Entry of Enveloped Viruses Into Host Cells: Fusion Activity of the Influenza Virus Hemagglutinin

ABSTRACT Membrane fusion mediated by influenza virus hemagglutinin (HA) is believed to proceed via the cooperative action of multiple HA trimers. To determine the minimal number of HA trimers required to trigger fusion, and to assess the importance of cooperativity between these HA trimers, we have generated virosomes containing coreconstituted HAs derived from two strains of virus with different pH dependencies for fusion, X-47 (optimal fusion at pH 5.1; threshold at pH 5.6) and A/Shangdong (optimal fusion at pH 5.6; threshold at pH 6.0), and measured fusion of these virosomes with erythrocyte ghosts by a fluorescence lipid mixing assay. Virosomes with different X-47-to-A/Shangdong HA ratios, at a constant HA-to-lipid ratio, showed comparable ghost-binding activities, and the low-pH-induced conformational change of A/Shangdong HA did not affect the fusion activity of X-47 HA. The initial rate of fusion of these virosomes at pH 5.7 increased directly proportional to the surface density of A/Shangdong HA, and a single A/Shangdong trimer per virosome appeared to suffice to induce fusion. The reciprocal of the lag time before the onset of fusion was directly proportional to the surface density of fusion-competent HA. These results support the notion that there is no cooperativity between HA trimers during influenza virus fusion.

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Man-Specific, GalNAc/T/Tn-Specific and Neu5Ac-Specific Seaweed Lectins as Glycan Probes for the SARS-CoV-2 (COVID-19) Coronavirus

Marine Drugs ◽

10.3390/md18110543 ◽

2020 ◽

Vol 18 (11) ◽

pp. 543

Author(s):

Annick Barre ◽

Els J.M. Van Damme ◽

Mathias Simplicien ◽

Hervé Benoist ◽

Pierre Rougé

Keyword(s):

Influenza Virus ◽

Antiviral Agents ◽

Host Cells ◽

Carbohydrate Binding ◽

Complex Type ◽

Enveloped Viruses ◽

High Mannose ◽

Hiv 1 ◽

Biomedical Interest

Seaweed lectins, especially high-mannose-specific lectins from red algae, have been identified as potential antiviral agents that are capable of blocking the replication of various enveloped viruses like influenza virus, herpes virus, and HIV-1 in vitro. Their antiviral activity depends on the recognition of glycoprotein receptors on the surface of sensitive host cells—in particular, hemagglutinin for influenza virus or gp120 for HIV-1, which in turn triggers fusion events, allowing the entry of the viral genome into the cells and its subsequent replication. The diversity of glycans present on the S-glycoproteins forming the spikes covering the SARS-CoV-2 envelope, essentially complex type N-glycans and high-mannose type N-glycans, suggests that high-mannose-specific seaweed lectins are particularly well adapted as glycan probes for coronaviruses. This review presents a detailed study of the carbohydrate-binding specificity of high-mannose-specific seaweed lectins, demonstrating their potential to be used as specific glycan probes for coronaviruses, as well as the biomedical interest for both the detection and immobilization of SARS-CoV-2 to avoid shedding of the virus into the environment. The use of these seaweed lectins as replication blockers for SARS-CoV-2 is also discussed.

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Strategy for Developing Medical Arsenals by Modulation of Membrane Fusion Activity of Influenza Virus Hemagglutinin

Journal of Bacteriology and Virology ◽

10.4167/jbv.2013.43.4.337 ◽

2013 ◽

Vol 43 (4) ◽

pp. 337

Author(s):

Sangmoo Lee ◽

Jin Il Kim ◽

Ilseob Lee ◽

Man-Seong Park

Keyword(s):

Influenza Virus ◽

Membrane Fusion ◽

Fusion Activity ◽

Influenza Virus Hemagglutinin

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Conformational Intermediates and Fusion Activity of Influenza Virus Hemagglutinin

Journal of Virology ◽

10.1128/jvi.73.6.4567-4574.1999 ◽

1999 ◽

Vol 73 (6) ◽

pp. 4567-4574 ◽

Cited By ~ 57

Author(s):

Thomas Korte ◽

Kai Ludwig ◽

Frank P. Booy ◽

Robert Blumenthal ◽

Andreas Herrmann

Keyword(s):

Influenza Virus ◽

High Resolution ◽

Low Ph ◽

Fusion Activity ◽

Native Structure ◽

Ph Values ◽

Influenza Virus Hemagglutinin ◽

High Resolution Structure ◽

H3 Subtype ◽

Resolution Structure

ABSTRACT Three strains of influenza virus (H1, H2, and H3) exhibited similar characteristics in the ability of their hemagglutinin (HA) to induce membrane fusion, but the HAs differed in their susceptibility to inactivation. The extent of inactivation depended on the pH of preincubation and was lowest for A/Japan (H2 subtype), in agreement with previous studies (A. Puri, F. Booy, R. W. Doms, J. M. White, and R. Blumenthal, J. Virol. 64:3824–3832, 1990). While significant inactivation of X31 (H3 subtype) was observed at 37°C at pH values corresponding to the maximum of fusion (about pH 5.0), no inactivation was seen at preincubation pH values 0.2 to 0.4 pH units higher. Surprisingly, low-pH preincubation under those conditions enhanced the fusion rates and extents of A/Japan as well as those of X31. For A/PR 8/34 (H1 subtype), neither a shift of the pH (to >5.0) nor a decrease of the temperature to 20°C was sufficient to prevent inactivation. We provide evidence that the activated HA is a conformational intermediate distinct from the native structure and from the final structure associated with the conformational change of HA, which is implicated by the high-resolution structure of the soluble trimeric fragment TBHA2 (P. A. Bullough, F. M. Hughson, J. J. Skehel, and D. C. Wiley, Nature 371:37–43, 1994).

