Glutathione peroxidases

doi:10.1016/j.bbagen.2012.11.020

Biochimica et Biophysica Acta (BBA) - General Subjects

Volume 1830, Issue 5, May 2013, Pages 3289-3303

https://doi.org/10.1016/j.bbagen.2012.11.020 Get rights and content

Abstract

Background

With increasing evidence that hydroperoxides are not only toxic but rather exert essential physiological functions, also hydroperoxide removing enzymes have to be re-viewed. In mammals, the peroxidases inter alia comprise the 8 glutathione peroxidases (GPx1–GPx8) so far identified.

Scope of the review

Since GPxs have recently been reviewed under various aspects, we here focus on novel findings considering their diverse physiological roles exceeding an antioxidant activity.

Major conclusions

GPxs are involved in balancing the H₂O₂ homeostasis in signalling cascades, e.g. in the insulin signalling pathway by GPx1; GPx2 plays a dual role in carcinogenesis depending on the mode of initiation and cancer stage; GPx3 is membrane associated possibly explaining a peroxidatic function despite low plasma concentrations of GSH; GPx4 has novel roles in the regulation of apoptosis and, together with GPx5, in male fertility. Functions of GPx6 are still unknown, and the proposed involvement of GPx7 and GPx8 in protein folding awaits elucidation.

General significance

Collectively, selenium-containing GPxs (GPx1–4 and 6) as well as their non-selenium congeners (GPx5, 7 and 8) became key players in important biological contexts far beyond the detoxification of hydroperoxides. This article is part of a Special Issue entitled Cellular functions of glutathione.

Highlights

► Novel functions of GPx1–8 regarding the essential physiological functions of ROS ► Balancing levels of H₂O₂ in, e.g., insulin signalling by GPx1 ► The role of GPx2 in cancer depends on the mode of initiation and cancer stage ► Specific roles of GPx4 in apoptosis and together with GPx5 in male fertility ► Downregulation as well as overexpression of GPxs can have harmful effects.

Introduction

Glutathione peroxidases (GPxs) belong to a family of phylogenetically related enzymes. Mammalian GPx1‐4 are selenoproteins with a selenocysteine (Sec) in the catalytic centre, GPx6 is a selenoprotein only in humans (see below). According to phylogeny, the GPx family consists of three evolutionary groups arising from a Cys-containing ancestor: GPx1/GPx2, GPx3/GPx5/GPx6 and GPx4/GPx7/GPx8 [1], [2], [3], [4]. The Cys-containing GPx7 and GPx8 evolved from a GPx4-like ancestor. GPx5 and GPx6 appeared to result from a tandem duplication of GPx3 [3]. GPx1 and GPx2 are a sub-clade of the tetrameric GPxs consisting of GPx1–3 and 5 and 6 [4].

For decades GPxs have been known to catalyze the reduction of H₂O₂ or organic hydroperoxides to water or the corresponding alcohols, respectively, typically using glutathione (GSH) as reductant [5]. The presence of Sec as the catalytic moiety was suggested to guarantee a fast reaction with the hydroperoxide and a fast reducibility by GSH. This characterization was well accepted as far as only the first 4 GPxs were known. They appeared to have an antioxidant function at different locations and cellular compartments, GPx1 ubiquitously in the cytosol and mitochondria, GPx2 in the intestinal epithelium, GPx3 in the plasma, all three thus working in the water phase, whereas GPx4 appeared to protect membranes from oxidative challenge. The situation became more complex when the next 4 GPxs were detected, GPx5, containing a cysteine instead of a Sec in the active centre was characterized as a secreted protein in the epididymis [6]. GPx6 turned out to be a selenoprotein in humans but not in rats or mice [7] and is expressed in the olfactory epithelium [8]. Also GPx7 and GPx8 are CysGPxs with low GPx activity. Meanwhile more than 700 CysGPx-homologous sequences were identified over all domains of life. It became clear that only a minority of the GPxs are selenoproteins. Invertebrate and plant CysGPxs do not rely on GSH as reductant but prefer so-called redoxins characterized by a CxxC motif, from which thioredoxins are most commonly used [1]. Therefore, the historical term ‘glutathione peroxidase’ only describes a small subgroup of the peroxidase family correctly [9].

