Multiple Strategies Reveal a Bidentate Interaction between the Nipah Virus Attachment and Fusion Glycoproteins

Mutations in the NDV fusion protein HR4 region decreased fusogenic activity due to failed protein expression

Newcastle disease virus (NDV) is the pathogen of a zoonosis that is primarily transmitted by poultry and has severe infectivity and a high fatality rate. Many studies have focused on the role of the NDV fusion (F) protein in the cell-cell membrane fusion process. However, little attention has been given to the heptad repeat region, HR4, which is located in the NDV F2 subunit. Here, site-directed mutants were constructed to study the function of the NDV F protein HR4 region and identify the key amino acids in this region. Nine conserved amino acids were substituted with alanine or the corresponding amino acid of other aligned paramyxoviruses. The desired mutants were examined for changes in fusogenic activity through three kinds of membrane fusion assays and expression and proteolysis through IFA, FACS and WB. The results showed that when conserved amino acids (L81, Y84, L88, L91, L92, P94, L95 and I99) were replaced with alanine, the fusogenic activity of the F protein was abolished, possibly because of failed protein expression not only on the cell surface but also inside cells. These data indicated that the conserved amino acids above in NDV F HR4 are critical for normal protein synthesis and expression, possibly for the stability of the F protein monomer, formation of trimer and conformational changes.

Potent human neutralizing antibodies against Nipah virus derived from two ancestral antibody heavy chains

Nipah virus (NiV) is a World Health Organization priority pathogen and there are currently no approved drugs for clinical immunotherapy. Through the use of a naïve human phage-displayed Fab library, two neutralizing antibodies (NiV41 and NiV42) targeting the NiV receptor binding protein (RBP) were identified. Following affinity maturation, antibodies derived from NiV41 display cross-reactivity against both NiV and Hendra virus (HeV), whereas the antibody based on NiV42 is only specific to NiV. Results of immunogenetic analysis reveal a correlation between the maturation of antibodies and their antiviral activity. In vivo testing of NiV41 and its mature form (41-6) show protective efficacy against a lethal NiV challenge in hamsters. Furthermore, a 2.88 Å Cryo-EM structure of the tetrameric RBP and antibody complex demonstrates that 41-6 blocks the receptor binding interface. These findings can be beneficial for the development of antiviral drugs and the design of vaccines with broad spectrum against henipaviruses.

The cryo-EM structure of homotetrameric attachment glycoprotein from langya henipavirus

Langya Henipavirus (LayV) infection is an emerging zoonotic disease that has been causing respiratory symptoms in China since 2019. For virus entry, LayV's genome encodes the fusion protein F and the attachment glycoprotein G. However, the structural and functional information regarding LayV-G remains unclear. In this study, we revealed that LayV-G cannot bind to the receptors found in other HNVs, such as ephrin B2/B3, and it shows different antigenicity from HeV-G and NiV-G. Furthermore, we determined the near full-length structure of LayV-G, which displays a distinct mushroom-shaped configuration, distinguishing it from other attachment glycoproteins of HNV. The stalk and transmembrane regions resemble the stem and root of mushroom and four downward-tilted head domains as mushroom cap potentially interact with the F protein and influence membrane fusion process. Our findings enhance the understanding of emerging HNVs that cause human diseases through zoonotic transmission and provide implication for LayV related vaccine development.

In silico identification of potential drug-like molecules against G glycoprotein of Nipah virus by molecular docking, DFT studies, and molecular dynamic simulation

Nipah virus (NiV) is a novel zoonotic pathogen that belongs to the Paramyxovirus family. The pathogen has infected a number of people in countries like Bangladesh, India, Singapore, and Malaysia with high mortality rates. Although the NiV has been classified as a biosafety level four pathogen (BSL-4), there is no drug approved for treatment against it. In this study, the G glycoprotein of the NiV was chosen as an antiviral target. Based on ADMET criteria, BBB- and BBB + group compounds were screened out of the Gold & platinum Asinex library containing 211620 compounds. After careful evaluation, the selected ligands were then virtually screened to identify the potential inhibitors against the G glycoprotein of the NiV through molecular docking, density functional theory (DFT), and molecular dynamic (MD) simulation studies. In our study we identified 5-(1,3-Benzodioxol-5-yl)-2-[(3-fluorobenzyl)sulfanyl]-5,8-dihydropyrido[2,3-d]pyrimidine-4,7(1H,6H)-dione (from BBB- group) and 7,7-Dimethyl-1-(4-methylphenyl)-3-(4-morpholinylcarbonyl)-7,8-dihydro-2,5(1H,6H)-quinolinedione) (from BBB + group) as potential compounds for the prevention and treatment of NiV related diseases.Communicated by Ramaswamy H. Sarma.

