Virus-like particle secretion and genotype-dependent immunogenicity of dengue virus serotype 2 DNA vaccine

Evaluation of the inhibitory potency of anti-dengue phytocompounds against DENV-2 NS2B-NS3 protease: virtual screening, ADMET profiling and molecular dynamics simulation investigations

Dengue fever has been a worldwide concern, with 50-100 million new infections each year mainly due to five different serotypes of the Dengue virus (DENV). Designing a perfect anti-dengue agent that can inhibit all the serotypes by distinguishing antigenic differences is quite difficult. Previous anti-dengue researches have included chemical compounds screening against DENV enzymes. The ongoing analysis is meant for investigation of the plant-based compounds as antagonistic to DENV-2 focusing on the specific NS2B-NS3Pro target, a trypsin like serine protease that cuts the DENV polyprotein into separate proteins crucial for viral reproduction. Initially, a virtual library of more than 130 phytocompounds was prepared from previously published reports of plants with anti-dengue properties, which were then virtually screened and shortlisted against the WT, H51N and S135A mutant of DENV-2 NS2B-NS3Pro. The three top-most compounds were viewed as Gallocatechin (GAL), Flavokawain-C (FLV), and Isorhamnetin (ISO) showing docking scores of -5.8, -5.7, -5.7 kcal/mol for WT, -7.5, -6.8, -7.6 kcal/mol for the H51N, and -6.9, -6.5, -6.1 kcal/mol for the S135A mutant protease, respectively. 100 ns long MD simulations and MM-GBSA based free energy calculations were performed on the NS2B-NS3Pro complexes to witness the relative binding affinity of the compounds and favourable molecular interactions network. A comprehensive analysis of the study reveals some promising outcomes with ISO as the topmost compound with favourable pharmacokinetic properties for the WT and mutants (H51N and S135A) as well, suggesting as a novel anti-NS2B-NS3Pro agent with better adapting characters in both the mutants.Communicated by Ramaswamy H. Sarma.

Investigating Lycotoxin-An1a (An1a), a defense antiviral peptide from Alopecosa nagpag venom as prospective anti-dengue agent against DENV-2 NS2B-NS3 protease

Dengue fever is a global health concern with no effective therapy. Screening synthetic chemicals, animal-originated compounds, and phytocompounds against Dengue virus (DENV) targets has failed to find dengue antivirals. The current study examines animal drugs as antagonists against NS2B-NS3Pro, one of DENV's most promising therapeutic targets for dengue fever. Antiviral-Lycotoxin-An1a (An1a), a defence antiviral peptide isolated from the venom of Alopecosa nagpag, a toxic spider. Based on prior in vitro research, it was discovered that the venom peptide suppresses the action of DENV-2 NS2B-NS3Pro. An1a peptide with NS2B-NS3Pro wild type (WT) and two mutants (H51N and S135A) was tested for anti-dengue characteristics using in silico analysis. The WT NS2B-NS3Pro has a catalytic triad of His51, Asp75, and Ser135 in the active site, but the mutants have N51 instead of His51 and Ala135 instead of Ser135. The dynamic sites of the three proteases (WT, H51N, S135A) and the peptide toxin (An1a) were taken into account to achieve molecular docking of An1a with WT NS2B-NS3Pro in conjunction with H51N and S135A. Cluspro-2 performs rigid-flexible docking to predict peptide binding affinity, effectiveness, and inhibitory consistency. Since the ligand had a higher binding affinity, docking score, and molecular interaction network, MD simulations and MM-GBSA free energy calculations were used to investigate the stability of the three protein-peptide complexes. The computer-aided screening and manufacture of spider venom-based anti-dengue medicines yielded intriguing results in the preliminary studies. This study is significant in defining the ideal therapeutic candidate against dengue infections.

Antibodies from dengue patients with prior exposure to Japanese encephalitis virus are broadly neutralizing against Zika virus

Exposure to multiple mosquito-borne flaviviruses within a lifetime is not uncommon; however, how sequential exposures to different flaviviruses shape the cross-reactive humoral response against an antigen from a different serocomplex has yet to be explored. Here, we report that dengue-infected individuals initially primed with the Japanese encephalitis virus (JEV) showed broad, highly neutralizing potencies against Zika virus (ZIKV). We also identified a rare class of ZIKV-cross-reactive human monoclonal antibodies with increased somatic hypermutation and broad neutralization against multiple flaviviruses. One huMAb, K8b, binds quaternary epitopes with heavy and light chains separately interacting with overlapping envelope protein dimer units spanning domains I, II, and III through cryo-electron microscopy and structure-based mutagenesis. JEV virus-like particle immunization in mice further confirmed that such cross-reactive antibodies, mainly IgG3 isotype, can be induced and proliferate through heterologous dengue virus (DENV) serotype 2 virus-like particle stimulation. Our findings highlight the role of prior immunity in JEV and DENV in shaping the breadth of humoral response and provide insights for future vaccination strategies in flavivirus-endemic countries.

