1
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Burata OE, O'Donnell E, Hyun J, Lucero RM, Thomas JE, Gibbs EM, Reacher I, Carney NA, Stockbridge RB. Peripheral positions encode transport specificity in the small multidrug resistance exporters. Proc Natl Acad Sci U S A 2024; 121:e2403273121. [PMID: 38865266 PMCID: PMC11194549 DOI: 10.1073/pnas.2403273121] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2024] [Accepted: 05/02/2024] [Indexed: 06/14/2024] Open
Abstract
In secondary active transporters, a relatively limited set of protein folds have evolved diverse solute transport functions. Because of the conformational changes inherent to transport, altering substrate specificity typically involves remodeling the entire structural landscape, limiting our understanding of how novel substrate specificities evolve. In the current work, we examine a structurally minimalist family of model transport proteins, the small multidrug resistance (SMR) transporters, to understand the molecular basis for the emergence of a novel substrate specificity. We engineer a selective SMR protein to promiscuously export quaternary ammonium antiseptics, similar to the activity of a clade of multidrug exporters in this family. Using combinatorial mutagenesis and deep sequencing, we identify the necessary and sufficient molecular determinants of this engineered activity. Using X-ray crystallography, solid-supported membrane electrophysiology, binding assays, and a proteoliposome-based quaternary ammonium antiseptic transport assay that we developed, we dissect the mechanistic contributions of these residues to substrate polyspecificity. We find that substrate preference changes not through modification of the residues that directly interact with the substrate but through mutations peripheral to the binding pocket. Our work provides molecular insight into substrate promiscuity among the SMRs and can be applied to understand multidrug export and the evolution of novel transport functions more generally.
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Affiliation(s)
- Olive E Burata
- Program in Chemical Biology, University of Michigan, Ann Arbor, MI 48109
| | - Ever O'Donnell
- Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, MI 48109
| | - Jeonghoon Hyun
- Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, MI 48109
| | - Rachael M Lucero
- Program in Chemical Biology, University of Michigan, Ann Arbor, MI 48109
| | - Junius E Thomas
- Program in Chemical Biology, University of Michigan, Ann Arbor, MI 48109
| | - Ethan M Gibbs
- Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, MI 48109
| | - Isabella Reacher
- Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, MI 48109
| | - Nolan A Carney
- Program in Chemical Biology, University of Michigan, Ann Arbor, MI 48109
| | - Randy B Stockbridge
- Program in Chemical Biology, University of Michigan, Ann Arbor, MI 48109
- Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, MI 48109
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2
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Li J, Her AS, Besch A, Ramirez-Cordero B, Crames M, Banigan JR, Mueller C, Marsiglia WM, Zhang Y, Traaseth NJ. Dynamics underlie the drug recognition mechanism by the efflux transporter EmrE. Nat Commun 2024; 15:4537. [PMID: 38806470 PMCID: PMC11133458 DOI: 10.1038/s41467-024-48803-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2023] [Accepted: 05/14/2024] [Indexed: 05/30/2024] Open
Abstract
The multidrug efflux transporter EmrE from Escherichia coli requires anionic residues in the substrate binding pocket for coupling drug transport with the proton motive force. Here, we show how protonation of a single membrane embedded glutamate residue (Glu14) within the homodimer of EmrE modulates the structure and dynamics in an allosteric manner using NMR spectroscopy. The structure of EmrE in the Glu14 protonated state displays a partially occluded conformation that is inaccessible for drug binding by the presence of aromatic residues in the binding pocket. Deprotonation of a single Glu14 residue in one monomer induces an equilibrium shift toward the open state by altering its side chain position and that of a nearby tryptophan residue. This structural change promotes an open conformation that facilitates drug binding through a conformational selection mechanism and increases the binding affinity by approximately 2000-fold. The prevalence of proton-coupled exchange in efflux systems suggests a mechanism that may be shared in other antiporters where acid/base chemistry modulates access of drugs to the substrate binding pocket.
