1
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Hou Z, Gangjee A, Matherly LH. The evolving biology of the proton‐coupled folate transporter: New insights into regulation, structure, and mechanism. FASEB J 2022; 36:e22164. [PMID: 35061292 PMCID: PMC8978580 DOI: 10.1096/fj.202101704r] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2021] [Revised: 12/15/2021] [Accepted: 01/03/2022] [Indexed: 01/19/2023]
Abstract
The human proton‐coupled folate transporter (PCFT; SLC46A1) or hPCFT was identified in 2006 as the principal folate transporter involved in the intestinal absorption of dietary folates. A rare autosomal recessive hereditary folate malabsorption syndrome is attributable to human SLC46A1 variants. The recognition that hPCFT was highly expressed in many tumors stimulated substantial interest in its potential for cytotoxic drug targeting, taking advantage of its high‐level transport activity under acidic pH conditions that characterize many tumors and its modest expression in most normal tissues. To better understand the basis for variations in hPCFT levels between tissues including human tumors, studies have examined the transcriptional regulation of hPCFT including the roles of CpG hypermethylation and critical transcription factors and cis elements. Additional focus involved identifying key structural and functional determinants of hPCFT transport that, combined with homology models based on structural homologies to the bacterial transporters GlpT and LacY, have enabled new structural and mechanistic insights. Recently, cryo‐electron microscopy structures of chicken PCFT in a substrate‐free state and in complex with the antifolate pemetrexed were reported, providing further structural insights into determinants of (anti)folate recognition and the mechanism of pH‐regulated (anti)folate transport by PCFT. Like many major facilitator proteins, hPCFT exists as a homo‐oligomer, and evidence suggests that homo‐oligomerization of hPCFT monomeric proteins may be important for its intracellular trafficking and/or transport function. Better understanding of the structure, function and regulation of hPCFT should facilitate the rational development of new therapeutic strategies for conditions associated with folate deficiency, as well as cancer.
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Affiliation(s)
- Zhanjun Hou
- Molecular Therapeutics Program Barbara Ann Karmanos Cancer Institute Detroit Michigan USA
- Department of Oncology Wayne State University School of Medicine Detroit Michigan USA
| | - Aleem Gangjee
- Division of Medicinal Chemistry Graduate School of Pharmaceutical Sciences Duquesne University Pittsburgh Pennsylvania USA
| | - Larry H. Matherly
- Molecular Therapeutics Program Barbara Ann Karmanos Cancer Institute Detroit Michigan USA
- Department of Oncology Wayne State University School of Medicine Detroit Michigan USA
- Department of Pharmacology Wayne State University School of Medicine Detroit Michigan USA
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2
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Henderson PJF, Maher C, Elbourne LDH, Eijkelkamp BA, Paulsen IT, Hassan KA. Physiological Functions of Bacterial "Multidrug" Efflux Pumps. Chem Rev 2021; 121:5417-5478. [PMID: 33761243 DOI: 10.1021/acs.chemrev.0c01226] [Citation(s) in RCA: 66] [Impact Index Per Article: 22.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Bacterial multidrug efflux pumps have come to prominence in human and veterinary pathogenesis because they help bacteria protect themselves against the antimicrobials used to overcome their infections. However, it is increasingly realized that many, probably most, such pumps have physiological roles that are distinct from protection of bacteria against antimicrobials administered by humans. Here we undertake a broad survey of the proteins involved, allied to detailed examples of their evolution, energetics, structures, chemical recognition, and molecular mechanisms, together with the experimental strategies that enable rapid and economical progress in understanding their true physiological roles. Once these roles are established, the knowledge can be harnessed to design more effective drugs, improve existing microbial production of drugs for clinical practice and of feedstocks for commercial exploitation, and even develop more sustainable biological processes that avoid, for example, utilization of petroleum.
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Affiliation(s)
- Peter J F Henderson
- School of Biomedical Sciences and Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds LS2 9JT, United Kingdom
| | - Claire Maher
- School of Environmental and Life Sciences, University of Newcastle, Callaghan 2308, New South Wales, Australia
| | - Liam D H Elbourne
- Department of Biomolecular Sciences, Macquarie University, Sydney 2109, New South Wales, Australia.,ARC Centre of Excellence in Synthetic Biology, Macquarie University, Sydney 2019, New South Wales, Australia
| | - Bart A Eijkelkamp
- College of Science and Engineering, Flinders University, Bedford Park 5042, South Australia, Australia
| | - Ian T Paulsen
- Department of Biomolecular Sciences, Macquarie University, Sydney 2109, New South Wales, Australia.,ARC Centre of Excellence in Synthetic Biology, Macquarie University, Sydney 2019, New South Wales, Australia
| | - Karl A Hassan
- School of Environmental and Life Sciences, University of Newcastle, Callaghan 2308, New South Wales, Australia.,ARC Centre of Excellence in Synthetic Biology, Macquarie University, Sydney 2019, New South Wales, Australia
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3
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Wei S, Yang Y, Tian W, Liu M, Yin S, Li J. Synergistic Activity of Fluoroquinolones Combining with Artesunate Against Multidrug-Resistant Escherichia coli. Microb Drug Resist 2019; 26:81-88. [PMID: 31738637 PMCID: PMC6978754 DOI: 10.1089/mdr.2018.0463] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
Multidrug resistance (MDR) is an increasing public health concern worldwide. Artesunate (ART) has been reported to be significantly effective in enhancing the effectiveness of various β-lactam antibiotics against MDR Escherichia coli via inhibiting the efflux pump genes. Apart from β-lactam antibiotics, there is no report regarding the potential synergistic effects of ART combining with fluoroquinolones (FQs). In this study, we investigated whether ART can enhance the antibacterial effects of FQs in vitro. The antibacterial activity of ART and antibiotics against 13 animal-derived E. coli clinical isolates was assessed for screening MDR strains. Then the synergistic activity of FQs with ART against MDR E. coli isolates was evaluated. Daunorubicin (DNR) accumulation within E. coli and messenger RNA (mRNA) expressions of acrA, acrB, tolC, and qnr genes were investigated. The results showed that ART did not show significant antimicrobial activity. However, a dramatically synergistic activity of ART combining with FQs was obsessed with (ΣFIC) = 0.12-0.33. ART increased the DNR accumulation and reduced acrAB-tolC mRNA expression, but enhanced the mRNA expression of qnrS and qnrB within MDR E. coli isolates. These findings suggest that ART can potentiate FQs activity which may be associated with drug accumulation by inhibiting the expression of acrAB-tolC.
