Structural biology of Zika virus and other flaviviruses

Design, synthesis and biological evaluation of dapsone derivatives with broad-spectrum antiviral activity

Inhibition of STAT2 degradation has emerged as a promising strategy for flaviviruses. The NS5 protein of the ZIKV and DENV-2 inhibits the IFN-Ⅰ antiviral response by degrading STAT2, thereby evading the host's immune defense. Therefore, the development of novel agents capable of inhibiting STAT2 degradation via targeted modulation constitutes a pivotal therapeutic strategy for controlling viral infections. In this study, HEK293TSTAT2-mCherry-Flag/rtTA-HA-NS5 cells were used as reporter tools. Through screening the ZINC drug-like database, the lead compound ZINC000060514583 was obtained and structurally modified to yield the optimized compounds SMU-1k, which significantly inhibited the degradation of STAT2. We verified its activity against ZIKV and DENV-2 through Western blotting, RT-qPCR, plaque formation assays, and immunofluorescence experiments. The results showed that SMU-1k significantly inhibited the expression of NS5 protein and restored the level of STAT2 to a certain extent. Additionally, the EC50 values of SMU-1k against ZIKV and DENV-2 were 7.08 ± 0.06 μM and 3.96 ± 0.11 μM, respectively, which helped to alleviate the cytopathic effects caused by ZIKV and DENV-2 infection. Here, we have successfully characterized a novel small-molecule compound that selectively blocks STAT2 proteasomal degradation while exhibiting potent dual antiviral efficacy against both ZIKV and DENV-2, thereby revealing a promising lead candidate for developing broad-spectrum antiviral therapeutics.

The HAVCR1-centric host factor network drives Zika virus vertical transmission

Zika virus (ZIKV) vertical transmission results in devastating congenital malformations and pregnancy complications; however, the specific receptor and host factors facilitating ZIKV maternal-fetal transmission remain elusive. Here, we employ a genome-wide CRISPR screening and identify multiple placenta-intrinsic factors modulating ZIKV infection. Our study unveils that hepatitis A virus cellular receptor 1 (HAVCR1) serves as a primary receptor governing ZIKV entry in placental trophoblasts. The GATA3-HAVCR1 axis regulates heterogeneous cell tropism in the placenta. Notably, placenta-specific Havcr1 deletion in mice significantly impairs ZIKV transplacental transmission and associated adverse pregnancy outcomes. Mechanistically, the immunoglobulin variable-like domain of HAVCR1 binds to ZIKV via domain III of envelope protein and virion-associated phosphatidylserine. Proteomic profiling and function analyses reveal that AP2S1 cooperates with HAVCR1 for ZIKV internalization through clathrin-mediated endocytosis. Overall, our work underscores the pivotal role of HAVCR1 in mediating ZIKV vertical transmission and highlights a therapeutic target for alleviating congenital Zika syndrome.

Virus-like particle vaccine with authentic quaternary epitopes protects against Zika virus-induced viremia and testicular damage

Zika virus (ZIKV) caused unprecedented outbreaks in South America and the Caribbean in 2015-2016, leading primarily to a series of abnormalities in neonates termed congenital Zika syndrome. The threat of ZIKV reemergence has seen the development of multiple ZIKV vaccines that are at the preclinical stage or in early-stage clinical trials. Herein, we describe a pathway to the development of ZIKV vaccines generated using a baculovirus-insect cell expression system, which is widely applied for the manufacture of biologics for human use. Virus-like particle (VLP) vaccines comprising CprME and subviral particle (SVP) vaccines comprising prME were evaluated for their ability to mediate protection against ZIKV challenge in Ifnar1-/- mice. Initial attempts resulted in VLP and SVP vaccines that failed to present quaternary epitopes and did not provide effective protection. To improve the SVP vaccine, two modifications were introduced: firstly, an alanine to cysteine substitution (A264C) in the E domain II region to promote the formation of stabilized E homodimers and, secondly, the use of Spodoptera frugiperda Sf9 insect cells that had been adapted to grow and produce vaccine at a neutral pH of 7. E homodimers largely retain their pre-fusion conformation at pH 7, which is a requirement for the induction of effective neutralizing antibody responses. The stabilized SVP-A26C vaccine induced high levels of neutralizing antibodies and protected male Ifnar1-/- mice against viremia and testicular damage. Our study reiterates the need to present the immune system with E dimers arranged in authentic quaternary conformations and provides a scalable production method for this novel ZIKV vaccine.IMPORTANCEWe describe the generation of a subviral particle (SVP) vaccine comprising prME proteins of ZIKV, with an envelope protein substitution, A264C, that stabilizes E dimer formation. The SVP vaccine was produced in a novel Sf9 insect cell line adapted to grow in suspension at pH 7. The study highlights the importance of challenge experiments to ascertain whether the responses induced by an experimental vaccine actually mediate protection against virus infection and disease. The study also reiterates the contention that effective flavivirus vaccines need to present the immunogen in an authentic tertiary and quaternary structure with a pre-fusion conformation.

Seropositivity to Dengue, Zika, Yellow Fever, and West Nile Viruses in Senegal, West Africa

West Africa serves as a critical region for the co-circulation of mosquito-borne flaviviruses, which often precipitate sporadic outbreaks. This study investigated the seropositivity to dengue virus serotypes 1-4 (DENV-1-4), Zika virus (ZIKV), yellow fever virus (YFV), and West Nile virus (WNV) in three regions of Senegal: Sindia, Thies, and Kedougou. We retrospectively analyzed 470 serum samples for flavivirus immunoglobulin G (IgG) using a DENV-2 envelope (E) ELISA. Our findings revealed an overall flavivirus seroprevalence of 37.23%. Among the DENV-2 E IgG positive samples, the proportion of subjects with IgG to DENV-1-4, ZIKV, YFV, or WNV NS1 was 57.14%, 12.57%, 80.57%, and 17.14%, respectively, with 66.86% harboring neutralizing antibodies against two or more flaviviruses. We also identified that residents in Sindia (ZIKV, aOR, 9.428; 95% CI: 1.882-47.223 and WNV, aOR, 6.039; 95% CI: 1.855-19.658) and Kedougou (ZIKV, aOR, 7.487; 95% CI: 1.658-33.808 and WNV, aOR, 1.142; 95% CI: 0.412-3.164) were at significant risk for ZIKV and WNV exposure. This study underscores the complexity of flavivirus epidemiology in West Africa and the necessity for enhanced surveillance to inform public health strategies.

Zika virus inhibits cell death by inhibiting the expression of NLRP3 and A20

Zika virus (ZIKV) is associated with microcephaly in neonates and neurological disorders in adults. Chronic ZIKV infection has been identified in the testes, indicating that the virus can lead to prolonged illness, yet its pathogenesis remains poorly understood. Here, we found that ZIKV infection does not induce significant cell death in mouse macrophages despite the critical role that cell death plays in the antiviral immune response. Furthermore, we discovered that ZIKV infection impairs the activation of the NLPR3-dependent inflammasome and inhibits apoptosis. Consequently, we investigated the regulatory mechanism of the NLRP3 inflammasome and apoptosis in the context of ZIKV infection. Our results revealed significant reductions in the protein expression levels of NLRP3 and A20, attributable to post-transcriptional or translational effects during ZIKV infection. These findings suggest that ZIKV infection may disrupt cell death pathways, leading to its pathogenicity.IMPORTANCEZika virus (ZIKV), first isolated from a nonhuman primate in Africa in 1947, was relatively understudied until 2016. By then, ZIKV had already been reported in more than 20 countries and territories. The infection poses a significant risk, as it is associated with microcephaly in infants and neurological disorders in adults; however, the underlying mechanisms responsible for these severe outcomes remain unclear. In this study, we demonstrate that ZIKV infection significantly reduces the expression of NLRP3 and A20 proteins through post-transcriptional or translational processes, which leads to inhibited cell death. These findings are critical because cell death plays a vital role in the host's antiviral immune response. Our findings highlight how ZIKV infection compromises essential cell death pathways, raising serious concerns about its pathogenesis. A comprehensive understanding of this disruption is vital for developing targeted interventions to mitigate the virus' impact on public health.

