Methionine Sulfoxide Reductase System Research Articles

HprSR Is a Reactive Chlorine Species-Sensing, Two-Component System in Escherichia coli.

Two-component systems (TCS) are signaling pathways that allow bacterial cells to sense, respond to, and adapt to fluctuating environments. Among the classical TCS of Escherichia coli, HprSR has recently been shown to be involved in the regulation of msrPQ, which encodes the periplasmic methionine sulfoxide reductase system. In this study, we demonstrated that hypochlorous acid (HOCl) induces the expression of msrPQ in an HprSR-dependent manner, whereas H2O2, NO, and paraquat (a superoxide generator) do not. Therefore, HprS appears to be an HOCl-sensing histidine kinase. Using a directed mutagenesis approach, we showed that Met residues located in the periplasmic loop of HprS are important for its activity: we provide evidence that as HOCl preferentially oxidizes Met residues, HprS could be activated via the reversible oxidation of its methionine residues, meaning that MsrPQ plays a role in switching HprSR off. We propose that the activation of HprS by HOCl could occur through a Met redox switch. HprSR appears to be the first characterized TCS able to detect reactive chlorine species (RCS) in E. coli. This study represents an important step toward understanding the mechanisms of RCS resistance in prokaryotes. IMPORTANCE Understanding how bacteria respond to oxidative stress at the molecular level is crucial in the fight against pathogens. HOCl is one of the most potent industrial and physiological microbicidal oxidants. Therefore, bacteria have developed counterstrategies to survive HOCl-induced stress. Over the last decade, important insights into these bacterial protection factors have been obtained. Our work establishes HprSR as a reactive chlorine species-sensing, two-component system in Escherichia coli MG1655, which regulates the expression of msrPQ, two genes encoding, a repair system for HOCl-oxidized proteins. Moreover, we provide evidence suggesting that HOCl could activate HprS through a methionine redox switch.

A previously uncharacterized two-component signaling system in uropathogenic Escherichia coli coordinates protection against host-derived oxidative stress with activation of hemolysin-mediated host cell pyroptosis.

Uropathogenic Escherichia coli (UPEC) deploy an array of virulence factors to successfully establish urinary tract infections. Hemolysin is a pore-forming toxin, and its expression correlates with the severity of UPEC infection. Two-component signaling systems (TCSs) are a major mechanism by which bacteria sense environmental cues and respond by initiating adaptive responses. Here, we began this study by characterizing a novel TCS (C3564/C3565, herein renamed orhK/orhR for oxidative resistance and hemolysis kinase/regulator) that is encoded on a UPEC pathogenicity island, using bioinformatic and biochemical approaches. A prevalence analysis indicates that orhK/orhR is highly associated with the UPEC pathotype, and it rarely occurs in other E. coli pathotypes tested. We then demonstrated that OrhK/OrhR directly activates the expression of a putative methionine sulfoxide reductase system (C3566/C3567) and hemolysin (HlyA) in response to host-derived hydrogen peroxide (H2O2) exposure. OrhK/OrhR increases UPEC resistance to H2O2 in vitro and survival in macrophages in cell culture via C3566/C3567. Additionally, OrhK/OrhR mediates hemolysin-induced renal epithelial cell and macrophage death via a pyroptosis pathway. Reducing intracellular H2O2 production by a chemical inhibitor impaired OrhK/OrhR-mediated activation of c3566-c3567 and hlyA. We also uncovered that UPEC links the two key virulence traits by cotranscribing the c3566-c3567 and hlyCABD operons. Taken together, our data suggest a paradigm in which a signal transduction system coordinates both bacterial pathogen defensive and offensive traits in the presence of host-derived signals; and this exquisite mechanism likely contributes to hemolysin-induced severe pathological outcomes.

Membrane-Bound Flavocytochrome MsrQ Is a Substrate of the Flavin Reductase Fre in Escherichia coli.

