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Affiliation(s)
- Christopher L. Cioffi
- Departments of Basic and Clinical Sciences and Pharmaceutical Sciences, Albany College of Pharmacy and Health Sciences , Albany, NY, USA
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2
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López-Corcuera B, Geerlings A, Aragón C. Glycine neurotransmitter transporters: an update. Mol Membr Biol 2009. [DOI: 10.1080/09687680010028762] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/16/2022]
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Abstract
Glycine has multiple neurotransmitter functions in the central nervous system (CNS). In the spinal cord and brainstem of vertebrates, it serves as a major inhibitory neurotransmitter. In addition, it participates in excitatory neurotransmission by modulating the activity of the N-methyl-D-aspartate (NMDA) subtype of glutamate receptors. The extracellular concentrations of glycine are regulated by Na+/Cl(-)-dependent glycine transporters (GlyTs), which are expressed in neurons and adjacent glial cells. Considerable progress has been made recently towards elucidating the in vivo roles of GlyTs in the CNS. The generation and analysis of animals carrying targeted disruptions of GlyT genes (GlyT knockout mice) have allowed investigators to examine the different contributions of individual GlyT subtypes to synaptic transmission. In addition, they have provided animal models for two hereditary human diseases, glycine encephalopathy and hyperekplexia. Selective GlyT inhibitors have been shown to modulate neurotransmission and might constitute promising therapeutic tools for the treatment of psychiatric and neurological disorders such as schizophrenia and pain. Therefore, pharmacological and genetic studies indicate that GlyTs are key regulators of both glycinergic inhibitory and glutamatergic excitatory neurotransmission. This chapter describes our present understanding of the functions of GlyTs and their involvement in the fine-tuning of neuronal communication.
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Affiliation(s)
- J Gomeza
- Department of Pharmacology, The Panum Institute, University of Copenhagen, Blegdamsvej 3, 2200 Copenhagen, Denmark.
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4
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Abstract
Glycine exerts multiple functions in the central nervous system, as an inhibitory neurotransmitter through activation of specific, Cl--permeable, ligand-gated ionotropic receptors and as an obligatory co-agonist with glutamate on the activation of N-methyl-D-aspartate (NMDA) receptors. In some areas of the central nervous system, glycine seems to be co-released with gamma-aminobutyric acid (GABA), the main inhibitory amino acid neurotransmitter. The synaptic action of glycine ends by active recapture through sodium- and chloride-coupled glycine transporters located in glial and neuronal plasma membranes, whose structure-function relationship is being studied. The trafficking and plasma membrane expressions of these proteins are controlled by regulatory mechanisms. Glycine transporter inhibitors may find application in the treatment of muscle tone defects, epilepsy, schizophrenia, pain and neurodegenerative disorders. This review deals on recent progress on localization, transport mechanisms, structure, regulation and pharmacology of the glycine transporters (GLYTs).
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Affiliation(s)
- Carmen Aragón
- Centro de Biología Molecular Severo Ochoa, Facultad de Ciencias, Universidad Autónoma de Madrid, 28049 Madrid, Spain.
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Martínez-Maza R, Poyatos I, López-Corcuera B, N úñez E, Giménez C, Zafra F, Aragón C. The role of N-glycosylation in transport to the plasma membrane and sorting of the neuronal glycine transporter GLYT2. J Biol Chem 2001; 276:2168-73. [PMID: 11036075 DOI: 10.1074/jbc.m006774200] [Citation(s) in RCA: 86] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Glycine transporter GLYT2 is an axonal glycoprotein involved in the removal of glycine from the synaptic cleft. To elucidate the role of the carbohydrate moiety on GLYT2 function, we analyzed the effect of the disruption of the putative N-glycosylation sites on the transport activity, intracellular traffic in COS cells, and asymmetrical distribution of this protein in polarized Madin-Darby canine kidney (MDCK) cells. Transport activity was reduced by 35-40% after enzymatic deglycosylation of the transporter reconstituted into liposomes. Site-directed mutagenesis of the four glycosylation sites (Asn-345, Asn-355, Asn-360, and Asn-366), located in the large extracellular loop of GLYT2, produced an inactive protein that was retained in intracellular compartments when transiently transfected in COS cells or in nonpolarized MDCK cells. When expressed in polarized MDCK cells, wild type GLYT2 localizes in the apical surface as assessed by transport and biotinylation assays. However, a partially unglycosylated mutant (triple mutant) was distributed in a nonpolarized manner in MDCK cells. The apical localization of GLYT2 occurred by a glycolipid rafts independent pathway.
