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Bogue D, Ryan G, Wassmer E, Research Consortium GE, Naik S. VAMP2 Gene-Related Neurodevelopmental Disorder: A Differential Diagnosis for Rett/Angelman-Type Spectrum of Disorders. Mol Syndromol 2023; 14:449-456. [PMID: 37901860 PMCID: PMC10601795 DOI: 10.1159/000530150] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2022] [Accepted: 03/08/2023] [Indexed: 10/31/2023] Open
Abstract
Introduction VAMP2 is an instrumental protein in neuronal synaptic transmission in the brain, facilitating neurotransmitter release. It is encoded by the VAMP2 gene, and pathogenic variants in this gene cause neurodevelopmental features including early onset axial hypotonia, intellectual disability, and features of autism spectrum disorder. To date, only three types of allelic variants (loss of function, in-frame deletions, and missense variants) in the VAMP2 gene have been previously reported in 11 patients with learning difficulties. Here, we describe a patient in whom a novel de novo pathogenic variant in the VAMP2 gene was identified. Case Presentation A 15-month-old girl presented with early onset hypotonia, global developmental delay, learning difficulties, microcephaly, nystagmus, strabismus, and stereotypies. Later, she developed a sleep disorder, challenging behaviour with self-injury, and scoliosis. Gene agnostic analysis of whole genome sequencing data identified a novel de novo heterozygous missense variant c.197G>C (p.Arg66Pro) in the VAMP2 gene SNARE motif region. Discussion This is the fourth report describing VAMP2 gene-related neurodevelopmental disorder. This report adds to the genotype-phenotype correlation and highlights this condition as an important differential diagnosis of Rett/Angelman-type spectrum of disorders. Patients presenting with features of either Rett syndrome or Angelman syndrome, in whom genetic testing is not suggestive, should be evaluated for variants in the VAMP2 gene, given the significant overlap in clinical presentation of these disorders.
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Affiliation(s)
- Danielle Bogue
- West Midlands Clinical Genetics Unit, Birmingham Women’s and Children’s NHS Foundation Trust, Birmingham, UK
| | - Gavin Ryan
- West Midlands Regional Genetics Laboratory, Birmingham Women’s and Children’s NHS Foundation Trust, Birmingham, UK
| | - Evangeline Wassmer
- Department of Neurology, Birmingham Women’s and Children’s NHS Foundation Trust, Birmingham, UK
- Institute of Health and Neurodevelopment, Aston University, Birmingham, UK
| | | | - Swati Naik
- West Midlands Clinical Genetics Unit, Birmingham Women’s and Children’s NHS Foundation Trust, Birmingham, UK
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2
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Palfreyman MT, West SE, Jorgensen EM. SNARE Proteins in Synaptic Vesicle Fusion. ADVANCES IN NEUROBIOLOGY 2023; 33:63-118. [PMID: 37615864 DOI: 10.1007/978-3-031-34229-5_4] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 08/25/2023]
Abstract
Neurotransmitters are stored in small membrane-bound vesicles at synapses; a subset of synaptic vesicles is docked at release sites. Fusion of docked vesicles with the plasma membrane releases neurotransmitters. Membrane fusion at synapses, as well as all trafficking steps of the secretory pathway, is mediated by SNARE proteins. The SNAREs are the minimal fusion machinery. They zipper from N-termini to membrane-anchored C-termini to form a 4-helix bundle that forces the apposed membranes to fuse. At synapses, the SNAREs comprise a single helix from syntaxin and synaptobrevin; SNAP-25 contributes the other two helices to complete the bundle. Unc13 mediates synaptic vesicle docking and converts syntaxin into the permissive "open" configuration. The SM protein, Unc18, is required to initiate and proofread SNARE assembly. The SNAREs are then held in a half-zippered state by synaptotagmin and complexin. Calcium removes the synaptotagmin and complexin block, and the SNAREs drive vesicle fusion. After fusion, NSF and alpha-SNAP unwind the SNAREs and thereby recharge the system for further rounds of fusion. In this chapter, we will describe the discovery of the SNAREs, their relevant structural features, models for their function, and the central role of Unc18. In addition, we will touch upon the regulation of SNARE complex formation by Unc13, complexin, and synaptotagmin.
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Affiliation(s)
- Mark T Palfreyman
- School of Biological Sciences, and Howard Hughes Medical Institute, University of Utah, Salt Lake City, UT, USA
| | - Sam E West
- School of Biological Sciences, and Howard Hughes Medical Institute, University of Utah, Salt Lake City, UT, USA
| | - Erik M Jorgensen
- School of Biological Sciences, and Howard Hughes Medical Institute, University of Utah, Salt Lake City, UT, USA.
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Zhao G, Xu H, Li H, Zhang J, Gao J, Cai M, Wang H, Shi Y, Wang H. Regulatory Mechanisms of SNAP-25-Associated Insulin Release Revealed by Live-Cell Confocal and Single-Molecule Localization Imaging. Anal Chem 2022; 94:15307-15314. [DOI: 10.1021/acs.analchem.2c02677] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Guanfang Zhao
- State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, Jilin 130022, P. R. China
- University of Science and Technology of China, Hefei, Anhui 230026, P. R. China
| | - Haijiao Xu
- State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, Jilin 130022, P. R. China
| | - Hongru Li
- State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, Jilin 130022, P. R. China
- University of Science and Technology of China, Hefei, Anhui 230026, P. R. China
| | - Jinrui Zhang
- State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, Jilin 130022, P. R. China
| | - Jing Gao
- State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, Jilin 130022, P. R. China
| | - Mingjun Cai
- State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, Jilin 130022, P. R. China
| | - Huili Wang
- State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, Jilin 130022, P. R. China
| | - Yan Shi
- State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, Jilin 130022, P. R. China
| | - Hongda Wang
- State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, Jilin 130022, P. R. China
- University of Science and Technology of China, Hefei, Anhui 230026, P. R. China
- Laboratory for Marine Biology and Biotechnology, Qingdao National Laboratory for Marine Science and Technology, Qingdao, Shandong 266237, P. R. China
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Simmons RL, Li H, Alten B, Santos MS, Jiang R, Paul B, Lalani SJ, Cortesi A, Parks K, Khandelwal N, Smith-Packard B, Phoong MA, Chez M, Fisher H, Scheuerle AE, Shinawi M, Hussain SA, Kavalali ET, Sherr EH, Voglmaier SM. Overcoming presynaptic effects of VAMP2 mutations with 4-aminopyridine treatment. Hum Mutat 2020; 41:1999-2011. [PMID: 32906212 PMCID: PMC10898792 DOI: 10.1002/humu.24109] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2020] [Revised: 08/03/2020] [Accepted: 09/04/2020] [Indexed: 12/18/2022]
Abstract
Clinical and genetic features of five unrelated patients with de novo pathogenic variants in the synaptic vesicle-associated membrane protein 2 (VAMP2) reveal common features of global developmental delay, autistic tendencies, behavioral disturbances, and a higher propensity to develop epilepsy. For one patient, a cognitively impaired adolescent with a de novo stop-gain VAMP2 mutation, we tested a potential treatment strategy, enhancing neurotransmission by prolonging action potentials with the aminopyridine family of potassium channel blockers, 4-aminopyridine and 3,4-diaminopyridine, in vitro and in vivo. Synaptic vesicle recycling and neurotransmission were assayed in neurons expressing three VAMP2 variants by live-cell imaging and electrophysiology. In cellular models, two variants decrease both the rate of exocytosis and the number of synaptic vesicles released from the recycling pool, compared with wild-type. Aminopyridine treatment increases the rate and extent of exocytosis and total synaptic charge transfer and desynchronizes GABA release. The clinical response of the patient to 2 years of off-label aminopyridine treatment includes improved emotional and behavioral regulation by parental report, and objective improvement in standardized cognitive measures. Aminopyridine treatment may extend to patients with pathogenic variants in VAMP2 and other genes influencing presynaptic function or GABAergic tone, and tested in vitro before treatment.