MsrPQ is a new type of methionine sulfoxide reductase (Msr) system found in bacteria. It is specifically involved in the repair of periplasmic methionine residues that are oxidized by hypochlorous acid. MsrP is a periplasmic molybdoenzyme that carries out the Msr activity, whereas MsrQ, an integral membrane-bound hemoprotein, acts as the physiological partner of MsrP to provide electrons for catalysis. Although MsrQ (YedZ) was associated since long with a protein superfamily named FRD (ferric reductase domain), including the eukaryotic NADPH oxidases and STEAP proteins, its biochemical properties are still sparsely documented. Here, we have investigated the cofactor content of the E. coli MsrQ and its mechanism of reduction by the flavin reductase Fre. We showed by electron paramagnetic resonance (EPR) spectroscopy that MsrQ contains a single highly anisotropic low-spin (HALS) b-type heme located on the periplasmic side of the membrane. We further demonstrated that MsrQ holds a flavin mononucleotide (FMN) cofactor that occupies the site where a second heme binds in other members of the FDR superfamily on the cytosolic side of the membrane. EPR spectroscopy indicates that the FMN cofactor can accommodate a radical semiquinone species. The cytosolic flavin reductase Fre was previously shown to reduce the MsrQ heme. Here, we demonstrated that Fre uses the FMN MsrQ cofactor as a substrate to catalyze the electron transfer from cytosolic NADH to the heme. Formation of a specific complex between MsrQ and Fre could favor this unprecedented mechanism, which most likely involves transfer of the reduced FMN cofactor from the Fre active site to MsrQ.

Methionine sulfoxide and the methionine sulfoxide reductase system as modulators of signal transduction pathways: a review.

Methionine oxidation and reduction is a common phenomenon occurring in biological systems under both physiological and oxidative-stress conditions. The levels of methionine sulfoxide (MetO) are dependent on the redox status in the cell or organ, and they are usually elevated under oxidative-stress conditions, aging, inflammation, and oxidative-stress related diseases. MetO modification of proteins may alter their function or cause the accumulation of toxic proteins in the cell/organ. Accordingly, the regulation of the level of MetO is mediated through the ubiquitous and evolutionary conserved methionine sulfoxide reductase (Msr) system and its associated redox molecules. Recent published research has provided new evidence for the involvement of free MetO or protein-bound MetO of specific proteins in several signal transduction pathways that are important for cellular function. In the current review, we will focus on the role of MetO in specific signal transduction pathways of various organisms, with relation to their physiological contexts, and discuss the contribution of the Msr system to the regulation of the observed MetO effect.

Staphylococcus aureus Peptide Methionine Sulfoxide Reductases Protect from Human Whole-Blood Killing.

The generation of oxidative stress is a host strategy used to control Staphylococcus aureus infections. Sulfur-containing amino acids, cysteine and methionine, are particularly susceptible to oxidation because of the inherent reactivity of sulfur. Due to the constant threat of protein oxidation, many systems evolved to protect S. aureus from protein oxidation or to repair protein oxidation after it occurs. The S. aureus peptide methionine sulfoxide reductase (Msr) system reduces methionine sulfoxide to methionine. Staphylococci have four Msr enzymes, which all perform this reaction. Deleting all four msr genes in USA300 LAC (Δmsr) sensitizes S. aureus to hypochlorous acid (HOCl) killing; however, the Δmsr strain does not exhibit increased sensitivity to H2O2 stress or superoxide anion stress generated by paraquat or pyocyanin. Consistent with increased susceptibility to HOCl killing, the Δmsr strain is slower to recover following coculture with both murine and human neutrophils than USA300 wild type. The Δmsr strain is attenuated for dissemination to the spleen following murine intraperitoneal infection and exhibits reduced bacterial burdens in a murine skin infection model. Notably, no differences in bacterial burdens were observed in any organ following murine intravenous infection. Consistent with these observations, USA300 wild-type and Δmsr strains have similar survival phenotypes when incubated with murine whole blood. However, the Δmsr strain is killed more efficiently by human whole blood. These findings indicate that species-specific immune cell composition of the blood may influence the importance of Msr enzymes during S. aureus infection of the human host.