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Affiliation(s)
- R Martínez-Maza
- Centro de Biologia Molecular Severo Ochoa, Facultad de Ciencias, Universidad Autónoma de Madrid, Consejo Superior de Investigaciones Cientificas, 28049 Madrid, Spain
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Zelikovic I, Budreau-Patters A. Cl- and membrane potential dependence of amino acid transport across the rat renal brush border membrane. Mol Genet Metab 1999; 67:236-47. [PMID: 10381331 DOI: 10.1006/mgme.1999.2866] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The relative roles of the anion present and the membrane potential in the operation of each of the seven amino acid transport systems in the renal tubular brush border membrane were explored by manipulating transmembrane potential and chemical gradients across the membrane. The effect of various external anions with different permeabilities of the membrane and of valinomycin-generated K+ diffusion potential on Na+-coupled amino acid accumulation by rat renal brush border membrane vesicles was examined. Accumulation of all amino acids examined, except for cystine, was membrane potential dependent. The highest voltage dependence was observed for taurine (equivalent to glucose) and l-methionine. Addition of taurine uptake values obtained under each electrical gradient (inside negative) and a chemical gradient (100 mM NaCl out) condition yielded markedly lower values than under conditions where there was a combined electrochemical gradient. Cl- gradient rather than merely imposing a voltage gradient was a specific mediator of Na+-coupled transport of l-proline, taurine, l-glutamic acid, and glycine across the brush border membrane. Cl- gradient alone under Na+-equilibrated conditions could energize an overshoot of taurine accumulation by vesicles providing evidence that taurine is energetically activated by and coupled to Cl- transport. These data suggest that Na+-linked transport of most amino acids across the tubular luminal membrane is an electrogenic positive process and for proline, taurine, glutamic acid, and glycine, a Cl--requiring process. A negative intracellular potential combined with luminal chloride is required for optimal Na+-coupled transport of these amino acids across the luminal membrane of the proximal tubule. The coupling of Cl- to the transport of these osmoprotective amino acids may enhance their volume regulatory effect in kidney cells and other mammalian cells.
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Affiliation(s)
- I Zelikovic
- Department of Pediatrics, University of Washington School of Medicine, Seattle, Washington, USA.
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Abstract
Rapid termination of the synaptic action of glutamate (Glu) and glycine (Gly) is achieved by uptake into the presynaptic terminal and glial cells. In the vertebrate CNS, Gly acts both as an inhibitory neurotransmitter and as a Glu modulator or coagonist at postsynaptic N-methyl-D-aspartate (NMDA) receptors. We have previously described NMDA receptors in Müller cells of chick retina coupled to the phosphoinositide cascade, the entry of calcium, and the activation of protein kinase C (PKC; López-Colomé et al. Glia 9:127-135, 1993). A colocalization of Gly transporters and NMDA receptors has been reported in brain tissue (Smith et al. Neuron 8:927-936, 1992); since the concentration of Gly could participate in the modulation of Glu excitatory transmission in the vertical pathways of the retina, transport of Gly in monolayer cultures of Müller cells was studied. Gly transport was found pH-sensitive with an optimum at pH 7.4. Kinetic analysis of the saturation curve for Gly within a concentration range of 0.01-2 mM, revealed two components of transport: a low-affinity system with Km = 1.7 mM, Vmax = 30 nmol/10 min/mg protein, and a high-affinity one with a Km = 27 microM, Vmax = 3 nmol/10 min/mg protein. Both systems were Na+ -dependent; the high-affinity system proved also dependent on external Cl- and was inhibited by sarcosine, characteristic of GLYT1 transporters. The inhibition of low-affinity uptake by 2-(methylamino)isobutyric acid (MeAIB) and 2-aminoisobutyric acid (AIB) suggests the presence of transport system A in Müller cells. The process is energy-requiring, since Gly transport was decreased by metabolic inhibitors. Data obtained are in keeping with a modulatory role for Müller glia on excitatory transmission in the retina.
