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J Bacteriol, May 1998, p. 2507-2514, Vol. 180, No. 9
Department of Microbiology, University of
Washington, Seattle, Washington 98195-7242
The maltose transport complex of Escherichia coli is a
well-studied example of an ATP-binding cassette transporter. The
complex, containing one copy each of the integral membrane proteins
MalG and MalF and two copies of the peripheral cytoplasmic membrane protein MalK, interacts with the periplasmic maltose-binding protein to
efficiently translocate maltose and maltodextrins across the bacterial
cytoplasmic membrane. To investigate the role of MalG both in
MalFGK2 assembly interactions and in subsequent transport interactions, we isolated and characterized 18 different MalG mutants,
each containing a 31-residue insertion in the protein. Eight insertions
mapping to distinct hydrophilic regions of MalG permitted either
assembly or both assembly and transport interactions to occur. In
particular, we isolated two insertions mapping to extracytoplasmic
(periplasmic) regions of MalG which preserved both assembly and
transport abilities, suggesting that these are permissive sites in the
protein. Another periplasmic insertion seems to affect only
transport-specific interactions between MalG and maltose-binding
protein, defining a novel class of MalG mutants. Finally, four MalG
mutant proteins, although stably expressed, are unable to assemble into
the MalFGK2 complex. These mutants contain insertions in
only two different hydrophilic regions of MalG, consistent with the
notion that a restricted number of domains in this protein are critical
complex assembly determinants. These MalG mutants will allow us to
further explore the intermolecular interactions of this model
transporter.
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Exploring the Role of Integral Membrane Proteins in
ATP-Binding Cassette Transporters: Analysis of a Collection of MalG
Insertion Mutants
*
Corresponding author. Mailing address: University of
Washington, Department of Microbiology, Box 357242, Seattle, WA
98195-7242. Phone: (206) 543-5485. Fax: (206) 543-8297. E-mail:
btraxler{at}u.washington.edu.
J Bacteriol, May 1998, p. 2507-2514, Vol. 180, No. 9
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
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