1
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Felipe R, Sarmiento-Jiménez J, Camafeita E, Vázquez J, López-Corcuera B. Role of palmitoylation on the neuronal glycine transporter GlyT2. J Neurochem 2024. [PMID: 39032066 DOI: 10.1111/jnc.16181] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2024] [Revised: 06/08/2024] [Accepted: 07/01/2024] [Indexed: 07/22/2024]
Abstract
The neuronal glycine transporter GlyT2 removes glycine from the synaptic cleft through active Na+, Cl-, and glycine cotransport contributing to the termination of the glycinergic signal as well as supplying substrate to the presynaptic terminal for the maintenance of the neurotransmitter content in synaptic vesicles. Patients with mutations in the human GlyT2 gene (SLC6A5), develop hyperekplexia or startle disease (OMIM 149400), characterized by hypertonia and exaggerated startle responses to trivial stimuli that may have lethal consequences in the neonates as a result of apnea episodes. Post-translational modifications in cysteine residues of GlyT2 are an aspect of structural interest we analyzed. Our study is compatible with a reversible and short-lived S-acylation in spinal cord membranes, detectable by biochemical and proteomics methods (acyl-Rac binding and IP-ABE) confirmed with positive and negative controls (palmitoylated and non-palmitoylated proteins). According to a short-lived modification, direct labeling using click chemistry was faint but mostly consistent. We have analyzed the physiological properties of a GlyT2 mutant lacking the cysteines with high prediction of palmitoylation and the mutant is less prone to be included in lipid rafts, an effect also observed upon treatment with the palmitoylation inhibitor 2-bromopalmitate. This work demonstrates there are determinants of lipid raft inclusion associated with the GlyT2 mutated cysteines, which are presumably modified by palmitoylation.
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Affiliation(s)
- R Felipe
- Departamento de Biología Molecular, Instituto de Biología Molecular (IUBM), Centro de Biología Molecular Severo Ochoa, Consejo Superior de Investigaciones Científicas-Universidad Autónoma de Madrid, Madrid, Spain
| | - J Sarmiento-Jiménez
- Departamento de Biología Molecular, Instituto de Biología Molecular (IUBM), Centro de Biología Molecular Severo Ochoa, Consejo Superior de Investigaciones Científicas-Universidad Autónoma de Madrid, Madrid, Spain
| | - E Camafeita
- Centro Nacional de Investigaciones Cardiovasculares. (ISCIII), Madrid, Spain
- CIBER de Enfermedades Cardiovasculares (CIBERCV), Madrid, Spain
| | - J Vázquez
- Centro Nacional de Investigaciones Cardiovasculares. (ISCIII), Madrid, Spain
- CIBER de Enfermedades Cardiovasculares (CIBERCV), Madrid, Spain
| | - B López-Corcuera
- Departamento de Biología Molecular, Instituto de Biología Molecular (IUBM), Centro de Biología Molecular Severo Ochoa, Consejo Superior de Investigaciones Científicas-Universidad Autónoma de Madrid, Madrid, Spain
- IdiPAZ-Hospital Universitario La Paz, Madrid, Spain
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2
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Piniella D, Zafra F. Functional crosstalk of the glycine transporter GlyT1 and NMDA receptors. Neuropharmacology 2023; 232:109514. [PMID: 37003571 DOI: 10.1016/j.neuropharm.2023.109514] [Citation(s) in RCA: 7] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2022] [Revised: 03/10/2023] [Accepted: 03/20/2023] [Indexed: 04/03/2023]
Abstract
NMDA-type glutamate receptors (NMDARs) constitute one of the main glutamate (Glu) targets in the central nervous system and are involved in synaptic plasticity, which is the molecular substrate of learning and memory. Hypofunction of NMDARs has been associated with schizophrenia, while overstimulation causes neuronal death in neurodegenerative diseases or in stroke. The function of NMDARs requires coincidental binding of Glu along with other cellular signals such as neuronal depolarization, and the presence of other endogenous ligands that modulate their activity by allosterism. Among these allosteric modulators are zinc, protons and Gly, which is an obligatory co-agonist. These characteristics differentiate NMDARs from other receptors, and their structural bases have begun to be established in recent years. In this review we focus on the crosstalk between Glu and glycine (Gly), whose concentration in the NMDAR microenvironment is maintained by various Gly transporters that remove or release it into the medium in a regulated manner. The GlyT1 transporter is particularly involved in this task, and has become a target of great interest for the treatment of schizophrenia since its inhibition leads to an increase in synaptic Gly levels that enhances the activity of NMDARs. However, the only drug that has completed phase III clinical trials did not yield the expected results. Notwithstanding, there are additional drugs that continue to be investigated, and it is hoped that knowledge gained from the recently published 3D structure of GlyT1 may allow the rational design of more effective new drugs.
