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

Abstract

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. cateogries 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 form "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.