Stabilization of full-length S-protein of SARS-Cov-2 coronavirus in SMA polymer for electron microscopy study

A detergent-free protocol for purification of the coronavirus prefusion S-protein using styrene- maleic acid copolymer (SMA) was developed. Expression of the S-protein was carried out in HEK293T cells. Two solubilization methods were used to purify and prepare the S-protein for microscopy: in NP-40 detergent and as part of SMA. The resulting preparations were examined in an electron microscope, and the particles of purified S-proteins were classified. Analysis of two-dimensional projections of the particles showed that the use of lipodiscs for solubilization leads to lower mobility of the purified protein on the substrate, compared to the protein in the detergent, which may further contribute to obtaining higher resolutions when studying the structure of membrane proteins.