Composition-dependent multivalency of peptide-peptide interactions revealed by tryptophan-scanning mutagenesis.

We have examined in this contribution the composition dependence of binding characteristics in peptide-peptide interactions between an oligopeptide octa-glycine and a series of tryptophan-containing octapeptides. The binding energy associated with tryptophan-glycine interactions manifests pronounced stepwise binding characteristics as the number of tryptophan increases from 0 to 8 in the octapeptides consisting only of glycine and can be attributed to mono-, di-, and tri-valent peptide-peptide interactions. At the same time, only weak fluctuations in binding energy were observed as the number of tryptophan increases from 2 to 7. Such distinctive nonlinearity of composition-dependent tryptophan-glycine binding energy characteristics due to continuously varying tryptophan compositions in the octapeptides could be considered as a reflection of combinatorial contributions due to the hydrogen bonds originated from the indole moieties of tryptophan with the main chains of octapeptide of glycine containing N-H and C=O moieties and the van der Waals interactions (including π-π and π-CH interactions) between peptides.