# Transport Mechanism of the Multidrug Resistance Efflux Protein, EmrE

> **NIH NIH R01** · UNIVERSITY OF WISCONSIN-MADISON · 2020 · $308,059

## Abstract

Project Summary/Abstract
Antibiotic resistance due to the activity of multidrug resistance (MDR) efflux pumps is one important
mechanism of bacterial drug resistance. EmrE is one of the smallest known MDR transporters, and it has
become a prototype for proton-coupled antiport. EmrE harnesses proton import to drive polyaromatic cation
efflux in E. coli, thus conferring resistance to a broad range of drugs. We have previously performed the first
quantitative measurement of conformational exchange between open-in and open-out states in a transporter
by NMR. Our newest result, asymmetric protonation of EmrE, directly contradicts the long-accepted single-site
alternating access model for coupled antiport of drugs and protons. It demonstrates how much is still unknown
about this deceptively simply transporter and suggests that the well-known promiscuity of MDR efflux pumps
may even be even greater. This project uses NMR spectroscopy and extensive liposomal transport assays to
investigate the detailed molecular mechanism of EmrE activity. NMR offers a unique tool because protein
conformational exchange and protonation events can be monitored separately and simultaneously, allowing
novel insight into how proton and drug transport are coupled. Our goal is to combine quantitative biophysical
data and functional assessment of the pH dependence and substrates properties that define EmrE activity to
develop a novel model for proton-coupled antiport. We will also test different hypotheses for how proton-
coupled antiport is achieved for such diverse substrates with different affinities and transport rates. The
insights we gain will aid future efforts to combat bacterial antibiotic resistance due to MDR efflux.

## Key facts

- **NIH application ID:** 9979945
- **Project number:** 5R01GM095839-09
- **Recipient organization:** UNIVERSITY OF WISCONSIN-MADISON
- **Principal Investigator:** Katherine Anne Henzler-Wildman
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2020
- **Award amount:** $308,059
- **Award type:** 5
- **Project period:** 2011-07-01 → 2022-07-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/9979945

## Citation

> US National Institutes of Health, RePORTER application 9979945, Transport Mechanism of the Multidrug Resistance Efflux Protein, EmrE (5R01GM095839-09). Retrieved via AI Analytics 2026-05-22 from https://api.ai-analytics.org/grant/nih/9979945. Licensed CC0.

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