Targeting the DENV NS2B-NS3 protease with active antiviral phytocompounds: structure-based virtual screening, molecular docking and molecular dynamics simulation studies

Dengue fever has been a global health concern. Mitigation is a challenging problem due to non-availability of workable treatments. The most difficult objective is to design a perfect anti-dengue agent capable of inhibiting infections caused by all four serotypes. Various tactics have been employed in the past to discover dengue antivirals, including screening of chemical compounds against dengue virus enzymes. The objective of the current study is to investigate phytocompounds as anti-dengue remedies that target the non-structural 2B and non-structural 3 protease (NS2B-NS3^pro), a possible therapeutic target for dengue fever. Initially, 300 + antiviral phytocompounds were collected from Duke’s phytochemical and ethnobotanical database and 30 phytocompounds with anti-dengue properties were identified from previously reported studies, which were virtually screened against NS2B-NS3^pro using molecular docking and toxicity evaluation. The top five most screened ligands were naringin, hesperidin, gossypol, maslinic acid and rhodiolin with binding affinities of − 8.7 kcal/mol, − 8.5 kcal/mol, − 8.5 kcal/mol, − 8.5 kcal/mol and − 8.1 kcal/mol, respectively. The finest docked compounds complexed with NS2B-NS3^pro were subjected for molecular dynamics (MD) simulations and binding free energy estimations through molecular mechanics generalized born surface area–based calculations. The results of the study are intriguing in the context of computer-aided screening and the binding affinities of the phytocompounds, proposing maslinic acid (MAS) as a potent bioactive antiviral for the development of phytocompound-based anti-dengue agent.

DENV-3 precursor membrane (prM) glycoprotein enhances E protein immunogenicity and confers protection against DENV-2 infections in a murine model

To improve a DNA vaccine containing the truncated dengue virus serotype 2 (DENV-2) envelope (E) protein and evaluate the influence of precursor membrane (prM) glycoprotein polymorphism on E protein immunogenicity, two vaccine candidates have been constructed by upstream insertion of the DENV-2 and DENV-3 prM genes into the DENV-2 E gene, named pCID2EtD2prM and pCID2EtD3prM, respectively. Both constructs were able to induce antibody production, which were neutralizing against DENV-2 in a murine model. Splenocytes of immunized groups, when challenged with virus, demonstrated Th1 cytokine pattern and proliferation, in addition to the increase of specific T cells. Vaccine candidates pCID2EtD2prM and pCID2EtD3prM confer 70% and 90% protection against DENV-2, respectively. The pCID2EtD3prM plasmid conferred only 40% protection in the lethal challenge with DENV-2. The results demonstrate that DENV-3 prM has a greater influence on the immunogenicity of the E protein and, probably due to its role as a chaperone, these results may be related to the correct folding and, consequently, an increase in the presentation efficiency of produced transcripts.

Plant-made dengue virus-like particles produced by co-expression of structural and non-structural proteins induce a humoral immune response in mice

Dengue virus (DENV) is an emerging threat causing an estimated 390 million infections per year. Dengvaxia, the only licensed vaccine, may not be adequately safe in young and seronegative patients; hence, development of a safer, more effective vaccine is of great public health interest. Virus-like particles (VLPs) are a safe and very efficient vaccine strategy, and DENV VLPs have been produced in various expression systems. Here, we describe the production of DENV VLPs in Nicotiana benthamiana using transient expression. The co-expression of DENV structural proteins (SP) and a truncated version of the non-structural proteins (NSPs), lacking NS5 that contains the RNA-dependent RNA polymerase, led to the assembly of DENV VLPs in plants. These VLPs were comparable in appearance and size to VLPs produced in mammalian cells. Contrary to data from other expression systems, expression of the protein complex prM-E was not successful, and strategies used in other expression systems to improve the VLP yield did not result in increased yields in plants but, rather, increased purification difficulties. Immunogenicity assays in BALB/c mice revealed that plant-made DENV1-SP + NSP VLPs led to a higher antibody response in mice compared with DENV-E domain III displayed inside bluetongue virus core-like particles and a DENV-E domain III subunit. These results are consistent with the idea that VLPs could be the optimal approach to creating candidate vaccines against enveloped viruses.

