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Milne RJ, Dibley KE, Bose J, Ashton AR, Ryan PR, Tyerman SD, Lagudah ES. Expression of the wheat multipathogen resistance hexose transporter Lr67res is associated with anion fluxes. PLANT PHYSIOLOGY 2023; 192:1254-1267. [PMID: 36806945 DOI: 10.1093/plphys/kiad104] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/14/2022] [Revised: 01/24/2023] [Accepted: 01/29/2023] [Indexed: 06/01/2023]
Abstract
Many disease resistance genes in wheat (Triticum aestivum L.) confer strong resistance to specific pathogen races or strains, and only a small number of genes confer multipathogen resistance. The Leaf rust resistance 67 (Lr67) gene fits into the latter category as it confers partial resistance to multiple biotrophic fungal pathogens in wheat and encodes a Sugar Transport Protein 13 (STP13) family hexose-proton symporter variant. Two mutations (G144R, V387L) in the resistant variant, Lr67res, differentiate it from the susceptible Lr67sus variant. The molecular function of the Lr67res protein is not understood, and this study aimed to broaden our knowledge on this topic. Biophysical analysis of the wheat Lr67sus and Lr67res protein variants was performed using Xenopus laevis oocytes as a heterologous expression system. Oocytes injected with Lr67sus displayed properties typically associated with proton-coupled sugar transport proteins-glucose-dependent inward currents, a Km of 110 ± 10 µM glucose, and a substrate selectivity permitting the transport of pentoses and hexoses. By contrast, Lr67res induced much larger sugar-independent inward currents in oocytes, implicating an alternative function. Since Lr67res is a mutated hexose-proton symporter, the possibility of protons underlying these currents was investigated but rejected. Instead, currents in Lr67res oocytes appeared to be dominated by anions. This conclusion was supported by electrophysiology and 36Cl- uptake studies and the similarities with oocytes expressing the known chloride channel from Torpedo marmorata, TmClC-0. This study provides insights into the function of an important disease resistance gene in wheat, which can be used to determine how this gene variant underpins disease resistance in planta.
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Affiliation(s)
- Ricky J Milne
- CSIRO, Agriculture and Food, Canberra, ACT 2601, Australia
| | | | - Jayakumar Bose
- Australian Research Council Centre of Excellence in Plant Energy Biology, School of Agriculture, Food and Wine, University of Adelaide, Urrbrae, SA 5064, Australia
- School of Science, Western Sydney University, Richmond, NSW 2753, Australia
| | | | - Peter R Ryan
- CSIRO, Agriculture and Food, Canberra, ACT 2601, Australia
| | - Stephen D Tyerman
- Australian Research Council Centre of Excellence in Plant Energy Biology, School of Agriculture, Food and Wine, University of Adelaide, Urrbrae, SA 5064, Australia
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2
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Terada T, Inui KI. Recent Advances in Structural Biology of Peptide Transporters. CURRENT TOPICS IN MEMBRANES 2012. [DOI: 10.1016/b978-0-12-394316-3.00008-9] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 03/14/2023]
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3
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Renna MD, Oyadeyi AS, Bossi E, Kottra G, Peres A. Functional and structural determinants of reverse operation in the pH-dependent oligopeptide transporter PepT1. Cell Mol Life Sci 2011; 68:2961-75. [PMID: 21181229 PMCID: PMC11115064 DOI: 10.1007/s00018-010-0604-3] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2010] [Revised: 10/20/2010] [Accepted: 11/25/2010] [Indexed: 10/18/2022]
Abstract
The functional and structural basis of reverse operation of PepT1 has been studied in Xenopus oocytes expressing the wild-type and mutated forms of this protein. Using brief pulses from a negative holding potential, wild-type and Arg282 mutants exhibit outward currents in the presence of Gly-Gln. The reversal potential of these currents is affected by both pH and substrate concentration, confirming coupled transport in the wild type and in the mutants as well. Long-lasting voltage and current-clamp experiments show that the outward currents are only temporary, and reflect accumulation and/or depletion effects near the membrane. The ability to operate in reverse mode was confirmed in all isoforms by intracellular injection of substrate. The role of Arg282 and Asp341 in the reverse transport was also investigated using charged substrates. Positive Lys-Gly (but not Gly-Lys) showed enhanced transport currents in the Arg282 mutants. In contrast, negative Gly-Asp and Asp-Gly elicited modest currents in all isoforms.
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Affiliation(s)
- Maria Daniela Renna
- Laboratory of Cellular and Molecular Physiology, Dept. of Biotechnology and Molecular Sciences, University of Insubria, Via Dunant 3, 21100 Varese, Italy
| | - Ayodele Stephen Oyadeyi
- Laboratory of Cellular and Molecular Physiology, Dept. of Biotechnology and Molecular Sciences, University of Insubria, Via Dunant 3, 21100 Varese, Italy
| | - Elena Bossi
- Laboratory of Cellular and Molecular Physiology, Dept. of Biotechnology and Molecular Sciences, University of Insubria, Via Dunant 3, 21100 Varese, Italy
- Center for Neurosciences, University of Insubria, 21100 Varese, Italy
| | - Gabor Kottra
- Molecular Nutrition Unit, Technische Universität München, Freising, Germany
| | - Antonio Peres
- Laboratory of Cellular and Molecular Physiology, Dept. of Biotechnology and Molecular Sciences, University of Insubria, Via Dunant 3, 21100 Varese, Italy
- Center for Neurosciences, University of Insubria, 21100 Varese, Italy
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4
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Suhre K, Shin SY, Petersen AK, Mohney RP, Meredith D, Wägele B, Altmaier E, Deloukas P, Erdmann J, Grundberg E, Hammond CJ, de Angelis MH, Kastenmüller G, Köttgen A, Kronenberg F, Mangino M, Meisinger C, Meitinger T, Mewes HW, Milburn MV, Prehn C, Raffler J, Ried JS, Römisch-Margl W, Samani NJ, Small KS, Wichmann HE, Zhai G, Illig T, Spector TD, Adamski J, Soranzo N, Gieger C. Human metabolic individuality in biomedical and pharmaceutical research. Nature 2011; 477:54-60. [PMID: 21886157 PMCID: PMC3832838 DOI: 10.1038/nature10354] [Citation(s) in RCA: 809] [Impact Index Per Article: 62.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2010] [Accepted: 06/30/2011] [Indexed: 01/08/2023]
Abstract
Genome-wide association studies (GWAS) have identified many risk loci for complex diseases, but effect sizes are typically small and information on the underlying biological processes is often lacking. Associations with metabolic traits as functional intermediates can overcome these problems and potentially inform individualized therapy. Here we report a comprehensive analysis of genotype-dependent metabolic phenotypes using a GWAS with non-targeted metabolomics. We identified 37 genetic loci associated with blood metabolite concentrations, of which 25 show effect sizes that are unusually high for GWAS and account for 10-60% differences in metabolite levels per allele copy. Our associations provide new functional insights for many disease-related associations that have been reported in previous studies, including those for cardiovascular and kidney disorders, type 2 diabetes, cancer, gout, venous thromboembolism and Crohn's disease. The study advances our knowledge of the genetic basis of metabolic individuality in humans and generates many new hypotheses for biomedical and pharmaceutical research.
