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Rizo J, Sari L, Jaczynska K, Rosenmund C, Lin MM. Molecular mechanism underlying SNARE-mediated membrane fusion enlightened by all-atom molecular dynamics simulations. Proc Natl Acad Sci U S A 2024; 121:e2321447121. [PMID: 38593076 PMCID: PMC11032479 DOI: 10.1073/pnas.2321447121] [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] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2023] [Accepted: 03/18/2024] [Indexed: 04/11/2024] Open
Abstract
The SNAP receptor (SNARE) proteins syntaxin-1, SNAP-25, and synaptobrevin mediate neurotransmitter release by forming tight SNARE complexes that fuse synaptic vesicles with the plasma membranes in microseconds. Membrane fusion is generally explained by the action of proteins on macroscopic membrane properties such as curvature, elastic modulus, and tension, and a widespread model envisions that the SNARE motifs, juxtamembrane linkers, and C-terminal transmembrane regions of synaptobrevin and syntaxin-1 form continuous helices that act mechanically as semirigid rods, squeezing the membranes together as they assemble ("zipper") from the N to the C termini. However, the mechanism underlying fast SNARE-induced membrane fusion remains unknown. We have used all-atom molecular dynamics simulations to investigate this mechanism. Our results need to be interpreted with caution because of the limited number and length of the simulations, but they suggest a model of membrane fusion that has a natural physicochemical basis, emphasizes local molecular events over general membrane properties, and explains extensive experimental data. In this model, the central event that initiates fast (microsecond scale) membrane fusion occurs when the SNARE helices zipper into the juxtamembrane linkers which, together with the adjacent transmembrane regions, promote encounters of acyl chains from both bilayers at the polar interface. The resulting hydrophobic nucleus rapidly expands into stalk-like structures that gradually progress to form a fusion pore, aided by the SNARE transmembrane regions and without clearly discernible intermediates. The propensity of polyunsaturated lipids to participate in encounters that initiate fusion suggests that these lipids may be important for the high speed of neurotransmitter release.
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Affiliation(s)
- Josep Rizo
- Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, TX75390
- Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, TX75390
- Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, TX75390
| | - Levent Sari
- Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, TX75390
- Green Center for Systems Biology, University of Texas Southwestern Medical Center, Dallas, TX75390
| | - Klaudia Jaczynska
- Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, TX75390
- Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, TX75390
- Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, TX75390
| | - Christian Rosenmund
- Institute of Neurophysiology, Charité—Universitätsmedizin Berlin, Berlin10117, Germany
- NeuroCure Cluster of Excellence, Berlin10117, Germany
| | - Milo M. Lin
- Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, TX75390
- Green Center for Systems Biology, University of Texas Southwestern Medical Center, Dallas, TX75390
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2
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Mosadegh S, Abtahi H, Amani J, Karizi SZ, Salmanian AH. Protective immunization against Enterohemorrhagic Escherichia coli and Shigella dysenteriae Type 1 by chitosan nanoparticle loaded with recombinant chimeric antigens comprising EIT and STX1B-IpaD. Microb Pathog 2023; 184:106344. [PMID: 37704060 DOI: 10.1016/j.micpath.2023.106344] [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] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2023] [Revised: 09/09/2023] [Accepted: 09/10/2023] [Indexed: 09/15/2023]
Abstract
Increasing evidence demonstrated that Enterohemorrhagic Escherichia coli (EHEC) and Shigella dysenteriae type 1 (S. dysenteriae1) are considered pathogens, that are connected with diarrhea and are still the greatest cause of death in children under the age of five years, worldwide. EHEC and S. dysenteriae 1 infections can be prevented and managed using a vaccination strategy against pathogen attachment stages. In this study, the chitosan nanostructures were loaded with recombinant EIT and STX1B-IpaD polypeptides. The immunogenic properties of this nano-vaccine candidate were investigated. The EIT and STX1B-IpaD recombinant proteins were heterologous expressed, purified, and confirmed by western blotting. The chitosan nanoparticles, were used to encapsulate the purified proteins. The immunogenicity of recombinant nano vaccine candidate, was examined in three groups of BalB/c mice by injection, oral delivery, and combination of oral-injection. ELISA and antibody titer, evaluated the humoral immune response. Finally, all three mice groups were challenged by two pathogens to test the ability of the nano-vaccine candidate to protect against bacterial infection. The Sereny test in guinea pigs was used to confirm the neutralizing effect of immune sera in controlling S. dysenteriae 1, infections. SDS-PAGE and western blotting, confirmed the presence and specificity of 63 and 27 kDa recombinant EIT and STX1B-IpaD, respectively. The results show that the nanoparticles containing recombinant proteins could stimulate the systemic and mucosal immune systems by producing IgG and IgA, respectively. The challenge test showed that, the candidate nano-vaccine could protect the animal model from bacterial infection. The combination of multiple recombinant proteins, carrying several epitopes and natural nanoparticles could evocate remarkable humoral and mucosal responses and improve the protection properties of synthetic antigens. Furthermore, compared with other available antigen delivery methods, using oral delivery as immune priming and injection as a booster method, could act as combinatorial methods to achieve a higher level of immunity. This approach could present an appropriate vaccine candidate against both EHEC and S. dysenteriae 1.
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Affiliation(s)
- Shadi Mosadegh
- Department of Biology, Science and Research Branch, Islamic Azad University, Tehran, Iran
| | - Hamid Abtahi
- Molecular and Medicine Research Center, Arak University of Medical Sciences, Arak, Iran
| | - Jafar Amani
- Applied Microbiology Research Center, Systems Biology and Poisonings Institute, Baqiyatallah University of Medical Sciences, Tehran, Iran
| | - Shohreh Zare Karizi
- Department of Biology, Varamin Pishva Branch, Islamic Azad University, Pishva, Varamin, Iran
| | - Ali Hatef Salmanian
- Department of Agricultural Biotechnology, National Institute of Genetic Engineering and Biotechnology (NIGEB), Tehran, Iran.
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3
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Grothe T, Walla PJ. Fluorescence Lifetime and Cross-correlation Spectroscopy for Observing Membrane Fusion of Liposome Models Containing Synaptic Proteins. Methods Mol Biol 2022; 2417:167-180. [PMID: 35099799 DOI: 10.1007/978-1-0716-1916-2_13] [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] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
Watching events of membrane fusion in real time and distinguishing between intermediate steps of these events is useful for mechanistic insights but at the same time a challenging task. In this chapter, we describe how to use fluorescence cross-correlation spectroscopy and Förster-resonance energy transfer to resolve the tethering and fusion of membranes by SNARE proteins (syntaxin-1, SNAP-25, and synaptobrevin-2) as an example. The given protocols can easily be adapted to other membrane proteins to investigate their ability to tether or even fuse vesicular membrane.
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Affiliation(s)
- Tobias Grothe
- Laboratory of Neurobiology, Max-Planck-Institute for Biophysical Chemistry, Göttingen, Germany
- Department of Biophysical Chemistry, Institute for Physical and Theoretical Chemistry, TU Braunschweig, Braunschweig, Germany
| | - Peter J Walla
- Laboratory of Neurobiology, Max-Planck-Institute for Biophysical Chemistry, Göttingen, Germany.
- Department of Biophysical Chemistry, Institute for Physical and Theoretical Chemistry, TU Braunschweig, Braunschweig, Germany.
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4
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Otrin L, Witkowska A, Marušič N, Zhao Z, Lira RB, Kyrilis FL, Hamdi F, Ivanov I, Lipowsky R, Kastritis PL, Dimova R, Sundmacher K, Jahn R, Vidaković-Koch T. En route to dynamic life processes by SNARE-mediated fusion of polymer and hybrid membranes. Nat Commun 2021; 12:4972. [PMID: 34404795 PMCID: PMC8371082 DOI: 10.1038/s41467-021-25294-z] [Citation(s) in RCA: 18] [Impact Index Per Article: 6.0] [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: 02/19/2021] [Accepted: 07/30/2021] [Indexed: 12/11/2022] Open
Abstract
A variety of artificial cells springs from the functionalization of liposomes with proteins. However, these models suffer from low durability without repair and replenishment mechanisms, which can be partly addressed by replacing the lipids with polymers. Yet natural membranes are also dynamically remodeled in multiple cellular processes. Here, we show that synthetic amphiphile membranes also undergo fusion, mediated by the protein machinery for synaptic secretion. We integrated fusogenic SNAREs in polymer and hybrid vesicles and observed efficient membrane and content mixing. We determined bending rigidity and pore edge tension as key parameters for fusion and described its plausible progression through cryo-EM snapshots. These findings demonstrate that dynamic membrane phenomena can be reconstituted in synthetic materials, thereby providing new tools for the assembly of synthetic protocells.
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Affiliation(s)
- Lado Otrin
- Electrochemical Energy Conversion, Max Planck Institute for Dynamics of Complex Technical Systems, Magdeburg, Germany.
| | - Agata Witkowska
- Laboratory of Neurobiology, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
- Department of Molecular Pharmacology and Cell Biology, Leibniz-Forschungsinstitut für Molekulare Pharmakologie (FMP), Berlin, Germany
| | - Nika Marušič
- Process Systems Engineering, Max Planck Institute for Dynamics of Complex Technical Systems, Magdeburg, Germany
| | - Ziliang Zhao
- Department of Theory and Bio-Systems, Max Planck Institute of Colloids and Interfaces, Potsdam, Germany
| | - Rafael B Lira
- Department of Theory and Bio-Systems, Max Planck Institute of Colloids and Interfaces, Potsdam, Germany
- Moleculaire Biofysica, Zernike Instituut, Rijksuniversiteit Groningen, Groningen, Netherlands
| | - Fotis L Kyrilis
- Interdisciplinary Research Center HALOmem & Institute of Biochemistry and Biotechnology, Martin Luther University Halle-Wittenberg, Biozentrum, Halle/Saale, Germany
| | - Farzad Hamdi
- Interdisciplinary Research Center HALOmem & Institute of Biochemistry and Biotechnology, Martin Luther University Halle-Wittenberg, Biozentrum, Halle/Saale, Germany
| | - Ivan Ivanov
- Process Systems Engineering, Max Planck Institute for Dynamics of Complex Technical Systems, Magdeburg, Germany
| | - Reinhard Lipowsky
- Department of Theory and Bio-Systems, Max Planck Institute of Colloids and Interfaces, Potsdam, Germany
| | - Panagiotis L Kastritis
- Interdisciplinary Research Center HALOmem & Institute of Biochemistry and Biotechnology, Martin Luther University Halle-Wittenberg, Biozentrum, Halle/Saale, Germany
| | - Rumiana Dimova
- Department of Theory and Bio-Systems, Max Planck Institute of Colloids and Interfaces, Potsdam, Germany
| | - Kai Sundmacher
- Process Systems Engineering, Max Planck Institute for Dynamics of Complex Technical Systems, Magdeburg, Germany
| | - Reinhard Jahn
- Laboratory of Neurobiology, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
| | - Tanja Vidaković-Koch
- Electrochemical Energy Conversion, Max Planck Institute for Dynamics of Complex Technical Systems, Magdeburg, Germany
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5
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Abstract
In this issue of Chemistry & Biology, Rickman and Davletov suggest a novel mechanism for biological lipids to regulate synaptic transmission in the brain. Physiologically relevant concentrations of arachidonic acid help to dissociate a protein complex involved in exocytosis.