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Affiliation(s)
- Roxanne L. Simmons
- Department of Neurology, Weill Institute for Neurosciences and Institute of Human Genetics. University of California San Francisco, School of Medicine, San Francisco, CA, USA
| | - Haiyan Li
- Department of Psychiatry, Weill Institute for Neurosciences and Kavli Institute for Fundamental Neuroscience University of California San Francisco, School of Medicine, San Francisco, CA, USA
| | - Baris Alten
- Department of Pharmacology, Vanderbilt University, Nashville, TN, USA
- Vanderbilt Brain Institute, Nashville, TN, USA
| | - Magda S. Santos
- Department of Psychiatry, Weill Institute for Neurosciences and Kavli Institute for Fundamental Neuroscience University of California San Francisco, School of Medicine, San Francisco, CA, USA
| | - Ruiji Jiang
- Department of Neurology, Weill Institute for Neurosciences and Institute of Human Genetics. University of California San Francisco, School of Medicine, San Francisco, CA, USA
| | - Brianna Paul
- Department of Neurology, Weill Institute for Neurosciences and Institute of Human Genetics. University of California San Francisco, School of Medicine, San Francisco, CA, USA
| | - Sanam J. Lalani
- Department of Neurology, Weill Institute for Neurosciences and Institute of Human Genetics. University of California San Francisco, School of Medicine, San Francisco, CA, USA
| | - Audrey Cortesi
- Department of Neurology, Weill Institute for Neurosciences and Institute of Human Genetics. University of California San Francisco, School of Medicine, San Francisco, CA, USA
| | - Kendall Parks
- Department of Neurology, Weill Institute for Neurosciences and Institute of Human Genetics. University of California San Francisco, School of Medicine, San Francisco, CA, USA
| | - Nitin Khandelwal
- Department of Neuroscience, UT Southwestern Medical Center, Dallas, TX, USA
| | | | - Malay A. Phoong
- Department of Neuroscience, Pediatric Neuropsychology, Sutter Medical Foundation, Sacramento, CA, USA
| | - Michael Chez
- Neuroscience Medical Group, Sutter Medical Foundation, Sacramento, CA, USA
| | - Heather Fisher
- Department of Genetics, Children’s Medical Center of Texas, Dallas, Texas, USA
| | - Angela E. Scheuerle
- Department of Pediatrics, Division of Genetics and Metabolism, UT Southwestern Medical Center, Dallas, TX, USA
| | - Marwan Shinawi
- Division of Genetics and Genomic Medicine, St. Louis Children’s Hospital, Washington University School of Medicine, St. Louis, MO, USA
| | - Shaun A. Hussain
- Department of Pediatrics, UCLA Mattel Children’s Hospital and Geffen School of Medicine, Los Angeles, CA, USA
| | - Ege T. Kavalali
- Department of Pharmacology, Vanderbilt University, Nashville, TN, USA
- Vanderbilt Brain Institute, Nashville, TN, USA
| | - Elliott H. Sherr
- Department of Neurology, Weill Institute for Neurosciences and Institute of Human Genetics. University of California San Francisco, School of Medicine, San Francisco, CA, USA
| | - Susan M. Voglmaier
- Department of Psychiatry, Weill Institute for Neurosciences and Kavli Institute for Fundamental Neuroscience University of California San Francisco, School of Medicine, San Francisco, CA, USA
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5
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Shaaban A, Dhara M, Frisch W, Harb A, Shaib AH, Becherer U, Bruns D, Mohrmann R. The SNAP-25 linker supports fusion intermediates by local lipid interactions. eLife 2019; 8:41720. [PMID: 30883328 PMCID: PMC6422494 DOI: 10.7554/elife.41720] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2018] [Accepted: 03/05/2019] [Indexed: 12/22/2022] Open
Abstract
SNAP-25 is an essential component of SNARE complexes driving fast Ca2+-dependent exocytosis. Yet, the functional implications of the tandem-like structure of SNAP-25 are unclear. Here, we have investigated the mechanistic role of the acylated “linker” domain that concatenates the two SNARE motifs within SNAP-25. Refuting older concepts of an inert connector, our detailed structure-function analysis in murine chromaffin cells demonstrates that linker motifs play a crucial role in vesicle priming, triggering, and fusion pore expansion. Mechanistically, we identify two synergistic functions of the SNAP-25 linker: First, linker motifs support t-SNARE interactions and accelerate ternary complex assembly. Second, the acylated N-terminal linker segment engages in local lipid interactions that facilitate fusion triggering and pore evolution, putatively establishing a favorable membrane configuration by shielding phospholipid headgroups and affecting curvature. Hence, the linker is a functional part of the fusion complex that promotes secretion by SNARE interactions as well as concerted lipid interplay.
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Affiliation(s)
- Ahmed Shaaban
- ZHMB, Saarland University, Homburg, Germany.,Department of Molecular Neurobiology, Max Planck Institute for Experimental Medicine, Göttingen, Germany
| | - Madhurima Dhara
- Institute for Physiology, Center of Integrative Physiology and Molecular Medicine, Saarland University, Homburg, Germany
| | - Walentina Frisch
- Institute for Physiology, Center of Integrative Physiology and Molecular Medicine, Saarland University, Homburg, Germany
| | - Ali Harb
- ZHMB, Saarland University, Homburg, Germany
| | - Ali H Shaib
- Department of Molecular Neurobiology, Max Planck Institute for Experimental Medicine, Göttingen, Germany
| | - Ute Becherer
- Institute for Physiology, Center of Integrative Physiology and Molecular Medicine, Saarland University, Homburg, Germany
| | - Dieter Bruns
- Institute for Physiology, Center of Integrative Physiology and Molecular Medicine, Saarland University, Homburg, Germany
| | - Ralf Mohrmann
- ZHMB, Saarland University, Homburg, Germany.,Institute for Physiology, Otto-von-Guericke University, Magdeburg, Germany.,Center for Behavioral Brain Science, Otto-von-Guericke University, Magdeburg, Germany
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6
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MacDougall DD, Lin Z, Chon NL, Jackman SL, Lin H, Knight JD, Anantharam A. The high-affinity calcium sensor synaptotagmin-7 serves multiple roles in regulated exocytosis. J Gen Physiol 2018; 150:783-807. [PMID: 29794152 PMCID: PMC5987875 DOI: 10.1085/jgp.201711944] [Citation(s) in RCA: 34] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2017] [Accepted: 05/07/2018] [Indexed: 12/19/2022] Open
Abstract
MacDougall et al. review the structure and function of the calcium sensor synaptotagmin-7 in exocytosis. Synaptotagmin (Syt) proteins comprise a 17-member family, many of which trigger exocytosis in response to calcium. Historically, most studies have focused on the isoform Syt-1, which serves as the primary calcium sensor in synchronous neurotransmitter release. Recently, Syt-7 has become a topic of broad interest because of its extreme calcium sensitivity and diversity of roles in a wide range of cell types. Here, we review the known and emerging roles of Syt-7 in various contexts and stress the importance of its actions. Unique functions of Syt-7 are discussed in light of recent imaging, electrophysiological, and computational studies. Particular emphasis is placed on Syt-7–dependent regulation of synaptic transmission and neuroendocrine cell secretion. Finally, based on biochemical and structural data, we propose a mechanism to link Syt-7’s role in membrane fusion with its role in subsequent fusion pore expansion via strong calcium-dependent phospholipid binding.