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Affiliation(s)
- SiMin Wei
- Department of Clinical Veterinary Medicine, School of Veterinary Medicine, Yangzhou University, Yangzhou, P.R. China.,Jiangsu Co-innovation Center for Prevention and Control of Important Animal Infectious Diseases and Zoonoses, Yangzhou, P.R. China
| | - YueFei Yang
- Department of Clinical Veterinary Medicine, School of Veterinary Medicine, Yangzhou University, Yangzhou, P.R. China.,Jiangsu Co-innovation Center for Prevention and Control of Important Animal Infectious Diseases and Zoonoses, Yangzhou, P.R. China
| | - Wei Tian
- Department of Clinical Veterinary Medicine, School of Veterinary Medicine, Yangzhou University, Yangzhou, P.R. China.,Jiangsu Co-innovation Center for Prevention and Control of Important Animal Infectious Diseases and Zoonoses, Yangzhou, P.R. China
| | - MingJiang Liu
- Department of Clinical Veterinary Medicine, School of Veterinary Medicine, Yangzhou University, Yangzhou, P.R. China.,Jiangsu Co-innovation Center for Prevention and Control of Important Animal Infectious Diseases and Zoonoses, Yangzhou, P.R. China
| | - ShaoJie Yin
- Department of Clinical Veterinary Medicine, School of Veterinary Medicine, Yangzhou University, Yangzhou, P.R. China.,Jiangsu Co-innovation Center for Prevention and Control of Important Animal Infectious Diseases and Zoonoses, Yangzhou, P.R. China
| | - JinGui Li
- Department of Clinical Veterinary Medicine, School of Veterinary Medicine, Yangzhou University, Yangzhou, P.R. China.,Jiangsu Co-innovation Center for Prevention and Control of Important Animal Infectious Diseases and Zoonoses, Yangzhou, P.R. China
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4
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Spengler G, Kincses A, Gajdács M, Amaral L. New Roads Leading to Old Destinations: Efflux Pumps as Targets to Reverse Multidrug Resistance in Bacteria. Molecules 2017; 22:molecules22030468. [PMID: 28294992 PMCID: PMC6155429 DOI: 10.3390/molecules22030468] [Citation(s) in RCA: 124] [Impact Index Per Article: 17.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2017] [Revised: 03/09/2017] [Accepted: 03/10/2017] [Indexed: 01/05/2023] Open
Abstract
Multidrug resistance (MDR) has appeared in response to selective pressures resulting from the incorrect use of antibiotics and other antimicrobials. This inappropriate application and mismanagement of antibiotics have led to serious problems in the therapy of infectious diseases. Bacteria can develop resistance by various mechanisms and one of the most important factors resulting in MDR is efflux pump-mediated resistance. Because of the importance of the efflux-related multidrug resistance the development of new therapeutic approaches aiming to inhibit bacterial efflux pumps is a promising way to combat bacteria having over-expressed MDR efflux systems. The definition of an efflux pump inhibitor (EPI) includes the ability to render the bacterium increasingly more sensitive to a given antibiotic or even reverse the multidrug resistant phenotype. In the recent years numerous EPIs have been developed, although so far their clinical application has not yet been achieved due to their in vivo toxicity and side effects. In this review, we aim to give a short overview of efflux mediated resistance in bacteria, EPI compounds of plant and synthetic origin, and the possible methods to investigate and screen EPI compounds in bacterial systems.
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Affiliation(s)
- Gabriella Spengler
- Department of Medical Microbiology and Immunobiology, Faculty of Medicine, University of Szeged, 6720 Szeged, Hungary.
| | - Annamária Kincses
- Department of Medical Microbiology and Immunobiology, Faculty of Medicine, University of Szeged, 6720 Szeged, Hungary.
| | - Márió Gajdács
- Department of Medical Microbiology and Immunobiology, Faculty of Medicine, University of Szeged, 6720 Szeged, Hungary.
| | - Leonard Amaral
- Department of Medical Microbiology and Immunobiology, Faculty of Medicine, University of Szeged, 6720 Szeged, Hungary.
- Travel Medicine, Institute of Hygiene and Tropical Medicine, Universidade Nova de Lisboa, 1349-008 Lisbon, Portugal.
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5
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Hou Z, Kugel Desmoulin S, Etnyre E, Olive M, Hsiung B, Cherian C, Wloszczynski PA, Moin K, Matherly LH. Identification and functional impact of homo-oligomers of the human proton-coupled folate transporter. J Biol Chem 2011; 287:4982-95. [PMID: 22179615 DOI: 10.1074/jbc.m111.306860] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
The proton-coupled folate transporter (PCFT; SLC46A1) is a proton-folate symporter that is abundantly expressed in solid tumors and normal tissues, such as duodenum. The acidic pH optimum for PCFT is relevant to intestinal absorption of folates and could afford a means of selectively targeting tumors with novel cytotoxic antifolates. PCFT is a member of the major facilitator superfamily of transporters. Because major facilitator superfamily members exist as homo-oligomers, we tested this for PCFT because such structures could be significant to PCFT mechanism and regulation. By transiently expressing PCFT in reduced folate carrier- and PCFT-null HeLa (R1-11) cells and chemical cross-linking with 1,1-methanediyl bismethanethiosulfonate and Western blotting, PCFT species with molecular masses approximating those of the PCFT dimer and higher order oligomers were detected. Blue native polyacrylamide gel electrophoresis identified PCFT dimer, trimer, and tetramer forms. PCFT monomers with hemagglutinin and His(10) epitope tags were co-expressed in R1-11 cells, solubilized, and bound to nickel affinity columns, establishing their physical associations. Co-expressing YPet and ECFP*-tagged PCFT monomers enabled transport and fluorescence resonance energy transfer in plasma membranes of R1-11 cells. Combined wild-type (WT) and inactive mutant P425R PCFTs were targeted to the cell surface by surface biotinylation/Western blots and confocal microscopy and functionally exhibited a "dominant-positive" phenotype, implying positive cooperativity between PCFT monomers and functional rescue of mutant by WT PCFT. Our results demonstrate the existence of PCFT homo-oligomers and imply their functional and regulatory impact. Better understanding of these higher order PCFT structures may lead to therapeutic applications related to folate uptake in hereditary folate malabsorption, and delivery of PCFT-targeted chemotherapy drugs for cancer.