3,5-Bis((E)-4-methoxybenzylidene)-1-(2-morpholinoethyl)piperidin-4-one

The 3,5-bis((E)-4-methoxybenzylidene)-1-(2-morpholinoethyl)piperidin-4-one (3) compound was synthesized by a two-step reaction with 92% yield. The chemical structure of compound 3 was confirmed by IR, NMR, and mass spectrometry. The title compound was screened for its anti-dengue activity against DENV2 NS2B-NS3 protease and showed 39.09% inhibitory activity at 200 µg/mL.

Recent Advances in the Development of Virus-Like Particle-Based Flavivirus Vaccines

Flaviviruses include several medically important viruses, such as Zika virus (ZIKV), Dengue virus (DENV), West Nile virus (WNV) and Japanese encephalitis virus (JEV). They have expanded in geographic distribution and refocused international attention in recent years. Vaccination is one of the most effective public health strategies for combating flavivirus infections. In this review, we summarized virus-like particle (VLP)-based vaccines against the above four mentioned flaviviruses. Potential strategies to improve the efficacy of VLP-based flavivirus vaccines were also illustrated. The applications of flavivirus VLPs as tools for viral detection and antiviral drug screening were finally proposed.

Cross-reactivity reduced dengue virus 2 vaccine has no cross-protection against heterotypic dengue viruses

Aim: This study assessed how prime-boost strategies influence the immunogenicity of a cross-reactivity reduced dengue virus 2 vaccine (DENV-2 RD). Materials & methods: Mice were immunized with DENV-2 RD vaccines in a heterologous DNA and virus-like particle (VLP) prime-boost. Elicited antibodies were analyzed for neutralization and protective efficacy against four DENV serotypes. Results: DENV-2 RD DNA-VLP had induced higher and broader levels of total IgG and neutralizing antibodies with statistically significant IgG titers against DENV-2 and -3. Only pups of DENV-2 RD DNA-VLP immunized female mice were fully protected against homotypic DENV challenge and partially protected (60% survival rate) against heterotypic DENV-3 lethal challenge. Conclusion: DENV-2 RD vaccine requires a multivalent format to effectively elicit a balanced and protective immunity across all four DENV serotypes.

Dengue proteins with their role in pathogenesis, and strategies for developing an effective anti-dengue treatment: A review

Dengue virus is an arbovirus belonging to class Flaviviridae Its clinical manifestation ranges from asymptomatic to extreme conditions (dengue hemorrhagic fever/dengue shock syndrome). A lot of research has been done on this ailment, yet there is no effective treatment available for the disease. This review provides the systematic understanding of all dengue proteins, role of its structural proteins (C-protein, E-protein, prM) in virus entry, assembly, and secretion in host cell, and nonstructural proteins (NS1, NS2a, NS2b, NS3, NS4a, NS4b, and NS5) in viral assembly, replication, and immune evasion during dengue progression and pathogenesis. Furthermore, the review has highlighted the controversies related to the only commercially available dengue vaccine, that is, Dengvaxia, and the risk associated with it. Lastly, it provides an insight regarding various approaches for developing an effective anti-dengue treatment.

Detection of Dengue viruses among febrile patients in Lagos, Nigeria and phylogenetics of circulating Dengue serotypes in Africa

Dengue fever, a mosquito borne viral disease, is caused by Dengue virus. This virus and its vector is endemic in most tropical countries including Nigeria. Dengue presents with febrile symptoms and is a major cause of morbidity and mortality in affected countries. The infection presently has no licensed drugs and vaccine is only available for previously exposed individuals. Despite the endemicity of Dengue in Nigeria, very few studies have identified circulating Dengue genotypes in the country. There is also sparse information on the occurrence, distribution and temporal patterns of circulating dengue virus serotypes as well as genotypes in Africa. This situation creates barriers to effective control of the infection in the continent. This study identified Dengue serotypes and genotypes among febrile patients in two health centers in Lagos, Nigeria. Phylogenetic analysis of Dengue sequences previously collected from African countries and submitted to GenBank database from 1944 till date was also performed. One hundred and thirty febrile persons were recruited for the study between April and August 2018. Eleven (8.5%) persons were Dengue virus positive. Dengue virus serotypes 1 (genotype I) and 3 (genotype I) were identified as actively circulating in Lagos, Nigeria. DENV 1 genotype V, DENV 2 cosmopolitan genotype and DENV 3 genotype III has over the years been the predominant circulating Dengue strains in Africa. Relative genotypic stability of circulating Dengue serotypes in Africa occurred over the past five decades. This may be due to limited investigations on circulating Dengue serotypes among asymptomatic individuals in the region as most studies focused on disease outbreaks and imported cases. There is the need to describe circulating Dengue genotypes in northern Africa, southern Africa as well as among asymptomatic individuals in other parts of Africa as this will provide further information on the diversity of Dengue genotypes circulating in the region.

