Resolution of conformation equilibria in linear peptides by circular dichroism in cryogenic solvents

The circular dichroism spectra of the synthetic peptide antigen, 209-222 of the surface glycoprotein of the rabies virus were recorded as a function of solvent composition and over the temperature range of +60 degrees C to -135 degrees C; beta-III and beta-II reverse turn conformations were found to exist in TFE/H2O (3:1) at room temperature and in ethanediol/H2O (2:1) below -110 degrees C respectively. Evidence, from comparison of observed and calculated spectra, is given to support the existence of a conformational equilibrium between a beta-II and a beta-III reverse turn. These data can serve as a basis for synthetic vaccine development and understanding the nature of polypeptide chain folding.