Section snippets

Structural aspects

The catalytic centre of GPxs has first been characterized as triad composed of Sec or Cys, Gln and Trp [10] and later turned out to be a tetrad with an additional Asn [11]. The tetrad is conserved in all members of the GPx family with so far 3 exceptions: the Gln is substituted by a Ser in mammalian GPx8 [4] and by Glu or Gly in two plant GPxs [12]. GPx1, 2, 3, 5 and 6 are homotetramers which might determine the specificity for soluble molecular weight hydroperoxides. GPx4, 7, and 8 are

SecGPxs

The selenol ( single bond SeH) in SecGPxs reacts in form of a selenolate with H₂O₂ to selenenic acid (SeOH) which is reduced back to SeH by 2 GSH forming GSSG and water [12], [14], [16]. ${GPx‐Se}^{-} {+ H}_{2} O_{2} \to {GPx‐SeOH+OH}^{-}$ ${GPx‐SeO}^{-} + H^{+} + GSH \to {GPx‐Se‐SG+H}_{2} O$ $GPx‐Se‐SG+GSH \to {GPx‐Se}^{-} + H^{+} + GSSG$

However, although often quoted as intermediate in the SecGPx cycle, the selenenic acid form has never been detected so far. Alternatively, a selenylamide bond similar to that present in the oxidized form of ebselen, is discussed [12], [17],

GPx1

GPx1 has been comprehensively reviewed recently [27]. We, therefore, give a short overview only and focus on novel aspects.

GPx1 was the first selenoprotein identified [28], [29]. It is a homotetramer and reacts with H₂O₂ and soluble low molecular mass hydroperoxides, such as t-butyl hydroperoxide, cumene hydroperoxide, hydroperoxy fatty acids [16] and even hydroperoxy lysophosphatides [30], but not with hydroperoxides of more complex lipids, which is the domain of GPx4. It contains all 5 amino

GPx2

GPx2 is a homotetramer and closely related to GPx1. Of the GSH binding amino acids only Lys 91' is replaced by glutamine and Arg185 by threonine, thus, specificity for GSH may be high. However, since the protein has not been purified so far, neither substrate preferences nor kinetic constants have yet been addressed. Within the family of SecGPxs, GPx2 ranks highest in the hierarchy (see GPx1) followed by GPx4, GPx3 and GPx1 [82]. GPx2 is mainly expressed in the gastrointestinal system including

GPx3

GPx3 is also similar to GPx1. It is a tetramer and contains two of the four arginines responsible for GSH binding, Arg 103 and 185 [113]. Rate constants for hydroperoxides (k _+ 1) are in the range of 10⁷ M^− 1 s^− 1 making GPx3 a peroxidase as efficient as GPx1. Rate constants for the reduction of the selenenic form by glutathione (k'_+ 2) are in the range of 10⁴–10⁵ M^− 1 s^− 1 indicating that GSH is a good substrate at least in vitro [13]. Also reactivity with thioredoxin and glutaredoxin has been reported

GPx4

GPx4 is a monomer and misses the dimer and tetramer interfaces as well as all amino acids involved in GSH binding in GPx1 [113]. Despite the loss of the binding sites, GPx4 still reacts with GSH [148] and not with thioredoxin [13]. GPx4 had initially been characterized as lipid peroxidation inhibiting protein (PIP) [149] due to its unique ability to reduce, besides H₂O₂ and small hydroperoxides in general, hydroperoxides in complex lipids such as phospholipid, cholesterol and cholesterolester

GPx5

GPx5 is an epididymis-specific CysGPx in mice, rats, pigs, monkey and humans. It is the closest homologue to GPx3. Together with GPx3, GPx5 represent more than 95% of epididymal GPx RNA and protein. The protein was found in epithelial cells and in the lumen of the epididymis, but also associated to the head region of spermatozoa transiting through the epididymis to the vas deferens [161]. Only Arg103 and 185 of the GSH binding amino acids in GPx1 are conserved in GPx5 [12]. However, kinetics

GPx6

GPx6 is a close homologue to GPx3, is a selenoprotein in humans but a CysGPx in rodents and other species [7]. Interestingly, it has a ‘fossil’ SECIS element which is evidence for the divergence of the gene after the split between the common human/rodent ancestor to restore the rodent gene back to a CysGPx. Based on phylogenic analysis CysGPx is proposed to be the ancestral form of GPxs [4]. Like GPx3 GPx6 is a homotetramer.