Production and Purification of Dengue Virus-like Particles from COS-1 Cells

Non-infectious virus-like particles (VLPs) containing dengue virus (DENV) pre-membrane (prM) and envelope (E) proteins have been demonstrated to be highly immunogenic and can be used as a potential vaccine candidate as well as a tool for serodiagnostic assays. Successful application of VLPs requires abundant, and high-purity production methods. Here, we describe a robust protocol for producing DENV VLPs from transiently-transformed or stable COS-1 cells and further provide an easily adaptable antigen purification method by sucrose gradient centrifugation.

Thioguanine-based DENV-2 NS2B/NS3 protease inhibitors: Virtual screening, synthesis, biological evaluation and molecular modelling

Dengue virus Type 2 (DENV-2) is predominant serotype causing major dengue epidemics. There are a number of studies carried out to find its effective antiviral, however to date, there is still no molecule either from peptide or small molecules released as a drug. The present study aims to identify small molecules inhibitor from National Cancer Institute database through virtual screening. One of the hits, D0713 (IC₅₀ = 62 μM) bearing thioguanine scaffold was derivatised into 21 compounds and evaluated for DENV-2 NS2B/NS3 protease inhibitory activity. Compounds 18 and 21 demonstrated the most potent activity with IC₅₀ of 0.38 μM and 16 μM, respectively. Molecular dynamics and MM/PBSA free energy of binding calculation were conducted to study the interaction mechanism of these compounds with the protease. The free energy of binding of 18 calculated by MM/PBSA is -16.10 kcal/mol compared to the known inhibitor, panduratin A (-11.27 kcal/mol), which corroborates well with the experimental observation. Results from molecular dynamics simulations also showed that both 18 and 21 bind in the active site and stabilised by the formation of hydrogen bonds with Asn174.

Epitope resurfacing on dengue virus-like particle vaccine preparation to induce broad neutralizing antibody

Dengue fever is caused by four different serotypes of dengue virus (DENV) which is the leading cause of worldwide arboviral diseases in humans. Virus-like particles (VLPs) containing flavivirus prM/E proteins have been demonstrated to be a potential vaccine candidate; however, the structure of dengue VLP is poorly understood. Herein VLP derived from DENV serotype-2 were engineered becoming highly matured (mD2VLP) and showed variable size distribution with diameter of ~31 nm forming the major population under cryo-electron microscopy examination. Furthermore, mD2VLP particles of 31 nm diameter possess a T = 1 icosahedral symmetry with a groove located within the E-protein dimers near the 2-fold vertices that exposed highly overlapping, cryptic neutralizing epitopes. Mice vaccinated with mD2VLP generated higher cross-reactive (CR) neutralization antibodies (NtAbs) and were fully protected against all 4 serotypes of DENV. Our results highlight the potential of ‘epitope-resurfaced’ mature-form D2VLPs in inducing quaternary structure-recognizing broad CR NtAbs to guide future dengue vaccine design.

An Envelope-Modified Tetravalent Dengue Virus-Like-Particle Vaccine Has Implications for Flavivirus Vaccine Design

