BIOMIMETIC MEMBRANE STUDIES USING NEUTRON REFLECTOMETRY.

Structures that serve as models of cell membranes are of fundamental importance in understanding such key biological processes as phospholipid self-assembly, molecular recognition and cell-protein interactions. Recent improvements in neutron reflectometry at the NIST Center for Neutron Research (NCNR), coupled with advances in biomimetic film fabrication at NIST, afford enhanced sensitivity for the study of membranes and membrane-protein complexes.

New phase-sensitive measurement techniques and model-independent data analysis methods developed at the NCNR have demonstrated the feasibility of obtaining reliable depth profiles of supported membranes in contact with biologically relevant aqueous environments, achieving subnanometer spatial resolutions.

Using these methods, the depth profile of a biomimetic membrane consisting of a self-assembled alkanethiol monolayer, anchored to a gold film, and a phospholipid layer self-assembled in situ from vesicles in solution has been measured. The results compare well with molecular dynamics simulations. The interaction of the peptide melittin with similar biomimetic films has also been probed, revealing that the small protein penetrates into the phospholipid leaflet of the film and perturbs the underlying alkane layer. Work using these advanced neutron capabilities is underway to study biomimetic films produced on engineered and cushioned surfaces which will enable the investigation of trans-membrane proteins.