1
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Marie AL, Gao Y, Ivanov AR. Native N-glycome profiling of single cells and ng-level blood isolates using label-free capillary electrophoresis-mass spectrometry. Nat Commun 2024; 15:3847. [PMID: 38719792 PMCID: PMC11079027 DOI: 10.1038/s41467-024-47772-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2023] [Accepted: 04/12/2024] [Indexed: 05/12/2024] Open
Abstract
The development of reliable single-cell dispensers and substantial sensitivity improvement in mass spectrometry made proteomic profiling of individual cells achievable. Yet, there are no established methods for single-cell glycome analysis due to the inability to amplify glycans and sample losses associated with sample processing and glycan labeling. In this work, we present an integrated platform coupling online in-capillary sample processing with high-sensitivity label-free capillary electrophoresis-mass spectrometry for N-glycan profiling of single mammalian cells. Direct and unbiased quantitative characterization of single-cell surface N-glycomes are demonstrated for HeLa and U87 cells, with the detection of up to 100 N-glycans per single cell. Interestingly, N-glycome alterations are unequivocally detected at the single-cell level in HeLa and U87 cells stimulated with lipopolysaccharide. The developed workflow is also applied to the profiling of ng-level amounts (5-500 ng) of blood-derived protein, extracellular vesicle, and total plasma isolates, resulting in over 170, 220, and 370 quantitated N-glycans, respectively.
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Affiliation(s)
- Anne-Lise Marie
- Barnett Institute of Chemical and Biological Analysis, Department of Chemistry and Chemical Biology, Northeastern University, 360 Huntington Ave., Boston, MA, 02115, US
| | - Yunfan Gao
- Barnett Institute of Chemical and Biological Analysis, Department of Chemistry and Chemical Biology, Northeastern University, 360 Huntington Ave., Boston, MA, 02115, US
| | - Alexander R Ivanov
- Barnett Institute of Chemical and Biological Analysis, Department of Chemistry and Chemical Biology, Northeastern University, 360 Huntington Ave., Boston, MA, 02115, US.
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2
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Ivanov A, Marie AL, Gao Y. In-capillary sample processing coupled to label-free capillary electrophoresis-mass spectrometry to decipher the native N-glycome of single mammalian cells and ng-level blood isolates. RESEARCH SQUARE 2023:rs.3.rs-3500983. [PMID: 38014012 PMCID: PMC10680937 DOI: 10.21203/rs.3.rs-3500983/v1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/29/2023]
Abstract
The development of reliable single-cell dispensers and substantial sensitivity improvement in mass spectrometry made proteomic profiling of individual cells achievable. Yet, there are no established methods for single-cell glycome analysis due to the inability to amplify glycans and sample losses associated with sample processing and glycan labeling. In this work, we developed an integrated platform coupling online in-capillary sample processing with high-sensitivity label-free capillary electrophoresis-mass spectrometry for N-glycan profiling of single mammalian cells. Direct and unbiased characterization and quantification of single-cell surface N-glycomes were demonstrated for HeLa and U87 cells, with the detection of up to 100 N-glycans per single cell. Interestingly, N-glycome alterations were unequivocally detected at the single-cell level in HeLa and U87 cells stimulated with lipopolysaccharide. The developed workflow was also applied to the profiling of ng-level amounts of blood-derived protein, extracellular vesicle, and total plasma isolates, resulting in over 170, 220, and 370 quantitated N-glycans, respectively.
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3
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Gao AYL, Lourdin-De Filippis E, Orlowski J, McKinney RA. Roles of Endomembrane Alkali Cation/Proton Exchangers in Synaptic Function and Neurodevelopmental Disorders. Front Physiol 2022; 13:892196. [PMID: 35547574 PMCID: PMC9081726 DOI: 10.3389/fphys.2022.892196] [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: 03/08/2022] [Accepted: 03/30/2022] [Indexed: 12/25/2022] Open
Abstract
Endomembrane alkali cation (Na+, K+)/proton (H+) exchangers (eNHEs) are increasingly associated with neurological disorders. These eNHEs play integral roles in regulating the luminal pH, processing, and trafficking of cargo along the secretory (Golgi and post-Golgi vesicles) and endocytic (early, recycling, and late endosomes) pathways, essential regulatory processes vital for neuronal development and plasticity. Given the complex morphology and compartmentalization of multipolar neurons, the contribution of eNHEs in maintaining optimal pH homeostasis and cargo trafficking is especially significant during periods of structural and functional development and remodeling. While the importance of eNHEs has been demonstrated in a variety of non-neuronal cell types, their involvement in neuronal function is less well understood. In this review, we will discuss their emerging roles in excitatory synaptic function, particularly as it pertains to cellular learning and remodeling. We will also explore their connections to neurodevelopmental conditions, including intellectual disability, autism, and attention deficit hyperactivity disorders.
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Affiliation(s)
- Andy Y L Gao
- Integrated Program in Neuroscience, McGill University, Montreal, QC, Canada.,Department of Pharmacology & Therapeutics, McGill University, Montreal, QC, Canada
| | | | - John Orlowski
- Department of Physiology, McGill University, Montreal, QC, Canada
| | - R Anne McKinney
- Department of Pharmacology & Therapeutics, McGill University, Montreal, QC, Canada
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4
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Elucidating the Mechanism Behind Sodium-Coupled Neurotransmitter Transporters by Reconstitution. Neurochem Res 2021; 47:127-137. [PMID: 34347265 DOI: 10.1007/s11064-021-03413-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2021] [Revised: 07/01/2021] [Accepted: 07/27/2021] [Indexed: 10/20/2022]
Abstract
Sodium-coupled neurotransmitter transporters play a fundamental role in the termination of synaptic neurotransmission, which makes them a major drug target. The reconstitution of these secondary active transporters into liposomes has shed light on their molecular transport mechanisms. From the earliest days of the reconstitution technique up to today's single-molecule studies, insights from live functioning transporters have been indispensable for our understanding of their physiological impact. The two classes of sodium-coupled neurotransmitter transporters, the neurotransmitter: sodium symporters and the excitatory amino acid transporters, have vastly different molecular structures, but complementary proteoliposome studies have sought to unravel their ion-dependence and transport kinetics. Furthermore, reconstitution experiments have been used on both protein classes to investigate the role of e.g. the lipid environment, of posttranslational modifications, and of specific amino acid residues in transport. Techniques that allow the detection of transport at a single-vesicle resolution have been developed, and single-molecule studies have started to reveal single transporter kinetics, which will expand our understanding of how transport across the membrane is facilitated at protein level. Here, we review a selection of the results and applications where the reconstitution of the two classes of neurotransmitter transporters has been instrumental.
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5
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Marques BL, Oliveira-Lima OC, Carvalho GA, de Almeida Chiarelli R, Ribeiro RI, Parreira RC, da Madeira Freitas EM, Resende RR, Klempin F, Ulrich H, Gomez RS, Pinto MCX. Neurobiology of glycine transporters: From molecules to behavior. Neurosci Biobehav Rev 2020; 118:97-110. [PMID: 32712279 DOI: 10.1016/j.neubiorev.2020.07.025] [Citation(s) in RCA: 22] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2020] [Revised: 07/07/2020] [Accepted: 07/17/2020] [Indexed: 12/16/2022]
Abstract
Glycine transporters (GlyTs) are Na+/Cl--dependent neurotransmitter transporters, responsible for l-glycine uptake into the central nervous system. GlyTs are members of the solute carrier family 6 (SLC6) and comprise glycine transporter type 1 (SLC6A9; GlyT1) and glycine transporter type 2 (SLC6A5; Glyt2). GlyT1 and GlyT2 are expressed on both astrocytes and neurons, but their expression pattern in brain tissue is foremost related to neurotransmission. GlyT2 is markedly expressed in brainstem, spinal cord and cerebellum, where it is responsible for glycine uptake into glycinergic and GABAergic terminals. GlyT1 is abundant in neocortex, thalamus and hippocampus, where it is expressed in astrocytes, and involved in glutamatergic neurotransmission. Consequently, inhibition of GlyT1 transporters can modulate glutamatergic neurotransmission through NMDA receptors, suggesting an alternative therapeutic strategy. In this review, we focus on recent progress in the understanding of GlyTs role in brain function and in various diseases, such as epilepsy, hyperekplexia, neuropathic pain, drug addiction, schizophrenia and stroke, as well as in neurodegenerative disorders.
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Affiliation(s)
- Bruno Lemes Marques
- Laboratório de Neuroquímica e Neurofarmacologia - Neurolab, Instituto de Ciências Biológicas, Universidade Federal de Goiás, Goiânia, GO, Brazil
| | - Onésia Cristina Oliveira-Lima
- Laboratório de Neuroquímica e Neurofarmacologia - Neurolab, Instituto de Ciências Biológicas, Universidade Federal de Goiás, Goiânia, GO, Brazil
| | - Gustavo Almeida Carvalho
- Laboratório de Neuroquímica e Neurofarmacologia - Neurolab, Instituto de Ciências Biológicas, Universidade Federal de Goiás, Goiânia, GO, Brazil
| | - Raphaela de Almeida Chiarelli
- Laboratório de Neuroquímica e Neurofarmacologia - Neurolab, Instituto de Ciências Biológicas, Universidade Federal de Goiás, Goiânia, GO, Brazil
| | - Raul Izidoro Ribeiro
- Laboratório de Neuroquímica e Neurofarmacologia - Neurolab, Instituto de Ciências Biológicas, Universidade Federal de Goiás, Goiânia, GO, Brazil
| | - Ricardo Cambraia Parreira
- Laboratório de Neuroquímica e Neurofarmacologia - Neurolab, Instituto de Ciências Biológicas, Universidade Federal de Goiás, Goiânia, GO, Brazil
| | - Elis Marra da Madeira Freitas
- Laboratório de Neuroquímica e Neurofarmacologia - Neurolab, Instituto de Ciências Biológicas, Universidade Federal de Goiás, Goiânia, GO, Brazil
| | - Rodrigo Ribeiro Resende
- Instituto de Ciências Biológicas, Universidade Federal de Minas Gerais, Belo Horizonte, MG, Brazil
| | | | - Henning Ulrich
- Departamento de Bioquímica, Instituto de Química, Universidade de São Paulo, São Paulo, SP, Brazil
| | - Renato Santiago Gomez
- Departamento de Cirurgia, Faculdade de Medicina, Universidade Federal de Minas Gerais, Belo Horizonte, MG, Brazil
| | - Mauro Cunha Xavier Pinto
- Laboratório de Neuroquímica e Neurofarmacologia - Neurolab, Instituto de Ciências Biológicas, Universidade Federal de Goiás, Goiânia, GO, Brazil.
