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1
INTROINI, BIANCA. "DESIGN OF CHIMERIC ION CHANNELS TO MONITOR CAMP-INDUCED CONFORMATIONAL CHANGES AND DYNAMICS." Doctoral thesis, Università degli Studi di Milano, 2020. http://hdl.handle.net/2434/719688.
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Hyperpolarization-activated cyclic nucleotide-gated (HCN1-4) channels are the molecular correlate of Ih (or If) current, which plays a key role in the control of neuronal and cardiac rhythmicity. HCNs are activated by the hyperpolarization of the membrane potential and further regulated by the direct binding of cyclic AMP (cAMP) to the cytoplasmic Cyclic Nucleotide Binding Domain (CNBD). cAMP binding determines the removal of the autoinhibitory action exerted by the CNBD on the pore opening and causes conformational changes that propagate from the CNBD to the pore through the C-linker, increasing channel open probability and speeding activation kinetics.
cAMP modulation of HCN controls rhythmicity and excitability at cardiac and neuronal level and pain perception. Thus, in order to understand several physiological functions, as well as diseases affecting both the cardiac and neuronal system, a detailed description of the cAMP-induced conformational changes is required. Moreover, functional studies indicate that cAMP binding to the CNBD induces the transition of the C-terminal domains, from dimer of dimer to tetramer and that this transition is driven by the movements of the C-linker.
The goal of this work is to describe the propagation of the movements through the C-linker to the pore. To this end, I have applied spectroscopic techniques, such as Electron Paramagnetic Resonance (EPR) and Double Electron-Electron Resonance (DEER) to study dynamic changes in the structure of the purified and labelled protein. First, I constructed a chimeric channel by fusing the C-linker/CNBD of human HCN4 to the prokaryotic pore domain of KcsA. This protein has the advantage that can be produced and easily purified in E. coli. Isothermal Titration Calorimetry (ITC) and Differential Scanning Calorimetry (DSC) measurements demonstrated that the purified chimera is able to bind cAMP. Particularly, ITC gave a Kd value of 1.7 μM, which agrees with the one previously published for the isolated C-linker/CNBD fragment of HCN4. Moreover, the rescue of a K+-uptake deficient E. coli strain demonstrated that the chimeric channel is able to conduct a K+ ions flow.
EPR-DEER experiments performed on the chimera revealed that the binding of cAMP to the CNBD domain causes clear conformational changes in the C-terminal region, which transits from a dimer of dimers conformation to a 4-fold symmetrical gating ring. These data confirm previous biochemical and functional indication obtained on the full-length channel and give further details on the direction and the extent of subunit displacement occurring during the conformational transition. The transition of the channel from a dimer of dimer to a tetrameric configuration of the cytosolic domain might reflect a pre-conditioning state for cAMP action on channel gating and partly explains the agonist activity exerted by cAMP on channel kinetics and open probability.
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Liu, Wenchao. "Investigation of electromagnetic field induced protein conformational changes using spectrofluorimetry." Thesis, University of Sheffield, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.574553.
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Spectrofluorimetry is utilized as a novel real time non-invasive optical assay to investigate whether the exposure of bovine serum albumin (BSA) to extremely low frequency (ELF) and radio frequency (RF) electromagnetic (EM) fields causes conformational changes in the protein distinct from those due to heating alone. Such conformational changes would alter the protein's fluorescence spectrum, and could indicate a potential for EM induced altered biological activity of proteins in-vivo. The development of both the ELF and RF exposure system are described, discussed and evaluated. Since ELF electric fields do not exhibit propagation phenomena within the dimensions of the apparatus, a quasi-static approach is taken and a stainless steel parallel-plate exposure system is designed in a cuvette. While at RF, FDTD software is employed to facilitate a TEM cell based exposure system evaluation and optimization, and also to provide preliminary SAR distributions in the BSA sample as a control for future experimental measurements. The sensitivity of the systemic methodology (including the statistical analysis method) is demonstrated, indicating that the system is capable of detecting fluorescence changes as small as 0.032%. At ELF, the effects of six different high field strength 100Hz EM exposure paradigms at different temperatures on BSA conformational changes are presented and critically discussed. While at RF, four different 430MHz exposure paradigms are applied, with either intermittent or continuous bursts of TETRA or CW signals, at different average SAR levels. Statistical tests are used to analyse the experimental data. Periodical fluorescence oscillations are observed under both ELF and RF exposures, but their origins are considered to be convection currents due to unevenly distributed energy injections into the solution.
