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Methionine Sulphoxide Reductase (methionine + sulphoxide_reductase)
Selected AbstractsMethionine sulphoxide reductase is an important antioxidant enzyme in the gastric pathogen Helicobacter pyloriMOLECULAR MICROBIOLOGY, Issue 2 2005Praveen Alamuri No abstract is available for this article. [source] Methionine sulphoxide reductase is an important antioxidant enzyme in the gastric pathogen Helicobacter pyloriMOLECULAR MICROBIOLOGY, Issue 5 2004Praveen Alamuri Summary The ability of Helicobacter pylori to colonize the stomach requires that it combat oxidative stress responses imposed by the host. The role of methionine sulfoxide reductase (Msr), a methionine repair enzyme, in H. pylori stress resistance was evaluated by a mutant analysis approach. An msr mutant strain lacked immunologically detectable sulphoxide reductase protein and also showed no enzyme activity when provided with oxidized methionines as substrates. The mutant strain showed diminished growth compared to the parent strain in the presence of chemical oxidants, and showed rapid viability loss when exposed to oxidizing conditions. The stress resistance and enzyme activity could be recovered by complementing the mutant with a functional copy of the msr gene. Upon fractionation of parent strain and the complemented mutant cells into membranes and cytoplasmic proteins, most of the immunologically detectable Msr was localized to the membrane, and this fraction contained all of the Msr activity. Qualitative detection of the whole cell protein pattern using 2,4-dinitro phenyl hydrazine (DNPH) showed a far greater number of oxidized protein species in the mutant than in the parent strain when the cells were subjected to oxygen, peroxide or s-nitrosoglutathione (GSNO) induced stress. Importantly, no oxidized proteins were discerned in either strain upon incubation in anaerobic conditions. A mutant strain that synthesized a truncated Msr (corresponding to the MsrA domain) was slightly more resistant to oxidative stress than the msr strain. Mouse colonization studies showed Msr is an important colonization factor, especially for effective longer-term (14 and 21 days) colonization. Complementation of the mutant msr strain by chromosomal insertion of a functional gene restored mouse colonization ability. [source] Origin and evolution of the protein-repairing enzymes methionine sulphoxide reductasesBIOLOGICAL REVIEWS, Issue 3 2008Xing-Hai Zhang Abstract The majority of extant life forms thrive in an O2 -rich environment, which unavoidably induces the production of reactive oxygen species (ROS) during cellular activities. ROS readily oxidize methionine (Met) residues in proteins/peptides to form methionine sulphoxide [Met(O)] that can lead to impaired protein function. Two methionine sulphoxide reductases, MsrA and MsrB, catalyse the reduction of the S and R epimers, respectively, of Met(O) in proteins to Met. The Msr system has two known functions in protecting cells against oxidative damage. The first is to repair proteins that have lost activity due to Met oxidation and the second is to function as part of a scavenger system to remove ROS through the reversible oxidation/reduction of Met residues in proteins. Bacterial, plant and animal cells lacking MsrA are known to be more sensitive to oxidative stress. The Msr system is considered an important cellular defence mechanism to protect against oxidative stress and may be involved in ageing/senescence. MsrA is present in all known eukaryotes and eubacteria and a majority of archaea, reflecting its essential role in cellular life. MsrB is found in all eukaryotes and the majority of eubacteria and archaea but is absent in some eubacteria and archaea, which may imply a less important role of MsrB compared to MsrA. MsrA and MsrB share no sequence or structure homology, and therefore probably emerged as a result of independent evolutionary events. The fact that some archaea lack msr genes raises the question of how these archaea cope with oxidative damage to proteins and consequently of the significance of msr evolution in oxic eukaryotes dealing with oxidative stress. Our best hypothesis is that the presence of ROS-destroying enzymes such as peroxiredoxins and a lower dissolved O2 concentration in those msr -lacking organisms grown at high temperatures might account for the successful survival of these organisms under oxidative stress. [source] | ||||||||||