Formation of styrene maleic acid lipid nanoparticles (SMALPs) using SMA thin film on a substrate

Despite the important role of membrane proteins in biological function and physiology, studying them remains challenging because of limited biomimetic systems for the protein to remain in its native membrane environment. Cryo electron microscopy (Cryo-EM) is emerging as a powerful tool for analyzing the structure of membrane proteins. However, Cryo-EM and other membrane protein analyses are better studied in a native lipid bilayer. Although traditional, mimetic systems have disadvantages that limit their use in the study of membrane proteins. As an alternative, styrene-maleic acid copolymers are used to form nanoparticles with POPC:POPG lipids. Traditional characterization of these styrene maleic acid lipid nanoparticles (SMALPs) includes dynamic light scattering (DLS), electron paramagnetic resonance (EPR), nuclear magnetic resonance (NMR), and transmission electron microscopy (TEM). In this study a new method was developed that utilizes SMALPs using a styrene-maleic acid copolymer (SMA) thin film on a TEM grid, acting as a substrate. By directly adding POPC: POPG lipid vesicles to the SMA coated grid SMALPs can be formed, visualized, and characterized by TEM without the need to make them in solution prior to imaging. We envision these functionalized grids could aid in single particle specimen preparation, increasing the efficiency of structural biology and biophysical techniques such as Cryo-EM.

Automated summary

Despite challenges in studying membrane proteins, cryo electron microscopy (Cryo-EM) is emerging as a powerful tool for their structural analysis. Traditional systems for studying membrane proteins have limitations, but styrene-maleic acid copolymers can form nanoparticles with lipids to overcome these challenges. A new method utilizing styrene-maleic acid copolymer thin film on a TEM grid was developed to directly form and visualize lipid nanoparticles (SMALPs) for the study of membrane proteins.