Fig. 3: NMR studies show that GRL0617 blocks the binding of ISG15 to SARS-CoV-2 PLpro.

a ¹H,¹⁵N-HSQC spectrum of ¹⁵N-ISG15. b HSQC spectrum of ¹⁵N-ISG15 (0.1 mM) and 0.15 mM PLpro. Peak broadening and peak intensity loss indicate binding of ISG15 to PLpro. c HSQC spectrum of ¹⁵N-ISG15 (0.1 mM) in the mixture of 0.15 mM PLpro and 0.25 mM GRL0617. Recovery of peak intensity suggests that GRL0617 binds to PLpro and displaces ISG15. d SARS-CoV-2 PLpro^C111S/GRL0617 structure in cartoon model. e ISG15 in the complex structure of human ISG15 C-UBL-PA/SARS-CoV-2 PLpro (PDB 6XA9 [https://doi.org/10.2210/pdb6xa9/pdb]) was superimposed on (d) showing steric clash of GRL0617 with the C-terminal tail of ISG15. f Ub in the complex structure of UbPA/SARS-CoV-2 PLpro (PDB 6XAA [https://doi.org/10.2210/pdb6xaa/pdb]) was superimposed on (d), showing steric clash of GRL0617 with the C-terminal tail of Ub.