1
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Ni C, Hong M. Oligomerization of drug transporters: Forms, functions, and mechanisms. Acta Pharm Sin B 2024; 14:1924-1938. [PMID: 38799641 PMCID: PMC11119549 DOI: 10.1016/j.apsb.2024.01.007] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2023] [Revised: 12/07/2023] [Accepted: 01/05/2024] [Indexed: 05/29/2024] Open
Abstract
Drug transporters are essential players in the transmembrane transport of a wide variety of clinical drugs. The broad substrate spectra and versatile distribution pattern of these membrane proteins infer their pharmacological and clinical significance. With our accumulating knowledge on the three-dimensional structure of drug transporters, their oligomerization status has become a topic of intense study due to the possible functional roles carried out by such kind of post-translational modification (PTM). In-depth studies of oligomeric complexes formed among drug transporters as well as their interactions with other regulatory proteins can help us better understand the regulatory mechanisms of these membrane proteins, provide clues for the development of novel drugs, and improve the therapeutic efficacy. In this review, we describe different oligomerization forms as well as their structural basis of major drug transporters in the ATP-binding cassette and solute carrier superfamilies, summarize our current knowledge on the influence of oligomerization for protein expression level and transport function of these membrane proteins, and discuss the regulatory mechanisms of oligomerization. Finally, we highlight the challenges associated with the current oligomerization studies and propose some thoughts on the pharmaceutical application of this important drug transporter PTM.
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Affiliation(s)
- Chunxu Ni
- College of Life Sciences, South China Agricultural University, Guangzhou 510642, China
| | - Mei Hong
- College of Life Sciences, South China Agricultural University, Guangzhou 510642, China
- Guangdong Provincial Key Laboratory of Protein Function and Regulation in Agricultural Organisms, South China Agricultural University, Guangzhou 510642, China
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2
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Wright NJ, Zhang F, Suo Y, Kong L, Yin Y, Fedor JG, Sharma K, Borgnia MJ, Im W, Lee SY. Antiviral drug recognition and elevator-type transport motions of CNT3. Nat Chem Biol 2024:10.1038/s41589-024-01559-8. [PMID: 38418906 DOI: 10.1038/s41589-024-01559-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2023] [Accepted: 01/22/2024] [Indexed: 03/02/2024]
Abstract
Nucleoside analogs have broad clinical utility as antiviral drugs. Key to their systemic distribution and cellular entry are human nucleoside transporters. Here, we establish that the human concentrative nucleoside transporter 3 (CNT3) interacts with antiviral drugs used in the treatment of coronavirus infections. We report high-resolution single-particle cryo-electron microscopy structures of bovine CNT3 complexed with antiviral nucleosides N4-hydroxycytidine, PSI-6206, GS-441524 and ribavirin, all in inward-facing states. Notably, we found that the orally bioavailable antiviral molnupiravir arrests CNT3 in four distinct conformations, allowing us to capture cryo-electron microscopy structures of drug-loaded outward-facing and drug-loaded intermediate states. Our studies uncover the conformational trajectory of CNT3 during membrane transport of a nucleoside analog antiviral drug, yield new insights into the role of interactions between the transport and the scaffold domains in elevator-like domain movements during drug translocation, and provide insights into the design of nucleoside analog antiviral prodrugs with improved oral bioavailability.
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Affiliation(s)
- Nicholas J Wright
- Department of Biochemistry, Duke University School of Medicine, Durham, NC, USA
| | - Feng Zhang
- Department of Biochemistry, Duke University School of Medicine, Durham, NC, USA
| | - Yang Suo
- Department of Biochemistry, Duke University School of Medicine, Durham, NC, USA
| | - Lingyang Kong
- Departments of Biological Sciences, Chemistry, and Bioengineering, Lehigh University, Bethlehem, PA, USA
| | - Ying Yin
- Department of Biochemistry, Duke University School of Medicine, Durham, NC, USA
| | - Justin G Fedor
- Department of Biochemistry, Duke University School of Medicine, Durham, NC, USA
| | - Kedar Sharma
- Department of Health and Human Services, Genome Integrity and Structural Biology Laboratory, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, Durham, NC, USA
| | - Mario J Borgnia
- Department of Health and Human Services, Genome Integrity and Structural Biology Laboratory, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, Durham, NC, USA
| | - Wonpil Im
- Departments of Biological Sciences, Chemistry, and Bioengineering, Lehigh University, Bethlehem, PA, USA
| | - Seok-Yong Lee
- Department of Biochemistry, Duke University School of Medicine, Durham, NC, USA.
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3
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Duan H, Hu K, Zheng D, Cheng Y, Zhang Z, Wang Y, Liang L, Hu J, Luo T. Recognition and release of uridine and hCNT3: From multivariate interactions to molecular design. Int J Biol Macromol 2022; 223:1562-1577. [PMID: 36402394 DOI: 10.1016/j.ijbiomac.2022.11.145] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2022] [Revised: 11/09/2022] [Accepted: 11/14/2022] [Indexed: 11/18/2022]
Abstract
As a vital target for the development of novel anti-cancer drugs, human concentrative nucleoside transporter 3 (hCNT3) has been widely concerned. Nevertheless, the lack of a comprehensive understanding of molecular interactions and motion mechanism has greatly hindered the development of novel inhibitors against hCNT3. In this paper, molecular recognition of hCNT3 with uridine was investigated with molecular docking, conventional molecular dynamics (CMD) simulations and adaptive steered molecular dynamics (ASMD) simulations; and then, the uridine derivatives with possibly highly inhibitory activity were designed. The result of CMD showed that more water-mediated H-bonds and lower binding free energy both explained higher recognition ability and transported efficiency of hCNT3. While during the ASMD simulation, nucleoside transport process involved the significant side-chain flip of residues F321 and Q142, a typical substrate-induced conformational change. By considering electronegativity, atomic radius, functional group and key H-bonds factors, 25 novel uridine derivatives were constructed. Subsequently, the receptor-ligand binding free energy was predicted by solvated interaction energy (SIE) method to determine the inhibitor c8 with the best potential performance. This work not only revealed molecular recognition and release mechanism of uridine with hCNT3, but also designed a series of uridine derivatives to obtain lead compounds with potential high activity.
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Affiliation(s)
- Huaichuan Duan
- Department of Head, Neck and Mammary Gland Oncology, Cancer Center, Clinical Research Center for Breast, West China Hospital, Sichuan University, Chengdu, China
| | - Kaixuan Hu
- School of Pharmaceutical Sciences, Jishou University, Jishou, China
| | - Dan Zheng
- Department of Head, Neck and Mammary Gland Oncology, Cancer Center, Clinical Research Center for Breast, West China Hospital, Sichuan University, Chengdu, China
| | - Yan Cheng
- Department of Head, Neck and Mammary Gland Oncology, Cancer Center, Clinical Research Center for Breast, West China Hospital, Sichuan University, Chengdu, China
| | - Zelan Zhang
- Key Laboratory of Medicinal and Edible Plants Resources Development of Sichuan Education Department, School of Pharmacy, Chengdu University, Chengdu, China
| | - Yueteng Wang
- Key Laboratory of Medicinal and Edible Plants Resources Development of Sichuan Education Department, School of Pharmacy, Chengdu University, Chengdu, China
| | - Li Liang
- Key Laboratory of Medicinal and Edible Plants Resources Development of Sichuan Education Department, School of Pharmacy, Chengdu University, Chengdu, China
| | - Jianping Hu
- Key Laboratory of Medicinal and Edible Plants Resources Development of Sichuan Education Department, School of Pharmacy, Chengdu University, Chengdu, China
| | - Ting Luo
- Department of Head, Neck and Mammary Gland Oncology, Cancer Center, Clinical Research Center for Breast, West China Hospital, Sichuan University, Chengdu, China.