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6
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Hauf K, Barsch L, Bauer D, Buchert R, Armbruster A, Frauenfeld L, Grasshoff U, Eulenburg V. GlyT1 encephalopathy: Characterization of presumably disease causing GlyT1 mutations. Neurochem Int 2020; 139:104813. [PMID: 32712301 DOI: 10.1016/j.neuint.2020.104813] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2020] [Revised: 06/26/2020] [Accepted: 07/09/2020] [Indexed: 12/22/2022]
Abstract
Glycine constitutes a major inhibitory neurotransmitter predominantly in caudal regions of the CNS. The extracellular glycine concentration is regulated synergistically by two high affinity, large capacity transporters GlyT1 and GlyT2. Both proteins are encoded by single genes SLC6A9 and SLC6A5, respectively. Mutations within the SLC6A5 gene encoding for GlyT2 have been demonstrated to be causative for hyperekplexia (OMIM #614618), a complex neuromuscular disease, in humans. In contrast, mutations within the SLC6A9 gene encoding for GlyT1 have been associated with GlyT1 encephalopathy (OMIM #601019), a disease causing severe postnatal respiratory deficiency, muscular hypotonia and arthrogryposis. The consequences of the respective GlyT1 mutations on the function of the transporter protein, however, have not yet been analysed. In this study we present the functional characterisation of three previously published GlyT1 mutations, two mutations predicted to cause truncation of GlyT1 (GlyT1Q573* and GlyT1K310F+fs*31) and one predicted to cause an amino acid exchange within transmembrane domain 7 of the transporter (GlyT1S407G), that are associated with GlyT1 encephalopathy. Additionally, the characterization of a novel mutation predicted to cause an amino acid exchange within transmembrane domain 1 (GlyT1V118M) identified in two fetuses showing increased nuchal translucency and arthrogryposis in routine ultrasound scans is demonstrated. We show that in recombinant systems the two presumably truncating mutations resulted in an intracellular retained GlyT1 protein lacking the intracellular C-terminal domain. In both cases this truncated protein did not show any residual transport activity. The point mutations, hGlyT1S407G and hGlyT1V118M, were processed correctly, but showed severely diminished activity, thus constituting a functional knock-out in-vivo. Taken together our data demonstrate that all analysed mutations of GlyT1 that have been identified in GlyT1 encephalopathy patients cause severe impairment of transporter function. This is consistent with the idea that loss of GlyT1 function is indeed causal for the disease phenotype.
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Affiliation(s)
- K Hauf
- Department of Anaesthesiology and Intensive Care, University of Leipzig, Leipzig, Germany
| | - L Barsch
- Department of Anaesthesiology and Intensive Care, University of Leipzig, Leipzig, Germany
| | - D Bauer
- Department of Biology, TU Darmstadt, Darmstadt, Germany
| | - R Buchert
- Institute of Medical Genetics and Applied Genomics, University of Tübingen, Tübingen, Germany
| | - A Armbruster
- Department of Biochemistry, University of Erlangen-Nuremberg, Erlangen, Germany
| | - L Frauenfeld
- Institute of Pathology and Neuropathology, University of Tübingen, Tübingen, Germany
| | - U Grasshoff
- Institute of Medical Genetics and Applied Genomics, University of Tübingen, Tübingen, Germany
| | - V Eulenburg
- Department of Anaesthesiology and Intensive Care, University of Leipzig, Leipzig, Germany; Department of Biochemistry, University of Erlangen-Nuremberg, Erlangen, Germany.
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7
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Kitzenmaier A, Schaefer N, Kasaragod VB, Polster T, Hantschmann R, Schindelin H, Villmann C. The P429L loss of function mutation of the human glycine transporter 2 associated with hyperekplexia. Eur J Neurosci 2019; 50:3906-3920. [DOI: 10.1111/ejn.14533] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2019] [Revised: 07/23/2019] [Accepted: 07/25/2019] [Indexed: 12/20/2022]
Affiliation(s)
- Alexandra Kitzenmaier
- Institute for Clinical Neurobiology Julius‐Maximilians‐University of Würzburg Würzburg Germany
| | - Natascha Schaefer
- Institute for Clinical Neurobiology Julius‐Maximilians‐University of Würzburg Würzburg Germany
| | - Vikram Babu Kasaragod
- Rudolf Virchow Centre for Experimental Biomedicine Julius‐Maximilians‐University of Würzburg Würzburg Germany
| | - Tilman Polster
- Pediatric Epileptology Mara Hospital Bethel Epilepsy Centre Bielefeld Germany
| | - Ralph Hantschmann
- Center for Developmental Pediatrics and Pediatric Neurology Hagen Germany
| | - Hermann Schindelin
- Rudolf Virchow Centre for Experimental Biomedicine Julius‐Maximilians‐University of Würzburg Würzburg Germany
| | - Carmen Villmann
- Institute for Clinical Neurobiology Julius‐Maximilians‐University of Würzburg Würzburg Germany
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8
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Khayat W, Hackett A, Shaw M, Ilie A, Dudding-Byth T, Kalscheuer VM, Christie L, Corbett MA, Juusola J, Friend KL, Kirmse BM, Gecz J, Field M, Orlowski J. A recurrent missense variant in SLC9A7 causes nonsyndromic X-linked intellectual disability with alteration of Golgi acidification and aberrant glycosylation. Hum Mol Genet 2019; 28:598-614. [PMID: 30335141 DOI: 10.1093/hmg/ddy371] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2018] [Accepted: 10/12/2018] [Indexed: 11/13/2022] Open
Abstract
We report two unrelated families with multigenerational nonsyndromic intellectual disability (ID) segregating with a recurrent de novo missense variant (c.1543C>T:p.Leu515Phe) in the alkali cation/proton exchanger gene SLC9A7 (also commonly referred to as NHE7). SLC9A7 is located on human X chromosome at Xp11.3 and has not yet been associated with a human phenotype. The gene is widely transcribed, but especially abundant in brain, skeletal muscle and various secretory tissues. Within cells, SLC9A7 resides in the Golgi apparatus, with prominent enrichment in the trans-Golgi network (TGN) and post-Golgi vesicles. In transfected Chinese hamster ovary AP-1 cells, the Leu515Phe mutant protein was correctly targeted to the TGN/post-Golgi vesicles, but its N-linked oligosaccharide maturation as well as that of a co-transfected secretory membrane glycoprotein, vesicular stomatitis virus G (VSVG) glycoprotein, was reduced compared to cells co-expressing SLC9A7 wild-type and VSVG. This correlated with alkalinization of the TGN/post-Golgi compartments, suggestive of a gain-of-function. Membrane trafficking of glycosylation-deficient Leu515Phe and co-transfected VSVG to the cell surface, however, was relatively unaffected. Mass spectrometry analysis of patient sera also revealed an abnormal N-glycosylation profile for transferrin, a clinical diagnostic marker for congenital disorders of glycosylation. These data implicate a crucial role for SLC9A7 in the regulation of TGN/post-Golgi pH homeostasis and glycosylation of exported cargo, which may underlie the cellular pathophysiology and neurodevelopmental deficits associated with this particular nonsyndromic form of X-linked ID.
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Affiliation(s)
- Wujood Khayat
- Department of Physiology, McGill University, Montreal, Quebec, Canada
| | - Anna Hackett
- Genetics of Learning Disability Service, Hunter Genetics, Waratah, NSW, Australia
| | - Marie Shaw
- Adelaide Medical School and Robinson Research Institute, The University of Adelaide, Adelaide, SA, Australia
| | - Alina Ilie
- Department of Physiology, McGill University, Montreal, Quebec, Canada
| | - Tracy Dudding-Byth
- Genetics of Learning Disability Service, Hunter Genetics, Waratah, NSW, Australia
| | - Vera M Kalscheuer
- Research Group Development and Disease, Max Planck Institute for Molecular Genetics, Berlin, Germany
| | - Louise Christie
- Genetics of Learning Disability Service, Hunter Genetics, Waratah, NSW, Australia
| | - Mark A Corbett
- Adelaide Medical School and Robinson Research Institute, The University of Adelaide, Adelaide, SA, Australia
| | | | - Kathryn L Friend
- Genetics and Molecular Pathology, SA Pathology, Adelaide, SA, Australia
| | - Brian M Kirmse
- Department of Pediatrics, Division of Medical Genetics, University of Mississippi Medical Center, Jackson, MS, USA
| | - Jozef Gecz
- Adelaide Medical School and Robinson Research Institute, The University of Adelaide, Adelaide, SA, Australia.,South Australian Health and Medical Research Institute, Adelaide, SA, Australia
| | - Michael Field
- Genetics of Learning Disability Service, Hunter Genetics, Waratah, NSW, Australia
| | - John Orlowski
- Department of Physiology, McGill University, Montreal, Quebec, Canada
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Horowitz B, Javitt G, Ilani T, Gat Y, Morgenstern D, Bard FA, Fass D. Quiescin sulfhydryl oxidase 1 (QSOX1) glycosite mutation perturbs secretion but not Golgi localization. Glycobiology 2018; 28:580-591. [PMID: 29757379 DOI: 10.1093/glycob/cwy044] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2017] [Accepted: 05/08/2018] [Indexed: 12/13/2022] Open
Abstract
Quiescin sulfhydryl oxidase 1 (QSOX1) catalyzes the formation of disulfide bonds in protein substrates. Unlike other enzymes with related activities, which are commonly found in the endoplasmic reticulum, QSOX1 is localized to the Golgi apparatus or secreted. QSOX1 is upregulated in quiescent fibroblast cells and secreted into the extracellular environment, where it contributes to extracellular matrix assembly. QSOX1 is also upregulated in adenocarcinomas, though the extent to which it is secreted in this context is currently unknown. To achieve a better understanding of factors that dictate QSOX1 localization and function, we aimed to determine how post-translational modifications affect QSOX1 trafficking and activity. We found a highly conserved N-linked glycosylation site to be required for QSOX1 secretion from fibroblasts and other cell types. Notably, QSOX1 lacking a glycan at this site arrives at the Golgi, suggesting that it passes endoplasmic reticulum quality control but is not further transported to the cell surface for secretion. The QSOX1 transmembrane segment is dispensable for Golgi localization and secretion, as fully luminal and transmembrane variants displayed the same trafficking behavior. This study provides a key example of the effect of glycosylation on Golgi exit and contributes to an understanding of late secretory sorting and quality control.
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Affiliation(s)
- Ben Horowitz
- Department of Structural Biology, Weizmann Institute of Science, Rehovot, Israel
| | - Gabriel Javitt
- Department of Structural Biology, Weizmann Institute of Science, Rehovot, Israel
| | - Tal Ilani
- Department of Structural Biology, Weizmann Institute of Science, Rehovot, Israel
| | - Yair Gat
- Department of Structural Biology, Weizmann Institute of Science, Rehovot, Israel
| | - David Morgenstern
- The Nancy and Stephen Grand Israel National Center for Personalized Medicine, Weizmann Institute of Science, Rehovot, Israel
| | - Frederic A Bard
- Institute of Molecular and Cell Biology, Agency for Science, Technology and Research, 61 Biopolis Drive, Proteos, Singapore
| | - Deborah Fass
- Department of Structural Biology, Weizmann Institute of Science, Rehovot, Israel
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10
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Le NQK, Sandag GA, Ou YY. Incorporating post translational modification information for enhancing the predictive performance of membrane transport proteins. Comput Biol Chem 2018; 77:251-260. [DOI: 10.1016/j.compbiolchem.2018.10.010] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2017] [Revised: 08/01/2018] [Accepted: 10/14/2018] [Indexed: 10/28/2022]
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11
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Tang Y, Cong X, Wang S, Fang S, Dong X, Yuan Y, Fan J. GnT-V promotes chemosensitivity to gemcitabine in bladder cancer cells through β1,6 GlcNAc branch modification of human equilibrative nucleoside transporter 1. Biochem Biophys Res Commun 2018; 503:3142-3148. [DOI: 10.1016/j.bbrc.2018.08.107] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2018] [Accepted: 08/15/2018] [Indexed: 12/26/2022]
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12
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López-Corcuera B, Arribas-González E, Aragón C. Hyperekplexia-associated mutations in the neuronal glycine transporter 2. Neurochem Int 2018; 123:95-100. [PMID: 29859229 DOI: 10.1016/j.neuint.2018.05.014] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2018] [Revised: 05/26/2018] [Accepted: 05/29/2018] [Indexed: 12/20/2022]
Abstract
Hyperekplexia or startle disease is a dysfunction of inhibitory glycinergic neurotransmission characterized by an exaggerated startle in response to trivial tactile or acoustic stimuli. Although rare, this disorder can have serious consequences, including sudden infant death. One of the most frequent causes of hyperekplexia are mutations in the SLC6A5 gene, encoding the neuronal glycine transporter 2 (GlyT2), a key component of inhibitory glycinergic presynapses involved in synaptic glycine recycling though sodium and chloride-dependent co-transport. Most GlyT2 mutations detected so far are recessive, but two dominant missense mutations have been described. The detailed analysis of these mutations has revealed structural cues on the quaternary structure of GlyT2, and opens the possibility that novel selective pharmacochaperones have potential therapeutic effects in hyperekplexia.
