1
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Zhou Y, Liao L, Wang C, Li J, Chi P, Xiao Q, Liu Q, Guo L, Sun L, Deng D. Cryo-EM structure of the human concentrative nucleoside transporter CNT3. PLoS Biol 2020; 18:e3000790. [PMID: 32776918 PMCID: PMC7440666 DOI: 10.1371/journal.pbio.3000790] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2020] [Revised: 08/20/2020] [Accepted: 07/20/2020] [Indexed: 01/17/2023] Open
Abstract
Concentrative nucleoside transporters (CNTs), members of the solute carrier (SLC) 28 transporter family, facilitate the salvage of nucleosides and therapeutic nucleoside derivatives across the plasma membrane. Despite decades of investigation, the structures of human CNTs remain unknown. We determined the cryogenic electron microscopy (cryo-EM) structure of human CNT (hCNT) 3 at an overall resolution of 3.6 Å. As with its bacterial homologs, hCNT3 presents a trimeric architecture with additional N-terminal transmembrane helices to stabilize the conserved central domains. The conserved binding sites for the substrate and sodium ions unravel the selective nucleoside transport and distinct coupling mechanism. Structural comparison of hCNT3 with bacterial homologs indicates that hCNT3 is stabilized in an inward-facing conformation. This study provides the molecular determinants for the transport mechanism of hCNTs and potentially facilitates the design of nucleoside drugs.
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Affiliation(s)
- Yanxia Zhou
- Division of Obstetrics, Key Laboratory of Birth Defects and Related Disease of Women and Children of MOE, State Key Laboratory of Biotherapy, West China Second Hospital, Sichuan University, Chengdu, China
| | - Lianghuan Liao
- Hefei National Laboratory for Physical Sciences at Microscale, CAS Centre for Excellence in Molecular Cell Science, School of Life Sciences, University of Science and Technology of China, Hefei, China
| | - Chen Wang
- Division of Obstetrics, Key Laboratory of Birth Defects and Related Disease of Women and Children of MOE, State Key Laboratory of Biotherapy, West China Second Hospital, Sichuan University, Chengdu, China
| | - Jialu Li
- Division of Obstetrics, Key Laboratory of Birth Defects and Related Disease of Women and Children of MOE, State Key Laboratory of Biotherapy, West China Second Hospital, Sichuan University, Chengdu, China
| | - Pengliang Chi
- Division of Obstetrics, Key Laboratory of Birth Defects and Related Disease of Women and Children of MOE, State Key Laboratory of Biotherapy, West China Second Hospital, Sichuan University, Chengdu, China
| | - Qingjie Xiao
- Division of Obstetrics, Key Laboratory of Birth Defects and Related Disease of Women and Children of MOE, State Key Laboratory of Biotherapy, West China Second Hospital, Sichuan University, Chengdu, China
| | - Qingting Liu
- Division of Obstetrics, Key Laboratory of Birth Defects and Related Disease of Women and Children of MOE, State Key Laboratory of Biotherapy, West China Second Hospital, Sichuan University, Chengdu, China
| | - Li Guo
- Division of Obstetrics, Key Laboratory of Birth Defects and Related Disease of Women and Children of MOE, State Key Laboratory of Biotherapy, West China Second Hospital, Sichuan University, Chengdu, China
| | - Linfeng Sun
- Hefei National Laboratory for Physical Sciences at Microscale, CAS Centre for Excellence in Molecular Cell Science, School of Life Sciences, University of Science and Technology of China, Hefei, China
- * E-mail: (LS); (DD)
| | - Dong Deng
- Division of Obstetrics, Key Laboratory of Birth Defects and Related Disease of Women and Children of MOE, State Key Laboratory of Biotherapy, West China Second Hospital, Sichuan University, Chengdu, China
- * E-mail: (LS); (DD)
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2
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Pastor-Anglada M, Pérez-Torras S. Who Is Who in Adenosine Transport. Front Pharmacol 2018; 9:627. [PMID: 29962948 PMCID: PMC6010718 DOI: 10.3389/fphar.2018.00627] [Citation(s) in RCA: 74] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2018] [Accepted: 05/24/2018] [Indexed: 12/13/2022] Open
Abstract
