N Protein Variants and Their Importance in Antibody Test and Design

The spike protein (S) of the virus has been utilized as the leading target antigen in diagnostic tests, epidemiological studies, and vaccine and drug development since the outbreak of the severe pandemic caused by SARS-CoV-2 infection.

The structural protein which packages viral RNA into new virions, nucleocapsid protein (N), is seen as the second key player in this life-or-death contest. A large number of studies showed that the N protein is expressed abundantly during infection and is extremely immunogenic, so it is suitable as an antibody target or diagnostic reagent.

Nucleocapsid protein is quite tolerant of mutations just as spike protein. It is divided into two main domains, the C-terminal dimerization domain (CTD) and the N-terminal RNA-binding domain (NTD), joined by a central serine/arginine-rich (SR)-linker. The NTD is highly divergent and interacts directly with the viral RNA.

During an immune response, the CTD is crucial for eliciting antibodies against SARS-CoV-2. The SR-linker harbors phosphorylation sites that are crucial for the modulation of nucleocapsid multimerization, cellular localization and translational inhibitory activity.

Figure 1. The structure of Nucleocapsid protein. Image Credit: ACROBiosystems

ACROBiosystems has developed a number of recombinant N protein variants based on comprehensive studies of reported mutations.

The co-occurring mutations R203K and G204R have an estimated frequency of >60% in global sequences and are the most common. This is comparable to the dominant D614G mutation on the spike protein. P13L, P80R, D103Y, S194L are some other frequently occurring mutations.

Figure 2. Current reported mutations on the Nucleocapsid protein. Image Credit: ACROBiosystems

At present, there is limited research into the specific functional consequences of these N protein mutations. The availability of a panel of N proteins with high bioactivity and purity has paved the way to systematically examine its implication in drug design and antibody testing.

Nucleocapsid protein variants list

Source: ACROBiosystems

Assay data

High purity

Image Credit: ACROBiosystems

High bioactivity

Image Credit: ACROBiosystems

References

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.

About ACROBiosystems

ACROBiosystems is a cornerstone enterprise of the pharmaceutical and biotechnology industries. Their mission is to help overcome challenges with innovative tools and solutions from discovery to the clinic. They supply life science tools designed to be used in discovery research and scalable to the clinical phase and beyond. By consistently adapting to new regulatory challenges and guidelines, ACROBiosystems delivers solutions, whether it comes through recombinant proteins, antibodies, assay kits, GMP-grade reagents, or custom services. ACROBiosystems empower scientists and engineers dedicated towards innovation to simplify and accelerate the development of new, better, and more affordable medicine.

Sponsored Content Policy: News-Medical.net publishes articles and related content that may be derived from sources where we have existing commercial relationships, provided such content adds value to the core editorial ethos of News-Medical.Net which is to educate and inform site visitors interested in medical research, science, medical devices and treatments.