5AZQ

Crystal structure of cyano-cobalt(III) tetradehydrocorrin in the heme pocket of horse heart myoglobin

Summary for 5AZQ

• Entry DOI: 10.2210/pdb5azq/pdb
• Related: 5AZR
• Descriptor: Myoglobin, (1R,19R) cobalt tetradehydrocorrin, (1S,19S) cobalt tetradehydrocorrin, ... (6 entities in total)
• Functional Keywords: globin fold, oxygen transport, muscles, redox enzyme
• Biological source: Equus caballus (Horse)
• Total number of polymer chains: 1
• Total formula weight: 18426.86

Authors

Mizohata, E.,Morita, Y.,Oohora, K.,Inoue, T.,Hayashi, T. (deposition date: 2015-10-21, release date: 2016-01-20, Last modification date: 2024-03-20)

Primary citation

Morita, Y.,Oohora, K.,Mizohata, E.,Sawada, A.,Kamachi, T.,Yoshizawa, K.,Inoue, T.,Hayashi, T.
Crystal Structures and Coordination Behavior of Aqua- and Cyano-Co(III) Tetradehydrocorrins in the Heme Pocket of Myoglobin
Inorg.Chem., 55:1287-1295, 2016

PubMed Abstract: Myoglobins reconstituted with aqua- and cyano-Co(III) tetradehydrocorrins, rMb(Co(III)(OH2)(TDHC)) and rMb(Co(III)(CN)(TDHC)), respectively, were prepared and investigated as models of a cobalamin-dependent enzyme. The former protein was obtained by oxidation of rMb(Co(II)(TDHC)) with K3[Fe(CN)6]. The cyanide-coordinated Co(III) species in the latter protein was prepared by ligand exchange of rMb(Co(III)(OH2)(TDHC)) with exogenous cyanide upon addition of KCN. The X-ray crystallographic study reveals the hexacoordinated structures of rMb(Co(III)(OH)(TDHC)) and rMb(Co(III)(CN)(TDHC)) at 1.20 and 1.40 Å resolution, respectively. The (13)C NMR chemical shifts of the cyanide in rMb(Co(III)(CN)(TDHC)) were determined to be 108.6 and 110.6 ppm. IR measurements show that the cyanide of rMb(Co(III)(CN)(TDHC)) has a stretching frequency peak at 2151 cm(-1) which is higher than that of cyanocobalamin. The (13)C NMR and IR measurements indicate weaker coordination of the cyanide to Co(III)(TDHC) relative to cobalamin, a vitamin B12 derivative. Thus, the extent of π-back-donation from the cobalt ion to the cyanide ion is lower in rMb(Co(III)(CN)(TDHC)). Furthermore, the pK(1/2) values of rMb(Co(III)(OH2)(TDHC)) and rMb(Co(III)(CN)(TDHC)) were determined by a pH titration experiment to be 3.2 and 5.5, respectively, indicating that the cyanide ligation weakens the Co-N(His93) bond. Theoretical calculations also demonstrate that the axial ligand exchange from water to cyanide elongates the Co-N(axial) bond with a decrease in the bond dissociation energy. Taken together, the cyano-Co(III) tetradehydrocorrin in myoglobin is appropriate for investigation as a structural analogue of methylcobalamin, a key intermediate in methionine synthase reaction.

PubMed: 26760442
DOI: 10.1021/acs.inorgchem.5b02598

Experimental method

X-RAY DIFFRACTION (1.4 Å)