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Affiliation(s)
- Karsten Suhre
- Institute of Bioinformatics and Systems Biology, Helmholtz Zentrum München, German Research Center for Environmental Health, Neuherberg, Germany
- Faculty of Biology, Ludwig-Maximilians-Universität, Planegg-Martinsried, Germany
- Department of Physiology and Biophysics, Weill Cornell Medical College in Qatar, Education City - Qatar Foundation, Doha, Qatar
| | - So-Youn Shin
- The Wellcome Trust Sanger Institute, Wellcome Trust Genome Campus, Hinxton UK
| | - Ann-Kristin Petersen
- Institute of Genetic Epidemiology, Helmholtz Zentrum München, German Research Center for Environmental Health, Neuherberg, Germany
| | | | - David Meredith
- School of Life Sciences, Oxford Brookes University, Headington, Oxford, UK
| | - Brigitte Wägele
- Institute of Bioinformatics and Systems Biology, Helmholtz Zentrum München, German Research Center for Environmental Health, Neuherberg, Germany
- Department of Genome-oriented Bioinformatics, Life and Food Science Center Weihenstephan, Technische Universität München, Freising-Weihenstephan, Germany
| | - Elisabeth Altmaier
- Institute of Bioinformatics and Systems Biology, Helmholtz Zentrum München, German Research Center for Environmental Health, Neuherberg, Germany
| | - CARDIoGRAM
- The member list of the CARDIoGRAM consortium is provided as Supplemental Information
| | - Panos Deloukas
- The Wellcome Trust Sanger Institute, Wellcome Trust Genome Campus, Hinxton UK
| | | | - Elin Grundberg
- The Wellcome Trust Sanger Institute, Wellcome Trust Genome Campus, Hinxton UK
- Department of Twin Research & Genetic Epidemiology, King’s College London, UK
| | | | - Martin Hrabé de Angelis
- Institute of Experimental Genetics, Genome Analysis Center, Helmholtz Zentrum München, German Research Center for Environmental Health, Neuherberg, Germany
- Institute of Experimental Genetics, Life and Food Science Center Weihenstephan, Technische Universität München, Freising-Weihenstephan, Germany
| | - Gabi Kastenmüller
- Institute of Bioinformatics and Systems Biology, Helmholtz Zentrum München, German Research Center for Environmental Health, Neuherberg, Germany
| | - Anna Köttgen
- Renal Division, University Hospital Freiburg, Germany
| | - Florian Kronenberg
- Division of Genetic Epidemiology, Department of Medical Genetics, Molecular and Clinical Pharmacology, Innsbruck Medical University, Innsbruck, Austria
| | - Massimo Mangino
- Department of Twin Research & Genetic Epidemiology, King’s College London, UK
| | - Christa Meisinger
- Institute of Epidemiology II, Helmholtz Zentrum München, German Research Center for Environmental Health, Neuherberg, Germany
| | - Thomas Meitinger
- Institute of Human Genetics, Helmholtz Zentrum München, German Research Center for Environmental Health, Neuherberg, Germany
- Institute of Human Genetics, Klinikum rechts der Isar, Technische Universität München, Munich, Germany
| | - Hans-Werner Mewes
- Institute of Bioinformatics and Systems Biology, Helmholtz Zentrum München, German Research Center for Environmental Health, Neuherberg, Germany
- Department of Genome-oriented Bioinformatics, Life and Food Science Center Weihenstephan, Technische Universität München, Freising-Weihenstephan, Germany
| | | | - Cornelia Prehn
- Institute of Experimental Genetics, Genome Analysis Center, Helmholtz Zentrum München, German Research Center for Environmental Health, Neuherberg, Germany
| | - Johannes Raffler
- Institute of Bioinformatics and Systems Biology, Helmholtz Zentrum München, German Research Center for Environmental Health, Neuherberg, Germany
- Faculty of Biology, Ludwig-Maximilians-Universität, Planegg-Martinsried, Germany
| | - Janina S. Ried
- The Wellcome Trust Sanger Institute, Wellcome Trust Genome Campus, Hinxton UK
| | - Werner Römisch-Margl
- Institute of Bioinformatics and Systems Biology, Helmholtz Zentrum München, German Research Center for Environmental Health, Neuherberg, Germany
| | - Nilesh J. Samani
- Department of Cardiovascular Sciences, University of Leicester, and Leicester NIHR Biomedical Research Unit in Cardiovascular Disease, Glenfield Hospital, Leicester, UK
| | - Kerrin S. Small
- Department of Twin Research & Genetic Epidemiology, King’s College London, UK
| | - H.-Erich Wichmann
- Institute of Epidemiology I, Helmholtz Zentrum München, German Research Center for Environmental Health, Neuherberg, Germany
- Institute of Medical Informatics, Biometry and Epidemiology, Chair of Epidemiology, Ludwig-Maximilians-Universität, Munich, Germany
- Klinikum Grosshadern, Munich, Germany
| | - Guangju Zhai
- Department of Twin Research & Genetic Epidemiology, King’s College London, UK
| | - Thomas Illig
- Unit for Molecular Epidemiology, Helmholtz Zentrum München, German Research Center for Environmental Health, Neuherberg, Germany
| | - Tim D. Spector
- Department of Twin Research & Genetic Epidemiology, King’s College London, UK
| | - Jerzy Adamski
- Institute of Experimental Genetics, Genome Analysis Center, Helmholtz Zentrum München, German Research Center for Environmental Health, Neuherberg, Germany
| | - Nicole Soranzo
- The Wellcome Trust Sanger Institute, Wellcome Trust Genome Campus, Hinxton UK
| | - Christian Gieger
- Institute of Genetic Epidemiology, Helmholtz Zentrum München, German Research Center for Environmental Health, Neuherberg, Germany
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Cano-Soldado P, Pastor-Anglada M. Transporters that translocate nucleosides and structural similar drugs: structural requirements for substrate recognition. Med Res Rev 2011; 32:428-57. [DOI: 10.1002/med.20221] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Affiliation(s)
- Pedro Cano-Soldado
- Departament de Bioquímica i Biologia Molecular; Institut de Biomedicina de la Universitat de Barcelona (IBUB); Universitat de Barcelona and CIBER EHD; Barcelona Spain
| | - Marçal Pastor-Anglada
- Departament de Bioquímica i Biologia Molecular; Institut de Biomedicina de la Universitat de Barcelona (IBUB); Universitat de Barcelona and CIBER EHD; Barcelona Spain
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Bossi E, Renna MD, Sangaletti R, D'Antoni F, Cherubino F, Kottra G, Peres A. Residues R282 and D341 act as electrostatic gates in the proton-dependent oligopeptide transporter PepT1. J Physiol 2010; 589:495-510. [PMID: 21115649 DOI: 10.1113/jphysiol.2010.200469] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
The oligopeptide transporter PepT1 is a protein found in the membrane of the cells of the intestinal walls, and represents the main route through which proteic nutrients are absorbed by the organism. Along the polypeptidic chain of this protein, two oppositely charged amino acids, an arginine in position 282 and an aspartate in position 341 of the sequence, have been hypothesised to form a barrier in the absorption pathway. In this paper we show that appropriate mutations of these amino acids change the properties of PepT1 in a way that confirms that these parts of the protein indeed act as an electrostatic gate in the transport process. The identification of the structural basis of the functional mechanism of this transporter is important because, in addition to its role in nutrient uptake, PepT1 represents a major pathway for the absorption of several therapeutic drugs.
