CobB/CobQ glutamine amidotransferase (IPR017929)
Short name: CobB/CobQ_GATase
Vitamin B12 (cobalamin) is an essential nutrient that serves as a co-factor for enzymatic reactions. The biosynthesis of this coenzyme is a complex process that is confined to certain prokaryotes and requires circa 25 different enzymes. During the assembly, six amide groups are introduced at the a, b, c, d, e and g carboxylates. In the aerobic and anaerobic biosynthetic pathways, the six amidation steps are carried out by two separate enzymes. Cobyrinic acid a,c-diamide synthethase (cbiA and cobB) is responsible for the introduction of the two amide groups at the a and c positions in either cobyrinic acid or hydrogenobrynic acid. The amidation of the b, d, e, and g carboxylate groups in adenosyl-Cob(I)yrinic acid a,c-diamide is catalysed by cobyric acid synthetase (cbiP and cobQ). Many of the enzymatic reactions for the aerobic biosynthesis of cobalamin are known for Pseudomonas denitrificans. The anaerobic pathway is found in other bacteria and archaea, such as Salmonella, Bacillus, Methanococcus and Propionibacterium species [PMID: 15311923].
The cobB and cobQ family proteins contain two separate domains involved in cobalamin biosynthesis, i.e. a synthetase domain including ATP-binding motifs in the N-terminal part and a glutamine amidotransferase (GATase) domain in the C-terminal part. The GATase domain is involved in glutamine binding, hydrolysis and transfer of the resulting ammonia to an acceptor. This domain resembles the GATases of class I, which are characterised by a conserved Cys-His-Glu active site, but the cobBQ-type GATases lack the Glu residue in this typical triad [PMID: 9575335, PMID: 10966576]. The cobBQ-type GATase domain shows also similarity to other GATase type 1 related domains/families, like PdxT/SNO, gamma-glutamyl hydrolase and PfpI endopeptidase.
Some proteins known to contain a cobBQ-type GATase domain:
- Salmonella typhimurium cobyrinic acid a,c-diamide synthase (cbiA), which is responsible for the amidation of carboxylic groups at positions a and c of either cobyrinic acid or hydrogenobrynic acid.
- P. denitrificans cobyrinic acid a,c-diamide synthase (cobB), which is responsible for the amidation of carboxylic groups at positions a and c of either cobyrinic acid or hydrogenobrynic acid.
- S. typhimurium cobyric acid synthase (cbiP), which catalyses amidations at positions b, d, e, and g on adenosylcobyrinic a,c-diamide.
- P. denitrificans cobyric acid synthase (cobQ), which catalyses amidations at positions b, d, e, and g on adenosylcobyrinic a,c-diamide.
- PS51274 (GATASE_COBBQ)