Fig. 3. Native MS of nsp7+8 complexes of seven CoVs representing five different CoV species.
Representative mass spectra showing distinct nsp7+8 complexation patterns that were classified into the three groups A, B, and AB. Complex formation triggered by Mpro (M)–mediated cleavage of 15 μM nsp7-8-His6 or MERS-CoV nsp7-11-His6 precursors in 300 mM AmAc, 1 mM dithiothreitol (DTT) (pH 8.0). (A) SARS-CoV and (B) SARS-CoV-2 from group A forming nsp7+8 (2:2) heterotetramers (red), (C) FIPV and (D) TGEV from group B forming nsp7+8 (2:1) heterotrimers (blue), and (E) HCoV-229E and (F) PEDV from group AB forming both complex stoichiometries. (G) MERS-CoV, also from group AB, produced from an nsp7-11-His6 precursor, additionally results in several processing intermediates that allow for an estimation of relative cleavage efficiencies at different cleavage sites. All groups form nsp7+8 (1:1) heterodimers as intermediate state (green).