SARS-CoV-2 Nucleocapsid Protein Has DNA-Melting and Strand-Annealing Activities With Different Properties From SARS-CoV-2 Nsp13

Since December 2019, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has spread throughout the world and has had a devastating impact on health and economy. The biochemical characterization of SARS-CoV-2 proteins is important for drug design and development. In this study, we discovered that the SARS-CoV-2 nucleocapsid protein can melt double-stranded DNA (dsDNA) in the 5′-3′ direction, similar to SARS-CoV-2 nonstructural protein 13. However, the unwinding activity of SARS-CoV-2 nucleocapsid protein was found to be more than 22 times weaker than that of SARS-CoV-2 nonstructural protein 13, and the melting process was independent of nucleoside triphosphates and Mg(2+). Interestingly, at low concentrations, the SARS-CoV-2 nucleocapsid protein exhibited a stronger annealing activity than SARS-CoV-2 nonstructural protein 13; however, at high concentrations, it promoted the melting of dsDNA. These findings have deepened our understanding of the SARS-CoV-2 nucleocapsid protein and will help provide novel insights into antiviral drug development.