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4
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Wiuf A, Steffen JH, Becares ER, Grønberg C, Mahato DR, Rasmussen SGF, Andersson M, Croll T, Gotfryd K, Gourdon P. The two-domain elevator-type mechanism of zinc-transporting ZIP proteins. SCIENCE ADVANCES 2022; 8:eabn4331. [PMID: 35857505 PMCID: PMC9278863 DOI: 10.1126/sciadv.abn4331] [Citation(s) in RCA: 14] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/01/2021] [Accepted: 05/27/2022] [Indexed: 05/13/2023]
Abstract
Zinc is essential for all organisms and yet detrimental at elevated levels. Hence, homeostasis of this metal is tightly regulated. The Zrt/Irt-like proteins (ZIPs) represent the only zinc importers in metazoans. Mutations in human ZIPs cause serious disorders, but the mechanism by which ZIPs transfer zinc remains elusive. Hitherto, structural information is only available for a model member, BbZIP, and as a single, ion-bound conformation, precluding mechanistic insights. Here, we elucidate an inward-open metal-free BbZIP structure, differing substantially in the relative positions of the two separate domains of ZIPs. With accompanying coevolutional analyses, mutagenesis, and uptake assays, the data point to an elevator-type transport mechanism, likely shared within the ZIP family, unifying earlier functional data. Moreover, the structure reveals a previously unknown ninth transmembrane segment that is important for activity in vivo. Our findings outline the mechanistic principles governing ZIP-protein transport and enhance the molecular understanding of ZIP-related disorders.
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Affiliation(s)
- Anders Wiuf
- Department of Biomedical Sciences, University of Copenhagen, Mærsk Tower 7-9, Nørre Allé 14, DK-2200 Copenhagen, Denmark
| | - Jonas Hyld Steffen
- Department of Biomedical Sciences, University of Copenhagen, Mærsk Tower 7-9, Nørre Allé 14, DK-2200 Copenhagen, Denmark
| | - Eva Ramos Becares
- Department of Biomedical Sciences, University of Copenhagen, Mærsk Tower 7-9, Nørre Allé 14, DK-2200 Copenhagen, Denmark
| | - Christina Grønberg
- Department of Biomedical Sciences, University of Copenhagen, Mærsk Tower 7-9, Nørre Allé 14, DK-2200 Copenhagen, Denmark
| | - Dhani Ram Mahato
- Department of Chemistry, Umeå University, Linnaeus Väg 10, SE-901 87 Umeå, Sweden
| | - Søren G. F. Rasmussen
- Department of Neuroscience, University of Copenhagen, Maersk Tower 7-5, Nørre Allé 14, DK-2200 Copenhagen, Denmark
| | - Magnus Andersson
- Department of Chemistry, Umeå University, Linnaeus Väg 10, SE-901 87 Umeå, Sweden
| | - Tristan Croll
- Cambridge Institute for Medical Research, Department of Haematology, University of Cambridge, Keith Peters Building, Hills Rd., Cambridge CB2 0XY, UK
| | - Kamil Gotfryd
- Department of Biomedical Sciences, University of Copenhagen, Mærsk Tower 7-9, Nørre Allé 14, DK-2200 Copenhagen, Denmark
| | - Pontus Gourdon
- Department of Biomedical Sciences, University of Copenhagen, Mærsk Tower 7-9, Nørre Allé 14, DK-2200 Copenhagen, Denmark
- Department of Experimental Medical Science, Lund University, Sölvegatan 19, SE-221 84 Lund, Sweden
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5
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Khera R, Mehdipour AR, Bolla JR, Kahnt J, Welsch S, Ermler U, Muenke C, Robinson CV, Hummer G, Xie H, Michel H. Cryo-EM structures of pentameric autoinducer-2 exporter from Escherichia coli reveal its transport mechanism. EMBO J 2022; 41:e109990. [PMID: 35698912 PMCID: PMC9475539 DOI: 10.15252/embj.2021109990] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2021] [Revised: 05/04/2022] [Accepted: 05/06/2022] [Indexed: 12/16/2022] Open
Abstract
Bacteria utilize small extracellular molecules to communicate in order to collectively coordinate their behaviors in response to the population density. Autoinducer-2 (AI-2), a universal molecule for both intra- and inter-species communication, is involved in the regulation of biofilm formation, virulence, motility, chemotaxis, and antibiotic resistance. While many studies have been devoted to understanding the biosynthesis and sensing of AI-2, very little information is available on its export. The protein TqsA from Escherichia coli, which belongs to the AI-2 exporter superfamily, has been shown to export AI-2. Here, we report the cryogenic electron microscopic structures of two AI-2 exporters (TqsA and YdiK) from E. coli at 3.35 Å and 2.80 Å resolutions, respectively. Our structures suggest that the AI-2 exporter exists as a homo-pentameric complex. In silico molecular docking and native mass spectrometry experiments were employed to demonstrate the interaction between AI-2 and TqsA, and the results highlight the functional importance of two helical hairpins in substrate binding. We propose that each monomer works as an independent functional unit utilizing an elevator-type transport mechanism.
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Affiliation(s)
- Radhika Khera
- Department of Molecular Membrane Biology, Max Planck Institute of Biophysics, Frankfurt am Main, Germany
| | - Ahmad R Mehdipour
- Department of Theoretical Biophysics, Max Planck Institute of Biophysics, Frankfurt am Main, Germany.,Centre for molecular modelling, Ghent University, Zwijnaarde, Belgium
| | - Jani R Bolla
- Physical and Theoretical Chemistry Laboratory, University of Oxford, Oxford, UK.,The Kavli Institute for Nanoscience Discovery, Oxford, UK.,Department of Plant Sciences, University of Oxford, Oxford, UK
| | - Joerg Kahnt
- Core Facility for Mass Spectrometry and Proteomics, Max Planck Institute for Terrestrial Microbiology, Marburg, Germany
| | - Sonja Welsch
- Central Electron Microscopy Facility, Max Planck Institute of Biophysics, Frankfurt am Main, Germany
| | - Ulrich Ermler
- Department of Molecular Membrane Biology, Max Planck Institute of Biophysics, Frankfurt am Main, Germany
| | - Cornelia Muenke
- Department of Molecular Membrane Biology, Max Planck Institute of Biophysics, Frankfurt am Main, Germany
| | - Carol V Robinson
- Physical and Theoretical Chemistry Laboratory, University of Oxford, Oxford, UK.,The Kavli Institute for Nanoscience Discovery, Oxford, UK
| | - Gerhard Hummer
- Department of Theoretical Biophysics, Max Planck Institute of Biophysics, Frankfurt am Main, Germany.,Institute of Biophysics, Goethe University Frankfurt, Frankfurt am Main, Germany
| | - Hao Xie
- Department of Molecular Membrane Biology, Max Planck Institute of Biophysics, Frankfurt am Main, Germany
| | - Hartmut Michel
- Department of Molecular Membrane Biology, Max Planck Institute of Biophysics, Frankfurt am Main, Germany
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6
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Chen I, Wu Q, Font J, Ryan RM. The twisting elevator mechanism of glutamate transporters reveals the structural basis for the dual transport-channel functions. Curr Opin Struct Biol 2022; 75:102405. [PMID: 35709614 DOI: 10.1016/j.sbi.2022.102405] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2022] [Revised: 05/10/2022] [Accepted: 05/12/2022] [Indexed: 11/16/2022]
Abstract
Glutamate transporters facilitate the removal of this excitatory neurotransmitter from the synapse. Increasing evidence indicates that this process is linked to intrinsic chloride channel activity that is thermodynamically uncoupled from substrate transport. A recent cryo-EM structure of GltPh - an archaeal homolog of the glutamate transporters - in an open channel state has shed light on the structural basis for channel opening formed at the interface of two domains within the transporter which is gated by two clusters of hydrophobic residues. These transporters cycle through several conformational states during the transport process, including the chloride conducting state, which appears to be stabilised by protein-membrane interactions and membrane deformation. Several point mutations that perturb the chloride conductance can have detrimental effects and are linked to the pathogenesis of the neurological disorder, episodic ataxia type 6.
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Affiliation(s)
- Ichia Chen
- School of Medical Sciences, Faculty of Medicine and Health, University of Sydney, NSW, Australia
| | - Qianyi Wu
- School of Medical Sciences, Faculty of Medicine and Health, University of Sydney, NSW, Australia
| | - Josep Font
- School of Medical Sciences, Faculty of Medicine and Health, University of Sydney, NSW, Australia
| | - Renae M Ryan
- School of Medical Sciences, Faculty of Medicine and Health, University of Sydney, NSW, Australia.
