Conformational variety of polyanionic peptides at low salt concentrations.
Résumé
Sequential oligo- and polypeptides based on glutamic acid and leucine residues have been synthesized. In pure water, they exhibit a random coil conformation. Addition of very small amounts of divalent metallic cations induces the formation of ordered structure in the peptides which remain in solution. Higher salt concentrations precipitate the peptides. Polypeptides with alternating glutamic acid and leucine residues undergo a coil to beta-sheet transition in the presence of Ca2+, Ba2+, Mn2+, Co2+, Zn2+ and Hg2+. Addition of Cu2+ or Fe3+ induces the formation of an alpha-helix. Solid amorphous CdS generates water soluble beta-sheets, as well. Sequential poly(Leu-Glu-Glu-Leu) adopts an alpha-helix in the presence of divalent cations. The sequence-dependent conformational diversity was extended to poly(Asp-Leu) and poly(Leu-Asp-Asp-Leu).