-2 at Z lines in skeletal muscle. We show that Enigma is present at the Z line in skeletal muscle and that the PDZ domain of Enigma binds to a skeletal muscle target, the actin-binding protein tropomyosin (skeletal β-TM). The interaction between Enigma and skeletal β-TM was specific for the PDZ domain of Enigma, was abolished by mutations in the PDZ domain, and required the PDZ-binding consensus sequence (Thr-Ser-Leu) at the extreme carboxyl terminus of skeletal β-TM. Enigma interacted with isoforms of tropomyosin expressed in C2C12 myotubes and formed an immunoprecipitable complex with skeletal β-TM in transfected cells. The association of Enigma with skeletal β-TM suggests a role for Enigma as an adapter protein that directs LIM-binding proteins to actin filaments of muscle cells.

The human homologue (hDIg) of the Drosophila discs-large tumor suppressor (DIg) is a multidomain protein consisting of a carboxyl-terminal guanylate kinase-like domain, an SH3 domain, and three slightly divergent copies of the PDZ (DHR/GLGF) domain. Here have examined the structural organization of the three PDZ domains of hDIg using a combination of protease digestion and in vitro binding measurements. Our results show that the PDZ domains are organized into two conformationally stable modules one (PDZ, consisting of PDZ domains 1 and 2, and the other (PDZ) corresponding to the third PDZ domain. Using amino acid sequencing and mass spectrometry, we determined the boundaries of the PDZ domains after digestion with endoproteinase Asp-N, trypsin, and alpha-chymotrypsin. The purified PDZ1+2, but not the PDZ3 domain, contains a high affinity binding site for the cytoplasmic domain of Shaker-type K+ channels. Similarly, we demonstrate that the PDZ1+2 domain can also specifically bind to ATP. Furthermore, we provide evidence for an in vivo interaction between hDIg and protein 4.1 and show that the hDIg protein contains a single high affinity protein 4.1-binding site that is not located within the PDZ domains. The results suggest a mechanism by which PDZ domain-binding proteins may be coupled to ATP and the membrane cytoskeleton via hDlg.

Zonula occludens proteins (ZOs), including ZO1/2/3, are tight junction-associated proteins. Each of them contains three PDZ domains. It has been demonstrated that ZO1 can form either homodimers or heterodimers with ZO2 or ZO3 through the second PDZ domain. However, the underlying structural basis is not well understood. In this study, the solution structure of the second PDZ domain of ZO2 (ZO2-PDZ2) was determined using NMR spectroscopy. The results revealed a novel dimerization mode for PDZ domains via three-dimensional domain swapping, which can be generalized to homodimers of ZO1-PDZ2 or ZO3-PDZ2 and heterodimers of ZO1-PDZ2/ZO2-PDZ2 or ZO1-PDZ2/ZO3-PDZ2 due to high conservation between PDZ2 domains in ZO proteins. Furthermore, GST pulldown experiments and immunoprecipitation studies demonstrated that interactions between ZO1-PDZ2 and ZO2-PDZ2 and their self-associations indeed exist both in vitro and in vivo. Chemical cross-linking and dynamic laser light scattering experiments revealed that both ZO1-PDZ2 and ZO2-PDZ2 can form oligomers in solution. This PDZ domain-mediated oligomerization of ZOs may provide a structural basis for the polymerization of claudins, namely the formation of tight junctions.