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Affiliation(s)
- Dolores Piniella
- Centro de Biología Molecular Severo Ochoa, Facultad de Ciencias, Consejo Superior de Investigaciones Científicas, Universidad Autónoma de Madrid, Madrid, Spain; IdiPAZ, Institute of Health Carlos III (ISCIII), Spain
| | - Francisco Zafra
- Centro de Biología Molecular Severo Ochoa, Facultad de Ciencias, Consejo Superior de Investigaciones Científicas, Universidad Autónoma de Madrid, Madrid, Spain; IdiPAZ, Institute of Health Carlos III (ISCIII), Spain.
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3
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Flux coupling, not specificity, shapes the transport and phylogeny of SLC6 glycine transporters. Proc Natl Acad Sci U S A 2022; 119:e2205874119. [PMID: 36191186 PMCID: PMC9564218 DOI: 10.1073/pnas.2205874119] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
ATB[Formula: see text] (SLC6A14) is a member of the amino acid transporter branch of the SLC6 family along with GlyT1 (SLC6A9) and GlyT2 (SLC6A5), two glycine-specific transporters coupled to 2:1 and 3:1 Na[Formula: see text]:Cl[Formula: see text], respectively. In contrast, ATB[Formula: see text] exhibits broad substrate specificity for all neutral and cationic amino acids, and its ionic coupling remains unsettled. Using the reversal potential slope method, we demonstrate a 3:1:1 Na[Formula: see text]:Cl[Formula: see text]:Gly stoichiometry for ATB[Formula: see text] that is consistent with its 2.1 e/Gly charge coupling. Like GlyT2, ATB[Formula: see text] behaves as a unidirectional transporter with virtually no glycine efflux at negative potentials after uptake, except by heteroexchange as remarkably shown by leucine activation of NMDARs in Xenopus oocytes coexpressing both membrane proteins. Analysis and computational modeling of the charge movement of ATB[Formula: see text] reveal a higher affinity for sodium in the absence of substrate than GlyT2 and a gating mechanism that locks Na[Formula: see text] into the apo-transporter at depolarized potentials. A 3:1 Na[Formula: see text]:Cl[Formula: see text] stoichiometry justifies the concentrative transport properties of ATB[Formula: see text] and explains its trophic role in tumor growth, while rationalizing its phylogenetic proximity to GlyT2 despite their extreme divergence in specificity.
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4
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Analysis of Binding Determinants for Different Classes of Competitive and Noncompetitive Inhibitors of Glycine Transporters. Int J Mol Sci 2022; 23:ijms23148050. [PMID: 35887394 PMCID: PMC9317360 DOI: 10.3390/ijms23148050] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2022] [Revised: 07/14/2022] [Accepted: 07/18/2022] [Indexed: 11/16/2022] Open
Abstract
Glycine transporters are interesting therapeutic targets as they play significant roles in glycinergic and glutamatergic systems. The search for new selective inhibitors of particular types of glycine transporters (GlyT-1 and GlyT-2) with beneficial kinetics is hampered by limited knowledge about the spatial structure of these proteins. In this study, a pool of homology models of GlyT-1 and GlyT-2 in different conformational states was constructed using the crystal structures of related transporters from the SLC6 family and the recently revealed structure of GlyT-1 in the inward-open state, in order to investigate their binding sites. The binding mode of the known GlyT-1 and GlyT-2 inhibitors was determined using molecular docking studies, molecular dynamics simulations, and MM-GBSA free energy calculations. The results of this study indicate that two amino acids, Gly373 and Leu476 in GlyT-1 and the corresponding Ser479 and Thr582 in GlyT-2, are mainly responsible for the selective binding of ligands within the S1 site. Apart from these, one pocket of the S2 site, which lies between TM3 and TM10, may also be important. Moreover, selective binding of noncompetitive GlyT-1 inhibitors in the intracellular release pathway is affected by hydrophobic interactions with Ile399, Met382, and Leu158. These results can be useful in the rational design of new glycine transporter inhibitors with desired selectivity and properties in the future.