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Affiliation(s)
- Jianping Li
- Department of Chemistry, New York University, New York, NY, USA
| | - Ampon Sae Her
- Department of Chemistry, New York University, New York, NY, USA
| | - Alida Besch
- Department of Chemistry, New York University, New York, NY, USA
| | | | - Maureen Crames
- Department of Chemistry, New York University, New York, NY, USA
| | - James R Banigan
- Department of Chemistry, New York University, New York, NY, USA
| | - Casey Mueller
- Department of Chemistry, New York University, New York, NY, USA
| | | | - Yingkai Zhang
- Department of Chemistry, New York University, New York, NY, USA
- Simons Center for Computational Physical Chemistry, New York University, New York, NY, USA
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3
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Li J, Li Y, Koide A, Kuang H, Torres VJ, Koide S, Wang DN, Traaseth NJ. Proton-coupled transport mechanism of the efflux pump NorA. Nat Commun 2024; 15:4494. [PMID: 38802368 PMCID: PMC11130294 DOI: 10.1038/s41467-024-48759-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2023] [Accepted: 05/13/2024] [Indexed: 05/29/2024] Open
Abstract
Efflux pump antiporters confer drug resistance to bacteria by coupling proton import with the expulsion of antibiotics from the cytoplasm. Despite efforts there remains a lack of understanding as to how acid/base chemistry drives drug efflux. Here, we uncover the proton-coupling mechanism of the Staphylococcus aureus efflux pump NorA by elucidating structures in various protonation states of two essential acidic residues using cryo-EM. Protonation of Glu222 and Asp307 within the C-terminal domain stabilized the inward-occluded conformation by forming hydrogen bonds between the acidic residues and a single helix within the N-terminal domain responsible for occluding the substrate binding pocket. Remarkably, deprotonation of both Glu222 and Asp307 is needed to release interdomain tethering interactions, leading to opening of the pocket for antibiotic entry. Hence, the two acidic residues serve as a "belt and suspenders" protection mechanism to prevent simultaneous binding of protons and drug that enforce NorA coupling stoichiometry and confer antibiotic resistance.
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Affiliation(s)
- Jianping Li
- Department of Chemistry, New York University, New York, NY, USA
| | - Yan Li
- Department of Cell Biology, New York University School of Medicine, New York, NY, USA
| | - Akiko Koide
- Perlmutter Cancer Center, New York University School of Medicine, New York, NY, USA
- Department of Medicine, New York University School of Medicine, New York, NY, USA
| | - Huihui Kuang
- Simons Electron Microscopy Center, New York Structural Biology Center, New York, NY, USA
| | - Victor J Torres
- Department of Microbiology, New York University School of Medicine, New York, NY, USA
- Antimicrobial-Resistant Pathogens Program, New York University School of Medicine, New York, NY, USA
| | - Shohei Koide
- Perlmutter Cancer Center, New York University School of Medicine, New York, NY, USA
- Department of Biochemistry and Molecular Pharmacology, New York University School of Medicine, New York, NY, USA
| | - Da-Neng Wang
- Department of Cell Biology, New York University School of Medicine, New York, NY, USA.
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4
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Prakash A, Li Z, Chirasani VR, Rasquinha JA, Valentin NH, Hubbard GB, Yin G, Dohlman HG, Campbell SL. Molecular and Functional Profiling of Gαi as an Intracellular pH Sensor. RESEARCH SQUARE 2024:rs.3.rs-4203924. [PMID: 38746411 PMCID: PMC11092800 DOI: 10.21203/rs.3.rs-4203924/v1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/16/2024]
Abstract
Heterotrimeric G proteins (Gα, Gβ and Gγ) act downstream of G-protein-coupled receptors (GPCRs) to mediate signaling pathways that regulate various physiological processes and human disease conditions. Previously, human Gαi and its yeast homolog Gpa1 have been reported to function as intracellular pH sensors, yet the pH sensing capabilities of Gαi and the underlying mechanism remain to be established. Herein, we identify a pH sensing network within Gαi, and evaluate the consequences of pH modulation on the structure and stability of the G-protein. We find that changes over the physiological pH range significantly alter the structure and stability of Gαi-GDP, with the protein undergoing a disorder-to-order transition as the pH is raised from 6.8 to 7.5. Further, we find that modulation of intracellular pH in HEK293 cells regulates Gαi-Gβγ release. Identification of key residues in the pH-sensing network allowed the generation of low pH mimetics that attenuate Gαi-Gβγ release. Our findings, taken together, indicate that pH-dependent structural changes in Gαi alter the agonist-mediated Gβγ dissociation necessary for proper signaling.
