Nicotinate-nucleotide-dimethylbenzimidazole phosphoribosyltransferase (DMB-PRT), also called CobT.
Nicotinate-nucleotide-dimethylbenzimidazole phosphoribosyltransferase (DMB-PRT/CobT, not to be confused with the CobT subunit of cobaltochelatase, which does not belong to this group) catalyzes the synthesis of alpha-ribazole-5'-phosphate, from nicotinate mononucleotide (NAMN) and 5,6-dimethylbenzimidazole (DMB). This function is essential to the anaerobic biosynthesis pathway of cobalamin (vitamin B12), which is the largest and most complex cofactor in a number of enzyme-catalyzed reactions in bacteria, archaea and eukaryotes. Only eubacteria and archaebacteria can synthesize vitamin B12; multicellular organisms have lost this ability during evolution. DMB-PRT/CobT works sequentially with CobC (a phosphatase) to couple the lower ligand of cobalamin to a ribosyl moiety. DMB is the most common lower ligand of cobamides; other lower ligands include adenine, 5-methoxybenzimidazole or phenol. It has been suggested that earlier metabolic or enzymatic steps may control which lower ligand is available to DMB-PRT/CobT. In Salmonella enterica, for example, the lower ligand is DMB under aerobic conditions and adenine or 2-methyladenine under anaerobic conditions. Salmonella enterica DMB-PRT/CobT is a homodimer with two active sites, each active site is comprised of residues from both monomers. This group includes two distinct subfamilies, one archaeal-like, the other comprised of bacterial sequences.
Structure:1JHA_A; Salmonella enterica CobT monomer binds nicotinate and adenosine monophosphate (the products of the reaction of adenine with NaMN), contacts at 4A. - View structure with Cn3D
Structure:1JHQ_A; Salmonella enterica CobT monomer binds nicotinate and N1-(5'-phospho -alpha -ribosyl)-5-methoxybenzimidazole (the products of the reaction of 5-methoxybenzimidazole with NaMN), contacts at 4A. - View structure with Cn3D