Extracellular adenosine concentrations are regulated by a panel of membrane transporters which, in most cases, mediate its uptake into cells. Adenosine transporters belong to two gene families encoding Equilibrative and Concentrative Nucleoside Transporter proteins (ENTs and CNTs, respectively). The lack of appropriate pharmacological tools targeting every transporter subtype has introduced some bias on the current knowledge of the role of these transporters in modulating adenosine levels. In this regard, ENT1, for which pharmacology is relatively well-developed, has often been identified as a major player in purinergic signaling. Nevertheless, other transporters such as CNT2 and CNT3 can also contribute to purinergic modulation based on their high affinity for adenosine and concentrative capacity. Moreover, both transporter proteins have also been shown to be under purinergic regulation via P1 receptors in different cell types, which further supports its relevance in purinergic signaling. Thus, several transporter proteins regulate extracellular adenosine levels. Moreover, CNT and ENT proteins are differentially expressed in tissues but also in particular cell types. Accordingly, transporter-mediated fine tuning of adenosine levels is cell and tissue specific. Future developments focusing on CNT pharmacology are needed to unveil transporter subtype-specific events.
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Affiliation(s)
- Marçal Pastor-Anglada
- Molecular Pharmacology and Experimental Therapeutics, Department of Biochemistry and Molecular Biomedicine, Institute of Biomedicine, University of Barcelona, Barcelona, Spain
- Oncology Program, National Biomedical Research Institute on Liver and Gastrointestinal Diseases – CIBER ehd, Institut de Recerca Sant Joan de Déu, Barcelona, Spain
| | - Sandra Pérez-Torras
- Molecular Pharmacology and Experimental Therapeutics, Department of Biochemistry and Molecular Biomedicine, Institute of Biomedicine, University of Barcelona, Barcelona, Spain
- Oncology Program, National Biomedical Research Institute on Liver and Gastrointestinal Diseases – CIBER ehd, Institut de Recerca Sant Joan de Déu, Barcelona, Spain
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3
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Latek D. Rosetta Broker for membrane protein structure prediction: concentrative nucleoside transporter 3 and corticotropin-releasing factor receptor 1 test cases. BMC STRUCTURAL BIOLOGY 2017; 17:8. [PMID: 28774292 PMCID: PMC5543540 DOI: 10.1186/s12900-017-0078-8] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/11/2017] [Accepted: 07/26/2017] [Indexed: 02/12/2023]
Abstract
Background Membrane proteins are difficult targets for structure prediction due to the limited structural data deposited in Protein Data Bank. Most computational methods for membrane protein structure prediction are based on the comparative modeling. There are only few de novo methods targeting that distinct protein family. In this work an example of such de novo method was used to structurally and functionally characterize two representatives of distinct membrane proteins families of solute carrier transporters and G protein-coupled receptors. The well-known Rosetta program and one of its protocols named Broker was used in two test cases. The first case was de novo structure prediction of three N-terminal transmembrane helices of the human concentrative nucleoside transporter 3 (hCNT3) homotrimer belonging to the solute carrier 28 family of transporters (SLC28). The second case concerned the large scale refinement of transmembrane helices of a homology model of the corticotropin-releasing factor receptor 1 (CRFR1) belonging to the G protein-coupled receptors family. Results The inward-facing model of the hCNT3 homotrimer was used to propose the functional impact of its single nucleotide polymorphisms. Additionally, the 100 ns molecular dynamics simulation of the unliganded hCNT3 model confirmed its validity and revealed mobility of the selected binding site and homotrimer interface residues. The large scale refinement of transmembrane helices of the CRFR1 homology model resulted in the significant improvement of its accuracy with respect to the crystal structure of CRFR1, especially in the binding site area. Consequently, the antagonist CP-376395 could be docked with Autodock VINA to the CRFR1 model without any steric clashes. Conclusions The presented work demonstrated that Rosetta Broker can be a versatile tool for solving various issues referring to protein biology. Two distinct examples of de novo membrane protein structure prediction presented here provided important insights into three major areas of protein biology. Namely, the dynamics of the inward-facing hCNT3 homotrimer system, the structural changes of the CRFR1 receptor upon the antagonist binding and finally, the role of single nucleotide polymorphisms in both, hCNT3 and CRFR1 proteins, were investigated. Electronic supplementary material The online version of this article (doi:10.1186/s12900-017-0078-8) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Dorota Latek
- Faculty of Chemistry, University of Warsaw, Pasteur St. 1, 02-093, Warsaw, Poland.
