Investigation of hybrid bilayer membranes with neutron reflectometry: Probing the interactions of melittin

Recent improvements in neutron reflectometry methodology have afforded enhanced sensitivity for the study of biomimetic membranes. The technique has been used to probe the interactions of the peptide toxin, melittin, with supported bilayers of phospholipid and octadecanethiol or thiahexa(ethylene oxide) alkane on gold. Improvements in instrumentation and experimental design permit neutron reflectivity measurements out to a wavevector transfer of 0.7 Angstrom (-1) and down to reflectivities approaching 10(-8), allowing unprecedented resolution of structural details in the bilayer. The data indicate that melittin strongly perturbs the phospholipid headgroup region and also affects the alkane chain region of the bilayer. There is no evidence for hydration of the ethylene oxide spacer region between the gold and alkane regions of the thiahexa(ethylene oxide) alkane/phospholipid bilayer, but a distinct shift of up to 3 Angstrom in the apparent location of the interface between the alkane and phospholipid regions is observed. This work shows that the neutron reflectometry technique is now sensitive to small changes in the reflected intensities, and these small changes can result in significant contributions to the resultant scattering length density profiles.