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Yang PF, Nie TL, Sun XN, Xu LX, Ma C, Wang F, Long LH, Chen JG. Wheel-Running Exercise Alleviates Anxiety-Like Behavior via Down-Regulating S-Nitrosylation of Gephyrin in the Basolateral Amygdala of Male Rats. ADVANCED SCIENCE (WEINHEIM, BADEN-WURTTEMBERG, GERMANY) 2024:e2400205. [PMID: 38965798 DOI: 10.1002/advs.202400205] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/07/2024] [Revised: 06/06/2024] [Indexed: 07/06/2024]
Abstract
Physical exercise has beneficial effect on anxiety disorders, but the underlying molecular mechanism remains largely unknown. Here, it is demonstrated that physical exercise can downregulate the S-nitrosylation of gephyrin (SNO-gephyrin) in the basolateral amygdala (BLA) to exert anxiolytic effects. It is found that the level of SNO-gephyrin is significantly increased in the BLA of high-anxiety rats and a downregulation of SNO-gephyrin at cysteines 212 and 284 produced anxiolytic effect. Mechanistically, inhibition of SNO-gephyrin by either Cys212 or Cys284 mutations increased the surface expression of GABAAR γ2 and the subsequent GABAergic neurotransmission, exerting anxiolytic effect in male rats. On the other side, overexpression of neuronal nitric oxide synthase in the BLA abolished the anxiolytic-like effects of physical exercise. This study reveals a key role of downregulating SNO-gephyrin in the anxiolytic effects of physical exercise, providing a new explanation for protein post-translational modifications in the brain after exercise.
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Affiliation(s)
- Ping-Fen Yang
- State Key Laboratory for Diagnosis and Treatment of Severe Zoonotic Infectious Diseases, Department of Pharmacology, School of Basic Medicine, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, 430030, China
- The Key Laboratory for Drug Target Researches and Pharmacodynamic Evaluation of Hubei Province, Wuhan, 430030, China
| | - Tai-Lei Nie
- State Key Laboratory for Diagnosis and Treatment of Severe Zoonotic Infectious Diseases, Department of Pharmacology, School of Basic Medicine, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, 430030, China
- The Key Laboratory for Drug Target Researches and Pharmacodynamic Evaluation of Hubei Province, Wuhan, 430030, China
| | - Xia-Nan Sun
- State Key Laboratory for Diagnosis and Treatment of Severe Zoonotic Infectious Diseases, Department of Pharmacology, School of Basic Medicine, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, 430030, China
- The Key Laboratory for Drug Target Researches and Pharmacodynamic Evaluation of Hubei Province, Wuhan, 430030, China
| | - Lan-Xin Xu
- State Key Laboratory for Diagnosis and Treatment of Severe Zoonotic Infectious Diseases, Department of Pharmacology, School of Basic Medicine, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, 430030, China
- The Key Laboratory for Drug Target Researches and Pharmacodynamic Evaluation of Hubei Province, Wuhan, 430030, China
| | - Cong Ma
- Key Laboratory of Molecular Biophysics of the Ministry of Education, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, 430030, China
| | - Fang Wang
- State Key Laboratory for Diagnosis and Treatment of Severe Zoonotic Infectious Diseases, Department of Pharmacology, School of Basic Medicine, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, 430030, China
- The Key Laboratory for Drug Target Researches and Pharmacodynamic Evaluation of Hubei Province, Wuhan, 430030, China
- Hubei Shizhen Laboratory, Wuhan, 430030, China
| | - Li-Hong Long
- State Key Laboratory for Diagnosis and Treatment of Severe Zoonotic Infectious Diseases, Department of Pharmacology, School of Basic Medicine, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, 430030, China
- The Key Laboratory for Drug Target Researches and Pharmacodynamic Evaluation of Hubei Province, Wuhan, 430030, China
- Hubei Shizhen Laboratory, Wuhan, 430030, China
| | - Jian-Guo Chen
- State Key Laboratory for Diagnosis and Treatment of Severe Zoonotic Infectious Diseases, Department of Pharmacology, School of Basic Medicine, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, 430030, China
- The Key Laboratory for Drug Target Researches and Pharmacodynamic Evaluation of Hubei Province, Wuhan, 430030, China
- Hubei Shizhen Laboratory, Wuhan, 430030, China
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Welle TM, Rajgor D, Garcia JD, Kareemo D, Zych SM, Gookin SE, Martinez TP, Dell’Acqua ML, Ford CP, Kennedy MJ, Smith KR. miRNA-mediated control of gephyrin synthesis drives sustained inhibitory synaptic plasticity. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.12.12.570420. [PMID: 38168421 PMCID: PMC10760056 DOI: 10.1101/2023.12.12.570420] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 01/05/2024]
Abstract
Activity-dependent protein synthesis is crucial for many long-lasting forms of synaptic plasticity. However, our understanding of the translational mechanisms controlling inhibitory synapses is limited. One distinct form of inhibitory long-term potentiation (iLTP) enhances postsynaptic clusters of GABAARs and the primary inhibitory scaffold, gephyrin, to promote sustained synaptic strengthening. While we previously found that persistent iLTP requires mRNA translation, the precise mechanisms controlling gephyrin translation during this process remain unknown. Here, we identify miR153 as a novel regulator of Gphn mRNA translation which controls gephyrin protein levels and synaptic clustering, ultimately impacting GABAergic synaptic structure and function. We find that iLTP induction downregulates miR153, reversing its translational suppression of Gphn mRNA and allowing for increased de novo gephyrin protein synthesis and synaptic clustering during iLTP. Finally, we find that reduced miR153 expression during iLTP is driven by an excitation-transcription coupling pathway involving calcineurin, NFAT and HDACs, which also controls the miRNA-dependent upregulation of GABAARs. Overall, this work delineates a miRNA-dependent post-transcriptional mechanism that controls the expression of the key synaptic scaffold, gephyrin, and may converge with parallel miRNA pathways to coordinate gene upregulation to maintain inhibitory synaptic plasticity.