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Affiliation(s)
- Elena Bossi
- Department of Biotechnology and Molecular Sciences, University of Insubria, Varese, Italy
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7
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Xu L, Li Y, Haworth IS, Davies DL. Functional role of the intracellular loop linking transmembrane domains 6 and 7 of the human dipeptide transporter hPEPT1. J Membr Biol 2010; 238:43-9. [PMID: 21104182 DOI: 10.1007/s00232-010-9317-7] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2010] [Accepted: 10/29/2010] [Indexed: 01/02/2023]
Abstract
The human intestinal di-/tripeptide transporter (hPEPT1) is a 12-transmembrane protein that facilitates transport of peptides from the intestine into the circulation. hPEPT1 is also an important target in oral delivery of drugs, but mechanistic and structural data for the protein are limited. In particular, there is little information on the function of the loops of the transporter. In this study, we show that mutation of several charged residues in the largest intracellular loop of hPEPT1 (loop 6-7, amino acids 224-278) significantly reduces hPEPT1 function. This loop has an asymmetric distribution of charged residues, with only positive charges in the N-terminal half and all five negative charges in the loop located in a small part of the C-terminal half. Point mutagenesis to alanine of three positive residues in the N-terminal half of loop 6-7 and four negative residues in the C-terminal half of the loop significantly reduced glycylsarcosine uptake. E267 was particularly sensitive to mutation, and kinetic analyses of E267A- and E267K-hPEPT1 gave V (max) values 10-fold lower than that for the wild-type protein. Secondary structure prediction suggested that loop 6-7 includes two amphipathic α-helices, with net positive and negative charges, respectively. We interpret the mutagenesis data in terms of interactions of the charged residues in loop 6-7 that may influence conformational changes of hPEPT1 during and after substrate transport.
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Affiliation(s)
- Liya Xu
- Alcohol and Brain Research Laboratory, Titus Family Department of Clinical Pharmacy and Pharmaceutical Economics and Policy, School of Pharmacy, University of Southern California, 1985 Zonal Avenue PSC 500, Los Angeles, CA 90033, USA
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8
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Pillai SM, Meredith D. SLC36A4 (hPAT4) is a high affinity amino acid transporter when expressed in Xenopus laevis oocytes. J Biol Chem 2010; 286:2455-60. [PMID: 21097500 DOI: 10.1074/jbc.m110.172403] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The SLC36 family of transporters consists of four genes, two of which, SLC36A1 and SLC36A2, have been demonstrated to code for human proton-coupled amino acid transporters or hPATs. Here we report the characterization of the fourth member of the family, SLC36A4 or hPAT4, which when expressed in Xenopus laevis oocytes also encodes a plasma membrane amino acid transporter, but one that is not proton-coupled and has a very high substrate affinity for the amino acids proline and tryptophan. hPAT4 in Xenopus oocytes mediated sodium-independent, electroneutral uptake of [(3)H]proline, with the highest rate of uptake when the uptake medium pH was 7.4 and an affinity of 3.13 μM. Tryptophan was also an excellently transported substrate with a similarly high affinity (1.72 μM). Other amino acids that inhibited [(3)H]proline were isoleucine (K(i) 0.23 mM), glutamine (0.43 mM), methionine (0.44 mM), and alanine (1.48 mM), and with lower affinity, glycine, threonine, and cysteine (K(i) >5 mM for all). Of the amino acids directly tested for transport, only proline, tryptophan, and alanine showed significant uptake, whereas glycine and cysteine did not. Of the non-proteogenic amino acids and drugs tested, only sarcosine produced inhibition (K(i) 1.09 mM), whereas γ-aminobutyric acid (GABA), β-alanine, L-Dopa, D-serine, and δ-aminolevulinic acid were without effect on [(3)H]proline uptake. This characterization of hPAT4 as a very high affinity/low capacity non-proton-coupled amino acid transporter raises questions about its physiological role, especially as the transport characteristics of hPAT4 are very similar to the Drosophila orthologue PATH, an amino acid "transceptor" that plays a role in nutrient sensing.
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9
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Foley DW, Rajamanickam J, Bailey PD, Meredith D. Bioavailability through PepT1: the role of computer modelling in intelligent drug design. Curr Comput Aided Drug Des 2010; 6:68-78. [PMID: 20370696 DOI: 10.2174/157340910790980133] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
In addition to being responsible for the majority of absorption of dietary nitrogen, the mammalian proton-coupled di- and tri-peptide transporter PepT1 is also recognised as a major route of drug delivery for several important classes of compound, including beta-lactam antibiotics and angiotensin-converting enzyme inhibitors. Thus there is considerable interest in the PepT1 protein and especially its substrate binding site. In the absence of a crystal structure, computer modelling has been used to try to understand the relationship between PepT1 3D structure and function. Two basic approaches have been taken: modelling the transporter protein, and modelling the substrate. For the former, computer modelling has evolved from early interpretations of the twelve transmembrane domain structure to more recent homology modelling based on recently crystallised bacterial members of the major facilitator superfamily (MFS). Substrate modelling has involved the proposal of a substrate binding template, to which all substrates must conform and from which the affinity of a substrate can be estimated relatively accurately, and identification of points of potential interaction of the substrate with the protein by developing a pharmacophore model of the substrates. Most recently, these two approaches have moved closer together, with the attempted docking of a substrate library onto a homology model of the human PepT1 protein. This article will review these two approaches in which computers have been applied to peptide transport and suggest how such computer modelling could affect drug design and delivery through PepT1.
