Self-Association of Disulfide-Dimerized Melittin Analogues†

Two cysteine substitutions of bee venom melittin have been synthesized to investigate the effects of disulfide cross-linking on the self-association properties of the peptide in solution. K23C melittin (mltK23C) was designed to link nonpolar surfaces of the amphipathic melittin helix on the basis of the close juxtaposition of pairs of K23 side chains in the crystal of the native melittin tetramer. K23Q/Q25C melittin (mltQ25C) was designed to link the polar surfaces of the peptide such that self-association in membrane bound states might be stabilized. The mltK23C disulfide dimer, (mltK23C)2, is highly structured at low pH under conditions where native melittin, and the mltK23C monomer, are unstructured. High-resolution NMR, circular dichroism, and fluorescence spectroscopy established that (mltK23C)2 is a helical monomer (pseudodimer) with stable helical segments between residues 2−13 and 15−25. Although the symmetrical nature of the pseudodimer prevented high-resolution structure determination, analysis ...