Two-phase induction of the nonnative alpha-helical form of beta-lactoglobulin in the presence of trifluoroethanol.

The trifluoroethanol-dependent induction of the nonnative alpha-helical form of beta-lactoglubulin has been studied by circular dichroism spectroscopy. Data analysis is performed by factor analysis and multivariate curve resolution. An intermediate form in the induction of the alpha-helical form of the beta-lactoglobulin has been identified at low TFE concentration. By application of an alternating least-squares algorithm, the CD spectrum corresponding to the intermediate form has been resolved. The deconvolution of this CD spectrum shows a secondary structure content more in agreement with the one predicted from the amino acid sequence than the secondary structure of the helical form obtained at higher TFE concentrations. The additional alpha-helical content of the form present at higher TFE concentrations could be due to nonspecific interaction of TFE with the polypeptide chain.