title: Electron spin resonance of calmodulin-vanadyl complexes.
abstract: X-band (9.2 GHz) electron spin resonance spectroscopy was used to investigate the binding of vanadyl to calmodulin. Solution spectra, obtained at ambient temperature with various VO2+:calmodulin molar ratios, suggested a binding stoichioimetry of 4 mol of VO2+/mol of protein and the possibility of two classes of binding sites. The latter was confirmed by using frozen solutions of calmodulin-VO2+ complexes that gave splitting of the spectral bands corresponding to the parallel components, which was particularly pronounced with the three high-field peaks. Competition of Ca2+ for the VO2+ binding sites was investigated, and the results indicated that two of the VO2+ sites corresponded to two of the Ca2+ sites; the other two VO2+ binding sites may have a higher affinity for VO2+ than for Ca2+ or they may correspond to Ca2+-independent sites. These results demonstrate that electron spin resonance spectroscopy can be used advantageously to probe subtle differences in the microenvironments of metal-binding sites in calmodulin.
authors.affiliation: Department of Chemistry, University of Miami, Florida 33124.
authors.forename: J
authors.initials: J
authors.lastname: Nieves
authors.forename: L
authors.initials: L
authors.lastname: Kim
authors.forename: D
authors.initials: D
authors.lastname: Puett
authors.forename: L
authors.initials: L
authors.lastname: Echegoyen
authors.forename: J
authors.initials: J
authors.lastname: Benabe
authors.forename: M
authors.initials: M
authors.lastname: Martinez-Maldonado
mesh_terms: D001665:Binding Sites; D002147:Calmodulin; D004578:Electron Spin Resonance Spectroscopy; D007700:Kinetics; D011485:Protein Binding; D011487:Protein Conformation; D014638:Vanadates
chemical_list: D002147:Calmodulin; D014638:Vanadates