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Affiliation(s)
- Beatriz López-Corcuera
- Centro de Biología Molecular ''Severo Ochoa'', Universidad Autónoma de Madrid-Consejo Superior de Investigaciones Científicas, Madrid, Spain; IdiPAZ-Hospital Universitario La Paz, Universidad Autónoma de Madrid, Madrid, Spain.
| | - Esther Arribas-González
- Centro de Biología Molecular ''Severo Ochoa'', Universidad Autónoma de Madrid-Consejo Superior de Investigaciones Científicas, Madrid, Spain; IdiPAZ-Hospital Universitario La Paz, Universidad Autónoma de Madrid, Madrid, Spain
| | - Carmen Aragón
- Centro de Biología Molecular ''Severo Ochoa'', Universidad Autónoma de Madrid-Consejo Superior de Investigaciones Científicas, Madrid, Spain; IdiPAZ-Hospital Universitario La Paz, Universidad Autónoma de Madrid, Madrid, Spain
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13
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Ge Y, Gu Y, Wang J, Zhang Z. Membrane topology of rat sodium-coupled neutral amino acid transporter 2 (SNAT2). BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2018; 1860:1460-1469. [PMID: 29678469 DOI: 10.1016/j.bbamem.2018.04.005] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/26/2018] [Revised: 03/24/2018] [Accepted: 04/15/2018] [Indexed: 11/19/2022]
Abstract
Sodium-coupled neutral amino acid transporter 2 (SNAT2) is a subtype of the amino acid transport system A that is widely expressed in mammalian tissues. It plays critical roles in glutamic acid-glutamine circulation, liver gluconeogenesis and other biological pathway. However, the topology of the SNAT2 amino acid transporter is unknown. Here we identified the topological structure of SNAT2 using bioinformatics analysis, Methoxy-polyethylene glycol maleimide (mPEG-Mal) chemical modification, protease cleavage assays, immunofluorescence and examination of glycosylation. Our results show that SNAT2 contains 11 transmembrane domains (TMDs) with an intracellular N terminus and an extracellular C terminus. Three N-glycosylation sites were verified at the largest extracellular loop. This model is consistent with the previous model of SNAT2 with the exception of a difference in number of glycosylation sites. This is the first time to confirm the SNAT2 membrane topology using experimental methods. Our study on SNAT2 topology provides valuable structural information of one of the solute carrier family 38 (SLC38) members.
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Affiliation(s)
- Yudan Ge
- College of Life Sciences and Biopharmaceutics, Shenyang Pharmaceutical University, Shenyang City 110016, China
| | - Yanting Gu
- College of Life Sciences and Biopharmaceutics, Shenyang Pharmaceutical University, Shenyang City 110016, China
| | - Jiahong Wang
- College of Life Sciences and Biopharmaceutics, Shenyang Pharmaceutical University, Shenyang City 110016, China
| | - Zhou Zhang
- College of Life Sciences and Biopharmaceutics, Shenyang Pharmaceutical University, Shenyang City 110016, China.
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14
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Velleman SG, Song Y. Development and Growth of the Avian Pectoralis Major (Breast) Muscle: Function of Syndecan-4 and Glypican-1 in Adult Myoblast Proliferation and Differentiation. Front Physiol 2017; 8:577. [PMID: 28848451 PMCID: PMC5550705 DOI: 10.3389/fphys.2017.00577] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2017] [Accepted: 07/25/2017] [Indexed: 12/19/2022] Open
Abstract
Muscle fiber number is determined around the time hatch with continued posthatch muscle growth being mediated by the adult myoblast, satellite cell, population of cells. Satellite cells are dynamic in their expression of proteins including the cell membrane associated proteoglycans, syndecan-4 and glypican-1. These proteoglycans play roles in organizing the extracellular environment in the satellite cell niche, cytoskeletal structure, cell-to-cell adhesion, satellite cell migration, and signal transduction. This review article focuses on syndecan-4 and glypican-1 as both are capable of regulating satellite cell responsiveness to fibroblast growth factor 2. Fibroblast growth factor 2 is a potent stimulator of muscle cell proliferation and a strong inhibitor of differentiation. Proteoglycans are composed of a central core protein defined functional domains, and covalently attached glycosaminoglycans and N-glycosylation chains. The functional association of these components with satellite cell function is discussed as well as an emerging role for microRNA regulation of syndecan-4 and glypican-1.
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Affiliation(s)
- Sandra G Velleman
- Department of Animal Sciences, The Ohio State UniversityWooster, OH, United States
| | - Yan Song
- Department of Medical Oncology, Dana-Farber Cancer Institute, Harvard Medical SchoolBoston, MA, United States
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15
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Subramanian VS, Sabui S, Teafatiller T, Bohl JA, Said HM. Structure/functional aspects of the human riboflavin transporter-3 ( SLC52A3): role of the predicted glycosylation and substrate-interacting sites. Am J Physiol Cell Physiol 2017; 313:C228-C238. [PMID: 28637675 PMCID: PMC5582875 DOI: 10.1152/ajpcell.00101.2017] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2017] [Revised: 06/05/2017] [Accepted: 06/16/2017] [Indexed: 11/22/2022]
Abstract
The human riboflavin (RF) transporter-3 (hRFVT-3; product of the SLC52A3 gene) plays an essential role in the intestinal RF absorption process and is expressed exclusively at the apical membrane domain of polarized enterocytes. Previous studies have characterized different physiological/biological aspects of this transporter, but nothing is known about the glycosylation status of the hRFVT-3 protein and role of this modification in its physiology/biology. Additionally, little is known about the residues in the hRFVT-3 protein that interact with the ligand, RF. We addressed these issues using appropriate biochemical/molecular approaches, a protein-docking model, and established intestinal/renal epithelial cells. Our results showed that the hRFVT-3 protein is glycosylated and that glycosylation is important for its function. Mutating the predicted N-glycosylation sites at Asn94 and Asn168 led to a significant decrease in RF uptake; it also led to a marked intracellular (in the endoplasmic reticulum, ER) retention of the mutated proteins as shown by live-cell confocal imaging studies. The protein-docking model used in this study has identified a number of putative substrate-interacting sites: Ser16, Ile20, Trp24, Phe142, Thr314, and Asn315 Mutating these potential interacting sites was indeed found to lead to a significant inhibition in RF uptake and to intracellular (ER) retention of the mutated proteins (except for the Phe142 mutant). These results demonstrate that the hRFVT-3 protein is glycosylated and this glycosylation is important for its function and cell surface expression. This study also identified a number of residues in the hRFVT-3 polypeptide that are important for its function/cell surface expression.
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Affiliation(s)
- Veedamali S Subramanian
- Departments of Medicine, Physiology/Biophysics, University of California, Irvine, California; and Department of Veterans Affairs Medical Center, Long Beach, California
| | - Subrata Sabui
- Departments of Medicine, Physiology/Biophysics, University of California, Irvine, California; and Department of Veterans Affairs Medical Center, Long Beach, California
| | - Trevor Teafatiller
- Departments of Medicine, Physiology/Biophysics, University of California, Irvine, California; and Department of Veterans Affairs Medical Center, Long Beach, California
| | - Jennifer A Bohl
- Departments of Medicine, Physiology/Biophysics, University of California, Irvine, California; and Department of Veterans Affairs Medical Center, Long Beach, California
| | - Hamid M Said
- Departments of Medicine, Physiology/Biophysics, University of California, Irvine, California; and Department of Veterans Affairs Medical Center, Long Beach, California
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16
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Wellendorph P, Jacobsen J, Skovgaard-Petersen J, Jurik A, Vogensen SB, Ecker G, Schousboe A, Krogsgaard-Larsen P, Clausen RP. γ-Aminobutyric Acid and Glycine Neurotransmitter Transporters. METHODS AND PRINCIPLES IN MEDICINAL CHEMISTRY 2017. [DOI: 10.1002/9783527679430.ch4] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Affiliation(s)
- Petrine Wellendorph
- University of Copenhagen; Faculty of Health and Medical Sciences, Department of Drug Design and Pharmacology; Universitetsparken 2, DK-2100 Copenhagen Denmark
| | - Julie Jacobsen
- University of Copenhagen; Faculty of Health and Medical Sciences, Department of Drug Design and Pharmacology; Universitetsparken 2, DK-2100 Copenhagen Denmark
| | - Jonas Skovgaard-Petersen
- University of Copenhagen; Faculty of Health and Medical Sciences, Department of Drug Design and Pharmacology; Universitetsparken 2, DK-2100 Copenhagen Denmark
| | - Andreas Jurik
- University of Vienna; Department of Pharmaceutical Chemistry; Althanstrasse 14, A-1090 Vienna Austria
| | - Stine B. Vogensen
- University of Copenhagen; Faculty of Health and Medical Sciences, Department of Drug Design and Pharmacology; Universitetsparken 2, DK-2100 Copenhagen Denmark
| | - Gerhard Ecker
- University of Vienna; Department of Pharmaceutical Chemistry; Althanstrasse 14, A-1090 Vienna Austria
| | - Arne Schousboe
- University of Copenhagen; Faculty of Health and Medical Sciences, Department of Drug Design and Pharmacology; Universitetsparken 2, DK-2100 Copenhagen Denmark
| | - Povl Krogsgaard-Larsen
- University of Copenhagen; Faculty of Health and Medical Sciences, Department of Drug Design and Pharmacology; Universitetsparken 2, DK-2100 Copenhagen Denmark
| | - Rasmus P. Clausen
- University of Copenhagen; Faculty of Health and Medical Sciences, Department of Drug Design and Pharmacology; Universitetsparken 2, DK-2100 Copenhagen Denmark
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17
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Abstract
Glycine, besides exerting essential metabolic functions, is an important inhibitory neurotransmitter in caudal areas of the central nervous system and also a positive neuromodulator at excitatory glutamate-mediated synapses. Glial cells provide metabolic support to neurons and modulate synaptic activity. Six transporters belonging to three solute carrier families (SLC6, SLC38, and SLC7) are capable of transporting glycine across the glial plasma membrane. The unique glial glycine-selective transporter GlyT1 (SLC6) is the main regulator of synaptic glycine concentrations, assisted by the neuronal GlyT2. The five additional glycine transporters ATB0,+, SNAT1, SNAT2, SNAT5, and LAT2 display broad amino acid specificity and have differential contributions to glial glycine transport. Glial glycine transporters are divergent in sequence but share a similar architecture displaying the 5 + 5 inverted fold originally characterized in the leucine transporter LeuT. The availability of protein crystals solved at high resolution for prokaryotic and, more recently, eukaryotic homologues of this superfamily has advanced significantly our understanding of the mechanism of glycine transport.
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18
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Glycinergic transmission: glycine transporter GlyT2 in neuronal pathologies. Neuronal Signal 2016; 1:NS20160009. [PMID: 32714574 PMCID: PMC7377260 DOI: 10.1042/ns20160009] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2016] [Revised: 11/04/2016] [Accepted: 11/09/2016] [Indexed: 11/17/2022] Open
Abstract
Glycinergic neurons are major contributors to the regulation of neuronal excitability, mainly in caudal areas of the nervous system. These neurons control fluxes of sensory information between the periphery and the CNS and diverse motor activities like locomotion, respiration or vocalization. The phenotype of a glycinergic neuron is determined by the expression of at least two proteins: GlyT2, a plasma membrane transporter of glycine, and VIAAT, a vesicular transporter shared by glycine and GABA. In this article, we review recent advances in understanding the role of GlyT2 in the pathophysiology of inhibitory glycinergic neurotransmission. GlyT2 mutations are associated to decreased glycinergic function that results in a rare movement disease termed hyperekplexia (HPX) or startle disease. In addition, glycinergic neurons control pain transmission in the dorsal spinal cord and their function is reduced in chronic pain states. A moderate inhibition of GlyT2 may potentiate glycinergic inhibition and constitutes an attractive target for pharmacological intervention against these devastating conditions.
