Secondary structure and lipid contact of a peptide antibiotic in phospholipid bilayers by REDOR

Abstract

The chemical shifts of specific 13C and 15N labels distributed throughout KIAGKIA-KIAGKIA-KIAGKIA (K3), an amphiphilic 21-residue antimicrobial peptide, prove that the peptide is in an all α-helical conformation in the bilayers of multilamellar vesicles (MLVs) containing dipalmitoylphosphatidylcholine and dipalmitoylphosphatidylglycerol (1:1). Rotational-echo double-resonance (REDOR) 13C{31P} and 15N{31P} experiments on the same labeled. MLVs show that on partitioning into the bilayer, the peptide chains remain in contact with lipid headgroups. The amphipathic lysine side chains of K3 in particular appear to play a key role in the electrostatic interactions with the acidic lipid headgroups. In addition to the extensive peptide-headgroup contact, 13C{19F} REDOR experiments on MLVs containing specifically 19F-labeled lipid tails suggest that a portion of the peptide is surrounded by a large number of lipid acyl chains. Complementary 31P{19F} REDOR experiments on these MLVs show an enhanced headgroup-lipid tail contact resulting from the presence of K3. Despite these distortions, static 31P NMR lineshapes indicate that the lamellar structure of the membrane is preserved.