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Affiliation(s)
- A Gadea
- Instituto de Fisiología Celular, Departamento de Neurociencias, UNAM, México, D.F., México
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8
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Aragón C, López-Corcuera B. Purification, hydrodynamic properties, and glycosylation analysis of glycine transporters. Methods Enzymol 1998; 296:3-17. [PMID: 9779437 DOI: 10.1016/s0076-6879(98)96003-7] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/09/2023]
Affiliation(s)
- C Aragón
- Centro de Biología Molecular Severo Ochoa, Facultad de Ciencias, Universidad Autónoma de Madrid, Spain
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9
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Villa A, García-Simón MI, Blanco P, Sesé B, Bogónez E, Satrustegui J. Affinity chromatography purification of mitochondrial inner membrane proteins with calcium transport activity. BIOCHIMICA ET BIOPHYSICA ACTA 1998; 1373:347-59. [PMID: 9733995 DOI: 10.1016/s0005-2736(98)00120-5] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Immobilized calcium affinity chromatography was used to obtain a preparation enriched in calcium transporters from Triton X-100 extracts of rat liver mitochondria inner membranes (PPCT). The PPCT were reconstituted into preformed asolectin liposomes which contained 120 mM KCl as internal high K+ medium. 45Ca2+ uptake into proteoliposomes was studied under conditions favoring electrophoretic uptake, and H+i/45Ca2+o or Na+i/45Ca2+o exchange, to test for the presence of the three calcium transport modes present in mitochondria. 45Ca2+ uptake in liposomes was studied in parallel. Na+i/45Ca2+o exchange activity was not detectable. H+i/45Ca2+o exchange activity measured in the presence of a pH gradient (acid inside) obtained after suspension in low K medium in the presence of nigericin, was 100-200 nmoles 45Ca2+ per mg protein in 30 s. 45Ca2+ uptake in voltage-dependent assays (a K+ diffusion membrane potential induced by valinomycin in the presence of methylamine) was not electrophoretic since it was stimulated by carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP) and probably due to secondary Ca2+/H+ countertransport. H+i/45Ca2+o uptake showed a saturable component at around 80 microM Ca and was coupled to an increase in internal pH in pyranine-loaded PPCT proteoliposomes. 45Ca2+ uptake in PPCT proteoliposomes could also be driven by a pH gradient obtained by raising external pH in high K+ medium. The results are consistent with the presence of a functional nH+/Ca2+ antiporter. Polyclonal antibodies raised against the PPCT were able to immunoprecipitate the H+/45Ca2+ uptake activity and recognized two major bands in the PPCT with molecular masses of about 66 kDa and 55 kDa. This is the first report of a partial purified protein(s) which may represent the H+/Ca2+ exchanger of the inner mitochondrial membrane, and represents an important step towards its identification.
