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Zhong J, Mo C, Zhang Y, Li L. A review of the Augustine blood group system. Int J Hematol 2024; 120:44-49. [PMID: 38767828 DOI: 10.1007/s12185-024-03791-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2024] [Revised: 05/05/2024] [Accepted: 05/13/2024] [Indexed: 05/22/2024]
Abstract
Augustine is a newly identified blood group system comprising four antigens, one of which is the high-frequency antigen Ata in the original "series". Four antigens are located on a multipass membrane glycoprotein equilibrative nucleoside transporter 1 (ENT1), and equilibrative nucleoside transporter is encoded by SLC29A1. In 2016, the International Society of Blood Transfusion (ISBT) recognised Augustine as a blood group system and numbered it as 036. The glycoprotein ENT1 transports nucleotides into cells to participate in the synthesis of DNA and RNA, and this is an important link for chemotherapeutic glycosides to enter tumour cells. Augustine antibodies are clinically relevant in blood transfusion and pregnancy.
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Affiliation(s)
- Jing Zhong
- Department of Blood Transfusion, The Central Hospital of Shaoyang, Shaoyang, China
| | - Chunping Mo
- Department of Blood Transfusion, The Central Hospital of Shaoyang, Shaoyang, China
| | - Yan Zhang
- Department of Blood Transfusion, The Central Hospital of Shaoyang, Shaoyang, China.
- Changchun Bioxun Biotechnology Limited Liability Company, 285 Xinpu Road, Changchun, Jilin, China.
| | - Lingbo Li
- Department of Blood Transfusion, The Central Hospital of Shaoyang, Shaoyang, China.
- Aikang MedTech Co., Ltd, 1A, Shijing Industrial Park, Pingkui Rd, Shijing St, Pingshan, Shenzhen, China.
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2
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Boakes JC, Harborne SPD, Ngo JTS, Pliotas C, Goldman A. Novel variants provide differential stabilisation of human equilibrative nucleoside transporter 1 states. Front Mol Biosci 2022; 9:970391. [DOI: 10.3389/fmolb.2022.970391] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2022] [Accepted: 10/27/2022] [Indexed: 11/10/2022] Open
Abstract
Human equilibrative nucleoside transporters represent a major pharmaceutical target for cardiac, cancer and viral therapies. Understanding the molecular basis for transport is crucial for the development of improved therapeutics through structure-based drug design. ENTs have been proposed to utilise an alternating access mechanism of action, similar to that of the major facilitator superfamily. However, ENTs lack functionally-essential features of that superfamily, suggesting that they may use a different transport mechanism. Understanding the molecular basis of their transport requires insight into diverse conformational states. Differences between intermediate states may be discrete and mediated by subtle gating interactions, such as salt bridges. We identified four variants of human equilibrative nucleoside transporter isoform 1 (hENT1) at the large intracellular loop (ICL6) and transmembrane helix 7 (TM7) that stabilise the apo-state (∆Tm 0.7–1.5°C). Furthermore, we showed that variants K263A (ICL6) and I282V (TM7) specifically stabilise the inhibitor-bound state of hENT1 (∆∆Tm 5.0 ± 1.7°C and 3.0 ± 1.8°C), supporting the role of ICL6 in hENT1 gating. Finally, we showed that, in comparison with wild type, variant T336A is destabilised by nitrobenzylthioinosine (∆∆Tm -4.7 ± 1.1°C) and binds it seven times worse. This residue may help determine inhibitor and substrate sensitivity. Residue K263 is not present in the solved structures, highlighting the need for further structural data that include the loop regions.