Abstract The Z-disk is a sophisticated structure that connects adjacent sarcomeres in striated muscle myofibrils. α-Actinin provides strength to the Z-disks by crosslinking the actin filaments of adjacent sarcomeres. α-Actinin is an antiparallel homodimer, composed of an N-terminal actin binding domain (ABD), the central rod domain, and two pairs of C-terminal EF-hands. The PDZ-LIM domain proteins interact with α-actinin at the Z-disk. Of these proteins, only the actinin-associated LIM protein (ALP), Z-band alternatively spliced PDZ-containing protein (ZASP/Cypher) and C-terminal LIM protein (CLP36) have a ZASP/Cypher-like (ZM) motif consisting of 26-27 conserved residues in the internal region between the PDZ and LIM domains. The aim of this work was to understand the molecular interplay between the ZM-motif containing members of the PDZ-LIM proteins and α-actinin. To unveil the biological relevance of the interaction between the PDZ-LIM proteins and α-actinin, naturally occurring human ZASP/Cypher mutations were analyzed. Two interaction sites were found between ALP, CLP36 and α-actinin using recombinant purified proteins in surface plasmon resonance (SPR) analysis. The PDZ domain of ALP and CLP36 recognized the C-terminus of α-actinin, whereas the internal regions bound to the rod domain. Further characterization showed that the ALP internal region adopts and extended conformation when interacting with α-actinin and that the ZM-motif partly mediated the interaction, but did not define the entire interaction area. ZASP/Cypher also interacted and competed with ALP in binding to the rod domain. The internal fragments containing the ZM-motif were important for co-localization of ALP and ZASP/Cypher with α-actinin at the Z-disks and on stress fibers. The absence of ALP and ZASP/Cypher in focal contacts indicates that other interacting molecules, for instance vinculin and integrin, may compete in binding to the rod in these areas or additional proteins are required in targeting to these locations. The co-localization of the ZASP/Cypher with α-actinin could be released by disrupting the stress fibers leading to an accumulation of α-actinin in the cell periphery, whereas ZASP/Cypher was not in these areas. This suggests that an intact cytoskeleton is important for ZASP/Cypher interaction with α-actinin. Earlier studies have shown that mutations in the ZASP/Cypher internal region are associated with muscular diseases. These mutations, however, did not affect ZASP/Cypher co-localization with α-actinin or the stability of ZASP/Cypher proteins. The Z-disk possesses a stretch sensor, which is involved in triggering hypertrophic growth as a compensatory mechanism to increased workloads. α-Actinin is a docking site of molecules that are involved in hypertrophic signaling cascades mediated by calsarcin-calcineurin and protein kinase C (PKC) isoforms. The internal interaction site may be involved in targeting PKCs, which bind to the LIM domains of ZASP/Cypher, to the Z-disks. The similar location of the internal interaction site with calsarcin on the rod suggests that ZASP/Cypher, ALP and CLP36 may regulate calsarcin-mediated hypertrophic signaling.

Wnt signalling is one the most important pathways involved in embryonic development. It controls a number of processes including cellular proliferation, stem cells maintenance, cell fate decisions and establishment of tissue polarity. It is also frequently deregulated in human cancers. Frizzled-7 is a member of the Frizzled family responsible for the signal transduction in Wnt signalling. Frizzled-7 has been reported to be upregulated in several types: of cancer. Furthermore, recent reports suggest that endocytosis of Frizzled may play a critical enhancing role in Wnt signal transduction, thus facilitating cancer development. We demonstrate here that the C-terminal PDZ binding motif (PDZ-BM) of Frizzled-7 contributes to signalling triggered by the receptor. We also explore the interaction between Frizzled-7 and syntenin-1, a PDZ domain containing protein that controls endocytic trafficking of various transmembrane proteins. We demonstrate that syntenin-1 regulates Frizzled-7 cell distribution and also modulates canonical Wnt signalling in epithelial breast cancer cells. Further, we report that the C-terminal PDZ-BM of Fz7 is indispensable for the receptor interaction with a number of PDZ proteins that control protein trafficking and cell polarity. Among these PDZ proteins are LNXl and LNX2, E3 ubiquitin ligases which are known to control trafficking of transmembrane proteins. In this study we characterize the interaction between Frizzled-7 and LNX2. We demonstrate that LNX2 influences ubiquitylation of Frizzled-7 and has the ability to moderate signal transduction within the canonical Wnt pathway in breast cancer cells.

