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Few Conserved Amino Acids in the Small Multidrug Resistance Transporter EmrE Influence Drug Polyselectivity. Antimicrob Agents Chemother 2018; 62:AAC.00461-18. [PMID: 29866867 DOI: 10.1128/aac.00461-18] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2018] [Accepted: 05/26/2018] [Indexed: 01/29/2023] Open
Abstract
EmrE is the archetypical member of the small multidrug resistance transporter family and confers resistance to a wide range of disinfectants and dyes known as quaternary cation compounds (QCCs). The aim of this study was to examine which conserved amino acids play an important role in substrate selectivity. On the basis of a previous analysis of EmrE homologues, a total of 33 conserved residues were targeted for cysteine or alanine replacement within E. coli EmrE. The antimicrobial resistance of each EmrE variant expressed in Escherichia coli strain JW0451 (lacking dominant pump acrB) to a collection of 16 different QCCs was tested using agar spot dilution plating to determine MIC values. The results determined that only a few conserved residues were drug polyselective, based on ≥4-fold decreases in MIC values: the active-site residue E14 (E14D and E14A) and 4 additional conserved residues (A10C, F44C, L47C, W63A). EmrE variants I11C, V15C, P32C, I62C, L93C, and S105C enhanced resistance to polyaromatic QCCs, while the remaining EmrE variants reduced resistance to one or more QCCs with shared chemical features: acylation, tri- and tetraphenylation, aromaticity, and dicationic charge. Mapping of EmrE variants onto transmembrane helical wheel projections using the highest resolved EmrE structure suggests that polyselective EmrE variants were located closest to the helical faces surrounding the predicted drug binding pocket, while EmrE variants with greater drug specificity mapped onto distal helical faces. This study reveals that few conserved residues are essential for drug polyselectivity and indicates that aromatic QCC selection involves a greater portion of conserved residues than that in other QCCs.
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Vitrac H, Dowhan W, Bogdanov M. Effects of mixed proximal and distal topogenic signals on the topological sensitivity of a membrane protein to the lipid environment. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2017; 1859:1291-1300. [PMID: 28432030 DOI: 10.1016/j.bbamem.2017.04.010] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/13/2016] [Revised: 03/27/2017] [Accepted: 04/12/2017] [Indexed: 10/19/2022]
Abstract
The final topology of membrane proteins is thought to be dictated primarily by the encoding sequence. However, according to the Charge Balance Rule the topogenic signals within nascent membrane proteins are interpreted in agreement with the Positive Inside Rule as influenced by the protein phospholipid environment. The role of long-range protein-lipid interactions in establishing a final uniform or dual topology is unknown. In order to address this role, we determined the positional dependence of the potency of charged residues as topological signals within Escherichia coli sucrose permease (CscB) in cells in which the zwitterionic phospholipid phosphatidylethanolamine (PE), acting as topological determinant, was either eliminated or tightly titrated. Although the position of a single or paired oppositely charged amino acid residues within an extramembrane domain (EMD), either proximal, central or distal to a transmembrane domain (TMD) end, does not appear to be important, the oppositely charged residues exert their topogenic effects separately only in the absence of PE. Thus, the Charge Balance Rule can be executed in a retrograde manner from any cytoplasmic EMD or any residue within an EMD most likely outside of the translocon. Moreover, CscB is inserted into the membrane in two opposite orientations at different ratios with the native orientation proportional to the mol % of PE. The results demonstrate how the cooperative contribution of lipid-protein interactions affects the potency of charged residues as topological signals, providing a molecular mechanism for the realization of single, equal or different amounts of oppositely oriented protein within the same membrane.
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Affiliation(s)
- Heidi Vitrac
- Department of Biochemistry and Molecular Biology, the University of Texas Health Science Center McGovern Medical School, Houston, TX 77030, USA
| | - William Dowhan
- Department of Biochemistry and Molecular Biology, the University of Texas Health Science Center McGovern Medical School, Houston, TX 77030, USA
| | - Mikhail Bogdanov
- Department of Biochemistry and Molecular Biology, the University of Texas Health Science Center McGovern Medical School, Houston, TX 77030, USA.
