1
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Kádková A, Murach J, Østergaard M, Malsam A, Malsam J, Lolicato F, Nickel W, Söllner TH, Sørensen JB. SNAP25 disease mutations change the energy landscape for synaptic exocytosis due to aberrant SNARE interactions. eLife 2024; 12:RP88619. [PMID: 38411501 PMCID: PMC10911398 DOI: 10.7554/elife.88619] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/28/2024] Open
Abstract
SNAP25 is one of three neuronal SNAREs driving synaptic vesicle exocytosis. We studied three mutations in SNAP25 that cause epileptic encephalopathy: V48F, and D166Y in the synaptotagmin-1 (Syt1)-binding interface, and I67N, which destabilizes the SNARE complex. All three mutations reduced Syt1-dependent vesicle docking to SNARE-carrying liposomes and Ca2+-stimulated membrane fusion in vitro and when expressed in mouse hippocampal neurons. The V48F and D166Y mutants (with potency D166Y > V48F) led to reduced readily releasable pool (RRP) size, due to increased spontaneous (miniature Excitatory Postsynaptic Current, mEPSC) release and decreased priming rates. These mutations lowered the energy barrier for fusion and increased the release probability, which are gain-of-function features not found in Syt1 knockout (KO) neurons; normalized mEPSC release rates were higher (potency D166Y > V48F) than in the Syt1 KO. These mutations (potency D166Y > V48F) increased spontaneous association to partner SNAREs, resulting in unregulated membrane fusion. In contrast, the I67N mutant decreased mEPSC frequency and evoked EPSC amplitudes due to an increase in the height of the energy barrier for fusion, whereas the RRP size was unaffected. This could be partly compensated by positive charges lowering the energy barrier. Overall, pathogenic mutations in SNAP25 cause complex changes in the energy landscape for priming and fusion.
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Affiliation(s)
- Anna Kádková
- Department of Neuroscience, University of CopenhagenCopenhagenDenmark
| | | | - Maiken Østergaard
- Department of Neuroscience, University of CopenhagenCopenhagenDenmark
| | - Andrea Malsam
- Heidelberg University Biochemistry CenterHeidelbergDenmark
| | - Jörg Malsam
- Heidelberg University Biochemistry CenterHeidelbergDenmark
| | - Fabio Lolicato
- Heidelberg University Biochemistry CenterHeidelbergDenmark
- Department of Physics, University of HelsinkiHelsinkiFinland
| | - Walter Nickel
- Heidelberg University Biochemistry CenterHeidelbergDenmark
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2
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Stefani I, Iwaszkiewicz J, Fasshauer D. Exploring the conformational changes of the Munc18-1/syntaxin 1a complex. Protein Sci 2023; 33:e4870. [PMID: 38109275 PMCID: PMC10895456 DOI: 10.1002/pro.4870] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2023] [Revised: 11/30/2023] [Accepted: 12/07/2023] [Indexed: 12/20/2023]
Abstract
Neurotransmitters are released from synaptic vesicles, the membrane of which fuses with the plasma membrane upon calcium influx. This membrane fusion reaction is driven by the formation of a tight complex comprising the plasma membrane N-ethylmaleimide-sensitive factor attachment receptor (SNARE) proteins syntaxin-1a and SNAP-25 with the vesicle SNARE protein synaptobrevin. The neuronal protein Munc18-1 forms a stable complex with syntaxin-1a. Biochemically, syntaxin-1a cannot escape the tight grip of Munc18-1, so formation of the SNARE complex is inhibited. However, Munc18-1 is essential for the release of neurotransmitters in vivo. It has therefore been assumed that Munc18-1 makes the bound syntaxin-1a available for SNARE complex formation. Exactly how this occurs is still unclear, but it is assumed that structural rearrangements occur. Here, we used a series of mutations to specifically weaken the complex at different positions in order to induce these rearrangements biochemically. Our approach was guided through sequence and structural analysis and supported by molecular dynamics simulations. Subsequently, we created a homology model showing the complex in an altered conformation. This conformation presumably represents a more open arrangement of syntaxin-1a that permits the formation of a SNARE complex to be initiated while still bound to Munc18-1. In the future, research should investigate how this central reaction for neuronal communication is controlled by other proteins.
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Affiliation(s)
- Ioanna Stefani
- Department of Computational BiologyUniversity of LausanneLausanneSwitzerland
| | | | - Dirk Fasshauer
- Department of Computational BiologyUniversity of LausanneLausanneSwitzerland
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3
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Hesselbarth J, Schmidt C. Mass spectrometry uncovers intermediates and off-pathway complexes for SNARE complex assembly. Commun Biol 2023; 6:198. [PMID: 36806321 PMCID: PMC9941103 DOI: 10.1038/s42003-023-04548-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2022] [Accepted: 02/01/2023] [Indexed: 02/22/2023] Open
Abstract
The SNARE complex assembles from vesicular Synaptobrevin-2 as well as Syntaxin-1 and SNAP25 both anchored to the presynaptic membrane. It mediates fusion of synaptic vesicles with the presynaptic plasma membrane resulting in exocytosis of neurotransmitters. While the general sequence of SNARE complex formation is well-established, our knowledge on possible intermediates and stable off-pathway complexes is incomplete. We, therefore, follow the stepwise assembly of the SNARE complex and target individual SNAREs, binary sub-complexes, the ternary SNARE complex as well as interactions with Complexin-1. Using native mass spectrometry, we identify the stoichiometry of sub-complexes and monitor oligomerisation of various assemblies. Importantly, we find that interactions with Complexin-1 reduce multimerisation of the ternary SNARE complex. Chemical cross-linking provides detailed insights into these interactions suggesting a role for membrane fusion. In summary, we unravel the stoichiometry of intermediates and off-pathway complexes and compile a road map of SNARE complex assembly including regulation by Complexin-1.
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Affiliation(s)
- Julia Hesselbarth
- Interdisciplinary Research Centre HALOmem, Charles Tanford Protein Centre, Institute of Biochemistry and Biotechnology, Martin Luther University Halle-Wittenberg, Halle, Germany
- Department of Chemistry - Biochemistry, Biocenter II, Johannes Gutenberg University Mainz, Mainz, Germany
| | - Carla Schmidt
- Interdisciplinary Research Centre HALOmem, Charles Tanford Protein Centre, Institute of Biochemistry and Biotechnology, Martin Luther University Halle-Wittenberg, Halle, Germany.
- Department of Chemistry - Biochemistry, Biocenter II, Johannes Gutenberg University Mainz, Mainz, Germany.
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4
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Urrego-Morales O, Gil-Lievana E, Ramirez-Mejia G, Francisco Rodríguez-Durán L, Lilia Escobar M, Delint-Ramirez I, Bermúdez-Rattoni F. Inhibition of hippocampal palmitoyl acyltransferase activity impairs spatial learning and memory consolidation. Neurobiol Learn Mem 2023; 200:107733. [PMID: 36804592 DOI: 10.1016/j.nlm.2023.107733] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2022] [Revised: 01/12/2023] [Accepted: 02/15/2023] [Indexed: 02/21/2023]
Abstract
Protein palmitoylation regulates trafficking, mobilization, localization, interaction, and distribution of proteins through the palmitoyl acyltransferases (PATs) enzymes. Protein palmitoylation controls rapid and dynamic changes of the synaptic architecture that modifies the efficiency and strength of synaptic connections, a fundamental mechanism to generate stable and long-lasting memory traces. Although protein palmitoylation in functional synaptic plasticity has been widely described, its role in learning and memory processes is poorly understood. In this work, we found that PATs inhibition into the hippocampus before and after the training of Morris water maze (MWM) and object location memory (OLM) impaired spatial learning. However, we demonstrated that PATs inhibition during the retrieval does not affect the expression of spatial memory in both MWM and OLM. Accordingly, long-term potentiation induction is impaired by inhibiting PATs into the hippocampus before high-frequency electrical stimulation but not after. These findings suggest that PATs activity is necessary to modify neural plasticity, a mechanism required for memory acquisition and consolidation. Like phosphorylation, active palmitoylation is required to regulate the function of already existing proteins that change synaptic strength in the hippocampus to acquire and later consolidate spatial memories.
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5
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Khalifeh D, Neveu E, Fasshauer D. Megaviruses contain various genes encoding for eukaryotic vesicle trafficking factors. Traffic 2022; 23:414-425. [PMID: 35701729 PMCID: PMC9546365 DOI: 10.1111/tra.12860] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2022] [Revised: 05/02/2022] [Accepted: 06/02/2022] [Indexed: 11/30/2022]
Abstract
Many intracellular pathogens, such as bacteria and large viruses, enter eukaryotic cells via phagocytosis, then replicate and proliferate inside the host. To avoid degradation in the phagosomes, they have developed strategies to modify vesicle trafficking. Although several strategies of bacteria have been characterized, it is not clear whether viruses also interfere with the vesicle trafficking of the host. Recently, we came across SNARE proteins encoded in the genomes of several bacteria of the order Legionellales. These pathogenic bacteria may use SNAREs to interfere with vesicle trafficking, since SNARE proteins are the core machinery for vesicle fusion during transport. They assemble into membrane-bridging SNARE complexes that bring membranes together. We now have also discovered SNARE proteins in the genomes of diverse giant viruses. Our biochemical experiments showed that these proteins are able to form SNARE complexes. We also found other key trafficking factors that work together with SNAREs such as NSF, SM, and Rab proteins encoded in the genomes of giant viruses, suggesting that viruses can make use of a large genetic repertoire of trafficking factors. Most giant viruses possess different collections, suggesting that these factors entered the viral genome multiple times. In the future, the molecular role of these factors during viral infection need to be studied.
