CTD of SARS-CoV-2 N protein is a cryptic domain for binding ATP and nucleic acid that interplay in modulating phase separation.

ABSTRACT

SARS-CoV-2 nucleocapsid (N) protein plays essential roles in many steps of the viral life cycle, thus representing a key drug target. N protein contains the folded N-/C-terminal domains (NTD/CTD) and three intrinsically disordered regions, while its functions including liquid-liquid phase separation (LLPS) depend on the capacity in binding various viral/host-cell RNA/DNA of diverse sequences. Previously NTD was established to bind various RNA/DNA while CTD to dimerize/oligomerize for forming high-order structures. By NMR, here for the first time we decrypt that CTD is not only capable of binding S2m, a specific probe derived from SARS-CoV-2 gRNA but with the affinity even higher than that of NTD. Very unexpectedly, ATP, the universal energy currency for all living cells with high cellular concentrations (2-16 mM), specifically binds CTD with Kd of 1.49 ± 0.28 mM. Strikingly, the ATP-binding residues of NTD/CTD are identical in the SARS-CoV-2 variants while ATP and S2m interplay in binding NTD/CTD, as well as in modulating LLPS critical for the viral life cycle. Results together not only define CTD as a novel binding domain for ATP and nucleic acid, but enforce our previous proposal that ATP has been evolutionarily exploited by SARS-CoV-2 to complete its life cycle in the host cell. Most importantly, the unique ATP-binding pockets on NTD/CTD may offer promising targets for design of specific anti-SARS-CoV-2 molecules to fight the pandemic. Fundamentally, ATP emerges to act at mM as a cellular factor to control the interface between the host cell and virus lacking the ability to generate ATP.