Activated Membrane Surfaces by Functionalized Peptides

Abstract

For integral membrane proteins (IMP), an assessment of their structures and interactions with other membrane proteins within a bio-mimetic lipid bilayer environment is critical for determining their cellular function. Hydrophobic sequences prevalent within the transmembrane domain(s) of IMPs, however, make these proteins susceptible to aggregation, and thus create difficulties in examining their structural and functional properties via canonical techniques. Working exclusively with transmembrane (TM) segments of polytopic membrane proteins - in the form of soluble peptides - bypasses many of the pitfalls of full-length protein preparations, while allowing for the opportunity to examine the properties of TM domains within bio-mimetic membrane environments. In this study, peptides mimicking the TM domains of the epidermal growth factor (EGFR) and CD4 receptors, both cell-signaling membrane proteins, have been reconstituted into POPC lipid bilayers. The formation of their native alpha-helical structure within vesicle membranes was observed from CD spectra, and proper orientation of the peptides passing through the membrane was demonstrated by tryptophan fluorescence using brominated lipids. Functionalized with an N-terminal biotin tag, and utilizing an engineered planar lipid bilayer system ideally set up for surface plasmon resonance measurements, the TM peptides demonstrated capabilities of “activating” a membrane surface by the capture of streptavidin. Prospectively, these peptides reconstituted as near-native membrane proteins within artificial bilayer systems could be utilized in formulating bioactive surfaces for powerful biomedical and biosensor applications. Novel techniques for re-forming the full-length IMP construct will be discussed.