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19
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N-Glycosylation influences transport, but not cellular trafficking, of a neuronal amino acid transporter SNAT1. Biochem J 2016; 473:4227-4242. [DOI: 10.1042/bcj20160724] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2016] [Revised: 09/12/2016] [Accepted: 09/20/2016] [Indexed: 11/17/2022]
Abstract
SNAT1 is a system N/A neutral amino acid transporter that primarily expresses in neurons and mediates the transport of l-glutamine (Gln). Gln is an important amino acid involved in multiple cellular functions and also is a precursor for neurotransmitters, glutamate and GABA. In the present study, we demonstrated that SNAT1 is an N-glycoprotein expressed in neurons. We identified three glycosylation sites at asparagine residues 251, 257 and 310 in SNAT1 protein, and that the first two are the primary sites. The biotinylation and confocal immunofluorescence analysis showed that the glycosylation-impaired mutants and deglycosylated SNAT1 were equally capable of expressing on the cell surface. However, l-Gln and 3H-labeled methyl amino isobutyrate (MeAIB) was significantly compromised in N-glycosylation-impaired mutants and deglycosylated SNAT1 when compared with the wild-type control. Taken together, these results suggest that SNAT1 is an N-glycosylated protein with three de novo glycosylation sites and N-glycosylation of SNAT1 may play an important role in the transport of substrates across the cell membrane.
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N-linked glycosylation of N48 is required for equilibrative nucleoside transporter 1 (ENT1) function. Biosci Rep 2016; 36:BSR20160063. [PMID: 27480168 PMCID: PMC5006311 DOI: 10.1042/bsr20160063] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/29/2016] [Accepted: 08/01/2016] [Indexed: 11/29/2022] Open
Abstract
Our study confirmed that Asn48 of hENT1 is the only N-glycosylated residue when expressed in HEK293 cells, and loss of the N-glycan resulted in less hENT1 at the plasma membrane, as well as a loss of function and protein–protein self-interaction. Human equilibrative nucleoside transporter 1 (hENT1) transports nucleosides and nucleoside analogue drugs across cellular membranes and is necessary for the uptake of many anti-cancer, anti-parasitic and anti-viral drugs. Previous work, and in silico prediction, suggest that hENT1 is glycosylated at Asn48 in the first extracellular loop of the protein and that glycosylation plays a role in correct localization and function of hENT1. Site-directed mutagenesis of wild-type (wt) hENT1 removed potential glycosylation sites. Constructs (wt 3xFLAG-hENT1, N48Q-3xFLAG-hENT1 or N288Q-3xFLAG-hENT2) were transiently transfected into HEK293 cells and cell lysates were treated with or without peptide–N-glycosidase F (PNGase-F), followed by immunoblotting analysis. Substitution of N48 prevents hENT1 glycosylation, confirming a single N-linked glycosylation site. N48Q-hENT1 protein is found at the plasma membrane in HEK293 cells but at lower levels compared with wt hENT1 based on S-(4-nitrobenzyl)-6-thioinosine (NBTI) binding analysis (wt 3xFLAG-ENT1 Bmax, 41.5±2.9 pmol/mg protein; N48Q-3xFLAG-ENT1 Bmax, 13.5±0.45 pmol/mg protein) and immunofluorescence microscopy. Although present at the membrane, chloroadenosine transport assays suggest that N48Q-hENT1 is non-functional (wt 3xFLAG-ENT1, 170.80±44.01 pmol/mg protein; N48Q-3xFLAG-ENT1, 57.91±17.06 pmol/mg protein; mock-transfected 74.31±19.65 pmol/mg protein). Co-immunoprecipitation analyses suggest that N48Q ENT1 is unable to interact with self or with wt hENT1. Based on these data we propose that glycosylation at N48 is critical for the localization, function and oligomerization of hENT1.
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21
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Nabokina SM, Subramanian VS, Said HM. The human colonic thiamine pyrophosphate transporter (hTPPT) is a glycoprotein and N-linked glycosylation is important for its function. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2016; 1858:866-71. [PMID: 26828122 DOI: 10.1016/j.bbamem.2016.01.028] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/24/2015] [Revised: 01/14/2016] [Accepted: 01/24/2016] [Indexed: 12/16/2022]
Abstract
The recently identified human thiamine pyrophosphate transporter (hTPPT; product of the SLC44A4 gene) is responsible for absorption of the microbiota-generated TPP in the large intestine. The hTPPT is highly expressed in the colon, but not in other regions of the intestinal tract and is localized exclusively at the apical membrane domain of epithelia. The hTPPT protein is predicted to have multiple TM domains with a number of putative N-glycosylation sites, but it is not known if the protein is actually glycosylated, and if so at which site, and their role in the functionality of the transporter. Using several approaches including inhibiting de novo N-glycosylation in human colonic epithelial NCM460 cells with tunicamycin as well as enzymatic de-glycosylation, we show that the hTPPT protein is, indeed, a glycoprotein. Glycosylation of hTPPT was shown, by mean of site-directed mutagenesis, to occur at Asn(69), Asn(155), Asn(197), Asn(393), and Asn(416). However, only N-glycosylation at Asn(69), Asn(155), and Asn(393) appeared to be important for transporter functionality possibly through an effect on protein conformation and/or interaction with its ligand (but not through changes in expression at the cell membrane as determined by live cell confocal imaging). Results of this study showed, for the first time, that the hTPPT is glycosylated and that N-linked glycosylation occurs at multiple sites with some of them being important for function. The results also provide an indirect support for a membrane topology for hTPPT with 10 transmembrane domains as predicted by the TMHMM transmembrane helixes prediction program.
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Affiliation(s)
- Svetlana M Nabokina
- Department of Medicine, University of California, Irvine, CA 92697, United States; Department of Physiology/Biophysics, University of California, Irvine, CA 92697, United States; Department of Veterans Affairs Medical Center, Long Beach, CA 90822, United States
| | - Veedamali S Subramanian
- Department of Medicine, University of California, Irvine, CA 92697, United States; Department of Physiology/Biophysics, University of California, Irvine, CA 92697, United States; Department of Veterans Affairs Medical Center, Long Beach, CA 90822, United States
| | - Hamid M Said
- Department of Medicine, University of California, Irvine, CA 92697, United States; Department of Physiology/Biophysics, University of California, Irvine, CA 92697, United States; Department of Veterans Affairs Medical Center, Long Beach, CA 90822, United States.
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22
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Glycosylation of solute carriers: mechanisms and functional consequences. Pflugers Arch 2015; 468:159-76. [PMID: 26383868 DOI: 10.1007/s00424-015-1730-4] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2015] [Revised: 08/19/2015] [Accepted: 08/21/2015] [Indexed: 12/21/2022]
Abstract
Solute carriers (SLCs) are one of the largest groups of multi-spanning membrane proteins in mammals and include ubiquitously expressed proteins as well as proteins with highly restricted tissue expression. A vast number of studies have addressed the function and organization of SLCs as well as their posttranslational regulation, but only relatively little is known about the role of SLC glycosylation. Glycosylation is one of the most abundant posttranslational modifications of animal proteins and through recent advances in our understanding of protein-glycan interactions, the functional roles of SLC glycosylation are slowly emerging. The purpose of this review is to provide a concise overview of the aspects of glycobiology most relevant to SLCs, to discuss the roles of glycosylation in the regulation and function of SLCs, and to outline the major open questions in this field, which can now be addressed given major technical advances in this and related fields of study in recent years.
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23
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Arribas-González E, de Juan-Sanz J, Aragón C, López-Corcuera B. Molecular basis of the dominant negative effect of a glycine transporter 2 mutation associated with hyperekplexia. J Biol Chem 2014; 290:2150-65. [PMID: 25480793 DOI: 10.1074/jbc.m114.587055] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Hyperekplexia or startle disease is a rare clinical syndrome characterized by an exaggerated startle in response to trivial tactile or acoustic stimuli. This neurological disorder can have serious consequences in neonates, provoking brain damage and/or sudden death due to apnea episodes and cardiorespiratory failure. Hyperekplexia is caused by defective inhibitory glycinergic neurotransmission. Mutations in the human SLC6A5 gene encoding the neuronal GlyT2 glycine transporter are responsible for the presynaptic form of the disease. GlyT2 mediates synaptic glycine recycling, which constitutes the main source of releasable transmitter at glycinergic synapses. Although the majority of GlyT2 mutations detected so far are recessive, a dominant negative mutant that affects GlyT2 trafficking does exist. In this study, we explore the properties and structural alterations of the S512R mutation in GlyT2. We analyze its dominant negative effect that retains wild-type GlyT2 in the endoplasmic reticulum (ER), preventing surface expression. We show that the presence of an arginine rather than serine 512 provoked transporter misfolding, enhanced association to the ER-chaperone calnexin, altered association with the coat-protein complex II component Sec24D, and thereby impeded ER exit. The S512R mutant formed oligomers with wild-type GlyT2 causing its retention in the ER. Overexpression of calnexin rescued wild-type GlyT2 from the dominant negative effect of the mutant, increasing the amount of transporter that reached the plasma membrane and dampening the interaction between the wild-type and mutant GlyT2. The ability of chemical chaperones to overcome the dominant negative effect of the disease mutation on the wild-type transporter was demonstrated in heterologous cells and primary neurons.
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Affiliation(s)
- Esther Arribas-González
- From the Departamento de Biología Molecular and Centro de Biología Molecular "Severo Ochoa," Consejo Superior de Investigaciones Científicas-Universidad Autónoma de Madrid, Madrid 28049, Spain, the IdiPAZ-Hospital Universitario La Paz, Universidad Autónoma de Madrid, Madrid 28046, Spain
| | - Jaime de Juan-Sanz
- From the Departamento de Biología Molecular and Centro de Biología Molecular "Severo Ochoa," Consejo Superior de Investigaciones Científicas-Universidad Autónoma de Madrid, Madrid 28049, Spain, the IdiPAZ-Hospital Universitario La Paz, Universidad Autónoma de Madrid, Madrid 28046, Spain the Centro de Investigación Biomédica en Red de Enfermedades Raras, Instituto de Salud Carlos III, Madrid 28029, Spain, and
| | - Carmen Aragón
- From the Departamento de Biología Molecular and Centro de Biología Molecular "Severo Ochoa," Consejo Superior de Investigaciones Científicas-Universidad Autónoma de Madrid, Madrid 28049, Spain, the IdiPAZ-Hospital Universitario La Paz, Universidad Autónoma de Madrid, Madrid 28046, Spain the Centro de Investigación Biomédica en Red de Enfermedades Raras, Instituto de Salud Carlos III, Madrid 28029, Spain, and
| | - Beatriz López-Corcuera
- From the Departamento de Biología Molecular and Centro de Biología Molecular "Severo Ochoa," Consejo Superior de Investigaciones Científicas-Universidad Autónoma de Madrid, Madrid 28049, Spain, the IdiPAZ-Hospital Universitario La Paz, Universidad Autónoma de Madrid, Madrid 28046, Spain the Centro de Investigación Biomédica en Red de Enfermedades Raras, Instituto de Salud Carlos III, Madrid 28029, Spain, and
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24
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Wang H, Zhou T, Peng J, Xu P, Dong N, Chen S, Wu Q. Distinct roles of N-glycosylation at different sites of corin in cell membrane targeting and ectodomain shedding. J Biol Chem 2014; 290:1654-63. [PMID: 25451932 DOI: 10.1074/jbc.m114.606442] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Corin is a membrane-bound protease essential for activating natriuretic peptides and regulating blood pressure. Human corin has 19 predicted N-glycosylation sites in its extracellular domains. It has been shown that N-glycans are required for corin cell surface expression and zymogen activation. It remains unknown, however, how N-glycans at different sites may regulate corin biosynthesis and processing. In this study, we examined corin mutants, in which each of the 19 predicted N-glycosylation sites was mutated individually. By Western analysis of corin proteins in cell lysate and conditioned medium from transfected HEK293 cells and HL-1 cardiomyocytes, we found that N-glycosylation at Asn-80 inhibited corin shedding in the juxtamembrane domain. Similarly, N-glycosylation at Asn-231 protected corin from autocleavage in the frizzled-1 domain. Moreover, N-glycosylation at Asn-697 in the scavenger receptor domain and at Asn-1022 in the protease domain is important for corin cell surface targeting and zymogen activation. We also found that the location of the N-glycosylation site in the protease domain was not critical. N-Glycosylation at Asn-1022 may be switched to different sites to promote corin zymogen activation. Together, our results show that N-glycans at different sites may play distinct roles in regulating the cell membrane targeting, zymogen activation, and ectodomain shedding of corin.
