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Trus M, Atlas D. Non-ionotropic voltage-gated calcium channel signaling. Channels (Austin) 2024; 18:2341077. [PMID: 38601983 PMCID: PMC11017947 DOI: 10.1080/19336950.2024.2341077] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2024] [Accepted: 04/04/2024] [Indexed: 04/12/2024] Open
Abstract
Voltage-gated calcium channels (VGCCs) are the major conduits for calcium ions (Ca2+) within excitable cells. Recent studies have highlighted the non-ionotropic functionality of VGCCs, revealing their capacity to activate intracellular pathways independently of ion flow. This non-ionotropic signaling mode plays a pivotal role in excitation-coupling processes, including gene transcription through excitation-transcription (ET), synaptic transmission via excitation-secretion (ES), and cardiac contraction through excitation-contraction (EC). However, it is noteworthy that these excitation-coupling processes require extracellular calcium (Ca2+) and Ca2+ occupancy of the channel ion pore. Analogous to the "non-canonical" characterization of the non-ionotropic signaling exhibited by the N-methyl-D-aspartate receptor (NMDA), which requires extracellular Ca2+ without the influx of ions, VGCC activation requires depolarization-triggered conformational change(s) concomitant with Ca2+ binding to the open channel. Here, we discuss the contributions of VGCCs to ES, ET, and EC coupling as Ca2+ binding macromolecules that transduces external stimuli to intracellular input prior to elevating intracellular Ca2+. We emphasize the recognition of calcium ion occupancy within the open ion-pore and its contribution to the excitation coupling processes that precede the influx of calcium. The non-ionotropic activation of VGCCs, triggered by the upstroke of an action potential, provides a conceptual framework to elucidate the mechanistic aspects underlying the microseconds nature of synaptic transmission, cardiac contractility, and the rapid induction of first-wave genes.
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Affiliation(s)
- Michael Trus
- Department of Biological Chemistry, Institute of Life Sciences, The Hebrew University of Jerusalem, Jerusalem, Israel
| | - Daphne Atlas
- Department of Biological Chemistry, Institute of Life Sciences, The Hebrew University of Jerusalem, Jerusalem, Israel
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Chen Y, Ning J, Shu L, Wen L, Yan B, Wang Z, Hu J, Zhou X, Tao Y, Xia X, Huang J. CPLX2 is a novel tumor suppressor and improves the prognosis in glioma. J Neurooncol 2024; 167:63-74. [PMID: 38427133 DOI: 10.1007/s11060-023-04548-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2023] [Accepted: 12/16/2023] [Indexed: 03/02/2024]
Abstract
BACKGROUND Glioma is a type of malignant cancer that affect the central nervous system. New predictive biomarkers have been investigated in recent years, but the clinical prognosis for glioma remains poor. The function of CPLX2 in glioma and the probable molecular mechanism of tumor suppression were the focus of this investigation. METHODS The glioma transcriptome profile was downloaded from The Cancer Genome Atlas (TCGA) and Chinese Glioma Genome Atlas (CGGA) databases for analysis of CPLX2 expression in glioma. RT-qPCR was performed to detect the expression of CPLX2 in 68 glioma subjects who have been followed up. Kaplan-Meier survival analyses were conducted to assess the effect of CPLX2 on the prognosis of glioma patients. The knockdown and overexpressed cell lines of CPLX2 were constructed to investigate the impact of CPLX2 on glioma. The cell growth, colony formation, and tumor formation in xenograft were performed. RESULTS The expression of CPLX2 was downregulated in glioma and was negatively correlated with the grade of glioma. The higher expression of CPLX2 predicted a longer survival, as indicated by the analysis of Kaplan-Meier survival curves. Overexpressed CPLX2 impaired tumorigenesis in glioma progression both in vivo and in vitro. Knocking down CPLX2 promoted the proliferation of glioma cells. The analysis of GSEA and co-expression analysis revealed that CPLX2 may affect the malignancy of glioma by regulating the hypoxia and inflammation pathways. CONCLUSIONS Our data indicated that CPLX2 functions as a tumor suppressor and could be used as a potential prognostic marker in glioma.
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Affiliation(s)
- Yuanbing Chen
- Department of Neurosurgery, Third Xiangya Hospital, Central South University, 410008, Changsha, Hunan, China
| | - Jieling Ning
- National Clinical Research Center for Geriatric Disorders, Xiangya Hospital, Central South University, 410008, Changsha, Hunan, China
- Department of Dermatology, Xiangya Hospital, Central South University, 410008, Changsha, Hunan, China
| | - Long Shu
- Key Laboratory of Carcinogenesis and Cancer Invasion, Ministry of Education, Department of Pathology, Xiangya Hospital, Central South University, 410078, Changsha, Hunan, China
- NHC Key Laboratory of Carcinogenesis (Central South University), Cancer Research Institute and School of Basic Medicine, Central South University, 410078, Changsha, Hunan, China
| | - Lingzhi Wen
- Key Laboratory of Carcinogenesis and Cancer Invasion, Ministry of Education, Department of Pathology, Xiangya Hospital, Central South University, 410078, Changsha, Hunan, China
- NHC Key Laboratory of Carcinogenesis (Central South University), Cancer Research Institute and School of Basic Medicine, Central South University, 410078, Changsha, Hunan, China
| | - Bokang Yan
- Key Laboratory of Carcinogenesis and Cancer Invasion, Ministry of Education, Department of Pathology, Xiangya Hospital, Central South University, 410078, Changsha, Hunan, China
- NHC Key Laboratory of Carcinogenesis (Central South University), Cancer Research Institute and School of Basic Medicine, Central South University, 410078, Changsha, Hunan, China
| | - Zuli Wang
- Key Laboratory of Carcinogenesis and Cancer Invasion, Ministry of Education, Department of Pathology, Xiangya Hospital, Central South University, 410078, Changsha, Hunan, China
- NHC Key Laboratory of Carcinogenesis (Central South University), Cancer Research Institute and School of Basic Medicine, Central South University, 410078, Changsha, Hunan, China
| | - Junhong Hu
- Department of Neurosurgery, Affiliated Hospital of Guilin Medical University, Guilin, Guangxi, China
| | - Xiaokun Zhou
- Department of Neurosurgery, Affiliated Hospital of Guilin Medical University, Guilin, Guangxi, China
| | - Yongguang Tao
- Key Laboratory of Carcinogenesis and Cancer Invasion, Ministry of Education, Department of Pathology, Xiangya Hospital, Central South University, 410078, Changsha, Hunan, China
- NHC Key Laboratory of Carcinogenesis (Central South University), Cancer Research Institute and School of Basic Medicine, Central South University, 410078, Changsha, Hunan, China
| | - Xuewei Xia
- Department of Neurosurgery, Affiliated Hospital of Guilin Medical University, Guilin, Guangxi, China.
