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X-ray structural characterization of imidazolylcobalamin and histidinylcobalamin: cobalamin models for aquacobalamin bound to the B12 transporter protein transcobalamin.

Hannibal L, Bunge SD, van Eldik R, Jacobsen DW, Kratky C, Gruber K, Brasch NE

Department of Chemistry and School of Biomedical Sciences, Kent State University, Kent, Ohio 44242, USA.

The X-ray structures of imidazolylcobalamin (ImCbl) and histidinylcobalamin (HisCbl) are reported. These structures are of interest given that the recent structures of human and bovine transcobalamin prepared in their holo forms from aquacobalamin show a histidine residue of the metalloprotein bound at the beta-axial site of the cobalamin (Wuerges, J. et al. Proc. Natl. Acad. Sci. U.S.A. 2006, 103, 4386-4391). The beta-axial Co-N bond distances for ImCbl and HisCbl are 1.94(1) and 1.951(7) A, respectively. The alpha-axial Co-N bond distances to the 5,6-dimethylbenzimidazole are 2.01(1) and 1.979(8) A for ImCbl and HisCbl, respectively, and are typical for cobalamins with weak sigma-donor ligands at the beta-axial site. The corrin fold angles of 11.8(3) degrees (ImCbl) and 12.0(3) degrees (HisCbl) are smaller than those typically observed for cobalamins.

Published 23 April 2007 in Inorg Chem, 46(9): 3613-8.
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