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 residue. Upon oxidative stress, may play a role in the preservation of mitochondrial integrity by decreasing the intracellular reactive oxygen species build-up through its scavenging role, hence contributing to cell survival and protein maintenance. [thioredoxin]-disulfide + H2O + L-methionyl-[protein] = [thioredoxin]-dithiol + L-methionyl-(R)-S-oxide-[protein] [thioredoxin]-disulfide + H2O + L-methionine = [thioredoxin]-dithiol + L-methionine (R)-S-oxide Binds 1 zinc ion per subunit. Ubiquitous. Detected in retina, ocular ciliary body, skeletal muscle, heart, colon, bone marrow, cerebellum, small intestine, fetal brain, fetal liver, kidney, spinal cord, lung, placenta and prostate. Belongs to the MsrB Met sulfoxide reductase family.