Methionine-sulfoxide reductase that specifically reduces methionine (R)-sulfoxide back to methionine (PubMed:11929995, PubMed:14699060, PubMed:23911929, PubMed:20605785). 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 (PubMed:14699060, PubMed:20605785). Acts as a regulator of actin assembly by reducing methionine (R)-sulfoxide mediated by MICALs (MICAL1, MICAL2 or MICAL3) on actin, thereby promoting filament repolymerization (PubMed:23911929). Plays a role in innate immunity by reducing oxidized actin, leading to actin repolymerization in macrophages (PubMed:23911929). [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. Truncated MSRB1/SEPX1 proteins produced by failed UGA/Sec decoding are ubiquitinated by the CRL2(FEM1C) E3 ubiquitin-protein ligase complex. Belongs to the MsrB Met sulfoxide reductase family.