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Affiliation(s)
- Ajit Prakash
- Department of Biochemistry & Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
| | - Zijian Li
- Department of Biochemistry & Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
| | - Venkata R. Chirasani
- Department of Biochemistry & Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
| | - Juhi A. Rasquinha
- Department of Biochemistry & Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
| | - Natalie H. Valentin
- Department of Pharmacology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA
| | - Garrett B. Hubbard
- Department of Biochemistry & Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
| | - Guowei Yin
- The Seventh Affiliated Hospital of Sun Yat-sen University, Shenzhen, 518107, China
| | - Henrik G. Dohlman
- Department of Pharmacology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA
| | - Sharon L. Campbell
- Department of Biochemistry & Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
- Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
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5
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Lucero RM, Demirer K, Yeh TJ, Stockbridge RB. Transport of metformin metabolites by guanidinium exporters of the small multidrug resistance family. J Gen Physiol 2024; 156:e202313464. [PMID: 38294434 PMCID: PMC10829512 DOI: 10.1085/jgp.202313464] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2023] [Revised: 12/01/2023] [Accepted: 01/04/2024] [Indexed: 02/01/2024] Open
Abstract
Proteins from the small multidrug resistance (SMR) family are frequently associated with horizontally transferred multidrug resistance gene arrays found in bacteria from wastewater and the human-adjacent biosphere. Recent studies suggest that a subset of SMR transporters might participate in the metabolism of the common pharmaceutical metformin by bacterial consortia. Here, we show that both genomic and plasmid-associated transporters of the SMRGdx functional subtype export byproducts of microbial metformin metabolism, with particularly high export efficiency for guanylurea. We use solid-supported membrane electrophysiology to evaluate the transport kinetics for guanylurea and native substrate guanidinium by four representative SMRGdx homologs. Using an internal reference to normalize independent electrophysiology experiments, we show that transport rates are comparable for genomic and plasmid-associated SMRGdx homologs, and using a proteoliposome-based transport assay, we show that 2 proton:1 substrate transport stoichiometry is maintained. Additional characterization of guanidinium and guanylurea export properties focuses on the structurally characterized homolog, Gdx-Clo, for which we examined the pH dependence and thermodynamics of substrate binding and solved an x-ray crystal structure with guanylurea bound. Together, these experiments contribute in two main ways. By providing the first detailed kinetic examination of the structurally characterized SMRGdx homolog Gdx-Clo, they provide a functional framework that will inform future mechanistic studies of this model transport protein. Second, this study casts light on a potential role for SMRGdx transporters in microbial handling of metformin and its microbial metabolic byproducts, providing insight into how native transport physiologies are co-opted to contend with new selective pressures.
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Affiliation(s)
- Rachael M. Lucero
- Program in Chemical Biology, University of Michigan, Ann Arbor, MI, USA
| | - Kemal Demirer
- Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, MI, USA
| | | | - Randy B. Stockbridge
- Program in Chemical Biology, University of Michigan, Ann Arbor, MI, USA
- Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, MI, USA
- Program in Biophysics, University of Michigan, Ann Arbor, MI, USA
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6
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Marulanda Valencia W, Pandit A. Photosystem II Subunit S (PsbS): A Nano Regulator of Plant Photosynthesis. J Mol Biol 2024; 436:168407. [PMID: 38109993 DOI: 10.1016/j.jmb.2023.168407] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2023] [Revised: 11/26/2023] [Accepted: 12/13/2023] [Indexed: 12/20/2023]
Abstract
Light is required for photosynthesis, but plants are often exposed to excess light, which can lead to photodamage and eventually cell death. To prevent this, they evolved photoprotective feedback mechanisms that regulate photosynthesis and trigger processes that dissipate light energy as heat, called non-photochemical quenching (NPQ). In excess light conditions, the light reaction and activity of Photosystem II (PSII) generates acidification of the thylakoid lumen, which is sensed by special pH-sensitive proteins called Photosystem II Subunit S (PsbS), actuating a photoprotective "switch" in the light-harvesting antenna. Despite its central role in regulating photosynthetic energy conversion, the molecular mechanism of PsbS as well as its interaction with partner proteins are not well understood. This review summarizes the current knowledge on the molecular structure and mechanistic aspects of the light-stress sensor PsbS and addresses open questions and challenges in the field regarding a full understanding of its functional mechanism and role in NPQ.