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7
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Kohga H, Mori T, Tanaka Y, Yoshikaie K, Taniguchi K, Fujimoto K, Fritz L, Schneider T, Tsukazaki T. Crystal structure of the lipid flippase MurJ in a "squeezed" form distinct from its inward- and outward-facing forms. Structure 2022; 30:1088-1097.e3. [PMID: 35660157 DOI: 10.1016/j.str.2022.05.008] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2022] [Revised: 03/15/2022] [Accepted: 05/10/2022] [Indexed: 11/29/2022]
Abstract
The bacterial peptidoglycan enclosing the cytoplasmic membrane is a fundamental cellular architecture. The integral membrane protein MurJ plays an essential role in flipping the cell wall building block Lipid II across the cytoplasmic membrane for peptidoglycan biosynthesis. Previously reported crystal structures of MurJ have elucidated its V-shaped inward- or outward-facing forms with an internal cavity for substrate binding. MurJ transports Lipid II using its cavity through conformational transitions between these two forms. Here, we report two crystal structures of inward-facing forms from Arsenophonus endosymbiont MurJ and an unprecedented crystal structure of Escherichia coli MurJ in a "squeezed" form, which lacks a cavity to accommodate the substrate, mainly because of the increased proximity of transmembrane helices 2 and 8. Subsequent molecular dynamics simulations supported the hypothesis that the squeezed form is an intermediate conformation. This study fills a gap in our understanding of the Lipid II flipping mechanism.
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Affiliation(s)
- Hidetaka Kohga
- Nara Institute of Science and Technology, Ikoma, Nara 630-0192, Japan
| | - Takaharu Mori
- Theoretical Molecular Science Laboratory, RIKEN Cluster for Pioneering Research, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
| | - Yoshiki Tanaka
- Nara Institute of Science and Technology, Ikoma, Nara 630-0192, Japan
| | | | | | - Kei Fujimoto
- Nara Institute of Science and Technology, Ikoma, Nara 630-0192, Japan
| | - Lisa Fritz
- Institute for Pharmaceutical Microbiology, University Hospital Bonn, University of Bonn, Meckenheimer Allee 168, 53115 Bonn, Germany
| | - Tanja Schneider
- Institute for Pharmaceutical Microbiology, University Hospital Bonn, University of Bonn, Meckenheimer Allee 168, 53115 Bonn, Germany
| | - Tomoya Tsukazaki
- Nara Institute of Science and Technology, Ikoma, Nara 630-0192, Japan.
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8
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Dinh HX, Singh D, Gomez de la Cruz D, Hensel G, Kumlehn J, Mascher M, Stein N, Perovic D, Ayliffe M, Moscou MJ, Park RF, Pourkheirandish M. The barley leaf rust resistance gene Rph3 encodes a predicted membrane protein and is induced upon infection by avirulent pathotypes of Puccinia hordei. Nat Commun 2022; 13:2386. [PMID: 35501307 PMCID: PMC9061838 DOI: 10.1038/s41467-022-29840-1] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2021] [Accepted: 04/03/2022] [Indexed: 01/04/2023] Open
Abstract
Leaf rust, caused by Puccinia hordei, is an economically significant disease of barley, but only a few major resistance genes to P. hordei (Rph) have been cloned. In this study, gene Rph3 was isolated by positional cloning and confirmed by mutational analysis and transgenic complementation. The Rph3 gene, which originated from wild barley and was first introgressed into cultivated Egyptian germplasm, encodes a unique predicted transmembrane resistance protein that differs from all known plant disease resistance proteins at the amino acid sequence level. Genetic profiles of diverse accessions indicated limited genetic diversity in Rph3 in domesticated germplasm, and higher diversity in wild barley from the Eastern Mediterranean region. The Rph3 gene was expressed only in interactions with Rph3-avirulent P. hordei isolates, a phenomenon also observed for transcription activator-like effector-dependent genes known as executors conferring resistance to Xanthomonas spp. Like known transmembrane executors such as Bs3 and Xa7, heterologous expression of Rph3 in N. benthamiana induced a cell death response. The isolation of Rph3 highlights convergent evolutionary processes in diverse plant-pathogen interaction systems, where similar defence mechanisms evolved independently in monocots and dicots. Leaf rust is an economically significant disease of barley. Here the authors describe cloning of the barley Rph3 leaf rust resistance gene and reveal it encodes a predicted transmembrane protein that is expressed upon infection by Rph3-avirulent Puccinia hordei isolates.
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9
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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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10
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Wright NJ, Lee SY. Recent advances on the inhibition of human solute carriers: Therapeutic implications and mechanistic insights. Curr Opin Struct Biol 2022; 74:102378. [PMID: 35487145 DOI: 10.1016/j.sbi.2022.102378] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2021] [Revised: 03/02/2022] [Accepted: 03/18/2022] [Indexed: 11/03/2022]
Abstract
Solute carriers (SLCs) are membrane transport proteins tasked with mediating passage of hydrophilic molecules across lipid bilayers. Despite the extensive roles played in all aspects of human biology, SLCs remain vastly under-explored as therapeutic targets. In this brief review, we first discuss a few successful cases of drugs that exert their mechanisms of action through inhibition of human SLCs, and introduce select examples of human SLCs that have untapped therapeutic potential. We then highlight two recent structural studies which uncovered detailed structural mechanisms of inhibition exhibited against two different human major facilitator superfamily (MFS) transporters of clinical relevance.
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Affiliation(s)
- Nicholas J Wright
- Department of Biochemistry, Duke University Medical Center, 303 Research Drive, Durham, NC, 27710, USA. https://twitter.com/@nick_rite
| | - Seok-Yong Lee
- Department of Biochemistry, Duke University Medical Center, 303 Research Drive, Durham, NC, 27710, USA.
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11
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Beckstein O, Naughton F. General principles of secondary active transporter function. BIOPHYSICS REVIEWS 2022; 3:011307. [PMID: 35434715 PMCID: PMC8984959 DOI: 10.1063/5.0047967] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/17/2021] [Accepted: 02/23/2022] [Indexed: 04/13/2023]
Abstract
Transport of ions and small molecules across the cell membrane against electrochemical gradients is catalyzed by integral membrane proteins that use a source of free energy to drive the energetically uphill flux of the transported substrate. Secondary active transporters couple the spontaneous influx of a "driving" ion such as Na+ or H+ to the flux of the substrate. The thermodynamics of such cyclical non-equilibrium systems are well understood, and recent work has focused on the molecular mechanism of secondary active transport. The fact that these transporters change their conformation between an inward-facing and outward-facing conformation in a cyclical fashion, called the alternating access model, is broadly recognized as the molecular framework in which to describe transporter function. However, only with the advent of high resolution crystal structures and detailed computer simulations, it has become possible to recognize common molecular-level principles between disparate transporter families. Inverted repeat symmetry in secondary active transporters has shed light onto how protein structures can encode a bi-stable two-state system. Based on structural data, three broad classes of alternating access transitions have been described as rocker-switch, rocking-bundle, and elevator mechanisms. More detailed analysis indicates that transporters can be understood as gated pores with at least two coupled gates. These gates are not just a convenient cartoon element to illustrate a putative mechanism but map to distinct parts of the transporter protein. Enumerating all distinct gate states naturally includes occluded states in the alternating access picture and also suggests what kind of protein conformations might be observable. By connecting the possible conformational states and ion/substrate bound states in a kinetic model, a unified picture emerges in which the symporter, antiporter, and uniporter functions are extremes in a continuum of functionality. As usual with biological systems, few principles and rules are absolute and exceptions are discussed as well as how biological complexity may be integrated in quantitative kinetic models that may provide a bridge from the structure to function.
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Affiliation(s)
- Oliver Beckstein
- Department of Physics, Arizona State University, Tempe, Arizona 85287, USA
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12
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Duan H, Zhou Y, Shi X, Luo Q, Gao J, Liang L, Liu W, Peng L, Deng D, Hu J. Allosteric and transport modulation of human concentrative nucleoside transporter 3 at the atomic scale. Phys Chem Chem Phys 2021; 23:25401-25413. [PMID: 34751688 DOI: 10.1039/d1cp03756k] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Nucleosides are important precursors of nucleotide synthesis in cells, and nucleoside transporters play an important role in many physiological processes by mediating transmembrane transport and absorption. During nucleoside transport, such proteins undergo a significant conformational transition between the outward- and inward-facing states, which leads to alternating access of the substrate-binding site to either side of the membrane. In this work, a variety of molecular simulation methods have been applied to comparatively investigate the motion modes of human concentrative nucleoside transporter 3 (hCNT3) in three states, as well as global and local cavity conformational changes; and finally, a possible elevator-like transport mechanism consistent with experimental data was proposed. The results of the Gaussian network model (GNM) and anisotropic network model (ANM) show that hCNT3 as a whole tends to contract inwards and shift towards a membrane inside, exhibiting an allosteric process that is more energetically favorable than the rigid conversion. To reveal the complete allosteric process of hCNT3 in detail, a series of intermediate conformations were obtained by an adaptive anisotropic network model (aANM). One of the simulated intermediate states is similar to that of a crystal structure, which indicates that the allosteric process is reliable; the state with lower energy is slightly inclined to the inward-facing structure rather than the expected intermediate crystal structure. The final HOLE analysis showed that except for the outward-facing state, the transport channels were gradually enlarged, which was conductive to the directional transport of nucleosides. Our work provides a theoretical basis for the multistep elevator-like transportation mechanism of nucleosides, which helps to further understand the dynamic recognition between nucleoside substrates and hCNT3 as well as the design of nucleoside anticancer drugs.