3
Wolter, Tino [Verfasser], and M. [Akademischer Betreuer] Elstner. "Light-induced conformational changes in proteins / Tino Wolter. Betreuer: M. Elstner." Karlsruhe : KIT-Bibliothek, 2013. http://d-nb.info/1046888870/34.
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Hedley, Diana. "Investigating agonist induced receptor conformational changes on the adenosine A2a receptor." Thesis, University of Reading, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.553235.
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G-protein coupled receptors (GPCRs) are one of the main targets for drug design. GPCR pharmaceutical research has bottlenecked on drug research, and the current assay systems are not creating therapeutic drugs from drug hits. The principal aim of this project was to establish a relationship between drug affinity (PKi) and drug intrinsic efficacy (Emax) using receptor conformational change parameters (measurements defined by fluorescence resonance energy transfer (FRET) experiments) to provide a new way of screening for the intrinsic efficacy of a drug. This project aimed to develop a drug screen based on the hypothesis that ligand intrinsic efficacy was linked to ligand induced receptor conformational change. Using FRET technology, the extent and rate of ligand induced receptor conformational changes were investigated. In contrast to the clear cut nature of ligand intrinsic efficacy and the extent of ligand induced receptor conformational change observed in the literature no correlation was found in this project on the FRET reporter construct A2A.4C.CFP. FRET studies revealed some key findings into the receptor activation mechanisms of the A2aR. Firstly, that different agoinsts induce different conformational states of the receptor and at different rates, thus these finding support activation models proposed by Koshland and are inline with work carried out by Kobilka. Secondly, that different agonists imposed different conformational restrictions/conditions on the resultant conformation of the second agonist applied. This finding opens up the possibility for drug design, as it is possible that the resultant conformation of a drug applied after the receptor has been activated by a previously applied agonist may result in a different pharmacological response, and hence may open up new avenues for investigation. cAMP functional studies were carried out to classify and rank the intrinsic efficacy of the test ligands and to assess effects of the mutations within the A2A.4C.CFP receptor on downstream signalling. All the ligands tested with the exception of compound 15 were reported to be full A2aR agonists in the literature. However compounds CV 1808 and 2Chloroadenosine both generated only partial responses in this assay. This finding may be reflective of differences in receptor activation mechanism of these two compounds compared to the other full agonists.
5
Gao, Meimei. "Reversibility of anesthetic-induced conformational and functional changes in the purple membrane." Thèse, Trois-Rivières : Université du Québec à Trois-Rivières, 2004. http://www.uqtr.ca/biblio/notice/resume/18186324R.pdf.
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Hörsch, Daniel [Verfasser]. "Monitoring light induced conformational changes in photoreceptors by time resolved spectroscopy / Daniel Hörsch." Berlin : Freie Universität Berlin, 2009. http://d-nb.info/1023623048/34.
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Fotheringham, Helen L. "Investigation of ligand-induced conformational changes of the dopamine D2s receptor using fluorescence resonance energy transfer." Thesis, University of Reading, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.558734.
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Approximately 50 % of current pharmaceutical drugs target the G protein-coupled receptor (GPCR) family, rendering an understanding of the mechanisms behind their actions critical. Dopamine is a key neurotransmitter involved in motor function and behaviour and has been associated with disorders such as Parkinson's disease and schizophrenia. Within the present study, a Fluorescence Resonance Energy Transfer (FRET)-based conformational change sensor was created to study dopamine D2S receptor responses to ligands to gain an understanding of the mechanisms underlying ligand-induced activation. Chimaeric receptors were created with a tetracysteine sequence FlAsH binding motif at varying positions within intracellular loop 3 and CFP fused to the C-terrninal where FlAsH and CFP formed a convenient FRET pair. The constructs were transiently transfected into HEK293 cells and characterised using confocal and FRET microscopy. The 353-CFP-D2s receptor was well expressed at the cell surface and produced agonist-induced FRET changes and therefore was used to create a stably expressing HEK293 cell line. Radioligand binding and eSS]GTPyS binding assays showed that the 353-CFP-D2s receptor had a pharmacological profile similar to the native D2S receptor. On application of agonist (NP A, dopamine, m-tyramine, p- tyramine and (- )-3-PPP) to the 353-CFP-D2s receptor, a concentration dependent decrease in FRET was detected which was completely reversed when agonist was removed. The extent of FRET response was found to broadly correlate with the extent of G protein activation. The forward rate constant of the FRET change was also found to alter in an agonist-concentration dependent manner while the reverse rate was concentration independent. Throughout the project, the control and optimisation of experimental variables was found to be crucial for successful use of this FRET -based system. In conclusion, this sensor and the use of this technique could be very useful to aid understanding of activation of this important GPCR. 111.
