This entry includes adenylyltransferase and sulfurtransferase MOCS3 and its homologue, Uba4, from yeasts.In budding yeasts, Uba4 receives sulphur from Nfs1 and Tum1 []. Uba4 then forms an acyl adenylate intermediate with the C-terminal of the Urm1 protein, and then forms an acyl disulfide bond between Uba4 Cys397 and the Urm1 C-terminal glycin []. Subsequently, the activated Urm1 acts as a sulphur carrier in the process of eukaryotic transfer RNA (tRNA) thiolation []. MOCS3 plays a central role in 2-thiolation of mcm5S2U at tRNA wobble positions of cytosolic tRNA(Lys), tRNA(Glu) and tRNA(Gln) []. It is also essential during biosynthesis of the molybdenum cofactor [, ]. MOCS3 acts by mediating the C-terminal thiocarboxylation of sulfur carriers Urm1 and MOCS2A (the small subunit of molybdopterin synthase) [, , , ].
This is a family of E1-like enzymes that contain the NAD/FAD-binding fold []. Proteins in this entry include ThiF/MoeB/HesA from bacteria and E1-like enzymes from eukaryotes. ThiF/MoeB/HesA are involved in molybdopterin and thiamine biosynthesis. The common reaction mechanism catalysed by MoeB and ThiF, like other E1 enzymes, begins with a nucleophilic attack of the C-terminal carboxylate of MoaD and ThiS, respectively, on the alpha-phosphate of an ATP molecule bound at the active site of the activating enzymes, leading to the formation of a high-energy acyladenylate intermediate and subsequently to the formation of a thiocarboxylate at the C termini of MoaD and ThiS. MoeB, as the MPT synthase (MoaE/MoaD complex) sulfurase, is involved in the biosynthesis of the molybdenum cofactor, a derivative of the tricyclic pterin, molybdopterin (MPT) []. ThiF catalyses the adenylation of ThiS, as part of the biosynthesis pathway of thiamin pyrophosphate (vitamin B1) []. Some ThiF/MoeB/HesA family members such as Atg7, MOCS3 andSAE1/2, have different functions. For instance, Atg7 is a protein-activating enzyme for multiple substrates [], while SAE1/2 acts as an E1 ligase for SUMO1, SUMO2, SUMO3, and probably SUMO4 []. MOCS3 is a adenylyltransferase and sulfurtransferase involved in 2-thiolation of mcm5S2U at tRNA wobble positions of cytosolic tRNA(Lys), tRNA(Glu) and tRNA(Gln) [].