| | - Jun Huang
- National Clinical Research Center for Geriatric Disorders, Xiangya Hospital, Central South University, 410008, Changsha, Hunan, China.
- Department of Neurosurgery, Xiangya Hospital, Central South University, 410008, Changsha, Hunan, China.
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Palfreyman MT, West SE, Jorgensen EM. SNARE Proteins in Synaptic Vesicle Fusion. ADVANCES IN NEUROBIOLOGY 2023; 33:63-118. [PMID: 37615864 DOI: 10.1007/978-3-031-34229-5_4] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 08/25/2023]
Abstract
Neurotransmitters are stored in small membrane-bound vesicles at synapses; a subset of synaptic vesicles is docked at release sites. Fusion of docked vesicles with the plasma membrane releases neurotransmitters. Membrane fusion at synapses, as well as all trafficking steps of the secretory pathway, is mediated by SNARE proteins. The SNAREs are the minimal fusion machinery. They zipper from N-termini to membrane-anchored C-termini to form a 4-helix bundle that forces the apposed membranes to fuse. At synapses, the SNAREs comprise a single helix from syntaxin and synaptobrevin; SNAP-25 contributes the other two helices to complete the bundle. Unc13 mediates synaptic vesicle docking and converts syntaxin into the permissive "open" configuration. The SM protein, Unc18, is required to initiate and proofread SNARE assembly. The SNAREs are then held in a half-zippered state by synaptotagmin and complexin. Calcium removes the synaptotagmin and complexin block, and the SNAREs drive vesicle fusion. After fusion, NSF and alpha-SNAP unwind the SNAREs and thereby recharge the system for further rounds of fusion. In this chapter, we will describe the discovery of the SNAREs, their relevant structural features, models for their function, and the central role of Unc18. In addition, we will touch upon the regulation of SNARE complex formation by Unc13, complexin, and synaptotagmin.
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Affiliation(s)
- Mark T Palfreyman
- School of Biological Sciences, and Howard Hughes Medical Institute, University of Utah, Salt Lake City, UT, USA
| | - Sam E West
- School of Biological Sciences, and Howard Hughes Medical Institute, University of Utah, Salt Lake City, UT, USA
| | - Erik M Jorgensen
- School of Biological Sciences, and Howard Hughes Medical Institute, University of Utah, Salt Lake City, UT, USA.
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4
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Atlas D. Revisiting the molecular basis of synaptic transmission. Prog Neurobiol 2022; 216:102312. [PMID: 35760141 DOI: 10.1016/j.pneurobio.2022.102312] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2022] [Revised: 06/12/2022] [Accepted: 06/20/2022] [Indexed: 10/17/2022]
Abstract
Measurements of the time elapsed during synaptic transmission has shown that synaptic vesicle (SV) fusion lags behind Ca2+-influx by approximately 60 microseconds (µsec). The conventional model cannot explain this extreme rapidity of the release event. Synaptic transmission occurs at the active zone (AZ), which comprises of two pools of SV, non-releasable "tethered" vesicles, and a readily-releasable pool of channel-associated Ca2+-primed vesicles, "RRP". A recent TIRF study at cerebellar-mossy fiber-terminal, showed that subsequent to an action potential, newly "tethered" vesicles, became fusion-competent in a Ca2+-dependent manner, 300-400 milliseconds after tethering, but were not fused. This time resolution may correspond to priming of tethered vesicles through Ca2+-binding to Syt1/Munc13-1/complexin. It confirms that Ca2+-priming and Ca2+-influx-independent fusion, are two distinct events. Notably, we have established that Ca2+ channel signals evoked-release in an ion flux-independent manner, demonstrated by Ca2+-impermeable channel, or a Ca2+ channel in which Ca2+ is replaced by impermeable La3+. Thus, conformational changes in a channel coupled to RRP appear to directly activate the release machinery and account for a µsec Ca2+-influx-independent vesicle fusion. Rapid vesicle fusion driven by non-ionotropic channel signaling strengthens a conformational-coupling mechanism of synaptic transmission, and contributes to better understanding of neuronal communication vital for brain function.
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Affiliation(s)
- Daphne Atlas
- Dept. of Biological Chemistry, Institute of Life Sciences, The Hebrew University of Jerusalem, Jerusalem, 91904 Israel.