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Affiliation(s)
- David W Foley
- Faculty of Natural Sciences, Keele University, Keele, Staffs ST5 5BG, UK
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10
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Pieri M, Christian HC, Wilkins RJ, Boyd CAR, Meredith D. The apical (hPepT1) and basolateral peptide transport systems of Caco-2 cells are regulated by AMP-activated protein kinase. Am J Physiol Gastrointest Liver Physiol 2010; 299:G136-43. [PMID: 20430871 PMCID: PMC2904111 DOI: 10.1152/ajpgi.00014.2010] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
The effect of 5-aminoimidazole-4-carboxamide-ribonucleoside (AICAR) activation of the AMP-activated protein kinase (AMPK) on the transport of the model radiolabeled dipeptide [(3)H]-D-Phe-L-Gln was investigated in the human epithelial colon cancer cell line Caco-2. Uptake and transepithelial fluxes of [(3)H]-D-Phe-L-Gln were carried out in differentiated Caco-2 cell monolayers, and hPepT1 and glucose transporter 2 (GLUT2) protein levels were quantified by immunogold electron microscopy. AICAR treatment of Caco-2 cells significantly inhibited apical [(3)H]-D-Phe-L-Gln uptake, matched by a decrease in brush-border membrane hPepT1 protein but with a concomitant increase in the facilitated glucose transporter GLUT2. A restructuring of the apical brush-border membrane was seen by electron microscopy. The hPepT1-mediated transepithelial (A-to-B) peptide flux across the Caco-2 monolayers showed no significant alteration in AICAR-treated cells. The electrical resistance in the AICAR-treated monolayers was significantly higher compared with control cells. Inhibition of the sodium/hydrogen exchanger 3 (NHE3) had an additive effect to AICAR, suggesting that the AMPK effect is not via NHE3. Fluorescence measurement of intracellular pH showed no reduction in the proton gradient driving PepT1-mediated apical uptake. The reduction in apical hPepT1 protein and dipeptide uptake after AICAR treatment in Caco-2 cells demonstrates a regulatory effect of AMPK on hPepT1, along with an influence on both the microvilli and tight junction structures. The absence of an associated reduction in transepithelial peptide movement implies an additional stimulatory effect of AICAR on the basolateral peptide transport system in these cells. These results provide a link between the hPepT1 transporter and the metabolic state of this model enterocyte.
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Affiliation(s)
- Myrtani Pieri
- 1School of Life Sciences, Oxford Brookes University, Headington, Oxford; ,2Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom
| | - Helen C. Christian
- 2Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom
| | - Robert J. Wilkins
- 2Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom
| | - C. A. R. Boyd
- 2Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom
| | - David Meredith
- 1School of Life Sciences, Oxford Brookes University, Headington, Oxford; ,2Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom
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Brandsch M, Knütter I, Bosse-Doenecke E. Pharmaceutical and pharmacological importance of peptide transporters. J Pharm Pharmacol 2010; 60:543-85. [DOI: 10.1211/jpp.60.5.0002] [Citation(s) in RCA: 179] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
AbstractPeptide transport is currently a prominent topic in membrane research. The transport proteins involved are under intense investigation because of their physiological importance in protein absorption and also because peptide transporters are possible vehicles for drug delivery. Moreover, in many tissues peptide carriers transduce peptidic signals across membranes that are relevant in information processing. The focus of this review is on the pharmaceutical relevance of the human peptide transporters PEPT1 and PEPT2. In addition to their physiological substrates, both carriers transport many β-lactam antibiotics, valaciclovir and other drugs and prodrugs because of their sterical resemblance to di- and tripeptides. The primary structure, tissue distribution and substrate specificity of PEPT1 and PEPT2 have been well characterized. However, there is a dearth of knowledge on the substrate binding sites and the three-dimensional structure of these proteins. Until this pivotal information becomes available by X-ray crystallography, the development of new drug substrates relies on classical transport studies combined with molecular modelling. In more than thirty years of research, data on the interaction of well over 700 di- and tripeptides, amino acid and peptide derivatives, drugs and prodrugs with peptide transporters have been gathered. The aim of this review is to put the reports on peptide transporter-mediated drug uptake into perspective. We also review the current knowledge on pharmacogenomics and clinical relevance of human peptide transporters. Finally, the reader's attention is drawn to other known or proposed human peptide-transporting proteins.
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Affiliation(s)
- Matthias Brandsch
- Membrane Transport Group, Biozentrum of the Martin-Luther-University Halle-Wittenberg, D-06120 Halle, Germany
| | - Ilka Knütter
- Membrane Transport Group, Biozentrum of the Martin-Luther-University Halle-Wittenberg, D-06120 Halle, Germany
| | - Eva Bosse-Doenecke
- Institute of Biochemistry/Biotechnology, Faculty of Science I, Martin-Luther-University Halle-Wittenberg, D-06120 Halle, Germany
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12
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Mutagenesis and cysteine scanning of transmembrane domain 10 of the human dipeptide transporter. Pharm Res 2009; 26:2358-66. [PMID: 19685173 DOI: 10.1007/s11095-009-9952-9] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2009] [Accepted: 07/30/2009] [Indexed: 02/06/2023]
Abstract
PURPOSE The human dipeptide transporter (hPEPT1) facilitates transport of dipeptides and drugs from the intestine into the circulation. The role of transmembrane domain 10 (TMD10) of hPEPT1 in substrate translocation was investigated using cysteine-scanning mutagenesis with 2-Trimethylammonioethyl methanethiosulfonate (MTSET). METHODS Each amino acid in TMD10 was mutated individually to cysteine, and transport of [(3)H]Gly-Sar was evaluated with and without MTSET following transfection of each mutant in HEK293 cells. Similar localization and expression levels of wild type (WT) hPEPT1 and all mutants were confirmed by immunostaining and biotinylation followed by western blot analysis. RESULTS E595C- and G594C-hPEPT1 showed negligible Gly-Sar uptake. E595D-hPEPT1 showed similar uptake to WT-hPEPT1, but E595K- and E595R-hPEPT1 did not transport Gly-Sar. Double mutations E595K/R282E and E595R/R282E did not restore uptake. G594A-hPEPT1 showed similar uptake to WT-hPEPT1, but G594V-hPEPT1 eliminated uptake. Y588C-hPEPT1 showed uptake of 20% that of WT-hPEPT1. MTSET modification supported a model of TMD10 with an amphipathic helix from I585 to V600 and increased solvent accessibility from T601 to F605. CONCLUSIONS Our results suggest that G594 and E595 in TMD10 of hPEPT1 have key roles in substrate transport and that Y588 may have an important secondary mechanistic role.
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13
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The transmembrane tyrosines Y56, Y91 and Y167 play important roles in determining the affinity and transport rate of the rabbit proton-coupled peptide transporter PepT1. Int J Biochem Cell Biol 2009; 41:2204-13. [PMID: 19389486 PMCID: PMC3510438 DOI: 10.1016/j.biocel.2009.04.014] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2009] [Revised: 04/09/2009] [Accepted: 04/15/2009] [Indexed: 11/24/2022]
Abstract
The mammalian proton-coupled peptide transporter PepT1 is widely accepted as the major route of uptake for dietary nitrogen, as well as being responsible for the oral absorption of a number of classes of drugs, including β-lactam antibiotics and angiotensin-converting enzyme (ACE) inhibitors. Using site-directed mutagenesis and zero-trans transport assays, we investigated the role of conserved tyrosines in the transmembrane domains (TMDs) of rabbit PepT1 as predicted by hydropathy plots. All the individual TMD tyrosines were substituted with phenylalanine and shown to retain the ability to traffic to the plasma membrane of Xenopus laevis oocytes. These single substitutions of TMD tyrosines by phenylalanine residues did not affect the proton dependence of peptide uptake, with all retaining wild-type PepT1-like pH dependence. Individual mutations of four of the nine TMD residue tyrosines (Y64, Y287, Y345 and Y587) were without measurable effect on PepT1 function, whereas the other five (Y12, Y56, Y91, Y167 and Y345) were shown to result in altered transport function compared to the wild-type PepT1. Intriguingly, the affinity of Y56F-PepT1 was found to be dramatically increased (approximately 100-fold) in comparison to that of the wild-type rabbit PepT1. Y91 mutations also affected the substrate affinity of the transporter, which increased in line with the hydrophilicity of the substituted amino acid (F > Y > Q > R). Y167 was demonstrated to play a pivotal role in rabbit PepT1 function since Y167F, Y167R and Y167Q demonstrated very little transport function. These results are discussed with regard to a proposed mechanism for PepT1 substrate binding.