Toll-like receptor response to Zika virus infection: progress toward infection control

Infection with the Zika virus (ZIKV) poses a threat to human health. An improved understanding of the host Toll-like receptor response, disease onset, and viral clearance in vivo and in vitro may lead to the development of therapeutic or prophylactic interventions against viral infections. Currently, no clinically approved ZIKV vaccine is available, highlighting the need for its development. In this study, we discuss the progress in the Zika vaccine, including advances in the use of Toll-like receptor agonists as vaccine adjuvants to enhance vaccine efficacy.

Intrauterine Zika Virus Infection: An Overview of the Current Findings

Zika virus (ZIKV) is a mosquito-borne flavivirus of the family Flaviviridae. The association between ZIKV and microcephaly was first described in Brazil in 2015. The risk of vertical transmission occurs in pregnant women with or without symptoms, and the risk of malformation appears to be worse when infection occurs in the first and second trimesters of pregnancy. The rate of vertical transmission varies from 26 to 65%, and not all fetuses develop malformations. The incidence of malformations resulting from transmission is uncertain, ranging from 6-8% in the US to 40% in Brazil. Congenital ZIKV syndrome is a set of clinical manifestations that can affect the fetus of a mother infected with ZIKV. The manifestations are broad and nonspecific, including microcephaly, subcortical calcifications, ocular changes, congenital contractures, early hypertension, and pyramidal and extrapyramidal signs. Other findings such as growth restriction and fetal miscarriage/death may also occur. Our aim in this article is to review the literature on mosquito transmission, clinical presentation, serologic diagnosis, intrauterine transmission, pre- and postnatal imaging diagnostic findings, and short- and long-term follow-up.

Phytomedical Properties of Carica papaya for Boosting Human Immunity Against Viral Infections

Carica papaya, a tropical fruit-bearing plant, has attracted significant attention for its diverse phytomedical properties and its ability to regulate both innate and adaptive immunity, making it a promising natural therapeutic agent. C. papaya is rich in bioactive compounds that play a multifaceted role in immunomodulation. These bioactive constituents have demonstrated efficacy not only against the dengue virus but also against other viral infections, including COVID-19 (Corona Virus Disease 2019), Human Immunodeficiency Virus (HIV), Zika virus, and others. The antiviral effects of C. papaya are achieved through its ability to enhance host immunity, mitigate inflammation, reduce oxidative stress, inhibit viral replication, and modulate immune responses. These mechanisms highlight its potential as a candidate for antiviral therapies, paving the way for further exploration of its pharmacological applications and promoting eco-friendly, accessible healthcare solutions for combating viral diseases. This review highlights the antiviral potential of C. papaya extracts in inhibiting viral replication and modulating immune responses, emphasizing the need for further studies and clinical trials to validate their efficacy against other medically significant viruses causing human diseases.

Advancements in dengue vaccines: A historical overview and pro-spects for following next-generation candidates

Dengue, caused by four serotypes of dengue viruses (DENV-1 to DENV-4), is the most prevalent and widely mosquito-borne viral disease affecting humans. Dengue virus (DENV) infection has been reported in over 100 countries, and approximately half of the world's population is now at risk. The paucity of universally licensed DENV vaccines highlights the urgent need to address this public health concern. Action and atten-tion to antibody-dependent enhancement increase the difficulty of vaccine development. With the worsen-ing dengue fever epidemic, Dengvaxia® (CYD-TDV) and Qdenga® (TAK-003) have been approved for use in specific populations in affected areas. However, these vaccines do not provide a balanced immune response to all four DENV serotypes and the vaccination cannot cover all populations. There is still a need to develop a safe, broad-spectrum, and effective vaccine to address the increasing number of dengue cases worldwide. This review provides an overview of the existing DENV vaccines, as well as potential candidates for future studies on DENV vaccine development, and discusses the challenges and possible solutions in the field.

The Zika virus NS5 protein binds HSP90 to suppress EGF-induced Akt signaling and trophoblast cell migration

Zika virus (ZIKV) infection during pregnancy can cause congenital Zika virus syndrome (CZV), including fetal growth restriction and death. In the developing placenta, trophoblast cells respond to epidermal growth factor (EGF) to migrate into the decidua to facilitate implantation and fetal development. EGF activates the Akt protein kinase, a master regulator of trophoblast cell migration. Akt signaling and stability are dependent on heat shock protein 90 (HSP90), which mediates the maturation of proteins necessary for EGF/Akt signaling. Here we show that ZIKV infection inhibits EGF-mediated Akt activation and downstream signaling to suppress trophoblast migration. The ZIKV non-structural protein 5 (NS5) is sufficient to inhibit trophoblast migration through its binding interaction with HSP90, leading to suppression of Akt phosphorylation and inhibition of EGF-induced trophoblast migration. Thus, ZIKV NS5/HSP90 interactions play a key role in disruption of trophoblast function, revealing an underlying cause of improper placental development and fetal disease.

Identification of Benzothiophene-Derived Inhibitors of Flaviviruses by Targeting RNA-Dependent RNA Polymerase

Flaviviruses such as Dengue, West Nile, and Zika viruses are mosquito-borne RNA viruses that can cause serious diseases in humans. To develop effective drugs for treating these viruses' infections, we create a new approach for developing common or shared drugs that may work for several different viral species of flaviviruses. It is based on the conserved RNA-dependent RNA polymerase (RdRp), which is the key enzyme for viral replication. We built up a common structure of RdRps (POLcon) from their consensus sequence. A conserved Triple-D structural motif was identified at the active site of POLcon that has been used for virtual compound screening. We have identified three inhibitors that have potent activities against Dengue, West Nile, and Zika viruses. All these three inhibitors are Benzothiophene derivatives. This is the first report of Benzothiophene-derived compounds as inhibitors for flaviviruses. Furthermore, our approach has provided a proof-of-concept that it is feasible to identify shared drugs for several different viral species of flaviviruses.

Key virulence factors responsible for differences in pathogenicity between clinically proven live-attenuated Japanese encephalitis vaccine SA14-14-2 and its pre-attenuated highly virulent parent SA14

Japanese encephalitis virus (JEV), a neuroinvasive and neurovirulent orthoflavivirus, can be prevented in humans with the SA14-14-2 vaccine, a live-attenuated version derived from the wild-type SA14 strain. To determine the viral factors responsible for the differences in pathogenicity between SA14 and SA14-14-2, we initially established a reverse genetics system that includes a pair of full-length infectious cDNAs for both strains. Using this cDNA pair, we then systematically exchanged genomic regions between SA14 and SA14-14-2 to generate 20 chimeric viruses and evaluated their replication capability in cell culture and their pathogenic potential in mice. Our findings revealed the following: (i) The single envelope (E) protein of SA14-14-2, which contains nine mutations (eight in the ectodomain and one in the stem region), is both necessary and sufficient to render SA14 non-neuroinvasive and non-neurovirulent. (ii) Conversely, the E protein of SA14 alone is necessary for SA14-14-2 to become highly neurovirulent, but it is not sufficient to make it highly neuroinvasive. (iii) The limited neuroinvasiveness of an SA14-14-2 derivative that contains the E gene of SA14 significantly increases (approaching that of the wild-type strain) when two viral nonstructural proteins are replaced by their counterparts from SA14: (a) NS1/1', which has four mutations on the external surface of the core β-ladder domain; and (b) NS2A, which has two mutations in the N-terminal region, including two non-transmembrane α-helices. In line with their roles in viral pathogenicity, the E, NS1/1', and NS2A genes all contribute to the enhanced spread of the virus in cell culture. Collectively, our data reveal for the first time that the E protein of JEV has a dual function: It is the master regulator of viral neurovirulence and also the primary initiator of viral neuroinvasion. After the initial E-mediated neuroinvasion, the NS1/1' and NS2A proteins act as secondary promoters, further amplifying viral neuroinvasiveness.