GPx6 was discovered by in silico analysis of putative odorant-binding

GPx7

GPx7 was first described as a novel glutathione peroxidase with a cysteine instead of Sec in the catalytic centre in Brca1-null mouse embryonic fibroblasts [196]. Due to its homology to phospholipid hydroperoxide GPx (PHGPx = GPx4) it was named non-selenocysteine PHGPx (NPGPx). Like GPx4, NPGPx is a monomer with a molecular mass of about 22 kDa in SDS-PAGE analysis. Unlike GPx4 it had little GPx activity when expressed in and purified from E. coli. A query to GenBank revealed that NPGPx was

GPx8

GPx8 has been detected in a phylogenetic analysis as a novel member belonging to the GPx family in mammalia and amphibia. Being the last representative detected it was named GPx8 [4]. It has the otherwise conserved glutamine in the catalytic tetrad exchanged by serine and lacks a resolving cysteine in the cysteine-block [4]. By containing a N-terminal signal peptide and a C-terminal ER membrane localization signal, GPx8 is a membrane protein of the endoplasmic reticulum [197]. However, little

Conclusion

With the increasing acknowledgement that hydroperoxides are not simply harmful ‘reactive oxygen species’ (ROS) but mediators of physiological processes also the role of GPxs has to be re-viewed. Physiologically produced ROS mainly are hydroperoxides. To make a reaction of hydroperoxides specific in the context of signalling they have to be sensed by proteins with highly reactive thiol or selenol groups which transfer the message to transducers and finally to the effector (see [50], [213]). GPxs

Acknowledgements

The work was supported by the German Research Council (DFG; Grant BR778/8-1)

References (213)

M. Maiorino et al.
The thioredoxin specificity of Drosophila GPx: a paradigm for a peroxiredoxin-like mechanism of many glutathione peroxidases
J. Mol. Biol.
(2007)
S. Toppo et al.
Catalytic mechanisms and specificities of glutathione peroxidases: variations of a basic scheme
Biochim. Biophys. Acta
(2009)
G. Takebe et al.
A comparative study on the hydroperoxide and thiol specificity of the glutathione peroxidase family and selenoprotein P
J. Biol. Chem.
(2002)
R. Brigelius-Flohé et al.
Estimation of individual types of glutathione peroxidases
Methods Enzymol.
(2002)
M.P. Rayman
Selenoproteins and human health: insights from epidemiological data
Biochim. Biophys. Acta
(2009)
L. Flohé et al.
Glutathione peroxidase: a selenoenzyme
FEBS Lett.
(1973)
H.S. Marinho et al.
Role of glutathione peroxidase and phospholipid hydroperoxide glutathione peroxidase in the reduction of lysophospholipid hydroperoxides
Free Radic. Biol. Med.
(1997)
Y.S. Ho et al.
Mice deficient in cellular glutathione peroxidase develop normally and show no increased sensitivity to hyperoxia
J. Biol. Chem.
(1997)
J.B. de Haan et al.
Mice with a homozygous null mutation for the most abundant glutathione peroxidase, Gpx1, show increased susceptibility to the oxidative stress- inducing agents paraquat and hydrogen peroxide
J. Biol. Chem.
(1998)
W.H. Cheng et al.
Cellular glutathione peroxidase is the mediator of body selenium to protect against paraquat lethality in transgenic mice
J. Nutr.
(1998)

Q. Shen et al.

Sequences in the 3′-untranslated region of the human cellular glutathione peroxidase gene are necessary and sufficient for selenocysteine incorporation at the UGA codon

J. Biol. Chem.

(1993)

F. Ding et al.

Identification of a protein component of a mammalian tRNA(Sec) complex implicated in the decoding of UGA as selenocysteine

RNA

(1999)

T.K. Sengupta et al.

Identification of nucleolin as an AU-rich element binding protein involved in bcl-2 mRNA stabilization

J. Biol. Chem.

(2004)

M. Fahling et al.

Role of nucleolin in posttranscriptional control of MMP-9 expression

Biochim. Biophys. Acta

(2005)

R. Wu et al.

Recognition and binding of the human selenocysteine insertion sequence by nucleolin

J. Cell. Biochem.

(2000)

L. Flohé

Changing paradigms in thiology from antioxidant defense toward redox regulation

Methods Enzymol.

(2010)

R. Brigelius-Flohé et al.

Basic principles and emerging concepts in the redox control of transcription factors

Antioxid. Redox Signal.

(2011)

H.Y. Won et al.

Glutathione peroxidase 1 deficiency attenuates allergen-induced airway inflammation by suppressing Th2 and Th17 cell development

Antioxid. Redox Signal.

(2010)

S.R. Lee et al.

Reversible inactivation of the tumor suppressor PTEN by H₂O₂

J. Biol. Chem.

(2002)

M.P. Czech et al.

Evidence for the involvement of sulfhydryl oxidation in the regulation of fat cell hexose transport by insulin

Proc. Natl. Acad. Sci. U. S. A.

(1974)

N. Bashan et al.

Positive and negative regulation of insulin signaling by reactive oxygen and nitrogen species

Physiol. Rev.

(2009)

A.S. Mueller et al.

Regulation of the insulin antagonistic protein tyrosine phosphatase 1B by dietary Se studied in growing rats

J. Nutr. Biochem.

(2009)

R. Brigelius-Flohé et al.