Human Anti-SARS-CoV-2 Nucleoprotein Monoclonal antibody, clone CO10

The nucleocapsid protein (N) of SARS-CoV-2 is an indispensable component of the viral structure, playing a crucial role in the virus's life cycle and serving multiple functions during infection of the host cell. COVID-19, caused by SARS-CoV-2, is an enveloped positive-sense RNA virus belonging to the β-coronavirus family, sharing high similarity with Middle East respiratory syndrome coronavirus (MERS-CoV) and the SARS-CoV outbreak in 2002. The SARS-CoV-2 genome encodes four structural proteins: envelope (E), membrane (M), spike (S), and nucleocapsid (N), with the nucleocapsid being the most conserved among them and one of the most abundant proteins produced after viral infection. It plays a central role in packaging and assembling viral RNA and directly influences the virus's transmissibility and pathogenicity. Comprising 419 amino acids, the nucleocapsid protein can be divided into several functional domains. These include a conserved N-terminal domain (NTD), a C-terminal domain (CTD), and highly flexible disordered regions (IDRs) such as the N-arm, a serine/arginine-rich central linker region (LKR), and the C-tail. These regions together determine the multifunctionality of the nucleocapsid protein, enabling it to efficiently bind viral RNA and perform different functions throughout the viral life cycle.

Figure 1. Illustration of the SARS-CoV-2 nucleocapsid protein (Source: Botova M, et al., 2024)

One of the nucleocapsid's most prominent functions is packaging the viral genome RNA into ribonucleoprotein complexes during viral replication. The NTD binds directly to RNA to maintain its stability, while the CTD promotes RNA dimerization and higher-order assembly steps, facilitating the assembly of viral particles. Structurally, the NTD forms a U-shaped structure with a core of five antiparallel β-strands and a basic β-hairpin that interacts with the negatively charged backbone of RNA, crucial for stabilizing the ribonucleoprotein complex. In contrast, the CTD's unique dimerization capacity, mediated by specific positively charged residues such as K256, K257, K261, and R262, plays a critical role in RNA dimer formation and in RNA binding and viral assembly. Beyond direct involvement in the viral assembly process, the nucleocapsid protein also helps the virus evade the host's immune defenses by modulating the host immune response. For instance, studies have shown that the nucleocapsid protein of SARS-CoV-2 can suppress the host cell's interferon response. Interferon is a key mechanism used by the host immune system to combat viral infections, and the nucleocapsid protein interferes with this signaling pathway to reduce interferon production, weakening the host's antiviral defenses. Additionally, the nucleocapsid protein interacts with other immune-regulatory mechanisms in the host, such as RNA interference (RNAi), and may influence apoptosis in host cells through these pathways. 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.

Given its central role in viral replication and immune regulation, the nucleocapsid protein has become a major focus of research related to SARS-CoV-2. Moreover, the nucleocapsid protein has shown great potential in vaccine development and drug discovery. First, the nucleocapsid protein is one of the main antigens that elicits a strong antibody response in the host during COVID-19 infection. The host generates a significant antibody response against the nucleocapsid protein after viral infection, making it a critical target for the development of diagnostic tools. Furthermore, the conservation of the nucleocapsid protein highlights its potential as a drug target. Since the nucleocapsid protein plays an essential role in the viral life cycle, inhibitors targeting it could effectively disrupt the viral replication process, thereby reducing viral spread. The diagnostic value of the nucleocapsid protein is not limited to its role in antibody responses. Nucleic acid testing is also a cornerstone of COVID-19 diagnostics, often using real-time reverse transcription polymerase chain reaction (RT-PCR) to detect SARS-CoV-2 RNA. This technique heavily relies on the nucleocapsid gene sequence, which is relatively stable and conserved within the viral genome, making it one of the primary targets for many RT-PCR detection systems. Although RT-PCR is the most widely used method for detecting SARS-CoV-2, it faces certain challenges, such as false negatives when testing upper respiratory tract samples. Therefore, combining antibody tests and antigen detection to complement molecular detection methods could improve diagnostic accuracy and sensitivity, especially across different stages of the disease. The nucleocapsid protein also plays a crucial role in vaccine development. Given its central role in viral replication and immune response, the nucleocapsid protein is a potential component in many vaccine designs. Targeting the nucleocapsid protein could induce a broad immune response in the host, which not only helps prevent infection but may also reduce viral transmission and disease severity. While most of the currently approved COVID-19 vaccines primarily rely on the spike protein (S protein), incorporating the nucleocapsid protein into vaccine designs could further enhance vaccine efficacy, especially against viral variants. In drug development, antiviral drugs targeting the nucleocapsid protein are also receiving considerable attention. Since the nucleocapsid protein is a key node in viral RNA packaging and the viral life cycle, drugs that inhibit its function may effectively block viral replication. Current antiviral drugs, such as remdesivir and favipiravir, primarily target the viral RNA-dependent RNA polymerase (RdRp), but drugs targeting the nucleocapsid protein could offer a novel therapeutic strategy, disrupting the efficient packaging of viral RNA and the assembly of viral particles.

Figure 2. Progress in SARS-CoV-2 nucleocapsid protein vaccine research (Source: Huang Y, et al., 2024)

Anti-COVID-19 nucleocapsid protein antibody
Anti-SARS-CoV-2 NP antibody
COVID-19 nucleoprotein antibody
Anti-SARS-CoV-2 nucleocapsid monoclonal antibody