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Membrane fusion activity of influenza virus
Abstract:
A simple assay is described to monitor fusion between fowl plague virus (FPV, an avian influenza A virus) and liposomes which allows the simultaneous quantitation of both lytic and non-lytic fusion events. As in fusion between viruses and the plasma membrane and in FPV-induced cell-cell fusion, the reaction only occurs at pH 5.5 or below, and it is fast, highly efficient, and essentially non-lytic when fresh virus and liposomes are used. The fusion occurs over a broad temperature range, and has no requirement for divalent cations. The fusion factor of influenza virus is a hemagglutinin (HA) spike which protrudes from the virus membrane and which is also responsible for virus binding to the host cell. The finding that fusion occurs as efficiently with liposomes containing or lacking virus receptor structures, further emphasizes the remarkable division of labor in the HA molecule: the receptor-binding sites are located in the globular HA1 domains and the fusion activation peptide is found at the N-terminal of HA2 in the stem region of the protein. The mechanism of fusion is discussed in terms of the three-dimensional structure of the HA and the conformational change which the protein undergoes at the fusion pH optimum.
Insights
A new assay quantifies fowl plague virus (FPV) fusion with liposomes. This method reveals FPV fusion is pH-dependent and efficient, highlighting the hemagglutinin protein's role in viral entry.
Area of Science:
- Virology
- Biochemistry
- Membrane Fusion
Background:
- Viral fusion is critical for host cell entry.
- Influenza A virus hemagglutinin (HA) mediates both receptor binding and membrane fusion.
- Understanding the molecular mechanisms of viral fusion is essential for developing antiviral strategies.
Purpose of the Study:
- To develop a simple assay for monitoring fowl plague virus (FPV) fusion with liposomes.
- To simultaneously quantify lytic and non-lytic fusion events.
- To investigate the biophysical parameters and mechanism of FPV-liposome fusion.
Main Methods:
- Development of a novel assay to monitor FPV-liposome fusion.
- Quantitation of both lytic and non-lytic fusion events.
- Analysis of fusion efficiency under varying pH, temperature, and cation conditions.
Main Results:
- The assay allows simultaneous quantitation of lytic and non-lytic fusion events.
- FPV-liposome fusion occurs efficiently at pH 5.5 or below, is fast, and largely non-lytic with fresh components.
- Fusion is independent of divalent cations and occurs over a broad temperature range.
- Fusion efficiency is similar with liposomes containing or lacking viral receptor structures.
Conclusions:
- The hemagglutinin (HA) protein exhibits a division of labor, with distinct domains for receptor binding (HA1) and fusion (HA2).
- The study provides insights into the conformational changes of HA during low-pH-induced fusion.
- The developed assay is a valuable tool for studying viral fusion mechanisms.