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Methionine Sulfoxide Reductases of Archaea antioxidants Review Methionine Sulfoxide Reductases of Archaea Julie A. Maupin-Furlow Department of Microbiology and Cell Science, University of Florida, Gainesville, FL 32611-0700, USA; jmaupin@ufl.edu; Tel.: +1-352-392-4095 Received: 29 August 2018; Accepted: 11 September 2018; Published: 20 September 2018 Abstract: Methionine sulfoxide reductases are found in all domains of life and are important in reversing the oxidative damage of the free and protein forms of methionine, a sulfur containing amino acid particularly sensitive to reactive oxygen species (ROS). Archaea are microbes of a domain of life distinct from bacteria and eukaryotes. Archaea are well known for their ability to withstand harsh environmental conditions that range from habitats of high ROS, such as hypersaline lakes of intense ultraviolet (UV) radiation and desiccation, to hydrothermal vents of low concentrations of dissolved oxygen at high temperature. Recent evidence reveals the methionine sulfoxide reductases of archaea function not only in the reduction of methionine sulfoxide but also in the ubiquitin-like modification of protein targets during oxidative stress, an association that appears evolutionarily conserved in eukaryotes. Here is reviewed methionine sulfoxide reductases and their distribution and function in archaea. Keywords: archaea; methionine sulfoxide reductase; reactive oxygen species; ubiquitin-like modification; thiol relay systems 1. Introduction 1 Reactive oxygen species (ROS), such as singlet oxygen ( O2), hydrogen peroxide (H2O2), − superoxide anion (O 2) and hydroxyl radical (HO•), can cause widespread damage to cells. Proteins, amino acids, lipids, nucleic acids, and carbohydrates are generally susceptible to ROS damage [1,2]. The sulfur containing amino acids, methionine (Met) and cysteine (Cys), whether in protein or free form, are particularly sensitive to oxidation by ROS [3,4]. Met oxidation leads to the formation of diastereoisomers of methionine sulfoxide (Met-S-O and Met-R-O) which can be further oxidized to methionine sulfone (Figure1). The accumulation of these oxidized methionine derivatives leads to protein carbonylation, aggregation and/or degradation. While methionine sulfone is irreversible, MetO can be repaired to Met by the action of methionine sulfoxide reductase (MSR) enzymes [5]. MSR enzymes are of structurally distinct families and substrate specificity. MSRA of the IPR036509 superfamily catalyzes the stereospecific reduction of Met-S-O in free and protein forms (Figure1) and can reduce N-Ac-L-MetO, dimethylsulfoxide (DMSO), L-ethionine sulfoxide and sulindac [6–8]. MSRB of the IPR028427 family reduces free and protein forms of Met-R-O [9]. fRMSR of the GAF (cGMP-specific phosphodiesterases, adenylyl cyclases and FhlA)-like domain superfamily (IPR029016) reduces only the free form of Met-R-O [10–12]. MSRP of the molybdopterin-dependent sulfite oxidase family reduces free and protein forms of Met-R-O and Met-S-O [13,14] and can reduce dimethylsulfoxide (DMSO), trimethylamine-N-oxide (TMAO) and phenylmethyl sulfoxide in vitro [15]. Members of the molybdopterin-dependent DMSO reductase family, such as BisC [16,17], DmsA [18], TorZ/MSRZ [19] and BisZ [20], reduce free and/or protein forms of MetO in addition to other substrates such as biotin sulfoxide, nicotinamide-N-oxide, adenosine-N-oxide, DMSO and/or TMAO. Antioxidants 2018, 7, 124; doi:10.3390/antiox7100124 www.mdpi.com/journal/antioxidants Antioxidants 2018, 7, 124 2 of 12 Antioxidants 2018, 7, x FOR PEER REVIEW 2 of 12 FigureFigure 1. Methionine 1. Methionine oxidation oxidation and and repair. repair. Methionine,Methionine, whether whether in inprotei proteinsns or as or a as free a freeamino amino acid, acid, is readily oxidized to a mixture of methionine sulfoxide diasteromers by reactive oxygen species is readily oxidized to a mixture of methionine sulfoxide diasteromers by reactive oxygen species (ROS) (ROS) and other oxidants. Of methionine sulfoxide reductase (MSR) enzymes, MSRA and other oxidants. Of methionine sulfoxide reductase (MSR) enzymes, MSRA stereospecifically reduces stereospecifically reduces methionine-S-sulfoxide, whereas MSRB is specific for the R-form of methionine-S-sulfoxide, whereas MSRB is specific for the R-form of methionine sulfoxide. Methionine methionine sulfoxide. Methionine sulfoxides, if not repaired, may be further oxidized by ROS to sulfoxides,produce if methionine not repaired, sulfone may or be radicals. further oxidized by ROS to produce methionine sulfone or radicals. CommonCommon to MSRA, to MSRA, MSRB MSRB and and fRMSR fRMSR is is thethe useuse of an active active site site cysteine cysteine (Cys (CysA) toA )catalyze to catalyze the the nucleophilicnucleophilic attack attack of the