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Bogdanov M, Dowhan W, Vitrac H. Lipids and topological rules governing membrane protein assembly. BIOCHIMICA ET BIOPHYSICA ACTA 2014; 1843:1475-88. [PMID: 24341994 PMCID: PMC4057987 DOI: 10.1016/j.bbamcr.2013.12.007] [Citation(s) in RCA: 96] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/04/2013] [Revised: 12/03/2013] [Accepted: 12/08/2013] [Indexed: 10/25/2022]
Abstract
Membrane protein folding and topogenesis are tuned to a given lipid profile since lipids and proteins have co-evolved to follow a set of interdependent rules governing final protein topological organization. Transmembrane domain (TMD) topology is determined via a dynamic process in which topogenic signals in the nascent protein are recognized and interpreted initially by the translocon followed by a given lipid profile in accordance with the Positive Inside Rule. The net zero charged phospholipid phosphatidylethanolamine and other neutral lipids dampen the translocation potential of negatively charged residues in favor of the cytoplasmic retention potential of positively charged residues (Charge Balance Rule). This explains why positively charged residues are more potent topological signals than negatively charged residues. Dynamic changes in orientation of TMDs during or after membrane insertion are attributed to non-sequential cooperative and collective lipid-protein charge interactions as well as long-term interactions within a protein. The proportion of dual topological conformers of a membrane protein varies in a dose responsive manner with changes in the membrane lipid composition not only in vivo but also in vitro and therefore is determined by the membrane lipid composition. Switching between two opposite TMD topologies can occur in either direction in vivo and also in liposomes (designated as fliposomes) independent of any other cellular factors. Such lipid-dependent post-insertional reversibility of TMD orientation indicates a thermodynamically driven process that can occur at any time and in any cell membrane driven by changes in the lipid composition. This dynamic view of protein topological organization influenced by the lipid environment reveals previously unrecognized possibilities for cellular regulation and understanding of disease states resulting from mis-folded proteins. This article is part of a Special Issue entitled: Protein trafficking and secretion in bacteria. Guest Editors: Anastassios Economou and Ross Dalbey.
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Affiliation(s)
- Mikhail Bogdanov
- Department of Biochemistry and Molecular Biology, University of Texas Medical School-Houston, Houston, TX 77030, USA.
| | - William Dowhan
- Department of Biochemistry and Molecular Biology, University of Texas Medical School-Houston, Houston, TX 77030, USA.
| | - Heidi Vitrac
- Department of Biochemistry and Molecular Biology, University of Texas Medical School-Houston, Houston, TX 77030, USA
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Kolbusz MA, Slotboom DJ, Lolkema JS. Genomic distribution of the small multidrug resistance protein EmrE over 29Escherichia colistrains reveals two forms of the protein. FEBS J 2012; 280:244-55. [DOI: 10.1111/febs.12065] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2012] [Revised: 11/08/2012] [Accepted: 11/12/2012] [Indexed: 11/29/2022]
Affiliation(s)
- Magdalena A. Kolbusz
- Molecular Microbiology, Groningen Biomolecular Sciences and Biotechnology Institute; University of Groningen; The Netherlands
| | - Dirk J. Slotboom
- Membrane Enzymology, Groningen Biomolecular Sciences and Biotechnology Institute; University of Groningen; The Netherlands
| | - Juke S. Lolkema
- Molecular Microbiology, Groningen Biomolecular Sciences and Biotechnology Institute; University of Groningen; The Netherlands
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Kolbusz MA, Slotboom DJ, Lolkema JS. Role of individual positive charges in the membrane orientation and activity of transporters of the small multidrug resistance family. Biochemistry 2012; 51:8867-76. [PMID: 23043311 DOI: 10.1021/bi300854c] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The effect of individual positively charged residues on the orientation in the membrane was analyzed in three dual-topology transporters of the small multidrug resistance (SMR) family: AAVE4701aave of Acidovorax avenae, EMREecol of Escherichia coli, and RRUA0272rrub of Rhodospirillum rubrum. It is shown that (i) individual positive charges have different impacts on the orientation, (ii) positive charges that are conserved in the three different proteins do not have the same impact on the orientation, (iii) positive charges in odd- and even-numbered loops have different impacts, (iv) for some, but not all, the impact depends on the presence of other positive charges, and (v) proteins from which all positive charges are removed in some cases are dual-topology proteins and in other cases have a single orientation. A small number of positive charges placed in the loops of the latter proteins results in the violation of the so-called positive-inside rule that has been reported previously [Kolbusz, M. A., et al. (2010) J. Mol. Biol. 402, 127-138]. We conclude that each positive charge shifts the distribution between the two orientations toward the state that has the positive charge in the cytoplasm but that intrinsic factors other than positive charges determine the orientation as well. The ability of the mutants of AAVE4701aave and EMREecol to confer resistance against ethidium bromide revealed an essential role in catalysis for a conserved pair of positive charges in the second loop. No significant relation between activity and the relative orientation of the monomeric subunits in the dimer could be demonstrated.