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Affiliation(s)
- Zhanjun Hou
- Developmental Therapeutics Program, Barbara Ann Karmanos Cancer Institute, Wayne State University School of Medicine, Detroit, Michigan 48201, USA
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6
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The pattern, association with multidrug-resistance and transferability of plasmid-mediated tetracycline resistance inEscherichia coli isolates from the poultry in Iran. ANN MICROBIOL 2009. [DOI: 10.1007/bf03178318] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022] Open
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7
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Hou Z, Matherly LH. Oligomeric structure of the human reduced folate carrier: identification of homo-oligomers and dominant-negative effects on carrier expression and function. J Biol Chem 2008; 284:3285-3293. [PMID: 19019821 DOI: 10.1074/jbc.m807206200] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The ubiquitously expressed reduced folate carrier (RFC) is the major transport system for folate cofactors in mammalian cells and tissues. Previous considerations of RFC structure and mechanism were based on the notion that RFC monomers were sufficient to mediate transport of folate and antifolate substrates. The present study examines the possibility that human RFC (hRFC) exists as higher order homo-oligomers. By chemical cross-linking, transiently expressed hRFC in hRFC-null HeLa (R5) cells with the homobifunctional cross-linker 1,3-propanediyl bis-methanethiosulfonate and Western blotting, hRFC species with molecular masses of hRFC homo-oligomers were identified. Hemagglutinin- and Myc epitope-tagged hRFC proteins expressed in R5 cells were co-immunoprecipitated from both membrane particulate and surface-enriched membrane fractions, indicating that oligomeric hRFC is expressed at the cell surface. By co-expression of wild type and inactive mutant S138C hRFCs, combined with surface biotinylation and confocal microscopy, a dominant-negative phenotype was demonstrated involving greatly decreased cell surface expression of both mutant and wild type carrier caused by impaired intracellular trafficking. For another hRFC mutant (R373A), expression of oligomeric wild type-mutant hRFC was accompanied by a significant and disproportionate loss of wild type activity unrelated to the level of surface carrier. Collectively, our results demonstrate the existence of hRFC homo-oligomers. They also establish the likely importance of these higher order hRFC structures to intracellular trafficking and carrier function.
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Affiliation(s)
- Zhanjun Hou
- Developmental Therapeutics Program, Barbara Ann Karmanos Cancer Institute, Wayne State University School of Medicine, Detroit, Michigan 48201
| | - Larry H Matherly
- Developmental Therapeutics Program, Barbara Ann Karmanos Cancer Institute, Wayne State University School of Medicine, Detroit, Michigan 48201; Cancer Biology Graduate Program, Wayne State University School of Medicine, Detroit, Michigan 48201; Department of Pharmacology, Wayne State University School of Medicine, Detroit, Michigan 48201.
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8
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Goddard AD, Moir JWB, Richardson DJ, Ferguson SJ. Interdependence of two NarK domains in a fused nitrate/nitrite transporter. Mol Microbiol 2008; 70:667-81. [PMID: 18823285 DOI: 10.1111/j.1365-2958.2008.06436.x] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Nitrate uptake is essential for various bacterial processes and combines with nitrite export to form the usual initial steps of denitrification, a process that reduces nitrate to dinitrogen gas. Although many bacterial species contain NarK-like transporters that are proposed to function as either nitrate/proton symporters or nitrate/nitrite antiporters based on sequence homology, these transporters remain, in general, poorly characterized. Several bacteria appear to contain a transporter that is a fusion of two NarK-like proteins, although the significance of this arrangement remains elusive. We demonstrate that NarK from Paracoccus denitrificans is expressed as a fusion of two NarK-like transporters. NarK1 and NarK2 are separately capable of supporting anaerobic denitrifying growth but with growth defects that are partially mitigated by coexpression of the two domains. NarK1 appears to be a nitrate/proton symporter with high affinity for nitrate and NarK2 a nitrate/nitrite antiporter with lower affinity for nitrate. Each transporter requires two conserved arginine residues for activity. A transporter consisting of inactivated NarK1 fused to active NarK2 has a dramatically increased affinity for nitrate compared with NarK2 alone, implying a functional interaction between the two domains. A potential model for nitrate and nitrite transport in P. denitrificans is proposed.
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Affiliation(s)
- Alan D Goddard
- Department of Biochemistry, University of Oxford, South Parks Road, Oxford, UK
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9
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Fang Y, Kolmakova-Partensky L, Miller C. A bacterial arginine-agmatine exchange transporter involved in extreme acid resistance. J Biol Chem 2006; 282:176-82. [PMID: 17099215 DOI: 10.1074/jbc.m610075200] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The arginine-dependent extreme acid resistance response of Escherichia coli operates by decarboxylating arginine. AdiC, a membrane antiporter, catalyzes arginine influx coupled to efflux of the decarboxylation product agmatine, effectively exporting a proton in each turnover. Using the adiC coding sequence under control of a tetracycline promoter in an E. coli vector, we expressed and purified the transport-protein with a yield of approximately 10 mg/liter bacterial culture. Glutaraldehyde cross-linking experiments indicate that the protein is a homodimer in detergent micelles and lipid membranes. Purified AdiC reconstituted into liposomes exchanges arginine and agmatine in a strictly coupled, electrogenic fashion. Kinetic analysis yields K(m) approximately 80 microm for Arg, in the same range as its dissociation constant determined by isothermal titration calorimetry.
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Affiliation(s)
- Yiling Fang
- Department of Biochemistry, Howard Hughes Medical Institute, Brandeis University, Waltham, Massachusetts 02454, USA
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10
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Geertsma ER, Duurkens RH, Poolman B. Functional interactions between the subunits of the lactose transporter from Streptococcus thermophilus. J Mol Biol 2005; 350:102-11. [PMID: 15919090 DOI: 10.1016/j.jmb.2005.04.047] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2005] [Revised: 04/21/2005] [Accepted: 04/22/2005] [Indexed: 11/16/2022]
Abstract
Although the quaternary state has been assessed in detail for only a few members of the major facilitator superfamily (MFS), it is clear that multiple oligomeric states are represented within the MFS. One of its members, the lactose transporter LacS from Streptococcus thermophilus assumes a dimeric structure in the membrane and in vitro analysis showed functional interactions between both subunits when proton motive force ((Delta)p)-driven transport was assayed. To study the interactions in further detail, a covalent dimer was constructed consisting of in tandem fused LacS subunits. These covalent dimers, composed of active and completely inactive subunits, were expressed in Escherichia coli, and initial rates of (Delta)p-driven lactose uptake and lactose counterflow were determined. We now show that also in vivo, both subunits interact functionally; that is, partial complementation of the inactive subunit was observed for both transport modes. Thus, both subunits interact functionally in (Delta)p-driven uptake and in counterflow transport. In addition, analysis of in tandem fused LacS subunits containing one regulatory LacS-IIA domain showed that regulation is primarily an intramolecular event.