of S the atom S atom of the of MetO the MetO substrate subs (Figuretrate (Figure2) [ 21 2)]. This[21]. attackThis attack results results in the in formation the of a tetrahedralformation of transition a tetrahedral state transition which is state rearranged which is to rearranged release Met to (therelease product) Met (the and product) form a and Cys Aformsulfenic − acid.a To Cys resolveA sulfenic this acid. inactive To resolve state, this a resolving inactive cysteinestate, a resolving (CysR) orcysteine reductant (CysR such) or reductant as glutathione such as (YS ) glutathione (YS−) serves as the nucleophile to attack the S atom of the CysA sulfenic acid (Figure 2, serves as the nucleophile to attack the S atom of the CysA sulfenic acid (Figure2, upper vs. lower). upper vs. lower). This attack releases water and forms a disulfide bond. In the CysR mechanism, an This attack releases water and forms a disulfide bond. In the CysR mechanism, an intradisulfide intradisulfide bond is formed between the CysA and CysR residues that can be rearranged by other bond is formed between the CysA and CysR residues that can be rearranged by other Cys residues on Cys residues on the enzyme. If a separate thiol molecule is used to resolve the CysA sulfenic acid, an the enzyme. If a separate thiol molecule is used to resolve the Cys sulfenic acid, an interdisulfide interdisulfide bond is formed. Ultimately, the inter- and intra-disulfideA bonds are reduced by thiol bondrelay is formed. systems Ultimately, such as nicotinamide the inter- and adenine intra-disulfide dinucleotide bonds (phosphate) are reduced hydrogen by thiol [NAD(P)H]- relay systems suchdependent as nicotinamide thioredoxin adenine reductase dinucleotide (TrxR)/thioredoxin (phosphate) (Trx) hydrogen or glutathione [NAD(P)H]-dependent reductase (GR)/glutathione thioredoxin reductase(GSH)/glutaredoxin (TrxR)/thioredoxin (Grx) systems (Trx) or [21]. glutathione This reductio reductasen recycles (GR)/glutathione the MSR enzyme (GSH)/glutaredoxinback to an active (Grx)state. systems [21]. This reduction recycles the MSR enzyme back to an active state. The reductionThe reduction of MetO of MetO by molybdopterin-dependent by molybdopterin-dependent enzymes enzymes relies relies upon upon two distincttwo distinct prosthetic groupsprosthetic (Figure groups3). Enzymes (Figure of3). theEnzymes DMSO of the reductase DMSO reductase family use family bis-MGD use bis-MGD (molybdopterin (molybdopterin guanine dinucleotide),guanine dinucleotide), a complex of a Mo complex and two of molybdopterinMo and two molybdopterin guanine dinucleotide guanine (MGD)dinucleotide cofactors, (MGD) for the cofactors, for the redox-active prosthetic group, while members of the sulfide oxidase family redox-active prosthetic group, while members of the sulfide oxidase family coordinate a di-oxo form of coordinate a di-oxo form of the molybdenum cofactor (di-oxo Moco) as the redox-active center [22]. the molybdenum cofactor (di-oxo Moco) as the redox-active center [22]. The source of electrons used The source of electrons used for molybdopterin-dependent reduction of MetO varies. For example, for molybdopterin-dependentthe DMSO reductase family member reduction BisC of of MetO Rhodobacter varies. sphaeroides For example, can use the electrons DMSO directly reductase from family memberNAD(P)H BisC of [23],Rhodobacter whereas E. sphaeroides coli BisC reliescan useupon electrons a protein-(SH) directly2 and from flavoprotein NAD(P)H relay [23 ],system whereas [24].E. coli BisC reliesThe sulfide upon oxidase a protein-(SH) family protein2 and flavoproteinMSRP, which relaycoordinates system di-oxo [24]. TheMoco sulfide through oxidase a conserved family Cys protein MSRP,residue which [15], coordinates resides in di-oxo the periplasmic Moco through space aof conserved gram-negative Cys residuebacteria [15[13].], residesMSRP reduces in the periplasmic MetO spaceusing of gram-negative electrons from MSRQ, bacteria an [ integral13]. MSRP b-type reduces heme transmembrane MetO using electrons protein of from the NADPH MSRQ, oxidase an integral b-typefamily heme [13,14], transmembrane which shuttles protein electrons of thefrom NADPH the quinone oxidase pool family[13,14]. [13,14], which shuttles electrons from the quinone pool [13,14]. Antioxidants 2018, 7, 124 3 of 12 Antioxidants 2018, 7, x FOR PEER REVIEW 3 of 12 Antioxidants 2018, 7, x FOR PEER REVIEW 3 of 12 FigureFigure 2. CatalyticCatalytic 2. Catalytic mechanism mechanism mechanism of of ofmethionine methionine methionine sulfoxide sulfoxide reductasesreductases reductases that that that use use use an an active active site site cysteine cysteine nucleophilenucleophile (Cys (CysAA) and A) and a resolving a resolving cysteinecysteine cysteine (Cys(Cys (CysRRR))) (blue)(blue)
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