adenylyltransferase & sulfurtransferase MOCS3; molybdenum cofactor synthesis protein 3; molybdopterin synthase sulfurylase; MPT synthase sulfurylase; includes: adenylyltransferase MOCS3; sulfur carrier protein MOCS2A adenylyltransferase; includes: sulfurtransferase MOCS3; sulfur carrier protein MOCS2A sulfurtransferase (MOCS3, UBA4)
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Function
- plays a central role in 2-thiolation of mcm(5)S(2)U at tRNA wobble positions of tRNA(Lys), tRNA(Glu) & tRNA(Gln)
- also essential during biosynthesis of the molybdenum cofactor
- acts by mediating the C-terminal thiocarboxylation of sulfur carriers URM1 & MOCS2A
- its N-terminus first activates URM1 & MOCS2A as acyl-adenylates (-COAMP), then the persulfide sulfur on the catalytic Cys is transferred to URM1 & MOCS2A to form thiocarboxylation (-COSH) of their C-terminus
- the reaction probably involves hydrogen sulfide that is generated from the persulfide intermediate & that acts as nucleophile towards URM1 & MOCS2A
- subsequently, a transient disulfide bond is formed
- does not use thiosulfate as sulfur donor; NFS1 probably acts as a sulfur donor for thiocarboxylation reactions
- tRNA modification; 5-methoxycarbonylmethyl-2-thiouridine- tRNA biosynthesis
- cofactor biosynthesis; molybdopterin biosynthesis
- interacts with NFS1
[MOCS2A] + ATP
<-->
adenylyl-[MOCS2A] + diphosphate adenylyl-[MOCS2A] + [MOCS3]-persulfide
<-->
[MOCS2A]-thiocarboxylate + AMP
Cofactor: binds 1 Zn+2 per subunit (putative)
Kinetic parameters:
- KM=0.25 mM for thiosulfate
- KM=0.28 mM for cyanide
Structure
- in the N-terminal section; belongs to the hesA/moeB/thiF family, UBA4 subfamily
- contains 1 rhodanese domain