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Affiliation(s)
- Huaichuan Duan
- School of Pharmacy, Sichuan Industrial Institute of Antibiotics, Chengdu University, Chengdu, China.
| | - Yanxia Zhou
- Key Laboratory of Birth Defects and Related Disease of Women and Children of MOE, State Key Laboratory of Biotherapy, Department of Obstetrics, West China Second Hospital, Sichuan University, Chengdu, China.
| | - Xiaodong Shi
- School of Pharmacy, Sichuan Industrial Institute of Antibiotics, Chengdu University, Chengdu, China.
| | - Qing Luo
- School of Pharmacy, Sichuan Industrial Institute of Antibiotics, Chengdu University, Chengdu, China.
| | - Jiaxing Gao
- School of Pharmacy, Sichuan Industrial Institute of Antibiotics, Chengdu University, Chengdu, China.
| | - Li Liang
- School of Pharmacy, Sichuan Industrial Institute of Antibiotics, Chengdu University, Chengdu, China.
| | - Wei Liu
- School of Pharmacy, Sichuan Industrial Institute of Antibiotics, Chengdu University, Chengdu, China.
| | - Lianxin Peng
- School of Pharmacy, Sichuan Industrial Institute of Antibiotics, Chengdu University, Chengdu, China.
| | - Dong Deng
- Key Laboratory of Birth Defects and Related Disease of Women and Children of MOE, State Key Laboratory of Biotherapy, Department of Obstetrics, West China Second Hospital, Sichuan University, Chengdu, China.
| | - Jianping Hu
- School of Pharmacy, Sichuan Industrial Institute of Antibiotics, Chengdu University, Chengdu, China.
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13
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Thermostability-based binding assays reveal complex interplay of cation, substrate and lipid binding in the bacterial DASS transporter, VcINDY. Biochem J 2021; 478:3847-3867. [PMID: 34643224 PMCID: PMC8652582 DOI: 10.1042/bcj20210061] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2021] [Revised: 10/08/2021] [Accepted: 10/13/2021] [Indexed: 12/04/2022]
Abstract
The divalent anion sodium symporter (DASS) family of transporters (SLC13 family in humans) are key regulators of metabolic homeostasis, disruption of which results in protection from diabetes and obesity, and inhibition of liver cancer cell proliferation. Thus, DASS transporter inhibitors are attractive targets in the treatment of chronic, age-related metabolic diseases. The characterisation of several DASS transporters has revealed variation in the substrate selectivity and flexibility in the coupling ion used to power transport. Here, using the model DASS co-transporter, VcINDY from Vibrio cholerae, we have examined the interplay of the three major interactions that occur during transport: the coupling ion, the substrate, and the lipid environment. Using a series of high-throughput thermostability-based interaction assays, we have shown that substrate binding is Na+-dependent; a requirement that is orchestrated through a combination of electrostatic attraction and Na+-induced priming of the binding site architecture. We have identified novel DASS ligands and revealed that ligand binding is dominated by the requirement of two carboxylate groups in the ligand that are precisely distanced to satisfy carboxylate interaction regions of the substrate-binding site. We have also identified a complex relationship between substrate and lipid interactions, which suggests a dynamic, regulatory role for lipids in VcINDY's transport cycle.
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14
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Gonzalez-Resines S, Quinn PJ, Naftalin RJ, Domene C. Multiple Interactions of Glucose with the Extra-Membranous Loops of GLUT1 Aid Transport. J Chem Inf Model 2021; 61:3559-3570. [PMID: 34260246 DOI: 10.1021/acs.jcim.1c00310] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Molecular dynamics simulations amounting to ≈8 μs demonstrate that the glucose transporter GLUT1 undergoes structural fluctuations mediated by the fluidity of the lipid bilayer and the proximity to glucose. The fluctuations of GLUT1 increase as the glucose concentration is raised. These fluctuations are more pronounced when the lipid bilayer is in the fluid compared to the gel phase. Glucose interactions are confined to the extra-membranous residues when the lipid is in the gel phase but diffuses into the transmembrane regions in the fluid phase. Proximity of glucose to GLUT1 causes asynchronous expansions of key bottlenecks at the internal and external openings of the central pore. This is accomplished only by small conformational changes at the single residue level that lower the resistance to glucose movements, thereby permitting unsteered glucose and water movements along the entire length of the pore. When glucose is near salt bridges located at the external and internal openings of the central pore, the distance separating the polar amino acid residues guarding these apertures tends to increase in both fluid and gel phases. It is evident that the multiplicity of glucose interactions, obtained with high concentrations, amplifies the structural fluctuations in GLUT1. The findings that most of the salt bridges and the bottlenecks appear to be operated by glucose proximity suggest that the main triggers to activation of transport are located within the solvent accessible linker regions in the extramembranous zones.
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Affiliation(s)
| | - Peter J Quinn
- Department of Biochemistry, King's College London, London WC2R 2LS, U.K
| | - Richard J Naftalin
- BHF Centre of Research Excellence, School of Medicine and Life Sciences, King's College London, London WC2R 2LS, U.K
| | - Carmen Domene
- Departments of Chemistry, University of Bath, Bath BA2 7AX, U.K.,Chemistry Research Laboratory, University of Oxford, Mansfield Road, Oxford OX1 3TA, U.K
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15
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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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16
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Molecular basis for substrate recognition by the bacterial nucleoside transporter NupG. J Biol Chem 2021; 296:100479. [PMID: 33640454 PMCID: PMC8042404 DOI: 10.1016/j.jbc.2021.100479] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2020] [Revised: 02/22/2021] [Accepted: 02/24/2021] [Indexed: 11/20/2022] Open
Abstract
Nucleoside homeostasis, which is mediated by transporters and channels, is essential for all life on Earth. In Escherichia coli, NupG mediates the transport of nucleosides and was deemed to be the prototype of the nucleoside proton symporter (NHS) family and the major facilitator superfamily. To date, the substrate recognition and transport mechanisms of NHS transporters are still elusive. Here, we report two crystal structures of NupG (WT and D323A NupG) resolved at 3.0 Å. Both structures reveal an identical inward-open conformation. Together with molecular docking and molecular dynamics simulations and in vitro uridine-binding assays, we found that the uridine binding site, which locates in the central cavity between N and C domains of NupG, is constituted by R136, T140, F143, Q225, N228, Q261, E264, Y318, and F322. Moreover, we found that D323 is very important for substrate binding via in vitro uridine-binding assays using D323 mutations, although it does not have a direct contact with uridine. Our structural and biochemical data therefore provide an important framework for the mechanistic understanding of nucleoside transporters of the NHS family.
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17
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Elevator-type mechanisms of membrane transport. Biochem Soc Trans 2021; 48:1227-1241. [PMID: 32369548 PMCID: PMC7329351 DOI: 10.1042/bst20200290] [Citation(s) in RCA: 61] [Impact Index Per Article: 20.3] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2020] [Revised: 03/29/2020] [Accepted: 03/31/2020] [Indexed: 12/13/2022]
Abstract
Membrane transporters are integral membrane proteins that mediate the passage of solutes across lipid bilayers. These proteins undergo conformational transitions between outward- and inward-facing states, which lead to alternating access of the substrate-binding site to the aqueous environment on either side of the membrane. Dozens of different transporter families have evolved, providing a wide variety of structural solutions to achieve alternating access. A sub-set of structurally diverse transporters operate by mechanisms that are collectively named 'elevator-type'. These transporters have one common characteristic: they contain a distinct protein domain that slides across the membrane as a rigid body, and in doing so it 'drags" the transported substrate along. Analysis of the global conformational changes that take place in membrane transporters using elevator-type mechanisms reveals that elevator-type movements can be achieved in more than one way. Molecular dynamics simulations and experimental data help to understand how lipid bilayer properties may affect elevator movements and vice versa.