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Affiliation(s)
- Matthijs Verhage
- Department of Functional Genomics, Center for Neurogenomics and Cognitive Research, Vrije Universiteit, Amsterdam, The Netherlands
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Hirano AA, Brandstätter JH, Brecha NC. Cellular distribution and subcellular localization of molecular components of vesicular transmitter release in horizontal cells of rabbit retina. J Comp Neurol 2005; 488:70-81. [PMID: 15912504 PMCID: PMC2820412 DOI: 10.1002/cne.20577] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
The mechanism underlying transmitter release from retinal horizontal cells is poorly understood. We investigated the possibility of vesicular transmitter release from mammalian horizontal cells by examining the expression of synaptic proteins that participate in vesicular transmitter release at chemical synapses. Using immunocytochemistry, we evaluated the cellular and subcellular distribution of complexin I/II, syntaxin-1, and synapsin I in rabbit retina. Strong labeling for complexin I/II, proteins that regulate a late step in vesicular transmitter release, was found in both synaptic layers of the retina, and in somata of A- and B-type horizontal cells, of gamma-aminobutyric acid (GABA)- and glycinergic amacrine cells, and of ganglion cells. Immunoelectron microscopy demonstrated the presence of complexin I/II in horizontal cell processes postsynaptic to rod and cone ribbon synapses. Syntaxin-1, a core protein of the soluble N-ethylmaleimide-sensitive-factor attachment protein receptor (SNARE) complex known to bind to complexin, and synapsin I, a synaptic vesicle-associated protein involved in the Ca(2+)-dependent recruitment of synaptic vesicles for transmitter release, were also present in the horizontal cells and their processes at photoreceptor synapses. Photoreceptors and bipolar cells did not express any of these proteins at their axon terminals. The presence of complexin I/II, syntaxin-1, and synapsin I in rabbit horizontal cell processes and tips suggests that a vesicular mechanism may underlie transmitter release from mammalian horizontal cells.
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Affiliation(s)
- Arlene A Hirano
- Department of Neurobiology & Medicine, Geffen School of Medicine at University of California at Los Angeles, 90095, USA.
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7
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Abstract
According to a popular theory, the three presynaptic SNARE proteins (syntaxin 1, synaptobrevin 2 and SNAP-25) drive neuroexocytosis by forming a complex that forces vesicle and plasma membranes together. However, individual reactions in this process have been difficult to resolve. Now, two groups have succeeded in studying a very early and a very late step in the fusion process.
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Affiliation(s)
- Jakob B Sørensen
- Max-Planck-Institute for Biophysical Chemistry, Am Fassberg 11, 37077 Göttingen, Germany.
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8
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Abstract
Epimorphin is representative of a unique class of stromal membrane-anchored proteins that plays distinct functions depending on its membrane topology. When exposed extracellularly, this molecule acts as a morphoregulator for various tissues including hair follicle epithelia. Previous study identified its functional domain (the pep7 domain: SIEQSCDQDE) for hair follicular morphogenesis followed by the successful generation of a chemically modified active peptide. Here, we report optimization of this peptide by the introduction of sequential mutations and subsequent structural determination. We found that three residues from the C-terminus are dispensable, and alternation of the seventh amino acid to an Alanine residue enhanced activity. To favour the biologically active conformation, epsilon-Acp (NH(CH(2))(5)CO) linked to a Cysteine residue was connected at the N-terminus followed by the introduction of an intramolecular disulphide bridge, the modification process of which could be included in the peptide synthesis. The obtained modified peptide, termed 'EPM (epimorphin-derived) peptide', has a Mw of 950 Da and exerts an inductive effect on hair follicle regeneration at a concentration of approximately 0.00001% or even lower. The action of this EPM peptide was more apparent in mice treated with 1% minoxidil, suggesting its potential clinical benefit as a new type of hair-regenerating agent.
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Affiliation(s)
- Yohei Hirai
- Department of Morphoregulation, Institute for Frontier Medical Sciences, Kyoto University, Kyoto, Japan
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9
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Li G, Yang Q, Alexander EA, Schwartz JH. Syntaxin 1A has a specific binding site in the H3 domain that is critical for targeting of H+-ATPase to apical membrane of renal epithelial cells. Am J Physiol Cell Physiol 2005; 289:C665-72. [PMID: 15872013 DOI: 10.1152/ajpcell.00041.2005] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
H+ transport in the collecting duct is regulated by exocytic insertion of H+-ATPase-laden vesicles into the apical membrane. The soluble N-ethylmaleimide-sensitive fusion protein attachment protein (SNAP) receptor (SNARE) proteins are critical for exocytosis. Syntaxin 1A contains three main domains, SNARE N, H3, and carboxy-terminal transmembrane domain. Several syntaxin isoforms form SNARE fusion complexes through the H3 domain; only syntaxin 1A, through its H3 domain, also binds H+-ATPase. This raised the possibility that there are separate binding sites within the H3 domain of syntaxin 1A for H+-ATPase and for SNARE proteins. A series of truncations in the H3 domain of syntaxin 1A were made and expressed as glutathione S-transferase (GST) fusion proteins. We determined the amount of H+-ATPase and SNARE proteins in rat kidney homogenate that complexed with GST-syntaxin molecules. Full-length syntaxin isoforms and syntaxin-1AΔC [amino acids (aa) 1–264] formed complexes with H+-ATPase and SNAP23 and vesicle-associated membrane polypeptide (VAMP). A cassette within the H3 portion was found that bound H+-ATPase (aa 235–264) and another that bound SNAP23 and VAMP (aa 190–234) to an equivalent degree as full-length syntaxin. However, the aa 235–264 cassette alone without the SNARE N (aa 1–160) does not bind but requires ligation to the SNARE N to bind H+-ATPase. When this chimerical construct was transected into inner medullary collecting duct cells it inhibited intracellular pH recovery, an index of H+-ATPase mediated secretion. We conclude that within the H3 domain of syntaxin 1A is a unique cassette that participates in the binding of the H+-ATPase to the apical membrane and confers specificity of syntaxin 1A in the process of H+-ATPase exocytosis.
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Affiliation(s)
- Guangmu Li
- Renal Section, Boston University Medical Center, Massachusetts, USA
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10
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Toonen RFG, de Vries KJ, Zalm R, Südhof TC, Verhage M. Munc18-1 stabilizes syntaxin 1, but is not essential for syntaxin 1 targeting and SNARE complex formation. J Neurochem 2005; 93:1393-400. [PMID: 15935055 DOI: 10.1111/j.1471-4159.2005.03128.x] [Citation(s) in RCA: 67] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Munc18-1, a member of the Sec1/Munc18 (SM) protein family, is essential for synaptic vesicle exocytosis. Munc18-1 binds tightly to the SNARE protein syntaxin 1, but the physiological significance and functional role of this interaction remain unclear. Here we show that syntaxin 1 levels are reduced by 70% in munc18-1 knockout mice. Pulse-chase analysis in transfected HEK293 cells revealed that Munc18-1 directly promotes the stability of syntaxin 1, consistent with a chaperone function. However, the residual syntaxin 1 in munc18-1 knockout mice is still correctly targeted to synapses and efficiently forms SDS-resistant SNARE complexes, demonstrating that Munc18-1 is not required for syntaxin 1 function as such. These data demonstrate that the Munc18-1 interaction with syntaxin 1 is physiologically important, but does not represent a classical chaperone-substrate relationship. Instead, the presence of SNARE complexes in the absence of membrane fusion in munc18-1 knockout mice indicates that Munc18-1 either controls the spatially correct assembly of core complexes for SNARE-dependent fusion, or acts as a direct component of the fusion machinery itself.
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Affiliation(s)
- Ruud F G Toonen
- Department of Functional Genomics, Center for Neurogenomics and Cognitive Research, Vrije Universiteit Amsterdam, Amsterdam, Netherlands
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11
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Karvar S, Zhu L, Crothers J, Wong W, Turkoz M, Forte JG. Cellular Localization and Stimulation-Associated Distribution Dynamics of Syntaxin-1 and Syntaxin-3 in Gastric Parietal Cells. Traffic 2005; 6:654-66. [PMID: 15998321 DOI: 10.1111/j.1600-0854.2005.00306.x] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
Syntaxins are differentially localized in polarized cells and play an important role in vesicle trafficking and membrane fusion. These soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) proteins are believed to be involved in tubulovesicle trafficking and membrane fusion during the secretory cycle of the gastric parietal cell. We examined the cellular localization and distribution of syntaxin-1 and syntaxin-3 in rabbit parietal cells. Fractionation of gastric epithelial cell membranes showed that syntaxin-1 was more abundant in a fraction enriched in apical plasma membranes, whereas syntaxin-3 was found predominantly in the H,K-ATPase-rich tubulovesicle fraction. We also examined the cellular localization of syntaxins in cultured parietal cells. Parietal cells were infected with CFP-syntaxin-1 and CFP-syntaxin-3 adenoviral constructs. Fluorescence microscopy of live and fixed cells demonstrated that syntaxin-1 was primarily on the apical membrane vacuoles of infected cells, but there was also the expression of syntaxin-1 in a subadjacent cytoplasmic compartment. In resting, non-secreting parietal cells, syntaxin-3 was distributed throughout the cytoplasmic compartment; after stimulation, syntaxin-3 translocated to the apical membrane vacuoles, there co-localizing with H,K-ATPase, syntaxin-1 and F-actin. The differential location of these syntaxin isoforms in gastric parietal cells suggests that these proteins may be critical for maintaining membrane compartment identity and that they may play important, but somewhat different, roles in the membrane recruitment processes associated with secretory activation.
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Affiliation(s)
- Serhan Karvar
- Department of Molecular and Cell Biology, University of California, Berkeley, CA 94720, USA
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12
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Constable JRL, Graham ME, Morgan A, Burgoyne RD. Amisyn regulates exocytosis and fusion pore stability by both syntaxin-dependent and syntaxin-independent mechanisms. J Biol Chem 2005; 280:31615-23. [PMID: 16033762 DOI: 10.1074/jbc.m505858200] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Amisyn and tomosyn are related by the possession of a C-terminal vesicle-associated membrane protein-like domain that allows them to bind to syntaxin 1 and assemble into SNARE complexes. The formation of inactive complexes may sequester syntaxin and allow tomosyn and amisyn to act as inhibitors of exocytosis. We aimed to use adrenal chromaffin and PC12 cells to probe this possible mode of action of amisyn and tomosyn in dense core granule exocytosis. Although tomosyn is expressed by adrenal chromaffin and PC12 cells, amisyn expression could not be detected allowing examination of the effect of introduction of amisyn expression onto a neuronal-like background. Overexpression of m-tomosyn1 and expression of amisyn both inhibited Ca2+-induced exocytosis in transfected PC12 cells. Surprisingly, this inhibition was not removed when amisyn and tomosyn constructs were used in which key residues required for efficient binding to syntaxin1 were mutated. The effect of amisyn was further characterized using carbon fiber amperometry in chromaffin cells. Expression of amisyn had no effect on the basic characteristics of the amperometric spikes but reduced the number of spikes elicited. This inhibitory action on the extent of exocytosis was also seen with the amisyn mutant deficient in syntaxin1 binding. In addition, expression of amisyn resulted in an increase in the lifetime of the prespike foot, and this effect was abolished by the mutations. These results show that tomosyn and amisyn can negatively regulate exocytosis independently of syntaxin and also that amisyn can regulate the stability of the fusion pore.
