A Comparison of Thiol Peroxidase Mechanisms

Abstract

Thiol peroxidases comprise glutathione peroxidases (GPx) and peroxiredoxins (Prx). The enzymes of both families reduce hydroperoxides with thiols by enzyme-substitution mechanisms. H(2)O(2) and organic hydroperoxides are reduced by all thiol peroxidases, most efficiently by SecGPxs, whereas fast peroxynitrite reduction is more common in Prxs. Reduction of lipid hydroperoxides is the domain of monomeric GPx4-type enzymes and of some Prxs. The catalysis starts with oxidation of an active-site selenocysteine (U(P)) or cysteine (C(P)). Activation of Cys (Sec) for hydroperoxide reduction in the GPx family is achieved by a typical tetrad composed of Cys (Sec), Asn, Gln, and Trp, whereas a triad of Cys Thr (or Ser) and Arg is the signature of Prx. In many of the CysGPxs and Prxs, a second Cys (C(R)) is required. In these 2-CysGPxs and 2-CysPrxs, the C(P) oxidized to a sulfenic acid forms an intra- or intermolecular disulfide (typical 2-CysPrx) with C(R), before a stepwise regeneration of ground-state enzyme by redoxin-type proteins can proceed. In SecGPxs and sporadically in Prxs, GSH is used as the reductant. Diversity combined with structural variability predestines thiol peroxidases for redox regulation via ROOH sensing and direct or indirect transduction of oxidant signals to specific protein targets.

A universal entropy-driven mechanism for thioredoxin–target recognition

“…Homology modeling of ScGpx3 using the template structure of bovine Gpx3 indicates that the catalytic cysteines of ScGpx3 are separated by 13 Å and that significant conformational restriction occurs upon intramolecular disulfide bond formation (32). Identical postoxidation conformational changes have also been reported for other known glutathione peroxidases (33). As expected, C32A Trx readily bound to ScGpx3 upon oxidation (ScGpx3-S 2 ) with H 2 O 2 in an entropy-driven recognition process, whereas only very weak binding was detectable with the double C38S/C82S variant used as a surrogate for reduced Gpx3 (Table 3 and SI Appendix, Fig.…”

Basic Principles and Emerging Concepts in the Redox Control of Transcription Factors

“…Mechanistically, the oxidative inactivation of phosphatases via cysteine oxidation involves reactions known from GPx or Prx mechanisms (127). A pivotal cysteine appears to be oxidized to a sulfenic acid (Eq.…”

Selenium‐containing amino acids as direct and indirect antioxidants

“…Thus, selenocystine can be reduced by Cys and GSH, and selenoglutathione diselenide (GSeSeG), and the mixed seleno-sulfide (GSeSG) can undergo ready reduction with dithiothreitol, GSH, a NADPH/glutathione reductase system, and a NADPH/glutathione reductase/GSH system (19,32). These reactions have precedence in the catalytic cycles of GPx and TrxR (33).…”

“…The GPxs were the first seleno protein family identified, and the members of this group are highly responsive to changes in selenium availability (37). The peroxidase activity of the Sec-containing GPxs depends on the redox state of the Sec and is influenced by proximal Gln and Trp residues within the catalytic center (33). Catalysis is proposed to occur via polarization of the peroxide À ÀOÀ ÀOÀ À bond by the carboxamide group of Gln, followed by nucleophilic attack by the (ionized) selenium group of Sec, and cleavage of the peroxyl bond (33).…”

“…The peroxidase activity of the Sec-containing GPxs depends on the redox state of the Sec and is influenced by proximal Gln and Trp residues within the catalytic center (33). Catalysis is proposed to occur via polarization of the peroxide À ÀOÀ ÀOÀ À bond by the carboxamide group of Gln, followed by nucleophilic attack by the (ionized) selenium group of Sec, and cleavage of the peroxyl bond (33). This process results in oxidation of the Sec to a selenenic acid (R-SeOH), which is subsequently reduced by two molecules of GSH, with the first reduction giving a selenosulfide (R-SeS-G), and the second converting this to the resting state selenol (R-SeH) with concomitant formation of glutathione disulfide (33).…”