VESICLE-BOUND CONFORMATION OF MELITTIN - TRANSFERRED NUCLEAR OVERHAUSER ENHANCEMENT ANALYSIS IN THE PRESENCE OF PERDEUTERATED PHOSPHATIDYLCHOLINE VESICLES

We determined a detailed conformation of the honeybee venom peptide melittin when bound to phosphatidylcholine vesicles using protein NMR. In the presence of vesicles of perdeuterated dipalmitoylglycerophosphocholine, two-dimensional transferred nuclear Overhauser enhancement (TRNOE) experiments were carried out. By a distance geometry calculation using NOE-derived distance constraints followed by a simulated annealing refinement, the N-terminal (Leu(6)-Leu(10)) and C-terminal (Leu(13)-Lys(21)) parts were found to have an alpha-helical conformation, whereas five C-terminal residues (Arg(22)-Gln(26)) did not show a unique conformation in the vesicle-bound state. The two alpha-helices were connected via a less structured segment (Thr(11)-Gly(12)) with a helix bend angle of 86 degrees +/- 34 degrees. Model distance geometry calculations using distance constraints extracted from a tetrameric melittin molecule in crystal assured us that the NOE constraints can accurately reproduce melittin's structure, as well as helping to interpret the NMR structures. Although the vesicle-bound conformation of melittin is similar to that occurring in a methanol solution and in dodecylphosphocholine micelles, significant differences were found in the conformation of C-terminal basic residues and the helix bend angle. This is the first study to clearly demonstrate conformation differences in micelle- and vesicle-bound peptides. In addition, lytic activity of melittin and its analogs showed better correlation with a peptide conformation in vesicles than in either methanol or micelles.