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Affiliation(s)
| | - Anjali Pandit
- Leiden Inst. of Chemistry, Gorlaeus Laboratory, Einsteinweg 55, 2300 RA Leiden, The Netherlands.
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7
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Kaur M, Arya P, Chosyang S, Singh B. Comprehending conformational changes in EmrE, multidrug transporter at different pH: insights from molecular dynamics simulations. J Biomol Struct Dyn 2024:1-14. [PMID: 38180013 DOI: 10.1080/07391102.2023.2298386] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2023] [Accepted: 12/18/2023] [Indexed: 01/06/2024]
Abstract
EmrE is a small multidrug resistance (SMR) pump of antiparallel topology that confers resistance to a broad range of polyaromatic cations in Escherichia coli. Atomic-level understanding of conformational changes for the selectivity of substrate and transport of a diverse array of drugs through the smallest known efflux pumps is crucial to multi-drug resistance. Therefore, the present study aims to provide insights into conformational changes during the transport through EmrE transporter at different pH. Molecular dynamics simulations have been carried out on the complete structure of EmrE in the absence of substrate. Computational analyses such as secondary structure, principal component, dynamic cross-correlation matrix, and hydrogen bond calculations have been performed. Analysis of MD trajectories in this study revealed pH-dependent interactions that influenced the structural dynamics of EmrE. Notably, at high pH, Glu14 and Tyr60 in both monomers formed electrostatic interactions, while these interactions decreased significantly at a low pH. Interestingly, a kink at helix 3 (H3) and dual open conformation of EmrE at low pH were also observed in contrast to a closed state discerned towards the periplasmic side at high pH. Significant interactions between C-terminal residues and residues at the edge of H1 & Loop1 and H3 & Loop3 were identified, suggesting their role in stabilizing the closed conformation of EmrE at the periplasmic end under high pH conditions. The present study enhances our understanding of EmrE's conformational changes, shedding light on the pH-dependent mechanisms that are likely to impact its function in multi-drug resistance.Communicated by Ramaswamy H. Sarma.
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Affiliation(s)
- Manpreet Kaur
- Bioinformatics Centre, CSIR-Institute of Microbial Technology, Chandigarh, India
- Academy of Scientific and Innovative Research (AcSIR), Ghaziabad, India
| | - Preeti Arya
- Bioinformatics Centre, CSIR-Institute of Microbial Technology, Chandigarh, India
- Faculty of Allied Health Sciences, Shree Guru Gobind Singh Tricentenary University, Gurugram, Haryana, India
| | - Stanzin Chosyang
- Bioinformatics Centre, CSIR-Institute of Microbial Technology, Chandigarh, India
- Academy of Scientific and Innovative Research (AcSIR), Ghaziabad, India
| | - Balvinder Singh
- Bioinformatics Centre, CSIR-Institute of Microbial Technology, Chandigarh, India
- Academy of Scientific and Innovative Research (AcSIR), Ghaziabad, India
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8
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Seppälä S, Gierke T, Schauer EE, Brown JL, O'Malley MA. Identification and expression of small multidrug resistance transporters in early-branching anaerobic fungi. Protein Sci 2023; 32:e4730. [PMID: 37470750 PMCID: PMC10443351 DOI: 10.1002/pro.4730] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2023] [Revised: 07/05/2023] [Accepted: 07/13/2023] [Indexed: 07/21/2023]
Abstract
Membrane-embedded transporters impart essential functions to cells as they mediate sensing and the uptake and extrusion of nutrients, waste products, and effector molecules. Promiscuous multidrug exporters are implicated in resistance to drugs and antibiotics and are highly relevant for microbial engineers who seek to enhance the tolerance of cell factory strains to hydrophobic bioproducts. Here, we report on the identification of small multidrug resistance (SMR) transporters in early-branching anaerobic fungi (Neocallimastigomycetes). The SMR class of transporters is commonly found in bacteria but has not previously been reported in eukaryotes. In this study, we show that SMR transporters from anaerobic fungi can be produced heterologously in the model yeast Saccharomyces cerevisiae, demonstrating the potential of these proteins as targets for further characterization. The discovery of these novel anaerobic fungal SMR transporters offers a promising path forward to enhance bioproduction from engineered microbial strains.