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4
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Stecula A, Schlessinger A, Giacomini KM, Sali A. Human Concentrative Nucleoside Transporter 3 (hCNT3, SLC28A3) Forms a Cyclic Homotrimer. Biochemistry 2017; 56:3475-3483. [PMID: 28661652 DOI: 10.1021/acs.biochem.7b00339] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Many anticancer and antiviral drugs are purine or pyrimidine analogues, which use membrane transporters to cross cellular membranes. Concentrative nucleoside transporters (CNTs) mediate the salvage of nucleosides and the transport of therapeutic nucleoside analogues across plasma membranes by coupling the transport of ligands to the sodium gradient. Of the three members of the human CNT family, CNT3 has the broadest selectivity and the widest expression profile. However, the molecular mechanisms of the transporter, including how it interacts with and translocates structurally diverse nucleosides and nucleoside analogues, are unclear. Recently, the crystal structure of vcCNT showed that the prokaryotic homologue of CNT3 forms a homotrimer. In this study, we successfully expressed and purified the wild type human homologue, hCNT3, demonstrating the homotrimer by size exclusion profiles and glutaraldehyde cross-linking. Further, by creating a series of cysteine mutants at highly conserved positions guided by comparative structure models, we cross-linked hCNT3 protomers in a cell-based assay, thus showing the existence of hCNT3 homotrimers in human cells. The presence and absence of cross-links at specific locations along TM9 informs us of important structural differences between vcCNT and hCNT3. Comparative modeling of the trimerization domain and sequence coevolution analysis both indicate that oligomerization is critical to the stability and function of hCNT3. In particular, trimerization appears to shorten the translocation path for nucleosides across the plasma membrane and may allow modulation of the transport function via allostery.
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Affiliation(s)
- Adrian Stecula
- Department of Bioengineering and Therapeutic Sciences, University of California, San Francisco , San Francisco, California 94158, United States
| | - Avner Schlessinger
- Department of Pharmacological Sciences, Icahn School of Medicine at Mount Sinai , New York, New York 10029, United States
| | - Kathleen M Giacomini
- Department of Bioengineering and Therapeutic Sciences, University of California, San Francisco , San Francisco, California 94158, United States.,California Institute for Quantitative Biosciences, University of California, San Francisco , San Francisco, California 94158, United States.,Department of Pharmaceutical Chemistry, University of California, San Francisco , San Francisco, California 94158, United States.,Institute for Human Genetics, University of California, San Francisco , San Francisco, California 94158, United States
| | - Andrej Sali
- Department of Bioengineering and Therapeutic Sciences, University of California, San Francisco , San Francisco, California 94158, United States.,California Institute for Quantitative Biosciences, University of California, San Francisco , San Francisco, California 94158, United States.,Department of Pharmaceutical Chemistry, University of California, San Francisco , San Francisco, California 94158, United States
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5
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The SLC28 (CNT) and SLC29 (ENT) nucleoside transporter families: a 30-year collaborative odyssey. Biochem Soc Trans 2017; 44:869-76. [PMID: 27284054 DOI: 10.1042/bst20160038] [Citation(s) in RCA: 68] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2016] [Indexed: 01/18/2023]
Abstract
Specialized nucleoside transporter (NT) proteins are required for passage of nucleosides and hydrophilic nucleoside analogues across biological membranes. Physiologic nucleosides serve as central salvage metabolites in nucleotide biosynthesis, and nucleoside analogues are used as chemotherapeutic agents in the treatment of cancer and antiviral diseases. The nucleoside adenosine modulates numerous cellular events via purino-receptor cell signalling pathways. Human NTs are divided into two structurally unrelated protein families: the SLC28 concentrative nucleoside transporter (CNT) family and the SLC29 equilibrative nucleoside transporter (ENT) family. Human CNTs are inwardly directed Na(+)-dependent nucleoside transporters found predominantly in intestinal and renal epithelial and other specialized cell types. Human ENTs mediate bidirectional fluxes of purine and pyrimidine nucleosides down their concentration gradients and are ubiquitously found in most, possibly all, cell types. Both protein families are evolutionarily old: CNTs are present in both eukaryotes and prokaryotes; ENTs are widely distributed in mammalian, lower vertebrate and other eukaryote species. This mini-review describes a 30-year collaboration with Professor Stephen Baldwin to identify and understand the structures and functions of these physiologically and clinically important transport proteins.
