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Article

X-ray Structural Characterization of Imidazolylcobalamin and Histidinylcobalamin: Cobalamin Models for Aquacobalamin Bound to the B₁₂ Transporter Protein Transcobalamin

Supporting Info

Luciana Hannibal,^†^‡^§ Scott D. Bunge,^† Rudi van Eldik, Donald W. Jacobsen,^‡^§ Christoph Kratky, Karl Gruber,* and Nicola E. Brasch*^†^‡

Department of Chemistry and School of Biomedical Sciences, Kent State University, Kent, Ohio 44242, Department of Cell Biology, Lerner Research Institute, The Cleveland Clinic, Cleveland, Ohio 44195, Institute for Inorganic Chemistry, University of Erlangen-Nrnberg, 91058 Erlangen, Germany, and Institute of Chemistry, University of Graz, A-8010 Graz, Austria

Inorg. Chem., 2007, 46 (9), pp 3613–3618

DOI: 10.1021/ic070022n

Publication Date (Web): April 4, 2007

†

Department of Chemistry, Kent State University.

‡

School of Biomedical Sciences, Kent State University.

The Cleveland Clinic.

University of Erlangen-Nürnberg.

University of Graz.

To whom correspondence should be addressed. E-mail: karl.gruber@uni-graz.at (K.G.), nbrasch@kent.edu (N.E.B.).

Abstract

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 β-axial site of the cobalamin (Wuerges, J. et al. Proc. Natl. Acad. Sci. U.S.A. 2006, 103, 4386−4391). The β-axial Co−N bond distances for ImCbl and HisCbl are 1.94(1) and 1.951(7) Å, respectively. The α-axial Co−N bond distances to the 5,6-dimethylbenzimidazole are 2.01(1) and 1.979(8) Å for ImCbl and HisCbl, respectively, and are typical for cobalamins with weak σ-donor ligands at the β-axial site. The corrin fold angles of 11.8(3)° (ImCbl) and 12.0(3)° (HisCbl) are smaller than those typically observed for cobalamins.

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