Catalyzes the oxidation of methanethiol, an organosulfur compound known to be produced in substantial amounts by gut bacteria (PubMed:29255262). 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. Interacts with USP33. May associate with Golgi membrane (By similarity). May associate with the membrane of autophagosomes (By similarity). Highly expressed in liver, kidney and, to a lesser extent, lung. The N-terminus is blocked. SELENBP1 knockout results in accumulation of dimethylsulfoxide in the plasma. Methanethiol oxidase activity measured in tissues from knockout mice is significantly lower that in normal tissues. Belongs to the selenium-binding protein family.