Enhanced sensitivity to conformation in various proteins. Vibrational circular dichroism results

Vibrational circular dichroism (VCD) spectra of several globular proteins dissolved in D2O are presented and compared to conventional UV-CD results. It can be seen that, for the alpha, beta, and alpha + beta categories of Levitt and Chothia [(1976) Nature 261, 552], VCD evidences much larger band shape variations, including sign alteration, than does UV-CD. A direct parallel is seen between the VCD of the alpha-helix found in model polypeptides and the amide I' VCD of myoglobin. Since all structural aspects of the protein contribute to the VCD on a roughly equal footing, a similar correlation of the chymotrypsin amide I' VCD with that of beta-sheet models is not as clear. In addition, the VCD of "random-coil"-type proteins is found to be clearly related to VCD results from "random-coil" polypeptides. Finally, simulations are presented to postulate the expected VCD for protein structures having conformations that lie between the limiting cases discussed here.