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Affiliation(s)
- John R L Constable
- Physiological Laboratory, School of Biomedical Sciences, University of Liverpool, Crown Street, Liverpool, L69 3BX, United Kingdom
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13
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Samuvel DJ, Jayanthi LD, Bhat NR, Ramamoorthy S. A role for p38 mitogen-activated protein kinase in the regulation of the serotonin transporter: evidence for distinct cellular mechanisms involved in transporter surface expression. J Neurosci 2005; 25:29-41. [PMID: 15634764 PMCID: PMC6725216 DOI: 10.1523/jneurosci.3754-04.2005] [Citation(s) in RCA: 169] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The serotonin transporter (SERT) is regulated by various signaling mechanisms that may operate to maintain appropriate levels of synaptic serotonin (5-HT). We demonstrate that one of the mitogen-activated protein kinases (MAPKs), p38 MAPK, regulates SERT. Treatment of rat midbrain synaptosomes with p38 MAPK-specific inhibitors, PD169316 [4-(4-fluorophenyl)-2-(4-nitrophenyl)-5-(4-pyridyl)-1H-imidazole] or SB203580 [4-(4-fluorophenyl)-2-(4-methylsulfinylphenyl)-5-(4-pyridyl)-1H-imidazole], reduced 5-HT uptake. An additive SERT inhibition by PD169316 and beta-phorbol 12-myristate 13-acetate (beta-PMA) indicated the involvement of a protein kinase C (PKC)-independent MAPK pathway. Kinetic studies indicated a significant decrease in the transport capacity (V(max)) after PD169316 treatment of synaptosomes. Biotinylation studies showed reduced SERT proteins in the plasma membrane of synaptosomes after p38 MAPK inhibition and PKC activation. Phosphorylation studies using synaptosomes revealed decreased SERT phosphorylation by PD169316 but increased phosphorylation by beta-PMA. d-Amphetamine enhanced SERT basal phosphorylation and PD169316 blocked this effect. SERT interaction with protein phosphatase 2A catalytic subunit and syntaxin 1A decreased after PD169316 or beta-PMA treatment of synaptosomes. In synaptosomes, PKC activation but not p38 MAPK inhibition resulted in SERT redistribution from cholesterolrich lipid raft fractions to nonlipid raft fractions. The presence of phospho-p38 MAPK in synaptosomes and human embryonic kidney 293 (HEK-293) cells suggested the presence of constitutively active p38 MAPK in these preparations. Cotransfection of HEK-293 cells with SERT and a constitutively active form of MAP kinase kinase 3b(E) [MKK3b(E)] increased 5-HT transport, and RNA interference targeted to p38 MAPK inhibited 5-HT uptake, confirming the involvement of active p38 MAPK in SERT expression. Although PD169316 inhibited SERT insertion to the plasma membrane, beta-PMA increased SERT internalization in HEK-293 cells. Together, these results indicate a distinct role of p38 MAPK in SERT regulation.
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Affiliation(s)
- Devadoss J Samuvel
- Department of Physiology and Neuroscience, Medical University of South Carolina, Charleston, South Carolina 29425, USA
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14
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Leung Y, Kang Y, Xia F, Sheu L, Gao X, Xie H, Tsushima R, Gaisano H. Open form of syntaxin-1A is a more potent inhibitor than wild-type syntaxin-1A of Kv2.1 channels. Biochem J 2005; 387:195-202. [PMID: 15518587 PMCID: PMC1134947 DOI: 10.1042/bj20041625] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
We have shown that SNARE (soluble N-ethylmaleimide-sensitive fusion protein attachment protein receptor) proteins not only participate directly in exocytosis, but also regulate the dominant membrane-repolarizing Kv channels (voltage-gated K+ channels), such as Kv2.1, in pancreatic beta-cells. In a recent report, we demonstrated that WT (wild-type) Syn-1A (syntaxin-1A) inhibits Kv2.1 channel trafficking and gating through binding to the cytoplasmic C-terminus of Kv2.1. During beta-cell exocytosis, Syn-1A converts from a closed form into an open form which reveals its active H3 domain to bind its SNARE partners SNAP-25 (synaptosome-associated protein of 25 kDa) and synaptobrevin. In the present study, we compared the effects of the WT Syn-1A and a mutant open form Syn-1A (L165A, E166A) on Kv2.1 channel trafficking and gating. When co-expressed in HEK-293 cells (human embryonic kidney-293 cells), the open form Syn-1A decreased Kv2.1 current density more than (P<0.05) the WT Syn-1A (166+/-35 and 371+/-93 pA/pF respectively; control=911+/-91 pA/pF). Confocal microscopy and biotinylation experiments showed that both the WT and open form Syn-1A inhibited Kv2.1 expression at the plasma membrane to a similar extent, suggesting that the stronger reduction of Kv2.1 current density by the open form compared with the WT Syn-1A is probably due to a stronger direct inhibition of channel activity. Consistently, dialysis of the recombinant open form Syn-1A protein into Kv2.1-expressing HEK-293 cells caused stronger inhibition of Kv2.1 current amplitude (P<0.05) than the WT Syn-1A protein (73+/-2 and 82+/-3% of the control respectively). We found that the H3 but not H(ABC) domain is the putative active domain of Syn-1A, which bound to and inhibited the Kv2.1 channel. When co-expressed in HEK-293 cells, the open-form Syn-1A slowed down Kv2.1 channel activation (tau=12.3+/-0.8 ms) much more than (P<0.05) WT Syn-1A (tau=7.9+/-0.8 ms; control tau=5.5+/-0.6 ms). In addition, only the open form Syn-1A, but not the WT Syn-1A, caused a significant (P<0.05) left-shift in the steady-state inactivation curve (V(1/2)=33.1+/-1.3 and -29.4+/-1.1 mV respectively; control V(1/2)=-24.8+/-2 mV). The present study therefore indicates that the open form of Syn-1A is more potent than the WT Syn-1A in inhibiting the Kv2.1 channel. Such stronger inhibition by the open form of Syn-1A may limit K+ efflux and thus decelerate membrane repolarization during exocytosis, leading to optimization of insulin release.
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Affiliation(s)
- Yuk M. Leung
- Departments of Medicine and Physiology, University of Toronto, Toronto, Canada M5S 1A8
| | - Youhou Kang
- Departments of Medicine and Physiology, University of Toronto, Toronto, Canada M5S 1A8
| | - Fuzhen Xia
- Departments of Medicine and Physiology, University of Toronto, Toronto, Canada M5S 1A8
| | - Laura Sheu
- Departments of Medicine and Physiology, University of Toronto, Toronto, Canada M5S 1A8
| | - Xiaodong Gao
- Departments of Medicine and Physiology, University of Toronto, Toronto, Canada M5S 1A8
| | - Huanli Xie
- Departments of Medicine and Physiology, University of Toronto, Toronto, Canada M5S 1A8
| | - Robert G. Tsushima
- Departments of Medicine and Physiology, University of Toronto, Toronto, Canada M5S 1A8
- Correspondence may be addressed to either of the authors (email and )
| | - Herbert Y. Gaisano
- Departments of Medicine and Physiology, University of Toronto, Toronto, Canada M5S 1A8
- Correspondence may be addressed to either of the authors (email and )
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15
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Abstract
SNARE (soluble N-ethylmaleimide-sensitive fusion protein attachment protein receptor) proteins are supposed to mediate the docking and/or fusion of the vesicle with the plasma membrane. However, it is not clearly understood how this process is regulated. In a search for potential SNARE regulators, we recently identified septin 5 (Sept5) as a novel SNARE interacting protein. Septins were first identified as filamentous proteins required for cytokinesis in yeast. Several septins have now been identified in mammals but little is known about their functions. We have previously shown that Sept5 is predominantly expressed in the brain, where it associates with vesicles and membranes through its interaction with the SNARE domain of syntaxin 1A. Furthermore, Sept5 appears to inhibit exocytosis, possibly by regulating vesicle targeting and/or fusion events. To gain insight into the role of Sept5, we have mapped the Sept5 domains important for syntaxin binding. We also investigated the ability of Sept5 to bind to syntaxin when in various protein complexes. Although Sept5 cannot bind an nSec1-syntaxin complex, it can bind syntaxin in a SNARE complex. This interaction is occluded by the binding of alpha-SNAP, suggesting that Sept5 may regulate the availability of SNARE proteins through its interaction with syntaxin and the 7 S complex.
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Affiliation(s)
- Crestina L. Beites
- *Programme in Cell Biology, Hospital for Sick Children, 555 University Avenue, Toronto, Canada M5G 1X8
- †Department of Biochemistry, University of Toronto, Toronto, Canada
| | - Kristen A. Campbell
- *Programme in Cell Biology, Hospital for Sick Children, 555 University Avenue, Toronto, Canada M5G 1X8
- †Department of Biochemistry, University of Toronto, Toronto, Canada
| | - William S. Trimble
- *Programme in Cell Biology, Hospital for Sick Children, 555 University Avenue, Toronto, Canada M5G 1X8
- †Department of Biochemistry, University of Toronto, Toronto, Canada
- To whom correspondence should be addressed (email )
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16
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Yokoyama CT, Myers SJ, Fu J, Mockus SM, Scheuer T, Catterall WA. Mechanism of SNARE protein binding and regulation of Cav2 channels by phosphorylation of the synaptic protein interaction site. Mol Cell Neurosci 2005; 28:1-17. [PMID: 15607937 DOI: 10.1016/j.mcn.2004.08.019] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/24/2003] [Revised: 06/02/2004] [Accepted: 08/02/2004] [Indexed: 11/30/2022] Open
Abstract
Ca(v)2.1 and Ca(v)2.2 channels conduct P/Q-type and N-type Ca(2+) currents that initiate neurotransmission and bind SNARE proteins through a synaptic protein interaction (synprint) site. PKC and CaMKII phosphorylate the synprint site and inhibit SNARE protein binding in vitro. Here we identify two separate microdomains that each bind syntaxin 1A and SNAP-25 in vitro and are regulated by PKC phosphorylation at serines 774 and 898 and CaMKII phosphorylation at serines 784 and 896. Activation of PKC resulted in its recruitment to and phosphorylation of Ca(V)2.2 channels, but PKC phosphorylation did not dissociate Ca(V)2.2 channel/syntaxin 1A complexes. Chimeric Ca(V)2.1a channels containing the synprint site of Ca(v)2.2 gain modulation by syntaxin 1A, which is blocked by PKC phosphorylation at the sites identified above. Our results support a bipartite model for the synprint site in which each SNARE-binding microdomain is controlled by a separate PKC and CaMKII phosphorylation site that regulates channel modulation by SNARE proteins.
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Affiliation(s)
- Charles T Yokoyama
- Department of Pharmacology, University of Washington, Seattle, WA 98195, USA
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17
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Abstract
The sperm acrosome is a large secretory granule that undergoes calcium-stimulated exocytosis by a mechanism analogous to neuronal secretion. In neurons the core SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) complex, composed of syntaxin (Stx), SNAP-25, and VAMP2, mediates vesicle fusion, whereas calcium regulation is thought to be accomplished by the synaptotagmin (Syt) family, some of which exhibit calcium-dependent binding to syntaxin and SNAP-25. Sperm express Syt VI and VIII and Stx2, which are co-localized to the acrosomal compartment where they might mediate exocytosis in response to calcium influx. Therefore, we examined the calcium dependence and isoform-specific interaction of Syt and Stx. We found that Stx2 binds to Syt I, VI, and VIII in a calcium-dependent manner with EC(50) values of 175, 233, and 96 mum calcium, respectively. We also determined that the EC(50) for calcium of the acrosome reaction in streptolysin O-permeabilized sperm is 87 mum, which closely coincides with the calcium sensitivity of Stx2 and Syt VIII interaction. Consistent with this is the greater potency of recombinant Syt VIII, VI, and Stx2 compared with other isoforms in inhibiting the acrosome reaction in streptolysin O-permeabilized sperm. Similarly, introduction of Syt VIII-specific antibodies was equally effective in inhibiting the acrosome fusion. Taken together, our data suggest a critical role for Syt VIII and Stx2 in membrane fusion and acrosome reaction in the sperm.