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18
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Huang Y, Jin F, Funato Y, Xu Z, Zhu W, Wang J, Sun M, Zhao Y, Yu Y, Miki H, Hattori M. Structural basis for the Mg 2+ recognition and regulation of the CorC Mg 2+ transporter. SCIENCE ADVANCES 2021; 7:7/7/eabe6140. [PMID: 33568487 PMCID: PMC7875539 DOI: 10.1126/sciadv.abe6140] [Citation(s) in RCA: 33] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/02/2020] [Accepted: 12/23/2020] [Indexed: 05/05/2023]
Abstract
The CNNM/CorC family proteins are Mg2+ transporters that are widely distributed in all domains of life. In bacteria, CorC has been implicated in the survival of pathogenic microorganisms. In humans, CNNM proteins are involved in various biological events, such as body absorption/reabsorption of Mg2+ and genetic disorders. Here, we determined the crystal structure of the Mg2+-bound CorC TM domain dimer. Each protomer has a single Mg2+ binding site with a fully dehydrated Mg2+ ion. The residues at the Mg2+ binding site are strictly conserved in both human CNNM2 and CNNM4, and many of these residues are associated with genetic diseases. Furthermore, we determined the structures of the CorC cytoplasmic region containing its regulatory ATP-binding domain. A combination of structural and functional analyses not only revealed the potential interface between the TM and cytoplasmic domains but also showed that ATP binding is important for the Mg2+ export activity of CorC.
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Affiliation(s)
- Yichen Huang
- State Key Laboratory of Genetic Engineering, Shanghai Key Laboratory of Bioactive Small Molecules, Collaborative Innovation Center of Genetics and Development, and Department of Physiology and Biophysics, School of Life Sciences, Fudan University, 2005 Songhu Road, Yangpu District, Shanghai 200438, China
| | - Fei Jin
- State Key Laboratory of Genetic Engineering, Shanghai Key Laboratory of Bioactive Small Molecules, Collaborative Innovation Center of Genetics and Development, and Department of Physiology and Biophysics, School of Life Sciences, Fudan University, 2005 Songhu Road, Yangpu District, Shanghai 200438, China
| | - Yosuke Funato
- Department of Cellular Regulation, Research Institute for Microbial Diseases, Osaka University, 3-1 Yamadaoka, Suita, Osaka 565-0871, Japan
| | - Zhijian Xu
- CAS Key Laboratory of Receptor Research and Drug Discovery and Design Center, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, 555 Zuchongzhi Road, Pudong New Area, Shanghai 201203, China
| | - Weiliang Zhu
- CAS Key Laboratory of Receptor Research and Drug Discovery and Design Center, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, 555 Zuchongzhi Road, Pudong New Area, Shanghai 201203, China
| | - Jing Wang
- School of Basic Medicine and Clinical Pharmacy, China Pharmaceutical University, Medical Building, Room 128, 639 Long-Mian Road, Nanjing 200098, China
| | - Minxuan Sun
- State Key Laboratory of Genetic Engineering, Shanghai Key Laboratory of Bioactive Small Molecules, Collaborative Innovation Center of Genetics and Development, and Department of Physiology and Biophysics, School of Life Sciences, Fudan University, 2005 Songhu Road, Yangpu District, Shanghai 200438, China
| | - Yimeng Zhao
- State Key Laboratory of Genetic Engineering, Shanghai Key Laboratory of Bioactive Small Molecules, Collaborative Innovation Center of Genetics and Development, and Department of Physiology and Biophysics, School of Life Sciences, Fudan University, 2005 Songhu Road, Yangpu District, Shanghai 200438, China
| | - Ye Yu
- School of Basic Medicine and Clinical Pharmacy, China Pharmaceutical University, Medical Building, Room 128, 639 Long-Mian Road, Nanjing 200098, China
| | - Hiroaki Miki
- Department of Cellular Regulation, Research Institute for Microbial Diseases, Osaka University, 3-1 Yamadaoka, Suita, Osaka 565-0871, Japan.
| | - Motoyuki Hattori
- State Key Laboratory of Genetic Engineering, Shanghai Key Laboratory of Bioactive Small Molecules, Collaborative Innovation Center of Genetics and Development, and Department of Physiology and Biophysics, School of Life Sciences, Fudan University, 2005 Songhu Road, Yangpu District, Shanghai 200438, China.
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19
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Dissecting the Conformational Dynamics of the Bile Acid Transporter Homologue ASBT NM. J Mol Biol 2021; 433:166764. [PMID: 33359100 DOI: 10.1016/j.jmb.2020.166764] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2020] [Revised: 12/11/2020] [Accepted: 12/11/2020] [Indexed: 11/21/2022]
Abstract
Apical sodium-dependent bile acid transporter (ASBT) catalyses uphill transport of bile acids using the electrochemical gradient of Na+ as the driving force. The crystal structures of two bacterial homologues ASBTNM and ASBTYf have previously been determined, with the former showing an inward-facing conformation, and the latter adopting an outward-facing conformation accomplished by the substitution of the critical Na+-binding residue glutamate-254 with an alanine residue. While the two crystal structures suggested an elevator-like movement to afford alternating access to the substrate binding site, the mechanistic role of Na+ and substrate in the conformational isomerization remains unclear. In this study, we utilized site-directed alkylation monitored by in-gel fluorescence (SDAF) to probe the solvent accessibility of the residues lining the substrate permeation pathway of ASBTNM under different Na+ and substrate conditions, and interpreted the conformational states inferred from the crystal structures. Unexpectedly, the crosslinking experiments demonstrated that ASBTNM is a monomer protein, unlike the other elevator-type transporters, usually forming a homodimer or a homotrimer. The conformational dynamics observed by the biochemical experiments were further validated using DEER measuring the distance between the spin-labelled pairs. Our results revealed that Na+ ions shift the conformational equilibrium of ASBTNM toward the inward-facing state thereby facilitating cytoplasmic uptake of substrate. The current findings provide a novel perspective on the conformational equilibrium of secondary active transporters.
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20
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Sampson CDD, Stewart MJ, Mindell JA, Mulligan C. Solvent accessibility changes in a Na +-dependent C 4-dicarboxylate transporter suggest differential substrate effects in a multistep mechanism. J Biol Chem 2020; 295:18524-18538. [PMID: 33087444 PMCID: PMC7939474 DOI: 10.1074/jbc.ra120.013894] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2020] [Revised: 10/06/2020] [Indexed: 11/06/2022] Open
Abstract
The divalent anion sodium symporter (DASS) family (SLC13) plays critical roles in metabolic homeostasis, influencing many processes, including fatty acid synthesis, insulin resistance, and adiposity. DASS transporters catalyze the Na+-driven concentrative uptake of Krebs cycle intermediates and sulfate into cells; disrupting their function can protect against age-related metabolic diseases and can extend lifespan. An inward-facing crystal structure and an outward-facing model of a bacterial DASS family member, VcINDY from Vibrio cholerae, predict an elevator-like transport mechanism involving a large rigid body movement of the substrate-binding site. How substrate binding influences the conformational state of VcINDY is currently unknown. Here, we probe the interaction between substrate binding and protein conformation by monitoring substrate-induced solvent accessibility changes of broadly distributed positions in VcINDY using a site-specific alkylation strategy. Our findings reveal that accessibility to all positions tested is modulated by the presence of substrates, with the majority becoming less accessible in the presence of saturating concentrations of both Na+ and succinate. We also observe separable effects of Na+ and succinate binding at several positions suggesting distinct effects of the two substrates. Furthermore, accessibility changes to a solely succinate-sensitive position suggests that substrate binding is a low-affinity, ordered process. Mapping these accessibility changes onto the structures of VcINDY suggests that Na+ binding drives the transporter into an as-yet-unidentified conformational state, involving rearrangement of the substrate-binding site-associated re-entrant hairpin loops. These findings provide insight into the mechanism of VcINDY, which is currently the only structurally characterized representative of the entire DASS family.
