SELF-INDUCED HELIX-SHEET CONFORMATIONAL TRANSITIONS OF AN AMPHIPHILIC PEPTIDE

An 18-residue amphiphilic peptide (NH2-GELELELEQQKLKLKLKG-COOH) was designed and prepared, and the helix-sheet conformational transition of the peptide was investigated by circular dichroism in aqueous solution of varying pH, peptide concentration and ionic strength. The conformation of the peptide was converted from a beta-sheet to alpha-helix from neutral pH to pH 2.0 or pH 12.0. At acidic condition, an alpha-helix to beta-sheet conformational transition was observed at increase of peptide concentration or addition of salt. An anion with higher valency effectively induced the conformational transition. The independency of alpha-helical content with peptide concentration indicated that the a-helix was monomeric structure, whereas the beta-sheet conformation formed an aggregated structure because of increase of the beta-sheet content with peptide concentration. The conformational transition was provided by self-association and dissociation of the peptide. The secondary structure of the peptide was significantly affected by altering hydrophobic as well as electrostatic interactions such as ionic and hydrogen bonds. Because it was also found that conformational transition takes place very rapidly, the peptide may have properties for rapid responsive materials in practical use.