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Affiliation(s)
- Eric R Geertsma
- Department of Biochemistry, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Nijenborgh 4, 9747 AG, Groningen, The Netherlands
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11
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Sapunaric FM, Levy SB. Substitutions in the interdomain loop of the Tn10 TetA efflux transporter alter tetracycline resistance and substrate specificity. Microbiology (Reading) 2005; 151:2315-2322. [PMID: 16000721 DOI: 10.1099/mic.0.27997-0] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Cysteine replacement of Asp190, Glu192 and Ser201 residues in the cytoplasmic interdomain loop of the TetA(B) tetracycline efflux antiporter from Tn10 reduces tetracycline resistance [Tamura, N., Konishi, S., Iwaki, S., Kimura-Someya, T., Nada, S. & Yamaguchi, A. (2001). J Biol Chem 276, 20330-20339]. It was found that these Cys substitutions altered the substrate specificity of TetA(B), increasing the relative resistance to doxycycline and minocycline over that to tetracycline by three- to sixfold. Substitutions of Asp190 and Glu192 by Ala, Asn and Gln also impaired the ability of TetA(B) to mediate tetracycline resistance while Ser201Ala and Ser201Thr substitutions did not. A Leu9Phe substitution in the first transmembrane helix of TetA(B) suppressed the Ser201Cys mutation, undoing the alterations in resistance and specificity. That the interdomain loop might contact substrate during transport, as is suggested from its role in substrate specificity, is unexpected considering that the primary sequence in the loop is not conserved among a group of otherwise homologous TetA proteins. However, in the interdomain loop of 11 of 14 homologous TetA efflux proteins, computational analysis revealed a short alpha-helix, which includes some residues affecting activity and substrate specificity. Perhaps this conserved secondary structure accounts for the role of the non-conserved interdomain loop in TetA function.
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Affiliation(s)
- Frédéric M Sapunaric
- The Center for Adaptation Genetics and Drug Resistance and Department of Molecular Biology and Microbiology, Tufts University School of Medicine, 136 Harrison Ave, Boston, MA 02111, USA
| | - Stuart B Levy
- The Center for Adaptation Genetics and Drug Resistance and Department of Molecular Biology and Microbiology, Tufts University School of Medicine, 136 Harrison Ave, Boston, MA 02111, USA
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12
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McMurry LM, Aldema-Ramos ML, Levy SB. Fe(2+)-tetracycline-mediated cleavage of the Tn10 tetracycline efflux protein TetA reveals a substrate binding site near glutamine 225 in transmembrane helix 7. J Bacteriol 2002; 184:5113-20. [PMID: 12193628 PMCID: PMC135328 DOI: 10.1128/jb.184.18.5113-5120.2002] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
TetA specified by Tn10 is a class B member of a group of related bacterial transport proteins of 12 transmembrane alpha helices that mediate resistance to the antibiotic tetracycline. A tetracycline-divalent metal cation complex is expelled from the cell in exchange for a entering proton. The site(s) where tetracycline binds to this export pump is not known. We found that, when chelated to tetracycline, Fe(2+) cleaved the backbone of TetA predominantly at a single position, glutamine 225 in transmembrane helix 7. The related class D TetA protein from plasmid RA1 was cut at exactly the same position. There was no cleavage with glycylcycline, an analog of tetracycline that does not bind to TetA. The Fe(2+)-tetracycline complex was not detectably transported by TetA. However, cleavage products of the same size as with Fe(2+) occurred with Co(2+), known to be cotransported with tetracycline. The known substrate Mg (2+)-tetracycline interfered with cleavage by Fe(2+). These findings suggest that cleavage results from binding at a substrate-specific site. Fe(2+) is known to be able to cleave amide bonds in proteins at distances up to approximately 12 A. We conclude that the alpha carbon of glutamine 225 is probably within 12 A of the position of the Fe(2+) ion in the Fe(2+)-tetracycline complex bound to the protein.
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Affiliation(s)
- Laura M McMurry
- Center for Adaptation Genetics and Drug Resistance and Department of Molecular Biology and Microbiology, Tufts University School of Medicine, Boston, Massachusetts 02111, USA.
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13
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14
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Abstract
Membranes are important sites for the regulation of metabolic functions because they contain transport molecules, which often catalyze the first step in a pathway, and signal-transduction components, which allow the cell to communicate with the environment. Given the catalytic importance of transport proteins and their role in membrane stability, it is possible that oligomerization is used to regulate their function. This review evaluates knowledge of the functions that are associated with the oligomeric organization of secondary transport proteins, which are a major class of solute-translocation systems in all living species.
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Affiliation(s)
- Liesbeth M Veenhoff
- Department of Biochemistry, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Nijenborgh 4 9747 AG Groningen, The Netherlands
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15
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Wolska KI, Bugajska E, Jurkiewicz D, Kuć M, Jóźwik A. Antibiotic susceptibility of Escherichia coli dnaK and dnaJ mutants. Microb Drug Resist 2001; 6:119-26. [PMID: 10990266 DOI: 10.1089/107662900419429] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The role of two chaperone proteins, DnaK and the cooperating factor DnaJ, in Escherichia coli antibiotic susceptibility to three antibiotics (a beta-lactam, chloramphenicol, tetracycline) has been studied. It was found that null dnaJ and dnaKdnaJ mutants are impaired in the functions leading to antibiotic susceptibility. The secretion of beta-lactamase to the periplasmic space is diminished in both mutants, and the additive effect of the two mutations was observed. The activity of chloramphenicol acetyltransferase is also impaired in an additive manner in both mutant strains. Tetracycline uptake is changed only in the double deletion mutant. These defects were observed only during incubation at high temperature (42 degrees C). Efficient complementation of some of these defects by the wild-type alleles introduced on low-copy number plasmid was achieved. Minimal inhibitory concentrations and the titer of the wild-type strains, delta dnaJ and delta dnaKdnaJ mutants treated with ampicillin, chloramphenicol, and tetracycline were also determined. Higher susceptibility of both mutants to chloramphenicol and tetracycline, as compared to their wild-type parent, was observed only after 1 h preincubation of cultures at 42 degrees C. On the contrary, both mutants were less susceptible to ampicillin than their parent strain.
