Native mass spectrometry reveals binding interactions of SARS-CoV-2 PLpro with inhibitors and ISG15

Here we used native mass spectrometry (native MS) to probe a SARS-CoV protease, PLpro, which plays critical roles in coronavirus disease by affecting viral protein production and antagonizing host antiviral responses. Ultraviolet photodissociation (UVPD) and variable temperature electrospray ionization (vT ESI) were used to localize binding sites of PLpro inhibitors and revealed the stabilizing effects of inhibitors on protein tertiary structure. We compared PLpro from SARS-CoV-1 and SARS-CoV-2 in terms of inhibitor and ISG15 interactions to discern possible differences in protease function. A PLpro mutant lacking a single cysteine was used to localize inhibitor binding, and thermodynamic measurements revealed that inhibitor PR-619 stabilized the folded PLpro structure. These results will inform further development of PLpro as a therapeutic target against SARS-CoV-2 and other emerging coronaviruses.