The Z-disc of striated muscle cells is a highly specialized three-dimensional structure which delineates the boundary of the individual sarcomeres. It accomplishes a unique role by anchoring actin filaments and acts as a molecular trigger for contraction. Beyond a well-defined structural role, in recent years it is emerging the hypothesis that Z-disc may be directly involved in the perception and transmission of muscular stress signals. To achieve these complex functions, many Z-disc proteins are involved in multiple protein interactions. The importance of these interactions is indicated by the fact that mutations in several Z-disc proteins can result in muscular dystrophies and/or cardiomyopathies in human and mice. The knowledge of Z-disc interactome and its regulation would improve by far the comprehension of the Z-disc biology and the onset of muscular disorders. The main goal of my project was to understand the complex network of protein-protein interactions occurring at the Z-disc of skeletal and cardiac muscle. In particular, my work was focused on two groups of Z-disc proteins: the FATZ and myotilin protein families on one hand, and some proteins belonging to the enigma family on the other hand. This work led to the identification of a specific interaction between the PDZ domains of enigma family members and the C-terminal five amino acids of the FATZ and myotilin families. The work of this thesis is part of a wider project involving the groups of Dr. G. Faulkner at ICGEB, Trieste, and Prof. O. Carpen at University of Turku, Finland. Together with our collaborators we noted that the C-terminal five amino acids of FATZ-1 (ETEEL), FATZ-2 (ESEDL), FATZ-3 (ESEEL), myotilin (ESEEL), palladin (ESEDL) and myopalladin (ESDEL) are highly similar. Searches in protein sequence database revealed that this E-[S/T]-[D/E]-[D/E]-L motif is restricted in Vertebrates to the FATZ and myotilin families of proteins, and it is evolutionary conserved from zebrafish to humans, indicating its importance for their biological function. The ELM program (a source for predicting functional sites in eukaryotic proteins) predicted that the terminal four amino acids of the FATZ family, myotilin, palladin and myopalladin constitute a binding motif for class III PDZ domain proteins (X-[D/E]-X-[V/I/L]). The first object of my work was to determine if the proteins with this new type of class III PDZ binding motif at their C-terminal could effectively bind PDZ domains. We knew from the literature that ZASP binds to all the three members of the FATZ family by means of its N-terminal PDZ domain, and that the C-terminal region of myotilin interacts with ZASP. In addition to ZASP, other two members of the enigma family of PDZ proteins, ALP and CLP-36, were included in this study. Both the full-length and the truncated (lacking the last five amino acids) version of the FATZ and myotilin families were produced as native proteins and tested for PDZ binding using the AlphaScreen (Amplified Luminescence Proximity Homogeneous Assay) technique. Biotinylated phosphorylated and non-phosphorylated peptides corresponding to the C-terminal five amino acids of the FATZ family, myotilin, palladin and myopalladin were also used in AlphaScreen interaction experiments, as well as a control peptide having E instead of L as its last amino acid (ESEEE). The results presented in this thesis show that the final five amino acids of the FATZ and myotilin families of proteins are responsible for the binding to the PDZ domains of ZASP, ALP and CLP-36, and that the nature of the last amino acid of the motif is crucial for the interaction. We also show that phosphorylation of the ligand sequence modulates the ability of the peptides to bind to the PDZ domains of the enigma family. ?-actinin-2 was included in this study as its C-terminus (GESDL) is classified as a class I PDZ binding motif that is able to bind to ZASP and ALP PDZ domains. AlphaScreen experiments confirm the binding of both the full-length and the C-terminal phosphorylated and non-phosphorylated peptides of ?-actinin-2 to the PDZ domains of ZASP and ALP, and they also reveal an interaction with the PDZ domain of CLP-36. These interactions were verified using another in vitro binding technique, the TranSignal PDZ Domain Array. Based on the results of the PDZ arrays, RIL was found to be another member of the enigma family capable to bind to the E-[S/T]-[D/E]-[D/E]-L motif. Therefore, these final five amino acids can be considered a novel type of class III PDZ binding motif specific for the PDZ domains of enigma proteins. To better quantify the strength of the noted interactions, SPR (Surface Plasmon Resonance) experiments were performed in the laboratory of Dr. A. Baines at University of Kent, UK. The affinities of the interactions between the PDZ domain of ZASP and some of the phosphorylated and non-phosphorylated peptides of the FATZ and myotilin families result to be in the nM range. The SPR results also demonstrate a new interaction between the PDZ domain of ZASP and ANKRD2. This protein is a member of the MARP family and it is thought to be involved in muscle stress response pathways. ANKRD2 localizes both in the sarcomeric I-band and the nucleus, and it is able to bind to several transcription factors, including YB-1, PML and p53. This interaction strengthens the hypothesis that, besides a structural function, Z-disc could have a role in cell signalling. The fact that at the Z-disc many proteins can interact with the same partners, it would be helpful to define the pattern and level of expression of the individual proteins in different muscle tissues. Another aim of my work was to measure the abundance of mRNAs of some Z-disc proteins using the Real-Time PCR technique. Four different muscles from adult mice were considered: tibialis (a fast-twitch skeletal muscle), soleus (a slow-twitch skeletal muscle), gastrocnemius (a skeletal muscle with mixed fibers) and heart (cardiac muscle). The different distribution of the FATZ proteins, myotilin and the alternatively spliced variants of ZASP suggest that, at least in mouse, the interactions between these proteins could be compartmentalized in distinct fiber types.
