The interaction of acetate and formate with cobalt carbonic anhydrase

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Abstract
The interaction of formate and acetate ions with cobalt‐substituted carbonic anhydrase (CA) has been investigated through 13C‐NMR and one‐dimensional and two‐dimensional 1H‐NMR spectroscopy. 13C data on formate are consistent with a regularly coordinated ligand, as previously proposed for the acetate anion [Bertini, I., Luchinat, C. & Scozzafava, A. (1977) J. Chem. Soc. Dalton Trans., 1962–1965]. 1H‐NOE experiments on both anions give evidence of through‐space interactions between ligand protons and protein protons. The latter are assigned to specific residues in the active cavity through nuclear Overhauser effect spectroscopy (NOESY) experiments. The 13C‐derived and 1H‐derived constrains allow reliable docking of these ligands in the active‐site cavity. The resulting geometries are similar to one another and consistent with five‐coordinated structures around the metal ion, as previously proposed from electronic spectroscopy [Bertini, I., Canti, G., Luchinat, C. & Scozzafava, A. (1978) J. Am. Chem. Soc. 100, 4873–4877].The results are discussed in light of the current debate on anion binding to metal ions in carbonic anhydrase [Lindahl, M., Svensson, A. & Liljas, A. (1992) Proteins, in the press]; Bertini, I., Luchinat, C., Pierattelli, R. & Vila, A. J. (1992) Inorg. Chem., in the press; Banci, L. & Merz, K. (1992) unpublished results] and, in particular, of the proposed long Zn‐O distance found in the recent X‐ray results on the formate adduct [Hakanson, K., Carlsson, M., Svensson, A. & Liljas, A. (1992) J. Mol. Biol., in the press].

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