Peptide investigations of pairwise interactions in the collagen triple-helix

Pairwise interactions have been studied for the major secondary structures in proteins. The present work extends the characterization of interactions between side-chains to the context of a collagen triple-helix. In this study, the most frequent Gly-X-Y tripeptide sequences in collagen are characterized in terms of interchain interactions between non-imino acid X and Y residues, through the use of host-guest peptides and statistical frequency analysis. Stabilities predicted on the basis of additivity show good agreement with experimental values for almost half of the peptides, indicating a lack of interaction. A small number of peptides have a stability lower than predicted, while a larger number are more stable than expected. Of all triplets containing residues of opposite charge, only Gly-Lys-Asp and Gly-Arg-Asp exhibit stabilizing electrostatic interactions, and these pairs are found together preferentially in collagens. Repulsion of like charges is observed in Gly-Arg-Lys, Gly-Lys-Arg, and Gly-Glu-Asp sequences, and a small degree of hydrophobic stabilization was observed for the Gly-Leu-Leu guest triplet. The data reported here help clarify basic principles of triple-helix stability. In addition, the experimentally determined stabilities of the tripeptide units found most frequently in collagens constitute a database useful for predicting triple-helix stability in peptides, collagens and other triple-helix-containing proteins.