Characterizing the structure of styrene-maleic acid copolymer-lipid nanoparticles (SMALPs) using RAFT polymerization for membrane protein spectroscopic studies

• Published in: Chemistry and physics of lipids Vol. 218; pp. 65 - 72
• Main Authors: Harding, Benjamin D., Dixit, Gunjan, Burridge, Kevin M., Sahu, Indra D., Dabney-Smith, Carole, Edelmann, Richard E., Konkolewicz, Dominik, Lorigan, Gary A.
• Format: Journal Article
• Language: English
• Published: Ireland Elsevier B.V 01-01-2019
• Subjects: Continuous wave-electron paramagnetic resonance; Dynamic Light Scattering; Dynamic light scattering (DLS); Lipids - chemistry; Maleates - chemistry; Membrane Proteins - chemistry; Microscopy, Electron, Transmission; Nanoparticles - chemistry; Polymerization; Polymers - chemistry; SMALPs; Styrene - chemistry; Styrene-maleic acid (StMa); Transmission electron microscopy (TEM); Vesicles; Vesicles; Continuous wave-electron paramagnetic resonance; Transmission electron microscopy (TEM); SMALPs; Styrene-maleic acid (StMa); Dynamic light scattering (DLS)
• ISSN: 0009-3084; 1873-2941
• DOI: 10.1016/j.chemphyslip.2018.12.002

•The size of styrene-maleic acid copolymer-lipid nanoparticles (SMALPs) were characterized using Dynamic Light Scattering.•EPR spectra showed the incorporation of a membrane protein into the nanoparticles and liposomes.•TEM images show the size and distribution of the SMALPs.
Membrane proteins play an important role in maintaining the structure and physiology of an organism. Despite their significance, spectroscopic studies involving membrane proteins remain challenging due to the difficulties in mimicking their native lipid bilayer environment. Membrane mimetic systems such as detergent micelles, liposomes, bicelles, nanodiscs, lipodisqs have improved the solubility and folding properties of the membrane proteins for structural studies, however, each mimetic system suffers from its own limitations. In this study, using three different lipid environments, vesicles were titrated with styrene-maleic acid (StMA) copolymer leading to a homogeneous SMALP system (∼10 nm) at a weight ratio of 1:1.5 (vesicle: StMA solution). A combination of Dynamic Light Scattering (DLS) and Transmission Electron Microscopy (TEM) was used to characterize these SMALPs. We used a controlled synthesis mechanism to synthesize StMA based block copolymers called reversible addition-fragmentation chain transfer polymerization (RAFT) SMALPs. Incorporation of the Voltage Sensor Domain of KCNQ1 (Q1-VSD) into RAFT SMALPs indicates that this is a promising application of this system to study membrane proteins using different biophysical techniques. V165C in Q1-VSD corresponding to the hydrophobic region was incorporated into the SMALP system. Continuous Wave-Electron Paramagnetic Resonance (CW-EPR) line shape analysis showed line shape broadening, exposing a lower rigid component and a faster component of the spin label.