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Wu Z, Han Z, Zhou W, Sun X, Chen L, Yang S, Hu J, Li C. Insight into the Nucleoside Transport and Inhibition of Human ENT1. Curr Res Struct Biol 2022; 4:192-205. [PMID: 35677775 PMCID: PMC9168172 DOI: 10.1016/j.crstbi.2022.05.005] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2022] [Revised: 05/02/2022] [Accepted: 05/18/2022] [Indexed: 12/03/2022] Open
Abstract
The human equilibrative nucleoside transporter 1 (hENT1) is an effective controller of adenosine signaling by regulating its extracellular and intracellular concentration, and has become a solid drug target of clinical used adenosine reuptake inhibitors (AdoRIs). Currently, the mechanisms of adenosine transport and inhibition for hENT1 remain unclear, which greatly limits the in-depth understanding of its inner workings as well as the development of novel inhibitors. In this work, the dynamic details of hENT1 underlie adenosine transport and the inhibition mechanism of the non-nucleoside AdoRIs dilazep both were investigated by comparative long-time unbiased molecular dynamics simulations. The calculation results show that the conformational transitions of hENT1 from the outward open to metastable occluded state are mainly driven by TM1, TM2, TM7 and TM9. One of the trimethoxyphenyl rings in dilazep serves as the adenosyl moiety of the endogenous adenosine substrate to competitively occupy the orthosteric site of hENT1. Due to extensive and various VDW interactions with N30, M33, M84, P308 and F334, the other trimethoxyphenyl ring is stuck in the opportunistic site near the extracellular side preventing the complete occlusion of thin gate simultaneously. Obviously, dilazep shows significant inhibitory activity by disrupting the local induce-fit action in substrate binding cavity and blocking the transport cycle of whole protein. This study not only reveals the nucleoside transport mechanism by hENT1 at atomic level, but also provides structural guidance for the subsequent design of novel non-nucleoside AdoRIs with enhanced pharmacologic properties. The transitions of hENT1 from the outward open to metastable occluded state are mainly driven by TM1, TM2, TM7 and TM9. The induce-fit action by adenosine recognition precedes. inward contraction of the extracellular side. Dilazep exerts its special hENT1 inhibitory function through competitive binding and allosteric regulation. A gating strategy of extracellular loop is revealed to ensure adenosine is firmly located in the transport cavity.
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Affiliation(s)
- Zhixiang Wu
- Faculty of Environmental and Life Sciences, Beijing University of Technology, Beijing, China
| | - Zhongjie Han
- Faculty of Environmental and Life Sciences, Beijing University of Technology, Beijing, China
| | - Wenxue Zhou
- Faculty of Environmental and Life Sciences, Beijing University of Technology, Beijing, China
| | - Xiaohan Sun
- Faculty of Environmental and Life Sciences, Beijing University of Technology, Beijing, China
| | - Lei Chen
- Faculty of Environmental and Life Sciences, Beijing University of Technology, Beijing, China
| | - Shuang Yang
- Faculty of Environmental and Life Sciences, Beijing University of Technology, Beijing, China
| | - Jianping Hu
- Key Laboratory of Medicinal and Edible Plants Resources, Development of Sichuan Education Department, School of Pharmacy, Chengdu University, Chengdu, China
- Corresponding author. Key Laboratory of Medicinal and Edible Plants Resources, Development of Sichuan Education Department, School of Pharmacy, Chengdu University, Chengdu, 610106, China.
| | - Chunhua Li
- Faculty of Environmental and Life Sciences, Beijing University of Technology, Beijing, China
- Corresponding author. Faculty of Environmental and Life Sciences, Beijing University of Technology, Beijing, 100124, China.
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Abstract
Nucleosides play central roles in all facets of life, from metabolism to cellular signaling. Because of their physiochemical properties, nucleosides are lipid bilayer impermeable and thus rely on dedicated transport systems to cross biological membranes. In humans, two unrelated protein families mediate nucleoside membrane transport: the concentrative and equilibrative nucleoside transporter families. The objective of this review is to provide a broad outlook on the current status of nucleoside transport research. We will discuss the role played by nucleoside transporters in human health and disease, with emphasis placed on recent structural advancements that have revealed detailed molecular principles of these important cellular transport systems and exploitable pharmacological features.
