STRUCTURAL CHARACTERIZATION OF THE NATURAL MEMBRANE-BOUND STATE OF MELITTIN - A FLUORESCENCE STUDY OF A DANSYLATED ANALOG

The binding of a dansylated analogue of melittin (DNC-melittin) to nat ural membranes is described. The cytolytic peptide from honey bee veno m melittin was enzymatically labelled in its glutamine-25 with the flu orescent probe monodansylcadaverine using guinea pig liver transglutam inase. The labelled peptide was characterised functionally in cytolyti c assays, and spectroscopically by circular dichroism and fluorescence . The behaviour of DNC-melittin was, in all respects, indistinguishabl e from that of the naturally occurring peptide. We used resonance ener gy transfer to measure the state of aggregation of melittin on the mem brane plane in synthetic and natural lipid bilayers. When bound to ery throcyte ghost membranes, the extent of energy transfer was found to b e equivalent to when bound to small unilamellar vesicles of phosphatid ylcholine. Our results correlate best with a proposed model in which t he initial interaction between melittin and the red blood cells could be merely electrostatic and the peptide remains in a low ct-helical co nformation. The next step would be a peptide stabilisation in the memb rane in a monomeric alpha-helical conformation that would imply the co llapse of the membrane structure and liberation of the cell contents. (C) 1997 Elsevier Science B.V.