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Affiliation(s)
- Connor D D Sampson
- School of Biosciences, University of Kent, Canterbury, Kent, United Kingdom
| | - Matthew J Stewart
- School of Biosciences, University of Kent, Canterbury, Kent, United Kingdom
| | - Joseph A Mindell
- Membrane Transport Biophysics Section, Porter Neuroscience Research Center, NINDS, National Institutes of Health, Bethesda, Maryland, USA
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21
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Hu J. Toward unzipping the ZIP metal transporters: structure, evolution, and implications on drug discovery against cancer. FEBS J 2020; 288:5805-5825. [PMID: 33296542 DOI: 10.1111/febs.15658] [Citation(s) in RCA: 33] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2020] [Revised: 11/30/2020] [Accepted: 12/07/2020] [Indexed: 12/13/2022]
Abstract
The Zrt-/Irt-like protein (ZIP) family consists of divalent metal transporters, ubiquitous in all kingdoms of life. Since the discovery of the first ZIPs in the 1990s, the ZIP family has been expanding to contain tens of thousands of members playing key roles in uptake and homeostasis of life-essential trace elements, primarily zinc, iron and manganese. Some family members are also responsible for toxic metal (particularly cadmium) absorption and distribution. Their central roles in trace element biology, and implications in many human diseases, including cancers, have elicited interest across multiple disciplines for potential applications in biomedicine, agriculture and environmental protection. In this review and perspective, selected areas under rapid progress in the last several years, including structural biology, evolution, and drug discovery against cancers, are summarised and commented. Future research to address the most prominent issues associated with transport and regulation mechanisms are also discussed.
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Affiliation(s)
- Jian Hu
- Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, MI, USA.,Department of Chemistry, Michigan State University, East Lansing, MI, USA
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22
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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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23
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Xue J, Xie T, Zeng W, Jiang Y, Bai XC. Cryo-EM structures of human ZnT8 in both outward- and inward-facing conformations. eLife 2020; 9:e58823. [PMID: 32723473 PMCID: PMC7428307 DOI: 10.7554/elife.58823] [Citation(s) in RCA: 36] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2020] [Accepted: 07/28/2020] [Indexed: 01/02/2023] Open
Abstract
ZnT8 is a Zn2+/H+ antiporter that belongs to SLC30 family and plays an essential role in regulating Zn2+ accumulation in the insulin secretory granules of pancreatic β cells. However, the Zn2+/H+ exchange mechanism of ZnT8 remains unclear due to the lack of high-resolution structures. Here, we report the cryo-EM structures of human ZnT8 (HsZnT8) in both outward- and inward-facing conformations. HsZnT8 forms a dimeric structure with four Zn2+ binding sites within each subunit: a highly conserved primary site in transmembrane domain (TMD) housing the Zn2+ substrate; an interfacial site between TMD and C-terminal domain (CTD) that modulates the Zn2+ transport activity of HsZnT8; and two adjacent sites buried in the cytosolic domain and chelated by conserved residues from CTD and the His-Cys-His (HCH) motif from the N-terminal segment of the neighboring subunit. A comparison of the outward- and inward-facing structures reveals that the TMD of each HsZnT8 subunit undergoes a large structural rearrangement, allowing for alternating access to the primary Zn2+ site during the transport cycle. Collectively, our studies provide the structural insights into the Zn2+/H+ exchange mechanism of HsZnT8.
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Affiliation(s)
- Jing Xue
- Howard Hughes Medical Institute and Department of Physiology, University of Texas Southwestern Medical CenterDallasUnited States
- Department of Biophysics, University of Texas Southwestern Medical CenterDallasUnited States
| | - Tian Xie
- Department of Biophysics, University of Texas Southwestern Medical CenterDallasUnited States
- Department of Cell Biology, University of Texas Southwestern Medical CenterDallasUnited States
| | - Weizhong Zeng
- Howard Hughes Medical Institute and Department of Physiology, University of Texas Southwestern Medical CenterDallasUnited States
- Department of Biophysics, University of Texas Southwestern Medical CenterDallasUnited States
| | - Youxing Jiang
- Howard Hughes Medical Institute and Department of Physiology, University of Texas Southwestern Medical CenterDallasUnited States
- Department of Biophysics, University of Texas Southwestern Medical CenterDallasUnited States
| | - Xiao-chen Bai
- Department of Biophysics, University of Texas Southwestern Medical CenterDallasUnited States
- Department of Cell Biology, University of Texas Southwestern Medical CenterDallasUnited States
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24
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Functional (un)cooperativity in elevator transport proteins. Biochem Soc Trans 2020; 48:1047-1055. [PMID: 32573703 DOI: 10.1042/bst20190970] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2020] [Revised: 05/26/2020] [Accepted: 05/28/2020] [Indexed: 11/17/2022]
Abstract
The activity of enzymes is subject to regulation at multiple levels. Cooperativity, the interconnected behavior of active sites within a protein complex, directly affects protein activity. Cooperativity is a mode of regulation that requires neither extrinsic factors nor protein modifications. Instead, it allows enzymes themselves to modulate reaction rates. Cooperativity is an important regulatory mechanism in soluble proteins, but also examples of cooperative membrane proteins have been described. In this review, we summarize the current knowledge on interprotomer cooperativity in elevator-type proteins, a class of membrane transporters characterized by large rigid-body movements perpendicular to the membrane, and highlight well-studied examples and experimental approaches.
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25
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Altaweraqi RA, Yao SYM, Smith KM, Cass CE, Young JD. HPLC reveals novel features of nucleoside and nucleobase homeostasis, nucleoside metabolism and nucleoside transport. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2020; 1862:183247. [PMID: 32126230 DOI: 10.1016/j.bbamem.2020.183247] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/06/2019] [Revised: 02/16/2020] [Accepted: 02/18/2020] [Indexed: 12/31/2022]
Abstract
Humans possess three members of the cation-coupled concentrative nucleoside transporter CNT (SLC 28) family, hCNT1-3: hCNT1 is selective for pyrimidine nucleosides but also transports adenosine, hCNT2 transports purine nucleosides and uridine, and hCNT3 transports both pyrimidine and purine nucleosides. hCNT1/2 transport nucleosides using the transmembrane Na+ electrochemical gradient, while hCNT3 is both Na+- and H+-coupled. By producing recombinant hCNT3 in Xenopus laevis oocytes, we have used radiochemical high performance liquid chromatography (HPLC) analysis to investigate the metabolic fate of transported [3H] or [14C] pyrimidine and purine nucleosides once inside cells. With the exception of adenosine, transported nucleosides were generally subject to minimal intracellular metabolism. We also used radiochemical HPLC analysis to study the mechanism by which adenosine functions as a low Km, low Vmax permeant of hCNT1. hCNT1-producing oocytes were pre-loaded with [3H] uridine, after which efflux of accumulated radioactivity was measured in transport medium alone, or in the presence of extracellular non-radiolabelled adenosine or uridine. hCNT1-mediated [3H]-efflux was stimulated by extracellular uridine, but inhibited by extracellular adenosine, with >95% of the radioactivity exiting cells being unmetabolized uridine, consistent with a low transmembrane mobility of the hCNT1/adenosine complex. Humans also possess four members of the equilibrative nucleoside transporter ENT (SLC 29) family, hENT1-4. Of these, hENT1 and hENT2 transport both nucleosides and nucleobases into and out of cells, but their relative contributions to nucleoside and nucleobase homeostasis and, in particular, to adenosine signaling via purinoreceptors, are not known. We therefore used HPLC to determine plasma nucleoside and nucleobase concentrations in wild-type, mENT1-, mENT2- and mENT1/mENT2-knockout (KO) mice, and to compare the findings with knockout of mCNT3. Results demonstrated that ENT1 was more important than ENT2 or CNT3 in determining plasma adenosine concentrations, indicated modest roles of ENT1 in the homeostasis of other nucleosides, and suggested that none of the transporters is a major participant in handling of nucleobases.
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Affiliation(s)
- Reema A Altaweraqi
- Membrane Protein Disease Research Group, Department of Physiology, University of Alberta, Edmonton, Alberta T6G 2H7, Canada
| | - Sylvia Y M Yao
- Membrane Protein Disease Research Group, Department of Physiology, University of Alberta, Edmonton, Alberta T6G 2H7, Canada
| | - Kyla M Smith
- Membrane Protein Disease Research Group, Department of Physiology, University of Alberta, Edmonton, Alberta T6G 2H7, Canada
| | - Carol E Cass
- Membrane Protein Disease Research Group, Department of Oncology, University of Alberta, Edmonton, Alberta T6G 2H7, Canada
| | - James D Young
- Membrane Protein Disease Research Group, Department of Physiology, University of Alberta, Edmonton, Alberta T6G 2H7, Canada.
