Conformational selection and functional dynamics of calmodulin: a (19)F nuclear magnetic resonance study.

Calcium-bound calmodulin (CaM-4Ca(2+)) is innately promiscuous with regard to its protein interaction network within the cell. A key facet of the interaction process involves conformational selection. In the absence of a binding peptide, CaM-4Ca(2+) adopts an equilibrium between a native state (N) and a weakly populated near-native peptide-bound-like state (I), whose lifetime is on the order of 1.

¹⁹F NMR studies of a desolvated near-native protein folding intermediate.

Although many proteins are recognized to undergo folding via an intermediate, the microscopic nature of folding intermediates is less understood. In this study, ¹⁹F NMR and near-UV circular dichroism (CD) are used to characterize a transition to a thermal folding intermediate of calmodulin, a water-soluble protein, which is biosynthetically enriched with 3-fluorophenylalanine (3F-Phe). ¹⁹F NMR solvent isotope shifts, resulting from replacing H₂O with D₂O, and paramagnetic shifts arising from dissolved O₂ are used to monitor changes in the water accessibility and hydrophobicity of the protein interior as the protein progresses from a native state to an unfolded state along a heat-denaturation pathway.