1L1D

The oxidation of methionine residues to methionine sulfoxide is implicated in ageing processes; the reduction of methionine sulfoxide protein residues is similarly implicated in antioxidant repair activity, but also the virulence of pathogenic organisms, such as Neisseria gonorrhoeae which secretes pilB. The modular pilB contains three domains; one is a methionine sulfoxide reductase (MsrA) which reduces S-methionine sulfoxide (S-chiral at sulphur), and another an MsrB (this entry) which reduces R-methionine sulfoxide. The two domains have no sequence homology but use the same mechanism - an example of the fusion of two convergently evolved enzymes.