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Affiliation(s)
- K I Wolska
- Department of Bacterial Genetics, Institute of Microbiology, University of Warsaw, Poland.
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16
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Yin CC, Aldema-Ramos ML, Borges-Walmsley MI, Taylor RW, Walmsley AR, Levy SB, Bullough PA. The quarternary molecular architecture of TetA, a secondary tetracycline transporter from Escherichia coli. Mol Microbiol 2000; 38:482-92. [PMID: 11069672 DOI: 10.1046/j.1365-2958.2000.02149.x] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
TetA, a tetracycline cation/proton antiporter, was expressed in Escherichia coli with a C-terminal tag of six histidines, solubilized in dodecyl maltoside and purified in a single step using Ni2+ affinity chromatography. Two-dimensional crystals were obtained after reconstitution of purified protein with lipids. Electron microscopy of negatively stained crystals revealed a trigonal symmetry, from which we infer that this secondary transporter has a trimeric structure. An overall molecular envelope can be described by a triangle of side approximately 100 A enclosing a central stain-filled depression. These dimensions are consistent with those obtained from projection views of single, isolated TetA particles that also display a trimeric architecture, confirming that the threefold symmetry is not simply a consequence of crystal-packing interactions. These data represent the first direct view of the quarternary arrangement of any antibiotic efflux pump. They are fully consistent with biochemical data on TetA, which indicate that it functions as a multimer and that the monomer consists of two domains, one of which plays the major part in oligomerization interactions.
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Affiliation(s)
- C C Yin
- Krebs Institute for Biomolecular Research, Department of Molecular Biology and Biotechnology, University of Sheffield, Firth Court, Western Bank, Sheffield S10 2TN, UK
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17
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Wong RS, McMurry LM, Levy SB. 'Intergenic' blr gene in Escherichia coli encodes a 41-residue membrane protein affecting intrinsic susceptibility to certain inhibitors of peptidoglycan synthesis. Mol Microbiol 2000; 37:364-70. [PMID: 10931331 DOI: 10.1046/j.1365-2958.2000.01998.x] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
In the annotation of genomic sequences, small open reading frames (ORFs) are often neglected, particularly if they have no homology to other ORFs or proteins. A mini-TnphoA insertion in a 602 bp 'intergenic' region of the Escherichia coli chromosome at genomic nucleotide 1702674 gave rise to a membrane-bound PhoA fusion protein and a two- to fourfold increase in the intrinsic susceptibility to a wide spectrum of beta-lactam antibiotics without affecting beta-lactamase activity or susceptibility to tetracycline, chloramphenicol, gentamicin or quinolones. Susceptibility was also increased to cycloserine and bacitracin, but not to fosfomycin or valinomycin; these drugs, like beta-lactams, inhibit peptidoglycan synthesis, although by different mechanisms. A clone bearing only 358 bp of this 'blr' region restored resistance to the parental level. Two amber mutations in the clone prevented such restoration and were counteracted by an amber suppressor, proving that the active species is a protein. The Blr protein has 41 amino acids, with a single predicted transmembrane helix, but no clear homology to any other protein. A transcriptional start exists 39 bp upstream from the translational start. The membrane location of Blr suggests that it may be part of an efflux pump or involved in murein metabolism. The results indicate that genes for other very small functional proteins may lie within 'intergenic' regions.
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Affiliation(s)
- R S Wong
- Center for Adaptation Genetics and Drug Resistance and the Department of Molecular Biology and Microbiology, Tufts University School of Medicine, 136 Harrison Avenue, Boston, MA 02111, USA
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18
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Magalhães VD, Castilho BA. Mini-Mu insertions in the tetracycline resistance determinant from Proteus mirabilis. Braz J Med Biol Res 1997; 30:363-7. [PMID: 9246234 DOI: 10.1590/s0100-879x1997000300009] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
The inducible tetracycline resistance determinant isolated from Proteus mirabilis cloned into the plasmid pACYC177 was mutagenized by insertion of a mini-Mu-lac phage in order to define the regions in the cloned sequences encoding the structural and regulatory proteins. Three different types of mutants were obtained: one lost the resistance phenotype and became Lac+; another expressed the resistance at lower levels and constitutively; the third was still dependent on induction but showed a lower minimal inhibitory concentration. The mutant phenotypes and the locations of the insertions indicate that the determinant is composed of a repressor gene and a structural gene which are not transcribed divergently as are other known tetracycline determinants isolated from Gram-negative bacteria.
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Affiliation(s)
- V D Magalhães
- Departamento de Microbiologia, Imunologia e Parasitologia, Escola Paulista de Medicina, Universidade Federal de Sö Paulo, Brasil
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19
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Mallonee DH, Hylemon PB. Sequencing and expression of a gene encoding a bile acid transporter from Eubacterium sp. strain VPI 12708. J Bacteriol 1996; 178:7053-8. [PMID: 8955384 PMCID: PMC178615 DOI: 10.1128/jb.178.24.7053-7058.1996] [Citation(s) in RCA: 67] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Eubacterium sp. strain VPI 12708 expresses inducible bile acid 7alpha-dehydroxylation activity via a multistep pathway. The genes encoding several of the inducible proteins involved in the pathway have been previously mapped to a bile acid-inducible (bai) operon in Eubacterium sp. strain VPI 12708. We now report the cloning, sequencing, and characterization of the baiG gene, which is part of the bai operon. The predicted amino acid sequence of the BaiG polypeptide shows significant homology to several membrane transport proteins, including sugar and antibiotic resistance transporters, which are members of the major facilitator superfamily. Hydrophilicity plots of BaiG show a high degree of similarity to class K and L TetA proteins from gram-positive bacteria, and, like these classes of TetA proteins, BaiG has 14 proposed transmembrane domains. The baiG gene was cloned into Escherichia coli and shown to confer an energy-dependent bile acid uptake activity. Primary bile acids were preferentially transported into E. coli cells expressing this gene, with at least sevenfold and fourfold increases in the uptake of cholic acid and chenodeoxycholic acid, respectively, over control reactions. Less transport activity was observed with cholylglycine, 7-oxocholic acid, and deoxycholic acid. The transport activity was inhibited by the proton ionophores carbonyl cyanide m-chlorophenylhydrazone, 2,4-dinitrophenol, and nigericin but not by the potassium ionophore valinomycin, suggesting that the transport is driven by the proton motive force across the cell membrane. In summary, we have cloned, sequenced, and expressed a bile acid-inducible bile acid transporter from Eubacterium sp. strain VPI 12708. To our knowledge, this is the first report of the cloning and expression of a gene encoding a procaryotic bile acid transporter.
