Infrared spectroscopic study of the metal-coordination structures of calcium-binding proteins.

Carboxylate (COO(-)) groups can coordinate to metal ions in of the following four modes: 'unidentate', 'bidentate', 'bridging' and 'pseudo-bridging' modes. COO(-) stretching frequencies provide information about the coordination modes of COO(-) groups to metal ions. We review the Fourier-transform infrared spectroscopy (FTIR) of side-chain COO(-) groups of Ca(2+)-binding proteins: pike parvalbumin pI 4.10, bovine calmodulin and Akazara scallop troponin C. FTIR spectroscopy of Akazara scallop troponin C has demonstrated that the coordination structure of Mg(2+) is distinctly different from that of Ca(2+) in the Ca(2+)-binding site. The assignments of the COO(-) antisymmetric stretch have been ensured on the basis of the spectra of calcium-binding peptide analogues. The downshift of the COO(-) antisymmetric stretching mode from 1565 cm(-1) to 1555-1540 cm(-1) upon Ca(2+) binding is a commonly observed feature of FTIR spectra for EF-hand proteins.