Styrene-maleic acid copolymer effects on the function of the GPCR rhodopsin in lipid nanoparticles.

Abstract Styrene-maleic acid (SMA) copolymers solubilize biological membranes to form lipid nanoparticles (SMALPs) that contain membrane proteins surrounded by native lipids, thus enabling the use of a variety of biophysical techniques for structural and functional studies. The question of whether SMALPs provide a truly natural environment or SMA solubilization affects the functional properties of membrane proteins, however, remains open. We address this question by comparing the photoactivation kinetics of rhodopsin, a G protein-coupled receptor (GPCR) in the disc membranes of rod cells, in native membrane and SMALPs prepared at different molar ratios between SMA(3:1) and rhodopsin. Time-resolved absorption spectroscopy, combined with complex kinetic analysis, reveals kinetic and mechanistic differences between the native membrane and SMA-stabilized environment. The results suggest a range of molar ratios for nanoparticles suitable for kinetic studies.