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Affiliation(s)
| | - Zesen Lin
- Department of Pharmacology, University of Michigan, Ann Arbor, MI
| | - Nara L Chon
- Department of Chemistry, University of Colorado, Denver, CO
| | - Skyler L Jackman
- Vollum Institute, Oregon Health & Science University, Portland, OR
| | - Hai Lin
- Department of Chemistry, University of Colorado, Denver, CO
| | | | - Arun Anantharam
- Department of Pharmacology, University of Michigan, Ann Arbor, MI
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7
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Sharma S, Lindau M. t-SNARE Transmembrane Domain Clustering Modulates Lipid Organization and Membrane Curvature. J Am Chem Soc 2017; 139:18440-18443. [PMID: 29231734 PMCID: PMC5802331 DOI: 10.1021/jacs.7b10677] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The t-SNARE complex plays a central role in neuronal fusion. Its components, syntaxin-1 and SNAP25, are largely present in individual clusters and partially colocalize at the presumptive fusion site. How these protein clusters modify local lipid composition and membrane morphology is largely unknown. In this work, using coarse-grained molecular dynamics, the transmembrane domains (TMDs) of t-SNARE complexes are shown to form aggregates leading to formation of lipid nanodomains, which are enriched in cholesterol, phosphatidylinositol 4,5-bisphosphate, and gangliosidic lipids. These nano-domains induce membrane curvature that would promote a closer contact between vesicle and plasma membrane.
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Affiliation(s)
- Satyan Sharma
- Laboratory of Nanoscale Cell Biology, Max-Planck-Institut für Biophysikalische Chemie , Göttingen 37077 Germany
| | - Manfred Lindau
- Laboratory of Nanoscale Cell Biology, Max-Planck-Institut für Biophysikalische Chemie , Göttingen 37077 Germany.,School of Applied and Engineering Physics, Cornell University , Ithaca, New York 14850, United States
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8
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Veleri S, Nellissery J, Mishra B, Manjunath SH, Brooks MJ, Dong L, Nagashima K, Qian H, Gao C, Sergeev YV, Huang XF, Qu J, Lu F, Cideciyan AV, Li T, Jin ZB, Fariss RN, Ratnapriya R, Jacobson SG, Swaroop A. REEP6 mediates trafficking of a subset of Clathrin-coated vesicles and is critical for rod photoreceptor function and survival. Hum Mol Genet 2017; 26:2218-2230. [PMID: 28369466 PMCID: PMC5458339 DOI: 10.1093/hmg/ddx111] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2016] [Accepted: 03/16/2017] [Indexed: 01/20/2023] Open
Abstract
In retinal photoreceptors, vectorial transport of cargo is critical for transduction of visual signals, and defects in intracellular trafficking can lead to photoreceptor degeneration and vision impairment. Molecular signatures associated with routing of transport vesicles in photoreceptors are poorly understood. We previously reported the identification of a novel rod photoreceptor specific isoform of Receptor Expression Enhancing Protein (REEP) 6, which belongs to a family of proteins involved in intracellular transport of receptors to the plasma membrane. Here we show that loss of REEP6 in mice (Reep6−/−) results in progressive retinal degeneration. Rod photoreceptor dysfunction is observed in Reep6−/− mice as early as one month of age and associated with aberrant accumulation of vacuole-like structures at the apical inner segment and reduction in selected rod phototransduction proteins. We demonstrate that REEP6 is detected in a subset of Clathrin-coated vesicles and interacts with the t-SNARE, Syntaxin3. In concordance with the rod degeneration phenotype in Reep6−/− mice, whole exome sequencing identified homozygous REEP6-E75K mutation in two retinitis pigmentosa families of different ethnicities. Our studies suggest a critical function of REEP6 in trafficking of cargo via a subset of Clathrin-coated vesicles to selected membrane sites in retinal rod photoreceptors.
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Affiliation(s)
- Shobi Veleri
- Neurobiology Neurodegeneration and Repair Laboratory
| | | | | | | | | | - Lijin Dong
- Genetic Engineering Core, National Eye Institute, National Institutes of Health, Bethesda, MD 20892, USA
| | - Kunio Nagashima
- Frederick National Laboratory for Cancer Research, Frederick, MD 21701, USA
| | - Haohua Qian
- Visual Function Core, 5Biological Imaging Core
| | - Chun Gao
- Ophthalmic Genetics and Visual Function Branch, National Eye Institute, National Institutes of Health, Bethesda, MD 20892, USA
| | - Yuri V Sergeev
- Ophthalmic Genetics and Visual Function Branch, National Eye Institute, National Institutes of Health, Bethesda, MD 20892, USA
| | - Xiu-Feng Huang
- The Eye Hospital of Wenzhou Medical University, Wenzhou 325027, China and
| | - Jia Qu
- The Eye Hospital of Wenzhou Medical University, Wenzhou 325027, China and
| | - Fan Lu
- The Eye Hospital of Wenzhou Medical University, Wenzhou 325027, China and
| | - Artur V Cideciyan
- Scheie Eye Institute, Department of Ophthalmology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA
| | - Tiansen Li
- Neurobiology Neurodegeneration and Repair Laboratory
| | - Zi-Bing Jin
- The Eye Hospital of Wenzhou Medical University, Wenzhou 325027, China and
| | - Robert N Fariss
- Ophthalmic Genetics and Visual Function Branch, National Eye Institute, National Institutes of Health, Bethesda, MD 20892, USA
| | | | - Samuel G Jacobson
- Scheie Eye Institute, Department of Ophthalmology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA
| | - Anand Swaroop
- Neurobiology Neurodegeneration and Repair Laboratory
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9
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Dhara M, Mohrmann R, Bruns D. v-SNARE function in chromaffin cells. Pflugers Arch 2017; 470:169-180. [PMID: 28887593 PMCID: PMC5748422 DOI: 10.1007/s00424-017-2066-z] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2017] [Revised: 08/28/2017] [Accepted: 08/29/2017] [Indexed: 01/04/2023]
Abstract
Vesicle fusion is elementary for intracellular trafficking and release of signal molecules, thus providing the basis for diverse forms of intercellular communication like hormonal regulation or synaptic transmission. A detailed characterization of the mechanisms underlying exocytosis is key to understand how the nervous system integrates information and generates appropriate responses to stimuli. The machinery for vesicular release employs common molecular players in different model systems including neuronal and neuroendocrine cells, in particular members of the SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptors) protein family, Sec1/Munc18-like proteins, and other accessory factors. To achieve temporal precision and speed, excitable cells utilize specialized regulatory proteins like synaptotagmin and complexin, whose interplay putatively synchronizes vesicle fusion and enhances stimulus-secretion coupling. In this review, we aim to highlight recent progress and emerging views on the molecular mechanisms, by which constitutively forming SNAREpins are organized in functional, tightly regulated units for synchronized release. Specifically, we will focus on the role of vesicle associated membrane proteins, also referred to as vesicular SNAREs, in fusion and rapid cargo discharge. We will further discuss the functions of SNARE regulators during exocytosis and focus on chromaffin cell as a model system of choice that allows for detailed structure-function analyses and direct measurements of vesicle fusion under precise control of intracellular [Ca]i.