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Abstract
α-Synuclein (α-synFL) is central to the pathogenesis of Parkinson's disease (PD), in which its nonfunctional oligomers accumulate and result in abnormal neurotransmission. The normal physiological function of this intrinsically disordered protein is still unclear. Although several previous studies demonstrated α-synFL's role in various membrane fusion steps, they produced conflicting outcomes regarding vesicular secretion. Here, we assess α-synFL's role in directly regulating individual exocytotic release events. We studied the micromillisecond dynamics of single recombinant fusion pores, the crucial kinetic intermediate of membrane fusion that tightly regulates the vesicular secretion in different cell types. α-SynFL accessed v-SNARE within the trans-SNARE complex to form an inhibitory complex. This activity was dependent on negatively charged phospholipids and resulted in decreased open probability of individual pores. The number of trans-SNARE complexes influenced α-synFL's inhibitory action. Regulatory factors that arrest SNARE complexes in different assembly states differentially modulate α-synFL's ability to alter fusion pore dynamics. α-SynFL regulates pore properties in the presence of Munc13-1 and Munc18, which stimulate α-SNAP/NSF-resistant SNARE complex formation. In the presence of synaptotagmin1(syt1), α-synFL contributes with apo-syt1 to act as a membrane fusion clamp, whereas Ca2+•syt1 triggered α-synFL-resistant SNARE complex formation that rendered α-synFL inactive in modulating pore properties. This study reveals a key role of α-synFL in controlling vesicular secretion.
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Complexin Suppresses Spontaneous Exocytosis by Capturing the Membrane-Proximal Regions of VAMP2 and SNAP25. Cell Rep 2021; 32:107926. [PMID: 32698012 PMCID: PMC7116205 DOI: 10.1016/j.celrep.2020.107926] [Citation(s) in RCA: 27] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2019] [Revised: 02/28/2020] [Accepted: 06/26/2020] [Indexed: 01/29/2023] Open
Abstract
The neuronal protein complexin contains multiple domains that exert clamping and facilitatory functions to tune spontaneous and action potential-triggered synaptic release. We address the clamping mechanism and show that the accessory helix of complexin arrests assembly of the soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complex that forms the core machinery of intracellular membrane fusion. In a reconstituted fusion assay, site-and stage-specific photo-cross-linking reveals that, prior to fusion, the complexin accessory helix laterally binds the membrane-proximal C-terminal ends of SNAP25 and VAMP2. Corresponding complexin interface mutants selectively increase spontaneous release of neuro-transmitters in living neurons, implying that the accessory helix suppresses final zippering/assembly of the SNARE four-helix bundle by restraining VAMP2 and SNAP25.
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Xu Y, Zhao XM, Liu J, Wang YY, Xiong LL, He XY, Wang TH. Complexin I knockout rats exhibit a complex neurobehavioral phenotype including profound ataxia and marked deficits in lifespan. Pflugers Arch 2019; 472:117-133. [PMID: 31875236 DOI: 10.1007/s00424-019-02337-5] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2019] [Revised: 11/27/2019] [Accepted: 11/28/2019] [Indexed: 02/07/2023]
Abstract
Complexin I (CPLX1), a presynaptic small molecule protein, forms SNARE complex in the central nervous system involved in the anchoring, pre-excitation, and fusion of axonal end vesicles. Abnormal expression of CPLX1 occurs in several neurodegenerative and psychiatric disorders that exhibit disrupted neurobehaviors. CPLX1 gene knockout induces severe ataxia and social behavioral deficits in mice, which has been poorly demonstrated. Here, to address the limitations of single-species models and to provide translational insights relevant to human diseases, we used CPLX1 knockout rats to further explore the function of the CPLX1 gene. The CRISPR/Cas9 gene editing system was adopted to generate CPLX1 knockout rats (CPLX1-/-). Then, we characterized the survival rate and behavioral phenotype of CPLX1-/- rats using behavioral analysis. To further explain this phenomenon, we performed blood glucose testing, Nissl staining, hematoxylin-eosin staining, and Golgi staining. We found that CPLX1-/- rats showed profound ataxia, dystonia, movement and exploratory deficits, and increased anxiety and sensory deficits but had normal cognitive function. Nevertheless, CPLX1-/- rats could swim without training. The abnormal histomorphology of the stomach and intestine were related to decreased weight and early death in these rats. Decreased dendritic branching was also found in spinal motor neurons in CPLX1-/- rats. In conclusion, CPLX1 gene knockout induced the abnormal histomorphology of the stomach and intestine and decreased dendritic branching in spinal motor neurons, causing different phenotypes between CPLX1-/- rats and mice, even though both of these phenotypes showed profound ataxia. These findings provide a new perspective for understanding the role of CPLX1.