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Affiliation(s)
- Hao Wang
- From the Department of Molecular Cardiology, Lerner Research Institute, Cleveland Clinic, Cleveland, Ohio 44195, the Department of Chemistry, Cleveland State University, Cleveland, Ohio 44115, and
| | - Tiantian Zhou
- the Cyrus Tang Hematology Center and Collaborative Innovation Center of Hematology, Soochow University, Suzhou 215123, China
| | - Jianhao Peng
- From the Department of Molecular Cardiology, Lerner Research Institute, Cleveland Clinic, Cleveland, Ohio 44195
| | - Ping Xu
- From the Department of Molecular Cardiology, Lerner Research Institute, Cleveland Clinic, Cleveland, Ohio 44195
| | - Ningzheng Dong
- the Cyrus Tang Hematology Center and Collaborative Innovation Center of Hematology, Soochow University, Suzhou 215123, China
| | - Shenghan Chen
- From the Department of Molecular Cardiology, Lerner Research Institute, Cleveland Clinic, Cleveland, Ohio 44195
| | - Qingyu Wu
- From the Department of Molecular Cardiology, Lerner Research Institute, Cleveland Clinic, Cleveland, Ohio 44195, the Department of Chemistry, Cleveland State University, Cleveland, Ohio 44115, and the Cyrus Tang Hematology Center and Collaborative Innovation Center of Hematology, Soochow University, Suzhou 215123, China
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25
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Stoops EH, Caplan MJ. Trafficking to the apical and basolateral membranes in polarized epithelial cells. J Am Soc Nephrol 2014; 25:1375-86. [PMID: 24652803 DOI: 10.1681/asn.2013080883] [Citation(s) in RCA: 74] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Renal epithelial cells must maintain distinct protein compositions in their apical and basolateral membranes in order to perform their transport functions. The creation of these polarized protein distributions depends on sorting signals that designate the trafficking route and site of ultimate functional residence for each protein. Segregation of newly synthesized apical and basolateral proteins into distinct carrier vesicles can occur at the trans-Golgi network, recycling endosomes, or a growing assortment of stations along the cellular trafficking pathway. The nature of the specific sorting signal and the mechanism through which it is interpreted can influence the route a protein takes through the cell. Cell type-specific variations in the targeting motifs of a protein, as are evident for Na,K-ATPase, demonstrate a remarkable capacity to adapt sorting pathways to different developmental states or physiologic requirements. This review summarizes our current understanding of apical and basolateral trafficking routes in polarized epithelial cells.
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Affiliation(s)
- Emily H Stoops
- Departments of Cellular & Molecular Physiology and Cell Biology, Yale University School of Medicine, New Haven, Connecticut
| | - Michael J Caplan
- Departments of Cellular & Molecular Physiology and Cell Biology, Yale University School of Medicine, New Haven, Connecticut
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26
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Scott H, Panin VM. The role of protein N-glycosylation in neural transmission. Glycobiology 2014; 24:407-17. [PMID: 24643084 DOI: 10.1093/glycob/cwu015] [Citation(s) in RCA: 78] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Recent studies have explored the function of N-linked glycosylation in the nervous system, demonstrating essential roles of carbohydrate structures in neural development. The function of N-glycans in neural physiology remains less understood; however, increasing evidence indicates that N-glycans can play specific modulatory roles controlling neural transmission and excitability of neural circuits. These roles are mediated via effects on synaptic proteins involved in neurotransmitter release, transporters that regulate nerotransmitter concentrations, neurotransmitter receptors, as well as via regulation of proteins that control excitability and response to milieu stimuli, such as voltage-gated ion channels and transient receptor potential channels, respectively. Sialylated N-glycan structures are among the most potent modulators of cell excitability, exerting prominent effects on voltage gated Na(+) and K(+) channels. This modulation appears to be underlain by complex molecular mechanisms involving electrostatic effects, as well as interaction modes based on more specific steric effects and interactions with lectins and other molecules. Data also indicate that particular features of N-glycans, such as their location on a protein and structural characteristics, can be specifically associated with the effect of glycosylation. These features and their functional implications can vary between different cell types, which highlight the importance of in vivo analyses of glycan functions. Experimental challenges are associated with the overwhelming complexity of the nervous system and glycosylation pathways in vertebrates, and thus model organisms like Drosophila should help elucidate evolutionarily conserved mechanisms underlying glycan functions. Recent studies supported this notion and shed light on functions of several glycosylation genes involved in the regulation of the nervous system.
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Affiliation(s)
- Hilary Scott
- Department of Biochemistry and Biophysics, Texas A&M University, 2128 TAMU, College Station, TX 77843, USA
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27
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Scott H, Panin VM. N-glycosylation in regulation of the nervous system. ADVANCES IN NEUROBIOLOGY 2014; 9:367-94. [PMID: 25151388 DOI: 10.1007/978-1-4939-1154-7_17] [Citation(s) in RCA: 59] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Protein N-glycosylation can influence the nervous system in a variety of ways by affecting functions of glycoproteins involved in nervous system development and physiology. The importance of N-glycans for different aspects of neural development has been well documented. For example, some N-linked carbohydrate structures were found to play key roles in neural cell adhesion and axonal targeting during development. At the same time, the involvement of glycosylation in the regulation of neural physiology remains less understood. Recent studies have implicated N-glycosylation in the regulation of neural transmission, revealing novel roles of glycans in synaptic processes and the control of neural excitability. N-Glycans were found to markedly affect the function of several types of synaptic proteins involved in key steps of synaptic transmission, including neurotransmitter release, reception, and uptake. Glycosylation also regulates a number of channel proteins, such as TRP channels that control responses to environmental stimuli and voltage-gated ion channels, the principal determinants of neuronal excitability. Sialylated carbohydrate structures play a particularly prominent part in the modulation of voltage-gated ion channels. Sialic acids appear to affect channel functions via several mechanisms, including charge interactions, as well as other interactions that probably engage steric effects and interactions with other molecules. Experiments also indicated that some structural features of glycans can be particularly important for their function. Since glycan structures can vary significantly between different cell types and depend on the metabolic state of the cell, it is important to analyze glycan functions using in vivo approaches. While the complexity of the nervous system and intricacies of glycosylation pathways can create serious obstacles for in vivo experiments in vertebrates, recent studies have indicated that more simple and experimentally tractable model organisms like Drosophila should provide important advantages for elucidating evolutionarily conserved functions of N-glycosylation in the nervous system.
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Affiliation(s)
- Hilary Scott
- Department of Biochemistry and Biophysics, Texas A&M University, 2128 TAMU, College Station, TX, 77843, USA
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28
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Shrimal S, Gilmore R. Glycosylation of closely spaced acceptor sites in human glycoproteins. J Cell Sci 2013; 126:5513-23. [PMID: 24105266 DOI: 10.1242/jcs.139584] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Asparagine-linked glycosylation of proteins by the oligosaccharyltransferase (OST) occurs when acceptor sites or sequons (N-x≠P-T/S) on nascent polypeptides enter the lumen of the rough endoplasmic reticulum. Metazoan organisms assemble two isoforms of the OST that have different catalytic subunits (STT3A or STT3B) and partially non-overlapping cellular roles. Potential glycosylation sites move past the STT3A complex, which is associated with the translocation channel, at the protein synthesis elongation rate. Here, we investigated whether close spacing between acceptor sites in a nascent protein promotes site skipping by the STT3A complex. Biosynthetic analysis of four human glycoproteins revealed that closely spaced sites are efficiently glycosylated by an STT3B-independent process unless the sequons contain non-optimal sequence features, including extreme close spacing between sequons (e.g. NxTNxT) or the presence of paired NxS sequons (e.g. NxSANxS). Many, but not all, glycosylation sites that are skipped by the STT3A complex can be glycosylated by the STT3B complex. Analysis of a murine glycoprotein database revealed that closely spaced sequons are surprisingly common, and are enriched for paired NxT sites when the gap between sequons is less than three residues.
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Affiliation(s)
- Shiteshu Shrimal
- Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, Worcester, MA 01605, USA
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Arribas-González E, Alonso-Torres P, Aragón C, López-Corcuera B. Calnexin-assisted biogenesis of the neuronal glycine transporter 2 (GlyT2). PLoS One 2013; 8:e63230. [PMID: 23650557 PMCID: PMC3641136 DOI: 10.1371/journal.pone.0063230] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2012] [Accepted: 03/30/2013] [Indexed: 11/20/2022] Open
Abstract
The neuronal transporter GlyT2 is a polytopic, 12-transmembrane domain, plasma membrane glycoprotein involved in the removal and recycling of synaptic glycine from inhibitory synapses. Mutations in the human GlyT2 gene (SLC6A5) that cause deficient glycine transport or defective GlyT2 trafficking are the second most common cause of hyperekplexia or startle disease. In this study we examined several aspects of GlyT2 biogenesis that involve the endoplasmic reticulum chaperone calnexin (CNX). CNX binds transiently to an intermediate under-glycosylated transporter precursor and facilitates GlyT2 processing. In cells expressing GlyT2, transporter accumulation and transport activity were attenuated by siRNA-mediated CNX knockdown and enhanced by CNX overexpression. GlyT2 binding to CNX was mediated by glycan and polypeptide-based interactions as revealed by pharmacological approaches and the behavior of GlyT2 N-glycan-deficient mutants. Moreover, transporter folding appeared to be stabilized by N-glycans. Co-expression of CNX and a fully non-glycosylated mutant rescues glycine transport but not mutant surface expression. Hence, CNX discriminates between different conformational states of GlyT2 displaying a lectin-independent chaperone activity. GlyT2 wild-type and mutant transporters were finally degraded in the lysosome. Our findings provide further insight into GlyT2 biogenesis, and a useful framework for the study of newly synthesized GlyT2 transporters bearing hyperekplexia mutations.