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Affiliation(s)
- D H Mallonee
- Department of Microbiology and Immunology, Medical College of Virginia, Richmond 23298-0678, USA
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20
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Chapter 8 Multidrug resistance in prokaryotes: Molecular mechanisms of drug efflux. ACTA ACUST UNITED AC 1996. [DOI: 10.1016/s1383-8121(96)80049-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
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21
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McNicholas P, McGlynn M, Guay GG, Rothstein DM. Genetic analysis suggests functional interactions between the N- and C-terminal domains of the TetA(C) efflux pump encoded by pBR322. J Bacteriol 1995; 177:5355-7. [PMID: 7665527 PMCID: PMC177333 DOI: 10.1128/jb.177.18.5355-5357.1995] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
Genetic analysis of the tetA(C) gene of pBR322 indicates the importance of two-cytoplasmic loops in the TetA(C) protein (P. McNicholas, I. Chopra, and D. M. Rothstein, J. Bacteriol. 174:7926-7933, 1992). In this study, we characterized second-site suppressor mutations that suggest a functional interaction between these two cytoplasmic regions of the protein.
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Affiliation(s)
- P McNicholas
- Department of Microbial Genetics and Biochemistry, Lederle Laboratories, Pearl River, New York 10965, USA
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22
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Allen NE. Biochemical mechanisms of resistance to non-cell wall antibacterial agents. PROGRESS IN MEDICINAL CHEMISTRY 1995; 32:157-238. [PMID: 8577918 DOI: 10.1016/s0079-6468(08)70454-5] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Affiliation(s)
- N E Allen
- Infectious Disease Research, Eli Lilly and Company, Indianapolis, IN 46285, USA
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23
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Douglas RM, Ritchie GY, Munro AW, McLaggan D, Booth IR. The K(+)-efflux system, KefC, in Escherichia coli: genetic evidence for oligomeric structure. Mol Membr Biol 1994; 11:55-61. [PMID: 8019602 DOI: 10.3109/09687689409161030] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
KefC is a glutathione-gated K(+)-efflux system that is widespread in Gram-negative bacteria and which plays a role in the protection of cells from the toxic effects of electrophilic reagents, such as N-ethylmaleimide (NEM). The KefC gene from Escherichia coli has been cloned and the DNA sequenced. A number of kefC mutants that affect K+ retention by the KefC system have been isolated and all retain activation by NEM. Cloned kefC was found to suppress the phenotype of two such mutants kefC121 and kefC103. Analysis of this phenomenon has shown that suppression is specific to the KefC system, but that cloned kefC from Klebsiella and Erwinia can also mediate suppression of the mutant phenotype. Plasmid constructs of the E. coli gene in which expression of the cloned gene was diminished showed induced ability to suppress the mutant phenotype. KefC'-'LacZ hybrid proteins were inserted in the membrane but did not suppress the mutant phenotype. Cloned kefC did not suppress a mutant kefB allele that exhibited a similar phenotype to the kefC121 allele. These data suggest that suppression is unlikely to arise from exclusion of the mutant form of the protein from the membrane. Furthermore, NEM-activated K+ efflux from a strain carrying both the mutant and cloned wild-type alleles was faster than when either allele was present in cells alone, suggesting that both forms of the protein are inserted into the membrane. These data are discussed in terms of a model for the KefC protein in which the protein is composed of one or more identical subunits that interact in the membrane.
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Affiliation(s)
- R M Douglas
- Department of Molecular and Cell Biology, University of Aberdeen, Marischal College, UK
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24
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Allard JD, Bertrand KP. Sequence of a class E tetracycline resistance gene from Escherichia coli and comparison of related tetracycline efflux proteins. J Bacteriol 1993; 175:4554-60. [PMID: 8331085 PMCID: PMC204899 DOI: 10.1128/jb.175.14.4554-4560.1993] [Citation(s) in RCA: 27] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
We determined the nucleotide sequence of the class E tetA gene on plasmid pSL1456 from Escherichia coli SLH1456A. The deduced amino acid sequence of the class E TetA protein shows 50 to 56% identity with the sequences of five related TetA proteins (classes A through D and G). Hydrophobicity profiles identify 12 putative transmembrane segments with similar boundaries in all six TetA sequences. The N-terminal alpha domain of the six sequences is more highly conserved than the C-terminal beta domain; the central hydrophilic loop connecting the alpha and beta domains is the least conserved region. Amino acid residues that have been shown to be important for class B (Tn10) TetA function are conserved in all six TetA sequences. Unlike the class B tetA gene, the class D and E tetA genes do not exhibit a negative gene dosage effect when present on multicopy plasmids derived from pACYC177.
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Affiliation(s)
- J D Allard
- Department of Microbiology, Washington State University, Pullman 99164
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25
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Morton TM, Eaton DM, Johnston JL, Archer GL. DNA sequence and units of transcription of the conjugative transfer gene complex (trs) of Staphylococcus aureus plasmid pGO1. J Bacteriol 1993; 175:4436-47. [PMID: 7687249 PMCID: PMC204884 DOI: 10.1128/jb.175.14.4436-4447.1993] [Citation(s) in RCA: 74] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
The conjugative transfer genes of 52-kb staphylococcal R plasmid pGO1 were localized to a single BglII restriction fragment and cloned in Escherichia coli. Sequence analysis of the 13,612-base transfer region, designated trs, identified 14 intact open reading frames (ORFs), 13 of which were transcribed in the same direction. Each ORF identified was preceded by a typical staphylococcal ribosomal binding sequence, and 10 of the 14 proteins predicted to be encoded by these ORFs were seen when an E. coli in vitro transcription-translation system was used. Functional transcription units were identified in a Staphylococcus aureus host by complementation of Tn917 inserts that abolished transfer and by Northern (RNA) blot analysis of pGO1 mRNA transcripts. These studies identified three complementation groups (trsA through trsC, trsD through trsK, and trsL-trsM) and four mRNA transcripts (trsA through trsC [1.8 kb], trsA-trsB [1.3 kb], trsL-trsM [1.5 kb], and trsN [400 bases]). No definite mRNA transcript was seen for the largest complementation group, trsD through trsK (10 kb). Comparison of predicted trs-encoded amino acid sequences to those in the data base showed 20% identity of trsK to three related genes necessary for conjugative transfer of plasmids in gram-negative species and 32% identity of trsC to a gene required for conjugative mobilization of plasmid pC221 from staphylococci.
