Spectroscopic studies of membrane proteins (MPs) are challenging due to difficulties in preparing homogenous and functional lipids that mimic the native lipid bilayer. It has recently been shown that styrene-maleic acid (StMA) copolymers act as a macromolecular surfactant and therefore facilitate the formation of disk-shaped styrene maleic acid lipid nanoparticles (SMALPs) that retain structural characteristics of native lipid membranes. We have previously reported controlled synthesis of SMA block copolymers using reversible addition-fragmentation chain transfer (RAFT) polymerization, and that alteration of the weight ratio of styrene to maleic acid affects nanoparticle size. RAFT-synthesis offers superior control over StMA polymer architecture compared to conventional radical polymerization techniques used for commercially available StMA. However, MPs have not yet been incorporated into lipid nanoparticles derived from RAFT-synthesized SMA. In this study, we aim to further characterize and optimize the incorporation of various sizes of MPs into RAFT SMALPs with 2:1 and 3:1 St/MA ratios. Purified mutants of voltage sensing domain of the potassium ion channel KCNQ1 and the associated KCNE1 protein were incorporated into SMALPs. Using EPR spin labels, changes in lipid dynamics and mobility were determined via EPR spectroscopy. This study further characterized SMALP mimetic systems and shows promise for SMALPs being a lipid bilayer mimetic. The study also shows SMALPs to be a protein-incorporated membrane mimetic at different particle sizes, including sizes above the 15 nm limit imposed by commercially available SMA.

EPR Characterization of incorporated membrane proteins into StMA-lipid nanoparticles

253rd National Meeting (2017)

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