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Affiliation(s)
- Esther Arribas-González
- Departamento de Biología Molecular and Centro de Biología Molecular “Severo Ochoa”, Consejo Superior de Investigaciones Científicas, Universidad Autónoma de Madrid, Madrid, Spain
- IdiPAZ-Hospital Universitario La Paz, Universidad Autónoma de Madrid, Madrid, Spain
| | - Pablo Alonso-Torres
- Departamento de Biología Molecular and Centro de Biología Molecular “Severo Ochoa”, Consejo Superior de Investigaciones Científicas, Universidad Autónoma de Madrid, Madrid, Spain
| | - Carmen Aragón
- Departamento de Biología Molecular and Centro de Biología Molecular “Severo Ochoa”, Consejo Superior de Investigaciones Científicas, Universidad Autónoma de Madrid, Madrid, Spain
- Centro de Investigación Biomédica en Red de Enfermedades Raras, Instituto de Salud Carlos III, Madrid, Spain
- IdiPAZ-Hospital Universitario La Paz, Universidad Autónoma de Madrid, Madrid, Spain
| | - Beatriz López-Corcuera
- Departamento de Biología Molecular and Centro de Biología Molecular “Severo Ochoa”, Consejo Superior de Investigaciones Científicas, Universidad Autónoma de Madrid, Madrid, Spain
- Centro de Investigación Biomédica en Red de Enfermedades Raras, Instituto de Salud Carlos III, Madrid, Spain
- IdiPAZ-Hospital Universitario La Paz, Universidad Autónoma de Madrid, Madrid, Spain
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GlyT1 and GlyT2 in brain astrocytes: expression, distribution and function. Brain Struct Funct 2013; 219:817-30. [DOI: 10.1007/s00429-013-0537-3] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2012] [Accepted: 03/02/2013] [Indexed: 11/25/2022]
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31
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Weiss N, Black SAG, Bladen C, Chen L, Zamponi GW. Surface expression and function of Cav3.2 T-type calcium channels are controlled by asparagine-linked glycosylation. Pflugers Arch 2013; 465:1159-70. [DOI: 10.1007/s00424-013-1259-3] [Citation(s) in RCA: 68] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2013] [Revised: 02/25/2013] [Accepted: 02/27/2013] [Indexed: 01/05/2023]
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NKCC1 upregulation disrupts chloride homeostasis in the hypothalamus and increases neuronal activity-sympathetic drive in hypertension. J Neurosci 2012; 32:8560-8. [PMID: 22723696 DOI: 10.1523/jneurosci.1346-12.2012] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Hypertension is a major risk factor for coronary artery disease, stroke, and kidney failure. However, the etiology of hypertension in most patients is poorly understood. Increased sympathetic drive emanating from the hypothalamic paraventricular nucleus (PVN) plays a major role in the development of hypertension. Na(+)-K(+)-2Cl(-) cotransporter-1 (NKCC1) in the brain is critically involved in maintaining chloride homeostasis and in neuronal responses mediated by GABA(A) receptors. Here we present novel evidence that the GABA reversal potential (E(GABA)) of PVN presympathetic neurons undergoes a depolarizing shift that diminishes GABA inhibition in spontaneously hypertensive rats (SHRs). Inhibition of NKCC1, but not KCC2, normalizes E(GABA) and restores GABA inhibition of PVN neurons in SHRs. The mRNA and protein levels of NKCC1, but not KCC2, in the PVN are significantly increased in SHRs, and the NKCC1 proteins on the plasma membrane are highly glycosylated. Inhibiting NKCC1 N-glycosylation restores E(GABA) and GABAergic inhibition of PVN presympathetic neurons in SHRs. Furthermore, NKCC1 inhibition significantly reduces the sympathetic vasomotor tone and augments the sympathoinhibitory responses to GABA(A) receptor activation in the PVN in SHRs. These findings suggest that increased NKCC1 activity and glycosylation disrupt chloride homeostasis and impair synaptic inhibition in the PVN to augment the sympathetic drive in hypertension. This information greatly improves our understanding of the pathogenesis of hypertension and helps to design better treatment strategies for neurogenic hypertension.
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Giménez C, Pérez-Siles G, Martínez-Villarreal J, Arribas-González E, Jiménez E, Núñez E, de Juan-Sanz J, Fernández-Sánchez E, García-Tardón N, Ibáñez I, Romanelli V, Nevado J, James VM, Topf M, Chung SK, Thomas RH, Desviat LR, Aragón C, Zafra F, Rees MI, Lapunzina P, Harvey RJ, López-Corcuera B. A novel dominant hyperekplexia mutation Y705C alters trafficking and biochemical properties of the presynaptic glycine transporter GlyT2. J Biol Chem 2012; 287:28986-9002. [PMID: 22753417 PMCID: PMC3436537 DOI: 10.1074/jbc.m111.319244] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2011] [Revised: 06/18/2012] [Indexed: 11/06/2022] Open
Abstract
Hyperekplexia or startle disease is characterized by an exaggerated startle response, evoked by tactile or auditory stimuli, producing hypertonia and apnea episodes. Although rare, this orphan disorder can have serious consequences, including sudden infant death. Dominant and recessive mutations in the human glycine receptor (GlyR) α1 gene (GLRA1) are the major cause of this disorder. However, recessive mutations in the presynaptic Na(+)/Cl(-)-dependent glycine transporter GlyT2 gene (SLC6A5) are rapidly emerging as a second major cause of startle disease. In this study, systematic DNA sequencing of SLC6A5 revealed a new dominant GlyT2 mutation: pY705C (c.2114A→G) in transmembrane domain 11, in eight individuals from Spain and the United Kingdom. Curiously, individuals harboring this mutation show significant variation in clinical presentation. In addition to classical hyperekplexia symptoms, some individuals had abnormal respiration, facial dysmorphism, delayed motor development, or intellectual disability. We functionally characterized this mutation using molecular modeling, electrophysiology, [(3)H]glycine transport, cell surface expression, and cysteine labeling assays. We found that the introduced cysteine interacts with the cysteine pair Cys-311-Cys-320 in the second external loop of GlyT2. This interaction impairs transporter maturation through the secretory pathway, reduces surface expression, and inhibits transport function. Additionally, Y705C presents altered H(+) and Zn(2+) dependence of glycine transport that may affect the function of glycinergic neurotransmission in vivo.
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Affiliation(s)
- Cecilio Giménez
- From the Departamento de Biología Molecular and Centro de Biología Molecular “Severo Ochoa,” (Consejo Superior de Investigaciones Científicas-Universidad Autónoma de Madrid), Madrid 28049, Spain
- the Centro de Investigación Biomédica en Red de Enfermedades Raras, Instituto de Salud Carlos III, Madrid 28029, Spain
- the IdiPAZ-Hospital Universitario La Paz
| | - Gonzalo Pérez-Siles
- From the Departamento de Biología Molecular and Centro de Biología Molecular “Severo Ochoa,” (Consejo Superior de Investigaciones Científicas-Universidad Autónoma de Madrid), Madrid 28049, Spain
- the Centro de Investigación Biomédica en Red de Enfermedades Raras, Instituto de Salud Carlos III, Madrid 28029, Spain
| | - Jaime Martínez-Villarreal
- From the Departamento de Biología Molecular and Centro de Biología Molecular “Severo Ochoa,” (Consejo Superior de Investigaciones Científicas-Universidad Autónoma de Madrid), Madrid 28049, Spain
- the Centro de Investigación Biomédica en Red de Enfermedades Raras, Instituto de Salud Carlos III, Madrid 28029, Spain
- the IdiPAZ-Hospital Universitario La Paz
| | - Esther Arribas-González
- From the Departamento de Biología Molecular and Centro de Biología Molecular “Severo Ochoa,” (Consejo Superior de Investigaciones Científicas-Universidad Autónoma de Madrid), Madrid 28049, Spain
- the IdiPAZ-Hospital Universitario La Paz
| | - Esperanza Jiménez
- From the Departamento de Biología Molecular and Centro de Biología Molecular “Severo Ochoa,” (Consejo Superior de Investigaciones Científicas-Universidad Autónoma de Madrid), Madrid 28049, Spain
- the Centro de Investigación Biomédica en Red de Enfermedades Raras, Instituto de Salud Carlos III, Madrid 28029, Spain
- the IdiPAZ-Hospital Universitario La Paz
| | - Enrique Núñez
- From the Departamento de Biología Molecular and Centro de Biología Molecular “Severo Ochoa,” (Consejo Superior de Investigaciones Científicas-Universidad Autónoma de Madrid), Madrid 28049, Spain
- the Centro de Investigación Biomédica en Red de Enfermedades Raras, Instituto de Salud Carlos III, Madrid 28029, Spain
- the IdiPAZ-Hospital Universitario La Paz
| | - Jaime de Juan-Sanz
- From the Departamento de Biología Molecular and Centro de Biología Molecular “Severo Ochoa,” (Consejo Superior de Investigaciones Científicas-Universidad Autónoma de Madrid), Madrid 28049, Spain
- the Centro de Investigación Biomédica en Red de Enfermedades Raras, Instituto de Salud Carlos III, Madrid 28029, Spain
- the IdiPAZ-Hospital Universitario La Paz
| | - Enrique Fernández-Sánchez
- From the Departamento de Biología Molecular and Centro de Biología Molecular “Severo Ochoa,” (Consejo Superior de Investigaciones Científicas-Universidad Autónoma de Madrid), Madrid 28049, Spain
| | - Noemí García-Tardón
- From the Departamento de Biología Molecular and Centro de Biología Molecular “Severo Ochoa,” (Consejo Superior de Investigaciones Científicas-Universidad Autónoma de Madrid), Madrid 28049, Spain
- the Centro de Investigación Biomédica en Red de Enfermedades Raras, Instituto de Salud Carlos III, Madrid 28029, Spain
- the IdiPAZ-Hospital Universitario La Paz
| | - Ignacio Ibáñez
- From the Departamento de Biología Molecular and Centro de Biología Molecular “Severo Ochoa,” (Consejo Superior de Investigaciones Científicas-Universidad Autónoma de Madrid), Madrid 28049, Spain
| | - Valeria Romanelli
- the Centro de Investigación Biomédica en Red de Enfermedades Raras, Instituto de Salud Carlos III, Madrid 28029, Spain
- the Instituto de Genética Médica y Molecular, IdiPAZ-Hospital Universitario La Paz, Universidad Autónoma de Madrid, Madrid 28046, Spain
| | - Julián Nevado
- the Centro de Investigación Biomédica en Red de Enfermedades Raras, Instituto de Salud Carlos III, Madrid 28029, Spain
- the Instituto de Genética Médica y Molecular, IdiPAZ-Hospital Universitario La Paz, Universidad Autónoma de Madrid, Madrid 28046, Spain
| | - Victoria M. James
- the Department of Pharmacology, University College London School of Pharmacy, London WC1N 1AX, United Kingdom
| | - Maya Topf
- the Institute of Structural and Molecular Biology, Crystallography, Birkbeck College, London WC1E 7HX, United Kingdom, and
| | - Seo-Kyung Chung
- the Institute of Life Science, College of Medicine, Swansea University, Swansea SA2 8PP, United Kingdom
| | - Rhys H. Thomas
- the Institute of Life Science, College of Medicine, Swansea University, Swansea SA2 8PP, United Kingdom
| | - Lourdes R. Desviat
- From the Departamento de Biología Molecular and Centro de Biología Molecular “Severo Ochoa,” (Consejo Superior de Investigaciones Científicas-Universidad Autónoma de Madrid), Madrid 28049, Spain
| | - Carmen Aragón
- From the Departamento de Biología Molecular and Centro de Biología Molecular “Severo Ochoa,” (Consejo Superior de Investigaciones Científicas-Universidad Autónoma de Madrid), Madrid 28049, Spain
- the Centro de Investigación Biomédica en Red de Enfermedades Raras, Instituto de Salud Carlos III, Madrid 28029, Spain
- the IdiPAZ-Hospital Universitario La Paz
| | - Francisco Zafra
- From the Departamento de Biología Molecular and Centro de Biología Molecular “Severo Ochoa,” (Consejo Superior de Investigaciones Científicas-Universidad Autónoma de Madrid), Madrid 28049, Spain
- the Centro de Investigación Biomédica en Red de Enfermedades Raras, Instituto de Salud Carlos III, Madrid 28029, Spain
- the IdiPAZ-Hospital Universitario La Paz
| | - Mark I. Rees
- the Institute of Life Science, College of Medicine, Swansea University, Swansea SA2 8PP, United Kingdom
| | - Pablo Lapunzina
- the Centro de Investigación Biomédica en Red de Enfermedades Raras, Instituto de Salud Carlos III, Madrid 28029, Spain
- the Instituto de Genética Médica y Molecular, IdiPAZ-Hospital Universitario La Paz, Universidad Autónoma de Madrid, Madrid 28046, Spain
| | - Robert J. Harvey
- the Department of Pharmacology, University College London School of Pharmacy, London WC1N 1AX, United Kingdom
| | - Beatriz López-Corcuera
- From the Departamento de Biología Molecular and Centro de Biología Molecular “Severo Ochoa,” (Consejo Superior de Investigaciones Científicas-Universidad Autónoma de Madrid), Madrid 28049, Spain
- the Centro de Investigación Biomédica en Red de Enfermedades Raras, Instituto de Salud Carlos III, Madrid 28029, Spain
- the IdiPAZ-Hospital Universitario La Paz
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Velleman SG. MEAT SCIENCE AND MUSCLE BIOLOGY SYMPOSIUM: Extracellular matrix regulation of skeletal muscle formation1,2. J Anim Sci 2012; 90:936-41. [DOI: 10.2527/jas.2011-4497] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Affiliation(s)
- S. G. Velleman
- Department of Animal Sciences, Ohio Agricultural Research and Development Center, The Ohio State University, Wooster 44691
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35
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de Juan-Sanz J, Zafra F, López-Corcuera B, Aragón C. Endocytosis of the neuronal glycine transporter GLYT2: role of membrane rafts and protein kinase C-dependent ubiquitination. Traffic 2011; 12:1850-67. [PMID: 21910806 DOI: 10.1111/j.1600-0854.2011.01278.x] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Glycinergic neurotransmission is terminated by sodium- and chloride-dependent plasma membrane transporters. The neuronal glycine transporter 2 (GLYT2) supplies the terminal with substrate to refill synaptic vesicles containing glycine. This crucial process is defective in human hyperekplexia, a condition that can be caused by mutations in GLYT2. Inhibitory glycinergic neurotransmission is modulated by the GLYT2 exocytosis/endocytosis equilibrium, although the mechanisms underlying the turnover of this transporter remain elusive. We studied GLYT2 internalization pathways and the role of ubiquitination and membrane raft association of the transporter in its endocytosis. Using pharmacological tools, dominant-negative mutants and small-interfering RNAs, we show that the clathrin-mediated pathway is the primary mechanism for constitutive and regulated GLYT2 endocytosis in heterologous cells and neurons. We show that GLYT2 is constitutively internalized from cell surface lipid rafts, remaining associated with rafts in subcellular recycling structures. Protein kinase C (PKC) negatively modulates GLYT2 via rapid and dynamic redistribution of GLYT2 from raft to non-raft membrane subdomains and increasing ubiquitinated GLYT2 endocytosis. This biphasic mechanism is a versatile means to modulate GLYT2 behavior and hence, inhibitory glycinergic neurotransmission. These findings may reveal new therapeutic targets to address glycinergic pathologies associated with alterations in GLYT2 trafficking.
