PMID:2156798
| Citation |
Lloyd, AD and Kadner, RJ (1990) Topology of the Escherichia coli uhpT sugar-phosphate transporter analyzed by using TnphoA fusions. J. Bacteriol. 172:1688-93 |
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| Abstract |
The Escherichia coli uhpT protein catalyzes the active transport of sugar-phosphates by an obligatory exchange mechanism. To examine its transmembrane topology, we isolated a collection of uhpT-phoA fusions encoding hybrid proteins of different lengths from the N terminus of UhpT fused to alkaline phosphatase by using transposon TnphoA. These fusions displayed different levels of alkaline phosphatase activity, although comparable levels of full-length UhpT-PhoA proteins were produced in maxicells of both high- and low-activity fusions. The full-length protein species were unstable and were degraded to the size of the alkaline phosphatase moiety in the case of a high-activity fusion or to small fragments in the case of a low-activity fusion. The enzyme activity present in low-activity fusions appeared to result from export of a small proportion of the fusion proteins to the periplasmic space. Although fusions were not obtained in all predicted extramembranous loops, the deduced topology of UhpT was consistent with a model of 12 membrane-spanning regions oriented with the amino and carboxyl termini in the cytoplasm. |
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| Keywords |
Bacterial Proteins/genetics; Bacterial Proteins/metabolism; Base Sequence; Carrier Proteins/genetics; Carrier Proteins/metabolism; Cloning, Molecular; DNA Transposable Elements; DNA, Recombinant/metabolism; Escherichia coli/genetics; Escherichia coli/metabolism; Escherichia coli Proteins; Molecular Sequence Data; Monosaccharide Transport Proteins; Oligonucleotide Probes; Plasmids; Protein Conformation; Recombinant Fusion Proteins/metabolism |
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