Self-association and membrane-binding behavior of melittins containing trifluoroleucine

We have investigated the effect of trifluoroleucine substitution on the mem brane-binding and tetramerization behavior of melittin. Analogues were synt hesized in which Leu 9, Leu 13, and all four intrinsic leucine residues of melittin were replaced by 5,5,5-trifluoroleucine. Both the mono- and tetra- substituted melittins were found to exhibit stronger self-association and e nhanced affinity for lipid bilayer membranes, compared to the wild-type pep tide. The extent of the observed effects depends on the site of introductio n of trifluoroleucine and, in the case of substitution at position 13, on t he stereochemistry of the trifluoroleucine side chain. Analysis of the memb rane association isotherms is consistent with aggregation of fluorinated me littins within the lipid bilayer. These results suggest that fluorocarbon-h ydrocarbon separation, in addition to an increase in hydrophobic character, contributes to enhanced membrane binding.