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Affiliation(s)
- Magdalena A Kolbusz
- Molecular Microbiology, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Groningen, The Netherlands
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Bay DC, Turner RJ. Membrane composition influences the topology bias of bacterial integral membrane proteins. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2012; 1828:260-70. [PMID: 22982496 DOI: 10.1016/j.bbamem.2012.09.003] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/23/2012] [Revised: 08/31/2012] [Accepted: 09/07/2012] [Indexed: 11/19/2022]
Abstract
Small multidrug resistance (SMR) protein family members confer bacterial resistance to toxic antiseptics and are believed to function as dual topology oligomers. If dual topology is essential for SMR activity, then the topology bias should change as bacterial membrane lipid compositions alter to maintain a "neutral" topology bias. To test this hypothesis, a bioinformatic analysis of bacterial SMR protein sequences was performed to determine a membrane protein topology based on charged amino acid residues within loops, and termini regions according to the positive inside rule. Three bacterial lipid membrane parameters were examined, providing the proportion of polar lipid head group charges at the membrane surface (PLH), the relative hydrophobic fatty acid length (FAL), and the proportion of fatty acid unsaturation (FAU). Our analysis indicates that individual SMR pairs, and to a lesser extent SMR singleton topology biases, are significantly correlated to increasing PLH, FAL and FAU differences validating the hypothesis. Correlations between the topology biases of SMR proteins identified in Gram+ compared to Gram- species and each lipid parameter demonstrated a linear inverse relationship.
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Affiliation(s)
- Denice C Bay
- Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada T2N 1N4
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Bogdanov M, Dowhan W. Lipid-dependent generation of dual topology for a membrane protein. J Biol Chem 2012; 287:37939-48. [PMID: 22969082 DOI: 10.1074/jbc.m112.404103] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
The mechanism by which membrane proteins exhibit structural and functional duality in the same membrane or different membranes is unknown. We posit that such duality is determined by both the protein sequence and the membrane lipid composition wherein a spatial or temporal change in the latter can result in a post-assembly change in protein structure and function. To investigate whether co-existence of multiple topological conformers is dependent on the membrane lipid composition, we determined the topological organization of lactose permease in an Escherichia coli model cell system in which phosphatidylethanolamine membrane content can be systematically varied. At intermediate levels of phosphatidylethanolamine a mixture of native and topologically mis-oriented conformers co-existed. There was no threshold level of phosphatidylethanolamine determining a sharp transition from one conformer to the other. Co-existing conformers were not in rapid equilibrium at a static lipid composition indicating that duality of topology is established during an early folding step. Depletion of intermediate levels of phosphatidylethanolamine after final protein assembly resulted in complete mis-orientation of the native conformer. Combined with previous results, such topological dynamics are reversible in both directions. We propose a thermodynamically based model for how lipid-protein interactions can result in a mixed topological organization and how changes in lipid composition can result in changes in the ratio of topologically distinct conformers of proteins. These observations demonstrate a potential lipid-dependent biological switch for generating dynamic structural and functional heterogeneity for a protein within the same membrane or between different membranes in more complex eukaryotic cells.