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14
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Meredith D. Review. The mammalian proton-coupled peptide cotransporter PepT1: sitting on the transporter-channel fence? Philos Trans R Soc Lond B Biol Sci 2009; 364:203-7. [PMID: 18957377 PMCID: PMC2674094 DOI: 10.1098/rstb.2008.0139] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The proton-coupled di- and tripeptide transporter PepT1 (SLC15a1) is the major route by which dietary nitrogen is taken up from the small intestine, as well as being the route of entry for important therapeutic (pro)drugs such as the beta-lactam antibiotics, angiotensin-converting enzyme inhibitors and antiviral and anti-cancer agents. PepT1 is a member of the major facilitator superfamily of 12 transmembrane domain transporter proteins. Expression studies in Xenopus laevis on rabbit PepT1 that had undergone site-directed mutagenesis of a conserved arginine residue (arginine282 in transmembrane domain 7) to a glutamate revealed that this residue played a role in the coupling of proton and peptide transport and prevented the movement of non-coupled ions during the transporter cycle. Mutations of arginine282 to other non-positive residues did not uncouple proton-peptide cotransport, but did allow additional ion movements when substrate was added. By contrast, mutations to positive residues appeared to function the same as wild-type. These findings are discussed in relation to the functional role that arginine282 may play in the way PepT1 operates, together with structural information from the homology model of PepT1 based on the Escherichia coli lactose permease crystal structure.
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Affiliation(s)
- David Meredith
- School of Life Sciences, Oxford Brookes University, Gipsy Lane, Headington, Oxford, UK.
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15
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Chloroquine resistance-conferring mutations in pfcrt give rise to a chloroquine-associated H+ leak from the malaria parasite's digestive vacuole. Antimicrob Agents Chemother 2008; 52:4374-80. [PMID: 18852275 DOI: 10.1128/aac.00666-08] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
Chloroquine resistance in the malaria parasite Plasmodium falciparum is conferred by mutations in the P. falciparum chloroquine resistance transporter (PfCRT). PfCRT localizes to the membrane of the parasite's internal digestive vacuole, an acidic organelle in which chloroquine accumulates to high concentrations and exerts its toxic effect. Mutations in PfCRT are thought to reduce chloroquine accumulation in this organelle. How they do so is the subject of ongoing debate. Recently we have shown that in the presence of chloroquine there is an increased leak of H+ from the digestive vacuole in chloroquine-resistant but not chloroquine-sensitive parasites. Here, using transfectant parasite strains of a single genetic background and differing only in their pfcrt allele, we show that chloroquine resistance-conferring PfCRT mutations are responsible for this chloroquine-associated H+ leak. This is consistent with the hypothesis that the chloroquine resistance-conferring forms of PfCRT mediate the efflux of chloroquine, in association with H+, from the malaria parasite's digestive vacuole.
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16
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Lehane AM, Hayward R, Saliba KJ, Kirk K. A verapamil-sensitive chloroquine-associated H+ leak from the digestive vacuole in chloroquine-resistant malaria parasites. J Cell Sci 2008; 121:1624-32. [PMID: 18445688 DOI: 10.1242/jcs.016758] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Chloroquine resistance in the malaria parasite Plasmodium falciparum has made malaria increasingly difficult to control. Chloroquine-resistant parasites accumulate less chloroquine than their chloroquine-sensitive counterparts; however, the mechanism underlying this remains unclear. The primary site of accumulation and antimalarial action of chloroquine is the internal acidic digestive vacuole of the parasite, the acidity of which is maintained by inwardly-directed H+ pumps, working against the (outward) leak of H+. In this study we have investigated the leak of H+ from the digestive vacuole of the parasite by monitoring the alkalinisation of the vacuole following inhibition of the H+-pumping V-type ATPase by concanamycin A. The rates of alkalinisation observed in three chloroquine-resistant strains were two- to fourfold higher than those measured in three chloroquine-sensitive strains. On addition of chloroquine there was a dramatic increase in the rate of alkalinisation in the chloroquine-resistant strains, whereas chloroquine caused the rate of alkalinisation to decrease in the chloroquine-sensitive strains. The chloroquine-associated increase in the rate of alkalinisation seen in chloroquine-resistant parasites was inhibited by the chloroquine-resistance reversal agent verapamil. The data are consistent with the hypothesis that in chloroquine-resistant parasites chloroquine effluxes from the digestive vacuole, in association with H+, via a verapamil-sensitive pathway.
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Affiliation(s)
- Adele M Lehane
- School of Biochemistry and Molecular Biology, The Australian National University, Canberra ACT 0200, Australia
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17
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Rønnestad I, Gavaia PJ, Viegas CSB, Verri T, Romano A, Nilsen TO, Jordal AEO, Kamisaka Y, Cancela ML. Oligopeptide transporter PepT1 in Atlantic cod (Gadus morhua L.): cloning, tissue expression and comparative aspects. ACTA ACUST UNITED AC 2008; 210:3883-96. [PMID: 17981856 DOI: 10.1242/jeb.007898] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
A novel full-length cDNA that encodes for the Atlantic cod (Gadus morhua L.) PepT1-type oligopeptide transporter has been cloned. This cDNA (named codPepT1) was 2,838 bp long, with an open reading frame of 2,190 bp encoding a putative protein of 729 amino acids. Comparison of the predicted Atlantic cod PepT1 protein with zebrafish, bird and mammalian orthologs allowed detection of many structural features that are highly conserved among all the vertebrate proteins analysed, including (1) a larger than expected area of hydrophobic amino acids in close proximity to the N terminus; (2) a single highly conserved cAMP/cGMP-dependent protein kinase phosphorylation motif; (3) a large N-glycosylation-rich region within the large extracellular loop; and (4) a conserved and previously undescribed stretch of 8-12 amino acid residues within the large extracellular loop. Expression analysis at the mRNA level indicated that Atlantic cod PepT1 is mainly expressed at intestinal level, but that it is also present in kidney and spleen. Analysis of its regional distribution along the intestinal tract of the fish revealed that PepT1 is ubiquitously expressed in all segments beyond the stomach, including the pyloric caeca, and through the whole midgut. Only in the last segment, which included the hindgut, was there a lower expression. Atlantic cod PepT1, the second teleost fish PepT1-type transporter documented to date, will contribute to the elucidation of the evolutionary and functional relationships among vertebrate peptide transporters. Moreover, it can represent a useful tool for the study of gut functional regionalization, as well as a marker for the analysis of temporal and spatial expression during ontogeny.
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Affiliation(s)
- Ivar Rønnestad
- University of Bergen, Department of Biology, N-5020 Bergen, Norway.