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Affiliation(s)
- Nicholas J. Wright
- Department of Biochemistry, Duke University Medical Center, 303 Research Drive, Durham, North Carolina, 27710, USA
| | - Seok-Yong Lee
- Department of Biochemistry, Duke University Medical Center, 303 Research Drive, Durham, North Carolina, 27710, USA
- Correspondence and requests for materials should be addressed to: S.-Y. Lee., , tel: 919-684-1005, fax: 919-684-8885
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Schmidl S, Tamayo Rojas SA, Iancu CV, Choe JY, Oreb M. Functional Expression of the Human Glucose Transporters GLUT2 and GLUT3 in Yeast Offers Novel Screening Systems for GLUT-Targeting Drugs. Front Mol Biosci 2021; 7:598419. [PMID: 33681287 PMCID: PMC7930720 DOI: 10.3389/fmolb.2020.598419] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2020] [Accepted: 12/23/2020] [Indexed: 01/31/2023] Open
Abstract
Human GLUT2 and GLUT3, members of the GLUT/SLC2 gene family, facilitate glucose transport in specific tissues. Their malfunction or misregulation is associated with serious diseases, including diabetes, metabolic syndrome, and cancer. Despite being promising drug targets, GLUTs have only a few specific inhibitors. To identify and characterize potential GLUT2 and GLUT3 ligands, we developed a whole-cell system based on a yeast strain deficient in hexose uptake, whose growth defect on glucose can be rescued by the functional expression of human transporters. The simplicity of handling yeast cells makes this platform convenient for screening potential GLUT2 and GLUT3 inhibitors in a growth-based manner, amenable to high-throughput approaches. Moreover, our expression system is less laborious for detailed kinetic characterization of inhibitors than alternative methods such as the preparation of proteoliposomes or uptake assays in Xenopus oocytes. We show that functional expression of GLUT2 in yeast requires the deletion of the extended extracellular loop connecting transmembrane domains TM1 and TM2, which appears to negatively affect the trafficking of the transporter in the heterologous expression system. Furthermore, single amino acid substitutions at specific positions of the transporter sequence appear to positively affect the functionality of both GLUT2 and GLUT3 in yeast. We show that these variants are sensitive to known inhibitors phloretin and quercetin, demonstrating the potential of our expression systems to significantly accelerate the discovery of compounds that modulate the hexose transport activity of GLUT2 and GLUT3.
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Affiliation(s)
- Sina Schmidl
- Institute of Molecular Biosciences, Faculty of Biological Sciences, Goethe University Frankfurt, Frankfurt am Main, Germany
| | - Sebastian A Tamayo Rojas
- Institute of Molecular Biosciences, Faculty of Biological Sciences, Goethe University Frankfurt, Frankfurt am Main, Germany
| | - Cristina V Iancu
- Department of Chemistry, East Carolina Diabetes and Obesity Institute, East Carolina University, Greenville, NC, United States
| | - Jun-Yong Choe
- Department of Chemistry, East Carolina Diabetes and Obesity Institute, East Carolina University, Greenville, NC, United States.,Department of Biochemistry and Molecular Biology, The Chicago Medical School, Rosalind Franklin University of Medicine and Science, North Chicago, IL, United States
| | - Mislav Oreb
- Institute of Molecular Biosciences, Faculty of Biological Sciences, Goethe University Frankfurt, Frankfurt am Main, Germany
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Equilibrative Nucleoside Transporter 2: Properties and Physiological Roles. BIOMED RESEARCH INTERNATIONAL 2020; 2020:5197626. [PMID: 33344638 PMCID: PMC7732376 DOI: 10.1155/2020/5197626] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/20/2020] [Revised: 11/05/2020] [Accepted: 11/16/2020] [Indexed: 02/06/2023]
Abstract
Equilibrative nucleoside transporter 2 (ENT2) is a bidirectional transporter embedded in the biological membrane and is ubiquitously found in most tissue and cell types. ENT2 mediates the uptake of purine and pyrimidine nucleosides and nucleobase besides transporting a variety of nucleoside-derived drugs, mostly in anticancer therapy. Since high expression of ENT2 has been correlated with advanced stages of different types of cancers, consequently, this has gained significant interest in the role of ENT2 as a potential therapeutic target. Furthermore, ENT2 plays critical roles in signaling pathway and cell cycle progression. Therefore, elucidating the physiological roles of ENT2 and its properties may contribute to a better understanding of ENT2 roles beyond their transportation mechanism. This review is aimed at highlighting the main roles of ENT2 and at providing a brief update on the recent research.