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Affiliation(s)
- Mikhail Bogdanov
- Department of Biochemistry and Molecular Biology, University of Texas Medical School at Houston, Houston, Texas 77303, USA.
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Spectroscopic analysis of small multidrug resistance protein EmrE in the presence of various quaternary cation compounds. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2012; 1818:1318-31. [PMID: 22326892 DOI: 10.1016/j.bbamem.2012.01.022] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/28/2011] [Revised: 01/09/2012] [Accepted: 01/26/2012] [Indexed: 12/12/2022]
Abstract
Escherichia coli EmrE protein is the archetypical member of the small multidrug resistance protein family in bacteria and confers host resistance to a wide assortment of toxic quaternary cation compounds by secondary active efflux. This protein can form a variety of multimers under various membrane mimetic conditions, and the consensus of most biochemical and biophysical studies indicate that the active form is a dimer. The purpose of this study is to characterize the conformation of organically extracted detergent solubilized EmrE protein known to predominate as monomer yet demonstrates ligand binding ability. Active site EmrE-E14 replacements were also examined as functionally inactive controls for this study. EmrE was solubilized in detergents, sodium dodecyl sulfate (SDS) and dodecyl maltoside (DDM), and protein conformation was examined in the presence of four known quaternary cation compound (QCC) substrates, tetraphenyl phosphonium (TPP), methyl viologen, cetylpyridinium, and ethidium. SDS-Tricine PAGE analysis of both detergent solubilized proteins revealed that DDM-EmrE preparations enhanced the formation of dimer (and in some cases trimer) forms in the presence of all four QCC above 25 QCC:1 EmrE molar ratios. Examination of EmrE and its active site variant tertiary structures in DDM by circular dichroism spectropolarimetry, intrinsic Trp fluorescence quenching and second order derivative ultraviolet absorbance revealed that the variant fails to bind TPP but interacts with all other compounds. The results of this study show that monomeric detergent solubilized EmrE is capable of forming multimeric complexes that are enhanced by chemically diverse QCCs.
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Gröger T, Nathoo S, Ku T, Sikora C, Turner RJ, Prenner EJ. Real-time imaging of lipid domains and distinct coexisting membrane protein clusters. Chem Phys Lipids 2011; 165:216-24. [PMID: 22227110 DOI: 10.1016/j.chemphyslip.2011.12.012] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2011] [Revised: 12/15/2011] [Accepted: 12/19/2011] [Indexed: 12/20/2022]
Abstract
A detailed understanding of biomembrane architecture is still a challenging task. Many in vitro studies have shown lipid domains but much less information is known about the lateral organization of membrane proteins because their hydrophobic nature limits the use of many experimental methods. We examined lipid domain formation in biomimetic Escherichia coli membranes composed of phosphatidylethanolamine and phosphatidylglycerol in the absence and presence of 1% and 5% (mol/mol) membrane multidrug resistance protein, EmrE. Monolayer isotherms demonstrated protein insertion into the lipid monolayer. Subsequently, Brewster angle microscopy was applied to image domains in lipid matrices and lipid-protein mixtures. The images showed a concentration dependent impact of the protein on lipid domain size and shape and more interestingly distinct coexisting protein clusters. Whereas lipid domains varied in size (14-47μm), protein clusters exhibited a narrow size distribution (2.6-4.8μm) suggesting a non-random process of cluster formation. A 3-D display clearly indicates that these proteins clusters protrude from the membrane plane. These data demonstrate distinct co-existing lipid domains and membrane protein clusters as the monofilm is being compressed and illustrate the significant mutual impact of lipid-protein interactions on lateral membrane architecture.
