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Oxidative protein folding describes the process by which disulfide bonds are inserted into proteins as they fold into their native structure. This involves two distinct phases, an oxidation phase where these covalent linkages are first introduced, and an isomerization phase in which incorrectly placed disulfides are shuffled leading to the native pairings. In eukaryotes, disulfide bond formation can be catalyzed by a number of flavin-dependent sulfhydryl oxidases. This dissertation work investigates how a particular flavin-dependent sulfhydryl oxidase, Quiescin-sulfhydryl oxidase (QSOX), cooperates with protein disulfide isomerase (PDI) to generate native pairings in two unfolded reduced proteins: ribonuclease A (RNase A, four disulfide bonds and 105 disulfide isomers of the fully oxidized protein) and avian riboflavin binding protein (RfBP, nine disulfide bonds and more than 34 million corresponding disulfide pairings). This QSOX/PDI in vitro folding system involves no functional interaction between the two enzymatic components; QSOX inserts disulfide bonds into protein substrates while PDI isomerizes the misplaced pairs to the native ones. Rapid refolding does not require glutathione or glutathione-based redox buffers. Refolding of RfBP is followed continuously by monitoring spectral changes experienced by the ligand, riboflavin, upon binding to the apoprotein. Efficient refolding of this protein only occurs with a large molar excess of reduced PDI over the folding client protein. These conditions likely mirror the environment of the endoplasmic reticulum lumen where small concentrations of nascent proteins are exposed to nearly mM levels of PDI. Subsequent studies performed in the absence of QSOX or redox buffers, explore the effectiveness of mixtures of oxidized and reduced PDI in refolding RfBP. Here, the fastest refolding of RfBP occurs with excess reduced PDI and just enough oxidized PDI to generate nine disulfides in the protein. The implications of these in vitro experiments for understanding oxidative folding processes in vivo are discussed. Although unfolded proteins have been proven to be excellent substrates of QSOX, a recent proposal suggests that it can also function in the generation of inter-domain and inter-protein disulfide bridges, where the substrates are already substantially or completely folded. This suggestion has been tested using wild type and mutant Escherichia coli thioredoxin as a model substrate. These folded substrates are, by comparison, poorly oxidized by QSOX which is consistent with the expected stringent steric requirements for efficient thiol/disulfide exchange reactions.
With contributions from experts in the field, this book provides a comprehensive overview of the oxidative folding of cysteine-rich peptides.
This book aims to cover the knowledge of protein folding accumulated from studies of disulfide-containing proteins, including methodologies, folding pathways, and folding mechanism of numerous extensively characterized disulfide proteins. Folding of Disulfide Proteins will be valuable supplementary reading for general biochemistry, biophysics, molecular biology, and cellular biology courses for graduate and undergraduate students. This book can also be used for specialized graduate-level biochemistry, biophysics, and molecular biology courses dedicated to protein folding as well as related biological problems and diseases. Will also be of interest to everybody interested in problems related to protein folding, and anyone who is interested in understanding the mechanism of protein misfolding and protein misfolding-related diseases.
The formation of disulphide bonds is probably the most influential modification of proteins. These bonds are unique among post-translational modifications of proteins as they can covalently link cysteine residues far apart in the primary sequence of a protein. This has the potential to convey stability to otherwise marginally stable structures of proteins. However, the reactivity of cysteines comes at a price: the potential to form incorrect disulphide bonds, interfere with folding, or even cause aggregation. An elaborate set of cellular machinery exists to catalyze and guide this process: facilitating bond formation, inhibiting unwanted pairings and scrutinizing the outcomes. Only in recent years has it become clear how intimately connected this cellular machinery is with protein folding helpers, organellar redox balance and cellular homeostasis as a whole. This book comprehensively covers the basic principles of disulphide bond formation in proteins and describes the enzymes involved in the correct oxidative folding of cysteine-containing proteins. The biotechnological and pharmaceutical relevance of proteins, their variants and synthetic replicates is continuously increasing. Consequently this book is an invaluable resource for protein chemists involved in realted research and production.
