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J. Virol., 09 1997, 6287-6295, Vol 71, No. 9
J Stone-Hulslander and TG Morrison
For many paramyxoviruses, including Newcastle disease virus (NDV),
syncytium formation requires the expression of both surface glycoproteins
(HN and F) in the same cell, and evidence suggests that fusion involves a
specific interaction between the HN and F proteins. Because a potential
interaction in paramyxovirus-infected cells has never been demonstrated,
such as interaction was explored by using coimmunoprecipitation and
cross-linking. Both HN and F proteins could be precipitated with
heterologous antisera after a 5-min radioactive pulse as well as after a
2-h chase in nonradioactive medium, but at low levels. Chemical
cross-linking increased detection of complexes containing HN and F proteins
at the cell surface. After cross-linking, intermediate- as well as
high-molecular-weight species containing both proteins were precipitated
with monospecific antisera. Precipitation of proteins with anti-HN after
cross-linking resulted in the detection of complexes which electrophresed
in the stacker region of the gel, from 160 to 300 kDa, at 150 kDa, and at
74 kDa. Precipitates obtained with anti-F after cross-linking contained
species which migrated in the stacker region of the gel, between 160 and
300 kDa, at 120 kDa, and at 66 kDa. The three to four discrete complexes
ranging in size from 160 to 300 kDa contained both HN and F proteins when
precipitated with either HN or F antisera. That cross-linking of complexes
containing both HN and F proteins was not simply a function of
overexpression of viral glycoproteins at the cell surface was addressed by
demonstrating cross-linking at early time points postinfection, when levels
of viral surface glycoproteins are low. Use of cells infected with an
avirulent strain of NDV showed that chemically cross-linked HN and F
proteins were precipitated independent of cleavage of F0. Furthermore,
under conditions that maximized HN protein binding to its receptor, there
was no change in the percentages of HN and F0 proteins precipitated with
heterologous antisera, but a decrease in F1 protein precipitated was
observed upon attachment. These data argue that the HN and F proteins
interact in the rough endoplasmic reticulum. Upon attachment of the HN
protein to its receptor, the HN protein undergoes a conformational change
which causes a conformational change in the associated F protein, releasing
the hydrophobic fusion peptide into the target membrane and initiating
fusion.
Copyright © 1997, American Society for Microbiology
Detection of an interaction between the HN and F proteins in Newcastle disease virus-infected cells
Department of Molecular Genetics and Microbiology, University of Massachusetts Medical School, Worcester 01655, USA.
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