Fig. 1

Vimentin as a cross-linked protein in association with the SARS-CoV spike protein-ACE2 complex. Vero E6 cells at 8 × 10⁶ were pre-incubated with SARS-CoV spike protein (1 μg/10⁶ cells) at 4 °C for various time periods as indicated followed by a treatment with the thiol-cleavable cross-linker DTSSP. Cell lysates were harvested and subjected to immunoprecipitation with anti-ACE2 antibodies. Vero E6 cells being treated by SARS-CoV VLPs for 0 min was used as the negative control. The immunoprecipitates were incubated with protein sample buffer with the addition of 5 % β-mercaptoethenol and subjected to SDS-PAGE. Proteins separated on the polyacrylamide gel were visualized by silver staining. The protein bands marked S1 to S7 were collected for LC-MS/MS analysis and results were shown. The number of matched spectra of the protein fragments compared to the published data was stated in parentheses. The detailed analysis of S3 was shown in the inset, where sequence comparison with data banks indicated the S3 protein to be vimentin. Underlines show the peptide sequences of 32 spectra