Nipah Virus Disease: Epidemiological, Clinical, Diagnostic and Legislative Aspects of This Unpredictable Emerging Zoonosis

Nipah virus (NiV) infection is a viral disease caused by a Henipavirus, belonging to the Paramyxoviridae family, responsible for a zoonosis. The course of the disease can be very serious and lead to death. NiV natural hosts are fruit bats (also known as megabats) belonging to the Pteropodidae family, especially those of the Pteropus genus. Natural infection in domestic animals has been described in farming pigs, horses, domestic and feral dogs and cats. Natural NiV transmission is possible intra-species (pig-to-pig, human-to-human) and inter-species (flying bat-to-human, pig-to-human, horse-to-human). The infection can be spread by humans or animals in different ways. It is peculiar how the viral transmission modes among different hosts also change depending on the geographical area for different reasons, including different breeding methods, eating habits and the recently identified genetic traits/molecular features of main virus proteins related to virulence. Outbreaks have been described in Malaysia, Singapore, Bangladesh, India and the Philippines with, in some cases, severe respiratory and neurological disease and high mortality in both humans and pigs. Diagnosis can be made using different methods including serological, molecular, virological and immunohistochemical methods. The cornerstones for control of the disease are biosecurity (via the correct management of reservoir and intermediate/amplifying hosts) and potential vaccines which are still under development. However, the evaluation of the potential influence of climate and anthropogenic changes on the NiV reservoir bats and their habitat as well as on disease spread and inter-specific infections is of great importance. Bats, as natural reservoirs of the virus, are responsible for the viral spread and, therefore, for the outbreaks of the disease in humans and animals. Due to the worldwide distribution of bats, potential new reports and spillovers are not to be dismissed in the future.

The Immunobiology of Nipah Virus

Nipah virus (NiV) is a highly lethal zoonotic paramyxovirus that emerged in Malaysia in 1998. It is a human pathogen capable of causing severe respiratory infection and encephalitis. The natural reservoir of NiV, Pteropus fruit bats, remains a continuous virus source for future outbreaks, although infection in the bats is largely asymptomatic. NiV provokes serious disease in various mammalian species. In the recent human NiV outbreaks in Bangladesh and India, both bats-to-human and human-to-human transmissions have been observed. NiV has been demonstrated to interfere with the innate immune response via interferon type I signaling, promoting viral dissemination and preventing antiviral response. Studies of humoral immunity in infected NiV patients and animal models have shown that NiV-specific antibodies were produced upon infection and were protective. Studies on cellular immunity response to NiV infection in human and animal models also found that the adaptive immune response, specifically CD4+ and CD8+ T cells, was stimulated upon NiV infection. The experimental vaccines and therapeutic strategies developed have provided insights into the immunological requirements for the development of successful medical countermeasures against NiV. This review summarizes the current understanding of NiV pathogenesis and innate and adaptive immune responses induced upon infection.

The nanoscale organization of Nipah virus matrix protein revealed by super-resolution microscopy

The matrix proteins (M) of many enveloped RNA viruses mediate virus assembly and budding. However, it remains poorly understood how M is involved in virus budding and how they interact with envelope proteins. Here, we show that the expression level of Nipah (NiV) M in particles produced by the host cells deviates from a Gamma distribution and does not reflect that of the host cells, indicating assembly of the NiV-M in the process. Our data reveal that NiV-M affects the circularity of the particles while the NiV envelope proteins do not. The organization of NiV envelope proteins on the membrane of the particles is similar to those that do not express NiV-M, suggesting that NiV-M does not directly interact with the envelope proteins during assembly and budding.

