NMR characterization of self-association of a helical peptide using deuterium exchange experiments

Abstract

The 15-residue hybrid peptide containing residues 1–7 from cecropin A and residues 2–9 from melittin, CA(1–7)M(2–9), is a potent antibiotic with broader activity than cecropin A but without the cytotoxic character of melittin. In the presence of the helix inducer hexafluoroisopropanol the peptide forms aggregates of amphipathic α-helices. Aggregation causes very slow proton-deuterium exchange in some amide protons in the C-terminal region. This provides a method for estimating the association constant (≈ 10 6 M −1) as well as the stoichiometry of the aggregates. Exchange could be mediated by helix breathing or could involve complete disruption of the helix. These two mechanisms can be differentiated by comparing the decay of nuclear Overhauser effect cross-peaks involving two amide protons with the decay of each individual proton.