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Affiliation(s)
- Thomas Gröger
- Helmholtz Zentrum München, German Research Center for Environmental Health, Neuherbeg, Germany
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10
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Bay DC, Turner RJ. Spectroscopic analysis of the intrinsic chromophores within small multidrug resistance protein SugE. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2011; 1808:2233-44. [PMID: 21600871 DOI: 10.1016/j.bbamem.2011.05.005] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/14/2011] [Revised: 05/03/2011] [Accepted: 05/04/2011] [Indexed: 11/16/2022]
Abstract
Small multidrug resistance (SMR) protein family member, SugE, is an integral inner membrane protein that confers host resistance to antiseptic quaternary cation compounds (QCC). SugE studies generally focus on its resistance to limited substrates in comparison to SMR protein EmrE. This study examines the conformational characteristics of SugE protein in two detergents, sodium dodecyl sulphate (SDS) and dodecyl maltoside (DDM), commonly used to study SMR proteins. The influence of cetylpyridinium (CTP) and cetrimide (CET) using SugE aromatic residues (4W, 2Y, 1F) as intrinsic spectroscopic probes was also determined. Organically extracted detergent solubilized Escherichia coli SugE protein was examined by SDS-Tricine PAGE and various spectroscopic techniques. SDS-Tricine PAGE analysis of SugE in either detergent demonstrates the protein predominates as a monomer but also dimerizes in SDS. Far-UV region circular dichroism (CD) analysis determined that the overall α-helix content SugE in SDS and DDM was almost identical and unaltered by QCC. Near-UV region CD, fluorescence, and second-derivative ultraviolet absorption (SDUV) indicated that only DDM-SugE promoted hydrophobic environments for its Trp and Tyr residues that were perturbed by QCC addition. This study identified that only the tertiary structure of SugE protein in DDM is altered by QCC.
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Affiliation(s)
- Denice C Bay
- Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada T2N 1N4
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Kolbusz MA, ter Horst R, Slotboom DJ, Lolkema JS. Orientation of small multidrug resistance transporter subunits in the membrane: correlation with the positive-inside rule. J Mol Biol 2010; 402:127-38. [PMID: 20643145 DOI: 10.1016/j.jmb.2010.07.019] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2010] [Revised: 07/07/2010] [Accepted: 07/08/2010] [Indexed: 11/26/2022]
Abstract
Small multidrug resistance (SMR) transport proteins provide a model for the evolution of larger two-domain transport proteins. The orientation in the membrane of 27 proteins from the SMR family was determined using the reporter fusion technique. Nine members were encoded monocistronically (singles) and shown to insert in both orientations (dual topology). Eighteen members were encoded in pairs on the chromosome and shown to insert in fixed orientations; the two proteins in each pair invariably had opposite orientations in the membrane. Interaction between the two proteins in pairs was demonstrated by copurification. The orientation in the membrane of either protein in the pair was affected only marginally by the presence of the other protein. For the proteins in pairs, the orientation in the membrane correlated well with the distribution of positively charges residues (R+K) over the cytoplasmic and extracellular loops (positive-inside rule). In contrast, dual-topology insertion of the singles was predicted less well by the positive-inside rule. Three singles were predicted to insert in a single orientation with the N-terminus and the C-terminus at the extracellular side of the membrane. Analysis of charge distributions suggests the requirement of a threshold number of charges in the cytoplasmic loops for the positive-inside rule to be of predictive value. It is concluded that a combined analysis of gene organization on the chromosome and phylogeny is sufficient to distinguish between fixed or dual topology of SMR members and, probably, similar types of membrane proteins. The positive-inside rule can be used to predict the orientation of members in pairs, but is not suitable as a sole predictor of dual topology.