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Affiliation(s)
- Theresa M. Welle
- Department of Pharmacology, University of Colorado School of Medicine, Anschutz Medical Campus, 12800 East 19th Avenue, Aurora, CO 80045
- T.M.W and D.R. contributed equally to this work
| | - Dipen Rajgor
- Department of Pharmacology, University of Colorado School of Medicine, Anschutz Medical Campus, 12800 East 19th Avenue, Aurora, CO 80045
- T.M.W and D.R. contributed equally to this work
| | - Joshua D. Garcia
- Department of Pharmacology, University of Colorado School of Medicine, Anschutz Medical Campus, 12800 East 19th Avenue, Aurora, CO 80045
| | - Dean Kareemo
- Department of Pharmacology, University of Colorado School of Medicine, Anschutz Medical Campus, 12800 East 19th Avenue, Aurora, CO 80045
| | - Sarah M. Zych
- Department of Pharmacology, University of Colorado School of Medicine, Anschutz Medical Campus, 12800 East 19th Avenue, Aurora, CO 80045
| | - Sara E. Gookin
- Department of Pharmacology, University of Colorado School of Medicine, Anschutz Medical Campus, 12800 East 19th Avenue, Aurora, CO 80045
| | - Tyler P. Martinez
- Department of Pharmacology, University of Colorado School of Medicine, Anschutz Medical Campus, 12800 East 19th Avenue, Aurora, CO 80045
| | - Mark L. Dell’Acqua
- Department of Pharmacology, University of Colorado School of Medicine, Anschutz Medical Campus, 12800 East 19th Avenue, Aurora, CO 80045
| | - Christopher P. Ford
- Department of Pharmacology, University of Colorado School of Medicine, Anschutz Medical Campus, 12800 East 19th Avenue, Aurora, CO 80045
| | - Matthew J. Kennedy
- Department of Pharmacology, University of Colorado School of Medicine, Anschutz Medical Campus, 12800 East 19th Avenue, Aurora, CO 80045
| | - Katharine R. Smith
- Department of Pharmacology, University of Colorado School of Medicine, Anschutz Medical Campus, 12800 East 19th Avenue, Aurora, CO 80045
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Automated Image Analysis Reveals Different Localization of Synaptic Gephyrin C4 Splice Variants. eNeuro 2023; 10:ENEURO.0102-22.2022. [PMID: 36543537 PMCID: PMC9831149 DOI: 10.1523/eneuro.0102-22.2022] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2022] [Revised: 11/12/2022] [Accepted: 12/13/2022] [Indexed: 12/24/2022] Open
Abstract
Postsynaptic scaffolding proteins function as central organization hubs, ensuring the synaptic localization of neurotransmitter receptors, trans-synaptic adhesion proteins, and signaling molecules. Gephyrin is the major postsynaptic scaffolding protein at glycinergic and a subset of GABAergic inhibitory synapses. In contrast to cells outside the CNS, where one gephyrin isoform is predominantly expressed, neurons express different splice variants. In this study, we characterized the expression and scaffolding of neuronal gephyrin isoforms differing in the inclusion of the C4 cassettes located in the central C-domain. In hippocampal and cortical neuronal populations, gephyrin P1, lacking additional cassettes, is the most abundantly expressed isoform. In addition, alternative splicing generated isoforms carrying predominantly C4a, and minor amounts of C4c or C4d cassettes. We detected no striking difference in C4 isoform expression between different neuron types and a single neuron can likely express all C4 isoforms. To avoid the cytosolic aggregates that are commonly observed upon exogenous gephyrin expression, we used adeno-associated virus (AAV)-mediated expression to analyze the scaffolding behavior of individual C4 isoforms in murine dissociated hippocampal glutamatergic neurons. While all isoforms showed similar clustering at GABAergic synapses, a thorough quantitative analysis revealed localization differences for the C4c isoform (also known as P2). Specifically, synaptic C4c isoform clusters showed a more distal dendritic localization and reduced occurrence at P1-predominating synapses. Additionally, inhibitory currents displayed faster decay kinetics in the presence of gephyrin C4c compared with P1. Therefore, inhibitory synapse heterogeneity may be influenced, at least in part, by mechanisms relating to C4 cassette splicing.
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Mayr SJ, Mendel RR, Schwarz G. Molybdenum cofactor biology, evolution and deficiency. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2020; 1868:118883. [PMID: 33017596 DOI: 10.1016/j.bbamcr.2020.118883] [Citation(s) in RCA: 33] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Received: 06/30/2020] [Revised: 09/21/2020] [Accepted: 09/24/2020] [Indexed: 12/14/2022]
Abstract
The molybdenum cofactor (Moco) represents an ancient metal‑sulfur cofactor, which participates as catalyst in carbon, nitrogen and sulfur cycles, both on individual and global scale. Given the diversity of biological processes dependent on Moco and their evolutionary age, Moco is traced back to the last universal common ancestor (LUCA), while Moco biosynthetic genes underwent significant changes through evolution and acquired additional functions. In this review, focused on eukaryotic Moco biology, we elucidate the benefits of gene fusions on Moco biosynthesis and beyond. While originally the gene fusions were driven by biosynthetic advantages such as coordinated expression of functionally related proteins and product/substrate channeling, they also served as origin for the development of novel functions. Today, Moco biosynthetic genes are involved in a multitude of cellular processes and loss of the according gene products result in severe disorders, both related to Moco biosynthesis and secondary enzyme functions.
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Affiliation(s)
- Simon J Mayr
- Institute of Biochemistry, Department of Chemistry, Center for Molecular Medicine, University of Cologne, Zuelpicher Str. 47, 50674 Koeln, Germany
| | - Ralf-R Mendel
- Institute of Plant Biology, Braunschweig University of Technology, Humboldtstr. 1, 38106 Braunschweig, Germany
| | - Guenter Schwarz
- Institute of Biochemistry, Department of Chemistry, Center for Molecular Medicine, University of Cologne, Zuelpicher Str. 47, 50674 Koeln, Germany.
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Khayenko V, Maric HM. Targeting GABA AR-Associated Proteins: New Modulators, Labels and Concepts. Front Mol Neurosci 2019; 12:162. [PMID: 31293385 PMCID: PMC6606717 DOI: 10.3389/fnmol.2019.00162] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2019] [Accepted: 06/12/2019] [Indexed: 12/21/2022] Open
Abstract
γ-aminobutyric acid type A receptors (GABAARs) are the major mediators of synaptic inhibition in the brain. Aberrant GABAAR activity or regulation is observed in various neurodevelopmental disorders, neurodegenerative diseases and mental illnesses, including epilepsy, Alzheimer’s and schizophrenia. Benzodiazepines, anesthetics and other pharmaceutics targeting these receptors find broad clinical use, but their inherent lack of receptor subtype specificity causes unavoidable side effects, raising a need for new or adjuvant medications. In this review article, we introduce a new strategy to modulate GABAeric signaling: targeting the intracellular protein interactors of GABAARs. Of special interest are scaffolding, anchoring and supporting proteins that display high GABAAR subtype specificity. Recent efforts to target gephyrin, the major intracellular integrator of GABAergic signaling, confirm that GABAAR-associated proteins can be successfully targeted through diverse molecules, including recombinant proteins, intrabodies, peptide-based probes and small molecules. Small-molecule artemisinins and peptides derived from endogenous interactors, that specifically target the universal receptor binding site of gephyrin, acutely affect synaptic GABAAR numbers and clustering, modifying neuronal transmission. Interference with GABAAR trafficking provides another way to modulate inhibitory signaling. Peptides blocking the binding site of GABAAR to AP2 increase the surface concentration of GABAAR clusters and enhance GABAergic signaling. Engineering of gephyrin binding peptides delivered superior means to interrogate neuronal structure and function. Fluorescent peptides, designed from gephyrin binders, enable live neuronal staining and visualization of gephyrin in the post synaptic sites with submicron resolution. We anticipate that in the future, novel fluorescent probes, with improved size and binding efficiency, may find wide application in super resolution microscopy studies, enlightening the nanoscale architecture of the inhibitory synapse. Broader studies on GABAAR accessory proteins and the identification of the exact molecular binding interfaces and affinities will advance the development of novel GABAAR modulators and following in vivo studies will reveal their clinical potential as adjuvant or stand-alone drugs.
