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

Recent improvements in neutron reflectometry methodology have afforded enha nced sensitivity for the study of biomimetic membranes. The technique has b een used to probe the interactions of the peptide toxin, melittin, with sup ported bilayers of phospholipid and octadecanethiol or thiahexa(ethylene ox ide) alkane on gold. Improvements in instrumentation and experimental desig n permit neutron reflectivity measurements out to a wavevector transfer of 0.7 Angstrom (-1) and down to reflectivities approaching 10(-8), allowing u nprecedented resolution of structural details in the bilayer. The data indi cate that melittin strongly perturbs the phospholipid headgroup region and also affects the alkane chain region of the bilayer. There is no evidence f or hydration of the ethylene oxide spacer region between the gold and alkan e regions of the thiahexa(ethylene oxide) alkane/phospholipid bilayer, but a distinct shift of up to 3 Angstrom in the apparent location of the interf ace between the alkane and phospholipid regions is observed. This work show s that the neutron reflectometry technique is now sensitive to small change s in the reflected intensities, and these small changes can result in signi ficant contributions to the resultant scattering length density profiles.