Dengue viruses (DENV) infect 50 to 100 million people each year. The spread of DENV-associated infections is one of the most serious public health problems worldwide, as there is no widely available vaccine or specific therapeutic for DENV infections. To address this, we developed a novel tetravalent dengue vaccine by utilizing virus-like particles (VLPs). We created recombinant DENV1 to -4 (DENV1-4) VLPs by coexpressing precursor membrane (prM) and envelope (E) proteins, with an F108A mutation in the fusion loop structure of E to increase the production of VLPs in mammalian cells. Immunization with DENV1-4 VLPs as individual, monovalent vaccines elicited strong neutralization activity against each DENV serotype in mice. For use as a tetravalent vaccine, DENV1-4 VLPs elicited high levels of neutralization activity against all four serotypes simultaneously. The neutralization antibody responses induced by the VLPs were significantly higher than those with DNA or recombinant E protein immunization. Moreover, antibody-dependent enhancement (ADE) was not observed against any serotype at a 1:10 serum dilution. We also demonstrated that the Zika virus (ZIKV) VLP production level was enhanced by introducing the same F108A mutation into the ZIKV envelope protein. Taken together, these results suggest that our strategy for DENV VLP production is applicable to other flavivirus VLP vaccine development, due to the similarity in viral structures, and they describe the promising development of an effective tetravalent vaccine against the prevalent flavivirus.IMPORTANCE Dengue virus poses one of the most serious public health problems worldwide, and the incidence of diseases caused by the virus has increased dramatically. Despite decades of effort, there is no effective treatment against dengue. A safe and potent vaccine against dengue is still needed. We developed a novel tetravalent dengue vaccine by using virus-like particles (VLPs), which are noninfectious because they lack the viral genome. Previous attempts of other groups to use dengue VLPs resulted in generally poor yields. We found that a critical amino acid mutation in the envelope protein enhances the production of VLPs. Our tetravalent vaccine elicited potent neutralizing antibody responses against all four DENV serotypes. Our findings can also be applied to vaccine development against other flaviviruses, such as Zika virus or West Nile virus.

Functional properties of DENV EDIII‑reactive antibodies in human DENV‑1‑infected sera and rabbit antiserum to EDIII

The envelope domain III (EDIII) of the dengue virus (DENV) has been confirmed to be involved in receptor binding. It is the target of specific neutralizing antibodies, and is considered to be a promising subunit dengue vaccine candidate. However, several recent studies have shown that anti‑EDIII antibodies contribute little to the neutralizing or enhancing ability of human DENV‑infected serum. The present study involved an analysis of the neutralization and antibody‑dependent enhancement (ADE) activities of EDIII‑reactive antibodies in human convalescent sera from patients with primary DENV‑1 infection and rabbit antiserum immunized with recombinant DENV‑1 EDIII protein. The results indicated that serum neutralization was not associated with titres of EDIII‑binding antibodies in the human DENV‑1‑infected sera. The depletion of anti‑EDIII antibodies from these serum samples revealed that the anti‑EDIII antibodies of the patients contributed little to neutralization and ADE. However, the EDIII‑reactive antibodies from the rabbit antiserum exhibited protective abilities of neutralization at a high dilution (~1:50,000) and ADE at a low dilution (~1:5,000) for the homotypic DENV infection. Notably, the rabbit antiserum displayed ADE activity only at a dilution of 1:40 for the heterotypic virus infection, which suggests that EDIII‑reactive antibodies may be safe in secondary infection with heterotypic viruses. These results suggest that DENV EDIII is not the predominant antigen of the DENV infection process; however, purified or recombinant DENV EDIII may be used as a subunit vaccine to provoke an effective and safe antibody response.

Secretion of dengue virus envelope protein ectodomain from mammalian cells is dependent on domain II serotype and affects the immune response upon DNA vaccination

Dengue virus (DENV) is currently among the most important human pathogens and affects millions of people throughout the tropical and subtropical regions of the world. Although it has been a World Health Organization priority for several years, there is still no efficient vaccine available to prevent infection. The envelope glycoprotein (E), exposed on the surface on infective viral particles, is the main target of neutralizing antibodies. For this reason it has been used as the antigen of choice for vaccine development efforts. Here we show a detailed analysis of factors involved in the expression, secretion and folding of E ectodomain from all four DENV serotypes in mammalian cells, and how this affects their ability to induce neutralizing antibody responses in DNA-vaccinated mice. Proper folding of E domain II (DII) is essential for efficient E ectodomain secretion, with DIII playing a significant role in stabilizing soluble dimers. We also show that the level of protein secreted from transfected cells determines the strength and efficiency of antibody responses in the context of DNA vaccination and should be considered a pivotal feature for the development of E-based DNA vaccines against DENV.