Il disco-Z del muscolo striato è una struttura molecolare altamente specializzata a livello della quale si instaurano numerose interazioni proteina-proteina. Il disco-Z delinea il confine dei singoli sarcomeri, fornendo un punto di ancoraggio per i filamenti sottili di actina; il loro scorrimento sui filamenti spessi di miosina produce la forza meccanica responsabile della contrazione. Uno dei ruoli chiave del disco-Z, dunque, è quello di trasmettere la tensione generata dalla struttura seriale dei sarcomeri lungo le miofibrille e, di conseguenza, lungo tutto il muscolo. Al di là di un evidente significato strutturale, negli ultimi anni sta diventando sempre più consistente l’ipotesi di un suo coinvolgimento anche nella percezione e nella trasmissione di segnali. L’importanza delle interazioni tra le proteine del disco-Z è indicata dal fatto che mutazioni in molte di queste proteine possono risultare in distrofie muscolari e/o cardiomiopatie sia in uomo sia in topo. Una più ampia conoscenza delle interazioni che si articolano a livello del disco-Z e, in generale, degli eventi che le regolano, aiuterebbe a chiarire la biologia del disco-Z e l’insorgenza di eventuali patologie associate. Il mio progetto di Dottorato è stato incentrato su due gruppi di proteine sarcomeriche e sulle loro interazioni: le proteine delle famiglie FATZ e miotilina da un lato, e alcune proteine appartenenti alla famiglia enigma dall’altro. Questo lavoro ha portato all’identificazione di un’interazione specifica tra i domini PDZ delle proteine della famiglia enigma e gli ultimi cinque residui aminoacidici presenti nelle proteine delle famiglie FATZ e miotilina. Il lavoro di questa tesi fa parte di un progetto più ampio che coinvolge i gruppi coordinati dalla Dr.ssa G. Faulkner dell’ICGEB, Trieste, e il Prof. O. Carpen dell’Università di Turku, Finlandia. Grazie alla loro collaborazione, è stato possibile notare che i cinque residui C-terminali delle proteine FATZ-1 (ETEEL), FATZ-2 (ESEDL), FATZ-3 (ESEEL), miotilina (ESEEL), palladina (ESEDL) e miopalladina (ESDEL) sono molto simili. Una ricerca effettuata in database di sequenze proteiche ha rivelato che questo motivo, E-[S/T]-[D/E]-[D/E]-L, è quasi esclusivamente ristretto nei Vertebrati alle proteine delle famiglie FATZ e miotilina; inoltre, esso sembra essere conservato da zebrafish ad uomo, suggerendo la sua importanza per le proteine che lo contengono. Il programma ELM (che predice siti funzionali in proteine eucariotiche) ha predetto che gli ultimi quattro amino acidi delle proteine FATZ, miotilina, palladina e miopalladina costituiscono un motivo di legame per le proteine con domini PDZ di classe III (X-[D/E]-X-[V/I/L]). Il mio primo obiettivo è stato quello di verificare se le proteine caratterizzate da questo nuovo motivo C-terminale potessero effettivamente legare domini PDZ. E’ noto dalla letteratura che tutti e tre i componenti della famiglia FATZ legano il PDZ di ZASP, e che l’interazione tra ZASP e miotilina è mediata dalla regione C-terminale di quest’ultima. Oltre a ZASP, altri due membri della famiglia enigma, ALP e CLP-36, sono stati inclusi nello studio. Le proteine della famiglia FATZ e miotilina sono state prodotte sia in versione full-length sia priva degli ultimi cinque amino acidi per essere utilizzate in saggi di interazione AlphaScreen (Amplified Luminescence Proximity Homogeneous Assay). Peptidi biotinilati, fosforilati e non, corrispondenti ai