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6
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Mulinta R, Yao SYM, Ng AML, Cass CE, Young JD. Substituted cysteine accessibility method (SCAM) analysis of the transport domain of human concentrative nucleoside transporter 3 (hCNT3) and other family members reveals features of structural and functional importance. J Biol Chem 2017; 292:9505-9522. [PMID: 28385889 PMCID: PMC5465479 DOI: 10.1074/jbc.m116.743997] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2016] [Revised: 03/31/2017] [Indexed: 12/13/2022] Open
Abstract
The human SLC28 family of concentrative nucleoside transporter (CNT) proteins has three members: hCNT1, hCNT2, and hCNT3. Na+-coupled hCNT1 and hCNT2 transport pyrimidine and purine nucleosides, respectively, whereas hCNT3 transports both pyrimidine and purine nucleosides utilizing Na+ and/or H+ electrochemical gradients. Escherichia coli CNT family member NupC resembles hCNT1 in permeant selectivity but is H+-coupled. Using heterologous expression in Xenopus oocytes and the engineered cysteine-less hCNT3 protein hCNT3(C-), substituted cysteine accessibility method analysis with the membrane-impermeant thiol reactive reagent p-chloromercuribenzene sulfonate was performed on the transport domain (interfacial helix 2, hairpin 1, putative transmembrane domain (TM) 7, and TM8), as well as TM9 of the scaffold domain of the protein. This systematic scan of the entire C-terminal half of hCNT3(C-) together with parallel studies of the transport domain of wild-type hCNT1 and the corresponding TMs of cysteine-less NupC(C-) yielded results that validate the newly developed structural homology model of CNT membrane architecture for human CNTs, revealed extended conformationally mobile regions within transport-domain TMs, identified pore-lining residues of functional importance, and provided evidence of an emerging novel elevator-type mechanism of transporter function.