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5
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Chan MC, Selvam B, Young HJ, Procko E, Shukla D. The substrate import mechanism of the human serotonin transporter. Biophys J 2022; 121:715-730. [PMID: 35114149 PMCID: PMC8943754 DOI: 10.1016/j.bpj.2022.01.024] [Citation(s) in RCA: 10] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2021] [Revised: 12/18/2021] [Accepted: 01/25/2022] [Indexed: 11/17/2022] Open
Abstract
The serotonin transporter (SERT) initiates the reuptake of extracellular serotonin in the synapse to terminate neurotransmission. The cryogenic electron microscopy structures of SERT bound to ibogaine and the physiological substrate serotonin resolved in different states have provided a glimpse of the functional conformations at atomistic resolution. However, the conformational dynamics and structural transitions to intermediate states are not fully understood. Furthermore, the molecular basis of how serotonin is recognized and transported remains unclear. In this study, we performed unbiased microsecond-long simulations of the human SERT to investigate the structural dynamics to various intermediate states and elucidated the complete substrate import pathway. Using Markov state models, we characterized a sequential order of conformational-driven ion-coupled substrate binding and transport events and calculated the free energy barriers of conformation transitions associated with the import mechanism. We find that the transition from the occluded to inward-facing state is the rate-limiting step for substrate import and that the substrate decreases the free energy barriers to achieve the inward-facing state. Our study provides insights on the molecular basis of dynamics-driven ion-substrate recognition and transport of SERT that can serve as a model for other closely related neurotransmitter transporters.
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Affiliation(s)
- Matthew C Chan
- Department of Chemical and Biomolecular Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois
| | - Balaji Selvam
- Department of Chemical and Biomolecular Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois
| | - Heather J Young
- Department of Biochemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois
| | - Erik Procko
- Department of Biochemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois; Center for Biophysics and Quantitative Biology, University of Illinois at Urbana-Champaign, Urbana, Illinois; Neuroscience Program, University of Illinois at Urbana-Champaign, Urbana, Illinois; Cancer Center at Illinois, University of Illinois at Urbana-Champaign, Urbana, Illinois
| | - Diwakar Shukla
- Department of Chemical and Biomolecular Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois; Center for Biophysics and Quantitative Biology, University of Illinois at Urbana-Champaign, Urbana, Illinois; Cancer Center at Illinois, University of Illinois at Urbana-Champaign, Urbana, Illinois; National Center for Supercomputing Applications, University of Illinois at Urbana-Champaign, Urbana, Illinois; Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, Illinois; NIH Center for Macromolecular Modeling and Bioinformatics, University of Illinois at Urbana-Champaign, Urbana, Illinois.
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6
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Frangos ZJ, Cantwell Chater RP, Vandenberg RJ. Glycine Transporter 2: Mechanism and Allosteric Modulation. Front Mol Biosci 2021; 8:734427. [PMID: 34805268 PMCID: PMC8602798 DOI: 10.3389/fmolb.2021.734427] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2021] [Accepted: 10/25/2021] [Indexed: 01/19/2023] Open
Abstract
Neurotransmitter sodium symporters (NSS) are a subfamily of SLC6 transporters responsible for regulating neurotransmitter signalling. They are a major target for psychoactive substances including antidepressants and drugs of abuse, prompting substantial research into their modulation and structure-function dynamics. Recently, a series of allosteric transport inhibitors have been identified, which may reduce side effect profiles, compared to orthosteric inhibitors. Allosteric inhibitors are also likely to provide different clearance kinetics compared to competitive inhibitors and potentially better clinical outcomes. Crystal structures and homology models have identified several allosteric modulatory sites on NSS including the vestibule allosteric site (VAS), lipid allosteric site (LAS) and cholesterol binding site (CHOL1). Whilst the architecture of eukaryotic NSS is generally well conserved there are differences in regions that form the VAS, LAS, and CHOL1. Here, we describe ligand-protein interactions that stabilize binding in each allosteric site and explore how differences between transporters could be exploited to generate NSS specific compounds with an emphasis on GlyT2 modulation.
