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J Biol Chem, Vol. 275, Issue 16, 11765-11770, April 21, 2000
Disulfide Bond Formation Is Not Required for Human Chorionic
Gonadotropin Subunit Association
STUDIES WITH DITHIOTHREITOL IN JEG-3 CELLS*
Vinod
Singh and
Wolfgang E.
Merz§
From the Biochemie-Zentrum Heidelberg, University of Heidelberg, Im
Neuenheimer Feld 328, 69120 Heidelberg, Germany
To study the influence of disulfide bridge
formation on the assembly of the subunits of human chorionic
gonadotropin in JEG-3 choriocarcinoma cells, dithiothreitol (DTT) was
used to create a reducing milieu in the endoplasmic reticulum (ER)
in vivo. In the presence of 5 mM DTT during
pulse-chase experiments all of the -subunit precursors observed in
unperturbed cells (p 0, p 1, p 2, and *) collapsed into the
p 0 form. The reducing milieu of the ER was reoxidized in
less than 5 min after removal of DTT from the medium. DTT markedly
increased the half-life of the p 0 precursor from 8.8 to
65.2 min. Under reoxidation conditions, the -subunit precursors folded back from p 0 in less than 5 min. In unperturbed
JEG-3 cells, the -subunit was present in both fully glycosylated and monoglycosylated precursor (pre- ) forms. The attachment of the second N-linked glycan residue of the -subunit was
accelerated in the presence of DTT, and consequently pre- -subunit
was missing from the DTT-treated cultures. The formation of
 -dimers appeared to be at least partially independent of the
oxidation state in the ER. The  -dimer was present under
conditions in which disulfide bridge formation was prevented by
exposure to 5 mM DTT before and during the pulse period.
This clearly suggests that the human chorionic gonadotropin subunits
may acquire association-competent conformations even when no disulfide
bridge formation has taken place.
*
This work was supported by Grant Me 545/10-1 from the
Deutsche Forschungsgemeinschaft, Bonn-Bad Godesberg (to W. E. M.) and a fellowship of the Alexander von Humboldt Foundation, Bonn-Bad Godesberg (to V. S.).The costs of publication of this
article were defrayed in part by the
payment of page charges. The article must therefore be hereby marked
"advertisement" in
accordance with 18 U.S.C. Section
1734 solely to indicate this fact.
Present address: Hormone Biochemistry Laboratory, Inst. of Self
Organizing Systems and Biophysics, North-Eastern Hill University, Permanent Campus, Shillong-793022, Meghalaya, India.
§
To whom correspondence should be addressed: Biochemie-Zentrum
Heidelberg, University of Heidelberg, Im Neuenheimer Feld 328, 69120 Heidelberg, Germany. Tel.: 49-6221-544181; Fax: 49-6221-545586; E-mail:
wolfgang.merz@urz.uni-heidelberg.de.
Copyright © 2000 by The American Society for Biochemistry and Molecular Biology, Inc.

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Copyright © 2000 by the American Society for Biochemistry and Molecular Biology.
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