Recombinant dengue virus type 3 envelope domain III protein from Escherichia coli

Selection and Characterization of Single-Stranded DNA Aptamers of Diagnostic Potential against the Whole Zika Virus

Zika virus became a major public health problem in early 2015, when cases of Guillain–Barré syndrome and microcephaly were associated with viral infection. Currently, ZIKV is endemic in all tropical areas of the world, and the chance for future Zika epidemics remains very real and accurate diagnosis is crucial. The aim of this work was to select specific ssDNA aptamers that bind to the entire Zika virus and can be used to compose specific diagnostics, without cross-reactivity with other flaviviruses. Zika virus was cultivated in Vero cells and used as a target for aptamer selection. Aptamers specific for the ZIKV were selected using whole-virus SELEX, with counterselection for other flavivirus. Secondary and tertiary structures were evaluated and the molecular anchoring between the aptamers and target were simulated by the HDOCK server. Aptamer interaction was evaluated by ELISA/ELASA and the dissociation constant (Kd) was calculated by thermophoresis. Four ZIKV-specific aptamers were selected. The best two were further characterized and proved to be specific for ZIKV. Aptamers are capable of binding specifically to the ZIKV and differentiate from Dengue virus. The aptamers selected in this work can be used as capture agents in the composition of diagnostic tests to specifically detect ZIKV infection.

Dengue and Zika virus multi-epitope antigen expression in insect cells

Dengue virus and Zika virus are arthropod-borne flaviviruses that cause millions of infections worldwide. The co-circulation of both viruses makes serological diagnosis difficult as they share high amino acid similarities in viral proteins. Antigens are one of the key reagents in the differential diagnosis of these viruses through the detection of IgG antibodies in serological assays during the convalescent-phase of infections. Here, we report the expression of Dengue virus (DENV) and Zika virus (ZIKV) antigens containing non-conserved and immunodominant amino acid sequences using the baculovirus expression vector system in insect cells. We designed DENV and ZIKV antigens based on the domain III of the E protein (EDIII) after analyzing previously reported epitopes and by multiple alignment of the most important flaviviruses. The ZIKV and DENV multi-epitope genes were designed as tandem repeats or impaired repeats separated by tetra- or hexa-glycine linkers. The biochemical analyses revealed adequate expression of the antigens. Then, the obtained multi-epitope antigens were semi-purified in a sucrose gradient and tested using patients' sera collected during the convalescent-phase that were previously diagnosed positive for anti-DENV and -ZIKV IgG antibodies. The optimal serum dilution was 1:200, and the mean absorbance values in the preliminary tests show that multi-epitope antigens have been recognized by human sera. The production of both antigens using the multi-epitope strategy in the eukaryotic system and based on the EDIII regions provide a proof of concept for the use of antigens in the differentiation between DENV and ZIKV.

Alanine Substitution Inactivates Cross-Reacting Epitopes in Dengue Virus Recombinant Envelope Proteins

The expansion of the habitat of mosquitoes belonging to the Aedes genus puts nearly half of the world's population at risk of contracting dengue fever, and a significant fraction will develop its serious hemorrhagic complication, which can be fatal if not diagnosed properly and treated in a timely fashion. Although several diagnostic methods have been approved for dengue diagnostics, their applicability is limited in rural areas of developing countries by sample preparation costs and methodological requirements, as well as cross-reactivity among the different serotypes of the Dengue virus and other flavivirus, such as the Zika virus. For these reasons, it is necessary to generate more specific antigens to improve serological methods that could be cheaper and used in field operations. Here, we describe a strategy for the inactivation of cross-reacting epitopes on the surface of the Dengue virus envelope protein through the synthetic generation of recombinant peptide sequences, where key amino acid residues from Dengue virus serotype 1 (DENV-1) and 2 (DENV-2) are substituted by alanine residues. The proteins thus generated are recognized by 88% of sera from Dengue NS1+ patients and show improved serotype specificity because they do not react with the antibodies present in seroconverted, PCR-serotyped DEN-4 infected patients.

Flavivirus Receptors: Diversity, Identity, and Cell Entry

Flaviviruses are emerging and re-emerging arthropod-borne pathogens responsible for significant mortality and morbidity worldwide. The genus comprises more than seventy small, positive-sense, single-stranded RNA viruses, which are responsible for a spectrum of human and animal diseases ranging in symptoms from mild, influenza-like infection to fatal encephalitis and haemorrhagic fever. Despite genomic and structural similarities across the genus, infections by different flaviviruses result in disparate clinical presentations. This review focusses on two haemorrhagic flaviviruses, dengue virus and yellow fever virus, and two neurotropic flaviviruses, Japanese encephalitis virus and Zika virus. We review current knowledge on host-pathogen interactions, virus entry strategies and tropism.