cinque amino acidi finali delle FATZ, miotilina, palladina e miopalladina sono stati inoltre impiegati nei saggi AlphaScreen, così come un peptide di controllo avente in ultima posizione un acido glutammico (E) invece che una leucina (L). I risultati riportati in questa tesi dimostrano che gli ultimi cinque amino acidi delle proteine delle famiglie FATZ e miotilina sono responsabili del legame ai domini PDZ di ZASP, ALP e CLP-36, e che la natura dell’ultimo residuo aminoacidico è cruciale per questa interazione. Inoltre, la fosforilazione del residuo di serina o treonina del ligando C-terminale può influenzare il legame dei peptidi nei confronti dei domini PDZ della famiglia enigma. La proteina ?-actinina-2 è stata introdotta nello studio, poiché la sua sequenza C-terminale (GESDL) è classificata come motivo di legame per i domini PDZ di classe I (X-[S/T]-X-[V/I/L]). Gli esperimenti AlphaScreen hanno confermato l’interazione di ?-actinina-2 (sia della forma full-length sia dei peptidi C-terminali, fosforilati e non) con i PDZ di ZASP e ALP, e hanno fatto emergere una nuova interazione con il PDZ di CLP-36. Molte di queste interazioni sono state verificate con un altro metodo di interazione proteina-proteina in vitro, il TranSignal PDZ Domain Array. Sulla base dei risultati di PDZ array è stato possibile identificare un altro membro della famiglia di proteine enigma, RIL, in grado di legare il motivo E-[S/T]-[D/E]-[D/E]-L. Possiamo considerare questi cinque amino acidi C-terminali come un nuovo motivo di legame per le proteine con domini PDZ di classe III, specifico per i domini PDZ delle proteine enigma. Per poter meglio quantificare la forza delle interazioni studiate, alcuni esperimenti di SPR (Surface Plasmon Resonance) sono stati eseguiti nel laboratorio del Dr. A. Baines all’Università di Kent, UK. Le affinità delle interazioni tra il dominio PDZ di ZASP e alcuni dei peptidi fosforilati e non-fosforilati delle famiglie di proteine FATZ e miotilina risultano essere nell’ordine del nM. Gli esperimenti di SPR hanno portato anche all’identificazione di un’interazione tra il PDZ di ZASP e ANKRD2. Si pensa che questa proteina, membro della famiglia MARP, sia coinvolta nelle vie di risposta a stress muscolari. ANKRD2 può trovarsi sia nella banda-I del sarcomero sia nel nucleo ed è in grado di legare diversi fattori di trascrizione, come YB-1, PML e p53. La scoperta di questa interazione rafforza l’ipotesi che il disco-Z, oltre ad un ruolo specificamente strutturale, potrebbe essere coinvolto in vie di segnalazione. Dal momento che a livello del disco-Z molte proteine hanno più di un partner proteico, sarebbe utile cercare di definire il livello e il profilo di espressione delle singole proteine in tessuti muscolari con diverse caratteristiche. Un altro obiettivo del mio lavoro è stato quindi quello di valutare l’abbondanza degli mRNA di alcune delle proteine del disco-Z da me studiate con la Real-Time PCR. Allo scopo sono stati presi in considerazione quattro tessuti muscolari di topo adulto: il tibiale (un muscolo scheletrico a contrazione rapida), il soleo (un muscolo scheletrico a contrazione lenta), il gastrocnemio (un muscolo scheletrico con fibre miste) e il muscolo cardiaco. La differente distribuzione delle FATZ, miotilina e ZASP (con le sue varianti di splicing) suggerisce che, almeno in topo, le interazioni tra queste proteine potrebbero essere compartimentalizzate in distinte fibre muscolari.

