Methionine Sulfoxide Reductase B3 (MSRB3)

Oxidation of free and protein-bound methionine residues to methionine sulfoxides can occur readily by reactive oxygen species. Methionine-R-sulfoxide reductases, such as MSRB3, catalyze the stereospecific reduction of methionine-R-sulfoxides to methionines. MSRB3 catalyzes the reduction of oxidized methionine residues and thus repairs oxidatively damaged proteins. The deduced 192-amino acid MSRB3A and 185-amino acid MSRB3B proteins differ in their N termini, but both contain a catalytic cysteine, activating aspartic acid and arginine residues, and 2 zinc-coordinating CxxC motifs, and terminate in a putative endoplasmic reticulum (ER) retention signal (KAEL). In addition, MSRB3A contains a putative N-terminal mitochondrial targeting signal, and MSRB3B contains a putative N-terminal mitochondrial targeting signal.