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Affiliation(s)
- A Villa
- Departamento de Biología Molecular, Centro de Biología Molecular 'Severo Ochoa', C.S.I.C.-Universidad Autónoma de Madrid, Campus de Cantoblanco, 28049-Madrid, Spain
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10
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Olivares L, Aragón C, Giménez C, Zafra F. The role of N-glycosylation in the targeting and activity of the GLYT1 glycine transporter. J Biol Chem 1995; 270:9437-42. [PMID: 7721869 DOI: 10.1074/jbc.270.16.9437] [Citation(s) in RCA: 82] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
To elucidate the role of N-glycosylation in the function of the high affinity glycine transporter GLYT1, we have investigated the effect of the glycosylation inhibitor tunicamycin as well as the effect of the disruption of the putative glycosylation sites by site-directed mutagenesis. SDS-polyacrylamide gel electrophoresis of proteins from GLYT1-transfected COS cells reveals a major band of 80-100 kDa and a minor one of 57 kDa. Treatment with tunicamycin produces a 40% inhibition in transport activity and a decrease in the intensity of the 80-100-kDa band, whereas the 57-kDa band decreases in size to yield a 47-kDa protein corresponding to the unglycosylated form of the transporter. Simultaneous mutation of Asn-169, Asn-172, Asn-182, and Asn-188 to Gln also produces the 47-kDa form of the protein, indicating that there are no additional sites for N-glycosylation. Progressive mutation of the potential glycosylation sites produces a progressive decrease in transport activity and in size of the protein, indicating that the four putative glycosylation sites are actually glycosylated. N-Glycosylation of the GLYT1 is not indispensable for the transport activity itself, as demonstrated by enzymatic deglycosylation of the transporter. Analysis of surface proteins by biotinylation and by immunofluorescence demonstrates that a significant portion of the unglycosylated GLYT1 mutant remains in the intracellular compartment. This suggests that the carbohydrate moiety of glycine transporter GLYT1 is necessary for the proper trafficking of the protein to the plasma membrane.
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Affiliation(s)
- L Olivares
- Centro de Biología Molecular Severo Ochoa, Facultad de Ciencias, Universidad Autónoma de Madrid, Spain
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11
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Affiliation(s)
- N C Danbolt
- Anatomical Institute, University of Oslo, Norway
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12
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Olivares L, Aragón C, Giménez C, Zafra F. Carboxyl terminus of the glycine transporter GLYT1 is necessary for correct processing of the protein. J Biol Chem 1994. [DOI: 10.1016/s0021-9258(18)46941-4] [Citation(s) in RCA: 27] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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Liu W, Leibach FH, Ganapathy V. Characterization of the glycine transport system GLYT 1 in human placental choriocarcinoma cells (JAR). BIOCHIMICA ET BIOPHYSICA ACTA 1994; 1194:176-84. [PMID: 8075134 DOI: 10.1016/0005-2736(94)90218-6] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Transport of glycine in confluent monolayer cultures of JAR human placental choriocarcinoma cells was investigated. Glycine uptake in these cells was made up of two components, one being Na(+)-dependent with no requirement for Cl- and the other being dependent on Na+ as well as Cl-. Substrate specificity studies indicated that distinct transport systems were responsible for these two components. Alanine inhibited the Na(+)-dependent glycine uptake preferentially and the Na(+)- and Cl(-)-dependent glycine uptake represented > 95% of total uptake in the presence of 5 mM alanine. Competition experiments revealed that the Na(+)- and Cl(-)-dependent transport system exhibited a very narrow substrate specificity with affinity toward only glycine and its derivatives such as sarcosine, glycine methyl ester and glycine ethyl ester. These characteristics identify the transport system as GLYT 1. This system showed high affinity for glycine, with a Michaelis-Menten constant of 15 microM. The Na+:Cl-: glycine stoichiometry appeared to be 2:1:1. Treatment of JAR cells with calmodulin antagonists resulted in the inhibition of the transport function of GLYT 1 and this inhibition was solely due to a decrease in the maximal velocity of the system with no change in the substrate affinity. It is concluded that the placental choriocarcinoma cell line JAR expresses robust activity of the glycine transporter GLYT 1 and that the activity of this transporter is under the regulation of calmodulin-dependent cellular processes.