Role of methionine sulfoxide reductase in Alzheimer's disease

Cellular oxidative damage has been implicated as one of the factors in Alzheimer's disease (AD) pathogenesis. One of the enzyme systems preventing protein oxidation in mammalian cells is the methionine sulfoxide reductase (MSR) system; MSR system is comprised of MSRA and MSRB, which reduce oxidized methionine residues (Met(O)) present in proteins back to methionine. Further, the MSR system scavenges reactive oxygen species (ROS), by permitting methionine residues in proteins to function as catalytic antioxidants. There is growing evidence from many studies on the affect of altered MSRA levels on AD progression in different animal models and, also that oxidized Met 35 will promote aggregation of toxic forms of Aß. Our research aims to further understand the role of MSRA and Met35 in the pathogenic processes of AD. For our studies we have used, AD transgenic mice, J20 APP-Tg that overexpresses Aß to analyze MSR levels and, variants of commercially available Aß (1-42) to assess the effect of methionine oxidation. Our preliminary results indicate that the level of MSRA was decreased in the transgenic mice as compared to the wild type mice. We have also observed in Aß peptide aggregation experiments, oxidized Met35 Aβformed high molecular weight fibrillar aggregates compared to the WT- Aβ and, if Met is replaced with norleucine (Nle) only monomers were formed. These results suggest that MSRA plays a role in Aß aggregation and these studies provide a potential therapeutic target for AD.

The Antioxidant Enzyme Methionine Sulfoxide Reductase A (MsrA) Interacts with Jab1/CSN5 and Regulates Its Function.

Methionine sulfoxide (MetO) is an oxidative posttranslational modification that primarily occurs under oxidative stress conditions, leading to alteration of protein structure and function. This modification is regulated by MetO reduction through the evolutionarily conserved methionine sulfoxide reductase (Msr) system. The Msr type A enzyme (MsrA) plays an important role as a cellular antioxidant and promotes cell survival. The ubiquitin- (Ub) like neddylation pathway, which is controlled by the c-Jun activation domain-binding protein-1 (Jab1), also affects cell survival. Jab1 negatively regulates expression of the cell cycle inhibitor cyclin-dependent kinase inhibitor 1B (P27) through binding and targeting P27 for ubiquitination and degradation. Here we report the finding that MsrA interacts with Jab1 and enhances Jab1′s deneddylase activity (removal of Nedd8). In turn, an increase is observed in the level of deneddylated Cullin-1 (Cul-1, a component of E3 Ub ligase complexes). Furthermore, the action of MsrA increases the binding affinity of Jab1 to P27, while MsrA ablation causes a dramatic increase in P27 expression. Thus, an interaction between MsrA and Jab1 is proposed to have a positive effect on the function of Jab1 and to serve as a means to regulate cellular resistance to oxidative stress and to enhance cell survival.

The Functions of the Mammalian Methionine Sulfoxide Reductase System and Related Diseases.

This review article describes and discusses the current knowledge on the general role of the methionine sulfoxide reductase (MSR) system and the particular role of MSR type A (MSRA) in mammals. A powerful tool to investigate the contribution of MSRA to molecular processes within a mammalian system/organism is the MSRA knockout. The deficiency of MSRA in this mouse model provides hints and evidence for this enzyme function in health and disease. Accordingly, the potential involvement of MSRA in the processes leading to neurodegenerative diseases, neurological disorders, cystic fibrosis, cancer, and hearing loss will be deliberated and evaluated.