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18
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Pieri M, Hall D, Price R, Bailey P, Meredith D. Site-directed mutagenesis of Arginine282 suggests how protons and peptides are co-transported by rabbit PepT1. Int J Biochem Cell Biol 2007; 40:721-30. [PMID: 18037334 PMCID: PMC2267855 DOI: 10.1016/j.biocel.2007.10.010] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2007] [Revised: 10/09/2007] [Accepted: 10/09/2007] [Indexed: 11/02/2022]
Abstract
The mammalian proton-coupled peptide transporter PepT1 is the major route of uptake for dietary nitrogen, as well as the oral absorption of a number of drugs, including beta-lactam antibiotics and angiotensin-converting enzyme inhibitors. Here we have used site-directed mutagenesis to investigate further the role of conserved charged residues in transmembrane domains. Mutation of rabbit PepT1 arginine282 (R282, transmembrane domain 7) to a positive (R282K) or physiologically titratable residue (R282H), resulted in a transporter with wild-type characteristics when expressed in Xenopus laevis oocytes. Neutral (R282A, R282Q) or negatively charged (R282D, R282E) substitutions gave a transporter that was not stimulated by external acidification (reducing pH(out) from 7.4 to 5.5) but transported at the same rate as the wild-type maximal rate (pH(out) 5.5); however, only the R282E mutation was unable to concentrate substrate above the extracellular level. All of the R282 mutants showed trans-stimulation of efflux comparable to the wild-type, except R282E-PepT1 which was faster. A conserved negatively charged residue, aspartate341 (D341) in transmembrane domain 8 was implicated in forming a charge pair with R282, as R282E/D341R- and R282D/D341R-PepT1 had wild-type transporter characteristics. Despite their differences in ability to accumulate substrate, both R282E- and R282D-PepT1 showed an increased charge:peptide stoichiometry over the wild-type 1:1 ratio for the neutral dipeptide Gly-l-Gln, measured using two-electrode voltage clamp. This extra charge movement was linked to substrate transport, as 4-aminobenzoic acid, which binds but is not translocated, did not induce membrane potential depolarisation in R282E-expressing oocytes. A model is proposed for the substrate binding/translocation process in PepT1.
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Affiliation(s)
- Myrtani Pieri
- Department of Physiology, Anatomy & Genetics, University of Oxford, Oxford OX1 3QX, UK
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19
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Hsiao YY, Pan YJ, Hsu SH, Huang YT, Liu TH, Lee CH, Lee CH, Liu PF, Chang WC, Wang YK, Chien LF, Pan RL. Functional roles of arginine residues in mung bean vacuolar H+-pyrophosphatase. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2007; 1767:965-73. [PMID: 17543272 DOI: 10.1016/j.bbabio.2007.04.007] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/06/2007] [Revised: 04/26/2007] [Accepted: 04/27/2007] [Indexed: 10/23/2022]
Abstract
Plant vacuolar H+-translocating inorganic pyrophosphatase (V-PPase EC 3.6.1.1) utilizes inorganic pyrophosphate (PPi) as an energy source to generate a H+ gradient potential for the secondary transport of ions and metabolites across the vacuole membrane. In this study, functional roles of arginine residues in mung bean V-PPase were determined by site-directed mutagenesis. Alignment of amino-acid sequence of K+-dependent V-PPases from several organisms showed that 11 of all 15 arginine residues were highly conserved. Arginine residues were individually substituted by alanine residues to produce R-->A-substituted V-PPases, which were then heterologously expressed in yeast. The characteristics of mutant variants were subsequently scrutinized. As a result, most R-->A-substituted V-PPases exhibited similar enzymatic activities to the wild-type with exception that R242A, R523A, and R609A mutants markedly lost their abilities of PPi hydrolysis and associated H+-translocation. Moreover, mutation on these three arginines altered the optimal pH and significantly reduced K+-stimulation for enzymatic activities, implying a conformational change or a modification in enzymatic reaction upon substitution. In particular, R242A performed striking resistance to specific arginine-modifiers, 2,3-butanedione and phenylglyoxal, revealing that Arg242 is most likely the primary target residue for these two reagents. The mutation at Arg242 also removed F- inhibition that is presumably derived from the interfering in the formation of substrate complex Mg2+-PPi. Our results suggest accordingly that active pocket of V-PPase probably contains the essential Arg242 which is embedded in a more hydrophobic environment.
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Affiliation(s)
- Yi-Yuong Hsiao
- Department of Life Sciences and Institute of Bioinformatics and Structural Biology, College of Life Sciences, National Tsing Hua University, Hsin Chu 30043, Taiwan
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20
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Sanchez CP, Rohrbach P, McLean JE, Fidock DA, Stein WD, Lanzer M. Differences in trans-stimulated chloroquine efflux kinetics are linked to PfCRT in Plasmodium falciparum. Mol Microbiol 2007; 64:407-20. [PMID: 17493125 PMCID: PMC2944662 DOI: 10.1111/j.1365-2958.2007.05664.x] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
The mechanism underpinning chloroquine drug resistance in the human malarial parasite Plasmodium falciparum has remained controversial. Currently discussed models include a carrier or a channel for chloroquine, the former actively expelling the drug, the latter facilitating its passive diffusion, out of the parasite's food vacuole, where chloroquine accumulates and inhibits haem detoxification. Here we have challenged both models using an established trans-stimulation efflux protocol. While carriers may demonstrate trans-stimulation, channels do not. Our data reveal that extracellular chloroquine stimulates chloroquine efflux in the presence and absence of metabolic energy in both chloroquine-sensitive and -resistant parasites, resulting in a hyperbolic increase in the apparent initial efflux rates as the concentration of external chloroquine increases. In the absence of metabolic energy, the apparent initial efflux rates were comparable in both parasites. Significant differences were only observed in the presence of metabolic energy, where consistently higher apparent initial efflux rates were found in chloroquine-resistant parasites. As trans-stimulation is characteristic of a carrier, and not a channel, we interpret our data in favour of a carrier for chloroquine being present in both chloroquine-sensitive and -resistant parasites, however, with different transport modalities.
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Affiliation(s)
- Cecilia P. Sanchez
- Hygiene Institut, Abteilung Parasitologie, Universitätsklinikum Heidelberg, Im Neuenheimer Feld 324, 69120 Heidelberg, Germany
| | - Petra Rohrbach
- Hygiene Institut, Abteilung Parasitologie, Universitätsklinikum Heidelberg, Im Neuenheimer Feld 324, 69120 Heidelberg, Germany
| | - Jeremy E. McLean
- Hygiene Institut, Abteilung Parasitologie, Universitätsklinikum Heidelberg, Im Neuenheimer Feld 324, 69120 Heidelberg, Germany
| | - David A. Fidock
- Department of Microbiology and Immunology, Albert Einstein College of Medicine, Bronx, NY 10461, USA
| | - Wilfred D. Stein
- Biological Chemistry, Silberman Institute of Life Sciences, Hebrew University of Jerusalem, Givat Ram, Jerusalem 91904, Israel
| | - Michael Lanzer
- Hygiene Institut, Abteilung Parasitologie, Universitätsklinikum Heidelberg, Im Neuenheimer Feld 324, 69120 Heidelberg, Germany
- For correspondence. ; Tel. (+49) 6221 567845; Fax (+49) 6221 564643
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21
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Sanchez CP, Stein WD, Lanzer M. Is PfCRT a channel or a carrier? Two competing models explaining chloroquine resistance in Plasmodium falciparum. Trends Parasitol 2007; 23:332-9. [PMID: 17493873 DOI: 10.1016/j.pt.2007.04.013] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2006] [Revised: 03/26/2007] [Accepted: 04/26/2007] [Indexed: 11/30/2022]
Abstract
Chloroquine (CQ), an antimalarial drug with a long history, now frequently fails in the field owing to the rapid spread of resistant Plasmodium falciparum strains. CQ resistance is linked to a K76T mutation in PfCRT, a membrane-located food vacuolar protein and member of the drug-metabolite transporter superfamily, but there is as yet no agreed mechanism of how mutated PfCRT brings about CQ resistance. Current models suggest that mutated PfCRT acts either as a channel or a transporter of CQ, enabling CQ to leave the digestive food vacuole of the parasite, in which the CQ accumulates. Here, we review the pros and cons of the carrier and transporter models in light of recent developments in the field.