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Affiliation(s)
- Darren M Hutt
- Ottawa Health Research Institute, Department of Cellular and Molecular Medicine, University of Ottawa, Ottawa, Ontario K1Y 4E9, Canada
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18
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Rickman C, Davletov B. Arachidonic Acid Allows SNARE Complex Formation in the Presence of Munc18. ACTA ACUST UNITED AC 2005; 12:545-53. [PMID: 15911375 DOI: 10.1016/j.chembiol.2005.03.004] [Citation(s) in RCA: 70] [Impact Index Per Article: 3.7] [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: 12/09/2004] [Revised: 02/21/2005] [Accepted: 03/09/2005] [Indexed: 11/25/2022]
Abstract
SNARE complex formation underlies intracellular membrane fusion in eukaryotic organisms; however, the factors regulating the SNARE assembly are not well understood. The neuronal SNARE complex is composed of synaptobrevin2, SNAP-25, and syntaxin1, the latter being under tight control by the cytosolic protein Munc18. We found that the inhibition of syntaxin1 by Munc18 both in nerve terminals and in defined in vitro reactions can be overcome by specific detergents. This serendipitous finding led us to screen biologically relevant fatty acids, revealing that unsaturated arachidonic and linolenic acids can stimulate Munc18-regulated SNARE complex formation in a direct manner. The direct effect of arachidonic acid on the syntaxin1/Munc18 complex suggests a mechanism for the activation of the SNARE assembly pathway and provides a lead for the further investigation of fatty acids that may regulate SNARE-mediated membrane fusion in eukaryotes.
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Affiliation(s)
- Colin Rickman
- MRC Laboratory of Molecular Biology, Cambridge, United Kingdom
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19
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Abstract
Munc-18 interacts with the SNARE protein syntaxin and is supposed to influence transmitter release by controlling the formation of exocytosis-relevant SNARE complexes. Here, we used combined biochemical and physiological analyses to study the role of the Munc-18/syntaxin interaction in large dense core vesicle (LDCV) exocytosis of neuroendocrine PC12 cells. We compared two Munc-18 mutants carrying mutations in the syntaxin-binding region and show that Munc-18's membrane association depends on direct binding to syntaxin. The data suggest that perturbation of syntaxin binding inhibits neurotransmitter release upstream of the individual fusion event implying an essential role of the Munc-18/syntaxin complex leading to exocytosis. Furthermore, we show that a Munc-18 mutant lacking any syntaxin binding has a stimulatory effect on secretion, and provide evidence that the Munc-18/Mint1 interaction may constitute a second pathway for Munc-18 to regulate exocytosis. We propose that Munc-18 represents a dynamic link between syntaxin-related and Mint1-related mechanisms, both involved in the control of LDCV exocytosis in neuroendocrine cells.
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Affiliation(s)
- Dagmar Schütz
- Max-Planck-Institute for Biophysical Chemistry, Department of Neurobiology, Am Fassberg 11, 37077 Göttingen, Germany
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20
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Gil C, Soler-Jover A, Blasi J, Aguilera J. Synaptic proteins and SNARE complexes are localized in lipid rafts from rat brain synaptosomes. Biochem Biophys Res Commun 2005; 329:117-24. [PMID: 15721282 DOI: 10.1016/j.bbrc.2005.01.111] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.4] [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: 01/11/2005] [Indexed: 12/17/2022]
Abstract
The biochemical characterization of the SNARE proteins present in lipid microdomains, also known as "lipid rafts," has been addressed in earlier studies, with conflicting data from different laboratories. In this study, we use rat brain synaptosomes as a model with which to examine the presence of proteins involved in exocytosis in detergent-resistant membranes (DRM), also known as 'lipid rafts.' By means of buoyancy analysis in sucrose gradients of Triton X-100-solubilized synaptosomes, we identified a pool of SNARE proteins (SNAP 25, syntaxin 1, and synaptobrevin2/VAMP2) significantly associated with DRM. Furthermore, Munc18, synaptophysin, and high amounts of the isoforms I and II of synaptotagmin were also found in DRM. In addition, SDS-resistant and temperature-dependent SNARE complexes were also detected in DRM. Treatment of synaptosomes with methyl-beta-cyclodextrin resulted in persistence of the proteins present in the DRM isolated using Triton X-100, whilst strongly impairing calcium-dependent glutamate release. The results from the present work show that lipid microdomains are sites where SNARE proteins and complexes are actually present, as well as important elements in the control of regulated exocytosis.
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Affiliation(s)
- Carles Gil
- Departament de Bioquímica i Biologia Molecular and Institut de Neurociències, Universitat Autònoma de Barcelona, Cerdanyola 08193, Catalunya, Spain.
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21
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Abstract
The assembly of multiprotein complexes at the membrane interface governs many signaling processes in cells. However, very few methods exist for obtaining biophysical information about protein complex formation at the membrane. We used single molecule fluorescence resonance energy transfer to study complexin and synaptotagmin interactions with the SNARE complex in deposited lipid bilayers. Using total internal reflectance microscopy, individual binding events at the membrane could be resolved despite an excess of unbound protein in solution. Fluorescence resonance energy transfer (FRET)-efficiency derived distances for the complexin-SNARE interaction were consistent with the crystal structure of the complexin-SNARE complex. The unstructured N-terminal region of complexin showed broad distributions of FRET efficiencies to the SNARE complex, suggesting that information on conformational variability can be obtained from FRET efficiency distributions. The low-affinity interaction of synaptotagmin with the SNARE complex changed dramatically upon addition of Ca2+ with high FRET efficiency interactions appearing between the C2B domain and linker domains of synaptotagmin and the membrane proximal portion of the SNARE complex. These results demonstrate that single molecule FRET can be used as a "spectroscopic ruler" to simultaneously gain structural and kinetic information about transient multiprotein complexes at the membrane interface.
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Affiliation(s)
- Mark E Bowen
- The Howard Hughes Medical Institute and Department of Molecular and Cellular Physiology, Stanford University, Stanford, California, USA
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22
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van Swinderen B, Greenspan RJ. Flexibility in a gene network affecting a simple behavior in Drosophila melanogaster. Genetics 2005; 169:2151-63. [PMID: 15687281 PMCID: PMC1449574 DOI: 10.1534/genetics.104.032631] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.4] [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: 06/21/2004] [Accepted: 01/12/2005] [Indexed: 11/18/2022] Open
Abstract
Gene interactions are emerging as central to understanding the realization of any phenotype. To probe the flexibility of interactions in a defined gene network, we isolated a set of 16 interacting genes in Drosophila, on the basis of their alteration of a quantitative behavioral phenotype-the loss of coordination in a temperature-sensitive allele of Syntaxin1A. The interactions inter se of this set of genes were then assayed in the presence and in the absence of the original Syntaxin1A mutation to ask whether the relationships among the 16 genes remain stable or differ after a change in genetic context. The pattern of epistatic interactions that occurs within this set of variants is dramatically altered in the two different genetic contexts. The results imply considerable flexibility in the network interactions of genes.
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23
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Bajohrs M, Rickman C, Binz T, Davletov B. A molecular basis underlying differences in the toxicity of botulinum serotypes A and E. EMBO Rep 2005; 5:1090-5. [PMID: 15486565 PMCID: PMC1299173 DOI: 10.1038/sj.embor.7400278] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.7] [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: 06/17/2004] [Revised: 08/31/2004] [Accepted: 09/20/2004] [Indexed: 11/08/2022] Open
Abstract
Botulinum neurotoxins (BoNTs) block neurotransmitter release through their specific proteolysis of the proteins responsible for vesicle exocytosis. Paradoxically, two serotypes of BoNTs, A and E, cleave the same molecule, synaptosome-associated protein with relative molecular mass 25K (SNAP-25), and yet they cause synaptic blockade with very different properties. Here we compared the action of BoNTs A and E on the plasma membrane fusion machinery composed of syntaxin and SNAP-25. We now show that the BoNT/A-cleaved SNAP-25 maintains its association with two syntaxin isoforms in vitro, which is mirrored by retention of SNAP-25 on the plasma membrane in vivo. In contrast, BoNT/E severely compromises the ability of SNAP-25 to bind the plasma membrane syntaxin isoforms, leading to dissociation of SNAP-25. The distinct properties of botulinum intoxication, therefore, can result from the ability of shortened SNAP-25 to maintain its association with syntaxins-in the case of BoNT/A poisoning resulting in unproductive syntaxin/SNAP-25 complexes that impede vesicle exocytosis.
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Affiliation(s)
- Mark Bajohrs
- MRC Laboratory of Molecular Biology, Hills Road, Cambridge CB2 2QH, UK
| | - Colin Rickman
- MRC Laboratory of Molecular Biology, Hills Road, Cambridge CB2 2QH, UK
| | - Thomas Binz
- Department of Biochemistry, Medizinische Hochschule Hannover, 30625 Hannover, Germany
| | - Bazbek Davletov
- MRC Laboratory of Molecular Biology, Hills Road, Cambridge CB2 2QH, UK
- Tel: +44 1223 402071; Fax: +44 1223 402310; E-mail:
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24
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Hawasli AH, Saifee O, Liu C, Nonet ML, Crowder CM. Resistance to volatile anesthetics by mutations enhancing excitatory neurotransmitter release in Caenorhabditis elegans. Genetics 2005; 168:831-43. [PMID: 15514057 PMCID: PMC1448830 DOI: 10.1534/genetics.104.030502] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
The molecular mechanisms whereby volatile general anesthetics (VAs) disrupt behavior remain undefined. In Caenorhabditis elegans mutations in the gene unc-64, which encodes the presynaptic protein syntaxin 1A, produce large allele-specific differences in VA sensitivity. UNC-64 syntaxin normally functions to mediate fusion of neurotransmitter vesicles with the presynaptic membrane. The precise role of syntaxin in the VA mechanism is as yet unclear, but a variety of results suggests that a protein interacting with syntaxin to regulate neurotransmitter release is essential for VA action in C. elegans. To identify additional proteins that function with syntaxin to control neurotransmitter release and VA action, we screened for suppressors of the phenotypes produced by unc-64 reduction of function. Loss-of-function mutations in slo-1, which encodes a Ca(2+)-activated K+ channel, and in unc-43, which encodes CaM-kinase II, and a gain-of-function mutation in egl-30, which encodes Gqalpha, were isolated as syntaxin suppressors. The slo-1 and egl-30 mutations conferred resistance to VAs, but unc-43 mutations did not. The effects of slo-1 and egl-30 on VA sensitivity can be explained by their actions upstream or parallel to syntaxin to increase the level of excitatory neurotransmitter release. These results strengthen the link between transmitter release and VA action.
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Affiliation(s)
- Ammar H Hawasli
- Department of Anesthesiology, Division of Biology and Biomedical Sciences, Washington University School of Medicine, Saint Louis, Missouri 63110, USA
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25
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Mitchell SJ, Ryan TA. Munc18-dependent regulation of synaptic vesicle exocytosis by syntaxin-1A in hippocampal neurons. Neuropharmacology 2005; 48:372-80. [PMID: 15721169 DOI: 10.1016/j.neuropharm.2004.10.017] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2004] [Revised: 09/10/2004] [Accepted: 10/15/2004] [Indexed: 11/17/2022]
Abstract
The fusion of secretory vesicles with the plasma membrane requires the formation of soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complexes between the vesicle-SNARE vesicle-associated membrane protein present on the vesicular membrane and the target-SNAREs SNAP-25 and syntaxin-1A. Syntaxin-1A fluctuates between an open and closed form allowing it to selectively bind to different biological effectors in different conformations. In the open form, it can participate in SNARE complex formation, however, in the closed form it negatively regulates N- and P/Q-type voltage-dependent calcium channels, and is capable of inhibiting calcium influx. Thus paradoxically, syntaxin appears to have both positive and negative roles in controlling calcium-driven synaptic vesicle fusion at synaptic terminals. We show here that overexpression of syntaxin-1A inhibited exocytosis, in a manner that could be rescued by either elevating or reducing external calcium, or increasing action potential firing frequency. Elevating the level of Munc18 by coexpression with syntaxin-1A also abolished this inhibition, suggesting that Munc18 serves to limit the negative regulatory role of syntaxin by binding to, and thereby buffering, its closed form. Our results also indicate that syntaxin can control the frequency-response characteristics of the presynaptic fusion machinery.