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Gan, Yu. "X-ray crystallographic studies of DNA structures : conformational changes induced by metal cations, organic ligands and sequence variation." Thesis, University of Reading, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.487234.
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This thesis concentrates on the study of DNA structures by X-ray crystallography. The first chapter introduces the molecules under study; whilst chapter two describes the theories and methodologies that are closely involved. The following three chapters contain the main results and describe eight refined structures. Chapter three examines ion influences upon an unusual non-planar G/C quadruplex formed by the heptamer nucleotide d(GCATGCT), in which the highly carcinogenic element nickel has be.en found to cause dramatic distortions in this otherwise very stable DNA structure: Chapter four is focused on the DNA-intercalator complexes formed between the hexamer nucleotide d(CGTACG) and two bis-acridine derivatives that differ at their linkers in terms of length and charge. It was found that the bis-acridine compound with a linker consisting of a nitrogen plus six carbon atoms was able to crosslink the DNA m~lecules in a novel wa.y, in which the acridine chromophore is rotated around its plane normal by 1800 away from the conformation found previously in the monomers and one side-chain attached bis-acridine derivatives. In the complex of the same oligonucleotide and another bis-acridine' derivative with a longer linker in the presence of C02 +, the best electron density around the ligand, compared with all the other reported analogues, was obtained from the in-house diffractometer. Chapter five describes two A-DNA structures formed by the same sequences that are crystallised in different spacegroups. The novel choice of the sequences was inspired by a recent publication reporting a statistical analysis of recombination sequences in the human genome. The chosen decamer nucleotide contains the recombination hotspot heptamer CCTCCCT. ., Chapter six presents the results of G-quadruplex crystallisation studies, and some preliminary X-ray diffraction data. Chapter seven, as the last chapter of the thesis, , lists the ongoing projects and describes future work.
9
Saba, Rami. "A contribution to the study of the bovine heart Na/Ca exchanger membrane topology and of the conformational changes induced by regulatory ligands binding." Doctoral thesis, Universite Libre de Bruxelles, 2000. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/211796.
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Schein, Peter Christian [Verfasser]. "Proteomic identification of posttranslational modifications: cAMP-induced changes of phosphorylation and investigation of novel approaches detecting posttranslational modifications at lysine and arginine residues / Peter Christian Schein." Bonn : Universitäts- und Landesbibliothek Bonn, 2020. http://d-nb.info/1208937456/34.
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Malloni, Wilhelm Massimiliano [Verfasser], and Hans Robert [Akademischer Betreuer] Kalbitzer. "AUREMOL-QTA, a program package for NMR based automated recognition and characterization of local and global conformational changes in proteins induced by ligand binding as external perturbation / Wilhelm Massimiliano Malloni. Betreuer: Hans Robert Kalbitzer." Regensburg : Universitätsbibliothek Regensburg, 2011. http://d-nb.info/1030178836/34.
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Guerriero, Andrew. "Variable pressure NMR analyses to assess compressive motion in PETNR and catalytically germane PETNR:Ligand complexes." Thesis, University of Manchester, 2012. https://www.research.manchester.ac.uk/portal/en/theses/variable-pressure-nmr-analyses-to-assess-compressive-motion-in-petnr-and-catalytically-germane-petnrligand-complexes(f9d8a882-b05b-47ac-86c4-3987c78e5494).html.