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Affiliation(s)
- Vladimir Khayenko
- Institute of Structural Biology, Rudolf Virchow Center for Experimental Biomedicine, University of Würzburg, Würzburg, Germany.,Department of Biotechnology and Biophysics, Biocenter, University of Würzburg, Würzburg, Germany
| | - Hans Michael Maric
- Institute of Structural Biology, Rudolf Virchow Center for Experimental Biomedicine, University of Würzburg, Würzburg, Germany.,Department of Biotechnology and Biophysics, Biocenter, University of Würzburg, Würzburg, Germany
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6
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Que L, Winterer J, Földy C. Deep Survey of GABAergic Interneurons: Emerging Insights From Gene-Isoform Transcriptomics. Front Mol Neurosci 2019; 12:115. [PMID: 31133800 PMCID: PMC6514532 DOI: 10.3389/fnmol.2019.00115] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2019] [Accepted: 04/23/2019] [Indexed: 11/13/2022] Open
Abstract
GABAergic interneuron diversity is a key feature in the brain that helps to create different brain activity patterns and behavioral states. Cell type classification schemes—based on anatomical, physiological and molecular features—have provided us with a detailed understanding of the distinct types that constitute this diversity and their contribution to brain function. Over recent years, the utility of single-cell RNAseq has majorly complemented this existing framework, vastly expanding our knowledge base, particularly regarding molecular features. Single-cell gene-expression profiles of tens of thousands of GABAergic cells from many different types are now available. The analysis of these data has shed new lights onto previous classification principles and illuminates a path towards a deeper understanding of molecular hallmarks behind interneuron diversity. A large part of such molecular features is synapse-related. These include ion channels and receptors, as well as key synaptic organizers and trans-synaptic signaling molecules. Increasing evidence suggests that transcriptional and post-transcriptional modifications further diversify these molecules and generate cell type-specific features. Thus, unraveling the cell type-specific nature of gene-isoform expression will be a key in cell type classification. This review article discusses progress in the transcriptomic survey of interneurons and insights that have begun to manifest from isoform-level analyses.
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Affiliation(s)
- Lin Que
- Laboratory of Neural Connectivity, Faculties of Medicine and Natural Sciences, Brain Research Institute, University of Zurich, Zurich, Switzerland
| | - Jochen Winterer
- Laboratory of Neural Connectivity, Faculties of Medicine and Natural Sciences, Brain Research Institute, University of Zurich, Zurich, Switzerland
| | - Csaba Földy
- Laboratory of Neural Connectivity, Faculties of Medicine and Natural Sciences, Brain Research Institute, University of Zurich, Zurich, Switzerland
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Kasaragod VB, Schindelin H. Structure-Function Relationships of Glycine and GABA A Receptors and Their Interplay With the Scaffolding Protein Gephyrin. Front Mol Neurosci 2018; 11:317. [PMID: 30258351 PMCID: PMC6143783 DOI: 10.3389/fnmol.2018.00317] [Citation(s) in RCA: 33] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2018] [Accepted: 08/16/2018] [Indexed: 12/03/2022] Open
Abstract
Glycine and γ-aminobutyric acid (GABA) are the major determinants of inhibition in the central nervous system (CNS). These neurotransmitters target glycine and GABAA receptors, respectively, which both belong to the Cys-loop superfamily of pentameric ligand-gated ion channels (pLGICs). Interactions of the neurotransmitters with the cognate receptors result in receptor opening and a subsequent influx of chloride ions, which, in turn, leads to hyperpolarization of the membrane potential, thus counteracting excitatory stimuli. The majority of glycine receptors and a significant fraction of GABAA receptors (GABAARs) are recruited and anchored to the post-synaptic membrane by the central scaffolding protein gephyrin. This ∼93 kDa moonlighting protein is structurally organized into an N-terminal G-domain (GephG) connected to a C-terminal E-domain (GephE) via a long unstructured linker. Both inhibitory neurotransmitter receptors interact via a short peptide motif located in the large cytoplasmic loop located in between transmembrane helices 3 and 4 (TM3-TM4) of the receptors with a universal receptor-binding epitope residing in GephE. Gephyrin engages in nearly identical interactions with the receptors at the N-terminal end of the peptide motif, and receptor-specific interaction toward the C-terminal region of the peptide. In addition to its receptor-anchoring function, gephyrin also interacts with a rather large collection of macromolecules including different cytoskeletal elements, thus acting as central scaffold at inhibitory post-synaptic specializations. Dysfunctions in receptor-mediated or gephyrin-mediated neurotransmission have been identified in various severe neurodevelopmental disorders. Although biochemical, cellular and electrophysiological studies have helped to understand the physiological and pharmacological roles of the receptors, recent high resolution structures of the receptors have strengthened our understanding of the receptors and their gating mechanisms. Besides that, multiple crystal structures of GephE in complex with receptor-derived peptides have shed light into receptor clustering by gephyrin at inhibitory post-synapses. This review will highlight recent biochemical and structural insights into gephyrin and the GlyRs as well as GABAA receptors, which provide a deeper understanding of the molecular machinery mediating inhibitory neurotransmission.
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Affiliation(s)
- Vikram B Kasaragod
- Institute of Structural Biology, Rudolf Virchow Center for Experimental Biomedicine, University of Würzburg, Würzburg, Germany
| | - Hermann Schindelin
- Institute of Structural Biology, Rudolf Virchow Center for Experimental Biomedicine, University of Würzburg, Würzburg, Germany
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Alvarez FJ. Gephyrin and the regulation of synaptic strength and dynamics at glycinergic inhibitory synapses. Brain Res Bull 2016; 129:50-65. [PMID: 27612963 DOI: 10.1016/j.brainresbull.2016.09.003] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2016] [Revised: 08/23/2016] [Accepted: 09/05/2016] [Indexed: 01/23/2023]
Abstract
Glycinergic synapses predominate in brainstem and spinal cord where they modulate motor and sensory processing. Their postsynaptic mechanisms have been considered rather simple because they lack a large variety of glycine receptor isoforms and have relatively simple postsynaptic densities at the ultrastructural level. However, this simplicity is misleading being their postsynaptic regions regulated by a variety of complex mechanisms controlling the efficacy of synaptic inhibition. Early studies suggested that glycinergic inhibitory strength and dynamics depend largely on structural features rather than on molecular complexity. These include regulation of the number of postsynaptic glycine receptors, their localization and the amount of co-localized GABAA receptors and GABA-glycine co-transmission. These properties we now know are under the control of gephyrin. Gephyrin is the first postsynaptic scaffolding protein ever discovered and it was recently found to display a large degree of variation and regulation by splice variants, posttranslational modifications, intracellular trafficking and interactions with the underlying cytoskeleton. Many of these mechanisms are governed by converging excitatory activity and regulate gephyrin oligomerization and receptor binding, the architecture of the postsynaptic density (and by extension the whole synaptic complex), receptor retention and stability. These newly uncovered molecular mechanisms define the size and number of gephyrin postsynaptic regions and the numbers and proportions of glycine and GABAA receptors contained within. All together, they control the emergence of glycinergic synapses of different strength and temporal properties to best match the excitatory drive received by each individual neuron or local dendritic compartment.