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Affiliation(s)
- Simon J Mitchell
- Department of Biochemistry, Weill Medical College of Cornell University, 1300 York Avenue, New York, NY 10021, USA
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26
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Cibulsky SM, Fei H, Levitan IB. Syntaxin-1A Binds to and Modulates the Slo Calcium-Activated Potassium Channel via an Interaction That Excludes Syntaxin Binding to Calcium Channels. J Neurophysiol 2005; 93:1393-405. [PMID: 15496493 DOI: 10.1152/jn.00789.2004] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
From its position in presynaptic nerve terminals, the large conductance Ca2+-activated K+ channel, Slo, regulates neurotransmitter release. Several other ion channels known to control neurotransmitter release have been implicated in physical interactions with the neurotransmitter release machinery. For example, the Cav2.2 (N-type) Ca2+ channel binds to and is modulated by syntaxin-1A and SNAP-25. Furthermore, a close juxtaposition of Slo and Cav2.2 is presumed to be necessary for functional coupling between the two channels, which has been shown in neurons. We report that Slo exhibits a strong association with syntaxin-1A. Robust co-immunoprecipitation of Slo and syntaxin-1A occurs from transfected HEK293 cells as well as from brain. However, despite this strong interaction and the known association between syntaxin-1A and the II–III loop of Cav2.2, these three proteins do not co-immunoprecipitate in a trimeric complex from transfected HEK293 cells. The Slo-syntaxin-1A co-immunoprecipitation is not significantly influenced by [Ca2+]. Multiple relatively weak interactions may sum up to a tight physical coupling of full-length Slo with syntaxin-1A: the C-terminal tail and the S0–S1 loop of Slo each co-immunoprecipitate with syntaxin-1A. The presence of syntaxin-1A leads to reduced Slo channel activity due to an increased V1/2 for activation in 100 nM, 1 μM, and 10 μM Ca2+, reduced voltage-sensitivity in 1 μM Ca2+, and slower rates of activation in 10 μM Ca2+. Potential physiological consequences of the interaction between Slo and syntaxin-1A include enhanced excitability through modulation of Slo channel activity and reduced neurotransmitter release due to disruption of syntaxin-1A binding to the Cav2.2 II–III loop.
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Affiliation(s)
- Susan M Cibulsky
- Department of Neuroscience, University of Pennsylvania, Philadelphia, Pennsylvania.
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27
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Yoo SH, You SH, Huh YH. Presence of syntaxin 1A in secretory granules of chromaffin cells and interaction with chromogranins A and B. FEBS Lett 2005; 579:222-8. [PMID: 15620717 DOI: 10.1016/j.febslet.2004.11.079] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [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: 10/06/2004] [Revised: 11/11/2004] [Accepted: 11/11/2004] [Indexed: 10/26/2022]
Abstract
Syntaxin 1A and synaptotagmin I are key participants of fusion complex formation during exocytotic processes, and syntaxin 1A is known to be present in the plasma membrane. Here, we show the presence of not only synaptotagmin I but also syntaxin 1A in secretory granules of bovine adrenal chromaffin cells by immunogold electron microscopy, and further demonstrate the interaction of these proteins with chromogranins A and B (CGA and CGB), two major proteins of secretory granules. Interaction between chromogranins and the components of fusion complex also suggests active participation of CGA and CGB in fusion complex formation and subsequent exocytosis.
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Affiliation(s)
- Seung Hyun Yoo
- Department of Biochemistry, National Creative Research Initiative Center for Secretory Granule Research, Inha University College of Medicine, Jung Gu, Incheon 400-712, Republic of Korea.
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28
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Abstract
ROMK potassium channels are present in the cortical collecting duct (CCD) of the kidney and serve as apical exit pathways for K+secretion in this nephron segment. K+secretion in the CCD is regulated by multiple factors. In this study, we show that syntaxin 1A, but not syntaxin 3 or 4, inhibited whole cell ROMK currents in Xenopus laevis oocytes. Syntaxin 1A, but not syntaxin 3 or 4, interacted with the COOH-terminal cytoplasmic domain of ROMK in intro. Coexpression with synaptobrevin 2 reversed inhibition of whole cell ROMK currents by syntaxin 1A. In excised inside-out membranes of oocytes, application of fusion proteins containing the cytoplasmic region of syntaxin 1A to the cytoplasmic face caused a dose-dependent inhibition of ROMK. We further examined regulation of the K+channels in the CCD by syntaxin 1A. Application of botulinum toxin C1 to the excised inside-out membranes of the CCD caused an increase in the activity of K+channels. In contrast, application of toxin B had no effects. These results suggest that syntaxin 1A causes a tonic inhibition of the K+channels in the apical membrane of the CCD. Binding of synaptobrevin 2 to syntaxin 1A during docking and fusion of transport vesicles to the plasma membranes of CCD may lead to activation of these channels.
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Affiliation(s)
- Tie-Jun Sun
- Department of Medicine, Division of Nephrology, University of Texas Southwestern Medical Center, 5323 Harry Hines Blvd., Dallas, TX 75390-8856, USA
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29
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Abstract
Epimorphin modulates epithelial morphogenesis in embryonic mouse organs. We previously suggested that epimorphin contributes to repair of bleomycin-induced pulmonary fibrosis in mice via epithelium-mesenchyme interactions. To clarify the role of epimorphin in human lungs, we evaluated epimorphin expression and localization in normal lungs, lungs with nonspecific interstitial pneumonia (NSIP), and lungs with usual interstitial pneumonia (UIP); we also studied the effect of recombinant epimorphin on cultured human alveolar epithelial cells in vitro. Northern and Western blotting analyses revealed that epimorphin expression in NSIP samples were significantly higher than those in control lungs and lungs with UIP. Immunohistochemistry showed strong epimorphin expression in mesenchymal cells of early fibrotic lesions and localization of epimorphin protein on mesenchymal cells and extracellular matrix of early fibrotic lesions in the nonspecific interstitial pneumonia group. Double-labeled fluorescent images revealed expression of matrix metalloproteinase 2 in re-epithelialized cells overlying epimorphin-positive early fibrotic lesions. Immunohistochemistry and metalloproteinase activity assay demonstrated augmented expression of metalloproteinase induced by recombinant epimorphin in human alveolar epithelial cells. These findings suggest that epimorphin contributes to repair of pulmonary fibrosis in nonspecific interstitial pneumonia, perhaps partly by inducing expression of matrix metalloproteinase 2, which is an important proteolytic factor in lung remodeling.
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Affiliation(s)
- Yasuhiro Terasaki
- Department of Cell Pathology, Postgraduate School of Medicine, Kumamoto University, Kumamoto, Japan
- Department of Analytic Human Pathology, Nippon Medical School, Tokyo, Japan
| | - Yuh Fukuda
- Department of Analytic Human Pathology, Nippon Medical School, Tokyo, Japan
| | - Moritaka Suga
- Department of Respiratory Medicine, Postgraduate School of Medicine, Kumamoto University, Kumamoto, Japan
| | - Naoki Ikeguchi
- Osaka R&D Laboratory (Yokohama-lab), Sumitomo Electric Industries, Yokohama, Japan
| | - Motohiro Takeya
- Department of Cell Pathology, Postgraduate School of Medicine, Kumamoto University, Kumamoto, Japan
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Abstract
We report cloning and characterization of coro, which codes for the Drosophila homologue of the F-actin binding protein coronin. Viable alleles of coro produce a variety of phenotypes in leg, wing and eye development, which are similar to the phenotypes observed as a result of mutations in genes associated with the actin cytoskeleton and/or membrane trafficking. Homozygous lethal mutations in coro results in the disruption of the actin cytoskeleton in wing imaginal discs. Formation of both basolateral septate junctions and apical adherens junctions are also adversely affected in epithelial cells. Both viable and lethal alleles of coro show genetic interactions with syntaxin1A, a gene required for membrane trafficking. They also show enhanced response to over-expression of Decapentaplegic (Dpp) and its receptor Thick vein. Tracing of Dpp morphogen using a Dpp::GFP fusion construct suggested defects in the endocytic pathway, which resulted in uniform distribution of Dpp along the AP axis rather than a gradient from the AP boundary. Our results provide a genetic link between endocytosis/exocytosis events involving F actin-coated vesicles and the establishment of morphogen gradient.
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Affiliation(s)
- V Bharathi
- Centre for Cellular and Molecular Biology, Uppal Road, Hyderabad, India 500 007
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Pickett JA, Thorn P, Edwardson JM. The Plasma Membrane Q-SNARE Syntaxin 2 Enters the Zymogen Granule Membrane during Exocytosis in the Pancreatic Acinar Cell. J Biol Chem 2005; 280:1506-11. [PMID: 15536072 DOI: 10.1074/jbc.m411967200] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
During exocytosis in the pancreatic acinar cell, zymogen granules fuse directly with the apical plasma membrane and also with granules that have themselves fused with the plasma membrane. Together, these primary and secondary fusion events constitute the process of compound exocytosis. It has been suggested that the sequential nature of primary and secondary fusion is a consequence of the requirement for plasma membrane soluble N-ethylmaleimide-sensitive fusion protein attachment protein receptors, such as syntaxin 2, to enter the membrane of the primary fused granule. We have tested this possibility by determining the location of syntaxin 2 in unstimulated and stimulated pancreatic acini. Syntaxin 2 was imaged by confocal immunofluorescence microscopy. Fused granules were detected both through their filling with the aqueous dye lysine-fixable Texas Red-dextran and through the decoration of their cytoplasmic surfaces with filamentous actin. In unstimulated cells, syntaxin 2 was exclusively present on the apical plasma membrane. In contrast, after stimulation, syntaxin 2 had moved into the membranes of fused granules, as judged by its location around dye-filled structures of 1-mum diameter that were coated with filamentous actin. At long times of stimulation (5 min), the majority (85%) of dye-filled granules were also positive for syntaxin 2. In contrast, at shorter times (1 min), more dye-filled granules (29%) were syntaxin 2-negative. We conclude that syntaxin 2 enters the membrane of a fused zymogen granule after the opening of the fusion pore, and we suggest that this movement might permit the onset of secondary fusion.
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Affiliation(s)
- James A Pickett
- Department of Pharmacology, University of Cambridge, Tennis Court Road, Cambridge CB2 1PD, United Kingdom
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32
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Zhu Y, Fei J, Schwarz W. Expression and transport function of the glutamate transporter EAAC1 inXenopus oocytes is regulated by syntaxin 1A. J Neurosci Res 2005; 79:503-8. [PMID: 15742465 DOI: 10.1002/jnr.20385] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
The function of several membrane proteins is regulated by interaction with the SNARE protein syntaxin 1A; this includes regulation of GAT1, the transporter for the dominating inhibitory neurotransmitter gamma-aminobutyric acid (GABA). Here we demonstrate that also EAAC1, the transporter for the dominating excitatory neurotransmitter, is down-regulated by interaction with syntaxin 1A. This is shown by coexpression of EAAC1 and syntaxin 1A in Xenopus oocytes. Total EAAC1 expression is not significantly affected by the coexpression of syntaxin 1A, but more proteins become targeted to the membrane as demonstrated by biotinylation. Colocalization by coimmunoprecipitation suggests direct interaction between the two proteins. In contrast to the number of transporters, the glutamate transport activity becomes reduced, and even stronger inhibition is observed for the EAAC1-mediated conductance uncoupled from glutamate translocation. We conclude that the interaction of syntaxin 1A with EAAC1 particularly disrupts the structure of the conductance pathway of EAAC1.