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Affiliation(s)
- Yang Xu
- Institute of Neurological Disease, Department of Anesthesiology, Translational Neuroscience Center, West China Hospital, Sichuan University & The Research Units of West China, Chinese Academy of Medical Sciences, Chengdu, 610041, China
| | - Xiao-Ming Zhao
- Institute of Neurological Disease, Department of Anesthesiology, Translational Neuroscience Center, West China Hospital, Sichuan University & The Research Units of West China, Chinese Academy of Medical Sciences, Chengdu, 610041, China.,Department of Basic Medicine, Medical School, Kunming University of Science and Technology, Kunming, 650500, China
| | - Jia Liu
- Institute of Neuroscience, Laboratory Zoology Department, Kunming Medical University, Kunming, 650500, China
| | - Yang-Yang Wang
- Institute of Neurological Disease, Department of Anesthesiology, Translational Neuroscience Center, West China Hospital, Sichuan University & The Research Units of West China, Chinese Academy of Medical Sciences, Chengdu, 610041, China
| | - Liu-Lin Xiong
- Institute of Neurological Disease, Department of Anesthesiology, Translational Neuroscience Center, West China Hospital, Sichuan University & The Research Units of West China, Chinese Academy of Medical Sciences, Chengdu, 610041, China
| | - Xiu-Ying He
- Institute of Neurological Disease, Department of Anesthesiology, Translational Neuroscience Center, West China Hospital, Sichuan University & The Research Units of West China, Chinese Academy of Medical Sciences, Chengdu, 610041, China
| | - Ting-Hua Wang
- Institute of Neurological Disease, Department of Anesthesiology, Translational Neuroscience Center, West China Hospital, Sichuan University & The Research Units of West China, Chinese Academy of Medical Sciences, Chengdu, 610041, China. .,Institute of Neuroscience, Laboratory Zoology Department, Kunming Medical University, Kunming, 650500, China.
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8
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Dynamic Light Scattering Analysis to Dissect Intermediates of SNARE-Mediated Membrane Fusion. Methods Mol Biol 2018. [PMID: 30317498 DOI: 10.1007/978-1-4939-8760-3_4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
Abstract
Dynamic light scattering (DLS) spectroscopy provides rapid information on the size distribution of a large number of particles in a mixture. Vesicle sizes change during the merger of lipid bilayers, and DLS analysis can provide rapid, accurate, and non-perturbative quantification of the size distribution of proteoliposomes in SNARE-dependent membrane fusion. In this chapter, we describe the methodologies and reagents used for DLS spectroscopy in a biochemical and biophysical study of SNARE-mediated membrane fusion.
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Ramos-Miguel A, Jones AA, Sawada K, Barr AM, Bayer TA, Falkai P, Leurgans SE, Schneider JA, Bennett DA, Honer WG. Frontotemporal dysregulation of the SNARE protein interactome is associated with faster cognitive decline in old age. Neurobiol Dis 2018; 114:31-44. [PMID: 29496544 PMCID: PMC6483375 DOI: 10.1016/j.nbd.2018.02.006] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2017] [Revised: 02/07/2018] [Accepted: 02/21/2018] [Indexed: 12/29/2022] Open
Abstract
The molecular underpinnings associated with cognitive reserve remain poorly understood. Because animal models fail to fully recapitulate the complexity of human brain aging, postmortem studies from well-designed cohorts are crucial to unmask mechanisms conferring cognitive resistance against cumulative neuropathologies. We tested the hypothesis that functionality of the SNARE protein interactome might be an important resilience factor preserving cognitive abilities in old age. Cognition was assessed annually in participants from the Rush "Memory and Aging Project" (MAP), a community-dwelling cohort representative of the overall aging population. Associations between cognition and postmortem neurochemical data were evaluated in functional assays quantifying various species of the SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) machinery in samples from the inferior temporal (IT, n = 154) and middle-frontal (MF, n = 174) gyri. Using blue-native gel electrophoresis, we isolated and quantified several types of complexes containing the three SNARE proteins (syntaxin-1, SNAP25, VAMP), as well as the GABAergic/glutamatergic selectively expressed complexins-I/II (CPLX1/2), in brain tissue homogenates and reconstitution assays with recombinant proteins. Multivariate analyses revealed significant associations between IT and MF neurochemical data (SNARE proteins and/or complexes), and multiple age-related neuropathologies, as well as with multiple cognitive domains of MAP participants. Controlling for demographic variables, neuropathologic indices and total synapse density, we found that temporal 150-kDa SNARE species (representative of pan-synaptic functionality) and frontal CPLX1/CPLX2 ratio of 500-kDa heteromeric species (representative of inhibitory/excitatory input functionality) were, among all the immunocharacterized complexes, the strongest predictors of cognitive function nearest death. Interestingly, these two neurochemical variables were associated with different cognitive domains. In addition, linear mixed effect models of global cognitive decline estimated that both 150-kDa SNARE levels and CPLX1/CPLX2 ratio were associated with better cognition and less decline over time. The results are consistent with previous studies reporting that synapse dysfunction (i.e. dysplasticity) may be initiated early, and relatively independent of neuropathology-driven synapse loss. Frontotemporal dysregulation of the GABAergic/glutamatergic stimuli might be a target for future drug development.