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Affiliation(s)
- Francisco J Alvarez
- Department of Physiology, Emory University, Atlanta, GA 30322-3110, United States.
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9
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Choii G, Ko J. Gephyrin: a central GABAergic synapse organizer. Exp Mol Med 2015; 47:e158. [PMID: 25882190 DOI: 10.1038/emm.2015.5] [Citation(s) in RCA: 91] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2014] [Accepted: 12/18/2014] [Indexed: 01/22/2023] Open
Abstract
Gephyrin is a central element that anchors, clusters and stabilizes glycine and γ-aminobutyric acid type A receptors at inhibitory synapses of the mammalian brain. It self-assembles into a hexagonal lattice and interacts with various inhibitory synaptic proteins. Intriguingly, the clustering of gephyrin, which is regulated by multiple posttranslational modifications, is critical for inhibitory synapse formation and function. In this review, we summarize the basic properties of gephyrin and describe recent findings regarding its roles in inhibitory synapse formation, function and plasticity. We will also discuss the implications for the pathophysiology of brain disorders and raise the remaining open questions in this field.
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Affiliation(s)
- Gayoung Choii
- Department of Biochemistry, College of Life Science and Biotechnology, Yonsei University, Seoul, Korea
| | - Jaewon Ko
- 1] Department of Biochemistry, College of Life Science and Biotechnology, Yonsei University, Seoul, Korea [2] Department of Psychiatry, Yonsei University College of Medicine, Seoul, Korea
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10
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Abstract
The neurotransmitters GABA and glycine mediate fast synaptic inhibition by activating ligand-gated chloride channels--namely, type A GABA (GABA(A)) and glycine receptors. Both types of receptors are anchored postsynaptically by gephyrin, which self-assembles into a scaffold and interacts with the cytoskeleton. Current research indicates that postsynaptic gephyrin clusters are dynamic assemblies that are held together and regulated by multiple protein-protein interactions. Moreover, post-translational modifications of gephyrin regulate the formation and plasticity of GABAergic synapses by altering the clustering properties of postsynaptic scaffolds and thereby the availability and function of receptors and other signalling molecules. Here, we discuss the formation and regulation of the gephyrin scaffold, its role in GABAergic and glycinergic synaptic function and the implications for the pathophysiology of brain disorders caused by abnormal inhibitory neurotransmission.
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Del Pino I, Koch D, Schemm R, Qualmann B, Betz H, Paarmann I. Proteomic analysis of glycine receptor β subunit (GlyRβ)-interacting proteins: evidence for syndapin I regulating synaptic glycine receptors. J Biol Chem 2014; 289:11396-11409. [PMID: 24509844 DOI: 10.1074/jbc.m113.504860] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Glycine receptors (GlyRs) mediate inhibitory neurotransmission in spinal cord and brainstem. They are clustered at inhibitory postsynapses via a tight interaction of their β subunits (GlyRβ) with the scaffolding protein gephyrin. In an attempt to isolate additional proteins interacting with GlyRβ, we performed pulldown experiments with rat brain extracts using a glutathione S-transferase fusion protein encompassing amino acids 378-455 of the large intracellular loop of GlyRβ as bait. This identified syndapin I (SdpI) as a novel interaction partner of GlyRβ that coimmunoprecipitates with native GlyRs from brainstem extracts. Both SdpI and SdpII bound efficiently to the intracellular loop of GlyRβ in vitro and colocalized with GlyRβ upon coexpression in COS-7 cells. The SdpI-binding site was mapped to a proline-rich sequence of 22 amino acids within the intracellular loop of GlyRβ. Deletion and point mutation analysis disclosed that SdpI binding to GlyRβ is Src homology 3 domain-dependent. In cultured rat spinal cord neurons, SdpI immunoreactivity was found to partially colocalize with marker proteins of inhibitory and excitatory synapses. When SdpI was acutely knocked down in cultured spinal cord neurons by viral miRNA expression, postsynaptic GlyR clusters were significantly reduced in both size and number. Similar changes in GlyR cluster properties were found in spinal cultures from SdpI-deficient mice. Our results are consistent with a role of SdpI in the trafficking and/or cytoskeletal anchoring of synaptic GlyRs.
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Affiliation(s)
- Isabel Del Pino
- Department of Neurochemistry, Max-Planck-Institute for Brain Research, D-60438 Frankfurt/Main
| | - Dennis Koch
- Institute for Biochemistry I, Jena University Hospital, Friedrich Schiller University Jena, D-07743 Jena
| | - Rudolf Schemm
- Department for Theoretical and Computational Biophysics, Max-Planck-Institute for Biophysical Chemistry, D-37077 Göttingen, and
| | - Britta Qualmann
- Institute for Biochemistry I, Jena University Hospital, Friedrich Schiller University Jena, D-07743 Jena
| | - Heinrich Betz
- Department of Neurochemistry, Max-Planck-Institute for Brain Research, D-60438 Frankfurt/Main,; Max-Planck Institute for Medical Research, 69120 Heidelberg, Germany.
| | - Ingo Paarmann
- Department of Neurochemistry, Max-Planck-Institute for Brain Research, D-60438 Frankfurt/Main,.
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Metal insertion into the molybdenum cofactor: product–substrate channelling demonstrates the functional origin of domain fusion in gephyrin. Biochem J 2013; 450:149-57. [DOI: 10.1042/bj20121078] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
The complexity of eukaryotic multicellular organisms relies on evolutionary developments that include compartmentalization, alternative splicing, protein domain fusion and post-translational modification. Mammalian gephyrin uniquely exemplifies these processes by combining two enzymatic functions within the biosynthesis of the Moco (molybdenum cofactor) in a multidomain protein. It also undergoes extensive alternative splicing, especially in neurons, where it also functions as a scaffold protein at inhibitory synapses. Two out of three gephyrin domains are homologous to bacterial Moco-synthetic proteins (G and E domain) while being fused by a third gephyrin-specific central C domain. In the present paper, we have established the in vitro Moco synthesis using purified components and demonstrated an over 300-fold increase in Moco synthesis for gephyrin compared with the isolated G domain, which synthesizes adenylylated molybdopterin, and E domain, which catalyses the metal insertion at physiological molybdate concentrations in an ATP-dependent manner. We show that the C domain impacts the catalytic efficacy of gephyrin, suggesting an important structural role in product–substrate channelling as depicted by a structural model that is in line with a face-to-face orientation of both active sites. Our functional studies demonstrate the evolutionary advantage of domain fusion in metabolic proteins, which can lead to the development of novel functions in higher eukaryotes.