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Affiliation(s)
- Dany Khalifeh
- Department of Computational Biology, University of Lausanne, Lausanne, Switzerland
| | - Emilie Neveu
- Department of Computational Biology, University of Lausanne, Lausanne, Switzerland
| | - Dirk Fasshauer
- Department of Computational Biology, University of Lausanne, Lausanne, Switzerland
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6
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Xu Y, Zhu L, Wang S, Ma C. Munc18 − Munc13‐dependent pathway of
SNARE
complex assembly is resistant to
NSF
and
α‐SNAP. FEBS J 2022; 289:6367-6384. [DOI: 10.1111/febs.16528] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2021] [Revised: 04/26/2022] [Accepted: 05/12/2022] [Indexed: 11/28/2022]
Affiliation(s)
- Yuanyuan Xu
- Key Laboratory of Molecular Biophysics of the Ministry of Education, College of Life Science and Technology Huazhong University of Science and Technology Wuhan China
| | - Le Zhu
- Key Laboratory of Molecular Biophysics of the Ministry of Education, College of Life Science and Technology Huazhong University of Science and Technology Wuhan China
| | - Shen Wang
- Key Laboratory of Molecular Biophysics of the Ministry of Education, College of Life Science and Technology Huazhong University of Science and Technology Wuhan 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 China
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7
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Abstract
Membrane fusion requires tethers, SNAREs of R, Qa, Qb, and Qc families, and chaperones of the SM, Sec17/SNAP, and Sec18/NSF families. SNAREs have N-domains, SNARE domains that zipper into 4-helical RQaQbQc coiled coils, a short juxtamembrane (Jx) domain, and (often) a C-terminal transmembrane anchor. We reconstitute fusion with purified components from yeast vacuoles, where the HOPS protein combines tethering and SM functions. The vacuolar Rab, lipids, and R-SNARE activate HOPS to bind Q-SNAREs and catalyze trans-SNARE associations. With SNAREs initially disassembled, as they are on the organelle, we now report that R- and Qa-SNAREs require their physiological juxtamembrane (Jx) regions for fusion. Swap of the Jx domain between the R- and Qa-SNAREs blocks fusion after SNARE association in trans. This block is bypassed by either Sec17, which drives fusion without requiring complete SNARE zippering, or transmembrane-anchored Qb-SNARE in complex with Qa. The abundance of the trans-SNARE complex is not the sole fusion determinant, as it is unaltered by Sec17, Jx swap, or the Qb-transmembrane anchor. The sensitivity of fusion to Jx swap in the absence of a Qb transmembrane anchor is inherent to the SNAREs, because it remains when a synthetic tether replaces HOPS.
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Affiliation(s)
- Amy Orr
- Department of Biochemistry and Cell Biology, Geisel School of Medicine at Dartmouth, 7200 Vail Building, Hanover, NH 03755
| | - Hongki Song
- Department of Biochemistry and Cell Biology, Geisel School of Medicine at Dartmouth, 7200 Vail Building, Hanover, NH 03755
| | - William Wickner
- Department of Biochemistry and Cell Biology, Geisel School of Medicine at Dartmouth, 7200 Vail Building, Hanover, NH 03755
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8
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Saikia N, Yanez-Orozco IS, Qiu R, Hao P, Milikisiyants S, Ou E, Hamilton GL, Weninger KR, Smirnova TI, Sanabria H, Ding F. Integrative structural dynamics probing of the conformational heterogeneity in synaptosomal-associated protein 25. Cell Rep Phys Sci 2021; 2:100616. [PMID: 34888535 PMCID: PMC8654206 DOI: 10.1016/j.xcrp.2021.100616] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
SNAP-25 (synaptosomal-associated protein of 25 kDa) is a prototypical intrinsically disordered protein (IDP) that is unstructured by itself but forms coiled-coil helices in the SNARE complex. With high conformational heterogeneity, detailed structural dynamics of unbound SNAP-25 remain elusive. Here, we report an integrative method to probe the structural dynamics of SNAP-25 by combining replica-exchange discrete molecular dynamics (rxDMD) simulations and label-based experiments at ensemble and single-molecule levels. The rxDMD simulations systematically characterize the coil-to-molten globular transition and reconstruct structural ensemble consistent with prior ensemble experiments. Label-based experiments using Förster resonance energy transfer and double electron-electron resonance further probe the conformational dynamics of SNAP-25. Agreements between simulations and experiments under both ensemble and single-molecule conditions allow us to assign specific helix-coil transitions in SNAP-25 that occur in submillisecond timescales and potentially play a vital role in forming the SNARE complex. We expect that this integrative approach may help further our understanding of IDPs.
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Affiliation(s)
- Nabanita Saikia
- Department of Physics and Astronomy, Clemson University, Clemson, SC 29634, USA
- Department of Chemistry, Navajo Technical University, Chinle, AZ 86503, USA
| | | | - Ruoyi Qiu
- Department of Physics, North Carolina State University, Raleigh, NC 27695, USA
| | - Pengyu Hao
- Department of Physics, North Carolina State University, Raleigh, NC 27695, USA
| | - Sergey Milikisiyants
- Department of Chemistry, North Carolina State University, Raleigh, NC 27695, USA
| | - Erkang Ou
- Department of Chemistry, North Carolina State University, Raleigh, NC 27695, USA
| | - George L. Hamilton
- Department of Physics and Astronomy, Clemson University, Clemson, SC 29634, USA
| | - Keith R. Weninger
- Department of Physics, North Carolina State University, Raleigh, NC 27695, USA
| | - Tatyana I. Smirnova
- Department of Chemistry, North Carolina State University, Raleigh, NC 27695, USA
| | - Hugo Sanabria
- Department of Physics and Astronomy, Clemson University, Clemson, SC 29634, USA
| | - Feng Ding
- Department of Physics and Astronomy, Clemson University, Clemson, SC 29634, USA
- Lead contact
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9
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Mertins J, Finke J, Sies R, Rink KM, Hasenauer J, Lang T. The mesoscale organization of syntaxin 1A and SNAP25 is determined by SNARE-SNARE interactions. eLife 2021; 10:69236. [PMID: 34779769 PMCID: PMC8629428 DOI: 10.7554/elife.69236] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2021] [Accepted: 11/14/2021] [Indexed: 01/01/2023] Open
Abstract
SNARE proteins have been described as the effectors of fusion events in the secretory pathway more than two decades ago. The strong interactions between SNARE domains are clearly important in membrane fusion, but it is unclear whether they are involved in any other cellular processes. Here, we analyzed two classical SNARE proteins, syntaxin 1A and SNAP25. Although they are supposed to be engaged in tight complexes, we surprisingly find them largely segregated in the plasma membrane. Syntaxin 1A only occupies a small fraction of the plasma membrane area. Yet, we find it is able to redistribute the far more abundant SNAP25 on the mesoscale by gathering crowds of SNAP25 molecules onto syntaxin clusters in a SNARE-domain-dependent manner. Our data suggest that SNARE domain interactions are not only involved in driving membrane fusion on the nanoscale, but also play an important role in controlling the general organization of proteins on the mesoscale. Further, we propose these mechanisms preserve active syntaxin 1A–SNAP25 complexes at the plasma membrane.
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Affiliation(s)
- Jasmin Mertins
- Departments of Membrane Biochemistry, Life & Medical Sciences (LIMES) Institute, University of Bonn, Bonn, Germany
| | - Jérôme Finke
- Departments of Membrane Biochemistry, Life & Medical Sciences (LIMES) Institute, University of Bonn, Bonn, Germany
| | - Ricarda Sies
- Departments of Membrane Biochemistry, Life & Medical Sciences (LIMES) Institute, University of Bonn, Bonn, Germany
| | - Kerstin M Rink
- Heidelberg University Biochemistry Center (BZH), Heidelberg, Germany
| | - Jan Hasenauer
- Computational Life Sciences, Life & Medical Sciences (LIMES) Institute, University of Bonn, Bonn, Germany.,Interdisciplinary Research Unit Mathematics and Life Sciences, University of Bonn, Bonn, Germany.,Institute of Computational Biology, Helmholtz Center Munich - German Research Center for Environmental Health, Neuherberg, Germany
| | - Thorsten Lang
- Departments of Membrane Biochemistry, Life & Medical Sciences (LIMES) Institute, University of Bonn, Bonn, Germany
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10
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Abstract
Synaptic vesicle release is regulated by upwards of 30 proteins at the fusion complex alone, but disruptions in any one of these components can have devastating consequences for neuronal communication. Aberrant molecular responses to calcium signaling at the pre-synaptic terminal dramatically affect vesicle trafficking, docking, fusion, and release. At the organismal level, this is reflected in disorders such as epilepsy, depression, and neurodegeneration. Among the myriad pre-synaptic proteins, perhaps the most functionally mysterious is synaptophysin (SYP). On its own, this vesicular transmembrane protein has been proposed to function as a calcium sensor, a cholesterol-binding protein, and to form ion channels across the phospholipid bilayer. The downstream effects of these functions are largely unknown. The physiological relevance of SYP is readily apparent in its interaction with synaptobrevin (VAMP2), an integral element of the neuronal SNARE complex. SNAREs, soluble NSF attachment protein receptors, comprise a family of proteins essential for vesicle fusion. The complex formed by SYP and VAMP2 is thought to be involved in both trafficking to the pre-synaptic membrane as well as regulation of SNARE complex formation. Recent structural observations specifically implicate the SYP/VAMP2 complex in anchoring the SNARE assembly at the pre-synaptic membrane prior to vesicle fusion. Thus, the SYP/VAMP2 complex appears vital to the form and function of neuronal exocytotic machinery.
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Affiliation(s)
- Dustin N. White
- MCD Biology, University of Colorado Boulder, Boulder, CO, United States
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11
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Song H, Torng TL, Orr AS, Brunger AT, Wickner WT. Sec17/Sec18 can support membrane fusion without help from completion of SNARE zippering. eLife 2021; 10:67578. [PMID: 33944780 PMCID: PMC8143792 DOI: 10.7554/elife.67578] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2021] [Accepted: 04/30/2021] [Indexed: 11/20/2022] Open
Abstract
Membrane fusion requires R-, Qa-, Qb-, and Qc-family SNAREs that zipper into RQaQbQc coiled coils, driven by the sequestration of apolar amino acids. Zippering has been thought to provide all the force driving fusion. Sec17/αSNAP can form an oligomeric assembly with SNAREs with the Sec17 C-terminus bound to Sec18/NSF, the central region bound to SNAREs, and a crucial apolar loop near the N-terminus poised to insert into membranes. We now report that Sec17 and Sec18 can drive robust fusion without requiring zippering completion. Zippering-driven fusion is blocked by deleting the C-terminal quarter of any Q-SNARE domain or by replacing the apolar amino acids of the Qa-SNARE that face the center of the 4-SNARE coiled coils with polar residues. These blocks, singly or combined, are bypassed by Sec17 and Sec18, and SNARE-dependent fusion is restored without help from completing zippering.
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Affiliation(s)
- Hongki Song
- Department of Biochemistry and Cell Biology Geisel School of Medicine at Dartmouth, Hanover, United States
| | - Thomas L Torng
- Department of Biochemistry and Cell Biology Geisel School of Medicine at Dartmouth, Hanover, United States
| | - Amy S Orr
- Department of Biochemistry and Cell Biology Geisel School of Medicine at Dartmouth, Hanover, United States
| | - Axel T Brunger
- Howard Hughes Medical Institute and Department of Molecular and Cellular Physiology Stanford University, Stanford, United States
| | - William T Wickner
- Department of Biochemistry and Cell Biology Geisel School of Medicine at Dartmouth, Hanover, United States
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12
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Wittig S, Ganzella M, Barth M, Kostmann S, Riedel D, Pérez-Lara Á, Jahn R, Schmidt C. Cross-linking mass spectrometry uncovers protein interactions and functional assemblies in synaptic vesicle membranes. Nat Commun 2021; 12:858. [PMID: 33558502 PMCID: PMC7870876 DOI: 10.1038/s41467-021-21102-w] [Citation(s) in RCA: 17] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2020] [Accepted: 12/18/2020] [Indexed: 02/08/2023] Open
Abstract
Synaptic vesicles are storage organelles for neurotransmitters. They pass through a trafficking cycle and fuse with the pre-synaptic membrane when an action potential arrives at the nerve terminal. While molecular components and biophysical parameters of synaptic vesicles have been determined, our knowledge on the protein interactions in their membranes is limited. Here, we apply cross-linking mass spectrometry to study interactions of synaptic vesicle proteins in an unbiased approach without the need for specific antibodies or detergent-solubilisation. Our large-scale analysis delivers a protein network of vesicle sub-populations and functional assemblies including an active and an inactive conformation of the vesicular ATPase complex as well as non-conventional arrangements of the luminal loops of SV2A, Synaptophysin and structurally related proteins. Based on this network, we specifically target Synaptobrevin-2, which connects with many proteins, in different approaches. Our results allow distinction of interactions caused by 'crowding' in the vesicle membrane from stable interaction modules.