Methionine sulfoxide reductase A (MsrA) mediates the ubiquitination of 14-3-3 protein isotypes in brain

The methionine sulfoxide reductase (Msr) system is known for its function in reducing protein-methionine sulfoxide to methionine. Recently, we showed that one member of the Msr system, MsrA, is involved in the ubiquitination-like process in Archaea. Here, the mammalian MsrA is demonstrated to mediate the ubiquitination of the 14-3-3 zeta protein and to promote the binding of 14-3-3 proteins to alpha synuclein in brain. MsrA was also found to enhance the ubiquitination and phosphorylation of Ser129 of alpha synuclein in brain. Furthermore, we demonstrate that, similarly to the archaeal MsrA, the mammalian MsrA can compete for capturing ubiquitin using the same active site it contains for methionine sulfoxide binding. Based on our previous observations showing that MsrA knockout mice have elevated expression levels of dopamine and 14-3-3 zeta and our current data, we propose that MsrA-dependent 14-3-3 zeta ubiquitination affects the regulation of alpha synuclein degradation and dopamine synthesis in the brain.

Mechanisms of neuroprotection against oxidative stress in the anoxia tolerant turtle Trachemys scripta

The detrimental effects of oxidative stress caused by the accumulation of Reactive Oxygen Species (ROS) have been acknowledged as major factors in aging, senescence, and several neurodegenerative conditions including Parkinson's Disease and stroke (ischemia/reperfusion). Mammalian models are extremely susceptible to these stresses and the restoration of oxygen after anoxia causes oxidative damage; however some organisms including the freshwater turtle Trachemys scripta can withstand such conditions without any apparent pathology. T. scripta thus provides us with a model in which we can investigate physiological mechanisms of neuroprotection in anoxia and reoxygenation without the damaging effects that come with oxidative stress.The ability of the turtle to survive these stressors is thought to be related to its high innate levels of antioxidants and its capacity to suppress ROS production. One potential antioxidant mechanism is the Methionine Sulfoxide Reductase System (Msr) that catalyzes the reduction of oxidized Methionine (Met) residues. Methionine residues are easily oxidized amino acids and oxidized Met is associated with decreased protein activity. Msr may also restore function to damaged proteins and it has been shown to scavenge ROS and thus ameliorate cellular damage.The present study investigated the role and regulation of MsrA in turtle primary neuronal cell cultures exposed to 4 hours of anoxia and 4 hours of anoxia followed by 4 hours of reoxygenation. Anoxia and anoxia/reoxygenation increase MsrA mRNA and protein levels, which suggests a protective role under these conditions. MsrA expression was then altered with target specific siRNA; we found that the knock down of MsrA expression resulted in decreased cell viability. As the factors that control MsrA expression in this model are still unknown, we also induced FOXO3a expression by transfecting a FOXO3a plasmid into the cells, as it has been shown to regulate MsrA levels in other animal models. The induction of FOXO3a protected neurons against cell death. Furthermore, treatment of cells with the green tea extract Epigallocatechin gallate (EGCG), which has antioxidant properties, results in increased expression of FOXO3a when the cells are exposed to oxidative stress. Together these results suggest that MsrA may play an important role in protection against anoxia and oxidative stress in the turtle brain, and may prove to be a target to treat diseases of ischemia and oxidative stress.Support or Funding InformationNIH‐NIA Project # 1R15AG033374‐01,FAU FoundationThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

A Two-component NADPH Oxidase (NOX)-like System in Bacteria Is Involved in the Electron Transfer Chain to the Methionine Sulfoxide Reductase MsrP

MsrPQ is a newly identified methionine sulfoxide reductase system found in bacteria, which appears to be specifically involved in the repair of periplasmic proteins oxidized by hypochlorous acid. It involves two proteins: a periplasmic one, MsrP, previously named YedY, carrying out the Msr activity, and MsrQ, an integral b-type heme membrane-spanning protein, which acts as the specific electron donor to MsrP. MsrQ, previously named YedZ, was mainly characterized by bioinformatics as a member of the FRD superfamily of heme-containing membrane proteins, which include the NADPH oxidase proteins (NOX/DUOX). Here we report a detailed biochemical characterization of the MsrQ protein from Escherichia coli We optimized conditions for the overexpression and membrane solubilization of an MsrQ-GFP fusion and set up a purification scheme allowing the production of pure MsrQ. Combining UV-visible spectroscopy, heme quantification, and site-directed mutagenesis of histidine residues, we demonstrated that MsrQ is able to bind two b-type hemes through the histidine residues conserved between the MsrQ and NOX protein families. In addition, we identify the E. coli flavin reductase Fre, which is related to the dehydrogenase domain of eukaryotic NOX enzymes, as an efficient cytosolic electron donor to the MsrQ heme moieties. Cross-linking experiments as well as surface Plasmon resonance showed that Fre interacts with MsrQ to form a specific complex. Taken together, these data support the identification of the first prokaryotic two-component protein system related to the eukaryotic NOX family and involved in the reduction of periplasmic oxidized proteins.