Membrane fusion by dengue virus: The first step

Flaviviruses include important human pathogens such as Dengue, Zika, West Nile, Yellow fever, Japanese encephalitis, and Tick-borne encephalitis viruses as well as some emerging viruses that affect millions of people worldwide. They fuse their membrane with the late endosomal one in a pH-dependent way and therefore the merging of the membranes is one of the main goals for obtaining new antivirals. The envelope E protein, a membrane fusion protein, is accountable for fusion and encompasses different domains involved in the fusion mechanism, including the fusion peptide segment. In this work we have used molecular dynamics to study the interaction of the distal end of domain II of the DENV envelope E protein with a membrane like the late endosomal membrane in order to observe the initiation of membrane fusion carried out by a number of trimers of the DENV envelope E protein interacting with a complex biomembrane and demonstrate its feasibility. Our results demonstrate the likelihood of membrane disorganization and pore formation by trimer complex organization, the amino acids responsible for such condition and the secondary structure arrangements needed for such fundamental process. At the same time, we define new targets of the envelope E protein sequence which could permit designing potent antiviral bioactive molecules.

A low pre-existing anti-NS1 humoral immunity to DENV is associated with microcephaly development after gestational ZIKV exposure

BACKGROUND

Gestational Zika virus (ZIKV) infection is associated with the development of congenital Zika syndrome (CZS), which includes microcephaly and fetal demise. The magnitude and quality of orthoflavivirus-specific humoral immunity have been previously linked to the development of CZS. However, the role of ZIKV NS1-specific humoral immunity in mothers and children with prenatal ZIKV exposure and CZS remains undefined. In addition, considering that most of the at-risk population lives in dengue virus (DENV)-endemic areas, it is not clear what is the association between pre-existing DENV NS1-specific humoral immunity and CZS.

METHODS

Here, we studied 328 mothers and children with a clinical diagnosis and seropositivity for ZIKV infection during pregnancy, included during the 2015-2016 ZIKV epidemic in Colombia. We also performed clinical evaluation and pediatric neurological follow-up. The relative levels of circulating NS1-specific IgM and IgG against ZIKV and DENV were evaluated in mothers and children, and the association with the development of microcephaly was analyzed.

RESULTS

DENV and ZIKV IgG-NS1 antibodies in pregnant women were placentally transferred, and this passage and its duration in children depended on the maternal levels of the antibodies. We reported that higher concentrations of pre-existing DENV, but not ZIKV IgG-NS1 antibodies, were associated with a reduced risk of CZS-related microcephaly. Also, we observed that the IgM-NS1 response in infants is long-term and has a minor association with poor outcomes.

CONCLUSIONS

The development of microcephaly in children prenatally exposed to ZIKV is associated with low plasma levels of placentally transferred, pre-existing DENV IgG-NS1 antibodies. These data are compatible with a protective role of anti-NS1 IgG antibodies against ZIKV infection during pregnancy and highlight the promising role of NS1 as an orthoflavivirus vaccine target in high-risk populations.

Comparison of Three Chimeric Zika Vaccine Prototypes Developed on the Genetic Background of the Clinically Proven Live-Attenuated Japanese Encephalitis Vaccine SA14-14-2

Zika virus (ZIKV) is a medically important mosquito-borne orthoflavivirus, but no vaccines are currently available to prevent ZIKV-associated disease. In this study, we compared three recombinant chimeric viruses developed as candidate vaccine prototypes (rJEV/ZIKVMR-766, rJEV/ZIKVP6-740, and rJEV/ZIKVPRVABC-59), in which the two neutralizing antibody-inducing prM and E genes from each of three genetically distinct ZIKV strains were used to replace the corresponding genes of the clinically proven live-attenuated Japanese encephalitis virus vaccine SA14-14-2 (rJEV). In WHO-certified Vero cells (a cell line suitable for vaccine production), rJEV/ZIKVP6-740 exhibited the slowest viral growth, formed the smallest plaques, and displayed a unique protein expression profile with the highest ratio of prM to cleaved M when compared to the other two chimeric viruses, rJEV/ZIKVMR-766 and rJEV/ZIKVPRVABC-59, as well as their vector, rJEV. In IFNAR-/- mice, an animal model of ZIKV infection, subcutaneous inoculation of rJEV/ZIKVP6-740 caused a low-level localized infection limited to the spleen, with no clinical signs of infection, weight loss, or mortality; in contrast, the other two chimeric viruses and their vector caused high-level systemic infections involving multiple organs, consistently leading to clear clinical signs of infection, rapid weight loss, and 100% mortality. Subsequently, subcutaneous immunization with rJEV/ZIKVP6-740 proved highly effective, offering complete protection against a lethal intramuscular ZIKV challenge 28 days after a single-dose immunization. This protection was specific to ZIKV prM/E and likely mediated by neutralizing antibodies targeting ZIKV prM/E. Therefore, our data indicate that the chimeric virus rJEV/ZIKVP6-740 is a highly promising vaccine prototype for developing a safe and effective vaccine for inducing neutralizing antibody-mediated protective immunity against ZIKV.

Identification and Evaluation of Natural Compounds as Potential Inhibitors of NS2B-NS3 Zika Virus Protease: A Computational Approach

The Zika virus (ZIKV), an arbovirus within the Flavivirus genus, is associated with severe neurological complications, including Guillain-Barré syndrome in affected individuals and microcephaly in infants born to infected mothers. With no approved vaccines or antiviral treatments available, there is an urgent need for effective therapeutic options. This study aimed to identify new natural compounds with inhibitory potential against the NS2B-NS3 protease (PDB ID: 5LC0), an essential enzyme in viral replication. An e-pharmacophore model was generated using a five-point (ADDRR) feature approach in the PHASE module of Schrodinger and used for the virtual screening of 26,689 natural compounds from the PubChem database. The screening yielded 14,277 prioritized compounds based on fitness scores, further refined through extra precision (XP) docking in GLIDE, resulting in 24 compounds. Eight top hits were selected following ADME analysis with SwissADME, and toxicity screening with ProTox-II identified four non-toxic lead candidates. Molecular dynamic simulations confirmed the stability of the three most promising leads, CID 44418637, CID 163078083, and CID 68734190, with binding affinities of - 7.721, - 8.226, and - 8.307 kcal/mol, respectively. MM/GBSA analysis revealed that Compounds 68734190 (- 50.192 kcal/mol) and 163078083 (- 49.947 kcal/mol) possess superior binding affinities to the ZIKV NS2B-NS3 protease compared to the reference compound (- 38.347 kcal/mol). Given their natural origin, these compounds may offer safer options to mitigate severe ZIKV-related symptoms while providing a favourable safety and pharmacokinetic profile. This study lays the groundwork for developing targeted ZIKV therapies, potentially addressing a significant unmet need in public health by reducing the incidence of ZIKV-related complications. Further experimental validation is required to confirm efficacy and address potential development challenges.

Advances in drug discovery of flavivirus NS2B-NS3pro serine protease inhibitors for the treatment of Dengue, Zika, and West Nile viruses

Flaviviruses are vector-borne RNA viruses that seriously threaten global public health due to their high transmission index in humans, mainly in endemic areas. They spread infectious diseases that affect approximately 400 million people globally, primarily in developing countries struggling with persistent epidemic diseases. Viral infections manifest as hemorrhagic fever, encephalitis, congenital abnormalities, and fatalities. Despite nearly two decades of drug discovery campaigns, researchers have not identified promising lead compounds for clinical trials to treat or prevent flavivirus infections. Although scientists have made substantial progress through drug discovery approaches and vaccine development, resolving this complex issue might need some time. New therapeutic agents that can safely and effectively target key components of flaviviruses need to be identified. NS2B-NS3pro is an extensively studied pharmacological target among viral proteases. It plays a key role in the viral replication cycle by cleaving the polyprotein of flaviviruses and triggering the formation of structural and non-structural proteins. In this review, studies published from 2014 to 2023 were examined, and the specificity profile of compounds targeting NS2B-NS3 pro proteases for treating flavivirus infections was focused on. Additionally, the latest advancements in clinical trials were discussed. This article might provide information on the prospects of this promising pharmacological target.

