Effects of trifluoroethanol on the conformations of peptides representing the entire sequence of bovine pancreatic trypsin inhibitor.

The effects of the cosolvent trifluoroethanol on the conformations of four peptides representing the entire sequence of bovine pancreatic trypsin inhibitor (BPTI) have been measured by CD and NMR. No substantial amounts of helical conformations were induced in one peptide with four proline residues dispersed throughout its sequence, and there were no substantial effects on its average conformational properties or on the interactions between neighboring residues that are normally evident. The other three peptides became helical, although not completely, over their entire lengths. There was a reasonable correlation between the induced content of alpha-helix and the predicted helical propensities of all four peptides. Only one of these peptides is helical in native BPTI; the other two are extended beta-strands. The latter two have an intrinsic propensity for helix formation, but a greater propensity for beta-sheet formation in folded proteins.