Lipid-protein interactions in biological membranes: A dynamic perspective

Though an increasing number of biological functions at the membrane are attributed to direct associations between lipid head groups and protein side chains or lipid protein hydrophobic attractive forces, surprisingly limited information is available about the dynamics of these interactions. The static in vitro representation provided by membrane protein structures, including very insightful lipid-protein binding geometries, still fails to recapitulate the dynamic behavior characteristic of lipid membranes. Experimental measures of the interaction time of lipid-protein association are very rare, and have only provided order-of-magnitude estimates in an extremely limited number of systems. In this review, a brief outline of the experimental approaches taken in this area to date is given. The bulk of the review will focus on two methods that are promising techniques for measuring lipid-protein interactions: time-resolved fluorescence microscopy, and two-dimensional infrared (2D IR) spectroscopy. Time-resolved fluorescence microscopy is the name given to a sophisticated toolbox of measurements taken using pulsed laser excitation and time-correlated single photon counting (TCSPC). With this technique the dynamics of interaction can be measured on the time scale of nanoseconds to milliseconds. 2D IR is a femtosecond nonlinear spectroscopy that can resolve vibrational coupling between lipids and proteins at molecular-scale distances and at time scales from femtoseconds to picoseconds. These two methods are poised to make significant advances in our understanding of the dynamic properties of biological membranes. This article is part of a Special Issue entitled: Membrane protein structure and function. (C) 2011 Elsevier B.V. All rights reserved.