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Affiliation(s)
- Sabine Wittig
- Interdisciplinary Research Centre HALOmem, Charles Tanford Protein Centre, Institute for Biochemistry and Biotechnology, Martin Luther University Halle-Wittenberg, Halle, Germany
| | - Marcelo Ganzella
- Department for Neurobiology, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
| | - Marie Barth
- Interdisciplinary Research Centre HALOmem, Charles Tanford Protein Centre, Institute for Biochemistry and Biotechnology, Martin Luther University Halle-Wittenberg, Halle, Germany
| | - Susann Kostmann
- Interdisciplinary Research Centre HALOmem, Charles Tanford Protein Centre, Institute for Biochemistry and Biotechnology, Martin Luther University Halle-Wittenberg, Halle, Germany
| | - Dietmar Riedel
- Department for Neurobiology, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
| | - Ángel Pérez-Lara
- Department for Neurobiology, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
- Department of Physical Chemistry, Faculty of Pharmacy, University of Granada, Granada, Spain
| | - Reinhard Jahn
- Department for Neurobiology, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
| | - Carla Schmidt
- Interdisciplinary Research Centre HALOmem, Charles Tanford Protein Centre, Institute for Biochemistry and Biotechnology, Martin Luther University Halle-Wittenberg, Halle, Germany.
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13
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Abstract
The past few years have resulted in an increased awareness and recognition of the prevalence and roles of intrinsically disordered proteins and protein regions (IDPs and IDRs, respectively) in synaptic vesicle trafficking and exocytosis and in overall synaptic organization. IDPs and IDRs constitute a class of proteins and protein regions that lack stable tertiary structure, but nevertheless retain biological function. Their significance in processes such as cell signaling is now well accepted, but their pervasiveness and importance in other areas of biology are not as widely appreciated. Here, we review the prevalence and functional roles of IDPs and IDRs associated with the release and recycling of synaptic vesicles at nerve terminals, as well as with the architecture of these terminals. We hope to promote awareness, especially among neuroscientists, of the importance of this class of proteins in these critical pathways and structures. The examples discussed illustrate some of the ways in which the structural flexibility conferred by intrinsic protein disorder can be functionally advantageous in the context of cellular trafficking and synaptic function.
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Affiliation(s)
- David Snead
- From the Department of Biochemistry, Weill Cornell Medicine, New York, New York 10021
| | - David Eliezer
- From the Department of Biochemistry, Weill Cornell Medicine, New York, New York 10021
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14
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Tian Z, Gong J, Crowe M, Lei M, Li D, Ji B, Diao J. Biochemical studies of membrane fusion at the single-particle level. Prog Lipid Res 2019; 73:92-100. [PMID: 30611882 DOI: 10.1016/j.plipres.2019.01.001] [Citation(s) in RCA: 33] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2018] [Revised: 01/01/2019] [Accepted: 01/02/2019] [Indexed: 01/21/2023]
Abstract
To study membrane fusion mediated by synaptic proteins, proteoliposomes have been widely used for in vitro ensemble measurements with limited insights into the fusion mechanism. Single-particle techniques have proven to be powerful in overcoming the limitations of traditional ensemble methods. Here, we summarize current single-particle methods in biophysical and biochemical studies of fusion mediated by soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs) and other synaptic proteins, together with their advantages and limitations.
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15
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Fiedler MRM, Barthel L, Kubisch C, Nai C, Meyer V. Construction of an improved Aspergillus niger platform for enhanced glucoamylase secretion. Microb Cell Fact 2018; 17:95. [PMID: 29908567 PMCID: PMC6004097 DOI: 10.1186/s12934-018-0941-8] [Citation(s) in RCA: 33] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2018] [Accepted: 06/08/2018] [Indexed: 01/02/2023] Open
Abstract
BACKGROUND The lifestyle of filamentous fungi depends on the secretion of hydrolytic enzymes into the surrounding medium, which degrade polymeric substances into monomers that are then taken up to sustain metabolism. This feature has been exploited in biotechnology to establish platform strains with high secretory capacity including Aspergillus niger. The accepted paradigm is that proteins become mainly secreted at the tips of fungal hyphae. However, it is still a matter of debate if the amount of growing hyphal tips in filamentous fungi correlates with an increase in secretion, with previous studies showing either a positive or no correlation. RESULTS Here, we followed a systematic approach to study protein secretion in A. niger. First, we put the glaA gene encoding for glucoamylase (GlaA), the most abundant secreted protein of A. niger, under control of the tunable Tet-on system. Regulation of glaA gene expression by omitting or adding the inducer doxycycline to cultivation media allowed us to study the effect of glaA under- or overexpression in the same isolate. By inducing glaA expression in a fluorescently tagged v-SNARE reporter strain expressing GFP-SncA, we could demonstrate that the amount of post-Golgi carriers indeed depends on and correlates with glaA gene expression. By deleting the racA gene, encoding the Rho-GTPase RacA in this isolate, we generated a strain which is identical to the parental strain with respect to biomass formation but produces about 20% more hyphal tips. This hyperbranching phenotype caused a more compact macromorphology in shake flask cultivations. When ensuring continuous high-level expression of glaA by repeated addition of doxycycline, this hyperbranching strain secreted up to four times more GlaA into the culture medium compared to its parental strain. CONCLUSION The data obtained in this study strongly indicate that A. niger responds to forced transcription of secretory enzymes with increased formation of post-Golgi carriers to efficiently accommodate the incoming cargo load. This physiological adaptation can be rationally exploited to generate hypersecretion platforms based on a hyperbranching phenotype. We propose that a racA deletion background serves as an excellent chassis for such hypersecretion strains.
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Affiliation(s)
- Markus R. M. Fiedler
- Department Applied and Molecular Microbiology, Institute of Biotechnology, Technische Universität Berlin, Gustav-Meyer-Allee 25, 13355 Berlin, Germany
| | - Lars Barthel
- Department Applied and Molecular Microbiology, Institute of Biotechnology, Technische Universität Berlin, Gustav-Meyer-Allee 25, 13355 Berlin, Germany
| | - Christin Kubisch
- Department Applied and Molecular Microbiology, Institute of Biotechnology, Technische Universität Berlin, Gustav-Meyer-Allee 25, 13355 Berlin, Germany
| | - Corrado Nai
- Department Applied and Molecular Microbiology, Institute of Biotechnology, Technische Universität Berlin, Gustav-Meyer-Allee 25, 13355 Berlin, Germany
| | - Vera Meyer
- Department Applied and Molecular Microbiology, Institute of Biotechnology, Technische Universität Berlin, Gustav-Meyer-Allee 25, 13355 Berlin, Germany
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Feltrup TM, Patel K, Kumar R, Cai S, Singh BR. A novel role of C-terminus in introducing a functionally flexible structure critical for the biological activity of botulinum neurotoxin. Sci Rep 2018; 8:8884. [PMID: 29891845 PMCID: PMC5995822 DOI: 10.1038/s41598-018-26764-z] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2017] [Accepted: 05/17/2018] [Indexed: 02/06/2023] Open
Abstract
Botulinum neurotoxin (BoNT) is responsible for botulism, a clinical condition resulting in flaccid muscle paralysis and potentially death. The light chain is responsible for its intracellular toxicity through its endopeptidase activity. Available crystal structures of BoNT/A light chains (LCA) are based on various truncated versions (tLCA) of the full-length LCA (fLCA) and do not necessarily reflect the true structure of LCA in solution. The understanding of the mechanism of action, longevity of intoxication, and an improved development of endopeptidase inhibitors are dependent on first having a better insight into the structure of LCA in solution. Using an array of biophysical techniques, we report that the fLCA structure is significantly more flexible than tLCA in solution, which may be responsible for its dramatically higher enzymatic activity. This seems to be achieved by a much stronger, more rapid binding to substrate (SNAP-25) of the fLCA compared to tLCA. These results suggest that the C-terminus of LCA plays a critical role in introducing a flexible structure, which is essential for its biological function. This is the first report of such a massive structural role of the C-terminus of a protein being critical for maintaining a functional state.
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Affiliation(s)
- Thomas M Feltrup
- Department of Chemistry & Biochemistry, University of Massachusetts Dartmouth, North Dartmouth, MA, 02747, USA
| | - Kruti Patel
- Department of Chemistry & Biochemistry, University of Massachusetts Dartmouth, North Dartmouth, MA, 02747, USA
| | - Raj Kumar
- Botulinum Research Center, Institute of Advanced Sciences, North Dartmouth, MA, 02747, USA
| | - Shuowei Cai
- Department of Chemistry & Biochemistry, University of Massachusetts Dartmouth, North Dartmouth, MA, 02747, USA
| | - Bal Ram Singh
- Botulinum Research Center, Institute of Advanced Sciences, North Dartmouth, MA, 02747, USA.
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17
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Affiliation(s)
- Ferenc Zsila
- Biomolecular Self-Assembly Group; Institute of Materials and Environmental Chemistry; Research Centre for Natural Sciences; Hungarian Academy of Sciences; 1117 Budapest Hungary
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18
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Dubuke ML, Maniatis S, Shaffer SA, Munson M. The Exocyst Subunit Sec6 Interacts with Assembled Exocytic SNARE Complexes. J Biol Chem 2015; 290:28245-28256. [PMID: 26446795 DOI: 10.1074/jbc.m115.673806] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2015] [Indexed: 11/06/2022] Open
Abstract
In eukaryotic cells, membrane-bound vesicles carry cargo between intracellular compartments, to and from the cell surface, and into the extracellular environment. Many conserved families of proteins are required for properly localized vesicle fusion, including the multisubunit tethering complexes and the SNARE complexes. These protein complexes work together to promote proper vesicle fusion in intracellular trafficking pathways. However, the mechanism by which the exocyst, the exocytosis-specific multisubunit tethering complex, interacts with the exocytic SNAREs to mediate vesicle targeting and fusion is currently unknown. We have demonstrated previously that the Saccharomyces cerevisiae exocyst subunit Sec6 directly bound the plasma membrane SNARE protein Sec9 in vitro and that Sec6 inhibited the assembly of the binary Sso1-Sec9 SNARE complex. Therefore, we hypothesized that the interaction between Sec6 and Sec9 prevented the assembly of premature SNARE complexes at sites of exocytosis. To map the determinants of this interaction, we used cross-linking and mass spectrometry analyses to identify residues required for binding. Mutation of residues identified by this approach resulted in a growth defect when introduced into yeast. Contrary to our previous hypothesis, we discovered that Sec6 does not change the rate of SNARE assembly but, rather, binds both the binary Sec9-Sso1 and ternary Sec9-Sso1-Snc2 SNARE complexes. Together, these results suggest a new model in which Sec6 promotes SNARE complex assembly, similar to the role proposed for other tether subunit-SNARE interactions.
