Stabilization of the ribonuclease S-peptide alpha-helix by trifluoroethanol.
The effects of trifluoroethanol (TFE) on the stability of the alpha-helix formed by ribonuclease S-peptide, residues 1-19 of ribonuclease A, were studied by measuring circular dichroism as a function of TFE concentration, pH, and temperature. The S-peptide forms an unusually stable alpha-helix, which is known to be stabilized by TFE. The magnitude of the effect of charged groups on the peptide, manifested by the change in alpha-helix stability as a function of pH, was not altered significantly by either TFE concentration or temperature, indicating that the lower dielectric constant of TFE is not important in the stabilization of this alpha-helix. This suggests that the alpha-helix might be stabilized by many interactions in addition to the effects of charges. The titration curve of circular dichroism vs. TFE concentration appears to be cooperative at 0 degree C, but becomes progressively less cooperative at temperatures between 25 and 75 degrees C. The properties of the TFE stabilization indicate that TFE might be a useful probe with which to measure the stability of marginally stable peptides and small proteins.
Nelson
J W
JW
Department of Biology, University of Pennsylvania, Philadelphia 19104.
Kallenbach
N R
NR
D002942:Circular Dichroism; D006863:Hydrogen-Ion Concentration; D010446:Peptide Fragments; D011487:Protein Conformation / Q000187:drug effects; D012260:Ribonucleases; D014270:Trifluoroethanol / Q000494:pharmacology
D010446:Peptide Fragments; C023560:ribonuclease S-peptide; D014270:Trifluoroethanol; D012260:Ribonucleases