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Affiliation(s)
- Ras Mulinta
- From the Membrane Protein Disease Research Group, Departments of Physiology and
| | - Sylvia Y M Yao
- From the Membrane Protein Disease Research Group, Departments of Physiology and
| | - Amy M L Ng
- From the Membrane Protein Disease Research Group, Departments of Physiology and
| | - Carol E Cass
- Oncology, University of Alberta, Edmonton, Alberta T6G 2H7, Canada and.,the Cross Cancer Institute, Edmonton, Alberta T6G 2H7, Canada
| | - James D Young
- From the Membrane Protein Disease Research Group, Departments of Physiology and
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7
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rCNT2 extracellular cysteines, Cys615
and Cys649
, are important for maturation and sorting to the plasma membrane. FEBS Lett 2014; 588:4382-9. [DOI: 10.1016/j.febslet.2014.10.006] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2014] [Revised: 09/27/2014] [Accepted: 10/06/2014] [Indexed: 12/11/2022]
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8
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Young JD, Yao SYM, Baldwin JM, Cass CE, Baldwin SA. The human concentrative and equilibrative nucleoside transporter families, SLC28 and SLC29. Mol Aspects Med 2013; 34:529-47. [PMID: 23506887 DOI: 10.1016/j.mam.2012.05.007] [Citation(s) in RCA: 244] [Impact Index Per Article: 22.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2012] [Accepted: 04/11/2012] [Indexed: 12/23/2022]
Abstract
Nucleoside transport in humans is mediated by members of two unrelated protein families, the SLC28 family of cation-linked concentrative nucleoside transporters (CNTs) and the SLC29 family of energy-independent, equilibrative nucleoside transporters (ENTs). These families contain three and four members, respectively, which differ both in the stoichiometry of cation coupling and in permeant selectivity. Together, they play key roles in nucleoside and nucleobase uptake for salvage pathways of nucleotide synthesis. Moreover, they facilitate cellular uptake of several nucleoside and nucleobase drugs used in cancer chemotherapy and treatment of viral infections. Thus, the transporter content of target cells can represent a key determinant of the response to treatment. In addition, by regulating the concentration of adenosine available to cell surface receptors, nucleoside transporters modulate many physiological processes ranging from neurotransmission to cardiovascular activity. This review describes the molecular and functional properties of the two transporter families, with a particular focus on their physiological roles in humans and relevance to disease treatment.
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Affiliation(s)
- James D Young
- Membrane Protein Research Group, Edmonton, Alberta, Canada T6G 2H7.
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9
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Errasti-Murugarren E, Fernández-Calotti P, Veyhl-Wichmann M, Diepold M, Pinilla-Macua I, Pérez-Torras S, Kipp H, Koepsell H, Pastor-Anglada M. Role of the Transporter Regulator Protein (RS1) in the Modulation of Concentrative Nucleoside Transporters (CNTs) in Epithelia. Mol Pharmacol 2012; 82:59-67. [DOI: 10.1124/mol.111.076992] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
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10
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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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11
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Johnson DE, Ai HW, Wong P, Young JD, Campbell RE, Casey JR. Red fluorescent protein pH biosensor to detect concentrative nucleoside transport. J Biol Chem 2009; 284:20499-511. [PMID: 19494110 PMCID: PMC2742814 DOI: 10.1074/jbc.m109.019042] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2009] [Indexed: 11/06/2022] Open
Abstract
Human concentrative nucleoside transporter, hCNT3, mediates Na+/nucleoside and H+/nucleoside co-transport. We describe a new approach to monitor H+/uridine co-transport in cultured mammalian cells, using a pH-sensitive monomeric red fluorescent protein variant, mNectarine, whose development and characterization are also reported here. A chimeric protein, mNectarine fused to the N terminus of hCNT3 (mNect.hCNT3), enabled measurement of pH at the intracellular surface of hCNT3. mNectarine fluorescence was monitored in HEK293 cells expressing mNect.hCNT3 or mNect.hCNT3-F563C, an inactive hCNT3 mutant. Free cytosolic mNect, mNect.hCNT3, and the traditional pH-sensitive dye, BCECF, reported cytosolic pH similarly in pH-clamped HEK293 cells. Cells were incubated at the permissive pH for H(+)-coupled nucleoside transport, pH 5.5, under both Na(+)-free and Na(+)-containing conditions. In mNect.hCNT3-expressing cells (but not under negative control conditions) the rate of acidification increased in media containing 0.5 mm uridine, providing the first direct evidence for H(+)-coupled uridine transport. At pH 5.5, there was no significant difference in uridine transport rates (coupled H+ flux) in the presence or absence of Na+ (1.09 +/- 0.11 or 1.18 +/- 0.32 mm min(-1), respectively). This suggests that in acidic Na(+)-containing conditions, 1 Na+ and 1 H+ are transported per uridine molecule, while in acidic Na(+)-free conditions, 1 H+ alone is transported/uridine. In acid environments, including renal proximal tubule, H+/nucleoside co-transport may drive nucleoside accumulation by hCNT3. Fusion of mNect to hCNT3 provided a simple, self-referencing, and effective way to monitor nucleoside transport, suggesting an approach that may have applications in assays of transport activity of other H(+)-coupled transport proteins.