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Affiliation(s)
- Susanna Seppälä
- Department of Chemical EngineeringUniversity of California Santa BarbaraSanta BarbaraCaliforniaUSA
| | - Taylor Gierke
- Department of Chemical EngineeringUniversity of California Santa BarbaraSanta BarbaraCaliforniaUSA
| | - Elizabeth E. Schauer
- Department of Chemical EngineeringUniversity of California Santa BarbaraSanta BarbaraCaliforniaUSA
| | - Jennifer L. Brown
- Department of Chemical EngineeringUniversity of California Santa BarbaraSanta BarbaraCaliforniaUSA
| | - Michelle A. O'Malley
- Department of Chemical EngineeringUniversity of California Santa BarbaraSanta BarbaraCaliforniaUSA
- Bioengineering ProgramUniversity of CaliforniaSanta BarbaraCaliforniaUSA
- Joint BioEnergy Institute (JBEI)EmeryvilleCaliforniaUSA
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9
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Lucero RM, Demirer K, Yeh TJ, Stockbridge RB. Transport of metformin metabolites by guanidinium exporters of the Small Multidrug Resistance family. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.08.10.552832. [PMID: 37645731 PMCID: PMC10461911 DOI: 10.1101/2023.08.10.552832] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 08/31/2023]
Abstract
Proteins from the Small Multidrug Resistance (SMR) family are frequently associated with horizontally transferred multidrug resistance gene arrays found in bacteria from wastewater and the human-adjacent biosphere. Recent studies suggest that a subset of SMR transporters might participate in metabolism of the common pharmaceutical metformin by bacterial consortia. Here, we show that both genomic and plasmid-associated transporters of the SMRGdx functional subtype export byproducts of microbial metformin metabolism, with particularly high export efficiency for guanylurea. We use solid supported membrane electrophysiology to evaluate the transport kinetics for guanylurea and native substrate guanidinium by four representative SMRGdx homologues. Using an internal reference to normalize independent electrophysiology experiments, we show that transport rates are comparable for genomic and plasmid-associated SMRGdx homologues, and using a proteoliposome-based transport assay, we show that 2 proton:1 substrate transport stoichiometry is maintained. Additional characterization of guanidinium and guanylurea export properties focuses on the structurally characterized homologue, Gdx-Clo, for which we examined the pH dependence and thermodynamics of substrate binding and solved an x-ray crystal structure with guanylurea bound. Together, these experiments contribute in two main ways. By providing the first detailed kinetic examination of the structurally characterized SMRGdx homologue Gdx-Clo, they provide a functional framework that will inform future mechanistic studies of this model transport protein. Second, this study casts light on a potential role for SMRGdx transporters in microbial handling of metformin and its microbial metabolic byproducts, providing insight into how native transport physiologies are co-opted to contend with new selective pressures.