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Affiliation(s)
- Yani Zhu
- Max-Planck Guest Laboratory at the Institute of Biochemistry and Cell Biology, CAS, Shanghai, China
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33
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Suga K, Tomiyama T, Mori H, Akagawa K. Syntaxin 5 interacts with presenilin holoproteins, but not with their N- or C-terminal fragments, and affects beta-amyloid peptide production. Biochem J 2004; 381:619-28. [PMID: 15109302 PMCID: PMC1133870 DOI: 10.1042/bj20040618] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.6] [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: 04/14/2004] [Accepted: 04/27/2004] [Indexed: 12/16/2022]
Abstract
Mutations in presenilins 1 and 2 (PS1 and PS2) account for the majority of cases of early-onset familial Alzheimer's disease. However, the trafficking and interaction of PSs with other proteins in the early secretory pathways are poorly understood. Using co-immunoprecipitation, we found that PS bound to Syx5 (syntaxin 5), which is a target-soluble N-ethylmaleimide-sensitive fusion protein attachment protein receptor involved in endoplasmic reticulum (ER)-Golgi vesicular transport in vivo. Syx5 interacted only with the full-length PS holoproteins and not with the naturally occurring N- or C-terminal fragments. The PS holoproteins co-immunoprecipitated with the mutant Syx5, which localized to the ER and Golgi compartments, despite the substitution of the transmembrane region with that of syntaxin 1A. In contrast, the transmembrane deletion mutant that localized to the cytosol, but not to the ER or Golgi compartments, did not co-immunoprecipitate the PS holoproteins. The PS1 variant linked to familial Alzheimer's disease (PS1DeltaE9), lacking the region that contains the endoproteolytic cleavage site in the cytoplasmic loop, showed markedly decreased binding to Syx5. Immunofluorescence and sucrose-density-gradient fractionation analyses showed that the full-length PS holoproteins co-localized with Syx5 to the ER and cis-Golgi compartments. Furthermore, Syx5 overexpression resulted in the accumulation of PS holoproteins and the beta-amyloid precursor protein, and reduced the secretion of the Abeta (amyloid beta) peptide in COS-7 cells. In summary, these results indicate that Syx5 binds to full-length PSs and affects the processing and trafficking of beta-amyloid precursor protein in the early secretory compartments.
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Affiliation(s)
- Kei Suga
- Department of Cell Physiology, Kyorin University School of Medicine, 6-20-2, Shinkawa, Mitaka, Tokyo 181-8611, Japan.
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Liu J, Ernst SA, Gladycheva SE, Lee YYF, Lentz SI, Ho CS, Li Q, Stuenkel EL. Fluorescence Resonance Energy Transfer Reports Properties of Syntaxin1A Interaction with Munc18-1 in Vivo. J Biol Chem 2004; 279:55924-36. [PMID: 15489225 DOI: 10.1074/jbc.m410024200] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Syntaxin1A, a neural-specific N-ethylmaleimide-sensitive factor attachment protein receptor protein essential to neurotransmitter release, in isolation forms a closed conformation with an N-terminal alpha-helix bundle folded upon the SNARE motif (H3 domain), thereby limiting interaction of the H3 domain with cognate SNAREs. Munc18-1, a neural-specific member of the Sec1/Munc18 protein family, binds to syntaxin1A, stabilizing this closed conformation. We used fluorescence resonance energy transfer (FRET) to characterize the Munc18-1/syntaxin1A interaction in intact cells. Enhanced cyan fluorescent protein-Munc18-1 and a citrine variant of enhanced yellow fluorescent protein-syntaxin1A, or mutants of these proteins, were expressed as donor and acceptor pairs in human embryonic kidney HEK293-S3 and adrenal chromaffin cells. Apparent FRET efficiency was measured using two independent approaches with complementary results that unambiguously verified FRET and provided a spatial map of FRET efficiency. In addition, enhanced cyan fluorescent protein-Munc18-1 and a citrine variant of enhanced yellow fluorescent protein-syntaxin1A colocalized with a Golgi marker and exhibited FRET at early expression times, whereas a strong plasma membrane colocalization, with similar FRET values, was apparent at later times. Trafficking of syntaxin1A to the plasma membrane was dependent on the presence of Munc18-1. Both syntaxin1A(L165A/E166A), a constitutively open conformation mutant, and syntaxin1A(I233A), an H3 domain point mutant, demonstrated apparent FRET efficiency that was reduced approximately 70% from control. In contrast, the H3 domain mutant syntaxin1A(I209A) had no effect. By using phosphomimetic mutants of Munc18-1, we also established that Ser-313, a Munc18-1 protein kinase C phosphorylation site, and Thr-574, a cyclin-dependent kinase 5 phosphorylation site, regulate Munc18-1/syntaxin1A interaction in HEK293-S3 and chromaffin cells. We conclude that FRET imaging in living cells may allow correlated regulation of Munc18-1/syntaxin1A interactions to Ca(2+)-regulated secretory events.
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Affiliation(s)
- Jiang Liu
- Department of Molecular and Integrative Physiology, The Medical School, University of Michigan, 7808 Medical Sciences II Building, Ann Arbor, MI 48109, USA
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35
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Ohara-Imaizumi M, Nishiwaki C, Nakamichi Y, Kikuta T, Nagai S, Nagamatsu S. Correlation of syntaxin-1 and SNAP-25 clusters with docking and fusion of insulin granules analysed by total internal reflection fluorescence microscopy. Diabetologia 2004; 47:2200-7. [PMID: 15647897 DOI: 10.1007/s00125-004-1579-0] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/10/2004] [Accepted: 08/05/2004] [Indexed: 11/27/2022]
Abstract
AIMS/HYPOTHESIS The interaction of syntaxin-1 and SNAP-25 with insulin exocytosis was examined using the diabetic Goto-Kakizaki (GK) rat and a total internal reflection fluorescence (TIRF) imaging system. METHODS Primary rat pancreatic beta cells were immunostained with anti-syntaxin-1A, anti-SNAP-25 and anti-insulin antibodies, and then observed by TIRF microscopy. The real-time image of GFP-labelled insulin granules motion was monitored by TIRF. RESULTS The number of syntaxin-1A and SNAP-25 clusters, and the number of docked insulin granules on the plasma membrane were reduced in GK beta cells. When GK rats were treated with daily insulin injection for 2 weeks, the number of syntaxin-1 and SNAP-25 clusters was restored, along with the number of docked insulin granules. The infection of GK beta cells with Adex1CA SNAP-25 increased the number of docked insulin granules. TIRF imaging analysis demonstrated that the decreased number of fusion events from previously docked insulin granules in GK beta cells was restored when the number of docked insulin granules increased by insulin treatment or Adex1CA SNAP-25 infection. CONCLUSIONS/INTERPRETATION There was a close correlation between the number of syntaxin-1 and SNAP-25 clusters and the number of docked insulin granules, which is associated with the fusion of insulin granules.
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Affiliation(s)
- M Ohara-Imaizumi
- Department of Biochemistry, Kyorin University School of Medicine, Mitaka, Tokyo 181-8611, Japan
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36
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Igaz LM, Bekinschtein P, Izquierdo I, Medina JH. One-trial aversive learning induces late changes in hippocampal CaMKIIα, Homer 1a, Syntaxin 1a and ERK2 protein levels. ACTA ACUST UNITED AC 2004; 132:1-12. [PMID: 15548423 DOI: 10.1016/j.molbrainres.2004.08.016] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/29/2004] [Indexed: 11/25/2022]
Abstract
Most studies regarding altered gene expression after learning are performed using multi-trial tasks, which do not allow a clear discrimination of memory acquisition, consolidation and retrieval. We screened for candidate memory-modulated genes in the hippocampus at 3 and 24 h after one-trial inhibitory avoidance (IA) training, using a cDNA array containing 1176 genes. While 33 genes were modulated by training (respect to shocked-only animals), most of them were upregulated (27 genes) and only 6 were downregulated. To confirm and extend these findings, we performed RT-PCRs and analyzed differences in protein levels in rat hippocampus using immunoblot assays. We found several proteins upregulated 24 h after training: extracellular signal-regulated kinase ERK2, Ca2+/calmodulin-dependent protein kinase II alpha (CaMKIIalpha), Syntaxin 1a, c-fos and Homer 1a. The total level of none of these proteins were found to be altered when measured 3-h post-training. Several of the mRNAs corresponding to the upregulated proteins were changed at 3 h but not 24 h. Additionally, a number of other candidates were identified for the first time as modulated by learning. The results presented here suggest that single-trial tasks can expose previously unseen differences in dynamic regulation of gene expression after behavioral manipulations, both at the transcriptional and translational levels, and reveal a diversity of gene products modulated by this task, allowing deeper understanding of the molecular basis of memory formation.
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Affiliation(s)
- Lionel Müller Igaz
- Instituto de Biologia Celular y Neurociencias, Facultad de Medicina, UBA, Paraguay 2155, piso 3, 1121 Buenos Aires, Argentina
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37
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Abstract
Prions cause transmissible and fatal diseases that are associated with spongiform degeneration, astrogliosis, and loss of axon terminals in the brains. To determine the expression of proteins involved in neurosecretion and synaptic functions after prion infection, gonadotropin-releasing hormone neuronal cell line subclone (GT1-1) was infected with the RML scrapie strain and analyzed by Western blotting, real time PCR, and immunohistochemistry. As revealed by Western blotting of lysates exposed to different temperatures, the levels of complexed SNAP-25, syntaxin 1A, and synaptophysin were decreased in scrapie-infected GT1-1 cells (ScGT1-1), whereas the level of monomeric forms of these proteins was increased and correlated to the level of scrapie prion protein (PrPSc). However, when complex formation was prevented by prolonged heating of samples in SDS, the levels of monomeric SNAP-25, syntaxin 1A and synaptophysin in ScGT1-1 cells were decreased in comparison to GT1-1 cells. The reduced level of SNAP-25 was observed as early as 32 days postinfection. Increased mRNA levels of both splice variants SNAP-25a and -b in ScGT1-1 cells were seen. No difference in the morphology, neuritic outgrowth or distribution of SNAP-25, syntaxin 1A, or synaptophysin could be observed in ScGT1-1 cells. Treatment with quinacrine or pentosan polysulfate cleared the PrPSc from the ScGT1-1 cell cultures, and the increase in levels of monomeric SNAP-25 and synaptophysin was reversible. These results indicate that a scrapie infection can cause changes in the expression of proteins involved in neuronal secretion, which may be of pathogenetic relevance for the axon terminal changes seen in prion-infected brains.
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Affiliation(s)
- Malin K Sandberg
- Department of Neuroscience, Karolinska Institutet, Retzius väg 8 B2: 5, Stockholm, S-171 77, Sweden.
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38
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Tsuk S, Michaelevski I, Bentley GN, Joho RH, Chikvashvili D, Lotan I. Kv2.1 channel activation and inactivation is influenced by physical interactions of both syntaxin 1A and the syntaxin 1A/soluble N-ethylmaleimide-sensitive factor-25 (t-SNARE) complex with the C terminus of the channel. Mol Pharmacol 2004; 67:480-8. [PMID: 15525758 DOI: 10.1124/mol.104.005314] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Kv2.1, the prevalent delayed-rectifier K(+) channel in neuroendocrine and endocrine cells, was suggested previously by our group to be modulated in islet beta-cells by syntaxin 1A (Syx) and soluble N-ethylmaleimide-sensitive factor attachment protein-25 (SNAP-25). We also demonstrated physical interactions in neuroendocrine cells between Kv2.1, Syx, and SNAP-25, characterized their effects on Kv2.1 activation and inactivation in Xenopus laevis oocytes, and suggested that they pertain to the assembly/disassembly of the Syx/SNAP-25 (t-SNARE) complex. In the present work, we established the existence of a causal relationship between the physical and the functional interactions of Syx with the Kv2.1 channel using three different peptides that compete with the channel for binding of Syx when injected into oocytes already coexpressing Syx with Kv2.1 in the plasma membrane: one peptide corresponding to the Syx-binding region on the N-type Ca(2+) channel, and two peptides corresponding to Syx-binding regions on the Kv2.1 C terminus. All peptides reversed the effects of Syx on Kv2.1, suggesting that the hyperpolarizing shifts of the steady-state inactivation and activation of Kv2.1 caused by Syx result from cell-surface protein-protein interactions and point to participation of the C terminus in such an interaction. In line with these findings, the effects of Syx were dissipated by partial deletions of the C terminus. Furthermore, the t-SNARE complex was shown to bind to the Kv2.1 C terminus, and its effects on the inactivation of Kv2.1 were dissipated by partial deletions of the C terminus. Taken together, these findings suggest that physical interactions of both Syx and the t-SNARE complex with the C terminus of Kv2.1 are involved in channel regulation.
