Protein Domain : Peptide methionine sulphoxide reductase MrsB domain IPR002579

Type	Domain
Description	Peptide methionine sulphoxide reductase (Msr) reverses the inactivation of many proteins due to the oxidation of critical methionine residues by reducing methionine sulphoxide, Met(O), to methionine [ ]. It is present in most living organisms, and the cognate structural gene belongs to the so-called minimum gene set [, ].The domains: MsrA and MsrB, reduce different epimeric forms of methionine sulphoxide. This group represents MsrB, the crystal structure of which has been determined to 1.8A [ ]. The overall structure shows no resemblance to the structures of MsrA () from other organisms; though the active sites show approximate mirror symmetry. In each case, conserved amino acid motifs mediate the stereo-specific recognition and reduction of the substrate. Unlike the MsrA domain, the MsrB domain activates the cysteine or selenocysteine nucleophile through a unique Cys-Arg-Asp/Glu catalytic triad. The collapse of the reaction intermediate most likely results in the formation of a sulphenic or selenenic acid moiety. Regeneration of the active site occurs through a series of thiol-disulphide exchange steps involving another active site Cys residue and thioredoxin. In a number of pathogenic bacteria, including Neisseria gonorrhoeae, the MsrA and MsrB domains are fused; the MsrA being N-terminal to MsrB. This arrangement is reversed in Treponema pallidum. In N. gonorrhoeae and Neisseria meningitidis, a thioredoxin domain is fused to the N terminus. This may function to reduce the active sites of the downstream MsrA and MsrB domains.
Short Name	Met_Sox_Rdtase_MsrB_dom