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Affiliation(s)
| | - Kemal Demirer
- Department of Molecular, Cellular, and Developmental Biology
| | - Trevor Justin Yeh
- Program in Biophysics, University of Michigan, Ann Arbor, MI 48109, USA
| | - Randy B Stockbridge
- Program in Chemical Biology
- Department of Molecular, Cellular, and Developmental Biology
- Program in Biophysics, University of Michigan, Ann Arbor, MI 48109, USA
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10
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Spreacker PJ, Thomas NE, Beeninga WF, Brousseau M, Porter CJ, Hibbs KM, Henzler-Wildman KA. Activating alternative transport modes in a multidrug resistance efflux pump to confer chemical susceptibility. Nat Commun 2022; 13:7655. [PMID: 36496486 PMCID: PMC9741644 DOI: 10.1038/s41467-022-35410-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2022] [Accepted: 12/01/2022] [Indexed: 12/13/2022] Open
Abstract
Small multidrug resistance (SMR) transporters contribute to antibiotic resistance through proton-coupled efflux of toxic compounds. Previous biophysical studies of the E. coli SMR transporter EmrE suggest that it should also be able to perform proton/toxin symport or uniport, leading to toxin susceptibility rather than resistance in vivo. Here we show EmrE does confer susceptibility to several previously uncharacterized small-molecule substrates in E. coli, including harmane. In vitro electrophysiology assays demonstrate that harmane binding triggers uncoupled proton flux through EmrE. Assays in E. coli are consistent with EmrE-mediated dissipation of the transmembrane pH gradient as the mechanism underlying the in vivo phenotype of harmane susceptibility. Furthermore, checkerboard assays show this alternative EmrE transport mode can synergize with some existing antibiotics, such as kanamycin. These results demonstrate that it is possible to not just inhibit multidrug efflux, but to activate alternative transport modes detrimental to bacteria, suggesting a strategy to address antibiotic resistance.
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Affiliation(s)
- Peyton J Spreacker
- Department of Biochemistry, University of Wisconsin-Madison, Madison, WI, 53703, USA
| | - Nathan E Thomas
- Department of Biochemistry, University of Wisconsin-Madison, Madison, WI, 53703, USA
- Department of Chemistry and Biochemistry, University of California-San Diego, La Jolla, CA, 92093, USA
| | - Will F Beeninga
- Department of Biochemistry, University of Wisconsin-Madison, Madison, WI, 53703, USA
| | - Merissa Brousseau
- Department of Biochemistry, University of Wisconsin-Madison, Madison, WI, 53703, USA
| | - Colin J Porter
- Department of Biochemistry, University of Wisconsin-Madison, Madison, WI, 53703, USA
| | - Kylie M Hibbs
- Department of Biochemistry, University of Wisconsin-Madison, Madison, WI, 53703, USA
| | - Katherine A Henzler-Wildman
- Department of Biochemistry, University of Wisconsin-Madison, Madison, WI, 53703, USA.
- National Magnetic Resonance Facility at Madison, University of Wisconsin-Madison, Madison, WI, 53703, USA.
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11
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Burata OE, Yeh TJ, Macdonald CB, Stockbridge RB. Still rocking in the structural era: A molecular overview of the small multidrug resistance (SMR) transporter family. J Biol Chem 2022; 298:102482. [PMID: 36100040 PMCID: PMC9574504 DOI: 10.1016/j.jbc.2022.102482] [Citation(s) in RCA: 10] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2022] [Revised: 08/24/2022] [Accepted: 09/07/2022] [Indexed: 11/20/2022] Open
Abstract
The small multidrug resistance (SMR) family is composed of widespread microbial membrane proteins that fulfill different transport functions. Four functional SMR subtypes have been identified, which variously transport the small, charged metabolite guanidinium, bulky hydrophobic drugs and antiseptics, polyamines, and glycolipids across the membrane bilayer. The transporters possess a minimalist architecture, with ∼100-residue subunits that require assembly into homodimers or heterodimers for transport. In part because of their simple construction, the SMRs are a tractable system for biochemical and biophysical analysis. Studies of SMR transporters over the last 25 years have yielded deep insights for diverse fields, including membrane protein topology and evolution, mechanisms of membrane transport, and bacterial multidrug resistance. Here, we review recent advances in understanding the structures and functions of SMR transporters. New molecular structures of SMRs representing two of the four functional subtypes reveal the conserved structural features that have permitted the emergence of disparate substrate transport functions in the SMR family and illuminate structural similarities with a distantly related membrane transporter family, SLC35/DMT.
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Affiliation(s)
- Olive E Burata
- Program in Chemical Biology, University of Michigan, Ann Arbor, Michigan, USA
| | - Trevor Justin Yeh
- Program in Biophysics, University of Michigan, Ann Arbor, Michigan, USA
| | | | - Randy B Stockbridge
- Program in Chemical Biology, University of Michigan, Ann Arbor, Michigan, USA; Program in Biophysics, University of Michigan, Ann Arbor, Michigan, USA; Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, Michigan, USA.
