Characterization of Phosphatidylcholine/Tween-80 Model Membranes for the NMR Study of Membrane Interactions

Abstract

Tween-80 (TW80) is a fatty acid ester (oleate) of sorbitan polyethoxylate known to be a mild non-ionic surfactant and is commonly used to solubilize membrane proteins. In order to facilitate the structural study of membrane proteins and peptides by nuclear magnetic resonance (NMR), we have developed bicelle-inspired mimetics made of TW80. More specifically, the detergent was mixed with phosphatidylcholines (PCs) having different acyl chain lengths. The resulting PC/TW80 systems were characterized by solution- and solid-state (SS) NMR. Our results show that dimyristoylPC (DMPC, 14:0) and dipalmitoylPC (DPPC, 16:0) self-assemble with TW80 to form magnetically-oriented structures at PC/detergent molar ratios (q) of 5≥q≥2 and 13≥q≥2, respectively, as demonstrated by 31P and 2H SS-NMR. Oriented systems are formed above the gel-to-fluid phase transition temperatures of the phospholipids, i.e. 23oC for DMPC and 42oC for DPPC, up to high temperatures (77°C). 31P solution NMR analysis demonstrates the formation of fast-tumbling isotropic structures at lower q ratios (q<2) for both PC/detergent membranes. The morphology and size of the PC/TW80 systems at various q ratios will be presented using dynamic light scattering data as well as cryo-electron microscopy and atomic force microscopy images. These new membrane mimetics should help studying membrane proteins and peptides by avoiding the detergent removal step during purification, and provide a new tool for the NMR study of membrane interactions.