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26
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Yao SYM, Young JD. Inward- and outward-facing homology modeling of human concentrative nucleoside transporter 3 (hCNT3) predicts an elevator-type transport mechanism. Channels (Austin) 2019; 12:291-298. [PMID: 30096006 PMCID: PMC6986796 DOI: 10.1080/19336950.2018.1506665] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
The human SLC28 family of concentrative (Na+-dependent) nucleoside transporters has three members, hCNT1, hCNT2 and hCNT3. Previously, we have used heterologous expression in Xenopus laevis oocytes in combination with an engineered cysteine-less hCNT3 protein hCNT3(C-) to undertake systematic substituted cysteine accessibility method (SCAM) analysis of the transporter using the membrane-impermeant thiol reactive reagent p-chloromercuribenzene sulfonate (PCMBS). A continuous sequence of more than 300 individual amino acid residue positions were investigated, including the entire transport domain of the protein, as well as important elements of the corresponding hCNT3 structural domain. We have now constructed 3D structural homology models of hCNT3 based upon inward-facing, intermediates and outward-facing crystal structures of the bacterial CNT Neisseria wadsworthii CNTNW to show that all previously identified PCMBS-sensitive residues in hCNT3 are located above (ie on the extracellular side of) the key diagonal barrier scaffold domain TM9 in the transporter’s outward-facing conformation. In addition, both the Na+ and permeant binding sites of the mobile transport domain of hCNT3 are elevated from below the scaffold domain TM9 in the inward-facing conformation to above TM9 in the outward-facing conformation. The hCNT3 homology models generated in the present study validate our previously published PCMBS SCAM data, and confirm an elevator-type mechanism of membrane transport.
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Affiliation(s)
- Sylvia Y M Yao
- a Membrane Protein Disease Research Group, Department of Physiology , University of Alberta , Edmonton , Canada
| | - James D Young
- a Membrane Protein Disease Research Group, Department of Physiology , University of Alberta , Edmonton , Canada
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27
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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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28
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Kuk ACY, Hao A, Guan Z, Lee SY. Visualizing conformation transitions of the Lipid II flippase MurJ. Nat Commun 2019; 10:1736. [PMID: 30988294 PMCID: PMC6465408 DOI: 10.1038/s41467-019-09658-0] [Citation(s) in RCA: 44] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2019] [Accepted: 03/22/2019] [Indexed: 02/06/2023] Open
Abstract
The biosynthesis of many polysaccharides, including bacterial peptidoglycan and eukaryotic N-linked glycans, requires transport of lipid-linked oligosaccharide (LLO) precursors across the membrane by specialized flippases. MurJ is the flippase for the lipid-linked peptidoglycan precursor Lipid II, a key player in bacterial cell wall synthesis, and a target of recently discovered antibacterials. However, the flipping mechanism of LLOs including Lipid II remains poorly understood due to a dearth of structural information. Here we report crystal structures of MurJ captured in inward-closed, inward-open, inward-occluded and outward-facing conformations. Together with mutagenesis studies, we elucidate the conformational transitions in MurJ that mediate lipid flipping, identify the key ion for function, and provide a framework for the development of inhibitors. MurJ is the flippase for the lipid-linked peptidoglycan precursor Lipid II, a key player in bacterial cell wall synthesis, but the flipping mechanism remains poorly understood. Here authors report crystal structures of MurJ in different conformations which shed light on the MurJ transitions that mediate lipid flipping.
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Affiliation(s)
- Alvin C Y Kuk
- Department of Biochemistry, Duke University Medical Center, 303 Research Drive, Durham, NC, 27710, USA
| | - Aili Hao
- Department of Biochemistry, Duke University Medical Center, 303 Research Drive, Durham, NC, 27710, USA
| | - Ziqiang Guan
- Department of Biochemistry, Duke University Medical Center, 303 Research Drive, Durham, NC, 27710, USA
| | - Seok-Yong Lee
- Department of Biochemistry, Duke University Medical Center, 303 Research Drive, Durham, NC, 27710, USA.
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29
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Garibsingh RAA, Otte NJ, Ndaru E, Colas C, Grewer C, Holst J, Schlessinger A. Homology Modeling Informs Ligand Discovery for the Glutamine Transporter ASCT2. Front Chem 2018; 6:279. [PMID: 30137742 PMCID: PMC6066518 DOI: 10.3389/fchem.2018.00279] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2018] [Accepted: 06/20/2018] [Indexed: 12/12/2022] Open
Abstract
The Alanine-Serine-Cysteine transporter (SLC1A5, ASCT2), is a neutral amino acid exchanger involved in the intracellular homeostasis of amino acids in peripheral tissues. Given its role in supplying glutamine to rapidly proliferating cancer cells in several tumor types such as triple-negative breast cancer and melanoma, ASCT2 has been identified as a key drug target. Here we use a range of computational methods, including homology modeling and ligand docking, in combination with cell-based assays, to develop hypotheses for structure-function relationships in ASCT2. We perform a phylogenetic analysis of the SLC1 family and its prokaryotic homologs to develop a useful multiple sequence alignment for this protein family. We then generate homology models of ASCT2 in two different conformations, based on the human EAAT1 structures. Using ligand enrichment calculations, the ASCT2 models are then compared to crystal structures of various homologs for their utility in discovering ASCT2 inhibitors. We use virtual screening, cellular uptake and electrophysiology experiments to identify a non-amino acid ASCT2 inhibitor that is predicted to interact with the ASCT2 substrate binding site. Our results provide insights into the structural basis of substrate specificity in the SLC1 family, as well as a framework for the design of future selective and potent ASCT2 inhibitors as cancer therapeutics.
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Affiliation(s)
- Rachel-Ann A Garibsingh
- Department of Pharmacological Sciences, Icahn School of Medicine at Mount Sinai, New York, NY, United States
| | - Nicholas J Otte
- Origins of Cancer Program, Centenary Institute, University of Sydney, Sydney, NSW, Australia.,Sydney Medical School, University of Sydney, Sydney, NSW, Australia
| | - Elias Ndaru
- Department of Chemistry, Binghamton University, Binghamton, NY, United States
| | - Claire Colas
- Department of Pharmacological Sciences, Icahn School of Medicine at Mount Sinai, New York, NY, United States
| | - Christof Grewer
- Department of Chemistry, Binghamton University, Binghamton, NY, United States
| | - Jeff Holst
- Origins of Cancer Program, Centenary Institute, University of Sydney, Sydney, NSW, Australia.,Sydney Medical School, University of Sydney, Sydney, NSW, Australia
| | - Avner Schlessinger
- Department of Pharmacological Sciences, Icahn School of Medicine at Mount Sinai, New York, NY, United States
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30
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Luo P, Dai S, Zeng J, Duan J, Shi H, Wang J. Inward-facing conformation of l-ascorbate transporter suggests an elevator mechanism. Cell Discov 2018; 4:35. [PMID: 30038796 PMCID: PMC6048161 DOI: 10.1038/s41421-018-0037-y] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2018] [Revised: 05/03/2018] [Accepted: 05/08/2018] [Indexed: 11/09/2022] Open
Abstract
Various bacteria can ferment vitamin C (l-ascorbate) under anaerobic conditions via the phosphoenolpyruvate-dependent phosphotransferase system (PTS). The PTSasc system is composed of two soluble energy-coupling proteins (EI and HPr) and an enzyme II complex (EIIA, EIIB, and EIIC) for the anaerobic uptake of ascorbate and its phosphorylation to l-ascorbate 6-phosphate in vivo. Crystal structures of the ascorbate-bound EIIC component from Escherichia coli are available in outward-open and occluded conformations, suggesting a possible elevator mechanism of membrane transport. Despite these advances, it remains unclear how EIIC actually transports the substrate across the membrane and interacts with EIIB, which transfers its phosphate group to the EIIC-embedding ascorbate. Here, we present the crystal structure of the EIICasc component from Pasteurella multocida in the inward-facing conformation. By comparing three conformational states, we confirmed the original proposed model: the ascorbate translocation can be achieved by a rigid-body movement of the substrate-binding core domain relative to the V motif domain, which brings along the transmembrane helices TM2 and TM7 of the V motif domain to undergo a winding at the pivotal positions. Together with an in vivo transport assay, we completed the picture of the transport cycle of the ascorbate superfamily of membrane-spanning EIIC components of the PTS system.
