The structure of melittin. A 1H-NMR study in methanol

The conformation of the 26-residue polypeptide melittin has been studied using 1H-NMR spectroscopy in methanolic solution. The 1H-NMR spectrum of melittin has been assigned using two-dimensional NMR techniques and the secondary structure has been calculated from nuclear Overhauser enhancement data using distance geometry and restrained molecular dynamics analyses. The structure is found to be mainly helical, and similar to that found in crystals from diffraction data: residues 2-11 and 13-26 form regular alpha-helices joined by a 'hinge' between residues 11-12. The structure in this hinge region is shown to be significantly different from that in the crystal structure, leading to a smaller angle between the two helices. The possible significance of the proline residues in this and similar membrane-spanning peptides is discussed.