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12
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Kermani AA, Burata OE, Koff BB, Koide A, Koide S, Stockbridge RB. Crystal structures of bacterial small multidrug resistance transporter EmrE in complex with structurally diverse substrates. eLife 2022; 11:76766. [PMID: 35254261 PMCID: PMC9000954 DOI: 10.7554/elife.76766] [Citation(s) in RCA: 12] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2022] [Accepted: 03/06/2022] [Indexed: 11/13/2022] Open
Abstract
Proteins from the bacterial small multidrug resistance (SMR) family are proton-coupled exporters of diverse antiseptics and antimicrobials, including polyaromatic cations and quaternary ammonium compounds. The transport mechanism of the Escherichia coli transporter, EmrE, has been studied extensively, but a lack of high-resolution structural information has impeded a structural description of its molecular mechanism. Here, we apply a novel approach, multipurpose crystallization chaperones, to solve several structures of EmrE, including a 2.9 Å structure at low pH without substrate. We report five additional structures in complex with structurally diverse transported substrates, including quaternary phosphonium, quaternary ammonium, and planar polyaromatic compounds. These structures show that binding site tryptophan and glutamate residues adopt different rotamers to conform to disparate structures without requiring major rearrangements of the backbone structure. Structural and functional comparison to Gdx-Clo, an SMR protein that transports a much narrower spectrum of substrates, suggests that in EmrE, a relatively sparse hydrogen bond network among binding site residues permits increased sidechain flexibility.
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Affiliation(s)
- Ali A Kermani
- Department of Molecular, Cellular and Developmental Biology, University of Michigan, Ann Arbor, United States
| | - Olive E Burata
- Department of Molecular, Cellular and Developmental Biology, University of Michigan, Ann Arbor, United States
| | - B Ben Koff
- Department of Molecular, Cellular and Developmental Biology, University of Michigan, Ann Arbor, United States
| | - Akiko Koide
- Laura and Isaac Perlmutter Cancer Center, New York University Langone Medical Center, New York, United States
| | - Shohei Koide
- Laura and Isaac Perlmutter Cancer Center, New York University Langone Medical Center, New York, United States
| | - Randy B Stockbridge
- Department of Molecular, Cellular and Developmental Biology, University of Michigan, Ann Arbor, United States
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13
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High-pH structure of EmrE reveals the mechanism of proton-coupled substrate transport. Nat Commun 2022; 13:991. [PMID: 35181664 PMCID: PMC8857205 DOI: 10.1038/s41467-022-28556-6] [Citation(s) in RCA: 12] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2021] [Accepted: 01/27/2022] [Indexed: 12/20/2022] Open
Abstract
The homo-dimeric bacterial membrane protein EmrE effluxes polyaromatic cationic substrates in a proton-coupled manner to cause multidrug resistance. We recently determined the structure of substrate-bound EmrE in phospholipid bilayers by measuring hundreds of protein-ligand HN–F distances for a fluorinated substrate, 4-fluoro-tetraphenylphosphonium (F4-TPP+), using solid-state NMR. This structure was solved at low pH where one of the two proton-binding Glu14 residues is protonated. Here, to understand how substrate transport depends on pH, we determine the structure of the EmrE-TPP complex at high pH, where both Glu14 residues are deprotonated. The high-pH complex exhibits an elongated and hydrated binding pocket in which the substrate is similarly exposed to the two sides of the membrane. In contrast, the low-pH complex asymmetrically exposes the substrate to one side of the membrane. These pH-dependent EmrE conformations provide detailed insights into the alternating-access model, and suggest that the high-pH conformation may facilitate proton binding in the presence of the substrate, thus accelerating the conformational change of EmrE to export the substrate. EmrE transporter effluxes cationic substrates across lipid membranes in a pH-coupled manner. Here, the authors solve the structure of ligand-bound EmrE at high pH by NMR, with insights into the transport mechanism.
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