Novel Roles of the Nipah Virus Attachment Glycoprotein and Its Mobility in Early and Late Membrane Fusion Steps

The Paramyxoviridae family comprises important pathogens that include measles (MeV), mumps, parainfluenza, and the emerging deadly zoonotic Nipah virus (NiV) and Hendra virus (HeV). Paramyxoviral entry into cells requires viral-cell membrane fusion, and formation of paramyxoviral pathognomonic syncytia requires cell-cell membrane fusion. Both events are coordinated by intricate interactions between the tetrameric attachment (G/H/HN) and trimeric fusion (F) glycoproteins. We report that receptor binding induces conformational changes in NiV G that expose its stalk domain, which triggers F through a cascade from prefusion to prehairpin intermediate (PHI) to postfusion conformations, executing membrane fusion. To decipher how the NiV G stalk may trigger F, we introduced cysteines along the G stalk to increase tetrameric strength and restrict stalk mobility. While most point mutants displayed near-wild-type levels of cell surface expression and receptor binding, most yielded increased NiV G oligomeric strength, and showed remarkably strong defects in syncytium formation. Furthermore, most of these mutants displayed stronger F/G interactions and significant defects in their ability to trigger F, indicating that NiV G stalk mobility is key to proper F triggering via moderate G/F interactions. Also remarkably, a mutant capable of triggering F and of fusion pore formation yielded little syncytium formation, implicating G or G/F interactions in a late step occurring post fusion pore formation, such as the extensive fusion pore expansion required for syncytium formation. This study uncovers novel mechanisms by which the G stalk and its oligomerization/mobility affect G/F interactions, the triggering of F, and a late fusion pore expansion step-exciting novel findings for paramyxoviral attachment glycoproteins. IMPORTANCE The important Paramyxoviridae family includes measles, mumps, human parainfluenza, and the emerging deadly zoonotic Nipah virus (NiV) and Hendra virus (HeV). The deadly emerging NiV can cause neurologic and respiratory symptoms in humans with a >60% mortality rate. NiV has two surface proteins, the receptor binding protein (G) and fusion (F) glycoproteins. They mediate the required membrane fusion during viral entry into host cells and during syncytium formation, a hallmark of paramyxoviral and NiV infections. We previously discovered that the G stalk domain is important for triggering F (via largely unknown mechanisms) to induce membrane fusion. Here, we uncovered new roles and mechanisms by which the G stalk and its mobility modulate the triggering of F and also unexpectedly affect a very late step in membrane fusion, namely fusion pore expansion. Importantly, these novel findings may extend to other paramyxoviruses, offering new potential targets for therapeutic interventions.

The Importance of Lipid Conjugation on Anti-Fusion Peptides against Nipah Virus

Nipah virus (NiV) is a recently emerging zoonotic virus that belongs to the Paramyxoviridae family and the Henipavirus genus. It causes a range of conditions, from asymptomatic infection to acute respiratory illness and fatal encephalitis. The high mortality rate of 40 to 90% ranks these viruses among the deadliest viruses known to infect humans. Currently, there is no antiviral drug available for Nipah virus disease and treatment is only supportive. Thus, there is an urgent demand for efficient antiviral therapies. NiV F protein, which catalyzes fusion between the viral and host membranes, is a potential target for antiviral drugs, as it is a key protein in the initial stages of infection. Fusion inhibitor peptides derived from the HRC-domain of the F protein are known to bind to their complementary domain in the protein’s transient intermediate state, preventing the formation of a six-helix bundle (6HB) thought to be responsible for driving the fusion of the viral and cell membranes. Here, we evaluated the biophysical and structural properties of four different C-terminal lipid-tagged peptides. Different compositions of the lipid tags were tested to search for properties that might promote efficacy and broad-spectrum activity. Fluorescence spectroscopy was used to study the interaction of the peptides with biomembrane model systems and human blood cells. In order to understand the structural properties of the peptides, circular dichroism measurements and molecular dynamics simulations were performed. Our results indicate a peptide preference for cholesterol-enriched membranes and a lipid conjugation-driven stabilization of the peptide α-helical secondary structure. This work may contribute for the development of highly effective viral fusion against NiV inhibitors.

