Structural Features of Membrane Fusion between Influenza Virus and Liposome as Revealed by Quick-Freezing Electron Microscopy

The structure of membrane fusion intermediates between the A/PR/8(H1N1) strain of influenza virus and a liposome composed of egg phosphatidylcholine, cholesterol, and glycophorin was studied using quick-freezing electron microscopy. Fusion by viral hemagglutinin protein was induced at pH 5.0 and 23°...

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Bibliographic Details
Published in:The Journal of cell biology 1997-06, Vol.137 (5), p.1041-1056
Main Authors: Kanaseki, Toku, Kawasaki, Kazunori, Murata, Masayuki, Ikeuchi, Yoko, Ohnishi, Shun-ichi
Format: Article
Language:English
Subjects:
Acids
Animals
Cell membranes
Cells
Cellular biology
Chick Embryo
Freeze Fracturing
Hemagglutinins - analysis
Hemagglutinins - metabolism
Hydrogen-Ion Concentration
Influenza
Influenza A virus
Intracellular Membranes - metabolism
Intracellular Membranes - ultrastructure
Intracellular Membranes - virology
Lipid bilayers
Liposomes
Liposomes - metabolism
Membranes
Mica
Orthomyxoviridae
Orthomyxoviridae - metabolism
Orthomyxoviridae - ultrastructure
P branes
Viral morphology
Virions
Viruses
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Summary:The structure of membrane fusion intermediates between the A/PR/8(H1N1) strain of influenza virus and a liposome composed of egg phosphatidylcholine, cholesterol, and glycophorin was studied using quick-freezing electron microscopy. Fusion by viral hemagglutinin protein was induced at pH 5.0 and 23°C. After a 19-s incubation under these conditions, small protrusions with a diameter of 10-20 nm were found on the fractured convex faces of the liposomal membranes, and small pits complementary to the protrusions were found on the concave faces. The protrusions and pits corresponded to fractured parts of outward bendings of the lipid bilayer or "microprotrusions of the lipid bilayer." At the loci of the protrusions and pits, liposomal membranes had local contacts with viral membranes. In many cases both the protrusions and the pits were aligned in regular polygonal arrangements, which were thought to reflect the array of hemagglutinin spikes on the viral surface. These structures were induced only when the medium was acidic with the virus present. Based on these observations, it was concluded that the microprotrusions of the lipid bilayer are induced by hemagglutinin protein. Furthermore, morphological evidence for the formation of the "initial fusion pore" at the microprotrusion was obtained. The protrusion on the convex face sometimes had a tiny hole with a diameter of
ISSN:0021-9525
1540-8140
DOI:10.1083/jcb.137.5.1041