This book contains a broad survey on the peroxiredoxins. It involves almost all groups that contributed significant insights into the emerging field. Coverage discusses the diverse biological roles of the new protein family in the context of other antioxidant systems like those based on heme or selenium catalysis. In addition, the book highlights related future perspectives.
This book contains a broad survey on the peroxiredoxins. It involves almost all groups that contributed significant insights into the emerging field. Coverage discusses the diverse biological roles of the new protein family in the context of other antioxidant systems like those based on heme or selenium catalysis. In addition, the book highlights related future perspectives.
The peroxiredoxin family was discovered approximately 30 years ago and is now recognized as one of the most important families of enzymes related to antioxidant defense and cellular signaling. Peroxiredoxin 6 shares the basic enzymatic functions that characterize this family, but also exhibits several unique and crucial activities. These include the ability to reduce phospholipid hydroperoxides, phospholipase A2 activity, and an acyl transferase activity that is important in phospholipid remodeling. This book describes the available models for investigating the unique functions of PRDX6 and its role in normal physiological function, as well its roles in the pathophysiology of diseases including cancer, diseases of the eye, and male fertility.
Peroxiredoxin (Prx) enzymes catalyze the reduction of hydrogen peroxide, peroxynitrous acid, and organic peroxides, and are extremely efficient peroxidases, with k[subscript cat]/K[subscript M] on the order of 107 - 108 M−1 s−1. Besides their role in oxidative stress defense, evidence has accumulated that some eukaryotes, including humans, use Prxs as switches to regulate peroxide levels for the purpose of signaling events triggered by hormones and growth factors. Their significance and relevance to human health is underscored by the occurrence of cancer in some Prx knockout mice; the overexpression of Prxs in certain cancers, and knockout/knockdown studies that show Prxs in pathogens can be important, and even essential, for pathogen viability and infectivity. Further, their ubiquity in all the kingdoms of life implies Prxs provide indispensible functions. This thesis reports on work aimed at characterizing aspects of Prx function and catalysis using model systems that behave well for experimentation, specifically focusing on detangling the multifaceted roles of conserved residues, catalytic conformation change, and hyperoxidative inactivation. Five chapters of original work include two review articles and three primary research reports. One review provides a relatively broad overview of Prx structure-function (Chapter 2) and the other focuses on observations related to understanding the physiological role(s) of Prxs especially summarizing the results of knockout/knockdown studies and assessing the natural distribution of an enzyme, sulfiredoxin, that is able to reactivate hyperoxidized Prxs (Chapter 3). The latter shows that many virulent bacterial and eukaryotic pathogens lack sulfiredoxin, implying that they are unable to rescue hyperoxidatively inactivated Prxs. Of the primary research reports, two studies using the model Prx Salmonella typhimurium alkyl hydroperoxide reductase C (StAhpC) assess the impact of modifications on structure and dynamics (Chapter 4) and define the roles of highly conserved residues as they pertain to catalysis, conformation change, and oligomerization (Chapter 5). The studies with StAhpC were enabled by the discovery that a previously studied crystal form of the locally-unfolded (LU) conformation of StAhpC is also able to accommodate the fully-folded (FF) conformation. The work includes presentations of the first crystal structure of the wild type enzyme in its substrate-ready form and also the structures of eight mutants of residues that are well-conserved in the Prx1 subfamily of Prxs. The work led to an awareness of how small shifts in the relative stabilities of the FF versus LU conformations could strongly influence Prx function, and this in turn led to the proposal of a novel idea for the design of selective inhibitors of Prxs as potential drug leads: to target regions involved in the catalytic conformation change to trap them in inactive states. The third primary research report (Chapter 6) presents an analysis of three crystal structures of the PrxQ subfamily that had been solved and deposited in the Protein Data Bank by structural genomics groups, but not described in publications. These three structures provided views of the only remaining undescribed type of Prx conformation change - that of the PrxQ group with a resolving Cys in helix 2. In addition to describing the conformation change, we also define roles for conserved residues from a structural perspective for this entire PrxQ subgroup. Finally, in a forward looking part of the thesis (Chapter 7) I describe initial work toward developing Xanthomonas campestris PrxQ (XcPrxQ) as a new model system for study. This enzyme has the advantage of being a monomer, unusual for Prxs, and this makes it more ideal for probing questions related to dynamics. The preliminary work with this system includes crystal structures solved at 1 Å resolution, the highest for any Prx, trapping all relevant active site oxidation states and a ligand-bound form, NMR backbone assignments for the reduced and oxidized forms, and in silico docking analyses aimed at discovering a conformation-stabilizing inhibitor. Furthermore, results showing that the protein in the crystal has strongly enhanced sensitivity to hyperoxidation validates my proposal that inhibitors stabilizing the FF conformation of Prxs will lead to hyperoxidative inactivation. Together, these results establish XcPrxQ as a promising model system for future study.