Redox Biology Poster Prize Winner P55 - Role of Oxidized Protein Repair in Human Skeletal Muscle

There is now increasing evidence that reactive oxygen species (ROS) are signalling molecules that regulate growth, differentiation, proliferation and apoptosis, at least in physiological concentration. However, when ROS levels overcome the capacity of cellular antioxidant systems, they damage cellular components such as nucleic acids, lipids and in particular proteins, inflicting alterations to cell structure and function. Oxidation of sulfur-containing aminoacids, like cysteine and methionine, within proteins, can be repaired by specific enzymatic systems. Indeed methionine sulfoxide is catalytically reduced back to methionine by the methionine sulfoxide reductase (Msr) system. We showed that this Msr system is involved in cellular protection against oxidative stress by preventing apoptosis and limiting irreversible protein oxidative damage. Furthermore, it has been demonstrated that the Msr system is no longer efficient during ageing and senescence as well as that Msr modulates longevity in animal models. In this work we analysed Msr expression in human skeletal muscle. We showed, using both primary and immortalized skeletal muscle cell lines, that the expression of the Msr system increases during differentiation, suggesting a role of this antioxidant system on myofibres formation. Since myoblasts senescence associated with less differentiation capacity and an abnormal production of ROS have been observed in some muscular dystrophies, we wondered about the state of the Msr system in late-onset myopathies, such as oculopharyngeal muscular dystrophy (OPMD). In OPMD we confirmed, at the transcription level, an increased expression of Msr with differentiation, both on immortalized and primary cell cultures, similarly to what we observed on control cell lines. Our aim is to characterize for the first time the role of a major oxidized protein repair system (Msr) in human skeletal muscle homeostasis and, in particular, in myotubes protection during oxidative stress conditions.

Induction of methionine sulfoxide reductase activity by pergolide, pergolide sulfoxide, and S-adenosyl-methionine in neuronal cells

The reduction of methionine sulfoxide in proteins is facilitated by the methionine sulfoxide reductase (Msr) system. The Msr reduction activity is important for protecting cells from oxidative stress related damages. Indeed, we have recently shown that treatment of cells with N-acetyl-methionine sulfoxide can increase Msr activity and protect neuronal cells from amyloid beta toxicity. Thus, in search of other similar Msr-inducing molecules, we examined the effects of pergolide, pergolide sulfoxide, and S-adenosyl-methionine on Msr activity in neuronal cells. Treatment of neuronal cells with a physiological range of pergolide and pergolide sulfoxide (0.5–1.0μM) caused an increase of about 40% in total Msr activity compared with non-treated control cells. This increase in activity correlated with similar increases in methionine sulfoxide reductase A protein expression levels. Similarly, treatment of cells with S-adenosyl methionine also increased cellular Msr activity, which was milder compared to increases induced by pergolide and pergolide sulfoxide. We found that all the examined compounds are able to increase cellular Msr activity to levels comparable to N-acetyl-methionine sulfoxide treatment. Pergolide, pergolide sulfoxide, and S-adenosyl methionine can cross the blood–brain barrier. Therefore, we hypothesize that they can be useful in the treatment of symptoms/pathologies that are associated with reduced Msr activity.

