This domain binds to B12 (adenosylcobamide)[1-3], it is found in several enzymes, such as glutamate mutase Swiss:Q05488, methionine synthase Swiss:Q99707 and methylmalonyl-CoA mutase Swiss:P22033. It contains a conserved DxHxxGx(41)SxVx(26)GG motif, which is important for B12 binding [2].

1: How a protein prepares for B12 binding: structure and dynamics of the B12-binding subunit of glutamate mutase from Clostridium tetanomorphum. Tollinger M, Konrat R, Hilbert BH, Marsh EN, Krautler B; Structure 1998;6:1021-1033. PMID:9739092

2: Role for vitamin B(12) in light induction of gene expression in the bacterium Myxococcus xanthus. Cervantes M, Murillo FJ; J Bacteriol. 2002;184:2215-2224. PMID:11914353

3: Vitamin B12 partners the CarH repressor to downregulate a photoinducible promoter in Myxococcus xanthus. Perez-Marin MC, Padmanabhan S, Polanco MC, Murillo FJ, Elias-Arnanz M; Mol Microbiol. 2008;67:804-819. PMID:18315685