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Affiliation(s)
- W Liu
- Department of Biochemistry and Molecular Biology, Medical College of Georgia, Augusta 30912-2100
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14
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Núñez E, Aragón C. Structural analysis and functional role of the carbohydrate component of glycine transporter. J Biol Chem 1994. [DOI: 10.1016/s0021-9258(19)89477-2] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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15
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Worrall DM, Williams DC. Sodium ion-dependent transporters for neurotransmitters: a review of recent developments. Biochem J 1994; 297 ( Pt 3):425-36. [PMID: 7906513 PMCID: PMC1137850 DOI: 10.1042/bj2970425] [Citation(s) in RCA: 60] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Affiliation(s)
- D M Worrall
- Department of Biochemistry, University College, Dublin, Ireland
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16
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Nakanishi M, Tetsuka T, Kagawa Y, Moriyama A, Sasaki M, Hirata H. Solubilization and reconstitution of high- and low-affinity Na(+)-dependent neutral L-alpha-amino acid transporters from rabbit small intestine. BIOCHIMICA ET BIOPHYSICA ACTA 1993; 1151:193-200. [PMID: 8373795 DOI: 10.1016/0005-2736(93)90104-8] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
High- and low-affinity Na(+)-dependent neutral L-alpha-amino acid transporters were solubilized with 0.25% octaethylene glycol dodecyl ether (C12E8) after removal of the proteins from the brush-border membrane vesicles with 2% CHAPS and 4 M urea. When the CHAPS-insoluble protein was treated with papain before its solubilization with C12E8, a substantial amount of protein was removed without any decrease of the transport activities. The solubilized transporters were reconstituted into proteoliposomes after removal of C12E8 with Bio-Beads SM2. Several parameters proved to be important for optimal reconstitution efficiency: (a) the type of detergent, and (b) the phospholipid/protein and detergent/protein ratio during reconstitution, and (c) the salt concentration during reconstitution. Reconstituted proteoliposomes showed rapid uptake of neutral L-alpha-amino acids but not imino acid, basic or acidic amino acids driven by an electrochemical potential of Na+ (out > in). The uptakes under low- and high-substrate condition were further augmented by an artificial membrane potential introduced by K+ diffusion via valinomycin (negative interior). Kinetic analysis revealed that both the brush-border membranes and the solubilized fraction involved two carrier-mediated pathways for alanine transport. The kinetic parameters were determined by curve fitting with a computer to be Kt1 = 0.28 mM (0.21 mM) and Kt2 = 43.2 mM (28.4 mM), respectively (those with brush-border membrane vesicles in parentheses). Studies on the specific activities for transport of individual amino acids under low or high substrate concentration and the cross-inhibitory effects of various amino acids on alanine uptake (low concentration) revealed that these transporters possess broad specificity for neutral L-alpha-amino acids.
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Affiliation(s)
- M Nakanishi
- Department of Biochemistry, Jichi Medical School, Tochigi, Japan
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17
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Hydrodynamic properties and immunological identification of the sodium- and chloride-coupled glycine transporter. J Biol Chem 1993. [DOI: 10.1016/s0021-9258(18)53987-9] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
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18
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Liu QR, Nelson H, Mandiyan S, López-Corcuera B, Nelson N. Cloning and expression of a glycine transporter from mouse brain. FEBS Lett 1992; 305:110-4. [PMID: 1618338 DOI: 10.1016/0014-5793(92)80875-h] [Citation(s) in RCA: 129] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
We have isolated a cDNA clone from a mouse brain library encoding the glycine transporter (GLYT). Xenopus oocytes injected with a synthetic mRNA accumulated [3h]glycine to levels of up to 80-fold above control values. The uptake was specific for glycine and dependent on the presence of Na+ and Cl- in the medium. The cDNA sequence predicts a highly hydrophobic protein of 633 amino acids with 12 potential transmembrane helices. The predicted amino acid sequence has 40-45% identity to the GABA, noradrenaline, serotonin and dopamine transporters. This implies that all of these neurotransmitter transporters may have evolved from a common ancestral gene that diverged into the GABA, glycine and catecholamine subfamilies at nearly the same time.