The Low-Density Lipoprotein Receptor-Related Protein-1 Is Essential for Dengue Virus Infection

Dengue virus (DENV) causes the most prevalent and rapidly spreading arboviral disease of humans. It enters human cells by receptor-mediated endocytosis. Numerous cell-surface proteins were proposed as DENV entry factors. Among these, the phosphatidylserine receptor TIM-1 is the only one known to mediate virus internalization. However, several cellular models lacking TIM-1 are permissive to DENV infection, suggesting that other receptors exist. Here, we show that the low-density lipoprotein receptor-related protein-1 (LRP1) binds DENV virions by interacting with the DIII of the viral envelope glycoprotein. DENV infection is effectively inhibited by the purified receptor at 5 × 10-8 mol/L, and the interaction of the envelope protein with LRP1 is also blocked by a natural ligand of LRP1. The depletion of LRP1 causes 100-fold lower production of infectious virus than controls. Our results indicate that LRP1 is another DENV receptor, thus becoming an attractive target to evaluate for the development of effective antiviral drugs against DENV.

ZIKV induces P62-mediated autophagic degradation of TRAF6 through TRAF6-NS1 interaction

Tumor necrosis factor receptor-associated factor 6 (TRAF6) is crucial in flavivirus infections, modulating the host immune response through interactions with viral proteins. Despite its importance, the relationship between TRAF6 and Zika virus (ZIKV) remains poorly understood. Our prior proteomics analysis revealed reduced TRAF6 protein levels in ZIKV-infected human trophoblast cells compared to non-infected controls. Subsequent studies in cell models and murine tissues confirmed a significant reduction in both TRAF6 mRNA and protein levels post-ZIKV infection. Further investigations unveiled that ZIKV induces P62-mediated degradation of TRAF6, with NS1 identified as the primary contributor. Co-localization and interaction studies demonstrated that NS1 promotes the association of P62, a key autophagy mediator, with TRAF6. Notably, our findings revealed TRAF6 enhances ZIKV infection, NS1 ubiquitination, NS1 expression, and the production of inflammatory cytokines and chemokines. These insights highlight the intricate TRAF6-ZIKV relationship, offering potential for drug targeting NS1-TRAF6 interactions to manage ZIKV infections effectively.

Distinct Replication Kinetics, Cytopathogenicity, and Immune Gene Regulation in Human Microglia Cells Infected with Asian and African Lineages of Zika Virus

Zika virus (ZIKV), a mosquito-borne flavivirus, is a significant global health concern due to its association with neurodevelopmental disorders such as congenital Zika syndrome (CZS). This study aimed to compare the replication kinetics, viral persistence, cytopathogenic effects, and immune gene expression in human microglia cells (CHME-3) infected with an Asian lineage ZIKV (PRVABC59, referred to as ZIKV-PRV) and an African lineage ZIKV (IBH30656, referred to as ZIKV-IBH). We found that ZIKV-PRV replicated more efficiently and persisted longer while inducing lower levels of cell death and inflammatory gene activation compared with ZIKV-IBH. These findings suggest that the enhanced replication and persistence of ZIKV-PRV, along with its ability to evade innate immune responses, may underlie its increased neuropathogenic potential, especially in the context of CZS. In contrast, ZIKV-IBH, with its stronger immune gene activation and higher cytopathogenicity, may lead to more acute infections with faster viral clearance, thereby reducing the likelihood of chronic central nervous system (CNS) infection. This study provides crucial insights into the molecular and cellular mechanisms driving the differential pathogenicity of ZIKV lineages and highlights the need for further research to pinpoint the viral factors responsible for these distinct clinical outcomes.

A Single-Dose mRNA Vaccine Employing Porous Silica Nanoparticles Induces Robust Immune Responses Against the Zika Virus

Recently, lipid nanoparticles (LNPs)-based mRNA delivery has been approved by the FDA for SARS-CoV-2 vaccines. However, there are still considerable points for improvement in LNPs. Especially, local administration of LNPs-formulated mRNA can cause off-target translation of mRNA in distal organs which can induce unintended adverse effects. With the hypothesis that large and rigid nanoparticles can be applied to enhance retention of nanoparticles at the injection site, a polyethyleneimine (PEI)-coated porous silica nanoparticles (PPSNs)-based mRNA delivery platform is designed. PPSNs not only facilitate localized translation of mRNA at the site of injection but also prolonged protein expression. It is further demonstrated that the development of a highly efficacious Zika virus (ZIKV) vaccine using mRNA encoding full-length ZIKV pre-membrane (prM) and envelope (E) protein delivered by PPSNs. The ZIKV prME mRNA-loaded PPSNs vaccine elicits robust immune responses, including high levels of neutralizing antibodies and ZIKV E-specific T cell responses in C57BL/6 mice. Moreover, a single injection of prME-PPSNs vaccine provided complete protection against the ZIKV challenge in mice.

The NS2B-PP1α-eIF2α axis: Inhibiting stress granule formation and Boosting Zika virus replication

Stress granules (SGs), formed by untranslated messenger ribonucleoproteins (mRNPs) during cellular stress in eukaryotes, have been linked to flavivirus interference without clear understanding. This study reveals the role of Zika virus (ZIKV) NS2B as a scaffold protein mediating interaction between protein phosphatase 1α (PP1α) and eukaryotic initiation factor 2α (eIF2α). This interaction promotes eIF2α dephosphorylation by PP1α, inhibiting SG formation. The NS2B-PP1α complex exhibits remarkable stability, resisting ubiquitin-induced degradation and amplifying eIF2α dephosphorylation, thus promoting ZIKV replication. In contrast, the NS2BV35A mutant, interacting exclusively with eIF2α, fails to inhibit SG formation, resulting in reduced viral replication and diminished impact on brain organoid growth. These findings reveal PP1α's dual role in ZIKV infection, inducing interferon production as an antiviral factor and suppressing SG formation as a viral promoter. Moreover, we found that NS2B also serves as a versatile mechanism employed by flaviviruses to counter host antiviral defenses, primarily by broadly inhibiting SG formation. This research advances our comprehension of the complex interplay in flavivirus-host interactions, offering potential for innovative therapeutic strategies against flavivirus infections.

New perspective of small-molecule antiviral drugs development for RNA viruses

High variability and adaptability of RNA viruses allows them to spread between humans and animals, causing large-scale infectious diseases which seriously threat human and animal health and social development. At present, AIDS, viral hepatitis and other viral diseases with high incidence and low cure rate are still spreading around the world. The outbreaks of Ebola, Zika, dengue and in particular of the global pandemic of COVID-19 have presented serious challenges to the global public health system. The development of highly effective and broad-spectrum antiviral drugs is a substantial and urgent research subject to deal with the current RNA virus infection and the possible new viral infections in the future. In recent years, with the rapid development of modern disciplines such as artificial intelligence technology, bioinformatics, molecular biology, and structural biology, some new strategies and targets for antivirals development have emerged. Here we review the main strategies and new targets for developing small-molecule antiviral drugs against RNA viruses through the analysis of the new drug development progress against several highly pathogenic RNA viruses, to provide clues for development of future antivirals.

A review on Zika vaccine development

Zika virus (ZIKV), which belongs to the Flavivirus family, is mainly transmitted via the bite of Aedes mosquitoes. In newborns, ZIKV infection can cause severe symptoms such as microcephaly, while in adults, it can lead to Guillain‒Barré syndrome (GBS). Due to the lack of specific therapeutic methods against ZIKV, the development of a safe and effective vaccine is extremely important. Several potential ZIKV vaccines, such as live attenuated, inactivated, nucleic acid, viral vector, and recombinant subunit vaccines, have demonstrated promising outcomes in clinical trials involving human participants. Therefore, in this review, the recent developmental progress, advantages and disadvantages of these five vaccine types are examined, and practical recommendations for future development are provided.