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Affiliation(s)
- Alfredo Ramos-Miguel
- BC Mental Health and Addictions Research Institute, 938 West 28th Avenue, Vancouver, BC V5Z 4H4, Canada; Department of Psychiatry, University of British Columbia, 2255 Wesbrook Mall, Vancouver, BC, V6T 2A1, Canada
| | - Andrea A Jones
- BC Mental Health and Addictions Research Institute, 938 West 28th Avenue, Vancouver, BC V5Z 4H4, Canada; Department of Psychiatry, University of British Columbia, 2255 Wesbrook Mall, Vancouver, BC, V6T 2A1, Canada
| | - Ken Sawada
- Kochi Medical School, Kohasu, Oko-cho, Nankoku, Kochi 783-8505, Japan
| | - Alasdair M Barr
- BC Mental Health and Addictions Research Institute, 938 West 28th Avenue, Vancouver, BC V5Z 4H4, Canada; Department of Anesthesiology, Pharmacology and Therapeutics, University of British Columbia, 2176 Health Sciences Mall, Vancouver, BC V6T 1Z3, Canada
| | - Thomas A Bayer
- Department of Psychiatry, University Medicine Goettingen, von-Siebold-Strasse 5, D-37075 Goettingen, Germany
| | - Peter Falkai
- Department of Psychiatry and Psychotherapy, Ludwig-Maximilians-University Munich, Nussbaumstrasse 7, D-80336 Munich, Germany
| | - Sue E Leurgans
- Rush Alzheimer's disease Center, Rush University Medical Center, 600 S. Paulina Street, Chicago, IL 60612, United States
| | - Julie A Schneider
- Rush Alzheimer's disease Center, Rush University Medical Center, 600 S. Paulina Street, Chicago, IL 60612, United States
| | - David A Bennett
- Rush Alzheimer's disease Center, Rush University Medical Center, 600 S. Paulina Street, Chicago, IL 60612, United States
| | - William G Honer
- BC Mental Health and Addictions Research Institute, 938 West 28th Avenue, Vancouver, BC V5Z 4H4, Canada; Department of Psychiatry, University of British Columbia, 2255 Wesbrook Mall, Vancouver, BC, V6T 2A1, Canada.
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10
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Wragg RT, Parisotto DA, Li Z, Terakawa MS, Snead D, Basu I, Weinstein H, Eliezer D, Dittman JS. Evolutionary Divergence of the C-terminal Domain of Complexin Accounts for Functional Disparities between Vertebrate and Invertebrate Complexins. Front Mol Neurosci 2017; 10:146. [PMID: 28603484 PMCID: PMC5445133 DOI: 10.3389/fnmol.2017.00146] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2017] [Accepted: 04/30/2017] [Indexed: 12/19/2022] Open
Abstract
Complexin is a critical presynaptic protein that regulates both spontaneous and calcium-triggered neurotransmitter release in all synapses. Although the SNARE-binding central helix of complexin is highly conserved and required for all known complexin functions, the remainder of the protein has profoundly diverged across the animal kingdom. Striking disparities in complexin inhibitory activity are observed between vertebrate and invertebrate complexins but little is known about the source of these differences or their relevance to the underlying mechanism of complexin regulation. We found that mouse complexin 1 (mCpx1) failed to inhibit neurotransmitter secretion in Caenorhabditis elegans neuromuscular junctions lacking the worm complexin 1 (CPX-1). This lack of inhibition stemmed from differences in the C-terminal domain (CTD) of mCpx1. Previous studies revealed that the CTD selectively binds to highly curved membranes and directs complexin to synaptic vesicles. Although mouse and worm complexin have similar lipid binding affinity, their last few amino acids differ in both hydrophobicity and in lipid binding conformation, and these differences strongly impacted CPX-1 inhibitory function. Moreover, function was not maintained if a critical amphipathic helix in the worm CPX-1 CTD was replaced with the corresponding mCpx1 amphipathic helix. Invertebrate complexins generally shared more C-terminal similarity with vertebrate complexin 3 and 4 isoforms, and the amphipathic region of mouse complexin 3 significantly restored inhibitory function to worm CPX-1. We hypothesize that the CTD of complexin is essential in conferring an inhibitory function to complexin, and that this inhibitory activity has been attenuated in the vertebrate complexin 1 and 2 isoforms. Thus, evolutionary changes in the complexin CTD differentially shape its synaptic role across phylogeny.
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Affiliation(s)
- Rachel T Wragg
- Department of Biochemistry, Weill Cornell Medical College, New YorkNY, United States
| | - Daniel A Parisotto
- Department of Biochemistry, Weill Cornell Medical College, New YorkNY, United States
| | - Zhenlong Li
- Department of Physiology and Biophysics, Weill Cornell Medical College, New YorkNY, United States
| | - Mayu S Terakawa
- Department of Biochemistry, Weill Cornell Medical College, New YorkNY, United States
| | - David Snead
- Department of Biochemistry, Weill Cornell Medical College, New YorkNY, United States
| | - Ishani Basu
- Department of Biochemistry, Weill Cornell Medical College, New YorkNY, United States
| | - Harel Weinstein
- Department of Physiology and Biophysics, Weill Cornell Medical College, New YorkNY, United States.,Institute for Computational Biomedicine, Weill Cornell Medical College, New YorkNY, United States
| | - David Eliezer
- Department of Biochemistry, Weill Cornell Medical College, New YorkNY, United States
| | - Jeremy S Dittman
- Department of Biochemistry, Weill Cornell Medical College, New YorkNY, United States
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11
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Keidel A, Bartsch TF, Florin EL. Direct observation of intermediate states in model membrane fusion. Sci Rep 2016; 6:23691. [PMID: 27029285 PMCID: PMC4814778 DOI: 10.1038/srep23691] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2015] [Accepted: 03/09/2016] [Indexed: 12/28/2022] Open
Abstract
We introduce a novel assay for membrane fusion of solid supported membranes on silica beads and on coverslips. Fusion of the lipid bilayers is induced by bringing an optically trapped bead in contact with the coverslip surface while observing the bead's thermal motion with microsecond temporal and nanometer spatial resolution using a three-dimensional position detector. The probability of fusion is controlled by the membrane tension on the particle. We show that the progression of fusion can be monitored by changes in the three-dimensional position histograms of the bead and in its rate of diffusion. We were able to observe all fusion intermediates including transient fusion, formation of a stalk, hemifusion and the completion of a fusion pore. Fusion intermediates are characterized by axial but not lateral confinement of the motion of the bead and independently by the change of its rate of diffusion due to the additional drag from the stalk-like connection between the two membranes. The detailed information provided by this assay makes it ideally suited for studies of early events in pure lipid bilayer fusion or fusion assisted by fusogenic molecules.