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Affiliation(s)
- Madhurima Dhara
- Molecular Neurophysiology, CIPMM, Medical Faculty, Saarland University, 66421, Homburg/Saar, Germany
| | - Ralf Mohrmann
- Zentrum für Human- und Molekularbiologie, Saarland University, 66421, Homburg/Saar, Germany
| | - Dieter Bruns
- Molecular Neurophysiology, CIPMM, Medical Faculty, Saarland University, 66421, Homburg/Saar, Germany.
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10
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A stochastic model of active zone material mediated synaptic vesicle docking and priming at resting active zones. Sci Rep 2017; 7:278. [PMID: 28325932 PMCID: PMC5428245 DOI: 10.1038/s41598-017-00360-z] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2016] [Accepted: 02/21/2017] [Indexed: 11/09/2022] Open
Abstract
Synaptic vesicles (SVs) fuse with the presynaptic membrane (PM) at specialized regions called active zones for synaptic transmission. SVs are associated with dense aggregates of macromolecules called active zone material (AZM) that has been thought to be involved in SV release. However, its role has recently begun to be elucidated. Several morphological studies proposed distinctively different AZM mediated SV docking and priming models: sequential and concurrent SV docking/priming. To explore ways to reconcile the contradictory models we develop a stochastic AZM mediated SV docking and priming model. We assume that the position of each connection site of the AZM macromolecules on their SV, directly linking the SV with the PM, varies by random shortening and lengthening of the macromolecules at resting active zones. We also perform computer simulations of SVs near the PM at resting active zones, and the results show that the distribution of the AZM connection sites can significantly affect the SV's docking efficiency and distribution of its contact area with the PM, thus priming and that the area correlates with the shape of the SVs providing a way to account for seemingly irreconcilable observations reported about the spatial relationship of SVs with the PM at active zones.
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11
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Gundersen CB. The Structure of the Synaptic Vesicle-Plasma Membrane Interface Constrains SNARE Models of Rapid, Synchronous Exocytosis at Nerve Terminals. Front Mol Neurosci 2017; 10:48. [PMID: 28280457 PMCID: PMC5321675 DOI: 10.3389/fnmol.2017.00048] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2016] [Accepted: 02/13/2017] [Indexed: 12/27/2022] Open
Abstract
Contemporary models of neurotransmitter release invoke direct or indirect interactions between the Ca2+ sensor, synaptotagmin and the incompletely zippered soluble, N-ethyl-maleimide-sensitive factor attachment protein receptor (SNARE) complex. However, recent electron microscopic (EM) investigations have raised pragmatic issues concerning the mechanism by which SNAREs trigger membrane fusion at nerve terminals. The first issue is related to the finding that the area of contact between a “fully primed” synaptic vesicle and the plasma membrane can exceed 600 nm2. Approximately four-thousands lipid molecules can inhabit this contact zone. Thus, renewed efforts will be needed to explain how the zippering of as few as two SNARE complexes mobilizes these lipids to achieve membrane fusion. The second issue emerges from the finding that “docking filaments” are sandwiched within the area of vesicle-plasma membrane contact. It is challenging to reconcile the location of these filaments with SNARE models of exocytosis. Instead, this commentary outlines how these data are more compatible with a model in which a cluster of synaptotagmins catalyzes exocytotic membrane fusion.
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Affiliation(s)
- Cameron B Gundersen
- Department of Molecular and Medical Pharmacology, David Geffen UCLA School of Medicine Los Angeles, CA, USA
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12
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13
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Han J, Pluhackova K, Wassenaar TA, Böckmann RA. Synaptobrevin Transmembrane Domain Dimerization Studied by Multiscale Molecular Dynamics Simulations. Biophys J 2016; 109:760-71. [PMID: 26287628 DOI: 10.1016/j.bpj.2015.06.049] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2015] [Revised: 06/25/2015] [Accepted: 06/25/2015] [Indexed: 11/25/2022] Open
Abstract
Synaptic vesicle fusion requires assembly of the SNARE complex composed of SNAP-25, syntaxin-1, and synaptobrevin-2 (sybII) proteins. The SNARE proteins found in vesicle membranes have previously been shown to dimerize via transmembrane (TM) domain interactions. While syntaxin homodimerization is supposed to promote the transition from hemifusion to complete fusion, the role of synaptobrevin's TM domain association in the fusion process remains poorly understood. Here, we combined coarse-grained and atomistic simulations to model the homodimerization of the sybII transmembrane domain and of selected TM mutants. The wild-type helix is shown to form a stable, right-handed dimer with the most populated helix-helix interface, including key residues predicted in a previous mutagenesis study. In addition, two alternative binding interfaces were discovered, which are essential to explain the experimentally observed higher-order oligomerization of sybII. In contrast, only one dimerization interface was found for a fusion-inactive poly-Leu mutant. Moreover, the association kinetics found for this mutant is lower as compared to the wild-type. These differences in dimerization between the wild-type and the poly-Leu mutant are suggested to be responsible for the reported differences in fusogenic activity between these peptides. This study provides molecular insight into the role of TM sequence specificity for peptide aggregation in membranes.
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Affiliation(s)
- Jing Han
- Computational Biology, Department of Biology, Friedrich-Alexander Universität Erlangen-Nürnberg, Erlangen, Germany
| | - Kristyna Pluhackova
- Computational Biology, Department of Biology, Friedrich-Alexander Universität Erlangen-Nürnberg, Erlangen, Germany
| | - Tsjerk A Wassenaar
- Computational Biology, Department of Biology, Friedrich-Alexander Universität Erlangen-Nürnberg, Erlangen, Germany
| | - Rainer A Böckmann
- Computational Biology, Department of Biology, Friedrich-Alexander Universität Erlangen-Nürnberg, Erlangen, Germany.
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14
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Abstract
The priming of a docked synaptic vesicle determines the probability of its membrane (VM) fusing with the presynaptic membrane (PM) when a nerve impulse arrives. To gain insight into the nature of priming, we searched by electron tomography for structural relationships correlated with fusion probability at active zones of axon terminals at frog neuromuscular junctions. For terminals fixed at rest, the contact area between the VM of docked vesicles and PM varied >10-fold with a normal distribution. There was no merging of the membranes. For terminals fixed during repetitive evoked synaptic transmission, the normal distribution of contact areas was shifted to the left, due in part to a decreased number of large contact areas, and there was a subpopulation of large contact areas where the membranes were hemifused, an intermediate preceding complete fusion. Thus, fusion probability of a docked vesicle is related to the extent of its VM-PM contact area. For terminals fixed 1 h after activity, the distribution of contact areas recovered to that at rest, indicating the extent of a VM-PM contact area is dynamic and in equilibrium. The extent of VM-PM contact areas in resting terminals correlated with eccentricity in vesicle shape caused by force toward the PM and with shortness of active zone material macromolecules linking vesicles to PM components, some thought to include Ca(2+) channels. We propose that priming is a variable continuum of events imposing variable fusion probability on each vesicle and is regulated by force-generating shortening of active zone material macromolecules in dynamic equilibrium.