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Kowalczyk S, Winkelmann A, Smolinsky B, Förstera B, Neundorf I, Schwarz G, Meier JC. Direct binding of GABAA receptor β2 and β3 subunits to gephyrin. Eur J Neurosci 2012. [PMID: 23205938 DOI: 10.1111/ejn.12078] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
GABAergic transmission is essential to brain function, and a large repertoire of GABA type A receptor (GABA(A) R) subunits is at a neuron's disposition to serve this function. The glycine receptor (GlyR)-associated protein gephyrin has been shown to be essential for the clustering of a subset of GABA(A) R. Despite recent progress in the field of gephyrin-dependent mechanisms of postsynaptic GABA(A) R stabilisation, the role of gephyrin in synaptic GABA(A) R localisation has remained a complex matter with many open questions. Here, we analysed comparatively the interaction of purified rat gephyrin and mouse brain gephyrin with the large cytoplasmic loops of GABA(A) R α1, α2, β2 and β3 subunits. Binding affinities were determined using surface plasmon resonance spectroscopy, and showed an ~ 20-fold lower affinity of the β2 loop to gephyrin as compared to the GlyR β loop-gephyrin interaction. We also probed in vivo binding in primary cortical neurons by the well-established use of chimaeras of GlyR α1 that harbour respective gephyrin-binding motifs derived from the different GABA(A) R subunits. These studies identify a novel gephyrin-binding motif in GABA(A) R β2 and β3 large cytoplasmic loops.
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Affiliation(s)
- Sarah Kowalczyk
- Department of Chemistry, Institute of Biochemistry, University of Cologne, Cologne, Germany
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14
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Herweg J, Schwarz G. Splice-specific glycine receptor binding, folding, and phosphorylation of the scaffolding protein gephyrin. J Biol Chem 2012; 287:12645-56. [PMID: 22351777 DOI: 10.1074/jbc.m112.341826] [Citation(s) in RCA: 55] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
The multimeric scaffolding protein gephyrin forms post-synaptic clusters at inhibitory sites, thereby anchoring inhibitory glycine (GlyR) and subsets of γ-aminobutyric acid type A (GABAA) receptors. Gephyrin is composed of three domains, the conserved N-terminal G- and C-terminal E-domain, connected by the central (C-) domain. In this study we investigated the oligomerization, folding and stability, GlyR β-loop binding, and phosphorylation of three gephyrin splice variants (Geph, Geph-C3, Geph-C4) after expression and purification from insect cells (Sf9). In contrast to Escherichia coli-derived trimeric gephyrin, we found that Sf9 gephyrins form hexamers as basic oligomeric form. In the case of Geph and Geph-C4, also high-oligomeric forms (∼900 kDa) were isolated. Partial proteolysis revealed a compact folding of the Gephyrin G and C domain in one complex, whereas a much lower stability for the E domain was found. After GlyR β-loop binding, the stability of the E domain increased in Geph and Geph-C4 significantly. In contrast, the E domain in Geph-C3 is less stable and binds the GlyR β-loop with one order of magnitude lower affinity. Finally, we identified 18 novel phosphorylation sites in gephyrin, of which all except one are located within the C domain. We propose two models for the domain arrangement in hexameric gephyrin based on the oligomerization of either the E or C domains, with the latter being crucial for the regulation of gephyrin clustering.
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Affiliation(s)
- Jens Herweg
- Institute of Biochemistry, Department of Chemistry and Center for Molecular Medicine, University of Cologne, 50674 Cologne, Germany
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15
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Expression and subcellular distribution of gephyrin in non-neuronal tissues and cells. Histochem Cell Biol 2012; 137:471-82. [PMID: 22270318 DOI: 10.1007/s00418-012-0914-7] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 01/05/2012] [Indexed: 10/14/2022]
Abstract
Gephyrin is a scaffolding protein required for the accumulation of inhibitory neurotransmitter receptors at neuronal postsynaptic membranes. In non-neuronal tissues, gephyrin is indispensible for the biosynthesis of molybdenum cofactor, the prosthetic group of oxidoreductases including sulfite oxidase and xanthine oxidase. However, the molecular and cellular basis of gephyrin's non-neuronal function is poorly understood; in particular, the roles of its splice variants remain enigmatic. Here, we used cDNA screening as well as Northern and immunoblot analyses to show that mammalian liver contains only a limited number of gephyrin splice variants, with the C3-containing variant being the predominant isoform. Using new and established anti-gephyrin antibodies in immunofluorescence and subcellular fractionation studies, we report that gephyrin localizes to the cytoplasm of both tissue hepatocytes and cultured immortalized cells. These findings were corroborated by RNA interference studies in which the cytosolic distribution was found to be abolished. Finally, by blue-native PAGE we show that cytoplasmic gephyrin is part of a ~600 kDa protein complex of yet unknown composition. Our data suggest that the expression pattern of non-neuronal gephyrin is simpler than indicated by previous evidence. In addition, gephyrin's presence in a cytosolic 600 kDa protein complex suggests that its metabolic and/or other non-neuronal functions are exerted in the cytoplasm and are not confined to a particular subcellular compartment.
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16
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Patrizi A, Viltono L, Frola E, Harvey K, Harvey RJ, Sassoè-Pognetto M. Selective localization of collybistin at a subset of inhibitory synapses in brain circuits. J Comp Neurol 2011; 520:130-41. [DOI: 10.1002/cne.22702] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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17
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del Pino I, Paarmann I, Karas M, Kilimann MW, Betz H. The trafficking proteins Vacuolar Protein Sorting 35 and Neurobeachin interact with the glycine receptor β-subunit. Biochem Biophys Res Commun 2011; 412:435-40. [PMID: 21821005 DOI: 10.1016/j.bbrc.2011.07.110] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2011] [Accepted: 07/25/2011] [Indexed: 10/17/2022]
Abstract
Inhibitory glycine receptors (GlyRs) are densely packed in the postsynaptic membrane due to a high-affinity interaction of their β-subunits with the scaffolding protein gephyrin. Here, we used an affinity-based proteomic approach to identify the trafficking proteins Vacuolar Protein Sorting 35 (Vps35) and Neurobeachin (Nbea) as novel GlyR β-subunit (GlyRβ) interacting proteins in rat brain. Recombinant Vps35 and a central fragment of Nbea bound to the large intracellular loop of GlyRβ in glutathione-S-transferase pull-downs; in addition, Vps35 displayed binding to gephyrin. Immunocytochemical staining of spinal cord sections revealed Nbea immunoreactivity apposed to and colocalizing with marker proteins of inhibitory synapses. Our data are consistent with roles of Vps35 and Nbea in the retrieval and post-Golgi trafficking of synaptic GlyRs and possibly other neurotransmitter receptors.