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Affiliation(s)
- Michelle L Dubuke
- Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, Worcester, Massachusetts 01605
| | - Stephanie Maniatis
- Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, Worcester, Massachusetts 01605; Proteomics and Mass Spectrometry Facility, University of Massachusetts Medical School, Shrewsbury, Massachusetts 01545
| | - Scott A Shaffer
- Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, Worcester, Massachusetts 01605; Proteomics and Mass Spectrometry Facility, University of Massachusetts Medical School, Shrewsbury, Massachusetts 01545
| | - Mary Munson
- Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, Worcester, Massachusetts 01605.
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Shen XM, Selcen D, Brengman J, Engel AG. Mutant SNAP25B causes myasthenia, cortical hyperexcitability, ataxia, and intellectual disability. Neurology 2014; 83:2247-55. [PMID: 25381298 DOI: 10.1212/wnl.0000000000001079] [Citation(s) in RCA: 84] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
OBJECTIVE To identify and characterize the molecular basis of a syndrome associated with myasthenia, cortical hyperexcitability, cerebellar ataxia, and intellectual disability. METHODS We performed in vitro microelectrode studies of neuromuscular transmission, performed exome and Sanger sequencing, and analyzed functional consequences of the identified mutation in expression studies. RESULTS Neuromuscular transmission at patient endplates was compromised by reduced evoked quantal release. Exome sequencing identified a dominant de novo variant, p.Ile67Asn, in SNAP25B, a SNARE protein essential for exocytosis of synaptic vesicles from nerve terminals and of dense-core vesicles from endocrine cells. Ca(2+)-triggered exocytosis is initiated when synaptobrevin attached to synaptic vesicles (v-SNARE) assembles with SNAP25B and syntaxin anchored in the presynaptic membrane (t-SNAREs) into an α-helical coiled-coil held together by hydrophobic interactions. Pathogenicity of the Ile67Asn mutation was confirmed by 2 measures. First, the Ca(2+) triggered fusion of liposomes incorporating v-SNARE with liposomes containing t-SNAREs was hindered when t-SNAREs harbored the mutant SNAP25B moiety. Second, depolarization of bovine chromaffin cells transfected with mutant SNAP25B or with mutant plus wild-type SNAP25B markedly reduced depolarization-evoked exocytosis compared with wild-type transfected cells. CONCLUSION Ile67Asn variant in SNAP25B is pathogenic because it inhibits synaptic vesicle exocytosis. We attribute the deleterious effects of the mutation to disruption of the hydrophobic α-helical coiled-coil structure of the SNARE complex by replacement of a highly hydrophobic isoleucine by a strongly hydrophilic asparagine.
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Affiliation(s)
- Xin-Ming Shen
- From the Department of Neurology and Neuromuscular Research Laboratory, Mayo Clinic, Rochester, MN.
| | - Duygu Selcen
- From the Department of Neurology and Neuromuscular Research Laboratory, Mayo Clinic, Rochester, MN
| | - Joan Brengman
- From the Department of Neurology and Neuromuscular Research Laboratory, Mayo Clinic, Rochester, MN
| | - Andrew G Engel
- From the Department of Neurology and Neuromuscular Research Laboratory, Mayo Clinic, Rochester, MN.
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20
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Chalbi M, Barraud-Lange V, Ravaux B, Howan K, Rodriguez N, Soule P, Ndzoudi A, Boucheix C, Rubinstein E, Wolf JP, Ziyyat A, Perez E, Pincet F, Gourier C. Binding of sperm protein Izumo1 and its egg receptor Juno drives Cd9 accumulation in the intercellular contact area prior to fusion during mammalian fertilization. Development 2014; 141:3732-9. [PMID: 25209248 DOI: 10.1242/dev.111534] [Citation(s) in RCA: 59] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Little is known about the molecular mechanisms that induce gamete fusion during mammalian fertilization. After initial contact, adhesion between gametes only leads to fusion in the presence of three membrane proteins that are necessary, but insufficient, for fusion: Izumo1 on sperm, its receptor Juno on egg and Cd9 on egg. What happens during this adhesion phase is a crucial issue. Here, we demonstrate that the intercellular adhesion that Izumo1 creates with Juno is conserved in mouse and human eggs. We show that, along with Izumo1, egg Cd9 concomitantly accumulates in the adhesion area. Without egg Cd9, the recruitment kinetics of Izumo1 are accelerated. Our results suggest that this process is conserved across species, as the adhesion partners, Izumo1 and its receptor, are interchangeable between mouse and human. Our findings suggest that Cd9 is a partner of Juno, and these discoveries allow us to propose a new model of the molecular mechanisms leading to gamete fusion, in which the adhesion-induced membrane organization assembles all key players of the fusion machinery.
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Affiliation(s)
- Myriam Chalbi
- Laboratoire de Physique Statistique, Ecole Normale Supérieure, Université Pierre et Marie Curie, Université Paris Diderot, Centre National de la Recherche Scientifique UMR8550, 24 rue Lhomond, Paris 75005, France
| | - Virginie Barraud-Lange
- Université Paris Descartes, Institut National de la Santé et de la Recherche Médicale U1016, Génomique, Epigénétique et Physiopathologie de la Reproduction, Service d'Histologie Embryologie Biologie de la Reproduction-CECOS, Hopital Cochin, AP-HP24 rue du Faubourg Saint-Jacques, Paris 75014, France
| | - Benjamin Ravaux
- Laboratoire de Physique Statistique, Ecole Normale Supérieure, Université Pierre et Marie Curie, Université Paris Diderot, Centre National de la Recherche Scientifique UMR8550, 24 rue Lhomond, Paris 75005, France
| | - Kevin Howan
- Laboratoire de Physique Statistique, Ecole Normale Supérieure, Université Pierre et Marie Curie, Université Paris Diderot, Centre National de la Recherche Scientifique UMR8550, 24 rue Lhomond, Paris 75005, France
| | - Nicolas Rodriguez
- Université Pierre et Marie Curie Laboratoire des biomolécules, Paris 75005, France
| | - Pierre Soule
- Université Pierre et Marie Curie Laboratoire des biomolécules, Paris 75005, France
| | - Arnaud Ndzoudi
- Université Paris Descartes, Institut National de la Santé et de la Recherche Médicale U1016, Génomique, Epigénétique et Physiopathologie de la Reproduction, Service d'Histologie Embryologie Biologie de la Reproduction-CECOS, Hopital Cochin, AP-HP24 rue du Faubourg Saint-Jacques, Paris 75014, France
| | - Claude Boucheix
- Institut National de la Santé et de la Recherche Médicale, U1004, 14 avenue Paul Vaillant Couturier, Villejuif 94800, France Université Paris-Sud, Institut André Lwoff, Villejuif 94800, France
| | - Eric Rubinstein
- Institut National de la Santé et de la Recherche Médicale, U1004, 14 avenue Paul Vaillant Couturier, Villejuif 94800, France Université Paris-Sud, Institut André Lwoff, Villejuif 94800, France
| | - Jean Philippe Wolf
- Université Paris Descartes, Institut National de la Santé et de la Recherche Médicale U1016, Génomique, Epigénétique et Physiopathologie de la Reproduction, Service d'Histologie Embryologie Biologie de la Reproduction-CECOS, Hopital Cochin, AP-HP24 rue du Faubourg Saint-Jacques, Paris 75014, France
| | - Ahmed Ziyyat
- Université Paris Descartes, Institut National de la Santé et de la Recherche Médicale U1016, Génomique, Epigénétique et Physiopathologie de la Reproduction, Service d'Histologie Embryologie Biologie de la Reproduction-CECOS, Hopital Cochin, AP-HP24 rue du Faubourg Saint-Jacques, Paris 75014, France
| | - Eric Perez
- Laboratoire de Physique Statistique, Ecole Normale Supérieure, Université Pierre et Marie Curie, Université Paris Diderot, Centre National de la Recherche Scientifique UMR8550, 24 rue Lhomond, Paris 75005, France
| | - Frédéric Pincet
- Laboratoire de Physique Statistique, Ecole Normale Supérieure, Université Pierre et Marie Curie, Université Paris Diderot, Centre National de la Recherche Scientifique UMR8550, 24 rue Lhomond, Paris 75005, France
| | - Christine Gourier
- Laboratoire de Physique Statistique, Ecole Normale Supérieure, Université Pierre et Marie Curie, Université Paris Diderot, Centre National de la Recherche Scientifique UMR8550, 24 rue Lhomond, Paris 75005, France
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Uversky VN. Wrecked regulation of intrinsically disordered proteins in diseases: pathogenicity of deregulated regulators. Front Mol Biosci 2014; 1:6. [PMID: 25988147 PMCID: PMC4428494 DOI: 10.3389/fmolb.2014.00006] [Citation(s) in RCA: 70] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2014] [Accepted: 07/06/2014] [Indexed: 12/14/2022] Open
Abstract
Biologically active proteins without stable tertiary structure are common in all known proteomes. Functions of these intrinsically disordered proteins (IDPs) are typically related to regulation, signaling, and control. Cellular levels of these important regulators are tightly regulated by a variety mechanisms ranging from firmly controlled expression to precisely targeted degradation. Functions of IDPs are controlled by binding to specific partners, alternative splicing, and posttranslational modifications among other means. In the norm, right amounts of precisely activated IDPs have to be present in right time at right places. Wrecked regulation brings havoc to the ordered world of disordered proteins, leading to protein misfolding, misidentification, and missignaling that give rise to numerous human diseases, such as cancer, cardiovascular disease, neurodegenerative diseases, and diabetes. Among factors inducing pathogenic transformations of IDPs are various cellular mechanisms, such as chromosomal translocations, damaged splicing, altered expression, frustrated posttranslational modifications, aberrant proteolytic degradation, and defective trafficking. This review presents some of the aspects of deregulated regulation of IDPs leading to human diseases.