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15
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Antoku Y, Dedecker P, Pinheiro PS, Vosch T, Sørensen JB. Spatial distribution and temporal evolution of DRONPA-fused SNAP25 clusters in adrenal chromaffin cells. Photochem Photobiol Sci 2016; 14:1005-12. [PMID: 25837695 DOI: 10.1039/c4pp00423j] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Sub-diffraction imaging of plasma membrane localized proteins, such as the SNARE (Soluble NSF Attachment Protein Receptor) proteins involved in exocytosis, in fixed cells have resulted in images with high spatial resolution, at the expense of dynamical information. Here, we have imaged localized fluorescence bursts of DRONPA-fused SNAP-25 molecules in live chromaffin cells by Total Internal Reflection Fluorescence (TIRF) imaging. We find that this method allows tracking protein cluster dynamics over relatively long times (∼20 min.), partly due to the diffusion into the TIRF field of fresh molecules, making possible the simultaneous identification of cluster size, location and temporal evolution. The results indicate that the DRONPA-fused SNAP-25 clusters display rich dynamics, going from staying constant to disappearing and reappearing in specific cluster domains within minutes.
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Affiliation(s)
- Yasuko Antoku
- Department of Neuroscience and Pharmacology and Center for Biomembranes in Nanomedicine (CBN), University of Copenhagen, Blegdamsvej 3, 2200 Copenhagen, Denmark.
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16
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The synaptotagmin juxtamembrane domain is involved in neuroexocytosis. FEBS Open Bio 2015; 5:388-96. [PMID: 25973365 PMCID: PMC4427626 DOI: 10.1016/j.fob.2015.04.013] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2015] [Revised: 04/21/2015] [Accepted: 04/23/2015] [Indexed: 12/21/2022] Open
Abstract
The highly cationic juxtamembrane segment of synaptotagmin juxtamembrane domain was synthesized. This peptide inhibits neurotransmitter release at the neuromuscular junction of mice and Drosophila. This peptide localizes mainly on the presynaptic membrane. The synaptotagmin juxtamembrane peptide binds monophosphoinositides in a Ca2+-independent manner. The juxtamembrane segment of synaptotagmin may contribute to the formation of the hemifusion intermediate.
Synaptotagmin is a synaptic vesicle membrane protein which changes conformation upon Ca2+ binding and triggers the fast neuroexocytosis that takes place at synapses. We have synthesized a series of peptides corresponding to the sequence of the cytosolic juxtamembrane domain of synaptotagmin, which is highly conserved among different isoforms and animal species, with or without either a hexyl hydrophobic chain or the hexyl group plus a fluorescein moiety. We show that these peptides inhibit neurotransmitter release, that they localize on the presynaptic membrane of the motor axon terminal at the neuromuscular junction and that they bind monophosphoinositides in a Ca2+-independent manner. Based on these findings, we propose that the juxtamembrane cytosolic domain of synaptotagmin binds the cytosolic layer of the presynaptic membrane at rest. This binding brings synaptic vesicles and plasma membrane in a very close apposition, favouring the formation of hemifusion intermediates that enable rapid vesicle fusion.
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Key Words
- Anionic phospholipids
- JMS, juxtamembrane segment
- Juxtamembrane domain
- NMJ, neuromuscular junction
- Neuroexocytosis
- Neuromuscular junction
- PM, presynaptic membrane
- SV, synaptic vesicles
- Synaptotagmin
- Syt, synaptotagmin
- TM, transmembrane
- h-FJMS, hexyl fluorescent juxtamembrane segment
- h-JMS, hexyl juxtamembrane segment
- h-sJMS, hexyl scrambled juxtamembrane segment
- α-BTX, alpha-bungarotoxin
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17
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Schotten S, Meijer M, Walter AM, Huson V, Mamer L, Kalogreades L, ter Veer M, Ruiter M, Brose N, Rosenmund C, Sørensen JB, Verhage M, Cornelisse LN. Additive effects on the energy barrier for synaptic vesicle fusion cause supralinear effects on the vesicle fusion rate. eLife 2015; 4:e05531. [PMID: 25871846 PMCID: PMC4426983 DOI: 10.7554/elife.05531] [Citation(s) in RCA: 39] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2014] [Accepted: 04/13/2015] [Indexed: 01/08/2023] Open
Abstract
The energy required to fuse synaptic vesicles with the plasma membrane
(‘activation energy’) is considered a major determinant in synaptic
efficacy. From reaction rate theory, we predict that a class of modulations exists,
which utilize linear modulation of the energy barrier for fusion to achieve
supralinear effects on the fusion rate. To test this prediction experimentally, we
developed a method to assess the number of releasable vesicles, rate constants for
vesicle priming, unpriming, and fusion, and the activation energy for fusion by
fitting a vesicle state model to synaptic responses induced by hypertonic solutions.
We show that complexinI/II deficiency or phorbol ester stimulation indeed affects
responses to hypertonic solution in a supralinear manner. An additive vs
multiplicative relationship between activation energy and fusion rate provides a
novel explanation for previously observed non-linear effects of
genetic/pharmacological perturbations on synaptic transmission and a novel
interpretation of the cooperative nature of Ca2+-dependent
release. DOI:http://dx.doi.org/10.7554/eLife.05531.001 Information is carried around our nervous system by cells called neurons, which are
connected to each other by junctions known as synapses. Within the neurons, there are
many small compartments known as synaptic vesicles that are essential to the transfer
of information from one neuron to the next. When one neuron is activated, the
synaptic vesicles fuse with the membrane surrounding the cell to release molecules
called neurotransmitters, which cross the synapse and activate the next neuron.