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7
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IMPROvER: the Integral Membrane Protein Stability Selector. Sci Rep 2020; 10:15165. [PMID: 32938971 PMCID: PMC7495477 DOI: 10.1038/s41598-020-71744-x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2019] [Accepted: 08/04/2020] [Indexed: 01/20/2023] Open
Abstract
Identifying stabilising variants of membrane protein targets is often required for structure determination. Our new computational pipeline, the Integral Membrane Protein Stability Selector (IMPROvER) provides a rational approach to variant selection by employing three independent approaches: deep-sequence, model-based and data-driven. In silico tests using known stability data, and in vitro tests using three membrane protein targets with 7, 11 and 16 transmembrane helices provided measures of success. In vitro, individual approaches alone all identified stabilising variants at a rate better than expected by random selection. Low numbers of overlapping predictions between approaches meant a greater success rate was achieved (fourfold better than random) when approaches were combined and selections restricted to the highest ranked sites. The mix of information IMPROvER uses can be extracted for any helical membrane protein. We have developed the first general-purpose tool for selecting stabilising variants of \documentclass[12pt]{minimal}
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\begin{document}$$\upalpha$$\end{document}α-helical membrane proteins, increasing efficiency and reducing workload. IMPROvER can be accessed at http://improver.ddns.net/IMPROvER/.
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Structures of human ENT1 in complex with adenosine reuptake inhibitors. Nat Struct Mol Biol 2019; 26:599-606. [PMID: 31235912 PMCID: PMC6705415 DOI: 10.1038/s41594-019-0245-7] [Citation(s) in RCA: 60] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2019] [Accepted: 05/08/2019] [Indexed: 02/06/2023]
Abstract
The human Equilibrative Nucleoside Transporter 1 (hENT1), a member of the SLC29 family, plays crucial roles in adenosine signaling, cellular uptake of nucleoside for DNA and RNA synthesis, and nucleoside-derived anticancer and antiviral drug transport in human. Because of its central role in adenosine signaling, it is the target of adenosine reuptake inhibitors (AdoRI), several of which are clinically used. Despite its importance in human physiology and pharmacology, the molecular basis of hENT1-mediated adenosine transport and its inhibition by AdoRIs are limited due to the absence of structural information on hENT1. Here we present crystal structures of hENT1 in complex with two chemically distinct AdoRIs: dilazep and S-(4-Nitrobenzyl)-6-thioinosine (NBMPR). Combined with mutagenesis study, our structural analyses elucidate two distinct inhibitory mechanisms exhibited on hENT1, while giving insight into adenosine recognition and transport. Our studies provide the platform for improved pharmacological intervention of adenosine and nucleoside analog drug transport by hENT1.
