cl00293

B12 binding domain (B12-BD). Most of the members bind different cobalamid derivates, like B12 (adenosylcobamide) or methylcobalamin or methyl-Co(III) 5-hydroxybenzimidazolylcobamide. This domain is found in several enzymes, such as glutamate mutase, methionine synthase and methylmalonyl-CoA mutase. Cobalamin undergoes a conformational change on binding the protein; the dimethylbenzimidazole group, which is coordinated to the cobalt in the free cofactor, moves away from the corrin and is replaced by a histidine contributed by the protein. The sequence Asp-X-His-X-X-Gly, which contains this histidine ligand, is conserved in many cobalamin-binding proteins. Not all members of this family contain the conserved binding motif.