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The involvement of dynamical fluctuations in driving enzymatic processes is widely accepted. With respect to NQM tunnelling enzymes, the role of promoting motions in facilitating hydrogenic transfers is well studied. Few studies have however, specifically attributed, dedicated dynamical fluctuations characterised by their timescales and magnitudes, as a function of a reaction coordinate, to specific groups in a protein system. An effectively full suite of backbone resonance assignments were obtained for PETNR and on relevant ligand complexes. This provided an essential platform on which residue specific, backbone amide fluctuations were assessed. This thesis documents the application of pressure up to 1500 bar, in tandem with high resolution TROSY based NMR analysis, as a means of studying residue specific, conformer exchange perturbations. Residue specific amide compression profiles of the PETNR:FMN free enzyme system, and complexes with progesterone and tetrahydropyridine dinucleotides have been obtained. The binding of progesterone appears to induce conformational tightening of residues within the active site vicinity. The complexation of PETNR:FMN with tetrahydropyridine dinucleotides, appears to stimulate conformational shifts towards intermediate, and in some cases, slow exchange regimes in multiple residues about the active site vicinity. This is evidenced by extensive intensity attenuation of 1H-15N TROSY resonances, on the binding of tetrahydropyridine dinucleotides at 1 bar pressure, and on going from 1 bar to 1500 bar pressure. Multiple regions of sequence, spatially clustering about the active site vicinity within a 10 Å sphere of the FMN binding pocket, display appreciable sensitivity to ligand binding. Differential responses of residues to the application of high pressure between complexes was noted within segments of these regions. A region of sequence, named the β-hairpin flap displays significant differential compression profiles between the PETNR:FMN free enzyme system, and associated progesterone and tetrahydropyridine dinucleotide complexes. A role in mediating ligand engagement is proposed for R130 and R142 in the β-hairpin flap. A central hydrogen bonding network, perhaps constituting a putative proton wire in the active site of the PETNR:FMN:Progesterone complex, has been identified that could enable the shuttling of protons following catalytic protonation of oxidative substrate. The resonance response behaviour of G185 acts as a sensitive reporter on the formation of these interactions, revealed by an interrogation of the differences in chemical shift changes on progesterone binding, and in response to high pressure. The recruitment of high resolution crystallographic data sets readily supported a structural and dynamical interpretation of the observed chemical shift responses to ligand binding at 1 bar pressure, and on the application high pressure. A definitive atomistic identification of fast motion contribution to activation barrier compression was not obtained. Nevertheless, detailed, residue specific amide compression profiles, and shifts in backbone amide conformational exchange regimes in response to ground state ligand binding, and at high pressure, have been catalogued in the PETNR:FMN free enzyme system. These dynamical profiles in the free enzyme are contrasted against comparative, residue specific observations in analogue complexes of the oxidative and reductive half reactions of PETNR.
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Yang, Hsin Yi, and 楊欣奕. "Substrate-induced conformational changes in ArsA protein." Thesis, 1994. http://ndltd.ncl.edu.tw/handle/08399571986983481911.
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碩士國立中山大學
生命科學研究所
82
ArsA蛋白質是陰離子傳輸系統的催化次單元，在其陰離子受質存在下，才 具備ATP水解的活性。先前研究顯示ArsA蛋白質的ATP接合部位與陰離子接 合部位有交互作用。以五種蛋白質水解酵素限制性的切除反應來偵測 ArsA蛋白質經受質ATP、鎂離子與陰離子等引發的結構變化時，trypsin的 切除反應確認了ATP與陰離子接合部位有交互作用，而elastase及 chymotrypsin A4切除反應則顯示了ATP接合部位與鎂離子接合部位有交互 作用。另受質和ArsA蛋白質接合的順序不同亦會造成ArsA蛋白質不同的結 構變化，其中加入ATP再加入陰離子與加入陰離子後再加入ATP，以 trypsin切除反應分析時，顯示後者多出一56kDa的產物。另外，63kDa ArsA蛋白質經trypsin水解後的61kDa與30kDa產物均不具催化活性，也失 去和Red Agarose接合的特性，但仍可與陰離子接合，此顯示被切去的 2kDa片段在ATP的接合及催化活性上扮演重要的角色，而陰離子接合部位 即位於此30kDa片段上。
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Voß, Béla. "Conformational Changes in Ligand Binding Processes." Doctoral thesis, 2015. http://hdl.handle.net/11858/00-1735-0000-0022-5EE0-6.
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Chen, Chia-Yi, and 陳佳儀. "Divalent cation-induced conformational changes and oligomerization of KChIP1." Thesis, 2003. http://ndltd.ncl.edu.tw/handle/18463816663669345440.