PSD-95/Dlg/ZO-1 (PDZ) domain - PDZ binding motif (PBM) interactions have been one of the most well studied protein-protein interaction systems through biochemical, biophysical and high-throughput screening (HTS) strategies. This has allowed us to understand the mechanism of individual PDZ-PBM interactions and the re-engineering of PBMs to bind tighter or to gain or lose certain specificity. However, there are several thousand native PDZ domains whose biological ligands remain unknown. Because of the low sequence identity among PDZ domain homologues, promiscuous binding profiles (defined as a PDZ domain that can accommodate a set of PBMs or a PBM that can be recognized by many PDZ domains), and context-dependent interaction mechanism, we have an inadequate understanding of the general molecular mechanisms that determine the PDZ-PBM specificity. Therefore, predicting PDZ specificity has been elusive. In addition, no de novo PBM ligand or artificial non-native PDZ domain have been successfully designed. This reflects the general challenges in understanding the general principles of PDZ-ligand interactions, namely that they are context-dependent, exhibit weak binding affinity, narrow binding energy range, and larger interaction surface than other protein-ligand interactions. Together, PDZ domains make good model systems to investigate the fundamental principles of protein-protein interactions with a wide spectrum of biomedical implications. My studies suggest that understanding PBM specificity with the set of structural positions forming the binding pocket can connect sequence, structure and function of a PDZ domain in a general context. They also suggest that this way of understanding the specificity will shed light on prediction and engineering of specificity rationally. Structural analysis on most of the available PDZ domain structures was established to support the principle (Chapter I). The principle was tested against two different types of PBM; C-terminal PBM (Chapter II) and internal PBM (Chapter III), and shown to support better understanding and design of PDZ domain specificity. We further applied the principle to design de novo PDZ domains, and the preliminary data hints that it is optimistic to engineer PDZ domain specificity (Appendix A and B).

AbstractThe Discovery of the novel optimized structures of small molecules for selective targeting is one of the challenging tasks in drug designing. Bioisosteres are the key components of the lead compound, which provide hidden power to the compound scaffold for selective targeting. We are presenting a database, named CoSSDb which stands for Co-crystallized Sub-Structure Database. The CoSSDb contains ligand sub-structures as possible bioisosteres. extracted from PDB files, available in Protein Data Bank. Sub-structures were extracted through an algorithm, which utilizes the location of atoms in the 3D domain of the complex ligand & protein. It processes the relative positioning of atoms for demarcation of the influential part of the ligand, which interacts with macromolecule and provides potency to that ligand for binding with a specific binding pocket of the protein. The algorithm was used to extract sub-structures from the ligands co-crystallized with proteins involved in cancer. About 7721 x-ray crystallography PDB files were processed, and 654 non-redundant substructures were identified. These sub-structures will be useful during designing & optimization of novel ligands for selective targets. The database is freely accessible at ‘https://opticket49.wixsite.com/substructdb’.