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Affiliation(s)
- Isabel del Pino
- Department of Neurochemistry, Max-Planck-Institute for Brain Research, D-60528 Frankfurt/Main, Germany
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18
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The biological role of the glycinergic synapse in early zebrafish motility. Neurosci Res 2011; 71:1-11. [PMID: 21712054 DOI: 10.1016/j.neures.2011.06.003] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2011] [Revised: 04/08/2011] [Accepted: 04/15/2011] [Indexed: 01/09/2023]
Abstract
Glycine mediates fast inhibitory neurotransmission in the spinal cord, brainstem and retina. Loss of synaptic glycinergic transmission in vertebrates leads to a severe locomotion defect characterized by an exaggerated startle response accompanied by transient muscle rigidity in response to sudden acoustic or tactile stimuli. Several molecular components of the glycinergic synapse have been characterized as an outcome of genetic and physiological analyses of synaptogenesis in mammals. Recently, the glycinergic synapse has been studied using a forward genetic approach in zebrafish. This review aims to discuss molecular components of the glycinergic synapse, such as glycine receptor subunits, gephyrin, gephyrin-binding proteins and glycine transporters, as well as recent studies relevant to the genetic analysis of the glycinergic synapse in zebrafish.
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19
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Machado P, Rostaing P, Guigonis JM, Renner M, Dumoulin A, Samson M, Vannier C, Triller A. Heat shock cognate protein 70 regulates gephyrin clustering. J Neurosci 2011; 31:3-14. [PMID: 21209184 PMCID: PMC6622739 DOI: 10.1523/jneurosci.2533-10.2011] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2010] [Revised: 07/27/2010] [Accepted: 08/02/2010] [Indexed: 11/21/2022] Open
Abstract
Formation and stabilization of postsynaptic glycine receptor (GlyR) clusters result from their association with the polymerized scaffold protein gephyrin. At the cell surface, lateral diffusion and local trapping of GlyR by synaptic gephyrin clusters is one of the main factors controlling their number. However, the mechanisms regulating gephyrin/GlyR cluster sizes are not fully understood. To identify molecular binding partners able to control gephyrin cluster stability, we performed pull-down assays with full-length or truncated gephyrin forms incubated in a rat spinal cord extract, combined with mass spectrometric analysis. We found that heat shock cognate protein 70 (Hsc70), a constitutive member of the heat shock protein 70 (Hsp70) family, selectively binds to the gephyrin G-domain. Immunoelectron microscopy of mouse spinal cord sections showed that Hsc70 could be colocalized with gephyrin at inhibitory synapses. Furthermore, ternary Hsc70-gephyrin-GlyR coclusters were formed following transfection of COS-7 cells. Upon overexpression of Hsc70 in mouse spinal cord neurons, synaptic accumulation of gephyrin was significantly decreased, but GlyR amounts were unaffected. In the same way, Hsc70 inhibition increased gephyrin accumulation at inhibitory synapses without modifying GlyR clustering. Single particle tracking experiments revealed that the increase of gephyrin molecules reduced GlyR diffusion rates without altering GlyR residency at synapses. Our findings demonstrate that Hsc70 regulates gephyrin polymerization independently of its interaction with GlyR. Therefore, gephyrin polymerization and synaptic clustering of GlyR are uncoupled events.
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Affiliation(s)
- Patricia Machado
- Institut de Biologie de l'Ecole Normale Supérieure
- Institut National de la Santé et de la Recherche Médicale U1024
- Centre National de la Recherche Scientifique Unité Mixte de Recherche 8197, 75005 Paris, France, and
| | - Philippe Rostaing
- Institut de Biologie de l'Ecole Normale Supérieure
- Institut National de la Santé et de la Recherche Médicale U1024
- Centre National de la Recherche Scientifique Unité Mixte de Recherche 8197, 75005 Paris, France, and
| | - Jean-Marie Guigonis
- Institut Fédératif de Recherche 50 - Université de Nice-Sophia Antipolis, Faculté de Médecine Pasteur, 06107 Nice, France
| | - Marianne Renner
- Institut de Biologie de l'Ecole Normale Supérieure
- Institut National de la Santé et de la Recherche Médicale U1024
- Centre National de la Recherche Scientifique Unité Mixte de Recherche 8197, 75005 Paris, France, and
| | - Andréa Dumoulin
- Institut de Biologie de l'Ecole Normale Supérieure
- Institut National de la Santé et de la Recherche Médicale U1024
- Centre National de la Recherche Scientifique Unité Mixte de Recherche 8197, 75005 Paris, France, and
| | - Michel Samson
- Institut Fédératif de Recherche 50 - Université de Nice-Sophia Antipolis, Faculté de Médecine Pasteur, 06107 Nice, France
| | - Christian Vannier
- Institut de Biologie de l'Ecole Normale Supérieure
- Institut National de la Santé et de la Recherche Médicale U1024
- Centre National de la Recherche Scientifique Unité Mixte de Recherche 8197, 75005 Paris, France, and
| | - Antoine Triller
- Institut de Biologie de l'Ecole Normale Supérieure
- Institut National de la Santé et de la Recherche Médicale U1024
- Centre National de la Recherche Scientifique Unité Mixte de Recherche 8197, 75005 Paris, France, and
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20
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Förstera B, Belaidi AA, Jüttner R, Bernert C, Tsokos M, Lehmann TN, Horn P, Dehnicke C, Schwarz G, Meier JC. Irregular RNA splicing curtails postsynaptic gephyrin in the cornu ammonis of patients with epilepsy. Brain 2010; 133:3778-94. [DOI: 10.1093/brain/awq298] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
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21
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Charrier C, Machado P, Tweedie-Cullen RY, Rutishauser D, Mansuy IM, Triller A. A crosstalk between β1 and β3 integrins controls glycine receptor and gephyrin trafficking at synapses. Nat Neurosci 2010; 13:1388-95. [DOI: 10.1038/nn.2645] [Citation(s) in RCA: 80] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2010] [Accepted: 08/26/2010] [Indexed: 01/24/2023]
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22
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Ogino K, Ramsden SL, Keib N, Schwarz G, Harvey RJ, Hirata H. Duplicated gephyrin genes showing distinct tissue distribution and alternative splicing patterns mediate molybdenum cofactor biosynthesis, glycine receptor clustering, and escape behavior in zebrafish. J Biol Chem 2010; 286:806-17. [PMID: 20843816 DOI: 10.1074/jbc.m110.125500] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Gephyrin mediates the postsynaptic clustering of glycine receptors (GlyRs) and GABA(A) receptors at inhibitory synapses and molybdenum-dependent enzyme (molybdoenzyme) activity in non-neuronal tissues. Gephyrin knock-out mice show a phenotype resembling both defective glycinergic transmission and molybdenum cofactor (Moco) deficiency and die within 1 day of birth due to starvation and dyspnea resulting from deficits in motor and respiratory networks, respectively. To address whether gephyrin function is conserved among vertebrates and whether gephyrin deficiency affects molybdoenzyme activity and motor development, we cloned and characterized zebrafish gephyrin genes. We report here that zebrafish have two gephyrin genes, gphna and gphnb. The former is expressed in all tissues and has both C3 and C4 cassette exons, and the latter is expressed predominantly in the brain and spinal cord and harbors only C4 cassette exons. We confirmed that all of the gphna and gphnb splicing isoforms have Moco synthetic activity. Antisense morpholino knockdown of either gphna or gphnb alone did not disturb synaptic clusters of GlyRs in the spinal cord and did not affect touch-evoked escape behaviors. However, on knockdown of both gphna and gphnb, embryos showed impairments in GlyR clustering in the spinal cord and, as a consequence, demonstrated touch-evoked startle response behavior by contracting antagonistic muscles simultaneously, instead of displaying early coiling and late swimming behaviors, which are executed by side-to-side muscle contractions. These data indicate that duplicated gephyrin genes mediate Moco biosynthesis and control postsynaptic clustering of GlyRs, thereby mediating key escape behaviors in zebrafish.