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MESH Headings
- Amino Acid Sequence
- Base Sequence
- Blotting, Northern
- Cloning, Molecular
- Conjugation, Genetic
- DNA, Bacterial/genetics
- DNA, Bacterial/isolation & purification
- Escherichia coli/genetics
- Genes, Bacterial
- Genetic Complementation Test
- Molecular Sequence Data
- Multigene Family
- Mutagenesis, Insertional
- Oligodeoxyribonucleotides
- Open Reading Frames
- Plasmids
- Polymerase Chain Reaction
- Promoter Regions, Genetic
- Protein Biosynthesis
- RNA, Bacterial/isolation & purification
- RNA, Messenger/metabolism
- Restriction Mapping
- Sequence Homology, Amino Acid
- Software
- Staphylococcus aureus/genetics
- Terminator Regions, Genetic
- Transcription, Genetic
- Transduction, Genetic
- Transformation, Bacterial
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Affiliation(s)
- T M Morton
- Department of Microbiology and Immunology, Medical College of Virginia/Virginia Commonwealth University, Richmond 23298-0049
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26
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McMurry LM, Stephan M, Levy SB. Decreased function of the class B tetracycline efflux protein Tet with mutations at aspartate 15, a putative intramembrane residue. J Bacteriol 1992; 174:6294-7. [PMID: 1328154 PMCID: PMC207700 DOI: 10.1128/jb.174.19.6294-6297.1992] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
The aspartate 15 residue within the first predicted intramembrane helix of the tetracycline efflux protein Tet has been conserved in four tetracycline resistance determinants from gram-negative bacteria. Its replacement in class B Tet by tyrosine, histidine, or asparagine resulted in a 60 to 85% loss of tetracycline resistance and a similar loss of tetracycline-proton antiport. The tyrosine and histidine substitutions lowered the Vmax of the efflux system by some 90% but did not alter the Km. The asparagine substitution raised the Km over 13-fold, while the Vmax was equal to or greater than that of the wild type. Therefore, although the nature of its role is unclear, aspartate 15 is important for normal Tet function.
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Affiliation(s)
- L M McMurry
- Department of Molecular Biology, Tufts University School of Medicine, Boston, Massachusetts 02111
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27
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Allard J, Bertrand K. Membrane topology of the pBR322 tetracycline resistance protein. TetA-PhoA gene fusions and implications for the mechanism of TetA membrane insertion. J Biol Chem 1992. [DOI: 10.1016/s0021-9258(19)37116-9] [Citation(s) in RCA: 48] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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28
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Affiliation(s)
- S B Levy
- Department of Molecular Biology, Tufts University School of Medicine, New England Medical Center, Boston, Massachusetts 02111
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29
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Rubin RA, Levy SB. Tet protein domains interact productively to mediate tetracycline resistance when present on separate polypeptides. J Bacteriol 1991; 173:4503-9. [PMID: 2066343 PMCID: PMC208114 DOI: 10.1128/jb.173.14.4503-4509.1991] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
Both domains, alpha and beta, of the cytoplasmic membrane-localized Tet proteins encoded by the tet gene family (classes A through E) are required for resistance to tetracycline (Tcr) in gram-negative bacteria. Two inactive proteins, each containing a mutation in the opposite domain, are capable of complementation to produce Tcr. Similarly, inactive hybrid proteins expressed by interdomain gene hybrids constructed between tet(B) and tet(C) [tet(B) alpha/(C) beta and tet(C) alpha/(B) beta] together produce significant Tcr via trans complementation (R.A. Rubin and S. B. Levy, J. Bacteriol. 172:2303-2312, 1990). A derivative of tet(B) was constructed to express the two domains of Tet(B) as separate polypeptides, neither containing intact the central, hydrophilic interdomain region. Cells harboring this tet(B) mutant expressed Tcr at about 20% the level conferred by intact tet(B). As expected, no detectable amount of a full-length Tet protein was expressed. A polypeptide corresponding to the alpha domain was observed. Interdomain hybrids between tet(B) and tet(C) containing a frameshift at the fusion junction, designed to result in expression of each of the four domains on separate polypeptides, showed trans complementation without production of detectable full-length proteins. Levels of Tcr were greater than or equal to those previously observed in complementations using full-length hybrid proteins. These results strongly suggest that polypeptides harboring individual alpha and beta domains, lacking an intact interdomain region, can interact productively in the cell to confer Tcr.
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Affiliation(s)
- R A Rubin
- Department of Molecular Biology, Tufts University School of Medicine, Boston, Massachusetts
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30
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Yun C, Van Doren S, Crofts A, Gennis R. The use of gene fusions to examine the membrane topology of the L-subunit of the photosynthetic reaction center and of the cytochrome b subunit of the bc1 complex from Rhodobacter sphaeroides. J Biol Chem 1991. [DOI: 10.1016/s0021-9258(18)99114-3] [Citation(s) in RCA: 49] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
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31
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DiRita VJ, Mekalanos JJ. Periplasmic interaction between two membrane regulatory proteins, ToxR and ToxS, results in signal transduction and transcriptional activation. Cell 1991; 64:29-37. [PMID: 1898871 DOI: 10.1016/0092-8674(91)90206-e] [Citation(s) in RCA: 170] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
ToxR is a transmembrane, DNA-binding protein that can activate transcription of genes encoding cholera toxin (ctxAB). Here we characterize ToxS, a 19 kd transmembrane regulatory protein that interacts with ToxR and stimulates its activity. If a portion of the periplasmic domain of ToxR is deleted, productive interaction with ToxS is abolished. A ToxR-PhoA fusion protein that retains most of the ToxR periplasmic region remains dependent on ToxS for its ToxR activity. ToxS protects this fusion from proteolytic cleavage, suggesting that these two proteins interact within the periplasm. Mutations in a short cytoplasmic domain of ToxR were isolated that disrupt the periplasmic interaction between ToxR and ToxS. This domain is shared by other bacterial transcriptional activators, suggesting that it may play a common role in function of these proteins and in the molecular mechanism of signal transduction.