Abstract The hydrolysis of a minor membrane phospholipid, phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P2) by a specific phospholipase C (PLC) is one of the earliest key events in the regulation of various cell functions by a number of extracellular signalling molecules (1). This reaction produces two intracellular messengers, diacylglycerol (DAG) and inositol 1,4,5-trisphosphate (Ins(1,4,5)P3), which mediate the activation of protein kinase C (PKC) and intracellular Ca2+ release, respectively. Ins(1,4,5)P3 is further converted by the action of several distinct kinases and phosphatases to various inositol phosphates, some of which have been implicated for distinct cellular functions (see Chapter 10). PtdIns(4,5)P2 is a precursor not only for Ins(1,4,5)P3 and DAG but also for the newly emerging messenger PtdIns(3,4,5)P3 that is produced by phosphoinositide 3-kinase (2; see also Chapter 2). PtdIns(3,4,5)P3 accumulates in cells that have been activated through protein tyrosine kinase (PTK)- and G-protein-linked receptors, and has been known to modulate the activities of cellular effector molecules, such as the small GTP-binding protein Rac, the Ser/Thr protein kinase B (PKB; also known as Akt), phosphoinositide-dependent kinase (PDK; also called PKB kinase), Bruton’s tyrosine kinase (Btk), certain isoforms of PKC, and Grp-1 (a guanine nucleotide exchange factor for the small G proteins ARF) (2). PtdIns(3,4,5)P3 also appears to function as a general component of PLC-γ-dependent calcium signalling pathway (see below). PtdIns(4,5)P2 directly modulates the function of protein kinase C, phospholipase D (PLD), and phospholipase A2 (PLA2) (3–5). PtdIns(4,5)P2 regulates actin polymerization and depolymerization processes by binding to actin regulatory proteins, such as profilin, cofilin, gelsolin, α-actinin, and gCap (6; see also Chapter 5). Finally, PtdIns(4,5)P2 binds to pleckstrin homology (PH) domains and thus serves as a membrane docking site for a host of PH domain-containing proteins (7).

Abstract The human PAX genes encode a group of sequence-specific transcription factors that play important roles in development and cell differentiation (Underhill, 2000; Chi and Epstein, 2002). Pax proteins are characterized by a 128–amino acid DNA-binding paired domain (PD) and are highly conserved in metazoans. Four of nine mammalian Pax proteins also contain a homeodomain (HD), and six are directly implicated in congenital syndromes or cancer in humans.

An analogous relationship exists between the kinematic structures of proteins and robotic mechanisms. Hence, using this analogy, we attempt to understand the internal motions of proteins from the perspective of robot kinematics. In this study, we propose a method called group forced response (GFR) method for predicting the internal motion of proteins on the basis of their three-dimensional structural data (PDB data). In this method, we apply forces in static equilibrium to groups of atoms (e.g., secondary structures, domains, and subunits) and not to specific atoms. Furthermore, we predict the internal motion of proteins by analyzing the relative motion caused among groups by the applied forces. First, we show a method for approximately modeling protein structures as a robotic mechanism and the basic kinematic equations of the model. Next, the GFR method is formulated (e.g., Jacobian matrix for group motions, magnitude of forces applied to groups, and decomposition of motions into modes according to structural compliances). Finally, we present example applications of the proposed method in real protein structures. Despite the approximations in the model, low computational cost, and use of simple calculation parameters, the results almost agree with measured internal motions.

Proteins assume a suitable spatial structure to effectively execute their intracellular functions. The occurrence of protein misfolding, resulting from single point mutations or external influences, along with the consequent buildup of protein aggregates, can lead to diverse pathological processes like neurodegenerative disorders. Protein misfolding serves as a risk indicator for Alzheimer’s disease (AD), the prevailing cause of neurodegenerative dementia in the elderly, characterized by gradual cognitive impairment. Several structure prediction algorithms and computational approaches have been developed to address this challenge. The present work focuses on specific proteins related to AD and aims to verify their conformation through ColabFold which utilizes the MMseqs2 algorithm to quickly provide multiple sequence alignments. The predicted models were then compared to selected PDB structures, a superposition was created and the TM-score and RMSD metrics were assessed. In addition, a comprehensive look into the superposed structures was performed to observe any potent deviations between pairs of residues. These notable findings encompass precise direct sequence-to-structure patterns found in individual AD polypeptides motifs and well-folded domains.