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Affiliation(s)
- Sharon Tsuk
- Department of Physiology and Pharmacology, Sackler Faculty of Medicine, Tel-Aviv University, 69978 Ramat-Aviv, Israel
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39
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Abstract
Upon Ca2+ influx synaptic vesicles fuse with the plasma membrane and release their neurotransmitter cargo into the synaptic cleft. Key players during this process are the Q-SNAREs syntaxin 1a and SNAP-25 and the R-SNARE synaptobrevin 2. It is thought that these membrane proteins gradually assemble into a tight trans-SNARE complex between vesicular and plasma membrane, ultimately leading to membrane fusion. Tomosyn is a soluble protein of 130 kDa that contains a COOH-terminal R-SNARE motif but lacks a transmembrane anchor. Its R-SNARE motif forms a stable core SNARE complex with syntaxin 1a and SNAP-25. Here we present the crystal structure of this core tomosyn SNARE complex at 2.0-A resolution. It consists of a four-helical bundle very similar to that of the SNARE complex containing synaptobrevin. Most differences are found on the surface, where they prevented tight binding of complexin. Both complexes form with similar rates as assessed by CD spectroscopy. In addition, synaptobrevin cannot displace the tomosyn helix from the tight complex and vice versa, indicating that both SNARE complexes represent end products. Moreover, data bank searches revealed that the R-SNARE motif of tomosyn is highly conserved throughout all eukaryotic kingdoms. This suggests that the formation of a tight SNARE complex is important for the function of tomosyn.
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Affiliation(s)
- Ajaybabu V Pobbati
- Department of Neurobiology, Max-Planck-Institute for Biophysical Chemistry, Am Fassberg 11, 37077 Göttingen, Germany
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40
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Allaman-Pillet N, Roduit R, Oberson A, Abdelli S, Ruiz J, Beckmann JS, Schorderet DF, Bonny C. Circadian regulation of islet genes involved in insulin production and secretion. Mol Cell Endocrinol 2004; 226:59-66. [PMID: 15489006 DOI: 10.1016/j.mce.2004.06.001] [Citation(s) in RCA: 73] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/14/2003] [Revised: 04/14/2004] [Accepted: 06/04/2004] [Indexed: 12/01/2022]
Abstract
Both transcription factors albumin site d-binding protein (DBP) and thyrotroph embryonic factor (TEF) are elements of the "cell-clock". Their circadian accumulation in suprachiasmatic nucleus (SCN) and peripheral tissues such as liver, kidney and lung is thought to participate in controlling circadian regulation of downstream genes. TEF and DBP control elements have never been investigated in the insulin-secreting cells, but impairment of the circadian rhythm of the beta-cells might be involved in the development of diabetic state as type 2 diabetics have lost daily temporal variations of insulin secretion. We investigated the expression pattern of TEF and DBP in insulin-secreting cells. TEF and DBP transcripts are expressed at extremely high levels in human pancreatic islets compared to other tissues, suggesting a potentially important circadian regulation of these cells. Both TEF and DPB accumulate in a circadian way in insulin-secreting cells after a serum shock known to restore circadian rhythms in cultured cells. In addition, the expression of islet-specific genes involved in glucose sensing (glucose transporter 2 (Glut2), glucokinase), insulin production (insulin) and secretion (migration inhibitory factor (MIF), somatostatin and syntaxin 1A) were modulated in the same daily rhythm as well. The circadian deregulation of these genes could therefore participate in the diabetic state development.
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Affiliation(s)
- N Allaman-Pillet
- Service of Medical Genetics and Unit of Molecular Genetics, Centre Hospitalier Universitaire Vaudois (CHUV), CH-1011 Lausanne, Switzerland.
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41
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Cui N, Kang Y, He Y, Leung YM, Xie H, Pasyk EA, Gao X, Sheu L, Hansen JB, Wahl P, Tsushima RG, Gaisano HY. H3 domain of syntaxin 1A inhibits KATP channels by its actions on the sulfonylurea receptor 1 nucleotide-binding folds-1 and -2. J Biol Chem 2004; 279:53259-65. [PMID: 15485808 DOI: 10.1074/jbc.m410171200] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The ATP-sensitive potassium (K(ATP)) channel in pancreatic islet beta cells consists of four pore-forming (Kir6.2) subunits and four regulatory sulfonylurea receptor (SUR1) subunits. In beta cells, the K(ATP) channel links intracellular metabolism to the dynamic regulation of the cell membrane potential that triggers insulin secretion. Syntaxin 1A (Syn-1A) is a SNARE protein that not only plays a direct role in exocytosis, but also binds and modulates voltage-gated K(+) and Ca(2+) channels to fine tune exocytosis. We recently reported that wild type Syn-1A inhibits rat islet beta cell K(ATP) channels and binds both nucleotide-binding folds (NBF-1 and NBF-2) of SUR1. However, wild type Syn-1A inhibition of rat islet beta cell K(ATP) channels seems to be mediated primarily via NBF-1. During exocytosis, Syn-1A undergoes a conformational change from a closed form to an open form, which would fully expose its active domain, the C-terminal H3 domain. Here, we show that the constitutively open form Syn-1A mutant (L165A/E166A) has a similar affinity to NBF-1 and NBF-2 as wild type Syn-1A and was equally effective in inhibiting the K(ATP) channels of rat pancreatic beta cells and a cell line (BA8) stably expressing SUR1/Kir6.2. Although dialysis of NBF-1 into BA8 and islet beta cells effectively blocked wild type and open form Syn-1A inhibition of the K(ATP) current, NBF-2 was also effective in blocking the open form Syn-1A inhibition. This prompted us to examine the specific domains within Syn-1A that would mediate its action on the K(ATP) channels. The C-terminal H3 domain of Syn-1A (Syn-1A-H3), but not the N-terminal H(ABC) domain (Syn-1A-H(ABC)), binds the SUR1 protein of BA8 cells, causing an inhibition of K(ATP) currents, and this inhibition was mediated via both NBF-1 and NBF-2. It therefore appears that the H3 domain of Syn-1A is the putative domain, which binds SUR1, but its distinct actions on the NBFs may depend on the conformation of Syn-1A occurring during exocytosis.
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Affiliation(s)
- Ningren Cui
- Department of Medicine, University of Toronto, Toronto M5S 1A8, Canada
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Marshall C, Hitman GA, Partridge CJ, Clark A, Ma H, Shearer TR, Turner MD. Evidence that an isoform of calpain-10 is a regulator of exocytosis in pancreatic beta-cells. Mol Endocrinol 2004; 19:213-24. [PMID: 15471947 DOI: 10.1210/me.2004-0064] [Citation(s) in RCA: 92] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Calpain-10 (CAPN10) is the first type 2 diabetes susceptibility gene to be identified through a genome scan, with polymorphisms being associated with altered CAPN10 expression. Functional data have been hitherto elusive, but we report here a corresponding increase between CAPN10 expression level and regulated insulin secretion. Pancreatic beta-cell secretory granule exocytosis is mediated by the soluble N-ethylmaleimide-sensitive fusion protein attachment receptor protein complex of synaptosomal-associated protein of 25 kDa (SNAP-25), syntaxin 1, and vesicle-associated membrane protein 2. We report, for the first time, direct binding of a calpain-10 isoform with members of this complex. Furthermore, SNAP-25 undergoes a Ca2+-dependent partial proteolysis during exocytosis, with calpain protease inhibitor similarly suppressing both insulin secretion and SNAP-25 proteolysis. Based upon these findings, we postulate that an isoform of calpain-10 is a Ca2+-sensor that functions to trigger exocytosis in pancreatic beta-cells.
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Affiliation(s)
- Catriona Marshall
- Centre for Diabetes and Metabolic Medicine, Institute of Cell and Molecular Science, Barts and The London, Queen Mary's School of Medicine and Dentistry, University of London, Whitechapel, London E1 1BB, United Kingdom
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Abstract
SV2 proteins are abundant synaptic vesicle proteins expressed in two major (SV2A and SV2B) and one minor (SV2C) isoform. SV2A and SV2B have been shown to be involved in the regulation of synaptic vesicle exocytosis. Previous studies found that SV2A, but not SV2B, can interact with the cytoplasmic domain of synaptotagmin 1, a Ca2+ sensor for synaptic vesicle exocytosis. To determine whether SV2B can interact with full-length synaptotagmin 1, we performed immunoprecipitations from brain protein extracts and found that SV2B interacts strongly with synaptotagmin 1 in a detergent-resistant, Ca2+ -independent manner. In contrast, an interaction between native SV2A and synaptotagmin 1 was not detectable under these conditions. The SV2B-synaptotagmin 1 complex also contained the synaptic t-SNARE proteins, syntaxin 1 and SNAP-25, suggesting that SV2B may participate in exocytosis by modulating the interaction of synaptotagmin 1 with t-SNARE proteins. Analysis of retinae in SV2B knock-out mice revealed a strong reduction in the level of synaptotagmin 1 in rod photoreceptor synapses, which are unique in that they express only the SV2B isoform. In contrast, other synaptic vesicle proteins were not affected by SV2B knock out, indicating a specific role for SV2B in the regulation of synaptotagmin 1 levels at certain synapses. These experiments suggest that the SV2B-synaptotagmin 1 complex is involved in the regulation of synaptotagmin 1 stability and/or trafficking. This study has demonstrated a new role of SV2B as a regulator of synaptotagmin 1 that is likely mediated by direct interaction of these two synaptic proteins.
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Affiliation(s)
- Diana R Lazzell
- WM Keck Center for Learning and Memory, Department of Neurobiology and Anatomy, University of Texas Medical School, Houston, Texas 77030, USA
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Su Q, Cai Q, Gerwin C, Smith CL, Sheng ZH. Syntabulin is a microtubule-associated protein implicated in syntaxin transport in neurons. Nat Cell Biol 2004; 6:941-53. [PMID: 15459722 DOI: 10.1038/ncb1169] [Citation(s) in RCA: 118] [Impact Index Per Article: 5.9] [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: 06/01/2004] [Accepted: 08/11/2004] [Indexed: 11/09/2022]
Abstract
Different types of cargo vesicles containing presynaptic proteins are transported from the nerve cell body to the nerve terminal, and participate in the formation of active zones. However, the identity of the membranous cargoes and the nature of the motor-cargo interactions remain unsolved. Here, we report the identification of a syntaxin-1-binding protein named syntabulin. Syntabulin attaches syntaxin-containing vesicles to microtubules and migrates with syntaxin within the processes of hippocampal neurons. Knock-down of syntabulin expression with targeted small interfering RNAs (siRNAs) or interference with the syntabulin-syntaxin interaction inhibit attachment of syntaxin-cargo vesicles to microtubules and reduce syntaxin-1 distribution in neuronal processes. Furthermore, conventional kinesin I heavy chain binds to syntabulin and associates with syntabulin-linked syntaxin vesicles in vivo. These findings suggest that syntabulin functions as a linker molecule that attaches syntaxin-cargo vesicles to kinesin I, enabling the transport of syntaxin-1 to neuronal processes.
