Biology subjects

Tan, B. H.

Publications and source records attributed to Tan, B. H..

8 recordsLinked to original sources

bioRxiv2026

Evidence for a biphasic mechanism of virus transmission of the human metapneumovirus in LLC-MK2 cell monolayers.

We examined transmission of the human metapneumovirus (HMPV) in LLC-MK2 cell monolayers using a low multiplicity of infection (moi). In this low moi infection model HMPV transmission initially occurred by localised cell-to-cell transmission, and the virus infectivity remained largely cell associated. At the later stages of infection more widespread virus transmission occurred and was associated with the presence of cell-free virus. The appearance of the cell-free virus correlated with changes in plasma membrane integrity and increased membrane permeability in the cell monolayers. Imaging analysis of HMPV infected cells at the early stages of infection showed the presence of numerous virus filaments attached to the surface of HMPV-infected cells. At the later stages of infection both virus filaments and virus particles with a spherical morphology that was attached to the distal ends of the virus filaments was noted. A proportion of these spherical particles detached from the virus filaments and attached to adjacent non-infected cells at the later stages of infection. The activation of the JNK and MAPKp38 signalling pathways in HMPV-infected cells correlated with increased HMPV replication and appearance of the cell-free virus infectivity. In addition, after the initial phase of STAT1 activation in HMPV-infected cells, both reduced expression of the STAT1 protein and the activated STAT1 protein occurred as the infection proceeded. Collectively, these data provide evidence for a biphasic mode of HMPV transmission involving different virus particle morphologies, a localised virus transmission by virus filaments followed by widespread virus transmission involving cell-free virus particles.

microbiology↗

bioRxiv2026

Evaluating the use of siRNA to silence the expression of the H5N2 virus polymerase genes as strategy to block the transmission of the avian H5N2 virus in mammalian cells.

We prepared siRNA libraries against the H5N2 virus NP gene, and the PA, PB1 and PB2 genes that express the proteins that form the virus polymerase complex. The antiviral activity of the siRNA libraries in H5N2 virus infected cells was initially assessed by using qPCR to measure the corresponding mRNA levels in the siRNA-treated cells. In this way siRNA molecules within each library were identified that exhibited to a greater than 70% reduction in levels of each target mRNA. A selection of these siRNA molecules was further evaluated for their antiviral activity in a multi-cycle H5N2 MDCK cell model. The siRNA molecules identified were successful in blocking virus transmission and lead to a reduction in influenza virus progeny virus production. This antiviral activity correlated with both the inhibition of nuclear export of the newly formed RNP complexs that arise from the transcriptional activity of the input virus, and the inhibition of the polymerase activity of the newly formed virus polymerase complexes. This study highlights the potential use of siRNA as a strategy to block virus transmission by targeting the avian influenza virus polymerase complex.

microbiology↗

bioRxiv2025

Analysis of the surface topology of respiratory syncytial virus particles that form on the surface of virus-infected cells.

The surface topology of virus filaments on respiratory syncytial virus (RSV)-infected cells was examined using field emission gun-scanning electron microscopy (FEG-SEM) and atomic force microscopy (AFM). FEG-SEM analysis of the surface of RSV-infected cells labelled with an anti-G protein antibody revealed the presence of virus filaments and clusters of the G protein distributed intermittently along their surface. RSV-infected cells thinly coated with chromium were imaged using FEG-SEM and revealed a distinct structured surface topology consisting of closely packed surface domains. The G protein clusters were only associated within a subset of these domains which suggested that this structured topology was mainly derived from the host cell, and the presence of the cell glycocalyx that coats the virus filaments was further suggested. Imaging of RSV-infected cells using AFM was undertaken as a different but complementary approach to the FEG-SEM analysis. Imaging using AFM revealed a similar structured surface topology on the virus filaments to that observed in the FEG-SEM analysis, indicating the consistency in the appearance of the virus surface topology using these different methods. Collectively, this study provides the first detailed imaging of the surface topology of the virus filaments as they form on RSV-infected cells. The imaging data is consistent with the envelopment of the virus filaments by the glycocalyx and highlights the complexity of the spatial organisation within the viral envelope.

microbiology↗

bioRxiv2024

Evidence that the cell glycocalyx envelops respiratory syncytial virus (RSV) particles that form on the surface of RSV-infected human airway cells.

We examined how respiratory syncytial virus (RSV) particles circumvent the overlying glycocalyx on virus-infected A549 cells. The glycocalyx was detected using the lectin WGA-AL488 probe, and the antibodies anti-HS and anti-syndecan-4 that detect heparin sulphate (HS) and the syndecan-4 protein (SYND4) respectively. Imaging of RSV-infected cells provided evidence that the glycocalyx envelopes the virus filaments as they form, and that components of the glycocalyx such as HS moieties and SYND4 are displayed on the surface of the mature virus filaments. Using recombinant expression of the G protein we also demonstrated that the G protein was trafficked into pre-existing filamentous cellular structures with a well-defined glycocalyx, suggesting that the glycocalyx is maintained at the site of virus particle assembly. These data provide evidence that during RSV particle assembly the virus filaments become enveloped by the glycocalyx, and that the glycocalyx should be considered as a structural component of RSV particles.

microbiology↗

bioRxiv2024

Evidence that the SARS-CoV-2 S protein undergoes a conformational change at the Golgi Complex that leads to the formation of virus neutralising antibody binding epitopes in the S1 protein subunit.