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Affiliation(s)
- Vladimir N Uversky
- Department of Molecular Medicine and USF Health Byrd Alzheimer's Research Institute, Morsani College of Medicine, University of South Florida Tampa, FL, USA ; Biology Department, Faculty of Science, King Abdulaziz University Jeddah, Saudi Arabia ; Laboratory of New Methods in Biology, Institute for Biological Instrumentation, Russian Academy of Sciences Moscow, Russia
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22
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Wesolowski J, Paumet F. Escherichia coli exposure inhibits exocytic SNARE-mediated membrane fusion in mast cells. Traffic 2014; 15:516-30. [PMID: 24494924 DOI: 10.1111/tra.12159] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2013] [Revised: 01/24/2014] [Accepted: 02/04/2014] [Indexed: 12/11/2022]
Abstract
Mast cells orchestrate the allergic response through the release of proinflammatory mediators, which is driven by the fusion of cytoplasmic secretory granules with the plasma membrane. During this process, SNARE proteins including Syntaxin4, SNAP23 and VAMP8 play a key role. Following stimulation, the kinase IKKβ interacts with and phosphorylates the t-SNARE SNAP23. Phosphorylated SNAP23 then associates with Syntaxin4 and the v-SNARE VAMP8 to form a ternary SNARE complex, which drives membrane fusion and mediator release. Interestingly, mast cell degranulation is impaired following exposure to bacteria such as Escherichia coli. However, the molecular mechanism(s) by which this occurs is unknown. Here, we show that E. coli exposure rapidly and additively inhibits degranulation in the RBL-2H3 rat mast cell line. Following co-culture with E. coli, the interaction between IKKβ and SNAP23 is disrupted, resulting in the hypophosphorylation of SNAP23. Subsequent formation of the ternary SNARE complex between SNAP23, Syntaxin4 and VAMP8 is strongly reduced. Collectively, these results demonstrate that E. coli exposure inhibits the formation of VAMP8-containing exocytic SNARE complexes and thus the release of VAMP8-dependent granules by interfering with SNAP23 phosphorylation.
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Affiliation(s)
- Jordan Wesolowski
- Department of Microbiology and Immunology, Thomas Jefferson University, Philadelphia, PA, USA
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Inoue N, Hamada D, Kamikubo H, Hirata K, Kataoka M, Yamamoto M, Ikawa M, Okabe M, Hagihara Y. Molecular dissection of IZUMO1, a sperm protein essential for sperm-egg fusion. Development 2013; 140:3221-9. [PMID: 23824580 DOI: 10.1242/dev.094854] [Citation(s) in RCA: 69] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Although the membrane fusion of spermatozoon and egg cells is the central event of fertilization, the underlying molecular mechanism remains virtually unknown. Gene disruption studies have showed that IZUMO1 on spermatozoon and CD9 on oocyte are essential transmembrane proteins in sperm-egg fusion. In this study, we dissected IZUMO1 protein to determine the domains that were required for the function of sperm-egg fusion. We found that a fragment of the N terminus (Asp5 to Leu113) interacts with fertilization inhibitory antibodies. It also binds to the egg surface and effectively inhibits fusion in vitro. We named this fragment 'IZUMO1 putative functional fragment (IZUMO1PFF)'. Surprisingly, IZUMO1PPF still maintains binding ability on the egg surface of Cd9(-/-) eggs. A series of biophysical measurements using circular dichroism, sedimentation equilibrium and small angle X-ray scattering revealed that IZUMO1PFF is composed of an N-terminal unfolded structure and a C-terminal ellipsoidal helix dimer. Egg binding and fusion inhibition were not observed in the IZUMO1PFF derivative, which was incapable of helix formation. These findings suggest that the formation of a helical dimer at the N-terminal region of IZUMO1 is required for its function. Cos-7 cells expressing the whole IZUMO1 molecule bound to eggs, and IZUMO1 accumulated at the interface between the two cells, but fusion was not observed. These observations suggest that IZUMO1 alone cannot promote sperm-egg membrane fusion, but it works as a factor that is related to the cellular surface interaction, such as the tethering of the membranes by a helical region corresponding to IZUMO1PFF-core.
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Affiliation(s)
- Naokazu Inoue
- Research Institute for Microbial Diseases, Osaka University, Yamadaoka 3-1, Suita, Osaka 565-0871, Japan
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Pertsinidis A, Mukherjee K, Sharma M, Pang ZP, Park SR, Zhang Y, Brunger AT, Südhof TC, Chu S. Ultrahigh-resolution imaging reveals formation of neuronal SNARE/Munc18 complexes in situ. Proc Natl Acad Sci U S A 2013; 110:E2812-20. [PMID: 23821748 DOI: 10.1073/pnas.1310654110] [Citation(s) in RCA: 85] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
Membrane fusion is mediated by complexes formed by SNAP-receptor (SNARE) and Secretory 1 (Sec1)/mammalian uncoordinated-18 (Munc18)-like (SM) proteins, but it is unclear when and how these complexes assemble. Here we describe an improved two-color fluorescence nanoscopy technique that can achieve effective resolutions of up to 7.5-nm full width at half maximum (3.2-nm localization precision), limited only by stochastic photon emission from single molecules. We use this technique to dissect the spatial relationships between the neuronal SM protein Munc18-1 and SNARE proteins syntaxin-1 and SNAP-25 (25 kDa synaptosome-associated protein). Strikingly, we observed nanoscale clusters consisting of syntaxin-1 and SNAP-25 that contained associated Munc18-1. Rescue experiments with syntaxin-1 mutants revealed that Munc18-1 recruitment to the plasma membrane depends on the Munc18-1 binding to the N-terminal peptide of syntaxin-1. Our results suggest that in a primary neuron, SNARE/SM protein complexes containing syntaxin-1, SNAP-25, and Munc18-1 are preassembled in microdomains on the presynaptic plasma membrane. Our superresolution imaging method provides a framework for investigating interactions between the synaptic vesicle fusion machinery and other subcellular systems in situ.
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Greitzer-Antes D, Barak-Broner N, Berlin S, Oron Y, Chikvashvili D, Lotan I. Tracking Ca2+-dependent and Ca2+-independent conformational transitions in syntaxin 1A during exocytosis in neuroendocrine cells. J Cell Sci 2013; 126:2914-23. [PMID: 23641074 DOI: 10.1242/jcs.124743] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
A key issue for understanding exocytosis is elucidating the various protein interactions and the associated conformational transitions underlying soluble N-ethylmeleimide-sensitive factor attachment protein receptor (SNARE) protein assembly. To monitor dynamic changes in syntaxin 1A (Syx) conformation along exocytosis, we constructed a novel fluorescent Syx-based probe that can be efficiently incorporated within endogenous SNARE complexes, support exocytosis, and report shifts in Syx between 'closed' and 'open' conformations by fluorescence resonance energy transfer analysis. Using this probe we resolve two distinct Syx conformational transitions during membrane depolarization-induced exocytosis in PC12 cells: a partial 'opening' in the absence of Ca(2+) entry and an additional 'opening' upon Ca(2+) entry. The Ca(2+)-dependent transition is abolished upon neutralization of the basic charges in the juxtamembrane regions of Syx, which also impairs exocytosis. These novel findings provide evidence of two conformational transitions in Syx during exocytosis, which have not been reported before: one transition directly induced by depolarization and an additional transition that involves the juxtamembrane region of Syx. The superior sensitivity of our probe also enabled detection of subtle Syx conformational changes upon interaction with VAMP2, which were absolutely dependent on the basic charges of the juxtamembrane region. Hence, our results further suggest that the Ca(2+)-dependent transition in Syx involves zippering between the membrane-proximal juxtamembrane regions of Syx and VAMP2 and support the recently implied existence of this zippering in the final phase of SNARE assembly to catalyze exocytosis.
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Affiliation(s)
- Dafna Greitzer-Antes
- Department of Physiology and Pharmacology, Sackler School of Medicine, Tel-Aviv University, Ramat Aviv 69978, Israel
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Varlamov O. Detection of SNARE complexes with FRET using the tetracysteine system. Biotechniques 2012; 52:103-8. [DOI: 10.2144/000113811] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2011] [Accepted: 12/30/2011] [Indexed: 11/23/2022] Open
Abstract
The three proteins synaptosomal-associated protein 25 (SNAP-25), Syntaxin-1a and vesicle-associated membrane protein (VAMP-2) are collectively called SNAREs (soluble N-ethylmaleimide-sensitive factor attachment protein receptors). By assembling into an exocytic complex, the three SNAREs help in catalyzing membrane fusion. Due to lack of probes that adequately reconstitute the intracellular behavior of endogenous SNAREs, the dynamics of SNARE complexes in living cells is poorly understood. Here we describe a new FRET-based probe, called Cerulean-SNAP-25-C4 (CSNAC), that can track the conformational changes undergone by SNAP-25 as exocytic complexes assemble. The fluorescent protein Cerulean was attached to the N terminus and served as a FRET donor. The biarsenical dye FlAsH served as a FRET acceptor and was attached to a short tetracysteine motif (C4) motif inserted into the so-called linker domain of SNAP-25. CSNAC reported successive FRET changes when first Syntaxin-1a and then VAMP-2 were added in vitro. Small tetracysteine insertions used as a FRET acceptor are expected to have less steric hindrance than previously used GFP-based fluorophores. We propose that genetically-encoded tetracysteine tags can be used to study regulated SNARE complex assembly in vivo.
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Alpadi K, Kulkarni A, Comte V, Reinhardt M, Schmidt A, Namjoshi S, Mayer A, Peters C. Sequential analysis of trans-SNARE formation in intracellular membrane fusion. PLoS Biol 2012; 10:e1001243. [PMID: 22272185 PMCID: PMC3260307 DOI: 10.1371/journal.pbio.1001243] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2011] [Accepted: 12/01/2011] [Indexed: 11/19/2022] Open
Abstract
SNARE complexes are required for membrane fusion in the endomembrane system. They contain coiled-coil bundles of four helices, three (Q(a), Q(b), and Q(c)) from target (t)-SNAREs and one (R) from the vesicular (v)-SNARE. NSF/Sec18 disrupts these cis-SNARE complexes, allowing reassembly of their subunits into trans-SNARE complexes and subsequent fusion. Studying these reactions in native yeast vacuoles, we found that NSF/Sec18 activates the vacuolar cis-SNARE complex by selectively displacing the vacuolar Q(a) SNARE, leaving behind a Q(bc)R subcomplex. This subcomplex serves as an acceptor for a Q(a) SNARE from the opposite membrane, leading to Q(a)-Q(bc)R trans-complexes. Activity tests of vacuoles with diagnostic distributions of inactivating mutations over the two fusion partners confirm that this distribution accounts for a major share of the fusion activity. The persistence of the Q(bc)R cis-complex and the formation of the Q(a)-Q(bc)R trans-complex are both sensitive to the Rab-GTPase inhibitor, GDI, and to mutations in the vacuolar tether complex, HOPS (HOmotypic fusion and vacuolar Protein Sorting complex). This suggests that the vacuolar Rab-GTPase, Ypt7, and HOPS restrict cis-SNARE disassembly and thereby bias trans-SNARE assembly into a preferred topology.
