Abstract

Several de novo designed ionic peptides that are able to undergo conformational change under the influence of temperature and pH were studied. These peptides have two distinct surfaces with regular repeats of alternating hydro-philic and hydrophobic side chains. This permits extensive ionic and hydrophobic interactions resulting in the formation of stable b-sheet assemblies. The other defining characteristic of this type of peptide is a cluster of negatively charged aspartic or glutamic acid residues located toward the N-terminus and positively charged arginine or lysine residues located toward the C-terminus. This arrangement of charge balances the a-helical dipole moment ~C r N!, resulting in a strong tendency to form stable a-helices as well. Therefore, these peptides can form both stable a-helices and b-sheets. They are also able to undergo abrupt structural transformations between these structures induced by temper-ature and pH changes. The amino acid sequence of these peptides permits both stable b-sheet and a-helix formation, resulting in a balance between these two forms as governed by the environment. Some segments in proteins may also undergo conformational changes in response to environmental changes. Analyzing the plasticity and dynamics of this type of peptide may provide insight into amyloid formation. Since these peptides have dynamic secondary structure, they will serve to refine our general understanding of protein structure.