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Rahman MF, Raj R, Govindarajan R. Identification of Structural and Molecular Features Involved in the Transport of 3'-Deoxy-Nucleoside Analogs by Human Equilibrative Nucleoside Transporter 3. Drug Metab Dispos 2018. [PMID: 29530865 PMCID: PMC5896370 DOI: 10.1124/dmd.117.079400] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
Combination antiretroviral drug treatments depend on 3′-deoxy-nucleoside analogs such as 3′-azido-3′-deoxythymidine (AZT) and 2′3′-dideoxyinosine (DDI). Despite being effective in inhibiting human immunodeficiency virus replication, these drugs produce a range of toxicities, including myopathy, pancreatitis, neuropathy, and lactic acidosis, that are generally considered as sequelae to mitochondrial damage. Although cell surface–localized nucleoside transporters, such as human equilibrative nucleoside transporter 2 (hENT2) and human concentrative nucleoside transporter 1 (hCNT1), are known to increase the carrier-mediated uptake of 3′-deoxy-nucleoside analogs into cells, another ubiquitously expressed intracellular nucleoside transporter (namely, hENT3) has been implicated in the mitochondrial transport of 3′-deoxy-nucleoside analogs. Using site-directed mutagenesis, generation of chimeric hENTs, and 3H-permeant flux measurements in mutant/chimeric RNA–injected Xenopus oocytes, here we identified the molecular determinants of hENT3 that dictate membrane translocation of 3′-deoxy-nucleoside analogs. Our findings demonstrated that whereas hENT1 had no significant transport activity toward 3′-deoxy-nucleoside analogs, hENT3 was capable of transporting 3′-deoxy-nucleoside analogs similar to hENT2. Transport analyses of hENT3-hENT1 chimeric constructs demonstrated that the N-terminal half of hENT3 is primarily responsible for the hENT3–3′-deoxy-nucleoside analog interaction. In addition, mutagenic studies identified that 225D and 231L in the N-terminal half of hENT3 partially contribute to the ability of hENT3 to transport AZT and DDI. The identification of the transporter segment and amino acid residues that are important in hENT3 transport of 3′-deoxy-nucleoside analogs may present a possible mechanism for overcoming the adverse toxicities associated with 3′-deoxy-nucleoside analog treatment and may guide rational development of novel nucleoside analogs.
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Affiliation(s)
- Md Fazlur Rahman
- Division of Pharmaceutics and Pharmaceutical Chemistry, College of Pharmacy (M.F.R., R.R., R.G.) and Translational Therapeutics, Ohio State University Comprehensive Cancer Center (R.G.), The Ohio State University, Columbus, Ohio
| | - Radhika Raj
- Division of Pharmaceutics and Pharmaceutical Chemistry, College of Pharmacy (M.F.R., R.R., R.G.) and Translational Therapeutics, Ohio State University Comprehensive Cancer Center (R.G.), The Ohio State University, Columbus, Ohio
| | - Rajgopal Govindarajan
- Division of Pharmaceutics and Pharmaceutical Chemistry, College of Pharmacy (M.F.R., R.R., R.G.) and Translational Therapeutics, Ohio State University Comprehensive Cancer Center (R.G.), The Ohio State University, Columbus, Ohio
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10
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Alarcón S, Garrido W, Vega G, Cappelli C, Suárez R, Oyarzún C, Quezada C, San Martín R. Deficient Insulin-mediated Upregulation of the Equilibrative Nucleoside Transporter 2 Contributes to Chronically Increased Adenosine in Diabetic Glomerulopathy. Sci Rep 2017; 7:9439. [PMID: 28842605 PMCID: PMC5572683 DOI: 10.1038/s41598-017-09783-0] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2017] [Accepted: 07/28/2017] [Indexed: 12/21/2022] Open
Abstract
Deficient insulin signaling is a key event mediating diabetic glomerulopathy. Additionally, diabetic kidney disease has been related to increased levels of adenosine. Therefore, we tested a link between insulin deficiency and dysregulated activity of the equilibrative nucleoside transporters (ENTs) responsible for controlling extracellular levels of adenosine. In ex vivo glomeruli, high D-glucose decreased nucleoside uptake mediated by ENT1 and ENT2 transporters, resulting in augmented extracellular levels of adenosine. This condition was reversed by exposure to insulin. Particularly, insulin through insulin receptor/PI3K pathway markedly upregulated ENT2 uptake activity to restores the extracellular basal level of adenosine. Using primary cultured rat podocytes as a cellular model, we found insulin was able to increase ENT2 maximal velocity of transport. Also, PI3K activity was necessary to maintain ENT2 protein levels in the long term. In glomeruli of streptozotocin-induced diabetic rats, insulin deficiency leads to decreased activity of ENT2 and chronically increased extracellular levels of adenosine. Treatment of diabetic rats with adenosine deaminase attenuated both the glomerular loss of nephrin and proteinuria. In conclusion, we evidenced ENT2 as a target of insulin signaling and sensitive to dysregulation in diabetes, leading to chronically increased extracellular adenosine levels and thereby setting conditions conducive to kidney injury.
