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 (By similarity). H2O + methanethiol + O2 = formaldehyde + H(+) + H2O2 + hydrogen sulfide Organosulfur degradation. Belongs to the selenium-binding protein family.