Dominant epitopes of cross-reactive anti-domain III human antibody response change from early to late convalescence of infection with dengue virus

Cross-neutralizing activity of human antibody response against Dengue virus complex (DENV) changes importantly over time. Domain III (DIII) of the envelope protein of DENV elicits a potently neutralizing and mostly type-specific IgG response. We used sera from 24 individuals from early- or late convalescence of DENV1 infection to investigate the evolution of anti-DIII human IgG with the time lapse since the infection. We evaluated the correlation between the serotype-specific reactivity against recombinant DIII proteins and the neutralization capacity against the four serotypes, and examined its behavior with the time of convalescence. Also, we use a library of 71 alanine mutants of surface-exposed amino acid residues to investigate the dominant epitopes. In early convalescence anti-DIII titers and potency of virus neutralization were positively associated with correlation coefficients from 0.82 to 1.0 for the four serotypes. For late convalescence, a positive correlation (r = 0.69) was found only for DENV1. The dominant epitope of the type-specific response is centered in the FG-loop (G383, E384, and K385) and includes most of the lateral ridge. The dominant epitope of the anti-DIII cross-reactive IgG in secondary infections shifts from the A-strand during early convalescence to a site centered in residues E314-H317 of the AB-loop and I352-E368 of the DI/DIII interface, in late convalescence. An immunoassay based on the detection of IgG anti-DIII response can be implemented for detection of infecting serotype in diagnosis of DENV infection, either primary or secondary. Human dominant epitopes of the cross-reactive circulating antibodies change with time of convalescence.

Global Prevalence of Zika and Chikungunya Coinfection: A Systematic Review and Meta-Analysis

Zika virus (ZIKV) and chikungunya virus (CHIKV) are arthropod-borne viruses with significant pathogenicity, posing a substantial health and economic burden on a global scale. Moreover, ZIKV-CHIKV coinfection imposes additional therapeutic challenges as there is no specific treatment for ZIKV or CHIKV infection. While a growing number of studies have documented the ZIKV-CHIKV coinfection, there is currently a lack of conclusive reports on this coinfection. Therefore, we performed a systematic review and meta-analysis to determine the true statistics of ZIKV-CHIKV coinfection in the global human population. Relevant studies were searched for in PubMed, Scopus, and Google Scholar without limitation in terms of language or publication date. A total of 33 studies containing 41,460 participants were included in this meta-analysis. The study protocol was registered with PROSPERO under the registration number CRD42020176409. The pooled prevalence and confidence intervals of ZIKV-CHIKV coinfection were computed using a random-effects model. The study estimated a combined global prevalence rate of 1.0% [95% CI: 0.7-1.2] for the occurrence of ZIKV-CHIKV coinfection. The region of North America (Mexico, Haiti, and Nicaragua) and the country of Haiti demonstrated maximum prevalence rates of 2.8% [95% CI: 1.5-4.1] and 3.5% [95% CI: 0.2-6.8], respectively. Moreover, the prevalence of coinfection was found to be higher in the paediatric group (2.1% [95% CI: 0.0-4.2]) in comparison with the adult group (0.7% [95% CI: 0.2-1.1]). These findings suggest that the occurrence of ZIKV-CHIKV coinfection varies geographically and by age group. The results of this meta-analysis will guide future investigations seeking to understand the underlying reasons for these variations and the causes of coinfection and to develop targeted prevention and control strategies.

N6-methyladenosine modification positively regulate Japanese encephalitis virus replication

N6-methyladenosine (m6A) is present in diverse viral RNA and plays important regulatory roles in virus replication and host antiviral innate immunity. However, the role of m6A in regulating JEV replication has not been investigated. Here, we show that the JEV genome contains m6A modification upon infection of mouse neuroblast cells (neuro2a). JEV infection results in a decrease in the expression of m6A writer METTL3 in mouse brain tissue. METTL3 knockdown by siRNA leads to a substantial decrease in JEV replication and the production of progeny viruses at 48 hpi. Mechanically, JEV triggered a considerable increase in the innate immune response of METTL3 knockdown neuro2a cells compared to the control cells. Our study has revealed the distinctive m6A signatures of both the virus and host in neuro2a cells infected with JEV, illustrating the positive role of m6A modification in JEV infection. Our study further enhances understanding of the role of m6A modification in Flaviviridae viruses.

The GA-Hecate Peptide inhibits the ZIKV Replicative Cycle in Different Steps and can Inhibit the Flavivirus NS2B-NS3 Protease after Cell Infection

BACKGROUND

Peptide drugs are advantageous because they are subject to rational design and exhibit highly diverse structures and broad biological activities. The NS2B-NS3 protein is a particularly promising flavivirus therapeutic target, with extensive research on the development of inhibitors as therapeutic candidates, and was used as a model in this work to determine the mechanism by which GA-Hecate inhibits ZIKV replication.

OBJECTIVE

The present study aimed to evaluate the potential of GA-Hecate, a new antiviral developed by our group, against the Brazilian Zika virus and to evaluate the mechanism of action of this compound on the flavivirus NS2B-NS3 protein.

METHODS

Solid-phase peptide Synthesis, High-Performance Liquid Chromatography, and Mass Spectrometry were used to obtain, purify, and characterize the synthesized compound. Real-time and enzymatic assays were used to determine the antiviral potential of GA-Hecate against ZIKV.

RESULTS

The RT-qPCR results showed that GA-Hecate decreased the number of ZIKV RNA copies in the virucidal, pre-treatment, and post-entry assays, with 5- to 6-fold fewer RNA copies at the higher nontoxic concentration in Vero cells (HNTC: 10 μM) than in the control cells. Enzymatic and kinetic assays indicated that GA-Hecate acts as a competitive ZIKV NS2B-NS3 protease inhibitor with an IC50 of 32 nM and has activity against the yellow fever virus protease.

CONCLUSION

The results highlight the antiviral potential of the GA-Hecate bioconjugate and open the door for the development of new antivirals.

Insight into the Natural Biomolecules (BMs): Promising Candidates as Zika Virus Inhibitors

Zika virus (ZIKV) is among the relatively new infectious disease threats that include SARS-CoV-2, coronavirus, monkeypox (Mpox) virus, etc. ZIKV has been reported to cause severe health risks to the fetus. To date, satisfactory treatment is still not available for the treatment of ZIKV infection. This review examines the last five years of work using natural biomolecules (BMs) to counteract the ZIKV through virtual screening and in vitro investigations. Virtual screening has identified doramectin, pinocembrin, hesperidins, epigallocatechin gallate, pedalitin, and quercetin as potentially active versus ZIKV infection. In vitro, testing has shown that nordihydroguaiaretic acid, mefloquine, isoquercitrin, glycyrrhetinic acid, patentiflorin-A, rottlerin, and harringtonine can reduce ZIKV infections in cell lines. However, in vivo, testing is limited, fortunately, emetine, rottlerin, patentiflorin-A, and lycorine have shown in vivo anti- ZIKV potential. This review focuses on natural biomolecules that show a particularly high selective index (>10). There is limited in vivo and clinical trial data for natural BMs, which needs to be an active area of investigation. This review aims to compile the known reference data and discuss the barriers associated with discovering and using natural BM agents to control ZIKV infection.

Preparation and characterization of inactivated tick-borne encephalitis virus samples for single-particle imaging at the European XFEL

X-ray imaging of virus particles at the European XFEL could eventually allow their complete structures to be solved, potentially approaching the resolution of other structural virology methods. To achieve this ambitious goal with today's technologies, about 1 ml of purified virus suspension containing at least 1012 particles per millilitre is required. Such large amounts of concentrated suspension have never before been obtained for enveloped viruses. Tick-borne encephalitis virus (TBEV) represents an attractive model system for the development of enveloped virus purification and concentration protocols, given the availability of large amounts of inactivated virus material provided by vaccine-manufacturing facilities. Here, the development of a TBEV vaccine purification and concentration scheme is presented combined with a quality-control protocol that allows substantial amounts of highly concentrated non-aggregated suspension to be obtained. Preliminary single-particle imaging experiments were performed for this sample at the European XFEL, showing distinct diffraction patterns.

EDIII-Fc induces protective immune responses against the Zika virus in mice and rhesus macaque

Zika virus can infect the fetus through the placental barrier, causing ZIKV congenital syndrome and even miscarriage, which can cause great harm to pregnant women and infants. Currently, there is no vaccine and drug available to combat the Zika virus. In this study, we designed a fusion protein named EDIII-Fc, including the EDIII region of Zika E protein and human IgG Fc fragment, and obtained 293T cells that stably secreted EDIII-Fc protein using the lentiviral expression system. Mice were immunized with the EDIII-Fc protein, and it was observed that viral replication was significantly inhibited in the immunized mice compared to non-immunized mice. In rhesus macaques, we found that EDIII-Fc effectively induce the secretion of neutralizing antibodies and T cell immunity. These experimental data provide valid data for further use of Zika virus E protein to prepare an effective, safe, affordable Zika vaccine.