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Affiliation(s)
- Jaime de Juan-Sanz
- Departamento de Biología Molecular and Centro de Biología Molecular Severo Ochoa, Universidad Autónoma de Madrid, Madrid, Spain
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Song Y, McFarland DC, Velleman SG. Fibroblast growth factor 2 and protein kinase C alpha are involved in syndecan-4 cytoplasmic domain modulation of turkey myogenic satellite cell proliferation. Comp Biochem Physiol A Mol Integr Physiol 2011; 161:44-52. [PMID: 21939780 DOI: 10.1016/j.cbpa.2011.09.001] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2011] [Revised: 09/02/2011] [Accepted: 09/04/2011] [Indexed: 11/19/2022]
Abstract
Syndecan-4 core protein is composed of extracellular, transmembrane, and cytoplasmic domains. The cytoplasmic domain functions in transmitting signals into the cell through the protein kinase C alpha (PKCα) pathway. The glycosaminoglycan (GAG) and N-linked glycosylated (N-glycosylated) chains attached to the extracellular domain influence cell proliferation. The current study investigated the function of syndecan-4 cytoplasmic domain in combination with GAG and N-glycosylated chains in turkey muscle cell proliferation, differentiation, fibroblast growth factor 2 (FGF2) responsiveness, and PKCα membrane localization. Syndecan-4 or syndecan-4 without the cytoplasmic domain and with or without the GAG and N-glycosylated chains were transfected or co-transfected with a small interfering RNA targeting syndecan-4 cytoplasmic domain into turkey muscle satellite cells. The overexpression of syndecan-4 mutants increased cell proliferation but did not change differentiation. Syndecan-4 mutants had increased cellular responsiveness to FGF2 during proliferation. Syndecan-4 increased PKCα cell membrane localization, whereas the syndecan-4 mutants decreased PKCα cell membrane localization compared to syndecan-4. However, compared to the cells without transfection, syndecan-4 mutants increased cell membrane localization of PKCα. These data indicated that the syndecan-4 cytoplasmic domain and the GAG and N-glycosylated chains are critical in syndecan-4 regulating satellite cell proliferation, responsiveness to FGF2, and PKCα cell membrane localization.
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Affiliation(s)
- Yan Song
- Department of Animal Sciences, Ohio Agricultural Research and Development Center, The Ohio State University, Wooster, OH 44691, USA.
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37
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Kristensen AS, Andersen J, Jørgensen TN, Sørensen L, Eriksen J, Loland CJ, Strømgaard K, Gether U. SLC6 neurotransmitter transporters: structure, function, and regulation. Pharmacol Rev 2011; 63:585-640. [PMID: 21752877 DOI: 10.1124/pr.108.000869] [Citation(s) in RCA: 591] [Impact Index Per Article: 45.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
The neurotransmitter transporters (NTTs) belonging to the solute carrier 6 (SLC6) gene family (also referred to as the neurotransmitter-sodium-symporter family or Na(+)/Cl(-)-dependent transporters) comprise a group of nine sodium- and chloride-dependent plasma membrane transporters for the monoamine neurotransmitters serotonin (5-hydroxytryptamine), dopamine, and norepinephrine, and the amino acid neurotransmitters GABA and glycine. The SLC6 NTTs are widely expressed in the mammalian brain and play an essential role in regulating neurotransmitter signaling and homeostasis by mediating uptake of released neurotransmitters from the extracellular space into neurons and glial cells. The transporters are targets for a wide range of therapeutic drugs used in treatment of psychiatric diseases, including major depression, anxiety disorders, attention deficit hyperactivity disorder and epilepsy. Furthermore, psychostimulants such as cocaine and amphetamines have the SLC6 NTTs as primary targets. Beginning with the determination of a high-resolution structure of a prokaryotic homolog of the mammalian SLC6 transporters in 2005, the understanding of the molecular structure, function, and pharmacology of these proteins has advanced rapidly. Furthermore, intensive efforts have been directed toward understanding the molecular and cellular mechanisms involved in regulation of the activity of this important class of transporters, leading to new methodological developments and important insights. This review provides an update of these advances and their implications for the current understanding of the SLC6 NTTs.
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Affiliation(s)
- Anders S Kristensen
- Department of Medicinal Chemistry, Faculty of Pharmaceutical Sciences, University of Copenhagen, Copenhagen, Denmark.
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38
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Tsachaki M, Serlidaki D, Fetani A, Zarkou V, Rozani I, Ghiso J, Efthimiopoulos S. Glycosylation of BRI2 on asparagine 170 is involved in its trafficking to the cell surface but not in its processing by furin or ADAM10. Glycobiology 2011; 21:1382-8. [PMID: 21752865 DOI: 10.1093/glycob/cwr097] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Two different mutated forms of BRI2 protein are linked with familial British and Danish dementias, which present neuropathological similarities with Alzheimer's disease. BRI2 is a type II transmembrane protein that is trafficked through the secretory pathway to the cell surface and is processed by furin and ADAM10 (a disintegrin and metalloproteinase domain 10) to release secreted fragments of unknown function. Its apparent molecular mass (42-44 kDa) is significantly higher than that predicted by the number and composition of amino acids (30 kDa) suggesting that BRI2 is glycosylated. In support, bioinformatics analysis indicated that BRI2 bears the consensus sequence Asn-Thr-Ser (residues 170-173) and could be N-glycosylated at Asn170. Given that N-glycosylation is considered essential for protein folding, processing and trafficking, we examined whether BRI2 is N-glycosylated. Treatment of HEK293 (human embryonic kidney) cells expressing BRI2 with the N-glycosylation inhibitor tunicamycin or mutation of Asn170 to alanine reduced its molecular mass by ~2 kDa. These data indicate that BRI2 is N-glycosylated at Asn170. To examine the effect of N-glycosylation on BRI2 trafficking at the cell surface, we performed biotinylation and (35)S methionine pulse-chase experiments. These experiments showed that mutation of Asn170 to alanine reduced BRI2 trafficking at the cell surface and its steady state levels at the plasma membrane. Furthermore, we obtained data indicating that this mutation did not affect cleavage of BRI2 by furin or ADAM10. Our results confirm the theoretical predictions that BRI2 is N-glycosylated at Asn170 and show that this post-translational modification is essential for its expression at the cell surface but not for its proteolytic processing.
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Affiliation(s)
- Maria Tsachaki
- Division of Animal and Human Physiology, Department of Biology, National and Kapodistrian University of Athens, 157 84 Panepistimiopolis, Ilisia, Athens, Greece
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Abstract
Synaptic incorporation of NMDA receptors (NMDARs) is regulated by GluN2 subunits with different rules controlling GluN2A- and GluN2B-containing receptors; whereas GluN2B-containing receptors are constitutively incorporated into synapses, GluN2A incorporation is activity-dependent. We expressed electrophysiologically tagged NMDARs in rat hippocampal slices to identify the molecular determinants controlling the mode of synaptic incorporation of NMDARs. Expressing chimeric GluN2 subunits, we identified a putative N-glycosylation site present in GluN2B, but not in GluN2A, as necessary and sufficient to drive NMDARs into synapses in an activity-independent manner. This suggests a novel mechanism for regulating activity-driven changes and trafficking of NMDARs to the synapse.
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40
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Song Y, McFarland DC, Velleman SG. Role of syndecan-4 side chains in turkey satellite cell growth and development. Dev Growth Differ 2011; 53:97-109. [PMID: 21261615 DOI: 10.1111/j.1440-169x.2010.01230.x] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Syndecan-4 is a cell membrane heparan sulfate proteoglycan that is composed of a core protein and covalently attached glycosaminoglycans (GAG) and N-linked glycosylated (N-glycosylated) chains. Syndecan-4 has been shown to function independent of its GAG chains. Syndecan-4 may derive its biological function from the N-glycosylated chains due to the biological role of N-glycosylated chains in protein folding and cell membrane localization. The objective of the current study was to investigate the role of syndecan-4 N-glycosylated chains and the interaction between GAG and N-glycosylated chains in turkey myogenic satellite cell proliferation, differentiation, and fibroblast growth factor 2 (FGF2) responsiveness. The wild type turkey syndecan-4 and the syndecan-4 without GAG chains were cloned into the expression vector pCMS-EGFP and used as templates to generate syndecan-4 N-glycosylated one-chain and no-chain mutants with or without GAG chains. The wild type syndecan-4, all of the syndecan-4 N-glycosylated chain mutants were transfected into turkey myogenic satellite cells. Cell proliferation, differentiation, and responsiveness to FGF2 were measured. The overexpression of syndecan-4 N-glycosylated mutants with or without GAG chains did not change cell proliferation, differentiation, and responsiveness to FGF2 compared to the wild type syndecan-4 except that the overexpression of syndecan-4 N-glycosylated mutants without GAG chains increased cell proliferation at 48 and 72 h post-transfection. These data suggest that syndecan-4 functions in an FGF2-independent manner, and the N-glycosylated and GAG chains are required for syndecan-4 to regulate turkey myogenic satellite cell proliferation, but not differentiation.