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Affiliation(s)
- Kannan Alpadi
- Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, Texas, United States of America
| | - Aditya Kulkarni
- Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, Texas, United States of America
| | - Veronique Comte
- Département de Biochimie, Université de Lausanne, Epalinges, Switzerland
| | - Monique Reinhardt
- Département de Biochimie, Université de Lausanne, Epalinges, Switzerland
| | - Andrea Schmidt
- Département de Biochimie, Université de Lausanne, Epalinges, Switzerland
| | - Sarita Namjoshi
- Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, Texas, United States of America
| | - Andreas Mayer
- Département de Biochimie, Université de Lausanne, Epalinges, Switzerland
| | - Christopher Peters
- Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, Texas, United States of America
- * E-mail:
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Choi UB, McCann JJ, Weninger KR, Bowen ME. Beyond the random coil: stochastic conformational switching in intrinsically disordered proteins. Structure 2011; 19:566-76. [PMID: 21481779 DOI: 10.1016/j.str.2011.01.011] [Citation(s) in RCA: 102] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2010] [Revised: 01/21/2011] [Accepted: 01/26/2011] [Indexed: 01/24/2023]
Abstract
Intrinsically disordered proteins (IDPs) participate in critical cellular functions that exploit the flexibility and rapid conformational fluctuations of their native state. Limited information about the native state of IDPs can be gained by the averaging over many heterogeneous molecules that is unavoidable in ensemble approaches. We used single molecule fluorescence to characterize native state conformational dynamics in five synaptic proteins confirmed to be disordered by other techniques. For three of the proteins, SNAP-25, synaptobrevin and complexin, their conformational dynamics could be described with a simple semiflexible polymer model. Surprisingly, two proteins, neuroligin and the NMDAR-2B glutamate receptor, were observed to stochastically switch among distinct conformational states despite the fact that they appeared intrinsically disordered by other measures. The hop-like intramolecular diffusion found in these proteins is suggested to define a class of functionality previously unrecognized for IDPs.
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Affiliation(s)
- Ucheor B Choi
- Department of Physics, North Carolina State University, Raleigh, NC 27695, USA
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Corbett MA, Schwake M, Bahlo M, Dibbens LM, Lin M, Gandolfo LC, Vears DF, O'Sullivan JD, Robertson T, Bayly MA, Gardner AE, Vlaar AM, Korenke GC, Bloem BR, de Coo IF, Verhagen JMA, Lehesjoki AE, Gecz J, Berkovic SF. A mutation in the Golgi Qb-SNARE gene GOSR2 causes progressive myoclonus epilepsy with early ataxia. Am J Hum Genet 2011; 88:657-63. [PMID: 21549339 DOI: 10.1016/j.ajhg.2011.04.011] [Citation(s) in RCA: 84] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2011] [Revised: 04/13/2011] [Accepted: 04/14/2011] [Indexed: 11/30/2022] Open
Abstract
The progressive myoclonus epilepsies (PMEs) are a group of predominantly recessive disorders that present with action myoclonus, tonic-clonic seizures, and progressive neurological decline. Many PMEs have similar clinical presentations yet are genetically heterogeneous, making accurate diagnosis difficult. A locus for PME was mapped in a consanguineous family with a single affected individual to chromosome 17q21. An identical-by-descent, homozygous mutation in GOSR2 (c.430G>T, p.Gly144Trp), a Golgi vesicle transport gene, was identified in this patient and in four apparently unrelated individuals. A comparison of the phenotypes in these patients defined a clinically distinct PME syndrome characterized by early-onset ataxia, action myoclonus by age 6, scoliosis, and mildly elevated serum creatine kinase. This p.Gly144Trp mutation is equivalent to a loss of function and results in failure of GOSR2 protein to localize to the cis-Golgi.
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Affiliation(s)
- Mark A Corbett
- Genetics and Molecular Pathology, SA Pathology, Adelaide, Australia
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Diefenbacher M, Thorsteinsdottir H, Spang A. The Dsl1 tethering complex actively participates in soluble NSF (N-ethylmaleimide-sensitive factor) attachment protein receptor (SNARE) complex assembly at the endoplasmic reticulum in Saccharomyces cerevisiae. J Biol Chem 2011; 286:25027-38. [PMID: 21482823 DOI: 10.1074/jbc.m110.215657] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
Intracellular transport is largely dependent on vesicles that bud off from one compartment and fuse with the target compartment. The first contact of an incoming vesicle with the target membrane is mediated by tethering factors. The tethering factor responsible for recruiting Golgi-derived vesicles to the ER is the Dsl1 tethering complex, which is comprised of the essential proteins Dsl1p, Dsl3p, and Tip20p. We investigated the role of the Tip20p subunit at the ER by analyzing two mutants, tip20-5 and tip20-8. Both mutants contained multiple mutations that were scattered throughout the TIP20 sequence. Individual mutations could not reproduce the temperature-sensitive phenotype of tip20-5 and tip20-8, indicating that the overall structure of Tip20p might be altered in the mutants. Using molecular dynamics simulations comparing Tip20p and Tip20-8p revealed that some regions, particularly the N-terminal domain and parts of the stalk region, were more flexible in the mutant protein, consistent with its increased susceptibility to proteolysis. Both Tip20-5p and Tip20-8p mutants prevented proper ER trans-SNARE complex assembly in vitro. Moreover, Tip20p mutant proteins disturbed the interaction between Dsl1p and the coatomer coat complex, indicating that the Dsl1p-coatomer interaction could be stabilized or regulated by Tip20p. We provide evidence for a direct role of the Dsl1 complex, in particular Tip20p, in the formation and stabilization of ER SNARE complexes.
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Affiliation(s)
- Melanie Diefenbacher
- Biozentrum, Growth & Development, University of Basel, Klingelbergstrasse 70, CH-4056 Basel, Switzerland
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Pochinyuk OM, Zaika OL, Sadovyi OV, Yavors’kaya OM, Lukyanetz EA. Involvement of Synaptic Protein Munc18 in the Process of Release of Catecholamines by Chromaffin Cells of the Rat Adrenal Gland. NEUROPHYSIOLOGY+ 2011; 42:244-250. [DOI: 10.1007/s11062-011-9156-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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Abstract
The SNARE proteins, syntaxin, SNAP-25, and synaptobrevin have long been known to provide the driving force for vesicle fusion in the process of regulated exocytosis. Of particular interest is the initial interaction between SNAP-25 and syntaxin to form the t-SNARE heterodimer, an acceptor for subsequent synaptobrevin engagement. In vitro studies have revealed at least two different dynamic conformations of t-SNARE heterodimer defined by the degree of association of the C-terminal SNARE motif of SNAP-25 with syntaxin. At the plasma membrane, these proteins are organized into dense clusters of 50-60 nm in diameter. More recently, the t-SNARE interaction within these clusters was investigated in live cells at the molecular level, estimating each cluster to contain 35-70 t-SNARE molecules. This work reported the presence of both partially and fully zippered t-SNARE complex at the plasma membrane in agreement with the earlier in vitro findings. It also revealed a spatial segregation into distinct clusters containing predominantly one conformation apparently patterned by the surrounding lipid environment. The reason for this dynamic t-SNARE complex in exocytosis is uncertain; however, it does take us one step closer to understand the complex sequence of events leading to vesicle fusion, emphasizing the role of both membrane proteins and lipids.
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Affiliation(s)
- Alison R Dun
- Centre for Integrative Physiology, University of Edinburgh Medical School, Hugh Robson Building, George Square, Edinburgh EH8 9XD, UK
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Boal F, Laguerre M, Milochau A, Lang J, Scotti PA. A charged prominence in the linker domain of the cysteine‐string protein Cspα mediates its regulated interaction with the calcium sensor synaptotagmin 9 during exocytosis. FASEB J 2010; 25:132-43. [DOI: 10.1096/fj.09-152033] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- Frédéric Boal
- Department of BiochemistrySchool of Medical SciencesUniversity of BristolBristolUK
| | - Michel Laguerre
- Unité Mixte de Recherche Centre National de la Recherche Scientifique 5248Universitedé Bordeaux IPessacFrance
| | - Alexandra Milochau
- Unité Mixte de Recherche Centre National de la Recherche Scientifique 5248Universitedé Bordeaux IPessacFrance
| | - Jochen Lang
- Unité Mixte de Recherche Centre National de la Recherche Scientifique 5248Universitedé Bordeaux IPessacFrance
| | - Pier A. Scotti
- Unité Mixte de Recherche Centre National de la Recherche Scientifique 5248Universitedé Bordeaux IPessacFrance
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Andreyeva A, Leshchyns'ka I, Knepper M, Betzel C, Redecke L, Sytnyk V, Schachner M. CHL1 is a selective organizer of the presynaptic machinery chaperoning the SNARE complex. PLoS One 2010; 5:e12018. [PMID: 20711454 PMCID: PMC2920317 DOI: 10.1371/journal.pone.0012018] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2010] [Accepted: 07/15/2010] [Indexed: 11/19/2022] Open
Abstract
Proteins constituting the presynaptic machinery of vesicle release undergo substantial conformational changes during the process of exocytosis. While changes in the conformation make proteins vulnerable to aggregation and degradation, little is known about synaptic chaperones which counteract these processes. We show that the cell adhesion molecule CHL1 directly interacts with and regulates the activity of the synaptic chaperones Hsc70, CSP and αSGT. CHL1, Hsc70, CSP and αSGT form predominantly CHL1/Hsc70/αSGT and CHL1/CSP complexes in synapses. Among the various complexes formed by CHL1, Hsc70, CSP and αSGT, SNAP25 and VAMP2 induce chaperone activity only in CHL1/Hsc70/αSGT and CHL1/CSP complexes, respectively, indicating a remarkable selectivity of a presynaptic chaperone activity for proteins of the exocytotic machinery. In mice with genetic ablation of CHL1, chaperone activity in synapses is reduced and the machinery for synaptic vesicle exocytosis and, in particular, the SNARE complex is unable to sustain prolonged synaptic activity. Thus, we reveal a novel role for a cell adhesion molecule in selective activation of the presynaptic chaperone machinery.
