Recombinant DENV type 1 NS1 [His]

Dengue virus (DENV) belongs to a serotype subgroup of the genus Flavivirus in the family Flaviviridae. It is mainly transmitted by vector insects such as Aedes aegypti and Aedes albopictus, causing dengue fever (DF), dengue hemorrhagic fever (DHF) and dengue shock syndrome (DSS). The morbidity and mortality of DHF and DSS are high. The virus is widely prevalent in tropical and subtropical regions around the world. The DENV genome is about 10700 bp long. The 5' end of the genome has a cap structure, the 3' end is CUOH, and there is no poly A structure. The ORF can be divided into two parts: the sequence of the 5' end 1/4 encodes the three structural proteins of the virus (core protein C, membrane-bound protein precursor PrM and envelope protein E); the sequence of the 3' end 3/4 encodes the seven non-structural proteins of the virus (NS1, NS2A, NS2B, NS3, NS4A, NS4B, NS5). The coding region of the DENV NS1 gene is 1056 bases, located between the E gene and the NS2A gene, and encodes a total of 352 amino acid residues. The NS1((Nonstructural protein 1)) monomer is highly hydrophilic and contains 12 cysteine residues, forming 6 discontinuous disulfide bonds to ensure the correct folding of the monomer and maintain the stability of the monomer structure.

Figure 1. Diagram with dengue virus and its four serotypes. (Sources: Islam MT, et al. 2021)

The dengue virus genomic RNA is a positive strand and is the mRNA for synthesizing viral proteins. Under the synergistic action of the virus and host proteases, the virus first directly uses the genomic RNA as a template to synthesize a polyprotein molecule of about 3,000 amino acids, and then processes it into various structural proteins and non-structural proteins of the virus. Structural proteins are the main components of viral particles. The C protein is rich in basic amino acids arginine and lysine residues, and has specific antigenic clusters on it, which are complement binding antigens. PrM is the precursor of the M protein. At the end of the maturation of viral particles, the PrM protein is enzymatically cleaved into the M protein. Both PrM and M proteins participate in the construction of the virus surface structure. The E protein performs some of the main biological functions of viral particles, such as cell tropism, cell fusion, and induction of hemagglutination inhibition antibodies and neutralizing antibody production. The E protein has neutralizing antigen epitopes, type-specific epitopes, dengue virus species and flavivirus-specific epitopes, and plays a vital role in the pathogenesis and immunity of dengue virus. Nonstructural proteins only exist in virus-infected host cells. They are enzymes or regulatory proteins of dengue virus, etc. They are closely related to virus replication, protein processing and virus assembly. The first nonstructural protein is NS1 protein, and its function in the life cycle of the virus is still unclear. NS2a is a protease, and NS2b has the function of cooperating with protease for enzymatic hydrolysis. NS3 and NS5 are nonstructural proteins with RNA polymerase activity. NS4a and NS4b are currently believed to be related to auxiliary factors of RNA polymerase.

The relative molecular mass of DENV NS1 is about 43,000. There are two main forms of this protein. The dimeric form of NS1 is mainly present in the cysts of infected virus cytoplasm and is related to the replication of viral dsRNA and other homologous viral genes. Non-structural proteins aggregate at the viral replication site in the cysts, and exist in small amounts on the cell membrane surface of infected virus cells, called membrane NS1 (mNS1); this protein is also secreted into mammalian cell culture fluid or infected patient plasma in the form of hexameric lipoprotein particles, called secretory NS1 (sNS1). NS1 antigen is a hallmark antigen for DENV infection and can appear earlier than IgM antibodies. After infection, NS1 antigen appears in the human body from the first day of fever and can last for 9 days. This antigen is of great significance for early diagnosis. Since there are many other pathogens in areas where dengue fever is prevalent that can cause clinical symptoms similar to DENV infection, and patients are at different stages of infection when they seek medical treatment, it is difficult to diagnose DENV infection through clinical symptoms. Therefore, etiological diagnosis is particularly important, especially for early targeted prevention and treatment of dengue shock that may occur later. Immunological testing is low-cost, simple and rapid, and is very suitable for dengue detection in economically underdeveloped areas. Dengue virus has four serotypes (DENV-1, DENV-2, DENV-3, DENV-4) that are inter-epidemic according to different antigenicity and show certain temporal and spatial distribution characteristics. Among them, cases in most areas are still dominated by DENV-1, DENV-2, and DENV-3. NS1 protein is an important non-structural protein encoded by the DENV genome, and its sequence is highly conserved. When the virus replicates itself, it also produces NS1, which will be released into the blood and can be used as a specific indicator for early laboratory diagnosis. 9-12 days after the initial infection, NS1 can still be detected in the blood. When infected again, the body already has NS1 antibodies, which can quickly clear NS1. 5-7 days after the onset of symptoms, NS1 can rarely be detected. Therefore, when diagnosing a secondary infection, NS1 needs to be tested in conjunction with DENV-specific IgM to assist in clinical diagnosis. A positive IgM antibody indicates that the patient has recently been infected with dengue virus and is suitable for early diagnosis of dengue fever. NS1 testing combined with IgG/IgM testing can provide more diagnostic information for NS1 negative results.

NS1
DENV-1 NS1
Dengue Virus Type 1 Nonstructural Protein 1
Dengue Virus NS1
Nonstructural Glycoprotein NS1