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Affiliation(s)
- Ping Luo
- State Key Laboratory of Membrane Biology, Beijing Advanced Innovation Center for Structural Biology, School of Life Sciences, Tsinghua University, 100084 Beijing, China
| | - Shuliu Dai
- State Key Laboratory of Membrane Biology, Beijing Advanced Innovation Center for Structural Biology, School of Life Sciences, Tsinghua University, 100084 Beijing, China
| | - Jianwei Zeng
- State Key Laboratory of Membrane Biology, Beijing Advanced Innovation Center for Structural Biology, School of Life Sciences, Tsinghua University, 100084 Beijing, China
| | - Jinsong Duan
- State Key Laboratory of Membrane Biology, Beijing Advanced Innovation Center for Structural Biology, School of Life Sciences, Tsinghua University, 100084 Beijing, China
| | - Hui Shi
- State Key Laboratory of Membrane Biology, Beijing Advanced Innovation Center for Structural Biology, School of Life Sciences, Tsinghua University, 100084 Beijing, China
| | - Jiawei Wang
- State Key Laboratory of Membrane Biology, Beijing Advanced Innovation Center for Structural Biology, School of Life Sciences, Tsinghua University, 100084 Beijing, China
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31
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Structure of an EIIC sugar transporter trapped in an inward-facing conformation. Proc Natl Acad Sci U S A 2018; 115:5962-5967. [PMID: 29784777 DOI: 10.1073/pnas.1800647115] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The phosphoenolpyruvate-dependent phosphotransferase system (PTS) transports sugar into bacteria and phosphorylates the sugar for metabolic consumption. The PTS is important for the survival of bacteria and thus a potential target for antibiotics, but its mechanism of sugar uptake and phosphorylation remains unclear. The PTS is composed of multiple proteins, and the membrane-embedded Enzyme IIC (EIIC) component transports sugars across the membrane. Crystal structures of two members of the glucose superfamily of EIICs, bcChbC and bcMalT, were solved in the inward-facing and outward-facing conformations, and the structures suggest that sugar translocation could be achieved by movement of a structured domain that contains the sugar-binding site. However, different conformations have not been captured on the same transporter to allow precise description of the conformational changes. Here we present a crystal structure of bcMalT trapped in an inward-facing conformation by a mercury ion that bridges two strategically placed cysteine residues. The structure allows direct comparison of the outward- and inward-facing conformations and reveals a large rigid-body motion of the sugar-binding domain and other conformational changes that accompany the rigid-body motion. All-atom molecular dynamics simulations show that the inward-facing structure is stable with or without the cross-linking. The conformational changes were further validated by single-molecule Föster resonance energy transfer (smFRET). Combined, these results establish the elevator-type mechanism of transport in the glucose superfamily of EIIC transporters.
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32
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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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33
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Ramírez-Guadiana FH, Meeske AJ, Rodrigues CDA, Barajas-Ornelas RDC, Kruse AC, Rudner DZ. A two-step transport pathway allows the mother cell to nurture the developing spore in Bacillus subtilis. PLoS Genet 2017; 13:e1007015. [PMID: 28945739 PMCID: PMC5629000 DOI: 10.1371/journal.pgen.1007015] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2017] [Revised: 10/05/2017] [Accepted: 09/09/2017] [Indexed: 11/18/2022] Open
Abstract
One of the hallmarks of bacterial endospore formation is the accumulation of high concentrations of pyridine-2,6-dicarboxylic acid (dipicolinic acid or DPA) in the developing spore. This small molecule comprises 5–15% of the dry weight of dormant spores and plays a central role in resistance to both wet heat and desiccation. DPA is synthesized in the mother cell at a late stage in sporulation and must be translocated across two membranes (the inner and outer forespore membranes) that separate the mother cell and forespore. The enzymes that synthesize DPA and the proteins required to translocate it across the inner forespore membrane were identified over two decades ago but the factors that transport DPA across the outer forespore membrane have remained mysterious. Here, we report that SpoVV (formerly YlbJ) is the missing DPA transporter. SpoVV is produced in the mother cell during the morphological process of engulfment and specifically localizes in the outer forespore membrane. Sporulating cells lacking SpoVV produce spores with low levels of DPA and cells engineered to express SpoVV and the DPA synthase during vegetative growth accumulate high levels of DPA in the culture medium. SpoVV resembles concentrative nucleoside transporters and mutagenesis of residues predicted to form the substrate-binding pocket supports the idea that SpoVV has a similar structure and could therefore function similarly. These findings provide a simple two-step transport mechanism by which the mother cell nurtures the developing spore. DPA produced in the mother cell is first translocated into the intermembrane space by SpoVV and is then imported into the forespore by the SpoVA complex. This pathway is likely to be broadly conserved as DPA synthase, SpoVV, and SpoVA proteins can be found in virtually all endospore forming bacteria. All pathogenic and non-pathogenic bacteria that differentiate into dormant endospores including Clostridium difficile, Bacillus anthracis, and Bacillus subtilis, contain very high concentrations of the small molecule dipicolinic acid (DPA). This molecule displaces water in the spore core where it plays an integral role in spore resistance and dormancy. DPA and its contribution to spore dehydration were discovered in 1953 but the molecular basis for its accumulation in the spore has remained unclear. The developing endospore resides within a mother cell that assembles protective layers around the spore and nurtures it by providing mother-cell-produced molecules. DPA is produced in the mother cell at a late stage in development and then must be translocated across two membranes into the spore core. Here, we report the discovery of the missing DPA transporter, homologs of which are present in virtually all endospore-forming bacteria. Our data provide evidence for a simple two-step transport pathway in which the mother cell nurtures the developing spore by sequentially moving DPA across the two membranes that surround it.
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Affiliation(s)
| | - Alexander J. Meeske
- Department of Microbiology and Immunobiology, Harvard Medical School, Boston, MA, United States of America
| | | | | | - Andrew C. Kruse
- Department of Biochemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA, United States of America
| | - David Z. Rudner
- Department of Microbiology and Immunobiology, Harvard Medical School, Boston, MA, United States of America
- * E-mail:
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34
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Rahman MF, Askwith C, Govindarajan R. Molecular determinants of acidic pH-dependent transport of human equilibrative nucleoside transporter 3. J Biol Chem 2017; 292:14775-14785. [PMID: 28729424 DOI: 10.1074/jbc.m117.787952] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2017] [Revised: 07/11/2017] [Indexed: 12/16/2022] Open
Abstract
Equilibrative nucleoside transporters (ENTs) translocate hydrophilic nucleosides across cellular membranes and are essential for salvage nucleotide synthesis and purinergic signaling. Unlike the prototypic human ENT members hENT1 and hENT2, which mediate plasma membrane nucleoside transport at pH 7.4, hENT3 is an acidic pH-activated lysosomal transporter partially localized to mitochondria. Recent studies demonstrate that hENT3 is indispensable for lysosomal homeostasis, and that mutations in hENT3 can result in a spectrum of lysosomal storage-like disorders. However, despite hENT3's prominent role in lysosome pathophysiology, the molecular basis of hENT3-mediated transport is unknown. Therefore, we sought to examine the mechanistic basis of acidic pH-driven hENT3 nucleoside transport with site-directed mutagenesis, homology modeling, and [3H]adenosine flux measurements in mutant RNA-injected Xenopus oocytes. Scanning mutagenesis of putative residues responsible for pH-dependent transport via hENT3 revealed that the ionization states of Asp-219 and Glu-447, and not His, strongly determined the pH-dependent transport permissible-impermissible states of the transporter. Except for substitution with certain isosteric and polar residues, substitution of either Asp-219 or Glu-447 with any other residues resulted in robust activity that was pH-independent. Dual substitution of Asp-219 and Glu-447 to Ala sustained pH-independent activity over a broad range of physiological pH (pH 5.5-7.4), which also maintained stringent substrate selectivity toward endogenous nucleosides and clinically used nucleoside drugs. Our results suggest a putative pH-sensing role for Asp-219 and Glu-447 in hENT3 and that the size, ionization state, or electronegative polarity at these positions is crucial for obligate acidic pH-dependent activity.
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Affiliation(s)
- Md Fazlur Rahman
- From the Division of Pharmaceutics and Pharmaceutical Chemistry, College of Pharmacy
| | | | - Rajgopal Govindarajan
- From the Division of Pharmaceutics and Pharmaceutical Chemistry, College of Pharmacy, .,the Translational Therapeutics Program, Ohio State University Comprehensive Cancer Center, Ohio State University, Columbus, Ohio 43210
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35
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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: 10] [Impact Index Per Article: 1.4] [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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