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Affiliation(s)
- Zachary J Frangos
- Transporter Biology Group, School of Medical Sciences, Faculty of Medicine and Health, University of Sydney, Sydney, NSW, Australia
| | - Ryan P Cantwell Chater
- Transporter Biology Group, School of Medical Sciences, Faculty of Medicine and Health, University of Sydney, Sydney, NSW, Australia
| | - Robert J Vandenberg
- Transporter Biology Group, School of Medical Sciences, Faculty of Medicine and Health, University of Sydney, Sydney, NSW, Australia
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7
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Benito-Muñoz C, Perona A, Felipe R, Pérez-Siles G, Núñez E, Aragón C, López-Corcuera B. Structural Determinants of the Neuronal Glycine Transporter 2 for the Selective Inhibitors ALX1393 and ORG25543. ACS Chem Neurosci 2021; 12:1860-1872. [PMID: 34003005 PMCID: PMC8691691 DOI: 10.1021/acschemneuro.0c00602] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
![]()
The
neuronal glycine transporter GlyT2 modulates inhibitory glycinergic
neurotransmission by controlling the extracellular concentration of
synaptic glycine and the supply of neurotransmitter to the presynaptic
terminal. Spinal cord glycinergic neurons present in the dorsal horn
diminish their activity in pathological pain conditions and behave
as gate keepers of the touch-pain circuitry. The pharmacological blockade
of GlyT2 reduces the progression of the painful signal to rostral
areas of the central nervous system by increasing glycine extracellular
levels, so it has analgesic action. O-[(2-benzyloxyphenyl-3-fluorophenyl)methyl]-l-serine (ALX1393) and N-[[1-(dimethylamino)cyclopentyl]methyl]-3,5-dimethoxy-4-(phenylmethoxy)benzamide
(ORG25543) are two selective GlyT2 inhibitors with nanomolar affinity
for the transporter and analgesic effects in pain animal models, although
with deficiencies which preclude further clinical development. In
this report, we performed a comparative ligand docking of ALX1393
and ORG25543 on a validated GlyT2 structural model including all ligand
sites constructed by homology with the crystallized dopamine transporter
from Drosophila melanogaster. Molecular dynamics
simulations and energy analysis of the complex and functional analysis
of a series of point mutants permitted to determine the structural
determinants of ALX1393 and ORG25543 discrimination by GlyT2. The
ligands establish simultaneous contacts with residues present in transmembrane
domains 1, 3, 6, and 8 and block the transporter in outward-facing
conformation and hence inhibit glycine transport. In addition, differential
interactions of ALX1393 with the cation bound at Na1 site and ORG25543
with TM10 define the differential sites of the inhibitors and explain
some of their individual features. Structural information about the
interactions with GlyT2 may provide useful tools for new drug discovery.