Vesicle fusion is carefully regulated to control the speed and amount of
neurotransmitter release, which determines the level of activation of the next
neuron. Vesicle fusion requires energy, much of which is provided by a set of proteins found
in the synapse. The minimum amount of energy required—called the activation
energy—is influenced by many factors, including the shape of the cell's
membrane at the synapse. It is thought that altering the activation energy required
for fusion may control the activity of synapses, but it is not possible to directly
measure this in living cells. To bypass this problem, Schotten, Meijer, Walter et al. established a new method to
study vesicle fusion. This method combines a mathematical model with experimental
data of the activity of synapses. First, the neurons were placed in a solution
containing the sugar sucrose, which triggered vesicle fusion by lowering the
activation energy. The increase in vesicle fusion was smaller in neurons that lacked
two proteins called complexin I and complexin II—which control vesicle
fusion—than in the normal neurons. A molecule called phorbol ester is also able to activate the release of
neurotransmitters. When cells were treated with both sucrose and phorbol ester, the
speed of vesicle fusion was greater. The experiments show that the effects of
sucrose, phorbol ester, and the complexins multiply together to dramatically alter
vesicle fusion. Schotten, Meijer, Walter et al. suggest a new model for how the activation energy of
vesicle fusion controls the transfer of information across synapses. This might shed
new light on how the efficiency of vesicle fusion is altered when neurons are highly
active, which is thought to have strong implications for how information is processed
in the brain. DOI:http://dx.doi.org/10.7554/eLife.05531.002
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Affiliation(s)
- Sebastiaan Schotten
- Department of Functional Genomics, Center for Neurogenomics and Cognitive Research, VU University Medical Center, Amsterdam, Netherlands
| | - Marieke Meijer
- Department of Functional Genomics, Center for Neurogenomics and Cognitive Research, VU University Medical Center, Amsterdam, Netherlands
| | - Alexander Matthias Walter
- Department of Functional Genomics, Center for Neurogenomics and Cognitive Research, VU University Medical Center, Amsterdam, Netherlands
| | - Vincent Huson
- Department of Functional Genomics, Center for Neurogenomics and Cognitive Research, VU University Medical Center, Amsterdam, Netherlands
| | - Lauren Mamer
- NeuroCure Cluster of Excellence, Neuroscience Research Center, Charité - Universitätsmedizin Berlin, Berlin, Germany
| | - Lawrence Kalogreades
- Department of Functional Genomics, Center for Neurogenomics and Cognitive Research, VU University Medical Center, Amsterdam, Netherlands
| | - Mirelle ter Veer
- Department of Functional Genomics, Center for Neurogenomics and Cognitive Research, VU University Medical Center, Amsterdam, Netherlands
| | - Marvin Ruiter
- Department of Functional Genomics, Center for Neurogenomics and Cognitive Research, VU University Medical Center, Amsterdam, Netherlands
| | - Nils Brose
- Department of Molecular Neurobiology, Max Planck Institute for Experimental Medicine, Göttingen, Germany
| | - Christian Rosenmund
- NeuroCure Cluster of Excellence, Neuroscience Research Center, Charité - Universitätsmedizin Berlin, Berlin, Germany
| | - Jakob Balslev Sørensen
- Department of Neuroscience and Pharmacology, Faculty of Health Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Matthijs Verhage
- Department of Functional Genomics, Center for Neurogenomics and Cognitive Research, VU University Medical Center, Amsterdam, Netherlands
| | - Lennart Niels Cornelisse
- Department of Functional Genomics, Center for Neurogenomics and Cognitive Research, VU University Medical Center, Amsterdam, Netherlands
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18
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Kawabata A, Serada S, Naka T, Mori Y. Human herpesvirus 6 gM/gN complex interacts with v-SNARE in infected cells. J Gen Virol 2014; 95:2769-2777. [PMID: 25209806 DOI: 10.1099/vir.0.069336-0] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
Human herpesvirus 6 (HHV-6) glycoprotein M (gM) is an envelope glycoprotein that associates with glycoprotein N (gN), forming the gM/gN protein complex, in a similar manner to the other herpesviruses. Liquid chromatography-MS/MS analysis showed that the HHV-6 gM/gN complex interacts with the v-SNARE protein, vesicle-associated membrane protein 3 (VAMP3). VAMP3 colocalized with the gM/gN complex at the trans-Golgi network and other compartments, possibly the late endosome in HHV-6-infected cells, and its expression gradually increased during the late phase of virus infection. Finally, VAMP3 was incorporated into mature virions and may be transported with the gM/gN complex.
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Affiliation(s)
- Akiko Kawabata
- Division of Clinical Virology, Center for Infectious Diseases, Kobe University Graduate School of Medicine, 7-5-1, Kusunoki-cho, Chuo-ku, Kobe 650-0017, Japan
| | - Satoshi Serada
- Laboratory of Immune Signal, Division of Biomedical Research, National Institute of Biomedical Innovation, 7-6-8, Saito-Asagi, Ibaraki, Osaka 567-0085, Japan
| | - Tetsuji Naka
- Laboratory of Immune Signal, Division of Biomedical Research, National Institute of Biomedical Innovation, 7-6-8, Saito-Asagi, Ibaraki, Osaka 567-0085, Japan
| | - Yasuko Mori
- Division of Clinical Virology, Center for Infectious Diseases, Kobe University Graduate School of Medicine, 7-5-1, Kusunoki-cho, Chuo-ku, Kobe 650-0017, Japan
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19
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Acuna C, Guo Q, Burré J, Sharma M, Sun J, Südhof TC. Microsecond dissection of neurotransmitter release: SNARE-complex assembly dictates speed and Ca²⁺ sensitivity. Neuron 2014; 82:1088-100. [PMID: 24908488 DOI: 10.1016/j.neuron.2014.04.020] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 04/07/2014] [Indexed: 10/25/2022]
Abstract
SNARE-complex assembly mediates synaptic vesicle fusion during neurotransmitter release and requires that the target-SNARE protein syntaxin-1 switches from a closed to an open conformation. Although many SNARE proteins are available per vesicle, only one to three SNARE complexes are minimally needed for a fusion reaction. Here, we use high-resolution measurements of synaptic transmission in the calyx-of-Held synapse from mutant mice in which syntaxin-1 is rendered constitutively open and SNARE-complex assembly is enhanced to examine the relation between SNARE-complex assembly and neurotransmitter release. We show that enhancing SNARE-complex assembly dramatically increases the speed of evoked release, potentiates the Ca(2+)-affinity of release, and accelerates fusion-pore expansion during individual vesicle fusion events. Our data indicate that the number of assembled SNARE complexes per vesicle during fusion determines the presynaptic release probability and fusion kinetics and suggest a mechanism whereby proteins (Munc13 or RIM) may control presynaptic plasticity by regulating SNARE-complex assembly.
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Affiliation(s)
- Claudio Acuna
- Department of Molecular and Cellular Physiology and Howard Hughes Medical Institute, Stanford University, 265 Campus Drive, Stanford, CA 94305-5453, USA.
| | - Qingchen Guo
- Institute of Biophysics, Chinese Academy of Sciences, 15 Datun Road, Chaoyang District, Beijing 100101, China
| | - Jacqueline Burré
- Department of Molecular and Cellular Physiology and Howard Hughes Medical Institute, Stanford University, 265 Campus Drive, Stanford, CA 94305-5453, USA
| | - Manu Sharma
- Department of Molecular and Cellular Physiology and Howard Hughes Medical Institute, Stanford University, 265 Campus Drive, Stanford, CA 94305-5453, USA
| | - Jianyuan Sun
- Institute of Biophysics, Chinese Academy of Sciences, 15 Datun Road, Chaoyang District, Beijing 100101, China; Center of Parkinson's Disease, Beijing Institute for Brain Disorders, 15 Datun Road, Chaoyang District, Beijing 100101, China
| | - Thomas C Südhof
- Department of Molecular and Cellular Physiology and Howard Hughes Medical Institute, Stanford University, 265 Campus Drive, Stanford, CA 94305-5453, USA.