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Affiliation(s)
- Andrea Keidel
- Center for Nonlinear Dynamics and Department of Physics, University of Texas at Austin, Austin, Texas 78712, USA
| | - Tobias F. Bartsch
- Center for Nonlinear Dynamics and Department of Physics, University of Texas at Austin, Austin, Texas 78712, USA
- Howard Hughes Medical Institute and Laboratory of Sensory Neuroscience, The Rockefeller University, New York, New York, 10065, USA
| | - Ernst-Ludwig Florin
- Center for Nonlinear Dynamics and Department of Physics, University of Texas at Austin, Austin, Texas 78712, USA
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12
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Yang Y, Heo P, Kong B, Park JB, Jung YH, Shin J, Jeong C, Kweon DH. Dynamic light scattering analysis of SNARE-driven membrane fusion and the effects of SNARE-binding flavonoids. Biochem Biophys Res Commun 2015; 465:864-70. [PMID: 26319432 DOI: 10.1016/j.bbrc.2015.08.111] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2015] [Accepted: 08/25/2015] [Indexed: 01/04/2023]
Abstract
Soluble N-ethylmaleimide-sensitive-factor attachment protein receptor (SNARE) proteins generate energy required for membrane fusion. They form a parallelly aligned four-helix bundle called the SNARE complex, whose formation is initiated from the N terminus and proceeds toward the membrane-proximal C terminus. Previously, we have shown that this zippering-like process can be controlled by several flavonoids that bind to the intermediate structures formed during the SNARE zippering. Here, our aim was to test whether the fluorescence resonance energy transfer signals that are observed during the inner leaflet mixing assay indeed represent the hemifused vesicles. We show that changes in vesicle size accompanying the merging of bilayers is a good measure of progression of the membrane fusion. Two merging vesicles with the same size D in diameter exhibited their hydrodynamic diameters 2D + d (d, intermembrane distance), 2D and 2D as membrane fusion progressed from vesicle docking to hemifusion and full fusion, respectively. A dynamic light scattering assay of membrane fusion suggested that myricetin stopped membrane fusion at the hemifusion state, whereas delphinidin and cyanidin prevented the docking of the vesicles. These results are consistent with our previous findings in fluorescence resonance energy transfer assays.
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Affiliation(s)
- Yoosoo Yang
- Department of Genetic Engineering and Center for Human Interface Nanotechnology, Sungkyunkwan University, Suwon 440-746, South Korea; Biomedical Research Institute, Korea Institute of Science and Technology, Seoul 136-791, South Korea
| | - Paul Heo
- Department of Genetic Engineering and Center for Human Interface Nanotechnology, Sungkyunkwan University, Suwon 440-746, South Korea
| | - Byoungjae Kong
- Department of Genetic Engineering and Center for Human Interface Nanotechnology, Sungkyunkwan University, Suwon 440-746, South Korea
| | - Jun-Bum Park
- Department of Genetic Engineering and Center for Human Interface Nanotechnology, Sungkyunkwan University, Suwon 440-746, South Korea
| | - Young-Hun Jung
- Department of Genetic Engineering and Center for Human Interface Nanotechnology, Sungkyunkwan University, Suwon 440-746, South Korea
| | - Jonghyeok Shin
- Department of Genetic Engineering and Center for Human Interface Nanotechnology, Sungkyunkwan University, Suwon 440-746, South Korea
| | - Cherlhyun Jeong
- Biomedical Research Institute, Korea Institute of Science and Technology, Seoul 136-791, South Korea
| | - Dae-Hyuk Kweon
- Department of Genetic Engineering and Center for Human Interface Nanotechnology, Sungkyunkwan University, Suwon 440-746, South Korea.
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13
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Li F, Kümmel D, Coleman J, Reinisch KM, Rothman JE, Pincet F. A half-zippered SNARE complex represents a functional intermediate in membrane fusion. J Am Chem Soc 2014; 136:3456-64. [PMID: 24533674 PMCID: PMC3985920 DOI: 10.1021/ja410690m] [Citation(s) in RCA: 53] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
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SNARE
(soluble N-ethylmaleimide-sensitive factor
attachment protein receptor) proteins mediate fusion by pulling biological
membranes together via a zippering mechanism. Recent biophysical studies
have shown that t- and v-SNAREs can assemble in multiple stages from
the N-termini toward the C-termini. Here we show that functionally,
membrane fusion requires a sequential, two-step folding pathway and
assign specific and distinct functions for each step. First, the N-terminal
domain (NTD) of the v-SNARE docks to the t-SNARE, which leads to a
conformational rearrangement into an activated half-zippered SNARE
complex. This partially assembled SNARE complex locks the C-terminal
(CTD) portion of the t-SNARE into the same structure as in the postfusion
4-helix bundle, thereby creating the binding site for the CTD of the
v-SNARE and enabling fusion. Then zippering of the remaining CTD,
the membrane-proximal linker (LD), and transmembrane (TMD) domains
is required and sufficient to trigger fusion. This intrinsic property
of the SNAREs fits well with the action of physiologically vital regulators
such as complexin. We also report that NTD assembly is the rate-limiting
step. Our findings provide a refined framework for delineating the
molecular mechanism of SNARE-mediated membrane fusion and action of
regulatory proteins.
