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Journal of Virology, February 2000, p. 1815-1826, Vol. 74, No. 4
National Institute of Animal Health,
Tsukuba,1 Institute of Life Science,
Soka University, Hachioji,2
Department of Pathology and Immunology, Faculty of Medicine,
Tokyo Medical and Dental University, Tokyo,3
and Division of Biology and Oncology, National Institute of
Radiological Sciences, Chiba,4 Japan
Received 26 July 1999/Accepted 17 November 1999
Ecotropic murine leukemia virus (MuLV) infection is initiated by
the interaction between the surface glycoprotein (SU) of the virus and
its cell-surface receptor mCAT-1. We investigated the SU-receptor
interaction by using a naturally occurring soluble SU which was encoded
by the envelope (env) gene of a defective endogenous MuLV, Fv-4r. Binding of the SU to
mCAT-1-positive mouse cells was completed by 1 min at 37°C. The SU
could not bind to mouse cells that were persistently infected by
ecotropic MuLVs (but not amphotropic or dualtropic MuLVs) or
transfected with wild-type ecotropic env genes or a mutant
env gene which can express only precursor Env protein that
is restricted to retention in the endoplasmic reticulum. These cells
were also resistant to superinfection by ecotropic MuLVs. Thus,
superinfection resistance correlated with the lack of SU-binding
capacity. After binding to the cells, the SU appeared to undergo some
conformational changes within 1 min in a temperature-dependent manner.
This was suggested by the different properties of two monoclonal
antibodies (MAbs) reactive with the same C-terminal half of the
Fv-4r SU domain, including a proline-rich motif
which was shown to be important for conformation of the SU and
interaction between the SU and the transmembrane protein. One MAb
reacting with the soluble SU bound to cells was dissociated by a
temperature shift from 4 to 37°C. Such dissociation was not observed
in cells synthesizing the SU or when another MAb was used, indicating
that the dissociation was not due to a temperature-dependent release of
the MAb but to possible conformational changes in the SU.
0022-538X/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Properties of the Naturally Occurring Soluble
Surface Glycoprotein of Ecotropic Murine Leukemia Virus: Binding
Specificity and Possible Conformational Change after Binding
to Receptor
*
Corresponding author. Mailing address: Laboratory of
Virological Products, National Institute of Animal Health, 3-1-1 Kannondai, Tsukuba, Ibaraki-ken 305-0856, Japan. Phone: 81-298-38-7757. Fax: 81-298-38-7880. E-mail:
hikeda{at}niah.affrc.go.ip.
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