Sequence effects on helix-sheet conformational transitions of designed amphiphilic peptides

Four Ib-residue amphiphilic peptides were designed and synthesized, and their helix-sheet conformational transitions were investigated by circular dichroism (CD) in aqueous solution at different pH, peptide concentration and ionic strength as well as in a water/HFLP mixture. The alpha-helical conformations existed as monomeric states, while the beta-sheet structures were formed by the aggregation of approximately 6 monomeric peptides for Peptide I, II, and III. The conformational transitions were provided by the self-association and dissociation of each peptide. The aggregated beta-sheet structures would be stabilized by intermolecular hydrophobic interactions and complementary ionic bonds in addition to the conventional hydrogen bonds. In contrast, the formation of alpha-helical conformations would be caused by intramolecular electrostatic interactions between charged residues and the intrinsic high alpha-helix propensities of constituent amino acids in addition to hydrogen bonds. These peptides could be useful models for studying the factors governing the stability of secondary and tertiary structures as well as conformational transitions for comprehending the principles of how proteins fold into native states.