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20
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Kurps J, Broeke JH, Cijsouw T, Kompatscher A, van Weering JRT, de Wit H. Quantitative image analysis tool to study the plasma membrane localization of proteins and cortical actin in neuroendocrine cells. J Neurosci Methods 2014; 236:1-10. [PMID: 25109903 DOI: 10.1016/j.jneumeth.2014.07.022] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2014] [Revised: 07/28/2014] [Accepted: 07/29/2014] [Indexed: 11/15/2022]
Abstract
BACKGROUND Adrenal chromaffin cells are a widely used model system to study regulated exocytosis and other membrane-associated processes. Alterations in the amount and localization of the proteins involved in these processes can be visualized with fluorescent probes that report the effect of different stimuli or genetic modifications. However, the quantitative analysis of such images remains difficult, especially when focused on specific locations, such as the plasma membrane. NEW METHOD We developed an image analysis algorithm, named plasma membrane analysis in chromaffin cells (PlasMACC). PlasMACC enables automatic detection of the plasma membrane region and quantitative analysis of multi-fluorescent signals from spherical cells. PlasMACC runs in the image analysis software ImageJ environment, it is user-friendly and freely available. RESULTS PlasMACC delivers detailed information about intensity, thickness and density of fluorescent signals at the plasma membrane of both living and fixed cells. Individual signals can be compared between cells and different signals within one cell can be correlated. PlasMACC can process conventional laser-scanning confocal images as well as data obtained by super-resolution methods such as structured illumination microscopy. COMPARISON WITH EXISTING METHOD(S) By comparing PlasMACC to methods currently used in the field, we show more consistent quantitative data due to the fully automated algorithm. PlasMACC also provides an expanded set of novel analysis parameters. CONCLUSION PlasMACC enables a detailed quantification of fluorescent signals at the plasma membrane of spherical cells in an unbiased and reliable fashion.
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Affiliation(s)
- Julia Kurps
- Department of Functional Genomics, Center for Neurogenomics and Cognitive Research, VU University Amsterdam and VU Medical Center, 1081 HV Amsterdam, Netherlands
| | - Jurjen H Broeke
- Department of Clinical Genetics, Center for Neurogenomics and Cognitive Research, VU University Amsterdam and VU Medical Center, 1081 HV Amsterdam, Netherlands
| | - Tony Cijsouw
- Department of Functional Genomics, Center for Neurogenomics and Cognitive Research, VU University Amsterdam and VU Medical Center, 1081 HV Amsterdam, Netherlands
| | - Andreas Kompatscher
- Department of Functional Genomics, Center for Neurogenomics and Cognitive Research, VU University Amsterdam and VU Medical Center, 1081 HV Amsterdam, Netherlands
| | - Jan R T van Weering
- Department of Clinical Genetics, Center for Neurogenomics and Cognitive Research, VU University Amsterdam and VU Medical Center, 1081 HV Amsterdam, Netherlands.
| | - Heidi de Wit
- Department of Clinical Genetics, Center for Neurogenomics and Cognitive Research, VU University Amsterdam and VU Medical Center, 1081 HV Amsterdam, Netherlands
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21
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Pantano S, Montecucco C. The blockade of the neurotransmitter release apparatus by botulinum neurotoxins. Cell Mol Life Sci 2014; 71:793-811. [PMID: 23749048 PMCID: PMC11113401 DOI: 10.1007/s00018-013-1380-7] [Citation(s) in RCA: 89] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2013] [Revised: 05/15/2013] [Accepted: 05/16/2013] [Indexed: 12/22/2022]
Abstract
The high toxicity of the seven serotypes of botulinum neurotoxins (BoNT/A to G), together with their specificity and reversibility, includes them in the list A of potential bioterrorism weapons and, at the same time, among the therapeutics of choice for a variety of human syndromes. They invade nerve terminals and cleave specifically the three proteins which form the heterotrimeric SNAP REceptors (SNARE) complex that mediates neurotransmitter release. The BoNT-induced cleavage of the SNARE proteins explains by itself the paralysing activity of the BoNTs because the truncated proteins cannot form the SNARE complex. However, in the case of BoNT/A, the most widely used toxin in therapy, additional factors come into play as it only removes a few residues from the synaptosomal associate protein of 25 kDa C-terminus and this results in a long duration of action. To explain these facts and other experimental data, we present here a model for the assembly of the neuroexocytosis apparatus in which Synaptotagmin and Complexin first assist the zippering of the SNARE complex, and then stabilize and clamp an octameric radial assembly of the SNARE complexes.
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Affiliation(s)
- Sergio Pantano
- Institut Pasteur de Montevideo, Calle Mataojo 2020, CP 11400 Montevideo, Uruguay
| | - Cesare Montecucco
- Department of Biomedical Sciences, University of Padova, Padua, Italy
- Institute of Neuroscience, National Research Council, Viale G. Colombo 3, 35121 Padua, Italy
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22
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Abstract
During an action potential, Ca(2+) entering a presynaptic terminal triggers synaptic vesicle exocytosis and neurotransmitter release in less than a millisecond. How does Ca(2+) stimulate release so rapidly and precisely? Work over the last decades revealed that Ca(2+) binding to synaptotagmin triggers release by stimulating synaptotagmin binding to a core fusion machinery composed of SNARE and SM proteins that mediates membrane fusion during exocytosis. Complexin adaptor proteins assist synaptotagmin by activating and clamping this core fusion machinery. Synaptic vesicles containing synaptotagmin are positioned at the active zone, the site of vesicle fusion, by a protein complex containing RIM proteins. RIM proteins activate docking and priming of synaptic vesicles and simultaneously recruit Ca(2+) channels to active zones, thereby connecting in a single complex primed synaptic vesicles to Ca(2+) channels. This architecture allows direct flow of Ca(2+) ions from Ca(2+) channels to synaptotagmin, which then triggers fusion, thus mediating tight millisecond coupling of an action potential to neurotransmitter release.
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Affiliation(s)
- Thomas C Südhof
- Department of Molecular and Cellular Physiology, and Howard Hughes Medical Institute, Lorry Lokey SIM1 Building, 265 Campus Drive, Stanford University School of Medicine, Stanford, CA 94305, USA.
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23
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Synaptotagmin interaction with SNAP-25 governs vesicle docking, priming, and fusion triggering. J Neurosci 2013; 33:14417-30. [PMID: 24005294 DOI: 10.1523/jneurosci.1236-13.2013] [Citation(s) in RCA: 59] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023] Open
Abstract
SNARE complex assembly constitutes a key step in exocytosis that is rendered Ca(2+)-dependent by interactions with synaptotagmin-1. Two putative sites for synaptotagmin binding have recently been identified in SNAP-25 using biochemical methods: one located around the center and another at the C-terminal end of the SNARE bundle. However, it is still unclear whether and how synaptotagmin-1 × SNARE interactions at these sites are involved in regulating fast neurotransmitter release. Here, we have used electrophysiological techniques with high time-resolution to directly investigate the mechanistic ramifications of proposed SNAP-25 × synaptotagmin-1 interaction in mouse chromaffin cells. We demonstrate that the postulated central binding domain surrounding layer zero covers both SNARE motifs of SNAP-25 and is essential for vesicle docking, priming, and fast fusion-triggering. Mutation of this site caused no further functional alterations in synaptotagmin-1-deficient cells, indicating that the central acidic patch indeed constitutes a mechanistically relevant synaptotagmin-1 interaction site. Moreover, our data show that the C-terminal binding interface only plays a subsidiary role in triggering but is required for the full size of the readily releasable pool. Intriguingly, we also found that mutation of synaptotagmin-1 interaction sites led to more pronounced phenotypes in the context of the adult neuronal isoform SNAP-25B than in the embryonic isoform SNAP-25A. Further experiments demonstrated that stronger synaptotagmin-1 × SNAP-25B interactions allow for the larger primed vesicle pool supported by SNAP-25 isoform B. Thus, synaptotagmin-1 × SNARE interactions are not only required for multiple mechanistic steps en route to fusion but also underlie the developmental control of the releasable vesicle pool.