Development of peptide-based chemiluminescence enzyme immunoassay (CLEIA) for diagnosis of dengue virus infection in human

Dengue is the most prevalent mosquito-borne viral disease in tropical and subtropical regions worldwide. Since its clinical symptoms are non-specific and easily mistaken as other kinds of infection, laboratory diagnosis is required to confirm dengue infections. In this study, ten peptides (E1-E10) from the envelope protein of dengue virus (DENV) were first identified using bioinformatic tool. The screened peptides were then synthesized for the peptide-based chemiluminescence enzyme immunoassay (CLEIA). Two peptides, E1 and E7, were found as the best candidate antigen and therefore used as downstream application in the development of low-cost peptide-based anti-DENV immunoglobulin M antibodies (IgM) indirect CLEIA. 176 serum samples were used to study the presence of anti-DENV IgM antibodies to evaluate the diagnostic ability of IgM-CLEIA. Receiver operating characteristic curve (ROC) was used to estimate the diagnostic cut-off value. The sensitivity and the specificity reached 82.5% and 94.6% respectively when peptide E1 was used, but declined to 79.2% and 92.9% respectively when peptide E7 was used. Therefore, the combination of E1 and E7 was used to improve the sensitivity and the specificity to 85.0% and 96.4% respectively in 1.5 h assay time, providing a potentially practical use for the diagnosis of DENV infections in patients' serum.

Dengue viruses and promising envelope protein domain III-based vaccines

Dengue viruses are emerging mosquito-borne pathogens belonging to Flaviviridae family which are transmitted to humans via the bites of infected mosquitoes Aedes aegypti and Aedes albopictus. Because of the wide distribution of these mosquito vectors, more than 2.5 billion people are approximately at risk of dengue infection. Dengue viruses cause dengue fever and severe life-threatening illnesses as well as dengue hemorrhagic fever and dengue shock syndrome. All four serotypes of dengue virus can cause dengue diseases, but the manifestations are nearly different depending on type of the virus in consequent infections. Infection by any serotype creates life-long immunity against the corresponding serotype and temporary immunity to the others. This transient immunity declines after a while (6 months to 2 years) and is not protective against other serotypes, even may enhance the severity of a secondary heterotypic infection with a different serotype through a phenomenon known as antibody-depended enhancement (ADE). Although, it can be one of the possible explanations for more severe dengue diseases in individuals infected with a different serotype after primary infection. The envelope protein (E protein) of dengue virus is responsible for a wide range of biological activities, including binding to host cell receptors and fusion to and entry into host cells. The E protein, and especially its domain III (EDIII), stimulates host immunity responses by inducing protective and neutralizing antibodies. Therefore, the dengue E protein is an important antigen for vaccine development and diagnostic purposes. Here, we have provided a comprehensive review of dengue disease, vaccine design challenges, and various approaches in dengue vaccine development with emphasizing on newly developed envelope domain III-based dengue vaccine candidates.

Production of dengue virus envelope protein domain III-based antigens in tobacco chloroplasts using inducible and constitutive expression systems

Dengue fever is a disease in many parts of the tropics and subtropics and about half the world's population is at risk of infection according to the World Health Organization. Dengue is caused by any of the four related dengue virus serotypes DEN-1, -2, -3 and -4, which are transmitted to people by Aedes aegypti mosquitoes. Currently there is only one vaccine (Dengvaxia(®)) available (limited to a few countries) on the market since 2015 after half a century's intensive efforts. Affordable and accessible vaccines against dengue are hence still urgently needed. The dengue envelop protein domain III (EDIII), which is capable of eliciting serotype-specific neutralizing antibodies, has become the focus for subunit vaccine development. To contribute to the development of an accessible and affordable dengue vaccine, in the current study we have used plant-based vaccine production systems to generate a dengue subunit vaccine candidate in tobacco. Chloroplast genome engineering was applied to express serotype-specific recombinant EDIII proteins in tobacco chloroplasts using both constitutive and ethanol-inducible expression systems. Expression of a tetravalent antigen fusion construct combining EDIII polypeptides from all four serotypes was also attempted. Transplastomic EDIII-expressing tobacco lines were obtained and homoplasmy was verified by Southern blot analysis. Northern blot analyses showed expression of EDIII antigen-encoding genes. EDIII protein accumulation levels varied for the different recombinant EDIII proteins and the different expression systems, and reached between 0.8 and 1.6 % of total cellular protein. Our study demonstrates the suitability of the chloroplast compartment as a production site for an EDIII-based vaccine candidate against dengue fever and presents a Gateway(®) plastid transformation vector for inducible transgene expression.

Production of recombinant nonstructural 1 protein in Escherichia coli for early detection of Japanese encephalitis virus infection

Japanese encephalitis is a major public health problem in South-East Asia and Western Pacific countries. The recombinant nonstructural 1 (rNS1) protein of Japanese encephalitis virus is a potential diagnostic as well as vaccine candidate. Developments of cost-effective and simple culture media as well as appropriate culture conditions are generally favourable for large-scale production of recombinant proteins. The effects of medium composition and cultivation conditions on the production of rNS1 protein were investigated in shake flask culture as well as batch cultivation of Escherichia coli. Further, the fed-batch process was also carried out for high cell density cultivation (HCDC) of E. coli expressing rNS1 protein. Isopropyl-β-d-thiogalactopyranoside (IPTG) was used to induce the expression of rNS1 protein at ∼ 13 g dry cell weight per litre of culture. The final dry cell weight after fed-batch cultivation was ∼ 17 g l(-1) . The Inclusion bodies were isolated and purified through affinity chromatography to give a final product yield of ∼ 142 mg l(-1) . The reactivity of purified protein was confirmed by Western blotting and Enzyme linked immunosorbent assay. These results show that rNS1 protein may be used as a diagnostic reagent or for further prophylactic studies. This approach of producing rNS1 protein in E. coli with high yield may also offer promising method for production of other viral recombinant proteins.