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Affiliation(s)
- Cristina Benito-Muñoz
- Departamento de Biología Molecular, Universidad Autónoma de Madrid, 28049 Madrid, Spain
- Centro de Biología Molecular “Severo Ochoa” Consejo Superior de Investigaciones Científicas, Universidad Autónoma de Madrid, 28049 Madrid, Spain
| | - Almudena Perona
- Departamento de Química en Ciencias Farmacéuticas, Universidad Complutense de Madrid, 28040 Madrid, Spain
| | - Raquel Felipe
- Departamento de Biología Molecular, Universidad Autónoma de Madrid, 28049 Madrid, Spain
- Centro de Biología Molecular “Severo Ochoa” Consejo Superior de Investigaciones Científicas, Universidad Autónoma de Madrid, 28049 Madrid, Spain
| | - Gonzalo Pérez-Siles
- Departamento de Biología Molecular, Universidad Autónoma de Madrid, 28049 Madrid, Spain
- Centro de Biología Molecular “Severo Ochoa” Consejo Superior de Investigaciones Científicas, Universidad Autónoma de Madrid, 28049 Madrid, Spain
| | - Enrique Núñez
- Departamento de Biología Molecular, Universidad Autónoma de Madrid, 28049 Madrid, Spain
- Centro de Biología Molecular “Severo Ochoa” Consejo Superior de Investigaciones Científicas, Universidad Autónoma de Madrid, 28049 Madrid, Spain
| | - Carmen Aragón
- Departamento de Biología Molecular, Universidad Autónoma de Madrid, 28049 Madrid, Spain
- Centro de Biología Molecular “Severo Ochoa” Consejo Superior de Investigaciones Científicas, Universidad Autónoma de Madrid, 28049 Madrid, Spain
- IdiPAZ-Hospital Universitario La Paz, Universidad Autónoma de Madrid, 28049 Madrid, Spain
| | - Beatriz López-Corcuera
- Departamento de Biología Molecular, Universidad Autónoma de Madrid, 28049 Madrid, Spain
- Centro de Biología Molecular “Severo Ochoa” Consejo Superior de Investigaciones Científicas, Universidad Autónoma de Madrid, 28049 Madrid, Spain
- IdiPAZ-Hospital Universitario La Paz, Universidad Autónoma de Madrid, 28049 Madrid, Spain
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8
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Rescue of two trafficking-defective variants of the neuronal glycine transporter GlyT2 associated to hyperekplexia. Neuropharmacology 2021; 189:108543. [PMID: 33794243 DOI: 10.1016/j.neuropharm.2021.108543] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2020] [Revised: 03/25/2021] [Accepted: 03/26/2021] [Indexed: 11/21/2022]
Abstract
Hyperekplexia is a rare sensorimotor syndrome characterized by pathological startle reflex in response to unexpected trivial stimuli for which there is no specific treatment. Neonates suffer from hypertonia and are at high risk of sudden death due to apnea episodes. Mutations in the human SLC6A5 gene encoding the neuronal glycine transporter GlyT2 may disrupt the inhibitory glycinergic neurotransmission and cause a presynaptic form of the disease. The phenotype of missense mutations giving rise to protein misfolding but maintaining residual activity could be rescued by facilitating folding or intracellular trafficking. In this report, we characterized the trafficking properties of two mutants associated with hyperekplexia (A277T and Y707C, rat numbering). Transporter molecules were partially retained in the endoplasmic reticulum showing increased interaction with the endoplasmic reticulum chaperone calnexin. One transporter variant had export difficulties and increased ubiquitination levels, suggestive of enhanced endoplasmic reticulum-associated degradation. However, the two mutant transporters were amenable to correction by calnexin overexpression. Within the search for compounds capable of rescuing mutant phenotypes, we found that the arachidonic acid derivative N-arachidonoyl glycine can rescue the trafficking defects of the two variants in heterologous cells and rat brain cortical neurons. N-arachidonoyl glycine improves the endoplasmic reticulum output by reducing the interaction transporter/calnexin, increasing membrane expression and improving transport activity in a comparable way as the well-established chemical chaperone 4-phenyl-butyrate. This work identifies N-arachidonoyl glycine as a promising compound with potential for hyperekplexia therapy.
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9
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Jiménez E, Fornés A, Felipe R, Núñez E, Aragón C, López-Corcuera B. Calcium-Dependent Regulation of the Neuronal Glycine Transporter GlyT2 by M2 Muscarinic Acetylcholine Receptors. Neurochem Res 2021; 47:190-203. [PMID: 33765249 DOI: 10.1007/s11064-021-03298-x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2020] [Revised: 02/23/2021] [Accepted: 03/12/2021] [Indexed: 10/21/2022]
Abstract
The neuronal glycine transporter GlyT2 modulates inhibitory glycinergic neurotransmission and plays a key role in regulating nociceptive signal progression. The cholinergic system acting through muscarinic acetylcholine receptors (mAChRs) also mediates important regulations of nociceptive transmission being the M2 subtype the most abundantly expressed in the spinal cord. Here we studied the effect of M2 mAChRs stimulation on GlyT2 function co-expressed in a heterologous system with negligible levels of muscarinic receptor activity. We found GlyT2 is down-regulated by carbachol in a calcium-dependent manner. Different components involved in cell calcium homeostasis were analysed to establish a role in the mechanism of GlyT2 inhibition. GlyT2 down-regulation by carbachol was increased by thapsigargin and reduced by internal store depletion, although calcium release from endoplasmic reticulum or mitochondria had a minor role on GlyT2 inhibition. Our results are consistent with a GlyT2 sensitivity to intracellular calcium mobilized by M2 mAChRs in the subcortical area of the plasma membrane. A crucial role of the plasma membrane sodium calcium exchanger NCX is proposed.