Antivirals targeting paramyxovirus membrane fusion

The Paramyxoviridae family includes enveloped single-stranded negative-sense RNA viruses such as measles, mumps, human parainfluenza, canine distemper, Hendra, and Nipah viruses, which cause a tremendous global health burden. The ability of paramyxoviral glycoproteins to merge viral and host membranes allows entry of the viral genome into host cells, as well as cell-cell fusion, an important contributor to disease progression. Recent molecular and structural advances in our understanding of the paramyxovirus membrane fusion machinery gave rise to various therapeutic approaches aiming at inhibiting viral infection, spread, and cytopathic effects. These therapeutic approaches include peptide mimics, antibodies, and small molecule inhibitors with various levels of success at inhibiting viral entry, increasing the potential of effective antiviral therapeutic development.

Headless Henipaviral Receptor Binding Glycoproteins Reveal Fusion Modulation by the Head/Stalk Interface and Post-receptor Binding Contributions of the Head Domain

Cedar virus (CedV) is a nonpathogenic member of the Henipavirus (HNV) genus of emerging viruses, which includes the deadly Nipah (NiV) and Hendra (HeV) viruses. CedV forms syncytia, a hallmark of henipaviral and paramyxoviral infections and pathogenicity. However, the intrinsic fusogenic capacity of CedV relative to NiV or HeV remains unquantified. HNV entry is mediated by concerted interactions between the attachment (G) and fusion (F) glycoproteins. Upon receptor binding by the HNV G head domain, a fusion-activating G stalk region is exposed and triggers F to undergo a conformational cascade that leads to viral entry or cell-cell fusion. Here, we demonstrate quantitatively that CedV is inherently significantly less fusogenic than NiV at equivalent G and F cell surface expression levels. We then generated and tested six headless CedV G mutants of distinct C-terminal stalk lengths, surprisingly revealing highly hyperfusogenic cell-cell fusion phenotypes 3- to 4-fold greater than wild-type CedV levels. Additionally, similarly to NiV, a headless HeV G mutant yielded a less pronounced hyperfusogenic phenotype compared to wild-type HeV. Further, coimmunoprecipitation and cell-cell fusion assays revealed heterotypic NiV/CedV functional G/F bidentate interactions, as well as evidence of HNV G head domain involvement beyond receptor binding or G stalk exposure. All evidence points to the G head/stalk junction being key to modulating HNV fusogenicity, supporting the notion that head domains play several distinct and central roles in modulating stalk domain fusion promotion. Further, this study exemplifies how CedV may help elucidate important mechanistic underpinnings of HNV entry and pathogenicity. IMPORTANCE The Henipavirus genus in the Paramyxoviridae family includes the zoonotic Nipah (NiV) and Hendra (HeV) viruses. NiV and HeV infections often cause fatal encephalitis and pneumonia, but no vaccines or therapeutics are currently approved for human use. Upon viral entry, Henipavirus infections yield the formation of multinucleated cells (syncytia). Viral entry and cell-cell fusion are mediated by the attachment (G) and fusion (F) glycoproteins. Cedar virus (CedV), a nonpathogenic henipavirus, may be a useful tool to gain knowledge on henipaviral pathogenicity. Here, using homotypic and heterotypic full-length and headless CedV, NiV, and HeV G/F combinations, we discovered that CedV G/F are significantly less fusogenic than NiV or HeV G/F, and that the G head/stalk junction is key to modulating cell-cell fusion, refining the mechanism of henipaviral membrane fusion events. Our study exemplifies how CedV may be a useful tool to elucidate broader mechanistic understanding for the important henipaviruses.

Novel Roles of the N1 Loop and N4 Alpha-Helical Region of the Nipah Virus Fusion Glycoprotein in Modulating Early and Late Steps of the Membrane Fusion Cascade

