sulfurtransferases

Sulfurtransferases are enzymes that catalyze the transfer of sulfane sulfur atoms from donor to acceptor molecules. They typically operate via a catalytic cysteine that forms a transient persulfide (Cys-SSH) intermediate, enabling sulfane sulfur to be moved between substrates. This enzymatic activity is distinct from sulfotransferases, which transfer sulfate groups.

The best-known members include the rhodanese (thiosulfate sulfurtransferase; EC 2.8.1.1) and 3-mercaptopyruvate sulfurtransferase (3-MST; EC 2.8.1.2). Rhodaneses are widespread in mitochondria and cytosol and participate in cyanide detoxification by transferring sulfur from thiosulfate to cyanide, yielding thiocyanate and sulfite. 3-MST participates in sulfur transfer from 3-mercaptopyruvate to various acceptors and contributes to cellular sulfane sulfur pools, playing a role in hydrogen sulfide metabolism in some tissues.

Other sulfurtransferases contain rhodanese-like domains and participate in diverse sulfur-trafficking pathways. These pathways include the biosynthesis and maturation of iron-sulfur clusters and the proper functioning of various oxidative enzymes. In bacteria and archaea, sulfur transfer is also involved in tRNA thiolation, supplying sulfur for the formation of thiolated uridine at the wobble position. In these contexts sulfur is often mobilized by a cysteine desulfurase such as IscS and handed off through rhodanese-family proteins to tRNA modification enzymes like MnmA or ThiI.

Overall, sulfurtransferases play key roles in sulfur metabolism, detoxification, metal cofactor assembly, and the modification of RNA, reflecting their central function in cellular sulfur trafficking.