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Affiliation(s)
- Cecilia P Sanchez
- Hygiene Institut, Abteilung Parasitologie, Universitätsklinikum Heidelberg, Im Neuenheimer Feld 324, 69120 Heidelberg, Germany
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22
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Abstract
The proton-coupled uptake of di- and tri-peptides is the major route of dietary nitrogen absorption in the intestine and of reabsorption of filtered protein in the kidney. In addition, the transporters involved, PepT1 (SLC15a1) and PepT2 (SLC15a2), are responsible for the uptake and tissue distribution of a wide range of pharmaceutically important compounds, including beta-lactam antibiotics, angiotensin-converting enzyme inhibitors, anti-cancer and anti-viral drugs. PepT1 and PepT2 are large proteins, with over 700 amino acids, and to date there are no reports of their crystal structures, nor of those of related proteins from lower organisms. Therefore there is virtually no information about the protein 3-D structure, although computer-based approaches have been used to both model the transmembrane domain (TM) layout and to produce a substrate binding template. These models will be discussed, and a new one proposed from homology modeling rabbit PepT1 to the recently crystallized bacterial transporters LacY and GlpT. Understanding the mechanism by which PepT1 and PepT2 bind and transport their substrates is of great interest to researchers, both in academia and in the pharmaceutical industries.
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Affiliation(s)
- D Meredith
- Department of Physiology, Anatomy & Genetics, Le Gros Clark Building, University of Oxford, South Parks Road, Oxford, OX1 3QX, UK.
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23
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Kulkarni AA, Davies DL, Links JS, Patel LN, Lee VHL, Haworth IS. A charge pair interaction between Arg282 in transmembrane segment 7 and Asp341 in transmembrane segment 8 of hPepT1. Pharm Res 2006; 24:66-72. [PMID: 17009102 DOI: 10.1007/s11095-006-9119-x] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2006] [Accepted: 07/12/2006] [Indexed: 11/30/2022]
Abstract
PURPOSE To determine whether R282 in transmembrane segment 7 (TMS7) of hPepT1 forms a salt bridge with D341 in TMS8. METHODS Mutated hPepT1 transporters containing point mutations at R282 and/or D341 were transiently transfected into HEK293 cells. Their steady state expression and functional activity were measured using immunoprecipitation and 3H-gly-sar uptake, respectively. Gly-sar uptake by cysteine mutants (R282C and D341C) was also measured in the presence and absence of cysteine-modifying MTS reagents. RESULTS The reverse-charge mutants R282D-hPepT1 and D341R-hPepT1 showed significantly reduced gly-sar uptake, but the double mutant (R282D/D341R-hPepT1) has functionality comparable to that of wild-type hPepT1. Gly-sar uptake by R282C-hPepT1 is reduced, but pre-incubation with 1 mM MTSET, a positively charged cysteine-modifying reagent, restored function to wild-type levels. Similarly, pre-incubation of D341C-hPepT1 with 10 mM MTSES, a negatively charged cysteine-modifying reagent, increased gly-sar uptake compared to unmodified D341C-hPepT1. In contrast, MTSET modification of D341C-hPepT1 (giving a positive charge at position 341) resulted in significant reduction in gly-sar uptake, compared to D341C-hPepT1. CONCLUSION Our results are consistent with a salt bridge between R282 and D341 in hPepT1, and we use these and other data to propose a role for the R282-D341 charge pair in the hPepT1 translocation mechanism.
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Affiliation(s)
- Ashutosh A Kulkarni
- Department of Pharmaceutical Sciences, University of Southern California, 1985 Zonal Avenue, Los Angeles, California 90089-9121, USA
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24
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Narváez AJ, Voevodskaya N, Thelander L, Gräslund A. The Involvement of Arg265 of Mouse Ribonucleotide Reductase R2 Protein in Proton Transfer and Catalysis. J Biol Chem 2006; 281:26022-8. [PMID: 16829694 DOI: 10.1074/jbc.m604598200] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Ribonucleotide reductase class I enzymes consist of two non-identical subunits, R1 and R2, the latter containing a diiron carboxylate center and a stable tyrosyl radical (Tyr*), both essential for catalysis. Catalysis is known to involve highly conserved amino acid residues covering a range of approximately 35 A and a concerted mechanism involving long range electron transfer, probably coupled to proton transfer. A number of residues involved in electron transfer in both the R1 and R2 proteins have been identified, but no direct model has been presented regarding the proton transfer side of the process. Arg265 is conserved in all known sequences of class Ia R2. In this study we have used site-directed mutagenesis to gain insight into the role of this residue, which lies close to the catalytically essential Asp266 and Trp103. Mutants to Arg265 included replacement by Ala, Glu, Gln, and Tyr. All mutants of Arg265 were found to have no or low catalytic activity with the exception of Arg265 to Glu, which shows approximately 40% of the activity of native R2. We also found that the Arg mutants were capable of stable tyrosyl radical generation, with similar kinetics of radical formation and R1 binding as native R2. Our results, supported by molecular modeling, strongly suggest that Arg265 is involved in the proton-coupled electron transfer pathway and may act as a proton mediator during catalysis.