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Affiliation(s)
- Kazutoyo Ogino
- Center for Frontier Research, National Institute of Genetics, 1111 Yata, Mishima 411-8540, Japan
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23
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Yu W, Charych EI, Serwanski DR, Li RW, Ali R, Bahr BA, De Blas AL. Gephyrin interacts with the glutamate receptor interacting protein 1 isoforms at GABAergic synapses. J Neurochem 2010; 105:2300-14. [PMID: 18315564 DOI: 10.1111/j.1471-4159.2008.05311.x] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
We have previously shown that the glutamate receptor interacting protein 1 (GRIP1) splice forms GRIP1a/b and GRIP1c4-7 are present at the GABAergic post-synaptic complex. Nevertheless, the role that these GRIP1 protein isoforms play at the GABAergic post-synaptic complex is not known. We are now showing that GRIP1c4-7 and GRIP1a/b interact with gephyrin, the main post-synaptic scaffold protein of GABAergic and glycinergic synapses. Gephyrin coprecipitates with GRIP1c4-7 or GRIP1a/b from rat brain extracts and from extracts of human embryonic kidney 293 cells that have been cotransfected with gephyrin and one of the GRIP1 protein isoforms. Moreover, purified gephyrin binds to purified GRIP1c4-7 or GRIP1a/b, indicating that gephyrin directly interacts with the common region of these GRIP1 proteins, which includes PDZ domains 4-7. An engineered deletion construct of GRIP1a/b (GRIP1a4-7), which both contains the aforementioned common region and binds to gephyrin, targets to the post-synaptic GABAergic complex of transfected cultured hippocampal neurons. In these hippocampal cultures, endogenous gephyrin colocalizes with endogenous GRIP1c4-7 and GRIP1a/b in over 90% of the GABAergic synapses. Double-labeling electron microscopy immunogold reveals that in the rat brain GRIP1c4-7 and GRIP1a/b colocalize with gephyrin at the post-synaptic complex of individual synapses. These results indicate that GRIP1c4-7 and GRIP1a/b colocalize and interact with gephyrin at the GABAergic post-synaptic complex and suggest that this interaction plays a role in GABAergic synaptic function.
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Affiliation(s)
- Wendou Yu
- Department of Physiology and Neurobiology, University of Connecticut, Storrs, Connecticut 06269-3156, USA
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24
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Abstract
Synapses between nerve cells in the mammalian brain are not only extremely numerous but also very diverse with respect to their structural and functional characteristics. This heterogeneity arises despite the fact that a set of common basic protein 'building blocks' is shared by many synapses. Among these, postsynaptic scaffolding proteins play a key role. They have the ability to assemble into membrane-tethered lattices and to adopt unique conformational states in different postsynaptic microenvironments, which may represent a key prerequisite of synapse heterogeneity. Analyses of such synaptic superstructures, rather than individual proteins and their interactions, are required to develop a mechanistic understanding of postsynaptic differentiation, synapse diversity, and dynamics.
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25
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Moritz A, Scheschonka A, Beckhaus T, Karas M, Betz H. Metabotropic glutamate receptor 4 interacts with microtubule-associated protein 1B. Biochem Biophys Res Commun 2009; 390:82-6. [DOI: 10.1016/j.bbrc.2009.09.070] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2009] [Accepted: 09/17/2009] [Indexed: 01/17/2023]
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26
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Ziegler E, Bodusch M, Song Y, Jahn K, Wolfes H, Steinlechner S, Dengler R, Bufler J, Krampfl K. Interaction of androsterone and progesterone with inhibitory ligand-gated ion channels: a patch clamp study. Naunyn Schmiedebergs Arch Pharmacol 2009; 380:277-91. [DOI: 10.1007/s00210-009-0440-x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2008] [Accepted: 07/20/2009] [Indexed: 10/20/2022]
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27
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Abstract
High local concentrations of glycine receptors (GlyRs) at inhibitory postsynaptic sites are achieved through their binding to the scaffold protein gephyrin. The N- and C-terminal domains of gephyrin are believed to trimerize and dimerize, respectively, thus contributing to the formation of submembranous gephyrin clusters at synapses. GlyRs are associated with gephyrin also at extrasynaptic locations. We have investigated how gephyrin oligomerization influences GlyR dynamics and clustering in COS-7 cells and in cultured spinal cord neurons. To this aim, we have expressed isolated N- and C-terminal domains of gephyrin that interfere with the oligomerization of the full-length protein. We also studied the effect of an endogenous splice variant, ge(2,4,5), with a decreased propensity to trimerize. A reduction of the size and number of gephyrin-GlyR clusters was found in cells expressing the various interfering gephyrin constructs. Using fluorescence recovery after photobleaching, we studied the exchange kinetics of synaptic gephyrin clusters. Real-time single-particle tracking was used to analyze the mobility of GlyRs. We found that all the tested constructs displayed faster rates of recovery than wild-type gephyrin and increased the mobility of extrasynaptic receptors, showing that gephyrin-gephyrin interactions modulate the lateral diffusion of GlyRs. Furthermore, we observed an inverse correlation between GlyR diffusion properties and gephyrin cluster size that depended on the number of binding sites blocked by the different constructs. Since alterations in the oligomerization properties of gephyrin are related to the dynamics of GlyRs, the gephyrin splice variant ge(2,4,5) may be implicated in the modulation of synaptic strength.
