Cation–π interactions studied in a model coiled‐coil peptide

Abstract

Cation–π interactions between aromatic amino acids and the positively charged residues lysine and arginine have been proposed to play an important role in stabilizing protein structure. We have used a peptide that adopts a coiled coil structure as a model system to evaluate the energetic contribution of cation–π interactions to protein folding. Peptides were designed in which phenylalanine, tyrosine, and tryptophan were placed at a solvent‐exposed position of the helix, one turn removed from an arginine residue that could provide a favorable cation–π interaction. Only the arginine–phenylalanine pairing provided significant stabilization of the peptide structure and it appears that hydrophobic packing, rather than the cation–π effect, is more likely to be responsible for the stability of this peptide. We conclude that any stabilizing effect of cation–π interactions in these peptides is much smaller than that predicted from computational studies.