What is Nucleoprotein

The nucleoprotein (NP) mainly refers to the nucleoprotein of human coronaviruses. It's a conjugated protein composed of the viral protein shell linked to single-stranded RNA. As a structural protein with no intrinsic enzymatic activity in SARS-CoV-2, N protein is a highly immunogenic and most abundant viral protein in infected cells.

What is the feature of the nucleoprotein structure?

Weihong Zeng's structural characterization of recombinant full-length N protein predicted it possesses two well-folded domains: the N-terminal domain (NTD) and the C-terminal domain (CTD). Both domains are rich in β-strands, while CTD bears some short helices. The N protein of SARS-CoV-2 has been found to exist as a dimer in solution through CTD-CTD interaction. The sequence of SARS-CoV-2 nucleoprotein is highly identical to that of SARS-CoV, and both of their two core domains and the linker are most conserved. Both NTD and CTD carrying positive charges on their surface may interpret the high binding affinity between the N protein and non-specific nucleic acid.

What is the function of nucleoprotein?

The N protein is essential for the package of the positive-stranded viral genome RNA into a helical ribonucleocapsid (RNP). After infection, the N protein enters the host cell with the viral RNA to facilitate its replication. It then interacts with the viral genome and membrane protein M to assemble virus particles. N protein is frequently used in vaccine development and serological assays based on its immunogenicity.