Catalyzes the oxidation of methanethiol, an organosulfur compound known to be produced in substantial amounts by gut bacteria (By similarity). Selenium-binding protein which may be involved in the sensing of reactive xenobiotics in the cytoplasm. May be involved in intra-Golgi protein transport (PubMed:10799528, PubMed:17377489). H2O + methanethiol + O2 = formaldehyde + H(+) + H2O2 + hydrogen sulfide Organosulfur degradation. Interacts with USP33. May associate with Golgi membrane (PubMed:17377489). May associate with the membrane of autophagosomes (PubMed:17377489). Present in liver and colon (at protein level). In liver, by 3,4,5,3',4'-pentachlorobiphenyl and 3-methylcholanthrene (at protein level). The N-terminus is blocked. In vivo target of mycophenolic acid, the active metabolite of the immunosuppressant mycophenolate mofetil. Belongs to the selenium-binding protein family.