InterPro domain: IPR002817

This entry includes phosphomethylpyrimidine synthases, including thiC from prokaryotes and AtTHIC from Arabidopsis. thiC is found within the thiamin biosynthesis operon and is involved in thiamin biosynthesis [ 1 ]. ThiC catalyzes 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 [ 2 , 3 ].

AtTHIC is involved in pyrimidine synthesis in the thiamine biosynthesis pathway of Arabidopsis. Heterologous expression of AtTHIC could functionally complement the thiC knock-out mutant of E. coli [ 4 ].

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 [ 5 ].

1. Thiamin biosynthesis in prokaryotes. Arch. Microbiol. 171, 293-300
2. Reconstitution of ThiC in thiamine pyrimidine biosynthesis expands the radical SAM superfamily. Nat. Chem. Biol. 4, 758-65
3. Biosynthesis of the thiamin pyrimidine: the reconstitution of a remarkable rearrangement reaction. Org. Biomol. Chem. 2, 2538-46
4. AtTHIC, a gene involved in thiamine biosynthesis in Arabidopsis thaliana. Cell Res. 18, 566-76
5. Anaerobic biosynthesis of the lower ligand of vitamin B12. Proc. Natl. Acad. Sci. U.S.A. 112, 10792-7