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). Widely expressed. Highly expressed in liver, lung, colon, prostate, kidney and pancreas. In brain, present both in neurons and glia (at protein level). Down-regulated in lung adenocarcinoma, colorectal carcinoma and ovarian cancer. Two-fold up-regulated in brain and blood from schizophrenia patients. Down-regulated by androgen in prostate cancer cells. Phosphorylated. The N-terminus is blocked. The disease is caused by variants affecting the gene represented in this entry. Belongs to the selenium-binding protein family.