Primary-sequence alignment and superposition of CobDH and homologous proteins for which crystal structures have been solved. (a) Multiple sequence alignment of all deposited proteins that bind methylcobalamin in the base-off/His-on form. The histidine side chain from the conserved cobalamin-binding motif DxHxxG forms a coordination bond with the central Co atom in all cases. Conserved residues of CobDH (Asp100, His102 and Ser147) are marked with asterisks. The alignment was performed using ClustalX (Larkin et al., 2007). (b) Stereoview of the superposition of CobDH (orange) with MetH (PDB entry 1bmt
; magenta; r.m.s. = 0.774 Å; Drennan et al., 1994) and MtaC (PDB entry 2i2x
; blue; r.m.s. = 0.772; Hagemeier et al., 2006). Protein backbone traces are shown in ribbon representation and the cobalamins and bound histidines are shown as sticks. In MetH the N-terminal helix-bundle domain covers the cobalamin from the top, whereas in CobDH and MtaC it is oriented parallel to the cobalamin-binding domain.