Nipah virus (NiV) is a zoonotic bat henipavirus in the family Paramyxoviridae NiV is deadly to humans, infecting host cells by direct fusion of the viral and host cell plasma membranes. This membrane fusion process is coordinated by the receptor-binding attachment (G) and fusion (F) glycoproteins. Upon G-receptor binding, F fuses membranes via a cascade that sequentially involves F-triggering, fusion pore formation, and viral or genome entry into cells. Using NiV as an important paramyxoviral model, we identified two novel regions in F that modulate the membrane fusion cascade. For paramyxoviruses and other viral families with class I fusion proteins, the heptad repeat 1 (HR1) and HR2 regions in the fusion protein prefusion conformation bind to form a six-helix bundle in the postfusion conformation. Here, structural comparisons between the F prefusion and postfusion conformations revealed that a short loop region (N1) undergoes dramatic spatial reorganization and a short alpha helix (N4) undergoes secondary structural changes. The roles of the N1 and N4 regions during the membrane fusion cascade, however, remain unknown for henipaviruses and paramyxoviruses. By performing alanine scanning mutagenesis and various functional analyses, we report that specific residues within these regions alter various steps in the membrane fusion cascade. While the N1 region affects early F-triggering, the N4 region affects F-triggering, F thermostability, and extensive fusion pore expansion during syncytium formation, also uncovering a link between F-G interactions and F-triggering. These novel mechanistic roles expand our understanding of henipaviral and paramyxoviral F-triggering, viral entry, and cell-cell fusion (syncytia), a pathognomonic feature of paramyxoviral infections.IMPORTANCE Henipaviruses infect bats, agriculturally important animals, and humans, with high mortality rates approaching ∼75% in humans. Known human outbreaks have been concentrated in Southeast Asia and Australia. Furthermore, about 20 new henipaviral species have been recently discovered in bats, with geographical spans in Asia, Africa, and South America. The development of antiviral therapeutics requires a thorough understanding of the mechanism of viral entry into host cells. In this study, we discovered novel roles of two regions within the fusion protein of the deadly henipavirus NiV. Such roles were in allowing viral entry into host cells and cell-cell fusion, a pathological hallmark of this and other paramyxoviruses. These novel roles were in the previously undescribed N1 and N4 regions within the fusion protein, modulating early and late steps of these important processes of viral infection and henipaviral disease. Notably, this knowledge may apply to other henipaviruses and more broadly to other paramyxoviruses.

Roles of Cholesterol in Early and Late Steps of the Nipah Virus Membrane Fusion Cascade

Cholesterol has been implicated in various viral life cycle steps for different enveloped viruses, including viral entry into host cells, cell-cell fusion, and viral budding from infected cells. Enveloped viruses acquire their membranes from their host cells. Although cholesterol has been associated with the binding and entry of various enveloped viruses into cells, cholesterol's exact function in the viral-cell membrane fusion process remains largely elusive, particularly for the paramyxoviruses. Furthermore, paramyxoviral fusion occurs at the host cell membrane and is essential for both virus entry (virus-cell fusion) and syncytium formation (cell-cell fusion), central to viral pathogenicity. Nipah virus (NiV) is a deadly member of the Paramyxoviridae family, which also includes Hendra, measles, mumps, human parainfluenza, and various veterinary viruses. The zoonotic NiV causes severe encephalitis, vasculopathy, and respiratory symptoms, leading to a high mortality rate in humans. We used NiV as a model to study the role of membrane cholesterol in paramyxoviral membrane fusion. We used a combination of methyl-beta cyclodextrin (MβCD), lovastatin, and cholesterol to deplete or enrich cell membrane cholesterol outside cytotoxic concentrations. We found that the levels of cellular membrane cholesterol directly correlated with the levels of cell-cell fusion induced. These phenotypes were paralleled using NiV/vesicular stomatitis virus (VSV)-pseudotyped viral infection assays. Remarkably, our mechanistic studies revealed that cholesterol reduces an early F-triggering step but enhances a late fusion pore formation step in the NiV membrane fusion cascade. Thus, our results expand our mechanistic understanding of the paramyxoviral/henipaviral entry and cell-cell fusion processes.IMPORTANCE Cholesterol has been implicated in various steps of the viral life cycle for different enveloped viruses. Nipah virus (NiV) is a highly pathogenic enveloped virus in the Henipavirus genus within the Paramyxoviridae family, capable of causing a high mortality rate in humans and high morbidity in domestic and agriculturally important animals. The role of cholesterol for NiV or the henipaviruses is unknown. Here, we show that the levels of cholesterol influence the levels of NiV-induced cell-cell membrane fusion during syncytium formation and virus-cell membrane fusion during viral entry. Furthermore, the specific role of cholesterol in membrane fusion is not well defined for the paramyxoviruses. We show that the levels of cholesterol affect an early F-triggering step and a late fusion pore formation step during the membrane fusion cascade. Thus, our results expand our mechanistic understanding of the viral entry and cell-cell fusion processes, which may aid the development of antivirals.