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Affiliation(s)
- Magdalena A Kolbusz
- Department of Molecular Microbiology, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Kerklaan 30, 9751 NN Haren, The Netherlands
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Lomovskaya O, Zgurskaya HI, Bostian K. Bacterial Multidrug Transporters: Molecular and Clinical Aspects. ACTA ACUST UNITED AC 2010. [DOI: 10.1002/9783527627424.ch5] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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Bay DC, Budiman RA, Nieh MP, Turner RJ. Multimeric forms of the small multidrug resistance protein EmrE in anionic detergent. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2009; 1798:526-35. [PMID: 20036636 DOI: 10.1016/j.bbamem.2009.12.017] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/01/2009] [Revised: 12/18/2009] [Accepted: 12/21/2009] [Indexed: 11/16/2022]
Abstract
Escherichia coli multidrug resistance protein E (EmrE) is a four transmembrane alpha-helix protein, and a member of the small multidrug resistance protein family that confers resistance to a broad range of quaternary cation compounds (QCC) via proton motive force. The multimeric states of EmrE protein during transport or ligand binding are variable and specific to the conditions of study. To explore EmrE multimerization further, EmrE extracted from E. coli membranes was solubilized in anionic detergent, sodium dodecyl sulphate (SDS), at varying protein concentrations. At low concentrations (</=1muM) in SDS-EmrE is monomeric, but upon increasing EmrE concentration, a variety of multimeric states can be observed by SDS-Tricine polyacrylamide gel electrophoresis (PAGE). Addition of the (QCC), tetraphenyl phosphonium (TPP), to SDS-EmrE samples enhanced EmrE multimer formation using SDS-Tricine PAGE. The relative shapes of EmrE multimers in SDS with or without TPP addition were determined by small angle neutron scattering (SANS) analysis and revealed that EmrE dimers altered in conformation depending on the SDS concentration. SANS analysis also revealed that relative shapes of larger EmrE multimers (>/=100nm sizes) altered in the presence of TPP. Circular dichroism spectropolarimetry displayed no differences in secondary structure under the conditions studied. Fluorescence spectroscopy of SDS-EmrE protein demonstrated that aromatic residues, Trp and Tyr, are more susceptible to SDS concentration than TPP addition, but both residues exhibit enhanced quenching at high ligand concentrations. Hence, EmrE forms various multimers in SDS that are influenced by detergent concentration and TPP substrate addition.
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Affiliation(s)
- Denice C Bay
- Department of Biological Sciences, University of Calgary, Calgary, Alberta T2N 1N4, Canada
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EmrE, a model for studying evolution and mechanism of ion-coupled transporters. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2009; 1794:748-62. [DOI: 10.1016/j.bbapap.2008.12.018] [Citation(s) in RCA: 130] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/27/2008] [Revised: 12/16/2008] [Accepted: 12/17/2008] [Indexed: 11/23/2022]
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Korkhov VM, Tate CG. An emerging consensus for the structure of EmrE. ACTA CRYSTALLOGRAPHICA. SECTION D, BIOLOGICAL CRYSTALLOGRAPHY 2009; 65:186-92. [PMID: 19171974 PMCID: PMC2631640 DOI: 10.1107/s0907444908036640] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/17/2008] [Accepted: 11/07/2008] [Indexed: 11/17/2022]
Abstract
The archetypical member of the small multidrug-resistance family is EmrE, a multidrug transporter that extrudes toxic polyaromatic cations from the cell coupled to the inward movement of protons down a concentration gradient. The architecture of EmrE was first defined from the analysis of two-dimensional crystals by cryoelectron microscopy (cryo-EM), which showed that EmrE was an unusual asymmetric dimer formed from a bundle of eight alpha-helices. The most favoured interpretation of the structure was that the monomers were oriented in opposite orientations in the membrane in an antiparallel orientation. A model was subsequently built based upon the cryo-EM data and evolutionary constraints and this model was consistent with mutagenic data indicating which amino-acid residues were important for substrate binding and transport. Two X-ray structures that differed significantly from the cryo-EM structure were subsequently retracted owing to a data-analysis error. However, the revised X-ray structure with substrate bound is extremely similar to the model built from the cryo-EM structure (r.m.s.d. of 1.4 A), suggesting that the proposed antiparallel orientation of the monomers is indeed correct; this represents a new structural paradigm in membrane-protein structures. The vast majority of mutagenic and biochemical data corroborate this structure, although cross-linking studies and recent EPR data apparently support a model of EmrE that contains parallel dimers.
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Mchaourab HS, Mishra S, Koteiche HA, Amadi SH. Role of Sequence Bias in the Topology of the Multidrug Transporter EmrE. Biochemistry 2008; 47:7980-2. [DOI: 10.1021/bi800628d] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Hassane S. Mchaourab
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, Tennessee 37232
| | - Sanjay Mishra
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, Tennessee 37232
| | - Hanane A. Koteiche
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, Tennessee 37232
| | - Sepan H. Amadi
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, Tennessee 37232
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