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Affiliation(s)
- Esperanza Jiménez
- Departamento de Biología Molecular and Centro de Biología Molecular "Severo Ochoa", Consejo Superior de Investigaciones Científicas-Universidad Autónoma de Madrid, 28049, Madrid, Spain
| | - Amparo Fornés
- Departamento de Biología Molecular and Centro de Biología Molecular "Severo Ochoa", Consejo Superior de Investigaciones Científicas-Universidad Autónoma de Madrid, 28049, Madrid, Spain.,Novartis Farmacéutica S.A., Basel, Switzerland
| | - Raquel Felipe
- Departamento de Biología Molecular and Centro de Biología Molecular "Severo Ochoa", Consejo Superior de Investigaciones Científicas-Universidad Autónoma de Madrid, 28049, Madrid, Spain
| | - Enrique Núñez
- Departamento de Biología Molecular and Centro de Biología Molecular "Severo Ochoa", Consejo Superior de Investigaciones Científicas-Universidad Autónoma de Madrid, 28049, Madrid, Spain.,IdiPAZ-Hospital Universitario La Paz, Madrid, Spain
| | - Carmen Aragón
- Departamento de Biología Molecular and Centro de Biología Molecular "Severo Ochoa", Consejo Superior de Investigaciones Científicas-Universidad Autónoma de Madrid, 28049, Madrid, Spain.,IdiPAZ-Hospital Universitario La Paz, 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, 28049, Madrid, Spain. .,IdiPAZ-Hospital Universitario La Paz, Madrid, Spain.
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10
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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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11
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Dafsari HS, Kawalia A, Sprute R, Karakaya M, Malenica A, Herkenrath P, Nürnberg P, Motameny S, Thiele H, Cirak S. Novel mutations in SLC6A5 with benign course in hyperekplexia. Cold Spring Harb Mol Case Stud 2019; 5:mcs.a004465. [PMID: 31604777 PMCID: PMC6913151 DOI: 10.1101/mcs.a004465] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2019] [Accepted: 09/23/2019] [Indexed: 01/01/2023] Open
Abstract
Infants suffering from life-threatening apnea, stridor, cyanosis, and increased muscle tone may often be misdiagnosed with infantile seizures and inappropriately treated because of lack and delay in genetic diagnosis. Here, we report a patient with increased muscle tone after birth and hypertonic attacks with life-threatening apnea but no epileptiform patterns in EEG recordings. We identified novel compound heterozygous variants in SLC6A5 (NM_004211.4:c.[1429T > C];[1430delC]) by trio whole-exome sequencing, containing a base deletion inherited by the asymptomatic mother leading to a frameshift (c.1430delC, p.Ser477PhefsTer9) and a de novo base exchange leading to an amino acid change (c.1429T > C, p.Ser477Pro). To date, there are four known disease-associated genes for primary hyperekplexia, all of which are involved in the functioning of glycinergic synapses. SLC6A5 encodes the sodium- and chloride-dependent glycine transporter 2 (GlyT2), which recaptures glycine, a major inhibitory transmitter in the brainstem and spinal cord. The diagnosis altered the patient's medical care to his benefit because SLC6A5 mutations with rather benign courses of hyperekplexia may be spared of needless pharmacotherapy. Symptoms eventually decreased in frequency until about once in 2 mo at 2 yr age. We present the first report of halting hyperekplexia episodes by maternal soothing in multiple instances. We highlight the importance of clarifying the genetic diagnosis by rapid next-generation sequencing techniques in this group of infantile apneic attacks with hyperekplexia due to the broad differential diagnoses.
