Figure 1.

Production of SARS-CoV-2 virus-like particles (VLPs).A, western blot analysis of the cell lysate and VLP fractions of individual expression of the four structural proteins 72-h posttransfection. Total protein content of cell lysates was used to normalize loading conditions and was quantified using the Pierce bicinchoninic acid assay. VLP loading was calculated as a constant ratio to normalized cell lysates. B, western blot analysis of the cell lysate and VLP fractions of additive combinations of M, N, and S. Total protein content of the cell lysates was used to normalize loading conditions and was quantified using the Pierce bicinchoninic acid assay. VLP loading was calculated as a constant ratio to normalized cell lysates. C, electron microscopy of SARS-CoV-2 VLPs. Purified M + N + E and M + N + E + S VLPs were added to glow discharged 400-mesh copper grids covered with carbon-coated collodion film. Grids were washed in one drop of water, stained in three drops of phosphotungstic acid (1.0% w/v), air dried, and imaged. White arrow demarcates zoomed image used for 1D. D, two S molecules on the left insert are magnified from marked with white arrow. The right insert corresponds to cryo-EM structure of trimeric S protein (PBD: 6ZWV). Its longest dimension is ∼170 Å, which is comparable to negative staining of S protein present around VLPs.