Fig. 7: The impact of viral proteins on ISG15 E1 charging.
From: Insights into the ISG15 transfer cascade by the UBE1L activating enzyme
a Structure of non-structural protein 1 from influenza B virus (NS1B) bound to ISG15 (pdb 3sdl)43 overlaid onto the UBE1L-UBE2L6 ISG15 adenylate complex. NS1B contacts the N-terminal ubiquitin-like fold (N-lobe) of ISG15, but not the C-terminal ubiquitin-like fold (C-lobe). The ISG15 adenylate and UBE1L adenylation active site are highlighted. b Structure of SARS-CoV2 papain-like protease (PLpro) bound to ISG15 (pdb 6yva)31. PLpro contacts both the N-lobe and C-lobe of ISG15. c Time course analysis of UBE1L charging assays in the presence of viral proteins. The catalytically inactive PLpro mutant Cys111Ala (CA) was used. d Analysis of UBE1L charging in the presence of viral proteins using fluorescence polarization (FP) assays. The indicated concentrations of NS1B, NS1B AA mutant (W36A/Q37A) and PLpro CA were added to fluorescent ISG15, followed by the addition of UBE1L to the sample. e Schematic of the proposed mechanisms to explain data shown in c and d. NS1B binds the N-lobe of ISG15 and remains bound during UBE1L charging, while PLpro CA competes with UBE1L for the C-lobe of ISG15. Experiments were performed independently in triplicate. Source data are provided in the Source Data file.
