Methionine-R-sulfoxide reductase which catalyzes the reduction of methionine sulfoxide (MetSO) to methionine in proteins. Plays a protective role against oxidative stress by restoring activity to proteins that have been inactivated by methionine oxidation. Protects iron-sulfur clusters from oxidative inactivation along with MXR1. Involved in the regulation of lifespan. [thioredoxin]-disulfide + H2O + L-methionyl-[protein] = [thioredoxin]-dithiol + L-methionyl-(R)-S-oxide-[protein] Binds 1 zinc ion per subunit. Present with 799 molecules/cell in log phase SD medium. Belongs to the MsrB Met sulfoxide reductase family.