Envelope-deforming antiviral peptide derived from influenza virus M2 protein.

Molecules interfering with lipid bilayer function exhibit strong antiviral activity against a broad range of enveloped viruses, with a lower risk of resistance development than that for viral protein-targeting drugs. Amphipathic peptides are rich sources of such membrane-interacting antivirals. Here, we report that influenza viruses were effectively inactivated by M2 AH, an amphipathic peptide derived from the M2 protein of the influenza virus. Although overall hydrophobicity () of M2 AH was not related to antiviral activity, modification of the hydrophobic moment (<µH>) of M2 AH dramatically altered the antiviral activity of this peptide. M2 MH, a derivative of M2 AH with a <µH> of 0.874, showed a half maximal inhibitory concentration (IC50) of 53.3 nM against the A/PR/8/34 strain (H1N1), which is 16-times lower than that of M2 AH. The selectivity index (IC50/CC50), where CC50 is the half maximal cytotoxic concentration, was 360 for M2 MH and 81 for M2 AH. Dynamic light scattering spectroscopy and electron microscopy revealed that M2 AH-derived peptides did not disrupt liposomes but altered the shape of viruses. This result suggests that the shape of virus envelope was closely related to its activity. Thus, we propose that deforming without rupturing the membranes may achieve a high selectivity index for peptide antivirals.

Conserved and host-specific features of influenza virion architecture.

Viruses use virions to spread between hosts, and virion composition is therefore the primary determinant of viral transmissibility and immunogenicity. However, the virions of many viruses are complex and pleomorphic, making them difficult to analyse in detail. Here we address this by identifying and quantifying virion proteins with mass spectrometry, producing a complete and quantified model of the hundreds of host-encoded and viral proteins that make up the pleomorphic virions of influenza viruses. We show that a conserved influenza virion architecture is maintained across diverse combinations of virus and host. This 'core' architecture, which includes substantial quantities of host proteins as well as the viral protein NS1, is elaborated with abundant host-dependent features. As a result, influenza virions produced by mammalian and avian hosts have distinct protein compositions. Finally, we note that influenza virions share an underlying protein composition with exosomes, suggesting that influenza virions form by subverting microvesicle production.

Influenza virus budding from the tips of cellular microvilli in differentiated human airway epithelial cells.

The epithelium of conducting airways represents the main target for influenza virus in mammals. However, the peculiarities of virus interactions with differentiated airway epithelial cells remain largely unknown. Here, influenza virus budding was studied in differentiated cultures of human tracheobronchial epithelial cells using transmission electron microscopy. Budding of spherical and filamentous virions was observed on the apical surfaces of cells with no association with cilia and secretory granules. Quantitative analysis of the distribution of viral buds on the cell surface indicated that the tips of the microvilli represented a prominent site of influenza virus budding in the human airway epithelium. As the microvilli of differentiated cells are involved in many fundamental cell functions, these data will prompt further studies on the biological significance of microvilli-associated budding for virus replication, transmission and pathogenicity.

[Establishment of localization ultrathin section for cytopathic cells].

OBJECTIVE: To establish a localization ultrathin section method through which target cytopathic cells could be sectioned in situ. METHODS: Lab-Tek Chamber slide system (177402) was selected as resin embedding mould. Cells infected with Human adenovirus type 5 (Ad5) or A/HN/SWL3/ 2009 (H1N1) influenza virus were embedded in situ as models. Target cytopathic cells were exposed by trimming, sectioned and observed under transmission electron microscope (TEM). RESULTS: Target cells could be sectioned in situ and virus particles could be found easily on sections. CONCLUSION: A localization ultrathin sectioning method was established and this technique could be applied in virus detection in cytopathic cells to improve TEM detection efficiency.

Polymer-attached zanamivir inhibits synergistically both early and late stages of influenza virus infection.

Covalently conjugating multiple copies of the drug zanamivir (ZA; the active ingredient in Relenza) via a flexible linker to poly-l-glutamine (PGN) enhances the anti-influenza virus activity by orders of magnitude. In this study, we investigated the mechanisms of this phenomenon. Like ZA itself, the PGN-attached drug (PGN-ZA) binds specifically to viral neuraminidase and inhibits both its enzymatic activity and the release of newly synthesized virions from infected cells. Unlike monomeric ZA, however, PGN-ZA also synergistically inhibits early stages of influenza virus infection, thus contributing to the markedly increased antiviral potency. This inhibition is not caused by a direct virucidal effect, aggregation of viruses, or inhibition of viral attachment to target cells and the subsequent endocytosis; rather, it is a result of interference with intracellular trafficking of the endocytosed viruses and the subsequent virus-endosome fusion. These findings both rationalize the great anti-influenza potency of PGN-ZA and reveal that attaching ZA to a polymeric chain confers a unique mechanism of antiviral action potentially useful for minimizing drug resistance.

Organization of the influenza virus replication machinery.

Influenza virus ribonucleoprotein complexes (RNPs) are central to the viral life cycle and in adaptation to new host species. RNPs are composed of the viral genome, viral polymerase, and many copies of the viral nucleoprotein. In vitro cell expression of all RNP protein components with four of the eight influenza virus gene segments enabled structural determination of native influenza virus RNPs by means of cryogenic electron microscopy (cryo-EM). The cryo-EM structure reveals the architecture and organization of the native RNP, defining the attributes of its largely helical structure and how polymerase interacts with nucleoprotein and the viral genome. Observations of branched-RNP structures in negative-stain electron microscopy and their putative identification as replication intermediates suggest a mechanism for viral replication by a second polymerase on the RNP template.