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Affiliation(s)
- Hormos Salimi Dafsari
- Department of Pediatrics, Faculty of Medicine and University Hospital Cologne, University of Cologne, Cologne 50931, Germany.,Center for Molecular Medicine (CMMC), Faculty of Medicine and University Hospital Cologne, University of Cologne, Cologne 50931, Germany
| | - Amit Kawalia
- Cologne Center for Genomics (CCG), Faculty of Medicine, University of Cologne, Cologne 50931, Germany
| | - Rosanne Sprute
- Department of Pediatrics, Faculty of Medicine and University Hospital Cologne, University of Cologne, Cologne 50931, Germany.,Center for Molecular Medicine (CMMC), Faculty of Medicine and University Hospital Cologne, University of Cologne, Cologne 50931, Germany
| | - Mert Karakaya
- Center for Molecular Medicine (CMMC), Faculty of Medicine and University Hospital Cologne, University of Cologne, Cologne 50931, Germany.,Institute of Human Genetics, Faculty of Medicine and University Hospital Cologne, University of Cologne, Cologne 50931, Germany
| | - Anna Malenica
- Department of Pediatrics, Faculty of Medicine and University Hospital Cologne, University of Cologne, Cologne 50931, Germany.,Center for Molecular Medicine (CMMC), Faculty of Medicine and University Hospital Cologne, University of Cologne, Cologne 50931, Germany
| | - Peter Herkenrath
- Department of Pediatrics, Faculty of Medicine and University Hospital Cologne, University of Cologne, Cologne 50931, Germany
| | - Peter Nürnberg
- Cologne Center for Genomics (CCG), Faculty of Medicine, University of Cologne, Cologne 50931, Germany
| | - Susanne Motameny
- Cologne Center for Genomics (CCG), Faculty of Medicine, University of Cologne, Cologne 50931, Germany
| | - Holger Thiele
- Cologne Center for Genomics (CCG), Faculty of Medicine, University of Cologne, Cologne 50931, Germany
| | - Sebahattin Cirak
- Department of Pediatrics, Faculty of Medicine and University Hospital Cologne, University of Cologne, Cologne 50931, Germany.,Center for Molecular Medicine (CMMC), Faculty of Medicine and University Hospital Cologne, University of Cologne, Cologne 50931, Germany.,Center for Rare Diseases, Faculty of Medicine and University Hospital Cologne, University of Cologne, Cologne 50931, Germany
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12
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Erdem FA, Ilic M, Koppensteiner P, Gołacki J, Lubec G, Freissmuth M, Sandtner W. A comparison of the transport kinetics of glycine transporter 1 and glycine transporter 2. J Gen Physiol 2019; 151:1035-1050. [PMID: 31270129 PMCID: PMC6683666 DOI: 10.1085/jgp.201912318] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2019] [Revised: 04/16/2019] [Accepted: 06/17/2019] [Indexed: 12/20/2022] Open
Abstract
Erdem et al. compare the kinetics of the SLC6 family glycine transporters GlyT1 and GlyT2. Though the two transporters are rate-limited by distinct reaction steps, they both display high transport capacity, with the kinetics of GlyT1 sufficient to supply extracellular glycine to the NMDA receptor. Transporters of the solute carrier 6 (SLC6) family translocate their cognate substrate together with Na+ and Cl−. Detailed kinetic models exist for the transporters of GABA (GAT1/SLC6A1) and the monoamines dopamine (DAT/SLC6A3) and serotonin (SERT/SLC6A4). Here, we posited that the transport cycle of individual SLC6 transporters reflects the physiological requirements they operate under. We tested this hypothesis by analyzing the transport cycle of glycine transporter 1 (GlyT1/SLC6A9) and glycine transporter 2 (GlyT2/SLC6A5). GlyT2 is the only SLC6 family member known to translocate glycine, Na+, and Cl− in a 1:3:1 stoichiometry. We analyzed partial reactions in real time by electrophysiological recordings. Contrary to monoamine transporters, both GlyTs were found to have a high transport capacity driven by rapid return of the empty transporter after release of Cl− on the intracellular side. Rapid cycling of both GlyTs was further supported by highly cooperative binding of cosubstrate ions and substrate such that their forward transport mode was maintained even under conditions of elevated intracellular Na+ or Cl−. The most important differences in the transport cycle of GlyT1 and GlyT2 arose from the kinetics of charge movement and the resulting voltage-dependent rate-limiting reactions: the kinetics of GlyT1 were governed by transition of the substrate-bound transporter from outward- to inward-facing conformations, whereas the kinetics of GlyT2 were governed by Na+ binding (or a related conformational change). Kinetic modeling showed that the kinetics of GlyT1 are ideally suited for supplying the extracellular glycine levels required for NMDA receptor activation.