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Affiliation(s)
- Qingning Su
- Synaptic Function Unit, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Building 35, Room 3B203, MSC 3701, 35 Convent Drive, Bethesda, MD 20892-3701, USA
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Abstract
At presynaptic terminals, intermixing during cycles of exocytosis and endocytosis challenges the molecular identity of the plasma and synaptic vesicle membranes. Although synaptic vesicle components are retrieved during recycling, the extent to which plasma membrane proteins enter the synaptic vesicle recycling pathway has not been examined. The target-SNARE (N-ethylmaleimide-sensitive factor attachment protein receptor) syntaxin-1 was shown previously to be present on putative synaptic vesicular membranes (Koh et al., 1993; Walch-Solimena et al., 1995; Kretzschmar et al., 1996), suggesting that syntaxin may cycle between the synaptic vesicle pool and the cell surface (Walch-Solimena et al., 1995). This implies that the molecular identity of the two membranes is not maintained during synaptic activity. Because the main role of syntaxin-1 is as a target-SNARE for vesicle fusion, appearance on synaptic vesicles could lead to futile interactions with vesicle-SNARE proteins. We investigated whether the subcellular localization of syntaxin-1A, tagged with the pH-sensitive fluorescent tag pHluorin, is regulated during neurotransmission using laser-scanning microscopy. We report here that syntaxin-1A is predominantly localized to the plasma membrane, with a small proportion present in an intracellular compartment with a lumenal pH consistent with synaptic vesicles. However, the internal fraction of syntaxin-1A is excluded from synaptic vesicles that undergo action potential-dependent recycling. These data indicate that the molecular identity of opposing exocytotic membranes is preserved by the sorting of syntaxin-1A from recycling synaptic vesicles.
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Affiliation(s)
- Simon J Mitchell
- Department of Biochemistry, Weill Medical College of Cornell University, New York, New York 10021, USA
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Kang Y, Leung YM, Manning-Fox JE, Xia F, Xie H, Sheu L, Tsushima RG, Light PE, Gaisano HY. Syntaxin-1A inhibits cardiac KATP channels by its actions on nucleotide binding folds 1 and 2 of sulfonylurea receptor 2A. J Biol Chem 2004; 279:47125-31. [PMID: 15339904 DOI: 10.1074/jbc.m404954200] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
ATP-sensitive potassium (KATP) channels couple the metabolic status of the cell to its membrane potential to regulate a number of cell actions, including secretion (neurons and neuroendocrine cells) and muscle contractility (skeletal, cardiac, and vascular smooth muscle). KATP channels consist of regulatory sulfonylurea receptors (SUR) and pore-forming (Kir6.X) subunits. We recently reported (Pasyk, E. A., Kang, Y., Huang, X., Cui, N., Sheu, L., and Gaisano, H. Y. (2004) J. Biol. Chem. 279, 4234-4240) that syntaxin-1A (Syn-1A), known to mediate exocytotic fusion, was capable of binding the nucleotide binding folds (NBF1 and C-terminal NBF2) of SUR1 to inhibit the KATP channels in insulin-secreting pancreatic islet beta cells. This prompted us to examine whether Syn-1A might modulate cardiac SUR2A/KATP channels. Here, we show that Syn-1A is present in the plasma membrane of rat cardiac myocytes and binds the SUR2A protein (of rat brain, heart, and human embryonic kidney 293 cells expressing SUR2A/Kir6. 2) at its NBF1 and NBF2 domains to decrease KATP channel activation. Unlike islet beta cells, in which Syn-1A inhibition of the channel activity was apparently mediated only via NBF1 and not NBF2 of SUR1, both exogenous recombinant NBF1 and NBF2 of SUR2A were found to abolish the inhibitory actions of Syn-1A on K(ATP) channels in rat cardiac myocytes and HEK293 cells expressing SUR2A/Kir6.2. Together with our recent report, this study suggests that Syn-1A binds both NBFs of SUR1 and SUR2A but appears to exhibit distinct interactions with NBF2 of these SUR proteins in modulating the KATP channels in islet beta cells and cardiac myocytes.
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MESH Headings
- ATP-Binding Cassette Transporters/chemistry
- ATP-Binding Cassette Transporters/metabolism
- Adenosine Triphosphate/chemistry
- Animals
- Antigens, Surface/biosynthesis
- Antigens, Surface/physiology
- Blotting, Western
- Brain/metabolism
- Cell Line
- Cell Membrane/metabolism
- Dose-Response Relationship, Drug
- Glutathione Transferase/metabolism
- Humans
- Islets of Langerhans/metabolism
- Male
- Microscopy, Confocal
- Myocardium/metabolism
- Myocytes, Cardiac/metabolism
- Nerve Tissue Proteins/biosynthesis
- Nerve Tissue Proteins/physiology
- Potassium Channels/chemistry
- Potassium Channels/metabolism
- Potassium Channels, Inwardly Rectifying/chemistry
- Potassium Channels, Inwardly Rectifying/metabolism
- Protein Binding
- Protein Folding
- Protein Structure, Tertiary
- Rats
- Rats, Sprague-Dawley
- Receptors, Drug/chemistry
- Receptors, Drug/metabolism
- Sulfonylurea Receptors
- Syntaxin 1
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Affiliation(s)
- Youhou Kang
- Department of Medicine, University of Toronto, Toronto M5S 1A8, Canada
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Sakisaka T, Baba T, Tanaka S, Izumi G, Yasumi M, Takai Y. Regulation of SNAREs by tomosyn and ROCK: implication in extension and retraction of neurites. ACTA ACUST UNITED AC 2004; 166:17-25. [PMID: 15240567 PMCID: PMC2172130 DOI: 10.1083/jcb.200405002] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.2] [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] [Indexed: 11/22/2022]
Abstract
Extension of neurites requires the SNARE-dependent fusion of plasmalemmal precursor vesicles with the plasma membrane of growth cones. Here, we show that tomosyn localizes at the palm of growth cones and inhibits the fusion of the vesicles there, thus promoting transport of the vesicles to the plasma membrane of the leading edges of growth cones. Tomosyn localizes because ROCK activated by Rho small G protein phosphorylates syntaxin-1, which increases the affinity of syntaxin-1 for tomosyn and forms a stable complex with tomosyn, resulting in inhibition of the formation of the SNARE complex. In retraction of neurites, tomosyn localizes all over the edges of the neurites and inhibits fusion of the vesicles with the plasma membrane. Thus, tomosyn demarcates the plasma membrane by binding to syntaxin-1 phosphorylated by ROCK, and thereby regulates extension and retraction of neurites.
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Affiliation(s)
- Toshiaki Sakisaka
- Department of Molecular Biology and Biochemistry, Osaka University Graduate School of Medicine/Faculty of Medicine, Suita, 565-0871, Japan
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Abstract
N- and P/Q-type Ca2+ channels are abundant in nerve terminals where they interact with proteins of the release apparatus, including syntaxin 1A and SNAP-25. In previous studies on N- or P/Q-type Ca2+ channels, syntaxin 1A co-expression reduced current amplitudes, increased voltage-dependent inactivation and/or enhanced G-protein inhibition. However, these studies were conducted in Ca2+ channels that exhibited significant voltage-dependent inactivation. We previously reported that N-type current in bovine chromaffin cells exhibits very little voltage-dependent inactivation and we identified the Ca2+ channel subunits involved. This study was undertaken to determine the effect of syntaxin 1A on this weakly inactivating Ca2+ channel. Co-expression of syntaxin 1A with the weakly inactivating bovine N-type Ca2+ channels in Xenopus oocytes did not appear to alter inactivation but dramatically reduced current amplitudes, without changing cell surface expression. To further understand the mechanisms of syntaxin 1A regulation of this weakly inactivating channel, we examined mutants of the alpha1B subunit, beta2a subunit and syntaxin 1A. We determined that the synprint site of alpha1B and the C-terminal third of syntaxin 1A were necessary for the reduced current amplitude. In addition we show that enhanced G-protein-dependent modulation of the Ca2+ current by syntaxin 1A cannot explain the large suppression of Ca2+ current observed. Of most significance, syntaxin 1A increased voltage-dependent inactivation in channels containing mutant beta2a subunits that cannot be palmitoylated. Our data suggest that changes in inactivation can not explain the reduction in current amplitude produced by co-expressing syntaxin and a weakly inactivating Ca2+ channel.
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Affiliation(s)
- Joyce H Hurley
- Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, IN 46202, USA.
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Abstract
Cleavage of amyloid-beta precursor protein (APP) by alpha-,beta-, and gamma-secretases releases an extracellular fragment called APPS, small Abeta peptides, and a short APP intracellular domain that may provide a transcriptional signal analogous to the Notch intracellular domain. Notch cleavage is activated by extracellular ligands on the cell surface, but the cellular localization of APP cleavage remains unclear. We now show that in transfected cultured cells, the plasma membrane SNARE protein syntaxin 1A, when expressed as a full-length protein, disrupts the Golgi apparatus and blocks trans-Golgi traffic and exocytosis. In contrast, truncated syntaxin 1A1-243 selectively abolishes exocytosis but has no apparent effect on trans-Golgi traffic or Golgi structure, whereas further truncated syntaxins 1A1-236 and 1A1-230 have no effect on either exocytosis or Golgi traffic. Using these syntaxin 1A fragments, we demonstrated that blocking trans-Golgi traffic greatly impairs APP cleavage and AICD-dependent nuclear signaling, whereas blocking exocytosis alone does not affect either process, even though secretion of APPS and Abeta40 peptide is abolished. Our data suggest that, different from Notch, cleavage of APP is independent of cell surface regulation by extracellular ligands but may be controlled by intracellular signaling.
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Affiliation(s)
- Mikhail Khvotchev
- Center for Basic Neuroscience, Department of Molecular Genetics, and Howard Hughes Medical Institute, The University of Texas Southwestern Medical Center, Dallas, Texas 75390-9111, USA
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Li Q, Lau A, Morris TJ, Guo L, Fordyce CB, Stanley EF. A syntaxin 1, Galpha(o), and N-type calcium channel complex at a presynaptic nerve terminal: analysis by quantitative immunocolocalization. J Neurosci 2004; 24:4070-81. [PMID: 15102922 PMCID: PMC6729428 DOI: 10.1523/jneurosci.0346-04.2004] [Citation(s) in RCA: 576] [Impact Index Per Article: 28.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Presynaptic Ca(V)2.2 (N-type) calcium channels are subject to modulation by interaction with syntaxin 1 and by a syntaxin 1-sensitive Galpha(O) G-protein pathway. We used biochemical analysis of neuronal tissue lysates and a new quantitative test of colocalization by intensity correlation analysis at the giant calyx-type presynaptic terminal of the chick ciliary ganglion to explore the association of Ca(V)2.2 with syntaxin 1 and Galpha(O). Ca(V)2.2 could be localized by immunocytochemistry (antibody Ab571) in puncta on the release site aspect of the presynaptic terminal and close to synaptic vesicle clouds. Syntaxin 1 coimmunoprecipitated with Ca(V)2.2 from chick brain and chick ciliary ganglia and was widely distributed on the presynaptic terminal membrane. A fraction of the total syntaxin 1 colocalized with the Ca(V)2.2 puncta, whereas the bulk colocalized with MUNC18-1. Galpha(O,) whether in its trimeric or monomeric state, did not coimmunoprecipitate with Ca(V)2.2, MUNC18-1, or syntaxin 1. However, the G-protein exhibited a punctate staining on the calyx membrane with an intensity that varied in synchrony with that for both Ca channels and syntaxin 1 but only weakly with MUNC18-1. Thus, syntaxin 1 appears to be a component of two separate complexes at the presynaptic terminal, a minor one at the transmitter release site with Ca(V)2.2 and Galpha(O), as well as in large clusters remote from the release site with MUNC18-1. These syntaxin 1 protein complexes may play distinct roles in presynaptic biology.
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Affiliation(s)
- Qi Li
- Cellular and Molecular Biology Division, Toronto Western Research Institute, University Health Network, Toronto, Ontario, M5T 2S8 Canada
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