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28
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Yan J, Olsen JV, Park KS, Li W, Bildl W, Schulte U, Aldrich RW, Fakler B, Trimmer JS. Profiling the phospho-status of the BKCa channel alpha subunit in rat brain reveals unexpected patterns and complexity. Mol Cell Proteomics 2008; 7:2188-98. [PMID: 18573811 DOI: 10.1074/mcp.m800063-mcp200] [Citation(s) in RCA: 68] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Molecular diversity of ion channel structure and function underlies variability in electrical signaling in nerve, muscle, and non-excitable cells. Protein phosphorylation and alternative splicing of pre-mRNA are two important mechanisms to generate structural and functional diversity of ion channels. However, systematic mass spectrometric analyses of in vivo phosphorylation and splice variants of ion channels in native tissues are largely lacking. Mammalian large-conductance calcium-activated potassium (BK(Ca)) channels are tetramers of alpha subunits (BKalpha) either alone or together with beta subunits, exhibit exceptionally large single channel conductance, and are dually activated by membrane depolarization and intracellular Ca(2+). The cytoplasmic C terminus of BKalpha is subjected to extensive pre-mRNA splicing and, as predicted by several algorithms, offers numerous phospho-acceptor amino acids. Here we use nanoflow liquid chromatography tandem mass spectrometry on BK(Ca) channels affinity-purified from rat brain to analyze in vivo BKalpha phosphorylation and splicing. We found 7 splice variations and identified as many as 30 Ser/Thr in vivo phosphorylation sites; most of which were not predicted by commonly used algorithms. Of the identified phosphosites 23 are located in the C terminus, four were found on splice insertions. Electrophysiological analyses of phospho- and dephosphomimetic mutants transiently expressed in HEK-293 cells suggest that phosphorylation of BKalpha differentially modulates the voltage- and Ca(2+)-dependence of channel activation. These results demonstrate that the pore-forming subunit of BK(Ca) channels is extensively phosphorylated in the mammalian brain providing a molecular basis for the regulation of firing pattern and excitability through dynamic modification of BKalpha structure and function.
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Affiliation(s)
- Jiusheng Yan
- Department of Neurobiology, Physiology and Behavior, College of Biological Sciences, University of California, Davis, California 95616, USA
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29
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Gephyrin: where do we stand, where do we go? Trends Neurosci 2008; 31:257-64. [DOI: 10.1016/j.tins.2008.02.006] [Citation(s) in RCA: 257] [Impact Index Per Article: 16.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2007] [Revised: 02/17/2008] [Accepted: 02/19/2008] [Indexed: 11/24/2022]
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30
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Smolinsky B, Eichler SA, Buchmeier S, Meier JC, Schwarz G. Splice-specific functions of gephyrin in molybdenum cofactor biosynthesis. J Biol Chem 2008; 283:17370-9. [PMID: 18411266 DOI: 10.1074/jbc.m800985200] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Gephyrin is a multifunctional protein involved in the clustering of inhibitory neuroreceptors. In addition, gephyrin catalyzes the last step in molybdenum cofactor (Moco) biosynthesis essential for the activities of Mo-dependent enzymes such as sulfite oxidase and xanthine oxidoreductase. Functional complexity and diversity of gephyrin is believed to be regulated by alternative splicing in a tissue-specific manner. Here, we investigated eight gephyrin variants with combinations of seven alternatively spliced exons located in the N-terminal G domain, the central domain, and the C-terminal E domain. Their activity in Moco synthesis was analyzed in vivo by reconstitution of gephyrin-deficient L929 cells, which were found to be defective in the G domain of gephyrin. Individual domain functions were assayed in addition and confirmed that variants containing either an additional C5 cassette or missing the C6 cassette are inactive in Moco synthesis. In contrast, different alterations within the central domain retained the Moco synthetic activity of gephyrin. The recombinant gephyrin G domain containing the C5 cassette forms dimers in solution, binds molybdopterin, but is unable to catalyze molybdopterin (MPT) adenylylation. Determination of Moco and MPT content in different tissues showed that besides liver and kidney, brain was capable of synthesizing Moco most efficiently. Subsequent analysis of cultured neurons and glia cells demonstrated glial Moco synthesis due to the expression of gephyrins containing the cassettes C2 and C6 with and without C3.1.
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Affiliation(s)
- Birthe Smolinsky
- Institute of Biochemistry and Center for Molecular Medicine, University of Cologne, 50674 Cologne, Germany
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31
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Papadopoulos T, Korte M, Eulenburg V, Kubota H, Retiounskaia M, Harvey RJ, Harvey K, O'Sullivan GA, Laube B, Hülsmann S, Geiger JRP, Betz H. Impaired GABAergic transmission and altered hippocampal synaptic plasticity in collybistin-deficient mice. EMBO J 2007; 26:3888-99. [PMID: 17690689 PMCID: PMC1994120 DOI: 10.1038/sj.emboj.7601819] [Citation(s) in RCA: 147] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2007] [Accepted: 07/19/2007] [Indexed: 11/09/2022] Open
Abstract
Collybistin (Cb) is a brain-specific guanine nucleotide exchange factor that has been implicated in plasma membrane targeting of the postsynaptic scaffolding protein gephyrin found at glycinergic and GABAergic synapses. Here we show that Cb-deficient mice display a region-specific loss of postsynaptic gephyrin and GABA(A) receptor clusters in the hippocampus and the basolateral amygdala. Cb deficiency is accompanied by significant changes in hippocampal synaptic plasticity, due to reduced dendritic GABAergic inhibition. Long-term potentiation is enhanced, and long-term depression reduced, in Cb-deficient hippocampal slices. Consistent with the anatomical and electrophysiological findings, the animals show increased levels of anxiety and impaired spatial learning. Together, our data indicate that Cb is essential for gephyrin-dependent clustering of a specific set of GABA(A) receptors, but not required for glycine receptor postsynaptic localization.
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Affiliation(s)
- Theofilos Papadopoulos
- Department of Neurochemistry, Max-Planck-Institute for Brain Research, Frankfurt, Germany
| | - Martin Korte
- Zoological Institute, Technical University Braunschweig, Braunschweig, Germany
| | - Volker Eulenburg
- Department of Neurochemistry, Max-Planck-Institute for Brain Research, Frankfurt, Germany
| | - Hisahiko Kubota
- Department of Neurochemistry, Max-Planck-Institute for Brain Research, Frankfurt, Germany
- Independent Hertie Research Group, Max-Planck-Institute for Brain Research, Frankfurt, Germany
| | - Marina Retiounskaia
- Department of Neurochemistry, Max-Planck-Institute for Brain Research, Frankfurt, Germany
| | - Robert J Harvey
- Department of Pharmacology, The School of Pharmacy, London, UK
| | - Kirsten Harvey
- Department of Pharmacology, The School of Pharmacy, London, UK
| | - Gregory A O'Sullivan
- Department of Neurochemistry, Max-Planck-Institute for Brain Research, Frankfurt, Germany
| | - Bodo Laube
- Department of Neurochemistry, Max-Planck-Institute for Brain Research, Frankfurt, Germany
| | - Swen Hülsmann
- Department of Neuro- and Sensory Physiology, University of Göttingen, Göttingen, Germany
| | - Jörg R P Geiger
- Independent Hertie Research Group, Max-Planck-Institute for Brain Research, Frankfurt, Germany
| | - Heinrich Betz
- Department of Neurochemistry, Max-Planck-Institute for Brain Research, Frankfurt, Germany
- Department of Neurochemistry, Max-Planck-Institute for Brain Research, Deutschordenstrassee 46, 60528 Frankfurt am Main, Germany. Tel.: +49 69 96769 220; Fax: +49 69 96769 441; E-mail:
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