Extended Data Fig. 3: Proteolytic processing of spike of different SARS-CoV-2 recombinant viruses.
From: Phenotypic evolution of SARS-CoV-2 spike during the COVID-19 pandemic
a, Western blotting of spike protein associated with SARS-CoV-2 virions released in supernatants of Calu-3 infected cells. An antibody against S2 was used to differentiated processed and unprocessed spike. SARS-CoV-2 N was used as an internal control for virus load. Experiments were repeated independently four times and representative blots are shown. b, Quantification of spike proteolytic cleavage resulting from four independent western blots as in (a). Results are expressed as cleaved S2 over total spike protein. c, Incorporation of spike on SARS-CoV-2 virions. Results are expressed as total spike per N protein and normalised to S:B.1 for comparisons. In general, we observed a trend for a marginal increase in spike processing for all viruses, although reaching statistical significance only with S:Kappa, S:B.1.1.318, S:BA.2.75 and S:BA.4/5. We also observed marginally higher levels of spike incorporation in S:Delta, S:Delta AY.1, S:Kappa and S:Lambda (Extended Data Fig. 3a, c). Nonetheless, the quantification of spike incorporation into viral particles (that is the ratio between S and N signal) did not show any significant difference for all variants compared to S:B.1 (Extended Data Fig. 3c). b,c, Data are mean ± standard error to the mean (SEM) of four independent experiments. Statistical significance between S:B.1 and the spike recombinant SARS-CoV-2 was determined by one-way ANOVA withmultiple comparisons between the different spike-bearing viruses and S:B.1 using the Holm-Ĺ Ădák post-hoc test. Significance is indicated with * p ≤ 0.05, ** p ≤ 0.01, *** p ≤ 0.001, **** p ≤ 0.0001.