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24
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Alpadi K, Kulkarni A, Namjoshi S, Srinivasan S, Sippel KH, Ayscough K, Zieger M, Schmidt A, Mayer A, Evangelista M, Quiocho FA, Peters C. Dynamin-SNARE interactions control trans-SNARE formation in intracellular membrane fusion. Nat Commun 2013; 4:1704. [PMID: 23591871 PMCID: PMC3630463 DOI: 10.1038/ncomms2724] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2012] [Accepted: 03/08/2013] [Indexed: 11/09/2022] Open
Abstract
The fundamental processes of membrane fission and fusion determine size and copy numbers of intracellular organelles. While SNARE proteins and tethering complexes mediate intracellular membrane fusion, fission requires the presence of dynamin or dynamin-related proteins. Here we study these reactions in native yeast vacuoles and find that the yeast dynamin homolog Vps1 is not only an essential part of the fission machinery, but also controls membrane fusion by generating an active Qa SNARE- tethering complex pool, which is essential for trans-SNARE formation. Our findings provide new insight into the role of dynamins in membrane fusion by directly acting on SNARE proteins.
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Affiliation(s)
- Kannan Alpadi
- Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, Texas 77030, USA
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25
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Hammel I, Meilijson I. Function suggests nano-structure: towards a unified theory for secretion rate, a statistical mechanics approach. J R Soc Interface 2013; 10:20130640. [PMID: 24004560 DOI: 10.1098/rsif.2013.0640] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023] Open
Abstract
The inventory of secretory granules along the plasma membrane can be viewed as maintained in two restricted compartments. The release-ready pool represents docked granules available for an initial stage of fast, immediate secretion, followed by a second stage of granule set-aside secretion pool, with significantly slower rate. Transmission electron microscopy ultra-structural investigations correlated with electrophysiological techniques and mathematical modelling have allowed the categorization of these secretory vesicle compartments, in which vesicles can be in various states of secretory competence. Using the above-mentioned approaches, the kinetics of single vesicle exocytosis can be worked out. The ultra-fast kinetics, explored in this study, represents the immediately available release-ready pool, in which granules bound to the plasma membrane are exocytosed upon Ca(2+) influx at the SNARE rosette at the base of porosomes. Formalizing Dodge and Rahamimoff findings on the effect of calcium concentration and incorporating the effect of SNARE transient rosette size, we postulate that secretion rate (rate), the number (X) of intracellular calcium ions available for fusion, calcium capacity (0 ≤ M ≤ 5) and the fusion nano-machine size (as measured by the SNARE rosette size K) satisfy the parsimonious M-K relation rate ≈ C × [Ca(2+)](min(X,M))e(-K/2).
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Affiliation(s)
- Ilan Hammel
- Sackler Faculty of Medicine, Department of Pathology, Tel Aviv University, Tel Aviv 6997801, Israel.
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26
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Megighian A, Zordan M, Pantano S, Scorzeto M, Rigoni M, Zanini D, Rossetto O, Montecucco C. Evidence for a radial SNARE super-complex mediating neurotransmitter release at the Drosophila neuromuscular junction. J Cell Sci 2013; 126:3134-40. [PMID: 23687382 DOI: 10.1242/jcs.123802] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
The SNARE proteins VAMP/synaptobrevin, SNAP-25 and syntaxin are core components of the apparatus that mediates neurotransmitter release. They form a heterotrimeric complex, and an undetermined number of SNARE complexes assemble to form a super-complex. Here, we present a radial model of this nanomachine. Experiments performed with botulinum neurotoxins led to the identification of one arginine residue in SNAP-25 and one aspartate residue in syntaxin (R206 and D253 in Drosophila melanogaster). These residues are highly conserved and predicted to play a major role in the protein-protein interactions between SNARE complexes by forming an ionic couple. Accordingly, we generated transgenic Drosophila lines expressing SNAREs mutated in these residues and performed an electrophysiological analysis of their neuromuscular junctions. Our results indicate that SNAP-25-R206 and syntaxin-D253 play a major role in neuroexocytosis and support a radial assembly of several SNARE complexes interacting via the ionic couple formed by these two residues.
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Affiliation(s)
- Aram Megighian
- Department of Biomedical Sciences, University of Padova, Via Ugo Bassi 56 B, 35121 Padova, Italy
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27
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Yang L, Dun AR, Martin KJ, Qiu Z, Dunn A, Lord GJ, Lu W, Duncan RR, Rickman C. Secretory vesicles are preferentially targeted to areas of low molecular SNARE density. PLoS One 2012; 7:e49514. [PMID: 23166692 PMCID: PMC3499460 DOI: 10.1371/journal.pone.0049514] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2012] [Accepted: 10/10/2012] [Indexed: 12/30/2022] Open
Abstract
Intercellular communication is commonly mediated by the regulated fusion, or exocytosis, of vesicles with the cell surface. SNARE (soluble N-ethymaleimide sensitive factor attachment protein receptor) proteins are the catalytic core of the secretory machinery, driving vesicle and plasma membrane merger. Plasma membrane SNAREs (tSNAREs) are proposed to reside in dense clusters containing many molecules, thus providing a concentrated reservoir to promote membrane fusion. However, biophysical experiments suggest that a small number of SNAREs are sufficient to drive a single fusion event. Here we show, using molecular imaging, that the majority of tSNARE molecules are spatially separated from secretory vesicles. Furthermore, the motilities of the individual tSNAREs are constrained in membrane micro-domains, maintaining a non-random molecular distribution and limiting the maximum number of molecules encountered by secretory vesicles. Together our results provide a new model for the molecular mechanism of regulated exocytosis and demonstrate the exquisite organization of the plasma membrane at the level of individual molecular machines.
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Affiliation(s)
- Lei Yang
- Institute of Biological Chemistry, Biophysics and Bioengineering, Heriot-Watt University, Edinburgh, United Kingdom
| | - Alison R. Dun
- Institute of Biological Chemistry, Biophysics and Bioengineering, Heriot-Watt University, Edinburgh, United Kingdom
| | - Kirsty J. Martin
- Institute of Biological Chemistry, Biophysics and Bioengineering, Heriot-Watt University, Edinburgh, United Kingdom
| | - Zhen Qiu
- Institute of Biological Chemistry, Biophysics and Bioengineering, Heriot-Watt University, Edinburgh, United Kingdom
| | - Andrew Dunn
- Institute of Biological Chemistry, Biophysics and Bioengineering, Heriot-Watt University, Edinburgh, United Kingdom
| | - Gabriel J. Lord
- Mathematical and Computer Sciences, Heriot-Watt University, Edinburgh, United Kingdom
| | - Weiping Lu
- Institute of Biological Chemistry, Biophysics and Bioengineering, Heriot-Watt University, Edinburgh, United Kingdom
| | - Rory R. Duncan
- Institute of Biological Chemistry, Biophysics and Bioengineering, Heriot-Watt University, Edinburgh, United Kingdom
| | - Colin Rickman
- Institute of Biological Chemistry, Biophysics and Bioengineering, Heriot-Watt University, Edinburgh, United Kingdom
- * E-mail:
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