Thermodynamic Scale of beta-Amino Acid Residue Propensities for an alpha-Helix-like Conformation

摘要

A thiol-thioester exchange system has been used to measure the propensities of diverse beta-amino acid residues to participate in an alpha-helix-like conformation. These measurements depend on formation of a parallel coiled-coil tertiary structure when two peptide segments become linked by thioester formation. One peptide segment contains a "guest" site that accommodates diverse beta residues and is distal to the coiled-coil interface. We find that helix propensity is influenced by side chain placement within the beta residue beta(3) (side chain adjacent to nitrogen) slightly favored relative to beta(2) (side chain adjacent to carbonyl). The previously recognized helix stabilization resulting from five-membered ring incorporation is quantified. These results are significant because so few quantitative thermodynamic measurements have been reported for alpha/beta-peptide folding.