Methionine sulfoxide reductases and methionine sulfoxide in the subterranean mole rat (Spalax): Characterization of expression under various oxygen conditions

The blind subterranean mole rat (Spalax ehrenbergi) exhibits a relatively long life span, which is attributed to an efficient antioxidant defense affording protection against accumulation of oxidative modifications of proteins. Methionine residues can be oxidized to methionine sulfoxide (MetO) and then enzymatically reduced by the methionine sulfoxide reductase (Msr) system. In the current study we have isolated the cDNA sequences of the Spalax Msr genes as well as 23 additional selenoproteins and monitored the activities of Msr enzymes in liver and brain of rat (Rattus norvegicus), Spalax galili, and Spalax judaei under normoxia, hypoxia, and hyperoxia. Under normoxia, the Msr activity was lower in S. galili in comparison to S. judaei and R. norvegicus especially in the brain. The pattern of Msr activity of the three species was similar throughout the tested conditions. However, exposure of the animals to hypoxia caused a significant enhancement of Msr activity, especially in S. galili. Hyperoxic exposure showed a highly significant induction of Msr activity compared with normoxic conditions for R. norvegicus and S. galili brain. It was concluded that among all species examined, S. galili appears to be more responsive to oxygen tension changes and that the Msr system is upregulated mainly by severe hypoxia.

Aβ-sulfoxide but not Aβ-sulfone reduces neurotoxicity through the methionine sulfoxide reductase system

Aβ-sulfoxide but not Aβ-sulfone reduces neurotoxicity through the methionine sulfoxide reductase system

A High-Throughput Screening Compatible Assay for Activators and Inhibitors of Methionine Sulfoxide Reductase A

The methionine sulfoxide reductase (Msr) system has been shown to play an important role in protecting cells against oxidative damage. This family of enzymes can repair damage to proteins resulting from the oxidation of methionine residues to methionine sulfoxide, caused by reactive oxygen species. Previous genetic studies in animals have shown that increased levels of methionine sulfoxide reductase enzyme A (MsrA), an important member of the Msr family, can protect cells against oxidative damage and increase life span. A high-throughput screening (HTS) compatible assay has been developed to search for both activators and inhibitors of MsrA. The assay involves a coupled reaction in which the oxidation of NADPH is measured by either spectrophotometric or fluorometric analysis. Previous studies had shown that MsrA has a broad substrate specificity and can reduce a variety of methyl sulfoxide compounds, including dimethylsulfoxide (DMSO). Since the chemicals in the screening library are dissolved in DMSO, which would compete with any of the standard substrates used for the determination of MsrA activity, an assay has been developed that uses the DMSO that is the solvent for the compounds in the library as the substrate for the MsrA enzyme. A specific activator of MsrA could have important therapeutic value for diseases that involve oxidative damage, especially age-related diseases, whereas a specific inhibitor of MsrA would have value for a variety of research studies.

Protein Carbonyl and the Methionine Sulfoxide Reductase System

The formation and accumulation of protein-carbonyl by reactive oxygen species may serve as a marker of oxidative stress, aging, and age-related diseases. Enzymatic reversal of the protein-carbonyl modification has not yet been detected. However, an enzymatic reversal of protein-methionine sulfoxide modification exists and is mediated by the methionine sulfoxide reductase (Msr) system. Methionine sulfoxide modifications to proteins may precede the formation of protein-carbonyl adducts because of consequent structural changes that increase the vulnerability of amino acid residues to carbonylation. Supportive evidence for this possibility arises from the elevated protein-carbonyl accumulations observed in organisms, such as yeast and mice, lacking the methionine sulfoxide reductase A (MsrA) enzyme. In addition, advanced age or enhanced oxidative-stress conditions foster the accumulations of protein-carbonyls. This review discusses the possible involvement of methionine sulfoxide formation in the occurrence of protein-carbonyl adducts and their relevance to the aging process and neurodegenerative diseases.