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Affiliation(s)
- Feng Li
- Department of Cell Biology, School of Medicine, Yale University , 333 Cedar Street, New Haven, Connecticut 06520, United States
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14
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Using Proteomics to Unravel the Mysterious Steps of the HBV-Life-Cycle. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2014; 806:453-81. [DOI: 10.1007/978-3-319-06068-2_22] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
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15
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Greitzer-Antes D, Barak-Broner N, Berlin S, Oron Y, Chikvashvili D, Lotan I. Tracking Ca2+-dependent and Ca2+-independent conformational transitions in syntaxin 1A during exocytosis in neuroendocrine cells. J Cell Sci 2013; 126:2914-23. [PMID: 23641074 DOI: 10.1242/jcs.124743] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
A key issue for understanding exocytosis is elucidating the various protein interactions and the associated conformational transitions underlying soluble N-ethylmeleimide-sensitive factor attachment protein receptor (SNARE) protein assembly. To monitor dynamic changes in syntaxin 1A (Syx) conformation along exocytosis, we constructed a novel fluorescent Syx-based probe that can be efficiently incorporated within endogenous SNARE complexes, support exocytosis, and report shifts in Syx between 'closed' and 'open' conformations by fluorescence resonance energy transfer analysis. Using this probe we resolve two distinct Syx conformational transitions during membrane depolarization-induced exocytosis in PC12 cells: a partial 'opening' in the absence of Ca(2+) entry and an additional 'opening' upon Ca(2+) entry. The Ca(2+)-dependent transition is abolished upon neutralization of the basic charges in the juxtamembrane regions of Syx, which also impairs exocytosis. These novel findings provide evidence of two conformational transitions in Syx during exocytosis, which have not been reported before: one transition directly induced by depolarization and an additional transition that involves the juxtamembrane region of Syx. The superior sensitivity of our probe also enabled detection of subtle Syx conformational changes upon interaction with VAMP2, which were absolutely dependent on the basic charges of the juxtamembrane region. Hence, our results further suggest that the Ca(2+)-dependent transition in Syx involves zippering between the membrane-proximal juxtamembrane regions of Syx and VAMP2 and support the recently implied existence of this zippering in the final phase of SNARE assembly to catalyze exocytosis.
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Affiliation(s)
- Dafna Greitzer-Antes
- Department of Physiology and Pharmacology, Sackler School of Medicine, Tel-Aviv University, Ramat Aviv 69978, Israel
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16
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Jung CH, Choi JK, Yang Y, Koh HJ, Heo P, Yoon KJ, Kim S, Park WS, Shing HJ, Kweon DH. A botulinum neurotoxin-like function of Potentilla chinensis extract that inhibits neuronal SNARE complex formation, membrane fusion, neuroexocytosis, and muscle contraction. PHARMACEUTICAL BIOLOGY 2012; 50:1157-1167. [PMID: 22881141 DOI: 10.3109/13880209.2012.661743] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
CONTEXT Botulinum neurotoxins (BoNTs) are popularly used to treat various diseases and for cosmetic purposes. They act by blocking neurotransmission through specific cleavage of soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) proteins. Recently, several polyphenols were shown to interfere with SNARE complex formation by wedging into the hydrophobic core interface, thereby leading to reduced neuroexocytosis. OBJECTIVE In order to find industrially-viable plant extract that functions like BoNT, 71 methanol extracts of flowers were screened and BoNT-like activity of selected extract was evaluated. MATERIALS AND METHODS After evaluating the inhibitory effect of 71 flower methanol extracts on SNARE complex formation, seven candidates were selected and they were subjected to SNARE-driven membrane fusion assay. Neurotransmitter release from neuronal PC12 cells and SNARE complex formation inside the cell was also evaluated. Finally, the effect of one selected extract on muscle contraction and digit abduction score was determined. RESULTS The extract of Potentilla chinensis Ser. (Rosaceae)(Chinese cinquefoil) flower inhibited neurotransmitter release from neuronal PC12 cells by approximately 90% at a concentration of 10 μg/mL. The extract inhibited neuroexocytosis by interfering with SNARE complex formation inside cells. It reduced muscle contraction of phrenic nerve-hemidiaphragm by approximately 70% in 60 min, which is comparable to the action of the Ca²⁺-channel blocker verapamil and BoNT type A. DISCUSSION AND CONCLUSION While BoNT blocks neuroexocytosis by cleaving SNARE proteins, the Potentilla chinensis extract exhibited the same activity by inhibiting SNARE complex formation. The extract paralyzed muscle as efficiently as BoNT, suggesting the potential versatility in cosmetics and therapeutics.