EphrinB2 clustering by Nipah virus G is required to activate and trap F intermediates at supported lipid bilayer-cell interfaces

Paramyxovirus membrane fusion requires an attachment protein that binds to a host cell receptor and a fusion protein that merges the viral and host membranes. For Nipah virus (NiV), the G attachment protein binds ephrinB2/B3 receptors and activates F-mediated fusion. To visualize dynamic events of these proteins at the membrane interface, we reconstituted NiV fusion activation by overlaying F- and G-expressing cells onto ephrinB2-functionalized supported lipid bilayers and used TIRF microscopy to follow F, G, and ephrinB2. We found that G and ephrinB2 form clusters and that oligomerization of ephrinB2 is necessary for F activation. Single-molecule tracking of F particles revealed accumulation of an immobilized intermediate upon activation. We found no evidence for stable F-G protein complexes before or after activation. These observations lead to a revised model for NiV fusion activation and provide a foundation for investigating other multicomponent viral fusion systems.

Phylogenetic and genetic analyses of the emerging Nipah virus from bats to humans

Little is known about the genetic features of Nipah virus (NiV) associated with virulence and transmission. Herein, phylogenetic and genetic analyses for all available NiV strains revealed sequence variations between the two genetic lineages of NiV with pathogenic differences, as well as among different strains within Bangladesh lineage. A total of 143 conserved amino acid differences, distributed among viral nucleocapsid (N), phosphoprotein (P), matrix protein (M), fusion protein (F) and glycoprotein (G), were revealed. Structural modeling revealed one key substitution (S3554N) in the viral G protein that might mediate a 12-amino-acid structural change from a loop into a β sheet. Multiple key amino acids substitutions in viral G protein were observed, which may alter viral fitness and transmissibility from bats to humans.

Differential Features of Fusion Activation within the Paramyxoviridae

Paramyxovirus (PMV) entry requires the coordinated action of two envelope glycoproteins, the receptor binding protein (RBP) and fusion protein (F). The sequence of events that occurs during the PMV entry process is tightly regulated. This regulation ensures entry will only initiate when the virion is in the vicinity of a target cell membrane. Here, we review recent structural and mechanistic studies to delineate the entry features that are shared and distinct amongst the Paramyxoviridae. In general, we observe overarching distinctions between the protein-using RBPs and the sialic acid- (SA-) using RBPs, including how their stalk domains differentially trigger F. Moreover, through sequence comparisons, we identify greater structural and functional conservation amongst the PMV fusion proteins, as compared to the RBPs. When examining the relative contributions to sequence conservation of the globular head versus stalk domains of the RBP, we observe that, for the protein-using PMVs, the stalk domains exhibit higher conservation and find the opposite trend is true for SA-using PMVs. A better understanding of conserved and distinct features that govern the entry of protein-using versus SA-using PMVs will inform the rational design of broader spectrum therapeutics that impede this process.

A structural basis for antibody-mediated neutralization of Nipah virus reveals a site of vulnerability at the fusion glycoprotein apex

Nipah virus (NiV) is a highly pathogenic paramyxovirus that causes frequent outbreaks of severe neurologic and respiratory disease in humans with high case fatality rates. The 2 glycoproteins displayed on the surface of the virus, NiV-G and NiV-F, mediate host-cell attachment and membrane fusion, respectively, and are targets of the host antibody response. Here, we provide a molecular basis for neutralization of NiV through antibody-mediated targeting of NiV-F. Structural characterization of a neutralizing antibody (nAb) in complex with trimeric prefusion NiV-F reveals an epitope at the membrane-distal domain III (DIII) of the molecule, a region that undergoes substantial refolding during host-cell entry. The epitope of this monoclonal antibody (mAb66) is primarily protein-specific and we observe that glycosylation at the periphery of the interface likely does not inhibit mAb66 binding to NiV-F. Further characterization reveals that a Hendra virus-F-specific nAb (mAb36) and many antibodies in an antihenipavirus-F polyclonal antibody mixture (pAb835) also target this region of the molecule. Integrated with previously reported paramyxovirus F-nAb structures, these data support a model whereby the membrane-distal region of the F protein is targeted by the antibody-mediated immune response across henipaviruses. Notably, our domain-specific sequence analysis reveals no evidence of selective pressure at this region of the molecule, suggestive that functional constraints prevent immune-driven sequence variation. Combined, our data reveal the membrane-distal region of NiV-F as a site of vulnerability on the NiV surface.