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Affiliation(s)
- Fatma Asli Erdem
- Institute of Pharmacology and the Gaston H. Glock Research Laboratories for Exploratory Drug Development, Center of Physiology and Pharmacology, Medical University of Vienna, Vienna, Austria
| | - Marija Ilic
- Department of Pharmaceutical Chemistry, Faculty of Life Sciences, University of Vienna, Vienna, Austria
| | | | - Jakub Gołacki
- Institute of Pharmacology and the Gaston H. Glock Research Laboratories for Exploratory Drug Development, Center of Physiology and Pharmacology, Medical University of Vienna, Vienna, Austria
| | - Gert Lubec
- Neuroproteomics, Paracelsus Private Medical University, Salzburg, Austria
| | - Michael Freissmuth
- Institute of Pharmacology and the Gaston H. Glock Research Laboratories for Exploratory Drug Development, Center of Physiology and Pharmacology, Medical University of Vienna, Vienna, Austria
| | - Walter Sandtner
- Institute of Pharmacology and the Gaston H. Glock Research Laboratories for Exploratory Drug Development, Center of Physiology and Pharmacology, Medical University of Vienna, Vienna, Austria
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Kickinger S, Hellsberg E, Frølund B, Schousboe A, Ecker GF, Wellendorph P. Structural and molecular aspects of betaine-GABA transporter 1 (BGT1) and its relation to brain function. Neuropharmacology 2019; 161:107644. [PMID: 31108110 DOI: 10.1016/j.neuropharm.2019.05.021] [Citation(s) in RCA: 23] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2019] [Revised: 04/14/2019] [Accepted: 05/16/2019] [Indexed: 01/09/2023]
Abstract
ɣ-aminobutyric-acid (GABA) functions as the principal inhibitory neurotransmitter in the central nervous system. Imbalances in GABAergic neurotransmission are involved in the pathophysiology of various neurological diseases such as epilepsy, Alzheimer's disease and stroke. GABA transporters (GATs) facilitate the termination of GABAergic signaling by transporting GABA together with sodium and chloride from the synaptic cleft into presynaptic neurons and surrounding glial cells. Four different GATs have been identified that all belong to the solute carrier 6 (SLC6) transporter family: GAT1-3 (SLC6A1, SLC6A13, SLC6A11) and betaine/GABA transporter 1 (BGT1, SLC6A12). BGT1 has emerged as an interesting target for treating epilepsy due to animal studies that reported anticonvulsant effects for the GAT1/BGT1 selective inhibitor EF1502 and the BGT1 selective inhibitor RPC-425. However, the precise involvement of BGT1 in epilepsy remains elusive because of its controversial expression levels in the brain and the lack of highly selective and potent tool compounds. This review gathers the current structural and functional knowledge on BGT1 with emphasis on brain relevance, discusses all available compounds, and tries to shed light on the molecular determinants driving BGT1 selectivity. This article is part of the issue entitled 'Special Issue on Neurotransmitter Transporters'.
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Affiliation(s)
- Stefanie Kickinger
- University of Vienna, Department of Pharmaceutical Chemistry, Althanstrasse 14, 1090, Vienna, Austria
| | - Eva Hellsberg
- University of Vienna, Department of Pharmaceutical Chemistry, Althanstrasse 14, 1090, Vienna, Austria
| | - Bente Frølund
- University of Copenhagen, Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, 2 Universitetsparken, 2100, Copenhagen, Denmark
| | - Arne Schousboe
- University of Copenhagen, Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, 2 Universitetsparken, 2100, Copenhagen, Denmark
| | - Gerhard F Ecker
- University of Vienna, Department of Pharmaceutical Chemistry, Althanstrasse 14, 1090, Vienna, Austria
| | - Petrine Wellendorph
- University of Copenhagen, Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, 2 Universitetsparken, 2100, Copenhagen, Denmark.
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