Methionine sulfoxide reductase A expression is regulated by the DAF‐16/FOXO pathway in Caenorhabditis elegans

The methionine sulfoxide reductase system has been implicated in aging and protection against oxidative stress. This conserved system reverses the oxidation of methionine residues within proteins. We analyzed one of the components of this system, the methionine sulfoxide reductase A gene, in Caenorhabditis elegans. We found that the msra-1 gene is expressed in most tissues, particularly in the intestine and the nervous system. Worms carrying a deletion of the msra-1 gene are more sensitive to oxidative stress, show chemotaxis and locomotory defects, and a 30% decrease in median survival. We established that msra-1 expression decreases during aging and is regulated by the DAF-16/FOXO3a transcription factor. The absence of this enzyme decreases median survival and affects oxidative stress resistance of long lived daf-2 worms. A similar effect of MSRA-1 absence in wild-type and daf-2 (where most antioxidant enzymes are activated) backgrounds, suggests that the lack of this member of the methionine repair system cannot be compensated by the general antioxidant response. Moreover, FOXO3a directly activates the human MsrA promoter in a cell culture system, implying that this could be a conserved mechanism of MsrA regulation. Our results suggest that repair of oxidative damage in proteins influences the rate at which tissues age. This repair mechanism, rather than the general decreased of radical oxygen species levels, could be one of the main determinants of organisms' lifespan.

Caloric restriction alleviates abnormal locomotor activity and dopamine levels in the brain of the methionine sulfoxide reductase A knockout mouse

Oxidative stress is associated with the aging process, a risk factor for neurodegenerative diseases, and decreased by reduced energy intake. Oxidative modifications can affect protein function; the sulfur-containing amino acids, including methionine, are particularly susceptible to oxidation. A methionine sulfoxide can be enzymatically reduced by the methionine sulfoxide reductase (Msr) system. Previously, we have shown that MsrA −/− mice exhibit altered locomotor activity and brain dopamine levels as function of age. Previous studies have demonstrated that a caloric restriction enhances antioxidant defense and reduces the action of reactive oxygen species. Here we examine locomotor behavior and dopamine levels of MsrA −/− mice after caloric restriction starting at eight months of age and ending at 17 months. The MsrA −/− mice did not have any significant difference in spontaneous distance traveled when compared to controls at 17 months of age. In contrast, our previous report showed decreased locomotor activity in the MsrA −/− mice at 12 months of age and older when fed ad-libitum. After completion of the caloric restriction diet, dopamine levels were comparable to control mice. This differs from the abnormal dopamine levels previously observed in MsrA −/− mice fed ad-libitum. Thus, caloric restriction had a neutralization effect on MsrA ablation. In summary, it is suggested that caloric restriction alleviates abnormal locomotor activity and dopamine levels in the brain of the methionine sulfoxide reductase A knockout mouse.

Impact of Hydrogen Peroxide on the Activity, Structure, and Conformational Stability of the Oxidized Protein Repair Enzyme Methionine Sulfoxide Reductase A

The oxidized protein repair methionine sulfoxide reductase (Msr) system has been implicated in aging, in longevity, and in the protection against oxidative stress. This system is made of two different enzymes (MsrA and MsrB) that catalyze the reduction of the two diastereoisomers S- and R-methionine sulfoxide back to methionine within proteins, respectively. Due to its role in cellular protection against oxidative stress that is believed to originate from its reactive oxygen species scavenging ability in combination with exposed methionine at the surface of proteins, the susceptibility of MsrA to hydrogen-peroxide-mediated oxidative inactivation has been analyzed. This study is particularly relevant to the oxidized protein repair function of MsrA in both fighting against oxidized protein formation and being exposed to oxidative stress situations. The enzymatic properties of MsrA indeed rely on the activation of the catalytic cysteine to the thiolate anion form that is potentially susceptible to oxidation by hydrogen peroxide. The residual activity and the redox status of the catalytic cysteine were monitored before and after treatment. These experiments showed that the enzyme is only inactivated by high doses of hydrogen peroxide. Although no significant structural modification was detected by near- and far-UV circular dichroism, the conformational stability of oxidized MsrA was decreased as compared to that of native MsrA, making it more prone to degradation by the 20S proteasome. Decreased conformational stability of oxidized MsrA may therefore be considered as a key factor for determining its increased susceptibility to degradation by the proteasome, hence avoiding its intracellular accumulation upon oxidative stress.