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Affiliation(s)
- Ana J Narváez
- Department of Biochemistry and Biophysics, Stockholm University, SE-10691 Stockholm, Sweden
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25
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Panitsas KE, Boyd CAR, Meredith D. Evidence that the rabbit proton-peptide co-transporter PepT1 is a multimer when expressed in Xenopus laevis oocytes. Pflugers Arch 2006; 452:53-63. [PMID: 16465547 DOI: 10.1007/s00424-005-0002-0] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2005] [Revised: 08/03/2005] [Accepted: 09/13/2005] [Indexed: 10/25/2022]
Abstract
To test whether the rabbit proton-coupled peptide transporter PepT1 is a multimer, we have employed a combination of transport assays, luminometry and site-directed mutagenesis. A functional epitope-tagged PepT1 construct (PepT1-FLAG) was co-expressed in Xenopus laevis oocytes with a non-functional but normally trafficked mutant form of the same transporter (W294F-PepT1). The amount of PepT1-FLAG cRNA injected into the oocytes was kept constant, while the amount of W294F-PepT1 cRNA was increased over the mole fraction range of 0 to 1. The uptake of [(3)H]-D: -Phe-L: -Gln into the oocytes was measured at pH(out) 5.5, and the surface expression of PepT1-FLAG was quantified by luminometry. As the mole fraction of injected W294F-PepT1 increased, the uptake of D: -Phe-L: -Gln decreased. This occurred despite the surface expression of PepT1-FLAG remaining constant, and so we can conclude that PepT1 must be a multimer. Assuming that PepT1 acts as a homomultimer, the best fit for the modelling suggests that PepT1 could be a tetramer, with a minimum requirement of two functional subunits in each protein complex. Western blotting also showed the presence of higher-order complexes of PepT1-FLAG in oocyte membranes. It should be noted that we cannot formally exclude the possibility that PepT1 interacts with unidentified Xenopus protein(s). The finding that PepT1 is a multimer has important implications for the molecular modelling of this protein.
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Affiliation(s)
- Konstantinos-E Panitsas
- Department of Human Anatomy and Genetics, University of Oxford, South Parks Road, OX1 3QX, Oxford, UK
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26
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Hauser M, Kauffman S, Naider F, Becker JM. Substrate preference is altered by mutations in the fifth transmembrane domain of Ptr2p, the di/tri-peptide transporter of Saccharomyces cerevisiae. Mol Membr Biol 2005; 22:215-27. [PMID: 16096264 DOI: 10.1080/09687860500093248] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Abstract
The integral membrane protein Ptr2p transports di/tri-peptides into the yeast Saccharomyces cerevisiae. The sequence FYXXINXG (FYING motif) in the 5th transmembrane domain (TM5) is invariably conserved among the members of the PTR (Peptide TRansport) family ranging from yeast to human. To test the role of TM5 in Ptr2p function, Ala-scanning mutagenesis of the 22 residues comprising TM5 was completed. All mutated transporters, with the exception of the Y248A mutant, were expressed as determined by immunoblots. In peptide-dependent growth assays, ten mutants of the non-FYING residues grew as well as wild-type Ptr2p on all twelve different peptides tested. All of the FYING motif mutants, except the non-expressed Y248A, plus seven other mutants in TM5 exhibited differential growth on peptides including Leu-Leu and Met-Met-Met indicating that these mutations conferred substrate preference. In assays measuring direct uptake of the radioactive peptides (3)H-Leu-Leu or (14)C-Met-Met-Met, the F, I and G mutants of the FYING motif did not demonstrate accumulation of these peptides over a ten minute interval. The mutation N252A of the FYING motif, along with L240A, M250A, and L258A, exhibited differential substrate preference for Met-Met-Met over Leu-Leu. Other mutations (T239A, Q241A, N242A, M245A, and A260) resulted in preference for Leu-Leu over Met-Met-Met. These data demonstrate that TM5, in particular its conserved FYING motif, is involved in substrate preference of Ptr2p.
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Affiliation(s)
- Melinda Hauser
- Department of Microbiology, Walters Life Sciences, University of Tennessee, Knoxville, TN 37996, USA
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27
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Bruce LJ, Robinson HC, Guizouarn H, Borgese F, Harrison P, King MJ, Goede JS, Coles SE, Gore DM, Lutz HU, Ficarella R, Layton DM, Iolascon A, Ellory JC, Stewart GW. Monovalent cation leaks in human red cells caused by single amino-acid substitutions in the transport domain of the band 3 chloride-bicarbonate exchanger, AE1. Nat Genet 2005; 37:1258-63. [PMID: 16227998 DOI: 10.1038/ng1656] [Citation(s) in RCA: 123] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2005] [Accepted: 08/17/2005] [Indexed: 11/09/2022]
Abstract
We identified 11 human pedigrees with dominantly inherited hemolytic anemias in both the hereditary stomatocytosis and spherocytosis classes. Affected individuals in these families had an increase in membrane permeability to Na and K that is particularly marked at 0 degrees C. We found that disease in these pedigrees was associated with a series of single amino-acid substitutions in the intramembrane domain of the erythrocyte band 3 anion exchanger, AE1. Anion movements were reduced in the abnormal red cells. The 'leak' cation fluxes were inhibited by SITS, dipyridamole and NS1652, chemically diverse inhibitors of band 3. Expression of the mutated genes in Xenopus laevis oocytes induced abnormal Na and K fluxes in the oocytes, and the induced Cl transport was low. These data are consistent with the suggestion that the substitutions convert the protein from an anion exchanger into an unregulated cation channel.
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Affiliation(s)
- Lesley J Bruce
- Bristol Institute for Transfusion Sciences, National Blood Service, Southmead, Bristol BS10 5ND, UK
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Våbenø J, Nielsen CU, Steffansen B, Lejon T, Sylte I, Jørgensen FS, Luthman K. Conformational restrictions in ligand binding to the human intestinal di-/tripeptide transporter: implications for design of hPEPT1 targeted prodrugs. Bioorg Med Chem 2005; 13:1977-88. [PMID: 15727852 DOI: 10.1016/j.bmc.2005.01.019] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2004] [Revised: 01/05/2005] [Accepted: 01/12/2005] [Indexed: 11/16/2022]
Abstract
The aim of the present study was to develop a computational method aiding the design of dipeptidomimetic pro-moieties targeting the human intestinal di-/tripeptide transporter hPEPT1. First, the conformation in which substrates bind to hPEPT1 (the bioactive conformation) was identified by conformational analysis and 2D dihedral driving analysis of 15 hPEPT1 substrates, which suggested that psi(1) approximately 165 degrees , omega(1) approximately 180 degrees , and phi(2) approximately 280 degrees were descriptive of the bioactive conformation. Subsequently, the conformational energy required to change the peptide backbone conformation (DeltaE(bbone)) from the global energy minimum conformation to the identified bioactive conformation was calculated for 20 hPEPT1 targeted model prodrugs with known K(i) values. Quantitatively, an inverse linear relationship (r(2)=0.81, q(2)=0.80) was obtained between DeltaE(bbone) and log1/K(i), showing that DeltaE(bbone) contributes significantly to the experimentally observed affinity for hPEPT1 ligands. Qualitatively, the results revealed that compounds classified as high affinity ligands (K(i)<0.5 mM) all have a calculated DeltaE(bbone)<1 kcal/mol, whereas medium and low-affinity compounds (0.5 mM<K(i)<15 mM) have DeltaE(bbone) values in the range 1-3 kcal/mol. The findings also shed new light on the basis for the experimentally observed stereoselectivity of hPEPT1.
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Affiliation(s)
- Jon Våbenø
- Department of Medicinal Chemistry, Institute of Pharmacy, University of Tromsø, N-9037 Tromsø, Norway
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Nielsen CU, Våbenø J, Andersen R, Brodin B, Steffansen B. Recent advances in therapeutic applications of human peptide transporters. Expert Opin Ther Pat 2005. [DOI: 10.1517/13543776.15.2.153] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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