Lipids are the solvent of cell communication. Approximately one third of human proteins have evolved to interact with membrane lipids, and these interactions mediate the flow of information between a cell and its surroundings. Membrane protein structure determination has advanced significantly over the past few years, but our knowledge of molecular structure and dynamics at the lipid-protein interface is still limited. This is because of the complexity of the plasma membrane and the difficulty of studying such interactions in situ at the single molecule level. An important mediator of lipid-protein interactions is the Coulombic attraction between anionic lipid head groups and cationic protein side chains. These electrostatic interactions are critical in cell signaling events like voltage-gated ion transport and growth factor signaling. While the importance of electrostatics at the membrane surface is well-appreciated, we do not have a predictive knowledge of the structure and dynamics of the lipid-protein interface. The long term goal of our research is to decode the role of lipid-protein interactions in cell signaling. The overall objective of this application is to investigate how electrostatic interactions drive the organization and dynamic assembly of lipid-protein complexes in cell signaling.
Previous work has shown that macromolecules with cationic sequences can form nano-domains with sequestered anionic lipids, which alters the lateral distribution and mobility of the membrane lipids. Such sequestration is believed to result from the formation of a lipid-macromolecule complex. To date, however, the molecular structure and dynamics of the lipid-polymer interface are poorly understood. We are investigating the behavior of polycationic peptides, proteins, and polymers on supported lipid bilayers doped with phosphatidylserine (PS) or phosphatidylinositol phosphate (PIP) lipids using time-resolved fluorescence microscopy – including pulsed interleaved excitation fluorescence cross-correlation spectroscopy (PIE-FCCS).
Shi, X., Li, X., Kaliszewski, M. J., Zhuang, X., and Smith, A. W. Tuning the mobility coupling of polycationic macromolecules and anionic phospholipids in supported lipid bilayers. (Submitted, in review).