InterPro domain: IPR003749

ThiS (thiaminS) is a 66 aa protein involved in sulphur transfer. ThiS is coded in the thiCEFSGH operon in Escherichia coli. This family of proteins have two conserved Glycines at the COOH terminus. Thiocarboxylate is formed at the last G in the activation process. Sulphur is transferred from ThiI to ThiS in a reaction catalysed by IscS [ 1 ]. MoaD, a protein involved in sulphur transfer during molybdopterin synthesis, is about the same length and shows limited sequence similarity to ThiS. Both have the conserved GG at the COOH end [ 2 ].

ThiS/MoaD proteins serve as sulfur carriers in thiamine and tungsten/molybdenum cofactor biosynthesis. Proteins in this entry also include TtuB from Thermus thermophilus. TtuB functions as the sulfur donor in the sulfurtransferase reaction catalyzed by TtuA [ 3 ]. It is also required for the 2-thiolation of 5-methyluridine residue at position 54 in the T loop of tRNAs, leading to 5-methyl-2-thiouridine (m5s2U or s2T). This modification allows thermal stabilization of tRNAs in thermophilic microorganisms, and is essential for cell growth at high temperatures [ 4 ].

1. The iscS gene in Escherichia coli is required for the biosynthesis of 4-thiouridine, thiamin, and NAD. J. Biol. Chem. 275, 20096-103
2. Role of the C-terminal Gly-Gly motif of Escherichia coli MoaD, a molybdenum cofactor biosynthesis protein with a ubiquitin fold. Biochemistry 46, 909-16
3. Biochemical and structural characterization of oxygen-sensitive 2-thiouridine synthesis catalyzed by an iron-sulfur protein TtuA. Proc. Natl. Acad. Sci. U.S.A. 114, 4954-4959
4. Identification of two tRNA thiolation genes required for cell growth at extremely high temperatures. J. Biol. Chem. 281, 14296-306