Conformational Effects of Calcium Release from Parvalbumin:  Comparison of Computational Simulations with Spectroscopic Investigations

The effect of Ca2+ binding to parvalbumin was monitored by probes of conformation including absorption, fluorescence, circular dichroism (CD), infrared (IR) spectroscopy and differential scanning calorimetry. These experimental studies were compared with molecular dynamics computations on the structures of the Ca-bound and Ca-free forms of cod parvalbumin. The UV CD spectra show that removal of calcium results in a decrease in the α-helical content of the protein. The IR amide I‘ and III‘ regions are very much affected by Ca removal and are indicative of significant perturbation of secondary structure. The fluorescence of tryptophan, the IR markers, and UV ellipticity all show changes with temperature, pointing to a lowering of protein stability upon Ca removal. These results are consistent with the structures obtained for both the Ca-bound and Ca-free proteins after 200 ps of solvated molecular dynamics simulations which show a decrease in the secondary structure upon Ca removal.