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碩士國立中山大學
生物醫學科學研究所
91
Abstract KChIPs are Kv channel-interacting proteins that bind to the cytoplasmic N-terminus of Kv4 ��-subunits and regulate the ion-current of Kv channel. Several isomeric KChIPs arise from alternative splicing have been identified. These KChIPs share a high degree of sequence homology at their C-terminal region which is constituted with four EF hands, but their N-terminus sequence is notably diversified. Among them, KChIP3/Calseniline/Dream has been found to be a multifunctional protein, and interacts with different targets according to its cellular sub-localization. Noticeably, KChIP3 shows a Ca2+-dependent DNA-binding and oligomerization. In the present study, using 5’-RACE PCR, the KChIP 1 and KChIP2 were successfully amplified from human brain and heart cDNA libraries, respectively. The recombinant KChIP proteins were prepared from E. coli expression system, and purified by His-bind resin or GST-resin according to their fusing proteins. The interaction between the KChIP proteins with divalent cations (Mg2+, Ca2+, Sr2+ and Ba2+) was explored by 8-anilinonaphthalene sulfonate (ANS) fluorescence. The results showed that KChIPs possessed both high affinity and low affinity Ca2+-binding sites. However, only one kind of binding-affinity for the other divalent cations was noted. Removal of EF hand 4 caused an abolishment of the high Ca2+-affinity, and the resulting mutated protein exhibited a similar binding affinity for Ca2+, Mg2+, Sr2+ and Ba2+. The mutant lacked EF hands 3 and 4 lost its ANS-binding ability, but it still could bind with Ca2+. Moreover, this mutated KChIP showed a noticeable change in its secondary structure as evidenced by CD spectra. The results of in vitro cross-linking indicated that KChIP1 and KChIP2 could form homo-oligomer in a Ca2+-dependent manner. Interestingly, hetero-oligomerization between KChIP1 and KChIP2 was noted as revealed by pull down assay. The N-terminal region was not involved in homo- or hetero-oligomerization of KChIPs. Taken together, our findings suggest that the integrity of EF hand 4 is essential for the high affinity for Ca2+, and both EF hands 3 and 4 are crucial for maintaining the conformation of KChIPs. However, the oligomerization reaction is highly dependent upon the presence of EF hands.
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Rahaman, Md Toheder. "Processing induced conformational changes of food proteins in relation to antigenicity." Thesis, 2016. https://vuir.vu.edu.au/32300/.
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Food allergy is one of the major public health concerns worldwide and its
prevalence has been increasing at an alarming rate over the time especially in the
industrialised countries. Most of the foods are processed into a variety of products
before consumption and undergo different physico-chemical alterations, which could
affect their antigenic potential. β-lactoglobulin, the major cow milk allergen, and gluten,
one of the main plant allergens, are also exposed to various processing steps prior to
packaging, distribution and consumption. Thus, the present research has focused on
effects of different applied processing conditions (pH, temperature and shear) on the
conformational changes of β-lg and gluten in relation to their antigenicity.
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Deshmukh, Sasmit S. "Light-induced conformational changes in the photosynthetic reaction center from Rhodobacter sphaeroides." Thesis, 2009. http://spectrum.library.concordia.ca/976425/1/MR63275.pdf.
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The photosynthetic reaction center (RC) from purple photosynthetic bacteria is a membrane-bound protein-pigment complex that serves as an excellent model for studying biological energy conversion. This energy conversion takes place by electron transfer reactions, which occur within the protein and are often coupled to conformational changes. In order to study these conformational changes, recovery of the oxidized bacteriochlorophyll dimer, from the RC of the purple photosynthetic bacterium Rhodobacter sphaeroides , to its original state was measured by light-minus-dark optical difference spectroscopy. Laser flash excitation generated an electron transfer that takes place across the membrane; creating the primary charge-separated state with a lifetime of 100 ms. Prolonged illumination induced subsequent conformational rearrangements in the RC protein complex which result in lifetimes of the same charge-separated state that are significantly different from that measured after flash excitation. The structural details of the conformational rearrangements on the molecular level will be discussed. The conformational changes were sensitive to duration and wavelength of illumination, pH, temperature, hydrophobic environment (liposome or detergent), head-group charge of the detergent, and presence of a bound metal ion. By systematically varying these parameters, we were able to extend the lifetime of the charge-separated state up to 21 mins. Based on these results, our goal is to utilize the bacterial RC protein complex as a biocapacitor, since the positive and negative charges are separated by a hydrophobic core of the protein with a low dielectric constant. This biocapacitor can be discharged rapidly by inducing pH jump.
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Amadi, Sepan Tariq Hassan. "Structure, dynamics and substrate-induced conformational changes of Escherichia coli multidrug transporter (EmrE)." Diss., 2010. http://etd.library.vanderbilt.edu/available/etd-04192010-162108/.
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WANG, YAO-FENG, and 王耀鋒. "Probing the methanol-induced conformational changes of proteins by electrospray ionization mass spectrometry." Thesis, 2003. http://ndltd.ncl.edu.tw/handle/85290097081776949304.
