A method for detergent-free isolation of membrane protein with its local lipid environment

Despite the great importance of membrane proteins, structural and functional studies present major challenges. A significant hurdle is the extraction of the functional protein from its natural lipid membrane. Traditionally achieved with detergents, purification procedures can be costly and time consuming. A critical flaw with detergent approaches is the removal of the protein from the native lipid environment required to maintain functionally stable protein. This protocol describes the preparation of Styrene Maleic Anhydride Co-polymer (SMA) to extract membrane proteins from prokaryotic and eukaryotic expression systems. Successful isolation into SMA lipid particles (SMALPs) allows membrane proteins to remain with native lipid, surrounded by SMA. We detail procedures for obtaining 25g of SMA (4 days), explain the preparation of both SMALPs with (2 days) and without (1-2 hours) protein, SMALP protein identification and estimation (4 hours), and detail biophysical methods to undertake initial structural studies to characterise SMALPs (~2 days). Together these methods provide a practical tool-kit for those wanting to use SMALPs to study membrane proteins.