Variable Macro X Domain of SARS-CoV-2 Retains the Ability to Bind ADP-ribose

David N. Frick; Rajdeep S. Virdi; Nemanja Vuksanovic; Narayan Dahal; Nicholas R Silvaggi

Conclusion-The significance of the study stems mainly from the demonstration that the SARS-CoV-2 macro X domain binds ADP ribose. This is the first step needed to justify screens for potential antivirals that bind in place of ADP ribose. More work needs to be done, however, to understand the antiviral potential of such compounds because the biological role for ADP-ribose binding is still not fully understood. Some work with alpha coronaviruses suggest that ADP-ribose binding by the macro X domain is not needed for viral replication. 13 However, studies with other (+)RNA viruses suggest that macrodomains are essential for virulence. 14 This work is also noteworthy because the synthetic codon-optimized plasmid reported here produces up to 100 mg of soluble macro X domain protein per liter of E. coli culture, and this protein retains a high affinity for ADP ribose. The protein could be used for structural studies and screening campaigns. Screening assays with the SARS-CoV-2 protein might actually be more efficient, since the SARS-CoV-2 protein binds ADP-ribose somewhat more tightly (Kd = 10 µM) than the SARS-CoV-1 protein (Kd = 24 µM). The recombinant protein reported here, together with the detailed structural information, might also be useful to others developing SARS-CoV-2 diagnostics and/or therapeutics.