Advances in diagnostics, vaccines and therapeutics for Nipah virus

Nipah virus is an emerging zoonotic paramyxovirus that causes severe and often fatal respiratory and neurological disease in humans. The virus was first discovered after an outbreak of encephalitis in pig farmers in Malaysia and Singapore with subsequent outbreaks in Bangladesh or India occurring almost annually. Due to the highly pathogenic nature of NiV, its pandemic potential, and the lack of licensed vaccines or therapeutics, there is a requirement for research and development into highly sensitive and specific diagnostic tools as well as antivirals and vaccines to help prevent and control future outbreak situations.

A stochastic assembly model for Nipah virus revealed by super-resolution microscopy

Understanding virus assembly mechanisms is important for developing therapeutic interventions. Nipah virus (NiV) is of interest because of its high mortality rate and efficient human-human transmissions. The current model for most enveloped viruses suggests that matrix proteins (M) recruit attachment glycoproteins (G) and fusion glycoproteins (F) to the assembly site at the plasma membrane. Here we report an assembly model that differs in many aspects from the current one. Examining NiV proteins on the cell plasma membrane using super-resolution microscopy reveals that clusters of F and G are randomly distributed on the plasma membrane regardless of the presence or absence of M. Our data suggests a model in which the M molecules assemble at the plasma membrane to form virus-like particles (VLPs), while the incorporation of F and G into the nascent VLPs is stochastic.

The Hemagglutinin-Neuraminidase (HN) Head Domain and the Fusion (F) Protein Stalk Domain of the Parainfluenza Viruses Affect the Specificity of the HN-F Interaction

Membrane fusion by the parainfluenza viruses is induced by virus-specific functional interaction between the attachment protein (HN) and the fusion (F) protein. This interaction is thought to be mediated by transient contacts between particular amino acids in the HN stalk domain and those in the F head domain. However, we recently reported that replacement of specified amino acids at or around the dimer interface of the HN head domain remarkably affected the F protein specificity. We then intended to further investigate this issue in the present study and revealed that the HPIV2 HN protein can be converted to an SV41 HN-like protein by substituting at least nine amino acids in the HPIV2 HN head domain with the SV41 HN counterparts in addition to the replacement of the stalk domain, indicating that specified amino acids in the HN head domain play very important roles in determining the specificity of the HN-F interaction. On the other hand, we previously reported that the PIV5 F protein can be converted to an SV41 F-like protein by replacing 21 amino acids in the head domain of the PIV5 F protein with those of the SV41 F protein. We then intended to further investigate this issue in the present study and found that replacement of 15 amino acids in the stalk domain in addition to the replacement of the 21 amino acids in the head domain of the PIV5 F protein resulted in creation of a more SV41 F-like protein, indicating that specified amino acids in the F stalk domain play important roles in determining the specificity of the HN-F interaction. These results suggest that the conformations of the HN stalk domain and the F head domain are dependent on the structures of the HN head domain and the F stalk domain, respectively. Presumably, the conformations of the former domains, which are considered directly involved in the HN-F interaction, can be modified by subtle changes in the structure of the latter domains, resulting in an altered specificity for the interacting partners.

Sortase-mediated chemical protein synthesis reveals the bidentate binding of bisphosphorylated p62 with K63 diubiquitin

Phosphorylation of S403 or S407 of the autophagic receptor protein p62 has recently been discovered to enhance the binding of p62 with ubiquitinated protein substrates to upregulate selective autophagy. To elucidate the molecular mechanism of how phosphorylation regulates the recruitment of ubiquitinated proteins, we report the first chemical synthesis of homogeneously phosphorylated p62, which enables the setting up of accurate in vitro systems for biochemical studies. Our synthesis employs the technology of sortase A-mediated protein hydrazide ligation, which successfully affords three types of phosphorylated p62 at the multi-milligram scale. Quantitative biochemical measurements show that the binding affinity of S403/S407-bisphosphorylated p62 to K63 diubiquitin is significantly higher than that of mono-phosphorylated p62. This finding suggests that phosphorylated S403 and S407 sites should bind to different epitopes on the ubiquitin chain. Furthermore, glutamate mutation is found to give a significantly impaired binding affinity, implying the necessity of using chemically synthesized phosphorylated p62 for the biochemical study of selective autophagy.