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Affiliation(s)
- Sebastián Alarcón
- Institute of Biochemistry and Microbiology, Science Faculty, Universidad Austral de Chile, Valdivia, Chile
| | - Wallys Garrido
- Institute of Biochemistry and Microbiology, Science Faculty, Universidad Austral de Chile, Valdivia, Chile
| | - Génesis Vega
- Institute of Biochemistry and Microbiology, Science Faculty, Universidad Austral de Chile, Valdivia, Chile
| | - Claudio Cappelli
- Institute of Biochemistry and Microbiology, Science Faculty, Universidad Austral de Chile, Valdivia, Chile
| | - Raibel Suárez
- Institute of Biochemistry and Microbiology, Science Faculty, Universidad Austral de Chile, Valdivia, Chile
| | - Carlos Oyarzún
- Institute of Biochemistry and Microbiology, Science Faculty, Universidad Austral de Chile, Valdivia, Chile
| | - Claudia Quezada
- Institute of Biochemistry and Microbiology, Science Faculty, Universidad Austral de Chile, Valdivia, Chile
| | - Rody San Martín
- Institute of Biochemistry and Microbiology, Science Faculty, Universidad Austral de Chile, Valdivia, Chile.
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Huang W, Zeng X, Shi Y, Liu M. Functional characterization of human equilibrative nucleoside transporter 1. Protein Cell 2017; 8:284-295. [PMID: 27995448 PMCID: PMC5359181 DOI: 10.1007/s13238-016-0350-x] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2016] [Accepted: 11/04/2016] [Indexed: 12/15/2022] Open
Abstract
Equilibrative nucleoside transporters (ENTs), which facilitate cross-membrane transport of nucleosides and nucleoside-derived drugs, play an important role in the salvage pathways of nucleotide synthesis, cancer chemotherapy, and treatment for virus infections. Functional characterization of ENTs at the molecular level remains technically challenging and hence scant. In this study, we report successful purification and biochemical characterization of human equilibrative nucleoside transporter 1 (hENT1) in vitro. The HEK293F-derived, recombinant hENT1 is homogenous and functionally active in proteoliposome-based counter flow assays. hENT1 transports the substrate adenosine with a Km of 215 ± 34 µmol/L and a Vmax of 578 ± 23.4 nmol mg-1 min-1. Adenosine uptake by hENT1 is competitively inhibited by nitrobenzylmercaptopurine ribonucleoside (NBMPR), nucleosides, deoxynucleosides, and nucleoside-derived anti-cancer and anti-viral drugs. Binding of hENT1 to adenosine, deoxyadenosine, and adenine by isothermal titration calorimetry is in general agreement with results of the competitive inhibition assays. These results validate hENT1 as a bona fide target for potential drug target and serve as a useful basis for future biophysical and structural studies.
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Affiliation(s)
- Weiyun Huang
- Beijing Advanced Innovation Center for Structural Biology, Tsinghua-Peking Joint Center for Life Sciences, School of Life Sciences, Tsinghua University, Beijing, 100084, China
| | - Xin Zeng
- Beijing Advanced Innovation Center for Structural Biology, Tsinghua-Peking Joint Center for Life Sciences, School of Life Sciences, Tsinghua University, Beijing, 100084, China
| | - Yigong Shi
- Beijing Advanced Innovation Center for Structural Biology, Tsinghua-Peking Joint Center for Life Sciences, School of Life Sciences, Tsinghua University, Beijing, 100084, China
| | - Minhao Liu
- Beijing Advanced Innovation Center for Structural Biology, Tsinghua-Peking Joint Center for Life Sciences, School of Life Sciences, Tsinghua University, Beijing, 100084, China.
