Methionine-sulfoxide reductase that specifically reduces methionine (R)-sulfoxide back to methionine. While in many cases methionine oxidation is the result of random oxidation following oxidative stress, methionine oxidation is also a post-translational modification that takes place on specific residues. Acts as a regulator of actin assembly by reducing methionine (R)-sulfoxide mediated by Mical on actin thereby promoting filament repolymerization. [thioredoxin]-disulfide + H2O + L-methionyl-[protein] = [thioredoxin]-dithiol + L-methionyl-(R)-S-oxide-[protein] Binds 1 zinc ion per subunit. Present in the embryonic nervous system (brain and cord) in neuronal cell bodies, along axons. Also present in embryonic muscles in motor axons. Localizes to growing bristle tips where it is distributed in small puntae. Present at and at sites of actin localization. The measured range is 1-155. Belongs to the MsrB Met sulfoxide reductase family.