The structure of native influenza virion ribonucleoproteins.

The influenza viruses cause annual epidemics of respiratory disease and occasional pandemics, which constitute a major public-health issue. The segmented negative-stranded RNAs are associated with the polymerase complex and nucleoprotein (NP), forming ribonucleoproteins (RNPs), which are responsible for virus transcription and replication. We describe the structure of native RNPs derived from virions. They show a double-helical conformation in which two NP strands of opposite polarity are associated with each other along the helix. Both strands are connected by a short loop at one end of the particle and interact with the polymerase complex at the other end. This structure will be relevant for unraveling the mechanisms of nuclear import of parental virus RNPs, their transcription and replication, and the encapsidation of progeny RNPs into virions.

Target-size embracing dimension for sensitive detection of viruses with various sizes and influenza virus strains.

The focused ion beam (FIB) technique was employed to precisely fabricate hexagon-like Au nano-rods (fibAu_h) arrays as a surface enhanced Raman scattering - active substrate. A "ring diameter" (D(R)) was created by the convergence of three fibAu_h with respect to the dimension of the target viruses (D(T)), such as adenovirus (Adeno), encephalomyocarditis virus (EMCV), influenza virus (H1N1) with different sizes. Three influenza A virus strains were also compared. The results indicate that as that with a D(R)/D(T) ratio of around 1, the discrimination ability for detecting the target viruses and SERS mechanism become obvious. The enhanced lightning rod effect surrounding the seized target virus is anticipated if its size and dimension is suitably embraced within three fibAu_h. Hence the as-designed fibAu_h sample with a target-size embracing dimension provides good discrimination ability for distinguishing virus of various sizes or virus strains.

Ultrastructural characterization of pandemic (H1N1) 2009 virus.

We evaluated pandemic influenza A (H1N1) 2009 virus isolates and respiratory tissues collected at autopsy by electron microscopy. Many morphologic characteristics were similar to those previously described for influenza virus. One of the distinctive features was dense tubular structures in the nuclei of infected cells.

Multiple organ invasion by viruses: pathological characteristics in three fatal cases of the 2009 pandemic influenza A/H1N1.

To further understand the pathological characteristics of multiple organ involvement of the 2009 pandemic influenza A/H1N1 infection, tissues of bronchial mucosa, lung, myocardium, gastrocnemius, and liver from 3 patients with fatal A/H1N1 infections were investigated by light microscopy and transmission electron microscopy. In all 3 patients, bronchial mucosa showed necrotizing bronchiolitis, epithelial necrosis and desquamation, and squamous metaplasia, while lung consolidation or fibrosis was identified. Myocardium and gastrocnemius exhibited focal necrosis and fibrosis, surrounded by muscle cells showing features of cell damage. In liver, there was widespread fatty degeneration and necrosis, most often around the central lobular vein and portal area. Viral particles were found in all samples, frequently located in endothelium, epithelium, and muscle cells. The observations demonstrate that in fatal cases of A/H1N1 infection, viruses not only infect the respiratory system, but also engage in multiple organ invasions, causing pathologic changes.

Organization of influenza A virus envelope at neutral and low pH.

Fusion of the influenza A H1N1 virus envelope with the endosomal membrane at low pH allows the intracellular delivery of the viral genome and plays an essential role in the infection process. Low pH induces an irreversible modification of the virus envelope, which has so far resisted 3D structural analysis, partly due to the virus pleiomorphy. This study showed that atomic force microscopy (AFM) in physiological buffer could be used to image the structural details of the virus envelope, both at neutral pH and after a low-pH treatment. At low and intermediate magnification, AFM of control virions confirmed both the pleiomorphy and the existence of zones devoid of glycoprotein spikes at the virus surface, as established by electron microscopy (EM). At higher magnification, the unique vertical resolution of the AFM in 3D topography demonstrated the lateral heterogeneity in spike distribution and strongly suggested that, at least locally, the spikes can be organized in an irregular honeycomb pattern. The surface honeycomb pattern was more easily detected due to an increase in spike height following low-pH treatment at low temperature, which probably prevented disruption of the organization. This enhanced contrast associated with low-pH treatment emphasized differences in the glycoprotein distribution between virions. It was concluded that, together with EM approaches, AFM may help to establish a correlation between surface structure and influenza virus infectivity/pathogenicity.

[Transmission electron microscopy investigation of the denudation of the envelope of influenza virus treated with Nonidet P-40 and the binding influence of antibody].

OBJECTIVE: Through observing the morphological changes of the prepared influenza viruses (H1N1) treated with the different concentration of Nonidet P-40 solutions and added with antibody against the influenza virus using transmission electron microscopy (TEM), to explore the principle of application of the internal antibody for immunoassay of influenza virus. METHODS: Through treating the virus samples with serial diluted Nonidet P-40 solutions from 0.01% to 0.2% and/or not adding antibody against the influenza virus, then investigating the samples by TEM to obtain the morphological changes of the virions. RESULTS: The serial images show that the denudation degree of the virions is proportional with the rise of NP-40 concentration, and partly denuded virion image appeared at 0.1% NP-40 treatment, also under this condition no influence was observed on antibody binding to the virus. CONCLUSION: This work demonstrated the interaction between influenza virion and its antibody under nonionic surfactants existing, which supports the advantages of sample preparation for immunoassay enveloped virus using internal antibody theoretically.