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Affiliation(s)
- Q R Liu
- Roche Institute of Molecular Biology, Roche Research Center, Nutley, NJ 07110
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19
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Smith KE, Borden LA, Hartig PR, Branchek T, Weinshank RL. Cloning and expression of a glycine transporter reveal colocalization with NMDA receptors. Neuron 1992; 8:927-35. [PMID: 1534013 DOI: 10.1016/0896-6273(92)90207-t] [Citation(s) in RCA: 331] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
A complementary DNA clone encoding a transporter for glycine has been isolated from rat brain, and its functional properties have been examined in mammalian cells. The transporter displays high affinity for glycine (KM approximately 100 microM) and is dependent on external Na+ and Cl-. Northern blot analysis indicates that the distribution of the mRNA encoding the glycine transporter is restricted to the nervous system. In situ hybridization data are consistent with roles for the transporter in both glycine neurotransmission and glycine modulation of N-methyl-D-aspartate (NMDA) receptors in the hippocampus. The identification of this transporter therefore opens the study of the molecular mechanisms underlying both inhibitory glycinergic transmission and NMDA-mediated excitatory transmission.
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Affiliation(s)
- K E Smith
- Synaptic Pharmaceutical Corporation, Paramus, New Jersey 07652
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20
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Purification of the sodium- and chloride-coupled glycine transporter from central nervous system. J Biol Chem 1991. [DOI: 10.1016/s0021-9258(18)54301-5] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
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21
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Alcántara R, López-Corcuera B, Aragón C. Group-selective reagent modification of the sodium- and chloride-coupled glycine transporter under native and reconstituted conditions. BIOCHIMICA ET BIOPHYSICA ACTA 1991; 1067:64-70. [PMID: 1651114 DOI: 10.1016/0005-2736(91)90026-5] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Glycine transporter from rat brain stem and spinal cord is inactivated by specific sulfhydryl reagents. Modification of lysine residues also promotes a decrease of the transporter activity but in a lesser extent than that promoted by thiol group reagents. Mercurials showed a more marked inhibitory effect than maleimide derivatives. SH groups display a similar reactivity for p-chloromercuribenzenesulfonate (pCMBS) and mersalyl in synaptosomal membrane vesicles and proteoliposomes reconstituted with the solubilized transporter. However, different reactivity is observed with N-ethylmaleimide (MalNEt), the greatest effect being attained in membrane vesicles. The rate of inactivation by pCMBS and MalNEt is pseudo-first-order showing time- and concentration-dependence. pCMBS and MalNEt decrease the Vmax for glycine transport and to a lesser extent act on the apparent Km. Treatment with dithiothreitol (DTT) of the transporter modified by pCMBS results in a complete restoration of transporter activity indicating that the effect exercised by the reagent is specific for cysteine residues on the protein. It is concluded that SH groups are involved in the glycine transporter function and that these critical residues are mostly located in a relatively hydrophilic environment of the protein.
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Affiliation(s)
- R Alcántara
- Departamento de Biología Molecular, Centro de Biología Molecular, Facultad de Ciencias, Universidad Autónoma, Madrid, Spain
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22
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Lopez-Corcuera B, Kanner BI, Aragón C. Reconstitution and partial purification of the sodium and chloride-coupled glycine transporter from rat spinal cord. BIOCHIMICA ET BIOPHYSICA ACTA 1989; 983:247-52. [PMID: 2569327 DOI: 10.1016/0005-2736(89)90240-x] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
The (Na+ + Cl-)-coupled glycine transporter has been solubilized from rat spinal cord with 2% cholate and purified 6-7-fold using Wheat Germ Agglutinin-Sepharose 4B. Transport activity - as determined upon reconstitution of the fraction into liposomes - was retained on the column and eluted by N-acetylglucosamine. When the glycoprotein fraction was depleted of the N-acetylglucosamine and applied to a second round of lectin-chromatography, the glycine transport activity was retained and again could be eluted by the sugar. The transporter activity reconstituted from the glycoprotein fraction retains the same features displayed in the synaptic plasma membrane vesicles, namely an absolute dependence on sodium and chloride, electrogenicity and efflux and exchange properties. These observations indicate that the (Na+ + Cl-)-coupled glycine transporter is a glycoprotein.
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Affiliation(s)
- B Lopez-Corcuera
- Departamento de Biología Molecular, Facultad de Ciencias, Universidad Autónoma, Madrid, Spain
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