Fig. 7. In vitro aggregation of the NSP11 proteins of SARS-CoV (NSP11-CoV) and SARS-CoV-2 (NSP11-CoV2).

a, d ThT fluorescence scan (λ_ex 440 nm) indicates an increase of ~2-fold at λ_max with NSP11-CoV and NSP11-CoV2 incubated samples, respectively. b, f CD spectra of 3 mg/ml monomeric peptides show the signature peaks at ~200 nm for disordered secondary structures. For NSP11-CoV aggregates (after 120 days incubation), a negative peak at 217 nm is observed corresponding to the presence of β-sheet structure; however, due to noise, the positive peak at ~200 nm is not clear. Similarly, for NSP11-CoV2 aggregates (after 192 h incubation), CD spectrum reveals β-sheet rich structure showing the characteristic positive and negative ellipticity peaks at 198.5 and 218.5 nm, respectively. Spectral data for aggregates is smoothened with 7 points using the FFT filter function. For NSP11-CoV and NSP11-CoV2 monomers, data is smoothened with 7 and 6 points, respectively, using the same function. c, h Morphology of NSP11-CoV (45 days) and NSP11-CoV2 fibrils (192 h) is observed using tapping-mode AFM where the scale bar represents 700 and 100 nm, respectively. Five micrographs were captured from same sample for each peptide aggregate. e Aggregation kinetics of NSP11-CoV2, monitored using ThT fluorescence. Each dotted symbol represents the average value of three technical replicates and error bar represents the SEM of these replicates. The wine-coloured line shows the sigmoidal fitting of data points that determines the T₅₀ of this reaction to be 66.73 ± 2.84 h. g Under HR-TEM, the NSP11-CoV2 fibrils appear unbranched at 192 h; the scale bar represents 200 nm. Fifteen micrographs were captured from the same grid. i Height profile of an NSP11-CoV2 amyloid fibril shown with green-coloured line in panel (h). Additional micrographs and height profiles are given in Supplementary Fig. 4. The source data are given in the Source Data file. Arb. units are arbitrary units.