Peroxiredoxin

Peroxiredoxins (Prxs, EC 1.11.1.15) are a ubiquitous family of antioxidant enzymes that also control cytokine-induced peroxide levels and thereby mediate signal transduction in mammalian cells. [cite journal |author=Rhee S, Chae H, Kim K |title=Peroxiredoxins: a historical overview and speculative preview of novel mechanisms and emerging concepts in cell signaling |journal=Free Radic Biol Med |volume=38 |issue=12 |pages=1543–52 |year=2005 |pmid=15917183 |doi=10.1016/j.freeradbiomed.2005.02.026] Peroxiredoxins can be regulated by changes to phosphorylation, redox and possibly oligomerization states. They are divided into three classes: typical 2-Cys Prxs; atypical 2-Cys Prxs; and 1-Cys Prxs. These enzymes share the same basic catalytic mechanism, in which a redox-active cysteine (the peroxidatic cysteine) in the active site is oxidized to a sulfenic acid by the peroxide substrate. [cite journal |author=Claiborne A, Yeh J, Mallett T, Luba J, Crane E, Charrier V, Parsonage D |title=Protein-sulfenic acids: diverse roles for an unlikely player in enzyme catalysis and redox regulation |journal=Biochemistry |volume=38 |issue=47 |pages=15407–16 |year=1999 |pmid=10569923 |doi=10.1021/bi992025k] The recycling of the sulfenic acid back to a thiol is what distinguishes the three enzyme classes, 2-Cys peroxiredoxins are reduced by thiols such as glutathione, while the 1-Cys enzymes may be reduced by ascorbic acid. [cite journal |author=Monteiro G, Horta BB, Pimenta DC, Augusto O, Netto LE |title=Reduction of 1-Cys peroxiredoxins by ascorbate changes the thiol-specific antioxidant paradigm, revealing another function of vitamin C |url=http://www.pnas.org/cgi/content/full/104/12/4886 |journal=Proc. Natl. Acad. Sci. U.S.A. |volume=104 |issue=12 |pages=4886–91 |year=2007 |pmid=17360337 |doi=10.1073/pnas.0700481104] Using crystal structures, a detailed catalytic cycle has been derived for typical 2-Cys Prxs, including a model for the redox-regulated oligomeric state proposed to control enzyme activity. [cite journal |author=Wood Z, Schröder E, Robin Harris J, Poole L |title=Structure, mechanism and regulation of peroxiredoxins |journal=Trends Biochem Sci |volume=28 |issue=1 |pages=32–40 |year=2003 |pmid=12517450 |doi=10.1016/S0968-0004(02)00003-8]

Alkyl hydroperoxide reductase (AhpC) is a bacterial enzyme responsible for directly reducing organic hyperoxides in its reduced dithiol form. [cite journal |author=Poole L |title=Bacterial defenses against oxidants: mechanistic features of cysteine-based peroxidases and their flavoprotein reductases |journal=Arch Biochem Biophys |volume=433 |issue=1 |pages=240–54 |year=2005 |pmid=15581580 |doi=10.1016/j.abb.2004.09.006] Thiol specific antioxidant (TSA) is a physiologically important antioxidant which constitutes an enzymatic defense against sulphur-containing radicals. [cite journal |author=Chae H, Rhee S |title=A thiol-specific antioxidant and sequence homology to various proteins of unknown function |journal=Biofactors |volume=4 |issue=3-4 |pages=177–80 |year=1994 |pmid=7916964] This family contains AhpC and TSA, as well as related proteins.

Some of the proteins in this family are allergens. Allergies are hypersensitivity reactions of the immune system to specific substances called allergens (such as pollen, stings, drugs, or food) that, in most people, result in no symptoms. A nomenclature system has been established for antigens (allergens) that cause IgE-mediated atopic allergies in humans. [WHO/IUIS Allergen Nomenclature Subcommittee King T.P., Hoffmann D., Loewenstein H., Marsh D.G., Platts-Mills T.A.E., Thomas W. Bull. World Health Organ. 72:797-806(1994)] This nomenclature system is defined by a designation that is composed of the first three letters of the genus; a space; the first letter of the species name; a space and an Arabic number. In the event that two species names have identical designations, they are discriminated from one another by adding one or more letters (as necessary) to each species designation.

ee also

*Peroxidase
*Catalase
*Oxidative stress
*Reactive oxygen species

References

This article uses material from the open-source database Pfam [http://www.sanger.ac.uk//cgi-bin/Pfam/getacc?PF00578 link]

External links

* [http://us.expasy.org/enzyme/1.11.1.15 Enzyme database entry on peroxiredoxins]