Sequence recombination improves target specificity in a redesigned collagen peptide abc-type heterotrimer

Stability of the collagen triple helix is largely governed by its imino acid content, namely the occurrence of proline and 4R-hydroxyproline at the X and Y positions, respectively, of the periodic (Gly-X-Y)(n) sequence. Although other amino acids at these positions reduce stability of the triple helix, this can be partially compensated by introducing intermolecular side-chain salt bridges. This approach was previously used to design an abc-type heterotrimer composed of one basic, one acidic, and one neutral imino acid rich chain (Gauba and Hartgerink, J Am Chem Soc 2007;129:15034-15041). In this study, an abc-type heterotrimer was designed to be the most stable species using a sequence recombination strategy that preserved both the amino acid composition and the network of interchain salt bridges of the original design. The target heterotrimer had the highest T(m) of 50 °C, 7 °C greater than the next most stable species. Stability of the heterotrimer decreased with increasing ionic strength, consistent with the role of intermolecular salt bridges in promoting stability. Quantitative meta-analysis of these results and published stability measurements on closely related peptides was used to discriminate the contributions of backbone propensity and side-chain electrostatics to collagen stability.