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Affiliation(s)
- V J DiRita
- Department of Microbiology and Molecular Genetics, Harvard Medical School, Boston, Massachusetts 02115
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32
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Hickman RK, McMurry LM, Levy SB. Overproduction and purification of the Tn10-specified inner membrane tetracycline resistance protein Tet using fusions to beta-galactosidase. Mol Microbiol 1990; 4:1241-51. [PMID: 2177817 DOI: 10.1111/j.1365-2958.1990.tb00703.x] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Tetracycline resistance in the Enterobacteriaceae is mediated by a number of genetically related, usually plasmid-borne, determinants which specify an efflux system involving an inner membrane protein, Tet. Attempts to overproduce the Tn10 (Class B)-encoded Tet in Escherichia coli by cloning the structural gene tet downstream of the lambda PL promoter under regulation by temperature-sensitive lambda repressor cI857 were unsuccessful; induction at 42 degrees C resulted in filamentous, non-viable cells containing little detectable overproduction of the protein. However, cells containing tet fused to lacZ were resistant to tetracycline at 30 degrees C and synthesized modest amounts of a large fusion protein when induced at 42 degrees C. Fusion of the N-terminal half or the first 38 amino acids of tet to lacZ did lead to increased production of fusion proteins. Fusions could be purified by size or by LacZ immunoaffinity or substrate-affinity chromatography. In the latter method, selected detergents were required to counteract nonspecific binding of Tet to the adsorbant. Amino acid sequencing of the N-terminus of Tet-LacZ fusion proteins indicated that most molecules were blocked at this terminus. The sequence of an unblocked subpopulation was consistent with that expected from the nucleotide sequence. A collagen peptide linker, genetically placed between tet and lacZ, allowed recovery of purified Tet protein after collagenase treatment of the purified fusion protein.
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Affiliation(s)
- R K Hickman
- Department of Molecular Biology and Microbiology, Tufts University School of Medicine, Boston, Massachusetts 02111
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33
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The use of gene fusions to determine the topology of all of the subunits of the cytochrome o terminal oxidase complex of Escherichia coli. J Biol Chem 1990. [DOI: 10.1016/s0021-9258(19)38256-0] [Citation(s) in RCA: 93] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
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34
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Abstract
A variety of bacterial functions are encoded on plasmids, extrachromosomal elements. Examples of plasmid-borne functions are antibiotic production and resistance, degradation of recalcitrant chemicals, virulence factors, and plant symbiotic properties. Several transport systems with diverse functions have recently been found to be carried on plasmids. These systems serve to either accumulate or extrude a compound from a cell. The focus of this review is to present a survey on several of these novel plasmid-borne transport systems emphasizing functions, components, and molecular genetics.
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Affiliation(s)
- L S Tisa
- Department of Biochemistry, Wayne State University, School of Medicine, Detroit, Michigan 48201
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35
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Rubin RA, Levy SB. Interdomain hybrid Tet proteins confer tetracycline resistance only when they are derived from closely related members of the tet gene family. J Bacteriol 1990; 172:2303-12. [PMID: 2185211 PMCID: PMC208863 DOI: 10.1128/jb.172.5.2303-2312.1990] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
Inner membrane Tet proteins encoded by tet genes in gram-negative bacteria mediate resistance to tetracycline (Tcr) by directing its export. Total sequences for class A, B, and C tet genes demonstrate that their products have a common ancestor, with Tet(A) and Tet(C) being more closely related (78% identical) than either is to Tet(B) (45% identical). The N- and C-terminal halves of Tet(B) and Tet(C) appear to comprise separate domains, and trans-complementation observed between tetracycline sensitive mutants in either domain of Tet(B) suggests separate but interactive functions for these domains. In this present study, interdomain hybrid genes were constructed to express hybrid tet products whose N- and C-terminal halves were derived from different family members [Tet(A/C), Tet(B/C), and Tet(C/B)]. Tet(A/C) specified a level of Tcr comparable to wild-type Tet(C) and 60% that of Tet(A), indicating that domains from these closely related tet products can function in cis. Although neither Tet(B/C) nor Tet(C/B) hybrids conferred significant Tcr, cells producing both of these types of hybrid proteins expressed substantial Tcr, indicating that productive interactions can occur in trans between Tet(B/C) and Tet(C/B). Taken together, these results suggest that highly specific interactions between the N- and C-terminal domains are necessary for Tcr and do not occur in individual hybrids derived from the more distant relatives, Tet(B) and Tet(C). This requirement for specific interactions suggests that N- and C-terminal domains have coevolved in each member of the Tet family.
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Affiliation(s)
- R A Rubin
- Department of Molecular Biology and Microbiology, Tufts University School of Medicine, Boston, Massachusetts 02111
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36
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Rubin RA, Levy SB, Heinrikson RL, Kézdy FJ. Gene duplication in the evolution of the two complementing domains of gram-negative bacterial tetracycline efflux proteins. Gene X 1990; 87:7-13. [PMID: 2332166 DOI: 10.1016/0378-1119(90)90489-e] [Citation(s) in RCA: 58] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
The resistance of Gram- bacteria to the broad-spectrum antibiotic tetracycline (Tc) results from energy-dependent drug efflux mediated by the tet gene product, the cytoplasmic membrane Tet protein. Amino acid (aa) sequences deduced from total tet nucleotide sequences of three different resistance determinants (classes A, B and C) indicate that the protein products [Tet(A), Tet(B), and Tet(C)] share a common ancestor. Hydropathic analysis of Tet sequences predicts twelve transmembrane segments in each protein, with six occurring in each half of the molecule. More importantly, the linear distributions of these segments in the N- and C-terminal halves are nearly identical, suggesting that the two halves of each Tet protein are related by a process of tandem gene duplication and divergence. Indeed, a variable but significant conservation of sequence was detected among the N- and C-terminal halves for all possible comparisons of the three proteins. Such conservation was not observed within other prokaryotic integral membrane proteins or when other prokaryotic proteins were compared to Tet halves. Similarity, both in sequence and in predicted transmembrane structural organization, strongly suggests that a common ancestor of Tet(A), Tet(B), and Tet(C) arose by duplication of a gene reading frame specifying a transmembrane protein of approximately 200 aa residues. The two halves of Tet proteins correspond to the two domains, alpha and beta, which have distinct, complementary roles in Tc efflux. Nevertheless, selective constraints to function in the cytoplasmic membrane have apparently led to maintenance of similar patterns of secondary structural organization in these complementary domains.
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Affiliation(s)
- R A Rubin
- Department of Molecular Biology and Microbiology, Tufts University School of Medicine, Boston, MA 02111
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37
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Eckert B, Beck CF. Topology of the transposon Tn10-encoded tetracycline resistance protein within the inner membrane of Escherichia coli. J Biol Chem 1989. [DOI: 10.1016/s0021-9258(18)80116-8] [Citation(s) in RCA: 54] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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