A single amino acid substitution in the capsid protein of Zika virus contributes to a neurovirulent phenotype

Increasing evidence shows the African lineage Zika virus (ZIKV) displays a more severe neurovirulence compared to the Asian ZIKV. However, viral determinants and the underlying mechanisms of enhanced virulence phenotype remain largely unknown. Herein, we identify a panel of amino acid substitutions that are unique to the African lineage of ZIKVs compared to the Asian lineage by phylogenetic analysis and sequence alignment. We then utilize reverse genetic technology to generate recombinant ZIKVs incorporating these lineage-specific substitutions based on an infectious cDNA clone of Asian ZIKV. Through in vitro characterization, we discover a mutant virus with a lysine to arginine substitution at position 101 of capsid (C) protein (termed K101R) displays a larger plaque phenotype, and replicates more efficiently in various cell lines. Moreover, K101R replicates more efficiently in mouse brains and induces stronger inflammatory responses than the wild type (WT) virus in neonatal mice. Finally, a combined analysis reveals the K101R substitution promotes the production of mature C protein without affecting its binding to viral RNA. Our study identifies the role of K101R substitution in the C protein in contributing to the enhanced virulent phenotype of the African lineage ZIKV, which expands our understanding of the complexity of ZIKV proteins.

Immunoinformatics-Based Identification of the Conserved Immunogenic Peptides Targeting of Zika Virus Precursor Membrane Protein

Zika virus infections lead to neurological complications such as congenital Zika syndrome and Guillain-Barré syndrome. Rising Zika infections in newborns and adults have triggered the need for vaccine development. In the current study, the precursor membrane (prM) protein of the Zika virus is explored for its functional importance and design of epitopes enriched conserved peptides with the usage of different immunoinformatics approach. Phylogenetic and mutational analyses inferred that the prM protein is highly conserved. Three conserved peptides containing multiple T and B cell epitopes were designed by employing different epitope prediction algorithms. IEDB population coverage analysis of selected peptides in six different continents has shown the population coverage of 60-99.8% (class I HLA) and 80-100% (class II HLA). Molecular docking of selected peptides/epitopes was carried out with each of class I and II HLA alleles using HADDOCK. A majority of peptide-HLA complex (pHLA) have HADDOCK scores found to be comparable and more than native-HLA complex representing the good binding interaction of peptides to HLA. Molecular dynamics simulation with best docked pHLA complexes revealed that pHLA complexes are stable with RMSD <5.5Å. Current work highlights the importance of prM as a strong antigenic protein and selected peptides have the potential to elicit humoral and cell-mediated immune responses.

Vector-Transmitted Flaviviruses: An Antiviral Molecules Overview

Flaviviruses cause numerous pathologies in humans across a broad clinical spectrum with potentially severe clinical manifestations, including hemorrhagic and neurological disorders. Among human flaviviruses, some viral proteins show high conservation and are good candidates as targets for drug design. From an epidemiological point of view, flaviviruses cause more than 400 million cases of infection worldwide each year. In particular, the Yellow Fever, dengue, West Nile, and Zika viruses have high morbidity and mortality-about an estimated 20,000 deaths per year. As they depend on human vectors, they have expanded their geographical range in recent years due to altered climatic and social conditions. Despite these epidemiological and clinical premises, there are limited antiviral treatments for these infections. In this review, we describe the major compounds that are currently under evaluation for the treatment of flavivirus infections and the challenges faced during clinical trials, outlining their mechanisms of action in order to present an overview of ongoing studies. According to our review, the absence of approved antivirals for flaviviruses led to in vitro and in vivo experiments aimed at identifying compounds that can interfere with one or more viral cycle steps. Still, the currently unavailability of approved antivirals poses a significant public health issue.

Identification of novel Zika virus NS3 protease inhibitors with different inhibition modes by integrative experimental and computational approaches

Zika virus (ZIKV) infection is associated with severe neurological disorders and congenital malformation. Despite efforts to eradicate the disease, there is still neither vaccine nor approved drugs to treat ZIKV infection. The NS2B-NS3 protease is a validated drug target since it is essential to polyprotein virus maturation. In the present study, we describe an experimental screening of 2,320 compounds from the chemical library of the Muséum National d'Histoire Naturelle of Paris on ZIKV NS2B-NS3 protease. A total of 96 hits were identified with 90% or more of inhibitory activity at 10 μM. Amongst the most active compounds, five were analyzed for their inhibitory mechanisms by kinetics assays and computational approaches such as molecular docking. 2-(3-methoxyphenoxy) benzoic acid (compound 945) show characteristics of a competitive inhibition (Ki = 0.49 μM) that was corroborated by its molecular docking at the active site of the NS2B-NS3 protease. Taxifolin (compound 2292) behaves as an allosteric inhibitor whereas 3,8,9-trihydroxy-2-methyl-1H-phenalen-1-one (compound 128), harmol (compound 368) and anthrapurpurin (compound 1499) show uncompetitive inhibitions. These new NS2B-NS3 protease inhibitors are valuable hits to further hit-to-lead optimization.

Advances in computational approaches to structure determination of alphaviruses and flaviviruses using cryo-electron microscopy

Advancements in the field of cryo-electron microscopy (cryo-EM) have greatly contributed to our current understanding of virus structures and life cycles. In this review, we discuss the application of single particle cryo-electron microscopy (EM) for the structure elucidation of small enveloped icosahedral viruses, namely, alpha- and flaviviruses. We focus on technical advances in cryo-EM data collection, image processing, three-dimensional reconstruction, and refinement strategies for obtaining high-resolution structures of these viruses. Each of these developments enabled new insights into the alpha- and flavivirus architecture, leading to a better understanding of their biology, pathogenesis, immune response, immunogen design, and therapeutic development.

Genotype Change in Circulating JEV Strains in Fujian Province, China

Japanese encephalitis (JE), found in pigs, is a serious mosquito-borne zoonotic infectious disease caused by the Japanese encephalitis virus (JEV). JEV is maintained in an enzootic cycle between mosquitoes and amplifying vertebrate hosts, mainly pigs and wading birds. It is transmitted to humans through the bite of an infected mosquito, allowing the pathogen to spread and cause disease epidemics. However, there is little research on JEV genotype variation in mosquitoes and pigs in Fujian province. Previous studies have shown that the main epidemic strain of JEV in Fujian Province is genotype III. In this study, a survey of mosquito species diversity in pig farms and molecular evolutionary analyses of JEV were conducted in Fujian, China, in the summer of 2019. A total of 19,177 mosquitoes were collected at four sites by UV trap. Four genera were identified, of which the Culex tritaeniorhynchus was the most common mosquito species, accounting for 76.4% of the total (14,651/19,177). Anopheles sinensi (19.25%, 3691/19,177) was the second largest species. High mosquito infection rateswere an important factor in the outbreak. The captured mosquito samples were milled and screened with JEV-specific primers. Five viruses were isolated, FJ1901, FJ1902, FJ1903, FJ1904, and FJ1905. Genetic affinity was determined by analyzing the envelope (E) gene variants. The results showed that they are JEV gene type I and most closely related to the strains SH-53 and SD0810. In this study, it was found through genetic evolution analysis that the main epidemic strain of JE in pig farms changed from gene type III to gene type I. Compared with the SH-53 and SD0810 strains, we found no change in key sites related to antigenic activity and neurovirulence of JEV in Fujian JEV and pig mosquito strains, respectively. The results of the study provide basic data for analyzing the genotypic shift of JEV in Fujian Province and support the prevention and control of JEV.

