Acid destabilization of a triple-helical peptide model of the macrophage scavenger receptor.

Electrostatic interactions were studied in a triple-helical peptide, (POG)3PKGQKGEKG(POG)4, which contains a lysine-rich 9 residue sequence from the collagen-like domain of the macrophage scavenger receptor (MSR). This peptide adopts a stable triple-helical conformation only when the pH is higher than 4.5, corresponding to ionization of the Glu side chain. Modeling shows Glu forms ion pairs with one of the Lys residues, stabilizing the structure. Previously studied collagen-like peptides show relatively small contributions of electrostatic interactions to stability. The large magnitude of the pH mediated structural changes seen for this peptide suggests that specific placement of charged residues in the triple-helix conformation can generate strong electrostatic interactions.