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Affiliation(s)
- Aksana Andreyeva
- Zentrum für Molekulare Neurobiologie, University of Hamburg, Hamburg, Germany
- Institute of Neuro- und Sensory Physiology, Heinrich Heine University, Düsseldorf, Germany
| | - Iryna Leshchyns'ka
- Zentrum für Molekulare Neurobiologie, University of Hamburg, Hamburg, Germany
- School of Biotechnology and Biomolecular Sciences, University of New South Wales, Sydney, New South Wales, Australia
| | - Michael Knepper
- Zentrum für Molekulare Neurobiologie, University of Hamburg, Hamburg, Germany
| | - Christian Betzel
- Institute of Biochemistry and Molecular Biology, University of Hamburg, Hamburg, Germany
| | - Lars Redecke
- Institute of Biochemistry and Molecular Biology, University of Hamburg, Hamburg, Germany
| | - Vladimir Sytnyk
- Zentrum für Molekulare Neurobiologie, University of Hamburg, Hamburg, Germany
- School of Biotechnology and Biomolecular Sciences, University of New South Wales, Sydney, New South Wales, Australia
- * E-mail: (MS); (VS)
| | - Melitta Schachner
- Zentrum für Molekulare Neurobiologie, University of Hamburg, Hamburg, Germany
- Center for Neuroscience, Shantou University Medical College, Shantou, China
- Keck Center for Collaborative Neuroscience, Rutgers University, Piscataway, New Jersey, United States of America
- * E-mail: (MS); (VS)
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35
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Feinshreiber L, Singer-Lahat D, Friedrich R, Matti U, Sheinin A, Yizhar O, Nachman R, Chikvashvili D, Rettig J, Ashery U, Lotan I. Non-conducting function of the Kv2.1 channel enables it to recruit vesicles for release in neuroendocrine and nerve cells. J Cell Sci 2010; 123:1940-7. [DOI: 10.1242/jcs.063719] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
Regulation of exocytosis by voltage-gated K+ channels has classically been viewed as inhibition mediated by K+ fluxes. We recently identified a new role for Kv2.1 in facilitating vesicle release from neuroendocrine cells, which is independent of K+ flux. Here, we show that Kv2.1-induced facilitation of release is not restricted to neuroendocrine cells, but also occurs in the somatic-vesicle release from dorsal-root-ganglion neurons and is mediated by direct association of Kv2.1 with syntaxin. We further show in adrenal chromaffin cells that facilitation induced by both wild-type and non-conducting mutant Kv2.1 channels in response to long stimulation persists during successive stimulation, and can be attributed to an increased number of exocytotic events and not to changes in single-spike kinetics. Moreover, rigorous analysis of the pools of released vesicles reveals that Kv2.1 enhances the rate of vesicle recruitment during stimulation with high Ca2+, without affecting the size of the readily releasable vesicle pool. These findings place a voltage-gated K+ channel among the syntaxin-binding proteins that directly regulate pre-fusion steps in exocytosis.
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Affiliation(s)
- Lori Feinshreiber
- Department of Physiology and Pharmacology, Sackler Faculty of Medicine, Tel Aviv University, 69978 Tel Aviv, Israel
| | - Dafna Singer-Lahat
- Department of Physiology and Pharmacology, Sackler Faculty of Medicine, Tel Aviv University, 69978 Tel Aviv, Israel
| | - Reut Friedrich
- Department of Neurobiochemistry, Life Science Institute, Tel Aviv University, 69978 Tel Aviv, Israel
| | - Ulf Matti
- Physiologisches Institut, Universität des Saarlandes, 66421 Homburg/Saar, Germany
| | - Anton Sheinin
- Department of Neurobiochemistry, Life Science Institute, Tel Aviv University, 69978 Tel Aviv, Israel
| | - Ofer Yizhar
- Department of Neurobiochemistry, Life Science Institute, Tel Aviv University, 69978 Tel Aviv, Israel
| | - Rachel Nachman
- Department of Physiology and Pharmacology, Sackler Faculty of Medicine, Tel Aviv University, 69978 Tel Aviv, Israel
| | - Dodo Chikvashvili
- Department of Physiology and Pharmacology, Sackler Faculty of Medicine, Tel Aviv University, 69978 Tel Aviv, Israel
| | - Jens Rettig
- Physiologisches Institut, Universität des Saarlandes, 66421 Homburg/Saar, Germany
| | - Uri Ashery
- Department of Neurobiochemistry, Life Science Institute, Tel Aviv University, 69978 Tel Aviv, Israel
| | - Ilana Lotan
- Department of Physiology and Pharmacology, Sackler Faculty of Medicine, Tel Aviv University, 69978 Tel Aviv, Israel
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Fletcher PL, Fletcher MD, Weninger K, Anderson TE, Martin BM. Vesicle-associated membrane protein (VAMP) cleavage by a new metalloprotease from the Brazilian scorpion Tityus serrulatus. J Biol Chem 2009; 285:7405-16. [PMID: 20026600 DOI: 10.1074/jbc.m109.028365] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
We present evidence that venom from the Brazilian scorpion Tityus serrulatus and a purified fraction selectively cleave essential SNARE proteins within exocrine pancreatic tissue. Western blotting for vesicle-associated membrane protein type v-SNARE proteins (or synaptobrevins) reveals characteristic alterations to venom-treated excised pancreatic lobules in vitro. Immunocytochemistry by electron microscopy confirms both the SNARE identity as VAMP2 and the proteolysis of VAMP2 as a marked decrease in secondary antibody-conjugated colloidal gold particles that are predominantly associated with mature zymogen granules. Studies with recombinant SNARE proteins were used to determine the specific cleavage site in VAMP2 and the susceptibility of VAMP8 (endobrevin). The VAMP2 cleavage site is between the transmembrane anchor and the SNARE motif that assembles into the ternary SNARE complex. Inclusion of divalent chelating agents (EDTA) with fraction nu, an otherwise active purified component from venom, eliminates SNARE proteolysis, suggesting the active protein is a metalloprotease. The unique cleavages of VAMP2 and VAMP8 may be linked to pancreatitis that develops following scorpion envenomation as both of these v-SNARE proteins are associated with zymogen granule membranes in pancreatic acinar cells. We have isolated antarease, a metalloprotease from fraction nu that cleaves VAMP2, and report its amino acid sequence.
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Affiliation(s)
- Paul L Fletcher
- Department of Microbiology and Immunology, Brody School of Medicine, East Carolina University, Greenville, North Carolina 27834, USA
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Williams D, Vicôgne J, Zaitseva I, McLaughlin S, Pessin JE. Evidence that electrostatic interactions between vesicle-associated membrane protein 2 and acidic phospholipids may modulate the fusion of transport vesicles with the plasma membrane. Mol Biol Cell 2009; 20:4910-9. [PMID: 19812247 DOI: 10.1091/mbc.e09-04-0284] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
The juxtamembrane domain of vesicle-associated membrane protein (VAMP) 2 (also known as synaptobrevin2) contains a conserved cluster of basic/hydrophobic residues that may play an important role in membrane fusion. Our measurements on peptides corresponding to this domain determine the electrostatic and hydrophobic energies by which this domain of VAMP2 could bind to the adjacent lipid bilayer in an insulin granule or other transport vesicle. Mutation of residues within the juxtamembrane domain that reduce the VAMP2 net positive charge, and thus its interaction with membranes, inhibits secretion of insulin granules in beta cells. Increasing salt concentration in permeabilized cells, which reduces electrostatic interactions, also results in an inhibition of insulin secretion. Similarly, amphipathic weak bases (e.g., sphingosine) that reverse the negative electrostatic surface potential of a bilayer reverse membrane binding of the positively charged juxtamembrane domain of a reconstituted VAMP2 protein and inhibit membrane fusion. We propose a model in which the positively charged VAMP and syntaxin juxtamembrane regions facilitate fusion by bridging the negatively charged vesicle and plasma membrane leaflets.
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Affiliation(s)
- Dumaine Williams
- Department of Medicine and Molecular Pharmacology, Albert Einstein College of Medicine, Bronx, NY 10461, USA
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Furgason ML, MacDonald C, Shanks SG, Ryder SP, Bryant NJ, Munson M. The N-terminal peptide of the syntaxin Tlg2p modulates binding of its closed conformation to Vps45p. Proc Natl Acad Sci U S A 2009; 106:14303-8. [PMID: 19667197 DOI: 10.1073/pnas.0902976106] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The Sec1/Munc18 (SM) protein family regulates intracellular trafficking through interactions with individual SNARE proteins and assembled SNARE complexes. Revealing a common mechanism of this regulation has been challenging, largely because of the multiple modes of interaction observed between SM proteins and their cognate syntaxin-type SNAREs. These modes include binding of the SM to a closed conformation of syntaxin, binding to the N-terminal peptide of syntaxin, binding to assembled SNARE complexes, and/or binding to nonsyntaxin SNAREs. The SM protein Vps45p, which regulates endosomal trafficking in yeast, binds the conserved N-terminal peptide of the syntaxin Tlg2p. We used size exclusion chromatography and a quantitative fluorescent gel mobility shift assay to reveal an additional binding site that does not require the Tlg2p N-peptide. Characterization of Tlg2p mutants and truncations indicate that this binding site corresponds to a closed conformation of Tlg2p. Furthermore, the Tlg2p N-peptide competes with the closed conformation for binding, suggesting a fundamental regulatory mechanism for SM-syntaxin interactions in SNARE assembly and membrane fusion.
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40
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Stein A, Weber G, Wahl MC, Jahn R. Helical extension of the neuronal SNARE complex into the membrane. Nature 2009; 460:525-8. [PMID: 19571812 DOI: 10.1038/nature08156] [Citation(s) in RCA: 330] [Impact Index Per Article: 22.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2009] [Accepted: 05/15/2009] [Indexed: 01/07/2023]
Abstract
Neurotransmission relies on synaptic vesicles fusing with the membrane of nerve cells to release their neurotransmitter content into the synaptic cleft, a process requiring the assembly of several members of the SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) family. SNAREs represent an evolutionarily conserved protein family that mediates membrane fusion in the secretory and endocytic pathways of eukaryotic cells. On membrane contact, these proteins assemble in trans between the membranes as a bundle of four alpha-helices, with the energy released during assembly being thought to drive fusion. However, it is unclear how the energy is transferred to the membranes and whether assembly is conformationally linked to fusion. Here, we report the X-ray structure of the neuronal SNARE complex, consisting of rat syntaxin 1A, SNAP-25 and synaptobrevin 2, with the carboxy-terminal linkers and transmembrane regions at 3.4 A resolution. The structure shows that assembly proceeds beyond the already known core SNARE complex, resulting in a continuous helical bundle that is further stabilized by side-chain interactions in the linker region. Our results suggest that the final phase of SNARE assembly is directly coupled to membrane merger.
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Abstract
SNAREs are essential components of the machinery for Ca(2+)-triggered fusion of synaptic vesicles with the plasma membrane, resulting in neurotransmitter release into the synaptic cleft. Although much is known about their biophysical and structural properties and their interactions with accessory proteins such as the Ca(2+) sensor synaptotagmin, their precise role in membrane fusion remains an enigma. Ensemble studies of liposomes with reconstituted SNAREs have demonstrated that SNAREs and accessory proteins can trigger lipid mixing/fusion, but the inability to study individual fusion events has precluded molecular insights into the fusion process. Thus, this field is ripe for studies with single-molecule methodology. In this review, we discuss applications of single-molecule approaches to observe reconstituted SNAREs, their complexes, associated proteins, and their effect on biological membranes. Some of the findings are provocative, such as the possibility of parallel and antiparallel SNARE complexes or of vesicle docking with only syntaxin and synaptobrevin, but have been confirmed by other experiments.