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Affiliation(s)
- Danielle E. Johnson
- From the Membrane Protein Research Group, Department of Physiology, University of Alberta, Edmonton, Alberta T6G 2H7 and
| | - Hui-wang Ai
- the Department of Chemistry, University of Alberta, Edmonton T6G 2G2, Canada
| | - Peter Wong
- the Department of Chemistry, University of Alberta, Edmonton T6G 2G2, Canada
| | - James D. Young
- From the Membrane Protein Research Group, Department of Physiology, University of Alberta, Edmonton, Alberta T6G 2H7 and
| | - Robert E. Campbell
- the Department of Chemistry, University of Alberta, Edmonton T6G 2G2, Canada
| | - Joseph R. Casey
- From the Membrane Protein Research Group, Department of Physiology, University of Alberta, Edmonton, Alberta T6G 2H7 and
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12
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Slugoski MD, Ng AML, Yao SYM, Lin CC, Mulinta R, Cass CE, Baldwin SA, Young JD. Substituted cysteine accessibility method analysis of human concentrative nucleoside transporter hCNT3 reveals a novel discontinuous region of functional importance within the CNT family motif (G/A)XKX3NEFVA(Y/M/F). J Biol Chem 2009; 284:17281-17292. [PMID: 19380585 DOI: 10.1074/jbc.m109.009704] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The human SLC28 family of integral membrane CNT (concentrative nucleoside transporter) proteins has three members, hCNT1, hCNT2, and hCNT3. Na(+)-coupled hCNT1 and hCNT2 transport pyrimidine and purine nucleosides, respectively, whereas hCNT3 mediates transport of both pyrimidine and purine nucleosides utilizing Na(+) and/or H(+) electrochemical gradients. These and other eukaryote CNTs are currently defined by a putative 13-transmembrane helix (TM) topology model with an intracellular N terminus and a glycosylated extracellular C terminus. Recent mutagenesis studies, however, have provided evidence supporting an alternative 15-TM membrane architecture. In the absence of CNT crystal structures, valuable information can be gained about residue localization and function using substituted cysteine accessibility method analysis with thiol-reactive reagents, such as p-chloromercuribenzene sulfonate. Using heterologous expression in Xenopus oocytes and the cysteineless hCNT3 protein hCNT3C-, substituted cysteine accessibility method analysis with p-chloromercuribenzene sulfonate was performed on the TM 11-13 region, including bridging extramembranous loops. The results identified residues of functional importance and, consistent with a new revised 15-TM CNT membrane architecture, suggest a novel membrane-associated topology for a region of the protein (TM 11A) that includes the highly conserved CNT family motif (G/A)XKX(3)NEFVA(Y/M/F).
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Affiliation(s)
| | - Amy M L Ng
- From the Departments of Physiology, Edmonton, Alberta T6G 2H7, Canada
| | - Sylvia Y M Yao
- From the Departments of Physiology, Edmonton, Alberta T6G 2H7, Canada
| | - Colin C Lin
- From the Departments of Physiology, Edmonton, Alberta T6G 2H7, Canada
| | - Ras Mulinta
- From the Departments of Physiology, Edmonton, Alberta T6G 2H7, Canada
| | - Carol E Cass
- Oncology, Membrane Protein Research Group, University of Alberta, Edmonton, Alberta T6G 2H7, Canada; Cross Cancer Institute, Edmonton, Alberta T6G 1Z2, Canada
| | - Stephen A Baldwin
- Astbury Centre for Structural Molecular Biology, Institute of Membrane and Systems Biology, University of Leeds, Leeds LS2 9JT, United Kingdom
| | - James D Young
- From the Departments of Physiology, Edmonton, Alberta T6G 2H7, Canada.
