Solid-phase synthesis of melittin: purification and functional characterization.
The main component of the honey bee venom, melittin, is a cationic polypeptide containing 26 amino acids. Exposure of lipid bilayers to this peptide results in the formation of anion-selective channels with a variety of unit conductances. One of the possible causes for this heterogeneity in the conductance could be heterogeneity of the melittin preparation, and indeed, the existence of two prominent forms of naturally occurring melittin, differing only at the N-terminal amino group, has been documented. This paper describes the synthesis of the major form of melittin, using stepwise solid-phase methodology and the demonstration that the synthetic melittin, devoid of the minor component (N-formylmelittin) and other contaminants, interacts with lipid bilayers to form channels which are qualitatively indistinguishable from the ones formed by the naturally occurring toxin. This result indicates that the heterogeneity in the channels produced in bilayers by bee venom is not due to differences in the channel-forming properties of the formyl and non-formyl melittin but rather to differences in the number and orientation of melittin monomers of identical primary structure as they aggregate to form channels in the lipid bilayer.