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Affiliation(s)
- Axel T Brunger
- The Howard Hughes Medical Institute and Departments of Molecular and Cellular Physiology, Neurology and Neurological Sciences, Structural Biology, and Photon Science, Stanford University, CA 94305, USA.
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Abstract
The fusion of synaptic vesicles with the pre-synaptic plasma membrane mediates the secretion of neurotransmitters at nerve terminals. This pathway is regulated by an array of protein-protein interactions. Of central importance are the soluble NSF (N-ethylmaleimide-sensitive factor) attachment protein receptor (SNARE) proteins syntaxin 1 and SNAP25, which are associated with the pre-synaptic plasma membrane and vesicle-associated membrane protein (VAMP2), a synaptic vesicle SNARE. Syntaxin 1, SNAP25 and VAMP2 interact to form a tight complex bridging the vesicle and plasma membranes, which has been suggested to represent the minimal membrane fusion machinery. Synaptic vesicle fusion is stimulated by a rise in intraterminal Ca2+ levels, and a major Ca2+ sensor for vesicle fusion is synaptotagmin I. Synaptotagmin is likely to couple Ca2+ entry to vesicle fusion via Ca2+-dependent and independent interactions with membrane phospholipids and the SNARE proteins. Intriguingly, syntaxin 1, SNAP25, VAMP2 and synaptotagmin I have all been reported to be modified by palmitoylation in neurons. In this review, we discuss the mechanisms and dynamics of palmitoylation of these proteins and speculate on how palmitoylation might contribute to the regulation of synaptic vesicle fusion.
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Affiliation(s)
- Gerald R Prescott
- Centre for Integrative Physiology, School of Biomedical Sciences, University of Edinburgh, Edinburgh, United Kingdom
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43
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Abstract
The three key players in the exocytotic release of neurotransmitters from synaptic vesicles are the SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) proteins synaptobrevin 2, syntaxin 1a, and SNAP-25. Their assembly into a tight four-helix bundle complex is thought to pull the two membranes into close proximity. It is debated, however, whether the energy generated suffices for membrane fusion. Here, we have determined the thermodynamic properties of the individual SNARE assembly steps by isothermal titration calorimetry. We found extremely large favorable enthalpy changes counterbalanced by positive entropy changes, reflecting the major conformational changes upon assembly. To circumvent the fact that ternary complex formation is essentially irreversible, we used a stabilized syntaxin-SNAP-25 heterodimer to study synaptobrevin binding. This strategy revealed that the N-terminal synaptobrevin coil binds reversibly with nanomolar affinity. This suggests that individual, membrane-bridging SNARE complexes can provide much less pulling force than previously claimed.
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Affiliation(s)
- Katrin Wiederhold
- Research Group Structural Biochemistry, Department of Neurobiology, Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, Göttingen, Germany
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44
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Weninger K, Bowen ME, Choi UB, Chu S, Brunger AT. Accessory proteins stabilize the acceptor complex for synaptobrevin, the 1:1 syntaxin/SNAP-25 complex. Structure 2008; 16:308-20. [PMID: 18275821 DOI: 10.1016/j.str.2007.12.010] [Citation(s) in RCA: 136] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2007] [Revised: 12/13/2007] [Accepted: 12/17/2007] [Indexed: 11/19/2022]
Abstract
Syntaxin/SNAP-25 interactions precede assembly of the ternary SNARE complex that is essential for neurotransmitter release. This binary complex has been difficult to characterize by bulk methods because of the prevalence of a 2:1 dead-end species. Here, using single-molecule fluorescence, we find the structure of the 1:1 syntaxin/SNAP-25 binary complex is variable, with states changing on the second timescale. One state corresponds to a parallel three-helix bundle, whereas other states show one of the SNAP-25 SNARE domains dissociated. Adding synaptobrevin suppresses the dissociated helix states. Remarkably, upon addition of complexin, Munc13, Munc18, or synaptotagmin, a similar effect is observed. Thus, the 1:1 binary complex is a dynamic acceptor for synaptobrevin binding, and accessory proteins stabilize this acceptor. In the cellular environment the binary complex is actively maintained in a configuration where it can rapidly interact with synaptobrevin, so formation is not likely a limiting step for neurotransmitter release.
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Affiliation(s)
- Keith Weninger
- Department of Physics, North Carolina State University, Raleigh, NC 27695-8202, USA
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Abstract
SNARE (soluble N-ethylmaleimide-sensitive fusion protein-attachment protein receptor) proteins involved in membrane fusion usually contain a conserved alpha-helix (SNARE motif) that is flanked by a C-terminal transmembrane domain. They can be classified into Q-SNARE and R-SNARE based on the structural property of their motifs. Assembly of four SNARE motifs (Qa, b, c and R) is supposed to trigger membrane fusion. We have previously shown that ER (endoplasmic reticulum)-localized syntaxin 18 (Qa) forms a complex with BNIP1 (Qb), p31/Use1 (Qc), Sec22b (R) and several peripheral membrane proteins. In the present study, we examined the interaction of syntaxin 18 with other SNAREs using pulldown assays and CD spectroscopy. We found that the association of syntaxin 18 with Sec22b induces an increase in alpha-helicity of their SNARE motifs, which results in the formation of high-affinity binding sites for BNIP1 and p31. This R-SNARE-dependent Q-SNARE assembly is quite different from the assembly mechanisms of SNAREs localized in organelles other than the ER. The implication of the mechanism of ER SNARE assembly is discussed in the context of the physiological roles of the syntaxin 18 complex.
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Abstract
Membrane trafficking in eukaryotic cells must be strictly regulated both temporally and spatially. The assembly at the plasma membrane of the ternary SNARE complex, formed between syntaxin1a, SNAP-25 and VAMP, is essential for efficient exocytotic membrane fusion. These exocytotic SNAREs are known to be highly promiscuous in their interactions with other non-cognate SNAREs. It is therefore an important cellular requirement to traffic exocytotic SNARE proteins through the endoplasmic reticulum and Golgi complex while avoiding ectopic interactions between SNARE proteins. Here, we show that syntaxin1a traffics in an inactive form to the plasma membrane, requiring a closed-form interaction, but not N-terminal binding, with munc18-1. If syntaxin is permitted to interact with SNAP-25, both proteins fail to traffic to the plasma membrane, becoming trapped in intracellular compartments. The munc18-1-syntaxin interactions must form before syntaxin encounters SNAP-25 in the Golgi complex, preventing the formation of intracellular exocytotic SNARE complexes there. Upon delivery to the plasma membrane, most SNARE clusters in resting cells do not produce detectable FRET between t-SNARE proteins. These observations highlight the crucial role that munc18-1 plays in trafficking syntaxin through the secretory pathway.
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Affiliation(s)
- Claire N Medine
- Centre for Integrative Physiology, University of Edinburgh, George Square, Edinburgh EH8 9XD, UK
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Abstract
In this report, we present features of the neuronal SNARE complex determined by atomistic molecular dynamics simulations. The results are robust for three models, varying force fields (AMBER and GROMOS) and solvent environment (explicit and implicit). An excellent agreement with experimental findings is observed. The SNARE core complex behaves like a stiff rod, with limited conformational dynamics. An accurate picture of the interactions within the complex emerges with a characteristic pattern of atomic contacts, hydrogen bonds, and salt bridges reinforcing the underlying layer structure. This supports the metaphor of a molecular Velcro strip that has been used by others to describe the neuronal fusion complex. No evidence for directionality in the formation of these interactions was found. Electrostatics largely dominates all interactions, with an acidic surface patch structuring the hydration layers surrounding the complex. The interactions within the four-helix bundle are asymmetric, with the synaptobrevin R-SNARE notably exhibiting an increased rigidity with respect to the three Q-SNARE helices. The interaction patterns we observe provide a new tool for interpreting the impact of mutations on the complex.
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Affiliation(s)
- Andrew G Engel
- Department of Neurology, Mayo Clinic, Rochester, MN, USA.
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Affiliation(s)
- Axel T Brunger
- * To whom correspondence should be addressed. E-mail: (ATB), (MM)
| | | | | | | | | | - Mauricio Montal
- * To whom correspondence should be addressed. E-mail: (ATB), (MM)
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Tyrrell M, Campanoni P, Sutter JU, Pratelli R, Paneque M, Sokolovski S, Blatt MR. Selective targeting of plasma membrane and tonoplast traffic by inhibitory (dominant-negative) SNARE fragments. Plant J 2007; 51:1099-115. [PMID: 17662029 DOI: 10.1111/j.1365-313x.2007.03206.x] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
Vesicle traffic underpins cell homeostasis, growth and development in plants, and is facilitated by a superfamily of proteins known as SNAREs [soluble NSF (N-ethylmaleimide-sensitive factor) attachment protein receptors] that interact to draw vesicle and target membrane surfaces together for fusion. Structural homologies, biochemical and genetic analyses have yielded information about the localization and possible roles of these proteins. However, remarkably little evidence is yet available that speaks directly to the functional specificities of these proteins in selected trafficking pathways in vivo. Previously, we found that expressing a cytosolic (so-called Sp2) fragment of one plasma membrane SNARE from tobacco and Arabidopsis had severe effects on growth, tissue development and secretory traffic to the plasma membrane. We have explored this dominant-negative approach further to examine the specificity and overlaps in Sp2 activity by generating a toolbox of truncated SNARE constructs and antibodies for transient expression and analysis. Using a quantitative ratiometric approach with secreted green fluorescent protein (secGFP), we report here that traffic to the plasma membrane is suppressed selectively by Sp2 fragments of plasma membrane SNAREs AtSYP121 and AtSYP122, but not of the closely related SNARE AtSYP111 nor of the SNARE AtSYP21 that resides at the pre-vacuolar compartment (PVC). By contrast, traffic of the YFP-tagged aquaporin fusion protein TIP1;1-YFP to the tonoplast was blocked (leading to its accumulation in the PVC) when co-expressed with the Sp2 fragment of AtSYP21, but not when co-expressed with that of AtSYP121. Export of secGFP was also sensitive to the Sp2 fragment of the novel, plant-specific SNARE AtSYP71 that was recently found to be present in detergent-resistant, plasma membrane fractions. Co-incubation analyses of the plasma membrane SNAREs with the regulatory subdomain included within the Sp2 fragments showed activity in destabilizing protein complexes, but only with the complementary SNAREs. We conclude that the Sp2 fragment action accurately reflects the known specificity and targeting of these SNAREs, implies functional overlaps that are of potential physiological interest, and underscores the use of a dominant-negative strategy in functional studies of a major subfamily of SNAREs in plants.
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Affiliation(s)
- Matthew Tyrrell
- Laboratory of Plant Physiology and Biophysics, IBLS, Plant Sciences, Bower Building, University of Glasgow, Glasgow G12 8QQ, UK
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