Human Anti-SARS-CoV-2 NP (N-term) Monoclonal Antibody, clone CO18

An essential part of the viral structure, the nucleocapsid protein (N) of SARS-CoV-2 performs several tasks during host cell infection and is vital to the virus' life cycle. SARS-CoV-2, the virus that causes COVID-19, is an enveloped positive-sense RNA virus that is a member of the β-coronavirus family. It shares a lot of similarities with the 2002 SARS-CoV outbreak and the Middle East respiratory syndrome coronavirus (MERS-CoV). Four structural proteins—envelope (E), membrane (M), spike (S), and nucleocapsid (N)—are encoded by the SARS-CoV-2 genome. Of these, nucleocapsid is the most conserved and one of the most abundant proteins generated following viral infection. It directly affects the virus's pathogenicity and transmissibility and is essential for the packaging and assembly of viral RNA. The nucleocapsid protein is made up of 419 amino acids and is separated into multiple functional domains. The N-arm, a serine/arginine-rich center linker region (LKR), and the C-tail are examples of extremely flexible disordered regions (IDRs), as are the conserved N-terminal domain (NTD) and C-terminal domain (CTD). Together, these domains give the nucleocapsid protein its multifunctionality, which allows it to effectively bind viral RNA and carry out many tasks during the viral life cycle.

During viral replication, the nucleocapsid's primary role is to package the RNA of the viral genome into ribonucleoprotein complexes. The CTD facilitates the formation of viral particles by encouraging RNA dimerization and higher-order assembly steps, whereas the NTD binds directly to RNA to preserve its stability. With a core composed of five antiparallel β-strands and a basic β-hairpin, the NTD creates a U-shaped structure that interacts with the negatively charged RNA backbone to stabilize the ribonucleoprotein complex. On the other hand, the CTD's special ability to dimerize, which is facilitated by particular positively charged residues like K256, K257, K261, and R262, is essential for the production of RNA dimers as well as for RNA binding and viral assembly. The nucleocapsid protein not only directly participates in the viral assembly process but also modifies the host immune response to aid the virus in avoiding the host's defenses. For example, research has demonstrated that the SARS-CoV-2 nucleocapsid protein can inhibit the interferon response of the host cell. The nucleocapsid protein disrupts this signaling route to lower interferon production, which erodes the host's antiviral defenses. Interferon is a crucial mechanism employed by the host immune system to fight viral infections. Furthermore, the nucleocapsid protein interacts with other host immune-regulatory processes, including RNA interference (RNAi), and may use these pathways to affect host cell death. These functions render the nucleocapsid protein a multifaceted protein, playing essential roles not only in the viral life cycle but also in the virus's struggle with the host's immune system.

Figure 1. Mechanism of Virus Assembly Mediated by SARS-CoV-2 N Protein (Source: Han Y, et al., 2024)

Research on SARS-CoV-2 has focused heavily on the nucleocapsid protein because of its crucial function in immune control and viral replication. Furthermore, the nucleocapsid protein has demonstrated significant promise in the creation of vaccines and the search for new drugs. First, during COVID-19 infection, one of the primary antigens that triggers a robust antibody response in the host is the nucleocapsid protein. Following viral infection, the host develops a strong antibody response against the nucleocapsid protein, which makes it a crucial target for the creation of diagnostic instruments. The nucleocapsid protein's potential as a therapeutic target is further highlighted by its conservation. Since the nucleocapsid protein is crucial to the viral life cycle, inhibitors that target it may be able to successfully stop the virus's replication, which would stop it from spreading. The nucleocapsid protein's diagnostic use extends beyond its function in antibody reactions. Another essential component of COVID-19 diagnostics is nucleic acid testing, which frequently uses real-time reverse transcription polymerase chain reaction (RT-PCR) to identify SARS-CoV-2 RNA. Since the nucleocapsid gene sequence is one of the main targets for many RT-PCR detection techniques and is comparatively stable and conserved within the viral genome, this methodology mainly depends on it. Despite being the most used technique for identifying SARS-CoV-2, RT-PCR has drawbacks, including false negative results when analyzing samples from the upper respiratory tract. As a result, enhancing molecular detection techniques with antibody testing and antigen detection may increase diagnostic sensitivity and accuracy, particularly at various disease stages. The creation of vaccines also heavily relies on the nucleocapsid protein. The nucleocapsid protein is a possible inclusion in numerous vaccines designs due to its pivotal function in viral proliferation and immune response. A wide immune response may be elicited in the host by targeting the nucleocapsid protein, which could lessen the severity of the disease and assist avoid infection. Although the spike protein (S protein) is the main component of the majority of the already licensed COVID-19 vaccines, adding the nucleocapsid protein to vaccine designs may increase vaccine efficacy even more, particularly against viral variations. Antiviral medications that target the nucleocapsid protein are also gaining a lot of attention in the therapeutic development process. Drugs that impede the nucleocapsid protein's function may successfully stop viral replication since it is an essential node in viral RNA packaging and the viral life cycle. The viral RNA-dependent RNA polymerase (RdRp) is the main target of current antiviral medications like remdesivir and favipiravir. However, pharmaceuticals that target the nucleocapsid protein may provide a unique treatment approach by interfering with the effective packaging of viral RNA and the assembly of viral particles.

Anti-COVID-19 nucleoprotein antibody (N-term)
SARS-CoV-2 nucleocapsid protein N-terminal antibody
COVID-19 NP N-term monoclonal antibody