The importance of N protein variants in antibody test and drug design

Since the outbreak of the severe pandemic caused  by SARS-CoV-2 infection, the spike protein (S) of the virus has been used as  the leading target antigen in epidemiological studies, diagnostic tests and  drug and vaccine development. Nucleocapsid protein (N), the structural protein  that packages viral RNA into new virions, is identified a second important  player in this life-or-death contest. A significant amount of studies demonstrated  that the N protein is highly immunogenic and is expressed abundantly during  infection, therefore suitable as a diagnostic reagent or antibody target. 

Related article: S protein: key to the pandemic

Like spike protein, nucleocapsid protein is quite  tolerant of mutations. This protein is divided into two main domains,  the N-terminal RNA-binding domain (NTD) and the C-terminal dimerization domain  (CTD), joined by a central serine/arginine-rich (SR)-linker. The NTD directly  interacts with the viral RNA and is highly divergent. The CTD is important for  eliciting antibodies against SARS-CoV-2 during an immune response. The SR-linker  harbors phosphorylation sites critical for the modulation of nucleocapsid  multimerization, translational inhibitory activity and cellular localization.

Figure 1. the structure  of Nucleocapsid protein

Based  on comprehensive studies of reported mutations, ACROBiosystems has developed  multiple recombinant N protein variants. The co-occuring mutations R203K and G204R are most common with an  estimated frequency of >60% in global sequences, which is comparable to the  dominant D614G mutation on the spike  protein. Other frequently occurred mutations include P13L,  P80R, D103Y,  S194L, etc.

Figure 2. current reported  mutations on the Nucleocapsid  protein

Research  into the specific functional consequences of these N protein mutations are currently  limited. The availability of a panel of N proteins with high purity and  bioactivity now paved your way to systematically examine its implication in  antibody testing and drug design.

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Assay Data

High  purity

SARS-CoV-2  Nucleocapsid protein, His Tag (Cat. No. NUN-C52H8) on SDS-PAGE under reducing (R) condition. The gel was  stained overnight with Coomassie Blue. The purity of the protein is greater  than 90%.

High  bioactivity

 Immobilized  SARS-CoV-2 Nucleocapsid protein, His Tag (Cat. No. NUN-C52H8) at 1 μg/mL (100 μL/well) can bind Anti-SARS-CoV-2  Nucleocapsid Antibody, Human IgG1 (Cat. No. NUN-S41A1) with a linear range of 0.06-1 ng/mL (QC tested).

 reference

1. Ye, Q, West, AMV, Silletti, S, Corbett, KD. Architecture and self-assembly of the SARS-CoV-2 nucleocapsid protein. Protein Science. 2020; 29: 1890– 1901. https://doi.org/10.1002/pro.3909

2. Troyano-Hernáez P, Reinosa R, Holguín Á.  Evolution of SARS-CoV-2 Envelope, Membrane, Nucleocapsid, and Spike Structural  Proteins from the Beginning of the Pandemic to September 2020: A Global and  Regional Approach by Epidemiological Week. Viruses. 2021 Feb;13(2). DOI:  10.3390/v13020243.

3. Rahman MS, Islam MR, Alam ASMRU, et al.  Evolutionary dynamics of SARS-CoV-2 nucleocapsid protein and its consequences.  J Med Virol. 2021 Apr;93(4):2177-2195. doi: 10.1002/jmv.26626. Epub 2020 Nov  10. PMID: 33095454.