Identification of binding sites for small molecules is critical in light of modern in silico and experimental methods for structure elucidation such as AlfaFold and CryoEM, respectively. The total number of entries in the PDB database is 208,702 through July 2023, and there are a large number of structural data without similar experimental entries and mechanistic or small molecule data. Herein, we report a simple, rapid, and efficient protocol for the identification of drug-like binding sites of small molecules using extended sampling with the self-developed molecular docking software CmDock. The protocol consists of preparing a docking receptor using the RbtProteinMapper method, which uses a full protein surface as a reference. Then, a series of drug-like interaction sampling probes are docked in an extended sampling of 1000 or more runs. The binding conformations calculated by the probes are analyzed using PacMAP reduction and DBSCAN density clustering to identify binding sites. The protocol is capable of identifying known binding sites of small molecules in a very short time frame. In addition, we demonstrate the application of the method to a known DNA Gyrase as well as to a STAT3 NTD domain system.

Original Objectives: 1. Purify and biochemically characterize RB60 orthologs in higher plant chloroplasts; 2. Clone the gene(s) encoding plant RB60 orthologs and determine their structure and expression; 3. Manipulate the expression of RB60; 4. Assay the effects of altered RB60 expression on thylakoid biogenesis and photosynthetic function in plants exposed to different light conditions. In addition, we also examined the gene structure and expression of RB60 orthologs in the non-vascular plant, Physcomitrella patens and cloned the poly(A)-binding protein orthologue (43 kDa RB47-like protein). This protein is believed to a partner that interacts with RB60 to bind to the psbA5' UTR. Thus, to obtain a comprehensive view of RB60 function requires analysis of its biochemical partners such as RB43. Background & Achievements: High levels of sunlight reduce photosynthesis in plants by damaging the photo system II reaction center (PSII) subunits, such as D1 (encoded by the chloroplast tpsbAgene). When the rate of D1 synthesis is less than the rate of photo damage, photo inhibition occurs and plant growth is decreased. Plants use light-activated translation and enhanced psbAmRNA stability to maintain D1 synthesis and replace the photo damaged 01. Despite the importance to photosynthetic capacity, these mechanisms are poorly understood in plants. One intriguing model derived from the algal chloroplast system, Chlamydomonas, implicates the role of three proteins (RB60, RB47, RB38) that bind to the psbAmRNA 5' untranslated leader (5' UTR) in the light to activate translation or enhance mRNA stability. RB60 is the key enzyme, protein D1sulfide isomerase (Pill), that regulates the psbA-RN :Binding proteins (RB's) by way of light-mediated redox potentials generated by the photosystems. However, proteins with these functions have not been described from higher plants. We provided compelling evidence for the existence of RB60, RB47 and RB38 orthologs in the vascular plant, Arabidopsis. Using gel mobility shift, Rnase protection and UV-crosslinking assays, we have shown that a dithiol redox mechanism which resembles a Pill (RB60) activity regulates the interaction of 43- and 30-kDa proteins with a thermolabile stem-loop in the 5' UTR of the psbAmRNA from Arabidopsis. We discovered, in Arabidopsis, the PD1 gene family consists of II members that differ in polypeptide length from 361 to 566 amino acids, presence of signal peptides, KDEL motifs, and the number and positions of thioredoxin domains. PD1's catalyze the reversible formation an disomerization of disulfide bonds necessary for the proper folding, assembly, activity, and secretion of numerous enzymes and structural proteins. PD1's have also evolved novel cellular redox functions, as single enzymes and as subunits of protein complexes in organelles. We provide evidence that at least one Pill is localized to the chloroplast. We have used PDI-specific polyclonal and monoclonal antisera to characterize the PD1 (55 kDa) in the chloroplast that is unevenly distributed between the stroma and pellet (containing membranes, DNA, polysomes, starch), being three-fold more abundant in the pellet phase. PD1-55 levels increase with light intensity and it assembles into a high molecular weight complex of ~230 kDa as determined on native blue gels. In vitro translation of all 11 different Pill's followed by microsomal membrane processing reactions were used to differentiate among PD1's localized in the endoplasmic reticulum or other organelles. These results will provide.1e insights into redox regulatory mechanisms involved in adaptation of the photosynthetic apparatus to light stress. Elucidating the genetic mechanisms and factors regulating chloroplast photosynthetic genes is important for developing strategies to improve photosynthetic efficiency, crop productivity and adaptation to high light environments.