B12-binding

This domain binds to B12 (adenosylcobamide), it is found in several enzymes, such as glutamate mutase Q05488, methionine synthase Q99707 and methylmalonyl-CoA mutase P22033.

The cobalamin (vitamin B12) binding domain has an alpha/beta fold that is a common motif found in several different cobalamin-binding proteins. Proteins containing this domain include methionine synthase, the small subunit of glutamate mutase PUBMED:10467146, and the alpha and beta subunits of methylmalonyl-CoA mutase. In methionine synthase, there is a second, adjacent domain involved in cobalamin binding that forms a 4-helical bundle cap (); in the conversion to the active conformation of this enzyme, the 4-helical cap rotates to allow the cobalamin cofactor to bind the activation domain () PUBMED:11731805.

The core structure of the cobalamin domain consists of 5 parallel beta-sheets, surrounded by 4-5 alpha helices in three layers, alpha/beta/alpha PUBMED:7992050. The fold of the domain resembles that of the nucleotide-binding proteins (a Rossman fold). Upon binding B12, important elements of the binding site appear to become structured, including an alpha-helix that forms on one side of the cleft accommodating the nucleotide 'tail' of the cofactor.

Alignment

Visualize domain structures

Species distribution