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Influenza–Host Interplay and Strategies for Universal Vaccine Development

Vaccines ◽

10.3390/vaccines8030548 ◽

2020 ◽

Vol 8 (3) ◽

pp. 548

Author(s):

Hye Suk Hwang ◽

Mincheol Chang ◽

Yoong Ahm Kim

Keyword(s):

Influenza Virus ◽

Influenza A ◽

Vaccine Development ◽

Current Knowledge ◽

Host Cells ◽

Influenza A Viruses ◽

Universal Vaccine ◽

Lectin Receptors ◽

Endosomal Membrane ◽

Influenza Virus Hemagglutinin

Influenza is an annual epidemic and an occasional pandemic caused by pathogens that are responsible for infectious respiratory disease. Humans are highly susceptible to the infection mediated by influenza A viruses (IAV). The entry of the virus is mediated by the influenza virus hemagglutinin (HA) glycoprotein that binds to the cellular sialic acid receptors and facilitates the fusion of the viral membrane with the endosomal membrane. During IAV infection, virus-derived pathogen-associated molecular patterns (PAMPs) are recognized by host intracellular specific sensors including toll-like receptors (TLRs), C-type lectin receptors, retinoic acid-inducible gene-I (RIG-I)-like receptors (RLRs), and nucleotide-binding oligomerization domain (NOD)-like receptors (NLRs) either on the cell surface or intracellularly in endosomes. Herein, we comprehensively review the current knowledge available on the entry of the influenza virus into host cells and the molecular details of the influenza virus–host interface. We also highlight certain strategies for the development of universal influenza vaccines.

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Membrane fusion activity of reconstituted vesicles of influenza virus hemagglutinin glycoproteins

Biochimica et Biophysica Acta (BBA) - Biomembranes ◽

10.1016/0005-2736(83)90534-5 ◽

1983 ◽

Vol 733 (2) ◽

pp. 286-290 ◽

Cited By ~ 26

Author(s):

Kazunori Kawasaki ◽

Satoshi B. Sato ◽

Shun-ichi Ohnishi

Keyword(s):

Influenza Virus ◽

Membrane Fusion ◽

Fusion Activity ◽

Influenza Virus Hemagglutinin

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Modification of the Cytoplasmic Domain of Influenza Virus Hemagglutinin Affects Enlargement of the Fusion Pore

Journal of Virology ◽

10.1128/jvi.74.16.7529-7537.2000 ◽

2000 ◽

Vol 74 (16) ◽

pp. 7529-7537 ◽

Cited By ~ 42

Author(s):

Christine Kozerski ◽

Evgeni Ponimaskin ◽

Britta Schroth-Diez ◽

Michael F. G. Schmidt ◽

Andreas Herrmann

Keyword(s):

Influenza Virus ◽

Membrane Fusion ◽

Transmembrane Domain ◽

Expression System ◽

Fusion Pore ◽

Target Cells ◽

Fusion Activity ◽

Wild Type ◽

Influenza Virus Hemagglutinin ◽

Pore Enlargement

ABSTRACT The fusion activity of chimeras of influenza virus hemagglutinin (HA) (from A/fpv/Rostock/34; subtype H7) with the transmembrane domain (TM) and/or cytoplasmic tail (CT) either from the nonviral, nonfusogenic T-cell surface protein CD4 or from the fusogenic Sendai virus F-protein was studied. Wild-type or chimeric HA was expressed in CV-1 cells by the transient T7-RNA-polymerase vaccinia virus expression system. Subsequently, the fusion activity of the expression products was monitored with red blood cells or ghosts as target cells. To assess the different steps of fusion, target cells were labeled with the fluorescent membrane label octadecyl rhodamine B-chloride (R18) (membrane fusion) and with the cytoplasmic fluorophores calcein (molecular weight [MW], 623; formation of small aqueous fusion pore) and tetramethylrhodamine-dextran (MW, 10,000; enlargement of fusion pore). All chimeric HA/F-proteins, as well as the chimera with the TM of CD4 and the CT of HA, were able to mediate the different steps of fusion very similarly to wild-type HA. Quite differently, chimeric proteins with the CT of CD4 were strongly impaired in mediating pore enlargement. However, membrane fusion and formation of small pores were similar to those of wild-type HA, indicating that the conformational change of the ectodomain and earlier fusion steps were not inhibited. Various properties of the CT which may affect pore enlargement are considered. We surmise that the hydrophobicity of the sequence adjacent to the transmembrane domain is important for pore dilation.

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