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J. Virol., 12 1997, 9278-9284, Vol 71, No. 12
VP Nguyen and BG Hogue
Coronaviruses assemble and obtain their envelope at membranes of the
intermediate compartment between the endoplasmic reticulum and Golgi
complex. Like other enveloped viruses, coronavirus assembly is presumably
dependent on protein localization and protein-protein as well as
protein-RNA interactions. We have used the bovine coronavirus (BCV) as a
model to study interactions between the viral proteins in virus-infected
cells that are important for coronavirus assembly. BCV is a prototype for
the coronaviruses that express an additional major structural protein, the
hemagglutinin esterase (HE), in addition to the spike (S) glycoprotein,
membrane (M) glycoprotein, and nucleocapsid (N) protein. Complexes
consisting of the M, S, and HE proteins were detected in virus-infected
cells by coimmunoprecipitations. Kinetic analyses demonstrated that S
protein and HE each quickly formed a complex with M protein after
synthesis, whereas heterocomplexes consisting of all three proteins formed
more slowly. The kinetics of HE biosynthesis revealed that the half-life of
oligomerization was approximately 30 min, which correlated with the
appearance of complexes consisting of M, HE, and S proteins, suggesting
that oligomerization and/or conformational changes may be important for the
S-M-HE protein complexes to form. Only HE dimers were found associated with
the heterocomplexes consisting of all three proteins. S-M-HE protein
complexes were detected prior to processing of the oligosaccharide chains
on HE, indicating that these protein complexes formed in a premedial Golgi
compartment before trimming of sugar chains. Transient coexpressions and
double-labeling immunofluorescence demonstrated that HE and S proteins
colocalized with M protein. This was further supported by
coimmunoprecipitation of specific HE-M and S-M protein complexes from
transfected cells, indicating that these proteins can form complexes in the
absence of other viral proteins.
Copyright © 1997, American Society for Microbiology
Protein interactions during coronavirus assembly
Division of Molecular Virology, Baylor College of Medicine, Houston, Texas 77030, USA.
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