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12
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Boswell-Casteel RC, Hays FA. Equilibrative nucleoside transporters-A review. NUCLEOSIDES NUCLEOTIDES & NUCLEIC ACIDS 2016; 36:7-30. [PMID: 27759477 DOI: 10.1080/15257770.2016.1210805] [Citation(s) in RCA: 125] [Impact Index Per Article: 15.6] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Equilibrative nucleoside transporters (ENTs) are polytopic integral membrane proteins that mediate the transport of nucleosides, nucleobases, and therapeutic analogs. The best-characterized ENTs are the human transporters hENT1 and hENT2. However, non-mammalian eukaryotic ENTs have also been studied (e.g., yeast, parasitic protozoa). ENTs are major pharmaceutical targets responsible for modulating the efficacy of more than 30 approved drugs. However, the molecular mechanisms and chemical determinants of ENT-mediated substrate recognition, binding, inhibition, and transport are poorly understood. This review highlights findings on the characterization of ENTs by surveying studies on genetics, permeant and inhibitor interactions, mutagenesis, and structural models of ENT function.
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Affiliation(s)
- Rebba C Boswell-Casteel
- a Department of Biochemistry and Molecular Biology , University of Oklahoma Health Sciences Center , Oklahoma City , OK , USA
| | - Franklin A Hays
- a Department of Biochemistry and Molecular Biology , University of Oklahoma Health Sciences Center , Oklahoma City , OK , USA.,b Stephenson Cancer Center , University of Oklahoma Health Sciences Center , Oklahoma City , OK , USA.,c Harold Hamm Diabetes Center , University of Oklahoma Health Sciences Center , Oklahoma City , OK , USA
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13
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N-linked glycosylation of N48 is required for equilibrative nucleoside transporter 1 (ENT1) function. Biosci Rep 2016; 36:BSR20160063. [PMID: 27480168 PMCID: PMC5006311 DOI: 10.1042/bsr20160063] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/29/2016] [Accepted: 08/01/2016] [Indexed: 11/29/2022] Open
Abstract
Our study confirmed that Asn48 of hENT1 is the only N-glycosylated residue when expressed in HEK293 cells, and loss of the N-glycan resulted in less hENT1 at the plasma membrane, as well as a loss of function and protein–protein self-interaction. Human equilibrative nucleoside transporter 1 (hENT1) transports nucleosides and nucleoside analogue drugs across cellular membranes and is necessary for the uptake of many anti-cancer, anti-parasitic and anti-viral drugs. Previous work, and in silico prediction, suggest that hENT1 is glycosylated at Asn48 in the first extracellular loop of the protein and that glycosylation plays a role in correct localization and function of hENT1. Site-directed mutagenesis of wild-type (wt) hENT1 removed potential glycosylation sites. Constructs (wt 3xFLAG-hENT1, N48Q-3xFLAG-hENT1 or N288Q-3xFLAG-hENT2) were transiently transfected into HEK293 cells and cell lysates were treated with or without peptide–N-glycosidase F (PNGase-F), followed by immunoblotting analysis. Substitution of N48 prevents hENT1 glycosylation, confirming a single N-linked glycosylation site. N48Q-hENT1 protein is found at the plasma membrane in HEK293 cells but at lower levels compared with wt hENT1 based on S-(4-nitrobenzyl)-6-thioinosine (NBTI) binding analysis (wt 3xFLAG-ENT1 Bmax, 41.5±2.9 pmol/mg protein; N48Q-3xFLAG-ENT1 Bmax, 13.5±0.45 pmol/mg protein) and immunofluorescence microscopy. Although present at the membrane, chloroadenosine transport assays suggest that N48Q-hENT1 is non-functional (wt 3xFLAG-ENT1, 170.80±44.01 pmol/mg protein; N48Q-3xFLAG-ENT1, 57.91±17.06 pmol/mg protein; mock-transfected 74.31±19.65 pmol/mg protein). Co-immunoprecipitation analyses suggest that N48Q ENT1 is unable to interact with self or with wt hENT1. Based on these data we propose that glycosylation at N48 is critical for the localization, function and oligomerization of hENT1.
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