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Affiliation(s)
- Yan Song
- Department of Animal Sciences, Ohio Agricultural Research and Development Center, The Ohio State University, Wooster, 44691, USA
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41
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Hu J, Reutter W, Fan H. Significance of N-Glycosylation and Sialylation of GABA Transporter 1. J Carbohydr Chem 2011. [DOI: 10.1080/07328303.2011.604455] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/15/2022]
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42
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Song Y, Nestor KE, McFarland DC, Velleman SG. Effect of glypican-1 covalently attached chains on turkey myogenic satellite cell proliferation, differentiation, and fibroblast growth factor 2 responsiveness. Poult Sci 2010; 89:123-34. [PMID: 20008810 DOI: 10.3382/ps.2009-00325] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Glypican-1 is a cell membrane heparan sulfate proteoglycan that is composed of a core protein and covalently attached glycosaminoglycan (GAG) chains and N-linked glycosylated (N-glycosylated) chains. The glypican-1 GAG chains are required for cell differentiation and responsiveness to fibroblast growth factor 2 (FGF2). The role of glypican-1 N-glycosylated chains in regulating cell activities has not been reported. The objective of the current study was to investigate the role of glypican-1 N-glycosylated chains and the interaction between N-glycosylated and GAG chains in turkey myogenic satellite cell proliferation, differentiation, and FGF2 responsiveness. The wild-type turkey glypican-1 and turkey glypican-1 with mutated GAG chain attachment sites were cloned into the pCMS-EGFP mammalian expression vector and were used as templates to generate glypican-1 N-glycosylated 1-chain and no-chain mutants with or without GAG chains by site-directed mutagenesis. The wild-type glypican-1 and all glypican-1 N-glycosylated 1-chain and no-chain mutants with or without GAG chains were transfected into turkey myogenic satellite cells. Cell proliferation, differentiation, and FGF2 responsiveness were measured. The overexpression of glypican-1 N-glycosylated 1-chain and no-chain mutants without GAG chains increased cell proliferation and differentiation compared with the wild-type glypican-1 but not the glypican-1 N-glycosylated mutants with GAG chains attached. Cells overexpressing glypican-1 N-glycosylated mutants with or without GAG chains increased cell responsiveness to FGF2 compared with wild-type glypican-1. These data suggest that glypican-1 N-glycosylated chains and GAG chains are critical in regulating turkey myogenic satellite cell proliferation, differentiation, and responsivness to FGF2.
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Affiliation(s)
- Y Song
- Department of Animal Sciences, Ohio Agricultural Research and Development Center, The Ohio State University, Wooster 44691, USA
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Cheng Y, Li M, Wang S, Peng H, Reid S, Ni N, Fang H, Xu W, Wang B. Carbohydrate biomarkers for future disease detection and treatment. Sci China Chem 2010; 53:3-20. [PMID: 32214994 PMCID: PMC7089153 DOI: 10.1007/s11426-010-0021-3] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2009] [Accepted: 10/09/2009] [Indexed: 12/28/2022]
Abstract
Carbohydrates are considered as one of the most important classes of biomarkers for cell types, disease states, protein functions, and developmental states. Carbohydrate "binders" that can specifically recognize a carbohydrate biomarker can be used for developing novel types of site specific delivery methods and imaging agents. In this review, we present selected examples of important carbohydrate biomarkers and how they can be targeted for the development of therapeutic and diagnostic agents. Examples are arranged based on disease categories including (1) infectious diseases, (2) cancer, (3) inflammation and immune responses, (4) signal transduction, (5) stem cell transformation, (6) embryo development, and (7) cardiovascular diseases, though some issues cross therapeutic boundaries.
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Affiliation(s)
- YunFeng Cheng
- Department of Chemistry, Georgia State University, Atlanta, GA 30303 USA
| | - MinYong Li
- Department of Medicinal Chemistry, School of Pharmacy, Shandong University, Jinan, 250012 China
| | - ShaoRu Wang
- Department of Chemistry, Georgia State University, Atlanta, GA 30303 USA
| | - HanJing Peng
- Department of Chemistry, Georgia State University, Atlanta, GA 30303 USA
| | - Suazette Reid
- Department of Chemistry, Georgia State University, Atlanta, GA 30303 USA
| | - NanTing Ni
- Department of Chemistry, Georgia State University, Atlanta, GA 30303 USA
| | - Hao Fang
- Department of Medicinal Chemistry, School of Pharmacy, Shandong University, Jinan, 250012 China
| | - WenFang Xu
- Department of Medicinal Chemistry, School of Pharmacy, Shandong University, Jinan, 250012 China
| | - BingHe Wang
- Department of Chemistry, Georgia State University, Atlanta, GA 30303 USA
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Subramanian VS, Marchant JS, Said HM. Molecular determinants dictating cell surface expression of the human sodium-dependent vitamin C transporter-2 in human liver cells. Am J Physiol Gastrointest Liver Physiol 2010; 298:G267-74. [PMID: 19926816 PMCID: PMC2822508 DOI: 10.1152/ajpgi.00435.2009] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
The human sodium-dependent vitamin C transporter-2 (hSVCT2) plays an important role in cellular accumulation of ascorbic acid in liver cells. However, little is known about the molecular determinants that direct hSVCT2 to the cell surface in hepatocytes. We addressed this issue using live cell imaging methods to resolve the distribution and trafficking of truncated or mutated hSVCT2 constructs in a cellular model of human hepatocytes, HepG2 cells. Whereas a full-length hSVCT2-yellow fluorescent protein (YFP) fusion protein was functionally expressed at the cell surface in HepG2 cells, serial truncation and mutation analysis demonstrated an essential role for both NH(2)- and COOH-terminal sequence(s) for cell surface expression and function. Video-rate confocal imaging showed evidence of dynamic hSVCT2-YFP containing intracellular trafficking vesicles, the motility of which was impaired following disruption of microtubules using nocodazole. However, in a HepG2 cell line stably expressing hSVCT2-YFP at the cell surface, plasma membrane levels of hSVCT2 were unaffected by inhibition of microtubule-associated motor proteins; rather, surface expression of hSVCT2-YFP was increased following treatment with myosin inhibitors. Together, these results show that 1) both NH(2)- and COOH-terminal sequences are essential for proper localization of hSVCT2, 2) cell surface delivery is dependent on intact microtubules, and 3) peripheral microfilaments regulate insertion and retrieval of hSVCT2 into the plasma membrane.
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Affiliation(s)
- Veedamali S. Subramanian
- Departments of 1Medicine, ,2Department of Physiology and Biophysics, University of California, Irvine, California; ,4Department of Veterans Affairs Medical Center, Long Beach, California
| | - Jonathan S. Marchant
- 3Department of Pharmacology, University of Minnesota Medical School, Minnesota; and
| | - Hamid M. Said
- Departments of 1Medicine, ,2Department of Physiology and Biophysics, University of California, Irvine, California; ,4Department of Veterans Affairs Medical Center, Long Beach, California
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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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Skropeta D. The effect of individual N-glycans on enzyme activity. Bioorg Med Chem 2009; 17:2645-53. [PMID: 19285412 DOI: 10.1016/j.bmc.2009.02.037] [Citation(s) in RCA: 138] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2008] [Revised: 02/11/2009] [Accepted: 02/13/2009] [Indexed: 01/08/2023]
Abstract
In a series of investigations, N-glycosylation has proven to be a key determinant of enzyme secretion, activity, binding affinity and substrate specificity, enabling a protein to fine-tune its activity. In the majority of cases elimination of all putative N-glycosylation sites of an enzyme results in significantly reduced protein secretion levels, while removal of individual N-glycosylation sites often leads to the expression of active enzymes showing markedly reduced catalytic activity, with the decreased activity often commensurate with the number of glycosylation sites available, and the fully deglycosylated enzymes showing only minimal activity relative to their glycosylated counterparts. On the other hand, several cases have also recently emerged where deglycosylation of an enzyme results in significantly increased catalytic activity, binding affinity and altered substrate specificity, highlighting the very unique and diverse roles that individual N-glycans play in regulating enzyme function.
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Affiliation(s)
- Danielle Skropeta
- School of Chemistry, University of Wollongong, Wollongong, NSW 2522, Australia.
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Catino MA, Paladino S, Tivodar S, Pocard T, Zurzolo C. N- andO-Glycans Are Not Directly Involved in the Oligomerization and Apical Sorting of GPI Proteins. Traffic 2008; 9:2141-50. [DOI: 10.1111/j.1600-0854.2008.00826.x] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Vagin O, Kraut JA, Sachs G. Role of N-glycosylation in trafficking of apical membrane proteins in epithelia. Am J Physiol Renal Physiol 2008; 296:F459-69. [PMID: 18971212 DOI: 10.1152/ajprenal.90340.2008] [Citation(s) in RCA: 154] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
Polarized distribution of plasma membrane transporters and receptors in epithelia is essential for vectorial functions of epithelia. This polarity is maintained by sorting of membrane proteins into apical or basolateral transport containers in the trans-Golgi network and/or endosomes followed by their delivery to the appropriate plasma membrane domains. Sorting depends on the recognition of sorting signals in proteins by specific sorting machinery. In the present review, we summarize experimental evidence for and against the hypothesis that N-glycans attached to the membrane proteins can act as apical sorting signals. Furthermore, we discuss the roles of N-glycans in the apical sorting event per se and their contribution to folding and quality control of glycoproteins in the endoplasmic reticulum or retention of glycoproteins in the plasma membrane. Finally, we review existing hypotheses on the mechanism of apical sorting and discuss the potential roles of the lectins, VIP36 and galectin-3, as putative apical sorting receptors.
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Affiliation(s)
- Olga Vagin
- Department of Physiology, David Geffen School of Medicine at University of California, Bldg. 113, Rm. 324, 11301 Wilshire Blvd., Los Angeles, California 90073, USA.
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Schilling K, Oberdick J, Rossi F, Baader SL. Besides Purkinje cells and granule neurons: an appraisal of the cell biology of the interneurons of the cerebellar cortex. Histochem Cell Biol 2008; 130:601-15. [PMID: 18677503 DOI: 10.1007/s00418-008-0483-y] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 07/15/2008] [Indexed: 01/29/2023]
Abstract
Ever since the groundbreaking work of Ramon y Cajal, the cerebellar cortex has been recognized as one of the most regularly structured and wired parts of the brain formed by a rather limited set of distinct cells. Its rather protracted course of development, which persists well into postnatal life, the availability of multiple natural mutants, and, more recently, the availability of distinct molecular genetic tools to identify and manipulate discrete cell types have suggested the cerebellar cortex as an excellent model to understand the formation and working of the central nervous system. However, the formulation of a unifying model of cerebellar function has so far proven to be a most cantankerous problem, not least because our understanding of the internal cerebellar cortical circuitry is clearly spotty. Recent research has highlighted the fact that cerebellar cortical interneurons are a quite more diverse and heterogeneous class of cells than generally appreciated, and have provided novel insights into the mechanisms that underpin the development and histogenetic integration of these cells. Here, we provide a short overview of cerebellar cortical interneuron diversity, and we summarize some recent results that are hoped to provide a primer on current understanding of cerebellar biology.
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Affiliation(s)
- Karl Schilling
- Anatomisches Institut, Anatomie und Zellbiologie, Rheinische Friedrich-Wilhelms-Universität, Nussalle 10, 53115 Bonn, Germany.
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