InterPro domain: IPR038521

This entry also includes 5-hydroxybenzimidazole synthase BzaA and BzaB. They are part of the bzaABCDE genes that are necessary and sufficient for the anaerobic biosynthesis of DMB (5,6-dimethylbenzimidazole), the "lower ligand" of vitamin B12 [ 1 ].

ThiC is found within the thiamin biosynthesis operon and is involved in thiamin biosynthesis [ 2 ]. It catalyses the synthesis of the hydroxymethylpyrimidine phosphate (HMP-P) moiety of thiamine from aminoimidazole ribotide (AIR) in a radical S-adenosyl-L-methionine (SAM)-dependent reaction [ 3 , 4 ].

BzaF, a radical SAM enzyme that catalyzes the conversion of aminoimidazole ribotide (AIR) to 5-hydroxybenzimidazole (5-HBI), is a paralogue of thiC [ 5 ].

This superfamily represents the core domain of these enzymes. Within ThiC, this superfamily makes up the central domain and the cavity of this barrel contains the putative active site. Structurally, this domain consists of 8 beta strands and 8 alpha helices arranged into a TIM barrel.

1. Anaerobic biosynthesis of the lower ligand of vitamin B12. Proc. Natl. Acad. Sci. U.S.A. 112, 10792-7
2. Thiamin biosynthesis in prokaryotes. Arch. Microbiol. 171, 293-300
3. Reconstitution of ThiC in thiamine pyrimidine biosynthesis expands the radical SAM superfamily. Nat. Chem. Biol. 4, 758-65
4. Biosynthesis of the thiamin pyrimidine: the reconstitution of a remarkable rearrangement reaction. Org. Biomol. Chem. 2, 2538-46
5. Anaerobic 5-Hydroxybenzimidazole Formation from Aminoimidazole Ribotide: An Unanticipated Intersection of Thiamin and Vitamin B₁₂ Biosynthesis. J. Am. Chem. Soc. 137, 10444-7