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碩士國立東華大學
化學系
91
Electrospray ionization mass spectrometry (ESI-MS) has been widely applied in medical, biochemical, and environmental researches. The utility of ESI lies in its ability to produce multiply charged gaseous ions directly from solution. The methanol induced conformational changes of cytochrome c from several animal cells under acidic conditions were studied. The charge state distributions of proteins that were produced during ESI were used to monitor the conformational transitions. At different methanol concentrations, cytochrome c transforms from folded state (0% methanol) into an intermediate state (30% methanol), a helical denatured state (50% methanol) and a helical denatured protected state (90% methanol). These transitions correlate well with earlier studies by optical methods. Further, hydrogen/deuterium exchange rates of cytochrome c from different animal cells at different methanol concentrations were followed by ESI-MS to probe the subtle changes in protein conformation. Accurate exchange rates were obtained by mixing proteins and monitoring their exchange rates simultaneously. The exchange rates for cytochrome c from horse, bovine and dog were comparable, and indicate that their conformations are similar. The exchange rates for the cytochrome c from rabbit and pigeon were different from those of horse at low methanol concentrations (less than 30% methanol), revealing that their conformations (rabbit and pigeon) differ from the others (horse, bovine and dog).
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黃韻潔. "Prediction of continuous B-cell epitopes using protein free energy associated with mutation-induced conformational changes." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/45965712009956631224.
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碩士國立交通大學
生醫工程研究所
100
Identification of B-cell epitopes plays an important role in vaccine development. Current prediction algorithms mostly rely on amino acid propensity scales and their variants, the results of which depend on a single antigenic phenotype. That viral sequences undergo continuous genetic changes, promoting the emergence of drug resistant strains, renders current prediction methods impractical. In this study, a novel set of features are proposed based on the protein free energy associated with point-mutated structures. To the best of our knowledge, this is the first attempt in this area to predict continuous B-cell epitopes based on protein free energy. I evaluated the novel features on k-nearest neighbor, support vector machine, and artificial neural network models, and achieved prediction accuracy of 74.3%, 66.1%, and 80.0% respectively. In comparison to current predictors, namely ABCPred, BCPred, and AAP, the energy-based models demonstrated better performance.
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Kristinsson, Hordur Gudjon. "Conformational and functional changes of hemoglobin and myosin induced by pH: Functional role in fish quality." 2002. https://scholarworks.umass.edu/dissertations/AAI3039370.
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Conformational and functional changes in trout hemoglobin and cod myosin were investigated at low and high pH and after subsequent refolding. Hemoglobin cooperatively unfolded at low pH to a “molten globular” state with different levels of structure depending on how low the pH was and if 500 mM NaCl was present. At low pH the heme lost its contact with the protein but was not released but the protein was fully dissociated. Alkaline pH had little effect on hemoglobin but the heme environment suggested a strong heme-distal histidine link at pH 10.5. Longer unfolding time, lower pH and higher ionic strength made it more difficult to refold hemoglobin. The more misfolded the protein was the more hydrophobic it became and the lower its solubility after refolding it to pH 5.5. The presence of salt greatly facilitated the hydrophobic aggregation. The more unfolded or misfolded the protein was the more pro-oxidative it became, maybe as a result of more exposed heme, heme and subunit dissociation and hemoglobin-membrane interactions. High pH completely suppressed pro-oxidative activity of hemoglobin, possibly due to a strong heme-distal histidine link preventing autoxidation. Helical structure of myosin rods was little affected at low and high but the head group was substantially unfolded. The protein was possibly fully dissociated at low pH while at high pH only half of the light chains dissociated. The myosin head was misfolded on refolding with increased hydrophobicity, reactive −SH groups, loss in ATPase activity and lower conformational stability. The heavy chains may have fully reassembled on refolding from acid pH but light chains failed to reassemble to the protein. Refolded myosin had almost identical solubility as native myosin at pH 7.5 while cod myofibrillar proteins had increased solubility after acid and alkali treatment compared to the untreated proteins. Myosin and myofibrillar proteins exhibited improved emulsification activity and stability at pH 7.5 after pH treatment. Myosin gelled at a lower temperature and formed stronger gels at pH 7.5 in 600 mM KCl. The pH treated myofibrillar proteins also gelled at a lower temperature than native myosin but had a different gelling mechanism on heating.
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Meyer-Lipp, Kerstin [Verfasser]. "Time resolved measurements of sugar binding induced conformational changes in the melibiose permease from Escherichia coli / von Kerstin Meyer-Lipp." 2008. http://d-nb.info/987243888/34.
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