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Studies on the Escherichia coli glucose-specific permease, PtsG, with a point mutation in its N-terminal amphipathic leader sequence

¹ Division of Biological Sciences, University of California at San Diego, La Jolla, CA 92093-0116, USA
² Department of Microbiology and Immunology, Faculty of Pharmacy, Ain Shams University, Al Khalifa Al Maamoun St, Abbassia, Cairo, Egypt
³ Department of Life Science, Jeonju University, Chonju, South Korea

Correspondence
Milton H. Saier Jr
msaier{at}ucsd.edu

Previous work has resulted in the isolation of several mutant glucose permeases (II^Glc or PtsG) of the Escherichia coli phosphotransferase system (PTS) with altered N-terminal amphipathic leader sequences. The mutations were reported to (1) broaden permease substrate specificity, (2) promote facilitated diffusion of some sugars and (3) increase ptsG gene transcription. Detailed biochemical analyses were conducted, showing that one such mutant (V12F-II^Glc) (1) contains dramatically increased amounts of II^Glc, (2) displays correspondingly increased in vitro phosphorylation and in vivo transport activities, (3) shows increased utilization of several metabolizable sugars and (4) shows decreased susceptibility to detergent activation. These results are interpreted as suggesting that the V12F substitution in the N-terminal amphipathic leader sequence of II^Glc alters the facility with which the permease is integrated into the membrane. Consequent changes in conformation alter its catalytic properties and increase its affinity for the pleiotropic transcriptional repressor, Mlc. These changes together are proposed to promote transcription of the ptsG gene and account for the observed phenotypic changes.

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