The formation of disulphide bonds is probably the most influential modification of proteins. These bonds are unique among post-translational modifications of proteins as they can covalently link cysteine residues far apart in the primary sequence of a protein. This has the potential to convey stability to otherwise marginally stable structures of proteins. However, the reactivity of cysteines comes at a price: the potential to form incorrect disulphide bonds, interfere with folding, or even cause aggregation. An elaborate set of cellular machinery exists to catalyze and guide this process: facilitating bond formation, inhibiting unwanted pairings and scrutinizing the outcomes. Only in recent years has it become clear how intimately connected this cellular machinery is with protein folding helpers, organellar redox balance and cellular homeostasis as a whole. This book comprehensively covers the basic principles of disulphide bond formation in proteins and describes the enzymes involved in the correct oxidative folding of cysteine-containing proteins. The biotechnological and pharmaceutical relevance of proteins, their variants and synthetic replicates is continuously increasing. Consequently this book is an invaluable resource for protein chemists involved in realted research and production.
Disulfide bond formation in vivo is linked to many essential intracellular processes; protein regulation and signaling, chemical transformations, and oxidative protein folding. Oxidative protein folding is an enzyme catalyzed process which is controlled by dedicated protein thiol oxidoreductases. In this work the oxidative protein folding within the mammalian endoplasmic reticulum (ER) is examined from an enzymological perspective. Evidence for the rapid reduction of PDI by reduced glutathione is presented in the context of PDI-first pathways. Next, strategies and challenges for the determination of the concentrations of reduced and oxidized glutathione and of the ratios of PDIred:PDIox is discussed. After a discussion of the use of natively encoded fluorescent probes to report the glutathione redox poise of the ER, a complementary strategy to discontinuously survey the redox state of as many redox-active disulfides as can be identified by ratiometric LC–MS–MS methods in order to better understand redox linked species. Next, we investigate the specificity of the human Mia40/lfALR system towards non-cognate unfolded protein substrates to assess whether the efficient introduction of disulfides requires a particular amino acid sequence context or the presence of an IMS targeting signal. Mia40 is found to be effective oxidant of non-cognate substrates, but is an ineffective protein disulfide isomerase when its ability to restore enzymatic activity from scrambled RNase is compared to that of protein disulfide isomerase. Mia40’s ability to bind amphipathic peptides tested by the insulin reductase assay. The consequences of these studies, mitochondrial oxidative protein folding, and the transit of polypeptides is discussed. Finally, the development of disulfide linked genetically encoded fluorescent probes for analyte-specific imaging are demonstrated. Current classes of intracellular probes depend on the selection of binding domains that either undergo conformational changes on analyte binding or can be linked to thiol redox chemistry. Here, novel probes were designed by fusing a flavoenzyme, whose fluorescence is quenched on reduction by the analyte of interest, with a GFP domain to allow for rapid and specific ratiometric sensing. Two flavoproteins, Escherichia coli thioredoxin reductase and Saccharomyces cerevisiae lipoamide hydrogenase, were successfully developed into thioredoxin and NAD+/NADH specific probes respectively and their performance was evaluated in vitro and in vivo. These genetically encoded fluorescent constructs represent a modular approach to intracellular probe design that should extend the range of metabolites that can be quantitated in living cells.
The past five years have seen a major leap forward in our understanding of the way proteins fold into their three-dimensional, functional conformations. The rapidly expanding literature covers in vivo as well as in vitro studies and forms the basis for an important biotechnology industry. In this volume, a group of leading scientists review and assess the experimental evidence that underpins these advances and look for signs of a general picture of how proteins fold. Contributors show how such conformational changes are leading to new insights into membrane translocation, pore formation, and the clinically important aggregation phenomena. Students and researchers of biochemistry and molecular biology will find this book to be the ideal introduction to an exciting field.
Assisting Oxidative Protein Folding: How Do Protein Disulphide-Isomerases Couple Conformational and Chemical Processes in Protein Folding?, by A. Katrine Wallis and Robert B. Freedman Peptide Bond cis/trans Isomerases: A Biocatalysis Perspective of Conformational Dynamics in Proteins, by Cordelia Schiene-Fischer, Tobias Aumüller and Gunter Fischer Small Heat-Shock Proteins: Paramedics of the Cell, by Gillian R. Hilton, Hadi Lioe, Florian Stengel, Andrew J. Baldwin und Justin L. P. Benesch Allostery in the Hsp70 Chaperone Proteins, by Erik R. P. Zuiderweg, Eric B. Bertelsen, Aikaterini Rousaki, Matthias P. Mayer, Jason E. Gestwicki and Atta Ahmad Hsp90: Structure and Function, by Sophie E. Jackson Extracellular Chaperones, by Rebecca A. Dabbs, Amy R. Wyatt, Justin J. Yerbury, Heath Ecroyd and Mark R. Wilson