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Electrostatic lock in the transport cycle of the multidrug resistance transporter EmrE
EmrE is a small, homodimeric membrane transporter that exploits the established electrochemical proton gradient across the Escherichia coli inner membrane to export toxic polyaromatic cations, prototypical of the wider small-multidrug resistance transporter family. While prior studies have establish...
Autores principales: | , , |
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Formato: | Online Artículo Texto |
Lenguaje: | English |
Publicado: |
National Academy of Sciences
2018
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Materias: | |
Acceso en línea: | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6094130/ https://www.ncbi.nlm.nih.gov/pubmed/30026196 http://dx.doi.org/10.1073/pnas.1722399115 |
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author | Vermaas, Josh V. Rempe, Susan B. Tajkhorshid, Emad |
author_facet | Vermaas, Josh V. Rempe, Susan B. Tajkhorshid, Emad |
author_sort | Vermaas, Josh V. |
collection | PubMed |
description | EmrE is a small, homodimeric membrane transporter that exploits the established electrochemical proton gradient across the Escherichia coli inner membrane to export toxic polyaromatic cations, prototypical of the wider small-multidrug resistance transporter family. While prior studies have established many fundamental aspects of the specificity and rate of substrate transport in EmrE, low resolution of available structures has hampered identification of the transport coupling mechanism. Here we present a complete, refined atomic structure of EmrE optimized against available cryo-electron microscopy (cryo-EM) data to delineate the critical interactions by which EmrE regulates its conformation during the transport process. With the model, we conduct molecular dynamics simulations of the transporter in explicit membranes to probe EmrE dynamics under different substrate loading and conformational states, representing different intermediates in the transport cycle. The refined model is stable under extended simulation. The water dynamics in simulation indicate that the hydrogen-bonding networks around a pair of solvent-exposed glutamate residues (E14) depend on the loading state of EmrE. One specific hydrogen bond from a tyrosine (Y60) on one monomer to a glutamate (E14) on the opposite monomer is especially critical, as it locks the protein conformation when the glutamate is deprotonated. The hydrogen bond provided by Y60 lowers the [Formula: see text] of one glutamate relative to the other, suggesting both glutamates should be protonated for the hydrogen bond to break and a substrate-free transition to take place. These findings establish the molecular mechanism for the coupling between proton transfer reactions and protein conformation in this proton-coupled secondary transporter. |
format | Online Article Text |
id | pubmed-6094130 |
institution | National Center for Biotechnology Information |
language | English |
publishDate | 2018 |
publisher | National Academy of Sciences |
record_format | MEDLINE/PubMed |
spelling | pubmed-60941302018-08-17 Electrostatic lock in the transport cycle of the multidrug resistance transporter EmrE Vermaas, Josh V. Rempe, Susan B. Tajkhorshid, Emad Proc Natl Acad Sci U S A PNAS Plus EmrE is a small, homodimeric membrane transporter that exploits the established electrochemical proton gradient across the Escherichia coli inner membrane to export toxic polyaromatic cations, prototypical of the wider small-multidrug resistance transporter family. While prior studies have established many fundamental aspects of the specificity and rate of substrate transport in EmrE, low resolution of available structures has hampered identification of the transport coupling mechanism. Here we present a complete, refined atomic structure of EmrE optimized against available cryo-electron microscopy (cryo-EM) data to delineate the critical interactions by which EmrE regulates its conformation during the transport process. With the model, we conduct molecular dynamics simulations of the transporter in explicit membranes to probe EmrE dynamics under different substrate loading and conformational states, representing different intermediates in the transport cycle. The refined model is stable under extended simulation. The water dynamics in simulation indicate that the hydrogen-bonding networks around a pair of solvent-exposed glutamate residues (E14) depend on the loading state of EmrE. One specific hydrogen bond from a tyrosine (Y60) on one monomer to a glutamate (E14) on the opposite monomer is especially critical, as it locks the protein conformation when the glutamate is deprotonated. The hydrogen bond provided by Y60 lowers the [Formula: see text] of one glutamate relative to the other, suggesting both glutamates should be protonated for the hydrogen bond to break and a substrate-free transition to take place. These findings establish the molecular mechanism for the coupling between proton transfer reactions and protein conformation in this proton-coupled secondary transporter. National Academy of Sciences 2018-08-07 2018-07-19 /pmc/articles/PMC6094130/ /pubmed/30026196 http://dx.doi.org/10.1073/pnas.1722399115 Text en Copyright © 2018 the Author(s). Published by PNAS. https://creativecommons.org/licenses/by-nc-nd/4.0/ This open access article is distributed under Creative Commons Attribution-NonCommercial-NoDerivatives License 4.0 (CC BY-NC-ND) (https://creativecommons.org/licenses/by-nc-nd/4.0/) . |
spellingShingle | PNAS Plus Vermaas, Josh V. Rempe, Susan B. Tajkhorshid, Emad Electrostatic lock in the transport cycle of the multidrug resistance transporter EmrE |
title | Electrostatic lock in the transport cycle of the multidrug resistance transporter EmrE |
title_full | Electrostatic lock in the transport cycle of the multidrug resistance transporter EmrE |
title_fullStr | Electrostatic lock in the transport cycle of the multidrug resistance transporter EmrE |
title_full_unstemmed | Electrostatic lock in the transport cycle of the multidrug resistance transporter EmrE |
title_short | Electrostatic lock in the transport cycle of the multidrug resistance transporter EmrE |
title_sort | electrostatic lock in the transport cycle of the multidrug resistance transporter emre |
topic | PNAS Plus |
url | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6094130/ https://www.ncbi.nlm.nih.gov/pubmed/30026196 http://dx.doi.org/10.1073/pnas.1722399115 |
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