This book provides an overview of antioxidants and antioxidant enzymes and their role in the mechanisms of signaling and cellular tolerance under stress in plant systems. Major reactive oxygen species (ROS)-scavenging/modulating enzymes include the superoxide dismutase (SOD) that dismutates O2 into H2O2, which is followed by the coordinated action of a set of enzymes including catalase (CAT), ascorbate peroxidase (APX), glutathione peroxidase (GPX) and peroxiredoxins (Prx) that remove H2O2. In addition to the ROS scavenging enzymes, a number of other enzymes are found in various subcellular compartments, which are involved in maintaining such redox homeostasis either by directly scavenging particular ROS and ROS-byproducts or by replenishing antioxidants. In that respect, these enzymes can be also considered antioxidants. Such enzymes include monodehydroascorbate reductase (MDAR), dehydroascorbate reductase (DHAR), glutathione reductase (GR), alternative oxidases (AOXs), peroxidases (PODs) and glutathione S-transferases (GSTs). Some non-enzymatic antioxidants, such as ascorbic acid (vitamin C), carotenes (provitamin A), tocopherols (vitamin E), and glutathione (GSH), work in concert with antioxidant enzymes to sustain an intracellular steady-state level of ROS that promotes plant growth, development, cell cycles and hormone signaling, and reinforces the responses to abiotic and biotic environmental stressors. Offering a unique compilation of information on antioxidants and antioxidant enzymes, this is a valuable resource for advanced students and researchers working on plant biochemistry, physiology, biotechnology, and signaling in cell organelles, and those specializing in plant enzyme technology.
The second edition of this encyclopedia presents over 400 biologically important signaling molecules and the content is built on the core concepts of their functions along with early findings written by some of the world’s foremost experts. The molecules are described by recognized leaders in each molecule. The interactions of these single molecules in signal transduction networks will also be explored. This encyclopedia marks a new era in overview of current cellular signaling molecules for the specialist and the interested non-specialist alike. Currently, there are more than 30,000 genes in human genome. However, not all the proteins encoded by these genes work equally in order to maintain homeostasis. Understanding the important signaling molecules as completely as possible will significantly improve our research-based teaching and scientific capabilities.
This Special Issue features recent data concerning thioredoxins and glutaredoxins from various biological systems, including bacteria, mammals, and plants. Four of the sixteen articles are review papers that deal with the regulation of development of the effect of hydrogen peroxide and the interactions between oxidants and reductants, the description of methionine sulfoxide reductases, detoxification enzymes that require thioredoxin or glutaredoxin, and the response of plants to cold stress, respectively. This is followed by eleven research articles that focus on a reductant of thioredoxin in bacteria, a thioredoxin reductase, and a variety of plant and bacterial thioredoxins, including the m, f, o, and h isoforms and their targets. Various parameters are studied, including genetic, structural, and physiological properties of these systems. The redox regulation of monodehydroascorbate reductase, aminolevulinic acid dehydratase, and cytosolic isocitrate dehydrogenase could have very important consequences in plant metabolism. Also, the properties of the mitochondrial o-type thioredoxins and their unexpected capacity to bind iron–sulfur center (ISC) structures open new developments concerning the redox mitochondrial function and possibly ISC assembly in mitochondria. The final paper discusses interesting biotechnological applications of thioredoxin for breadmaking.
This volume, along with its companion (volume 474), presents methods and protocols dealing with thiol oxidation-reduction reactions and their implications as they relate to cell signaling. The critically acclaimed laboratory standard for 40 years, Methods in Enzymology is one of the most highly respected publications in the field of biochemistry. Since 1955, each volume has been eagerly awaited, frequently consulted, and praised by researchers and reviewers alike. Over 450 volumes have been published to date, and much of the material is relevant even today--truly an essential publication for researchers in all fields of life sciences. Along with companion volume, provides a full overview of techniques necessary to the study of thiol redox in relation to cell signaling Gathers tried and tested techniques from global labs, offering both new and tried-and-true methods Relevant background and reference information given for procedures can be used as a guide to developing protocols in a number of disciplines