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13
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Slugoski MD, Smith KM, Ng AML, Yao SYM, Karpinski E, Cass CE, Baldwin SA, Young JD. Conserved glutamate residues Glu-343 and Glu-519 provide mechanistic insights into cation/nucleoside cotransport by human concentrative nucleoside transporter hCNT3. J Biol Chem 2009; 284:17266-17280. [PMID: 19380587 DOI: 10.1074/jbc.m109.009613] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
Human concentrative nucleoside transporter 3 (hCNT3) utilizes electrochemical gradients of both Na(+) and H(+) to accumulate pyrimidine and purine nucleosides within cells. We have employed radioisotope flux and electrophysiological techniques in combination with site-directed mutagenesis and heterologous expression in Xenopus oocytes to identify two conserved pore-lining glutamate residues (Glu-343 and Glu-519) with essential roles in hCNT3 Na(+)/nucleoside and H(+)/nucleoside cotransport. Mutation of Glu-343 and Glu-519 to aspartate, glutamine, and cysteine severely compromised hCNT3 transport function, and changes included altered nucleoside and cation activation kinetics (all mutants), loss or impairment of H(+) dependence (all mutants), shift in Na(+):nucleoside stoichiometry from 2:1 to 1:1 (E519C), complete loss of catalytic activity (E519Q) and, similar to the corresponding mutant in Na(+)-specific hCNT1, uncoupled Na(+) currents (E343Q). Consistent with close-proximity integration of cation/solute-binding sites within a common cation/permeant translocation pore, mutation of Glu-343 and Glu-519 also altered hCNT3 nucleoside transport selectivity. Both residues were accessible to the external medium and inhibited by p-chloromercuribenzene sulfonate when converted to cysteine.
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Affiliation(s)
| | - Kyla M Smith
- From the Departments of Physiology, Edmonton, Alberta T6G 2H7, Canada
| | - Amy M L Ng
- From the Departments of Physiology, Edmonton, Alberta T6G 2H7, Canada
| | - Sylvia Y M Yao
- From the Departments of Physiology, Edmonton, Alberta T6G 2H7, Canada
| | - Edward Karpinski
- From the Departments of Physiology, Edmonton, Alberta T6G 2H7, Canada
| | - Carol E Cass
- Oncology, Membrane Protein Research Group, University of Alberta, Edmonton, Alberta T6G 2H7, Canada; Cross Cancer Institute, Edmonton, Alberta T6G 1Z2, Canada
| | - Stephen A Baldwin
- Astbury Centre for Structural Molecular Biology, Institute of Membrane and Systems Biology, University of Leeds, Leeds LS2 9JT, United Kingdom
| | - James D Young
- From the Departments of Physiology, Edmonton, Alberta T6G 2H7, Canada.
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14
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Errasti‐Murugarren E, Molina‐Arcas M, Casado FJ, Pastor‐Anglada M. A splice variant of the
SLC28A3
gene encodes a novel human concentrative nucleoside transporter‐3 (hCNT3) protein localized in the endoplasmic reticulum. FASEB J 2008; 23:172-82. [DOI: 10.1096/fj.08-113902] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Affiliation(s)
- Ekaitz Errasti‐Murugarren
- Departament de Bioquímica i Biologia Molecular, Facultat de BiologiaInstitut de Biomedicina, CIBER EHD, Universitat de BarcelonaBarcelonaSpain
| | - Miriam Molina‐Arcas
- Departament de Bioquímica i Biologia Molecular, Facultat de BiologiaInstitut de Biomedicina, CIBER EHD, Universitat de BarcelonaBarcelonaSpain
| | - Fco Javier Casado
- Departament de Bioquímica i Biologia Molecular, Facultat de BiologiaInstitut de Biomedicina, CIBER EHD, Universitat de BarcelonaBarcelonaSpain
| | - Marcal Pastor‐Anglada
- Departament de Bioquímica i Biologia Molecular, Facultat de BiologiaInstitut de Biomedicina, CIBER EHD, Universitat de BarcelonaBarcelonaSpain
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