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Journal of Bacteriology, January 1999, p. 462-468, Vol. 181, No. 2
Department of Molecular Biology, The Hebrew
University-Hadassah Medical School, Jerusalem 91120, Israel
Received 25 June 1998/Accepted 6 November 1998
The Escherichia coli BglF protein, an enzyme II of the
phosphoenolpyruvate-dependent carbohydrate phosphotransferase system, has several enzymatic activities. In the absence of
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Copyright © 1999, American Society for Microbiology. All rights reserved.
BglF, the Escherichia coli
-Glucoside
Permease and Sensor of the bgl System: Domain
Requirements of the Different Catalytic Activities
-glucosides, it
phosphorylates BglG, a positive regulator of bgl operon
transcription, thus inactivating BglG. In the presence of
-glucosides, it activates BglG by dephosphorylating it and, at the
same time, transports
-glucosides into the cell and phosphorylates
them. BglF is composed of two hydrophilic domains, IIAbgl
and IIBbgl, and a membrane-bound domain,
IICbgl, which are covalently linked in the order
IIBCAbgl. Cys-24 in the IIBbgl domain is
essential for all the phosphorylation and dephosphorylation activities
of BglF. We have investigated the domain requirement of the different
functions carried out by BglF. To this end, we cloned the individual
BglF domains, as well as the domain pairs IIBCbgl and
IICAbgl, and tested which domains and which combinations
are required for the catalysis of the different functions, both in
vitro and in vivo. We show here that the IIB and IIC domains, linked to each other (IIBCbgl), are required for the sugar-driven
reactions, i.e., sugar phosphotransfer and BglG activation by
dephosphorylation. In contrast, phosphorylated IIBbgl alone
can catalyze BglG inactivation by phosphorylation. Thus, the
sugar-induced and noninduced functions have different structural requirements. Our results suggest that catalysis of the sugar-induced functions depends on specific interactions between IIBbgl
and IICbgl which occur upon the interaction of BglF with
the sugar.
*
Corresponding author. Mailing address: Department of
Molecular Biology, The Hebrew University-Hadassah Medical School, POB 12272, Jerusalem 91120, Israel. Phone: 972 2 675 8460. Fax: 972 2 678 4010. E-mail: amster{at}cc.huji.ac.il.
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