pfam11760: CbiG_N (This model is not part of the current CDD release)
Cobalamin synthesis G N-terminal
Members of this family are involved in cobalamin synthesis. The gene from Synechocystis sp has been designated cbiH but in fact represents a fusion between cbiH and cbiG. As other multi-functional proteins involved in cobalamin biosynthesis catalyze adjacent steps in the pathway, including CysG, CobL (CbiET), CobIJ and CobA-HemD, it is therefore possible that CbiG catalyzes a reaction step adjacent to CbiH. In the anaerobic pathway such a step could be the formation of a gamma lactone, which is thought to help to mediate the anaerobic ring contraction process. Within the cobalamin synthesis pathway CbiG catalyzes the both the opening of the lactone ring and the extrusion of the two-carbon fragment of cobalt-precorrin-5A from C-20 and its associated methyl group (deacylation) to give cobalt-precorrin-5B. The N-terminal of the enzyme is conserved in this family, and the C-terminal and the mid-sections are conserved independently in other families, CbiG_C and CbiG_mid, although the distinct function of each region is unclear.
Jiyao W et al.(2023). "The conserved domain database in 2023.",