Towards Detergent Free Solubilization of Membrane Proteins into Nanodiscs: A Biophysical Study on the Interaction between Styrene Maleic Acid (SMA) Copolymers and Synthetic Phospholipid Vesicles

Abstract

Recently, it has been discovered that SMA copolymers are able to solubilize membrane proteins in the form of styrene maleic acid lipid particles (SMALPs) without the use of destabilizing detergents [1,2]. In order to understand this unique property of SMA we studied the solubilization of multilamellar vesicles (MLVs) of synthetic saturated phospholipids by SMA as function of acyl chain length and temperature. The rate of solublization was monitored by transmission experiments. It was found that SMA polymers are excellent phospholipid membrane solubilizers, that are able to solubilize below, at and above gel to crystalline liquid phase temperature, with most efficient solubilization close to and at the gel to liquid-crystalline phase transition temperature (Tm). The formation of ∼10 nm diameter SMALPs, also referred to as lipid-nanodisks was verified by negative stain-transmission electron microscopy (TEM) and dynamic light scattering (DLS). Comparison with the recombinant apolipoprotein MSP1D1 showed that SMA is a significantly more potent membrane solubilizer than MSP1D1. Based on these and other results we developed a model for the mode of action of SMA that will be presented here.Our study contributes to the fundamental knowledge about the molecular mode of action of SMA, which is essential to develop general methods to succesfully extract membrane proteins directly from their native environment in the form of lipid-nanodiscs. As proof of principle that this is indeed possible, we succeeded in purifying the potassium channel KcsA from the inner membrane of E-coli using the SMA technology. These results and some of its implications will be presented in an accompanying poster.1. Knowles et al., 2009, JACS, 131, 7484-7485.2. Orwick et al., 2012, Angew.Chem., 51,1-6