Secretory pathways and multiple functions of nonstructural protein 1 in flavivirus infection

The genus Flavivirus contains a wide variety of viruses that cause severe disease in humans, including dengue virus, yellow fever virus, Zika virus, West Nile virus, Japanese encephalitis virus and tick-borne encephalitis virus. Nonstructural protein 1 (NS1) is a glycoprotein that encodes a 352-amino-acid polypeptide and has a molecular weight of 46-55 kDa depending on its glycosylation status. NS1 is highly conserved among multiple flaviviruses and occurs in distinct forms, including a dimeric form within the endoplasmic reticulum, a cell-associated form on the plasma membrane, or a secreted hexameric form (sNS1) trafficked to the extracellular matrix. Intracellular dimeric NS1 interacts with other NSs to participate in viral replication and virion maturation, while extracellular sNS1 plays a critical role in immune evasion, flavivirus pathogenesis and interactions with natural vectors. In this review, we provide an overview of recent research progress on flavivirus NS1, including research on the structural details, the secretory pathways in mammalian and mosquito cells and the multiple functions in viral replication, immune evasion, pathogenesis and interaction with natural hosts, drawing together the previous data to determine the properties of this protein.

Proposal of Model for Evaluation of Viral Kinetics of African/Asian/Brazilian-Zika virus Strains (Step Growth Curve) in Trophoblastic Cell Lines

The Zika virus (ZIKV) epidemic brought new discoveries regarding arboviruses, especially flaviviruses, as ZIKV was described as sexually and vertically transmitted. The latter shows severe consequences for the embryo/fetus, such as congenital microcephaly and deficiency of the neural system, currently known as Congenital ZIKV Syndrome (CZS). To better understand ZIKV dynamics in trophoblastic cells present in the first trimester of pregnancy (BeWo, HTR-8, and control cell HuH-7), an experiment of viral kinetics was performed for African MR766 low passage and Asian-Brazilian IEC ZIKV lineages. The results were described independently and demonstrated that the three placental cells lines are permissive and susceptible to ZIKV. We noticed cytopathic effects that are typical in in vitro viral infection in BeWo and HTR-8. Regarding kinetics, MR766lp showed peaks of viral loads in 24 and 48 hpi for all cell types tested, as well as marked cells death after peak production. On the other hand, the HTR-8 lineage inoculated with ZIKV-IEC exhibited increased viral production in 144 hpi, with a peak between 24 and 96 hpi. Furthermore, IEC had peak variations of viral production for BeWo in 144 hpi. Considering such in vitro results, the hypothesis that maternal fetal transmission is probably a way of virus transmission between the mother and the embryo/fetus is maintained.

Antiviral Evaluation of New Synthetic Bioconjugates Based on GA-Hecate: A New Class of Antivirals Targeting Different Steps of Zika Virus Replication

Re-emerging arboviruses represent a serious health problem due to their rapid vector-mediated spread, mainly in urban tropical areas. The 2013-2015 Zika virus (ZIKV) outbreak in South and Central America has been associated with cases of microcephaly in newborns and Guillain-Barret syndrome. We previously showed that the conjugate gallic acid-Hecate (GA-FALALKALKKALKKLKKALKKAL-CONH2)-is an efficient inhibitor of the hepatitis C virus. Here, we show that the Hecate peptide is degraded in human blood serum into three major metabolites. These metabolites conjugated with gallic acid were synthesized and their effect on ZIKV replication in cultured cells was evaluated. The GA-metabolite 5 (GA-FALALKALKKALKKL-COOH) was the most efficient in inhibiting two ZIKV strains of African and Asian lineage at the stage of both virus entry (virucidal and protective) and replication (post-entry). We also demonstrate that GA-metabolite 5 does not affect cell growth after 7 days of continuous treatment. Thus, this study identifies a new synthetic antiviral compound targeting different steps of ZIKV replication in vitro and with the potential for broad reactivity against other flaviviruses. Our work highlights a promising strategy for the development of new antivirals based on peptide metabolism and bioconjugation.

Mice as an Animal Model for Japanese Encephalitis Virus Research: Mouse Susceptibility, Infection Route, and Viral Pathogenesis

Japanese encephalitis virus (JEV), a zoonotic flavivirus, is principally transmitted by hematophagous mosquitoes, continually between susceptible animals and incidentally from those animals to humans. For almost a century since its discovery, JEV was geographically confined to the Asia-Pacific region with recurrent sizable outbreaks involving wildlife, livestock, and people. However, over the past decade, it has been detected for the first time in Europe (Italy) and Africa (Angola) but has yet to cause any recognizable outbreaks in humans. JEV infection leads to a broad spectrum of clinical outcomes, ranging from asymptomatic conditions to self-limiting febrile illnesses to life-threatening neurological complications, particularly Japanese encephalitis (JE). No clinically proven antiviral drugs are available to treat the development and progression of JE. There are, however, several live and killed vaccines that have been commercialized to prevent the infection and transmission of JEV, yet this virus remains the main cause of acute encephalitis syndrome with high morbidity and mortality among children in the endemic regions. Therefore, significant research efforts have been directed toward understanding the neuropathogenesis of JE to facilitate the development of effective treatments for the disease. Thus far, multiple laboratory animal models have been established for the study of JEV infection. In this review, we focus on mice, the most extensively used animal model for JEV research, and summarize the major findings on mouse susceptibility, infection route, and viral pathogenesis reported in the past and present, and discuss some unanswered key questions for future studies.

Vaccine development for mosquito-borne viral diseases

Mosquito-borne viral diseases are a group of viral illnesses that are predominantly transmitted by mosquitoes, including viruses from the Togaviridae and Flaviviridae families. In recent years, outbreaks caused by Dengue and Zika viruses from the Flaviviridae family, and Chikungunya virus from the Togaviridae family, have raised significant concerns for public health. However, there are currently no safe and effective vaccines available for these viruses, except for CYD-TDV, which has been licensed for Dengue virus. Efforts to control the transmission of COVID-19, such as home quarantine and travel restrictions, have somewhat limited the spread of mosquito-borne viral diseases. Several vaccine platforms, including inactivated vaccines, viral-vector vaccines, live attenuated vaccines, protein vaccines, and nucleic acid vaccines, are being developed to combat these viruses. This review analyzes the various vaccine platforms against Dengue, Zika, and Chikungunya viruses and provides valuable insights for responding to potential outbreaks.

Development of an optical sandwich ELONA using a pair of DNA aptamers for yellow fever virus NS1

Here, we proposed an enzyme-linked oligonucleotide assay (ELONA) for yellow fever (YF) diagnosis that uses a pair of aptamers, YFns1-4 and YFns1-31. The aptamers were selected to specifically bind to nonstructural protein 1 (NS1), which is secreted at a high concentration after YF infection. We applied the aptamers which did not interfere with each other on binding to the NS1 in a sandwich ELONA. In the assay, the best detection sensitivity was obtained when the combination of YFns1-31 as a capture aptamer and YFns1-4 as a detect aptamer was used. The sensitivity could be attributed to the results of the direct ELONA with each YFns1-4 and YFns1-31; a great absorbance intensity and a broad detectable range of NS1, respectively. The sandwich ELONA achieved a low detection limit of 0.85 nM in buffer and was highly specific to the YFV-NS1 as its detection signals were significantly distinct from those of other flavivirus-derived NS1. In addition, the assay showed a desirable sensitivity in serum-spiked condition. Our developed sandwich ELONA can be a new practical and applicable serological diagnostics in YF endemic regions where other flaviviruses coexist and facilities for complex diagnostic tests are lacking.

SERTAD3 induces proteasomal degradation of ZIKV capsid protein and represents a therapeutic target

Zika virus (ZIKV) is a mosquito-borne RNA virus that belongs to the Flaviviridae family. While flavivirus replication is known to occur in the cytoplasm, a significant portion of the viral capsid protein localizes to the nucleus during infection. However, the role of the nuclear capsid is less clear. Herein, we demonstrated SERTA domain containing 3 (SERTAD3) as an antiviral interferon stimulatory gene product had an antiviral ability to ZIKV but not JEV. Mechanistically, we found that SERTAD3 interacted with the capsid protein of ZIKV in the nucleolus and reduced capsid protein abundance through proteasomal degradation. Furthermore, an eight amino acid peptide of SERTAD3 was identified as the minimum motif that binds with ZIKV capsid protein. Remarkably, the eight amino acids synthetic peptide from SERTAD3 significantly prevented ZIKV infection in culture and pregnant mouse models. Taken together, these findings not only reveal the function of SERTAD3 in promoting proteasomal degradation of a specific viral protein but also provide a promising host-targeted therapeutic strategy against ZIKV infection.