Recombinant SARS-CoV-2 S protein expression was examined in Vero cells by imaging using the human monoclonal antibody panel (PD4, PD5, sc23, and sc29). The PD4 and sc29 antibodies recognised conformational specific epitopes in the S2 protein subunit at the Endoplasmic reticulum and Golgi complex. While PD5 and sc23 detected conformationally specific epitopes in the S1 protein subunit at the Golgi complex, only PD5 recognised the receptor binding domain (RBD). A comparison of the staining patterns of PD5 with non-conformationally specific antibodies that recognises the S1 subunit and RBD suggested the PD5 recognised a conformational structure within the S1 protein subunit. Our data suggests the antibody binding epitopes recognised by the human monoclonal antibodies formed at different locations in the secretory pathway during S protein transport, but a conformational change in the S1 protein subunit at the Golgi complex formed antibody binding epitopes that are recognised by virus neutralizing antibodies.

microbiology↗

bioRxiv2023

Binary Ethyleneimine inactivated- Encephalomyocarditis virus as an experimental vaccine candidate showed strong neutralization responses.

A novel Encephalomyocarditis virus (EMCV) of the group 3 cluster (EMCV-3) was first reported in 2002 to be responsible for the deaths of orang-utans in an outbreak in the Singapore Zoo. After this first outbreak, sporadic infections among the primate population caused by EMCV-3 continued to be reported, suggesting that the virus remains prevalent in Singapore. To prevent future infections, we constructed an experimental vaccine using binary ethylenimine (BE) to inactivate the EMCV-3 virus. The immunological performance of the BE-inactivated (BEI) virus was analysed in mice and the neutralising titre of the immune sera measured against the wild-type EMCV-3. The BEI virus showed a strong immunological response in BALB/c mice at 1: 40,960 titre, suggesting that it can be used as a promising experimental vaccine candidate to prevent EMCV-3 infections.

microbiology↗

bioRxiv2022

Evidence for a functional interaction between the respiratory syncytial virus fusion and attachment proteins in the envelope of infectious virus particles.

We have examined the interaction between the respiratory syncytial virus (RSV) F and G proteins on the surface of infected cells during multiple cycle infection using a low multiplicity of infection (MOI) model, and on the surface of virus particles that were isolated from infected cells. A combination of the proximity ligation assay (PLA) and confocal microscopy was used to demonstrate the interaction between the F and G proteins within the virus filaments on infected cells. Co-precipitation of the F and G proteins was confirmed using detergent extracts prepared from infected cells and in detergent extracts prepared from purified virus particles. The influence of the G protein in mediating virus spread in the low MOI model was further examined using the recombinant virus isolates rg224RSV (that expresses all virus proteins) and rg224RSV-{Delta}G (which does not express the G protein). While cells could be initially infected by both viruses, the rg224RSV-{Delta}G virus exhibited severely impaired localised virus transmission in the multiple cycle infection assay. Collectively these data provide evidence that the F and G proteins interact within the envelope of RSV particles, and suggests that this interaction may promote virus transmission. The interaction between these proteins in a single protein complex represents a potential new target for the development of antivirus strategies and in the development of RSV vaccine candidates.

microbiology↗

bioRxiv2021

The cellular characterisation of SARS-CoV-2 spike protein in virus-infected cells using Receptor Binding Domain-binding specific human monoclonal antibodies.

A human monoclonal antibody panel (PD4, PD5, PD7, SC23 and SC29) was isolated from the B cells of convalescent patients and used to examine the S protein in SARS-CoV-2- infected cells. While all five antibodies bound conformational-specific epitopes within SARS-CoV-2 Spike (S) protein, only PD5, PD7, and SC23 were able to bind to the Receptor Binding Domain (RBD). Immunofluorescence microscopy was used to examine the S protein RBD in cells infected with the Singapore isolates SARS-CoV-2/0334 and SARS-CoV-2/1302. The RBD-binders exhibited a distinct cytoplasmic staining pattern that was primarily localised within the Golgi complex and was distinct from the diffuse cytoplasmic staining pattern exhibited by the non-RBD binders (PD4 and SC29). These data indicated that the S protein adopted a conformation in the Golgi complex that enabled the RBD recognition by the RBD-binders. The RBD-binders also recognised the uncleaved S protein indicating that S protein cleavage was not required for RBD recognition. Electron microscopy indicated high levels of cell-associated virus particles, and multiple cycle virus infection using RBD-binder staining provided evidence for direct cell-to-cell transmission for both isolates. Although similar levels of RBD-binder staining was demonstrated for each isolate, the SARS-CoV-2/1302 exhibited slower rates of cell-to-cell transmission. These data suggest that a conformational change in the S protein occurs during its transit through the Golgi complex that enables RBD recognition by the RBD-binders, and suggests that these antibodies can be used to monitor S protein RBD formation during the early stages of infection. ImportanceThe SARS CoV-2 spike (S) protein receptor binding domain (RBD) mediates the attachment of SARS CoV-2 to the host cell. This interaction plays an essential role in initiating virus infection and the S protein RBD is therefore a focus of therapeutic and vaccine interventions. However, new virus variants have emerged with altered biological properties in the RBD that can potentially negate these interventions. Therefore an improved understanding of the biological properties of the RBD in virus-infected cells may offer future therapeutic strategies to mitigate SARS CoV-2 infection. We used physiologically relevant antibodies that were isolated from the B cells of convalescent COVID19 patients to monitor the RBD in cells infected with SARS CoV-2 clinical isolates. These immunological reagents specifically recognise the correctly folded RBD and were used to monitor the appearance of the RBD in SARS CoV-2-infected cells and identified the site where the RDB first appears.

microbiology↗