Dynamic associations between lipids and adsorbed biopolymers are central to assembly and function in biological membranes. The electrostatic component of these interactions has been recognized as a key feature, but is difficult to probe directly <i>in situ</i>. Phosphoinositides (PI) are anionic lipids that are particularly important in cell communication across the plasma membrane. Many proposals have been made about how PI lipids interact with cationic residues on the adsorbed protein, but these have been difficult to probe experimentally. Here we report on dynamic associations of phosphatidylinositol 4,5-bisphosphate (PI(4,5)P<sub>2</sub>) lipids with adsorbed cationic peptides. We study these interactions in a novel asymmetric supported lipid bilayer using time resolved fluorescence methods like single particle tracking (SPT) and pulsed interleaved excitation fluorescence cross-correlation spectroscopy (PIE-FCCS). With SPT we observe individual lipid binding events, from which we quantify residence times and the dependence on solution ionic strength. With PIE-FCCS we observe and characterize a population of low-mobility lipid-peptide clusters. This approach allows us resolve the chemical details of electrostatic interactions in biological membranes.

Correlating lipid-protein interactions with single particle tracking and PIE-FCCS

251st National Meeting (2016)

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