Dengue E Protein Domain III-Based DNA Immunisation Induces Strong Antibody Responses to All Four Viral Serotypes

Dengue virus (DENV) infection is a major emerging disease widely distributed throughout the tropical and subtropical regions of the world affecting several millions of people. Despite constants efforts, no specific treatment or effective vaccine is yet available. Here we show a novel design of a DNA immunisation strategy that resulted in the induction of strong antibody responses with high neutralisation titres in mice against all four viral serotypes. The immunogenic molecule is an engineered version of the domain III (DIII) of the virus E protein fused to the dimerising CH3 domain of the IgG immunoglobulin H chain. The DIII sequences were also codon-optimised for expression in mammalian cells. While DIII alone is very poorly secreted, the codon-optimised fusion protein is rightly expressed, folded and secreted at high levels, thus inducing strong antibody responses. Mice were immunised using gene-gun technology, an efficient way of intradermal delivery of the plasmid DNA, and the vaccine was able to induce neutralising titres against all serotypes. Additionally, all sera showed reactivity to a recombinant DIII version and the recombinant E protein produced and secreted from mammalian cells in a mono-biotinylated form when tested in a conformational ELISA. Sera were also highly reactive to infective viral particles in a virus-capture ELISA and specific for each serotype as revealed by the low cross-reactive and cross-neutralising activities. The serotype specific sera did not induce antibody dependent enhancement of infection (ADE) in non-homologous virus serotypes. A tetravalent immunisation protocol in mice showed induction of neutralising antibodies against all four dengue serotypes as well.

Dengue disease is a mosquito-borne viral infection caused by Dengue virus (DENV), one of the most important human pathogens worldwide. DENV infection produces a systemic disease with a broad symptomatic spectrum ranging from mild febrile illness (Dengue Fever, DF) to severe haemorrhagic manifestations (Dengue Haemorrhagic fever and Dengue Shock Syndrome, DHF and DSS respectively). To date there is no vaccine available to prevent dengue disease. We show here a strategy of immunisation, tested in mice, that elicits a strong immune response against the four different DENV serotypes. The novelties presented in our work open the way to the development of an efficient vaccine accessible to developing countries.

Scanning mutagenesis studies reveal a potential intramolecular interaction within the C-terminal half of dengue virus NS2A involved in viral RNA replication and virus assembly and secretion

The NS2A protein of dengue virus (DENV) has eight predicted transmembrane segments (pTMSs; pTMS1 to pTMS8). NS2A has been shown to participate in RNA replication, virion assembly, and the host antiviral response. However, the role of the amino acid residues within the pTMS regions of NS2A during the virus life cycle is poorly understood. In the study described here, we explored the function of DENV NS2A by introducing a series of double or triple alanine substitutions into the C-terminal half (pTMS4 to pTMS8) of NS2A in the context of a DENV infectious clone or subgenomic replicon. Fourteen (8 within pTMS8) of 35 NS2A mutants displayed a lethal phenotype due to impairment of RNA replication by a replicon assay. Three NS2A mutants with mutations within pTMS7, the CM20, CM25, and CM27 mutants, displayed similar phenotypes, low virus yields (>100-fold reduction), wild-type-like replicon activity, and low infectious virus-like particle yields by transient trans-packaging experiments, suggesting a defect in virus assembly and secretion. The sequencing of revertant viruses derived from CM20, CM25, and CM27 mutant viruses revealed a consensus reversion mutation, leucine (L) to phenylalanine (F), at codon 181 within pTMS7. The introduction of an L181F mutation into a full-length NS2A mutant, i.e., the CM20, CM25, and CM27 constructs, completely restored wild-type infectivity. Notably, L181F also substantially rescued the other severely RNA replication-defective mutants with mutations within pTMS4, pTMS6, and pTMS8, i.e., the CM2, CM3, CM13, CM31, and CM32 mutants. In conclusion, the results revealed the essential roles of pTMS4 to pTMS8 of NS2A in RNA replication and/or virus assembly and secretion. The intramolecular interaction between pTMS7 and pTMS4, pTMS6, or pTMS8 of the NS2A protein was also implicated.

IMPORTANCE

The reported characterization of the C-terminal half of dengue virus NS2A is the first comprehensive mutagenesis study to investigate the function of flavivirus NS2A involved in the steps of the virus life cycle. In particular, detailed mapping of the amino acid residues within the predicted transmembrane segments (pTMSs) of NS2A involved in RNA replication and/or virus assembly and secretion was performed. A revertant genetics study also revealed that L181F within pTMS7 is a consensus reversion mutation that rescues both RNA replication-defective and virus assembly- and secretion-defective mutants with mutations within the other three pTMSs of NS2A. Collectively, these findings elucidate the role played by NS2A during the virus life cycle, possibly through the intricate intramolecular interaction between pTMS7 and other pTMSs within the NS2A protein.