|
|
|
|
|
|
|
||
* Department of Cell Biology, Tokyo Metropolitan Institute for Neuroscience, Tokyo 183; 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 <4 nm in the center. The pits transformed into
narrow membrane connections <10 nm in width, bridging viruses and liposomes. The structures of the fusion
pore and fusion neck with larger sizes were also observed,
indicating growth of the protrusions and pits to distinct fusion sites. We propose that the microprotrusion of
the lipid bilayer is a fusion intermediate induced by hemagglutinin protein, and suggest that the extraordinarily
high curvature of this membrane structure is a clue to
the onset of fusion. The possible architecture of the fusion intermediate is discussed with regard to the localization of intramembrane particles at the microprotrusion.
Cellular Biophysics Laboratory,
National Institute of Bioscience and Human Technology, Tsukuba 305; and § Department of Biophysics, Faculty of Science,
Kyoto University, Kyoto 606, Japan
CiteULike 
Complore 
Connotea 
Del.icio.us 
Digg 
Reddit 
Technorati What's this?
This article has been cited by other articles:
|
|
