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pH Regulation of Electrogenic Sugar/H(+) Symport in MFS Sugar Permeases

Bacterial sugar symporters in the Major Facilitator Superfamily (MFS) use the H(+) (and in a few cases Na(+)) electrochemical gradients to achieve active transport of sugar into the cell. Because a number of structures of MFS sugar symporters have been solved recently, molecular insight into the tra...

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Autores principales: Bazzone, Andre, Madej, M. Gregor, Kaback, H. Ronald, Fendler, Klaus
Formato: Online Artículo Texto
Lenguaje:English
Publicado: Public Library of Science 2016
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4882079/
https://www.ncbi.nlm.nih.gov/pubmed/27227677
http://dx.doi.org/10.1371/journal.pone.0156392
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author Bazzone, Andre
Madej, M. Gregor
Kaback, H. Ronald
Fendler, Klaus
author_facet Bazzone, Andre
Madej, M. Gregor
Kaback, H. Ronald
Fendler, Klaus
author_sort Bazzone, Andre
collection PubMed
description Bacterial sugar symporters in the Major Facilitator Superfamily (MFS) use the H(+) (and in a few cases Na(+)) electrochemical gradients to achieve active transport of sugar into the cell. Because a number of structures of MFS sugar symporters have been solved recently, molecular insight into the transport mechanism is possible from detailed functional analysis. We present here a comparative electrophysiological study of the lactose permease (LacY), the fucose permease (FucP) and the xylose permease (XylE), which reveals common mechanistic principles and differences. In all three symporters energetically downhill electrogenic sugar/H(+) symport is observed. Comparison of the pH dependence of symport at symmetrical pH exhibits broad bell-shaped pH profiles extending over 3 to 6 pH units and a decrease at extremely alkaline pH ≥ 9.4 and at acidic to neutral pH = 4.6–7.5. The pH dependence can be described by an acidic to neutral apparent pK (pK(app)) and an alkaline pK(app). Experimental evidence suggests that the alkaline pK(app) is due to H(+) depletion at the protonation site, while the acidic pK(app) is due to inhibition of deprotonation. Since previous studies suggest that a single carboxyl group in LacY (Glu325) may be the only side chain directly involved in H(+) translocation and a carboxyl side chain with similar properties has been identified in FucP (Asp46) and XylE (Asp27), the present results imply that the pK of this residue is switched during H(+)/sugar symport in all three symporters.
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spelling pubmed-48820792016-06-10 pH Regulation of Electrogenic Sugar/H(+) Symport in MFS Sugar Permeases Bazzone, Andre Madej, M. Gregor Kaback, H. Ronald Fendler, Klaus PLoS One Research Article Bacterial sugar symporters in the Major Facilitator Superfamily (MFS) use the H(+) (and in a few cases Na(+)) electrochemical gradients to achieve active transport of sugar into the cell. Because a number of structures of MFS sugar symporters have been solved recently, molecular insight into the transport mechanism is possible from detailed functional analysis. We present here a comparative electrophysiological study of the lactose permease (LacY), the fucose permease (FucP) and the xylose permease (XylE), which reveals common mechanistic principles and differences. In all three symporters energetically downhill electrogenic sugar/H(+) symport is observed. Comparison of the pH dependence of symport at symmetrical pH exhibits broad bell-shaped pH profiles extending over 3 to 6 pH units and a decrease at extremely alkaline pH ≥ 9.4 and at acidic to neutral pH = 4.6–7.5. The pH dependence can be described by an acidic to neutral apparent pK (pK(app)) and an alkaline pK(app). Experimental evidence suggests that the alkaline pK(app) is due to H(+) depletion at the protonation site, while the acidic pK(app) is due to inhibition of deprotonation. Since previous studies suggest that a single carboxyl group in LacY (Glu325) may be the only side chain directly involved in H(+) translocation and a carboxyl side chain with similar properties has been identified in FucP (Asp46) and XylE (Asp27), the present results imply that the pK of this residue is switched during H(+)/sugar symport in all three symporters. Public Library of Science 2016-05-26 /pmc/articles/PMC4882079/ /pubmed/27227677 http://dx.doi.org/10.1371/journal.pone.0156392 Text en https://creativecommons.org/publicdomain/zero/1.0/ This is an open access article, free of all copyright, and may be freely reproduced, distributed, transmitted, modified, built upon, or otherwise used by anyone for any lawful purpose. The work is made available under the Creative Commons CC0 (https://creativecommons.org/publicdomain/zero/1.0/) public domain dedication.
spellingShingle Research Article
Bazzone, Andre
Madej, M. Gregor
Kaback, H. Ronald
Fendler, Klaus
pH Regulation of Electrogenic Sugar/H(+) Symport in MFS Sugar Permeases
title pH Regulation of Electrogenic Sugar/H(+) Symport in MFS Sugar Permeases
title_full pH Regulation of Electrogenic Sugar/H(+) Symport in MFS Sugar Permeases
title_fullStr pH Regulation of Electrogenic Sugar/H(+) Symport in MFS Sugar Permeases
title_full_unstemmed pH Regulation of Electrogenic Sugar/H(+) Symport in MFS Sugar Permeases
title_short pH Regulation of Electrogenic Sugar/H(+) Symport in MFS Sugar Permeases
title_sort ph regulation of electrogenic sugar/h(+) symport in mfs sugar permeases
topic Research Article
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4882079/
https://www.ncbi.nlm.nih.gov/pubmed/27227677
http://dx.doi.org/10.1371/journal.pone.0156392
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