Structural studies of membrane lytic peptides: A comparison of magainin and melittin
Ludtke, Steven Jay
Huang, Huey W.
Doctor of Philosophy
Magainin and melittin are 2 members of a class of small amphipathic helical peptides which act as potent antibiotics or toxins. It has been shown that the peptides in this class interact directly with the lipid bilayer rather than with protein targets within the membrane. Using oriented circular dichroism, lamellar x-ray diffraction and small angle in-plane neutron scattering we have determined the structures formed by these peptides on association with the bilayer. We have found that magainin forms 'wormhole' channels in the lipid bilayer and melittin solubilizes the membrane by the formation of peptide bounded discoid micelles. This is compared with our earlier results for alamethicin which forms channels using the barrel-stave model. The discovery that three ostensibly similar peptides form completely different structures is quite surprising, and emphasizes how much work remains to be done in this field. Hopefully the methods used and the motifs identified in this thesis will provide a good basis for continuing studies of similar peptides.