Cysteine Substitutions for Individual Residues in Helix VI of the Melibiose Carrier of Escherichia coli

Cysteine Substitutions for Individual Residues in Helix VI of the Melibiose Carrier of... The melibiose carrier of Escherichia coli is a cytoplasmic membrane protein that mediates the cotransport of galactosides with H+, Na+, or Li+. In this study we used cysteine-scanning mutagenesis to try to gain information about the position of transmembrane helix VI in the three-dimensional structure of the melibiose carrier. We constructed 23 individual cysteine substitutions in helix VI and an adjacent loop of the carrier. The resulting melibiose carriers retained 22–100% of their ability to transport melibiose. We tested the effect of the hydrophilic sulfhydryl reagent p-chloromercuri-benzenesulfonic acid (PCMBS) on the cysteine-substitution mutants and we found that there was no inhibition of melibiose transport in any of the mutants. We suggest that helix VI is imbedded in phospholipid and does not face the aqueous channel through which melibiose passes. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png The Journal of Membrane Biology Springer Journals

Cysteine Substitutions for Individual Residues in Helix VI of the Melibiose Carrier of Escherichia coli

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Publisher
Springer-Verlag
Copyright
Copyright © Inc. by 2001 Springer-Verlag New York
Subject
Life Sciences; Biochemistry, general; Human Physiology
ISSN
0022-2631
eISSN
1432-1424
D.O.I.
10.1007/s00232-001-0053-x
Publisher site
See Article on Publisher Site

Abstract

The melibiose carrier of Escherichia coli is a cytoplasmic membrane protein that mediates the cotransport of galactosides with H+, Na+, or Li+. In this study we used cysteine-scanning mutagenesis to try to gain information about the position of transmembrane helix VI in the three-dimensional structure of the melibiose carrier. We constructed 23 individual cysteine substitutions in helix VI and an adjacent loop of the carrier. The resulting melibiose carriers retained 22–100% of their ability to transport melibiose. We tested the effect of the hydrophilic sulfhydryl reagent p-chloromercuri-benzenesulfonic acid (PCMBS) on the cysteine-substitution mutants and we found that there was no inhibition of melibiose transport in any of the mutants. We suggest that helix VI is imbedded in phospholipid and does not face the aqueous channel through which melibiose passes.

Journal

The Journal of Membrane BiologySpringer Journals

Published: Sep 1, 2001

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