Flavivirus prM interacts with MDA5 and MAVS to inhibit RLR antiviral signaling

BACKGROUND

Vector-borne flaviviruses, including tick-borne encephalitis virus (TBEV), Zika virus (ZIKV), West Nile virus (WNV), yellow fever virus (YFV), dengue virus (DENV), and Japanese encephalitis virus (JEV), pose a growing threat to public health worldwide, and have evolved complex mechanisms to overcome host antiviral innate immunity. However, the underlying mechanisms of flavivirus structural proteins to evade host immune response remain elusive.

RESULTS

We showed that TBEV structural protein, pre-membrane (prM) protein, could inhibit type I interferon (IFN-I) production. Mechanically, TBEV prM interacted with both MDA5 and MAVS and interfered with the formation of MDA5-MAVS complex, thereby impeding the nuclear translocation and dimerization of IRF3 to inhibit RLR antiviral signaling. ZIKV and WNV prM was also demonstrated to interact with both MDA5 and MAVS, while dengue virus serotype 2 (DENV2) and YFV prM associated only with MDA5 or MAVS to suppress IFN-I production. In contrast, JEV prM could not suppress IFN-I production. Overexpression of TBEV and ZIKV prM significantly promoted the replication of TBEV and Sendai virus.

CONCLUSION

Our findings reveal the immune evasion mechanisms of flavivirus prM, which may contribute to understanding flavivirus pathogenicity, therapeutic intervention and vaccine development.

Promising Marine Natural Products for Tackling Viral Outbreaks: A Focus on Possible Targets and Structure-activity Relationship

Recently, people worldwide have experienced several outbreaks caused by viruses that have attracted much interest globally, such as HIV, Zika, Ebola, and the one being faced, SARSCoV- 2 viruses. Unfortunately, the availability of drugs giving satisfying outcomes in curing those diseases is limited. Therefore, it is necessary to dig deeper to provide compounds that can tackle the causative viruses. Meanwhile, the efforts to explore marine natural products have been gaining great interest as the products have consistently shown several promising biological activities, including antiviral activity. This review summarizes some products extracted from marine organisms, such as seaweeds, seagrasses, sponges, and marine bacteria, reported in recent years to have potential antiviral activities tested through several methods. The mechanisms by which those compounds exert their antiviral effects are also described here, with several main mechanisms closely associated with the ability of the products to block the entry of the viruses into the host cells, inhibiting replication or transcription of the viral genetic material, and disturbing the assembly of viral components. In addition, the structure-activity relationship of the compounds is also highlighted by focusing on six groups of marine compounds, namely sulfated polysaccharides, phlorotannins, terpenoids, lectins, alkaloids, and flavonoids. In conclusion, due to their uniqueness compared to substances extracted from terrestrial sources, marine organisms provide abundant products having promising activities as antiviral agents that can be explored to tackle virus-caused outbreaks.

CRISPR-Based Diagnostics: Challenges and Potential Solutions toward Point-of-Care Applications

The COVID-19 pandemic has challenged the conventional diagnostic field and revealed the need for decentralized Point of Care (POC) solutions. Although nucleic acid testing is considered to be the most sensitive and specific disease detection method, conventional testing platforms are expensive, confined to central laboratories, and are not deployable in low-resource settings. CRISPR-based diagnostics have emerged as promising tools capable of revolutionizing the field of molecular diagnostics. These platforms are inexpensive, simple, and do not require the use of special instrumentation, suggesting they could democratize access to disease diagnostics. However, there are several obstacles to the use of the current platforms for POC applications, including difficulties in sample processing and stability. In this review, we discuss key advancements in the field, with an emphasis on the challenges of sample processing, stability, multiplexing, amplification-free detection, signal interpretation, and process automation. We also discuss potential solutions for revolutionizing CRISPR-based diagnostics toward sample-to-answer diagnostic solutions for POC and home use.

Identification and characterization of key residues in Zika virus envelope protein for virus assembly and entry

Zika virus (ZIKV), a family member in the Flavivirus genus, has re-emerged as a global public health concern. The envelope (E) proteins of flaviviruses play a dual role in viral assembly and entry. To identify the key residues of E in virus entry, we generated a ZIKV trans-complemented particle (ZIKV_TCP) system, in which a subgenomic reporter replicon was packaged by trans-complementation with expression of CprME. We performed mutagenesis studies of the loop regions that protrude from the surface of the virion in the E ectodomains (DI, DII, DIII). Most mutated ZIKV_TCPs exhibited deficient egress. Mutations in DII and in the hinge region of DI and DIII affected prM expression. With a bioorthogonal system, photocrosslinking experiments identified crosslinked intracellular E trimers and demonstrated that egress-deficient mutants in DIII impaired E trimerization. Of these mutants, an E-trimerization-dead mutation D389A that nears the E-E interface between two neighbouring spikes in the immature virion completely abolished viral egress. Several mutations abolished ZIKV_TCPs’ entry, without severely affecting viral egress. Further virus binding experiments demonstrated a deficiency of the mutated ZIKV_TCPs in virus attachment. Strikingly, synthesized peptide containing residues of two mutants (268-273aa in DII) could bind to host cells and significantly compete for viral attachment and interfere with viral infection, suggesting an important role of these resides in virus entry. Our findings uncovered the requirement for DIII mediated-E trimerization in viral egress, and discovered a key residue group in DII that participates in virus entry.

Electron microscopy holdings of the Protein Data Bank: the impact of the resolution revolution, new validation tools, and implications for the future

As a discipline, structural biology has been transformed by the three-dimensional electron microscopy (3DEM) "Resolution Revolution" made possible by convergence of robust cryo-preservation of vitrified biological materials, sample handling systems, and measurement stages operating a liquid nitrogen temperature, improvements in electron optics that preserve phase information at the atomic level, direct electron detectors (DEDs), high-speed computing with graphics processing units, and rapid advances in data acquisition and processing software. 3DEM structure information (atomic coordinates and related metadata) are archived in the open-access Protein Data Bank (PDB), which currently holds more than 11,000 3DEM structures of proteins and nucleic acids, and their complexes with one another and small-molecule ligands (~ 6% of the archive). Underlying experimental data (3DEM density maps and related metadata) are stored in the Electron Microscopy Data Bank (EMDB), which currently holds more than 21,000 3DEM density maps. After describing the history of the PDB and the Worldwide Protein Data Bank (wwPDB) partnership, which jointly manages both the PDB and EMDB archives, this review examines the origins of the resolution revolution and analyzes its impact on structural biology viewed through the lens of PDB holdings. Six areas of focus exemplifying the impact of 3DEM across the biosciences are discussed in detail (icosahedral viruses, ribosomes, integral membrane proteins, SARS-CoV-2 spike proteins, cryogenic electron tomography, and integrative structure determination combining 3DEM with complementary biophysical measurement techniques), followed by a review of 3DEM structure validation by the wwPDB that underscores the importance of community engagement.

The Japanese Encephalitis Antigenic Complex Viruses: From Structure to Immunity

In the last three decades, several flaviviruses of concern that belong to different antigenic groups have expanded geographically. This has resulted in the presence of often more than one virus from a single antigenic group in some areas, while in Europe, Africa and Australia, additionally, multiple viruses belonging to the Japanese encephalitis (JE) serogroup co-circulate. Morphological heterogeneity of flaviviruses dictates antibody recognition and affects virus neutralization, which influences infection control. The latter is further impacted by sequential infections involving diverse flaviviruses co-circulating within a region and their cross-reactivity. The ensuing complex molecular virus-host interplay leads to either cross-protection or disease enhancement; however, the molecular determinants and mechanisms driving these outcomes are unclear. In this review, we provide an overview of the epidemiology of four JE serocomplex viruses, parameters affecting flaviviral heterogeneity and antibody recognition, host immune responses and the current knowledge of the cross-reactivity involving JE serocomplex flaviviruses that leads to differential clinical outcomes, which may inform future preventative and therapeutic interventions.