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Affiliation(s)
- Chang-Hwa Jung
- School of Life Science and Biotechnology and Center for Human Interface Nano Technology, Sungkyunkwan University, Gyeonggi-do, Korea
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17
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Neurotransmitter release mechanisms studied in Caenorhabditis elegans. Cell Calcium 2012; 52:289-95. [DOI: 10.1016/j.ceca.2012.03.005] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2012] [Revised: 03/19/2012] [Accepted: 03/25/2012] [Indexed: 01/15/2023]
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18
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Martin JA, Hu Z, Fenz KM, Fernandez J, Dittman JS. Complexin has opposite effects on two modes of synaptic vesicle fusion. Curr Biol 2011; 21:97-105. [PMID: 21215634 PMCID: PMC3026084 DOI: 10.1016/j.cub.2010.12.014] [Citation(s) in RCA: 113] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2010] [Revised: 12/08/2010] [Accepted: 12/08/2010] [Indexed: 11/16/2022]
Abstract
BACKGROUND Synaptic transmission can occur in a binary or graded fashion, depending on whether transmitter release is triggered by action potentials or by gradual changes in membrane potential. Molecular differences of these two types of fusion events and their differential regulation in a physiological context have yet to be addressed. Complexin is a conserved SNARE-binding protein that has been proposed to regulate both spontaneous and stimulus-evoked synaptic vesicle (SV) fusion. RESULTS Here we examine complexin function at a graded synapse in C. elegans. Null complexin (cpx-1) mutants are viable, although nervous system function is significantly impaired. Loss of CPX-1 results in a 3-fold increase in the rate of tonic synaptic transmission at the neuromuscular junction, whereas stimulus-evoked SV fusion is decreased 10-fold. A truncated CPX-1 missing its C-terminal domain can rescue stimulus-evoked synaptic vesicle exocytosis but fails to suppress tonic activity, demonstrating that these two modes of exocytosis can be distinguished at the molecular level. A CPX-1 variant with impaired SNARE binding also rescues evoked, but not tonic, neurotransmitter release. Finally, tonic, but not evoked, release can be rescued in a syntaxin point mutant by removing CPX-1. Rescue of either form of exocytosis partially restores locomotory behavior, indicating that both types of synaptic transmission are relevant. CONCLUSION These observations suggest a dual role for CPX-1: suppressing SV exocytosis, driven by low levels of endogenous neural activity, while promoting synchronous fusion of SVs driven by a depolarizing stimulus. Thus, patterns of synaptic activity regulate complexin's inhibitory and permissive roles at a graded synapse.
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Affiliation(s)
| | - Zhitao Hu
- Department of Molecular Biology Simches 7 Massachusetts General Hospital 185 Cambridge St. Boston, MA 02114
| | - Katherine M. Fenz
- Department of Biochemistry Weill Cornell Medical School 1300 York Ave. New York, NY 10065
- Department of Molecular Biology Simches 7 Massachusetts General Hospital 185 Cambridge St. Boston, MA 02114
| | - Joel Fernandez
- Department of Biochemistry Weill Cornell Medical School 1300 York Ave. New York, NY 10065
- Department of Molecular Biology Simches 7 Massachusetts General Hospital 185 Cambridge St. Boston, MA 02114
| | - Jeremy S. Dittman
- Corresponding author contact information: Jeremy S. Dittman Department of Biochemistry Weill Cornell Medical School 1300 York Ave. New York, NY 10065 phone: (212) 746-5224 fax: (212) 746-8875
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19
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Glynn D, Gibson HE, Harte MK, Reim K, Jones S, Reynolds GP, Morton AJ. Clorgyline-mediated reversal of neurological deficits in a Complexin 2 knockout mouse. Hum Mol Genet 2010; 19:3402-12. [PMID: 20584925 DOI: 10.1093/hmg/ddq252] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Complexin 2 is a protein modulator of neurotransmitter release that is downregulated in humans suffering from depression, animal models of depression and neurological disorders such as Huntington's disease in which depression is a major symptom. Although complexin 2 knockout (Cplx2-/-) mice are overtly normal, they show significant abnormalities in cognitive function and synaptic plasticity. Here we show that Cplx2-/- mice also have disturbances in emotional behaviours that include abnormal social interactions and depressive-like behaviour. Since neurotransmitter deficiencies are thought to underlie depression, we examined neurotransmitter levels in Cplx2-/- mice and found a significant decrease in levels of noradrenaline and the serotonin metabolite 5-hydroxyindoleacetic acid in the hippocampus. Chronic treatment with clorgyline, an irreversible inhibitor of monoamine oxidase A, restored hippocampal noradrenaline to normal levels (from 60 to 97% of vehicle-treated Cplx2+/+ mice, P<0.001), and reversed the behavioural deficits seen in Cplx2-/- mice. For example, clorgyline-treated Cplx2-/- mice spent significantly more time interacting with a novel visitor mouse compared with vehicle-treated Cplx2-/- mice in the social recognition test (34 compared with 13%, P<0.01). We were also able to reverse the selective deficit seen in mossy fibre-long-term potentiation (MF-LTP) in Cplx2-/- mice using the noradrenergic agonist isoprenaline. Pre-treatment with isoprenaline in vitro increased MF-LTP by 125% (P<0.001), thus restoring it to control levels. Our data strongly support the idea that complexin 2 is a key player in normal neurological function, and that downregulation of complexin 2 could lead to changes in neurotransmitter release sufficient to cause significant behavioural abnormalities such as depression.
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Affiliation(s)
- Dervila Glynn
- Department of Pharmacology, University of Cambridge, Tennis Court Road, Cambridge CB2 1PD, UK
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20
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Alpha-synuclein sequesters arachidonic acid to modulate SNARE-mediated exocytosis. EMBO Rep 2010; 11:528-33. [PMID: 20489724 DOI: 10.1038/embor.2010.66] [Citation(s) in RCA: 92] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2009] [Revised: 03/22/2010] [Accepted: 04/14/2010] [Indexed: 01/06/2023] Open
Abstract
Alpha-synuclein is a synaptic modulatory protein implicated in the pathogenesis of Parkinson disease. The precise functions of this small cytosolic protein are still under investigation. alpha-Synuclein has been proposed to regulate soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) proteins involved in vesicle fusion. Interestingly, alpha-synuclein fails to interact with SNARE proteins in conventional protein-binding assays, thus suggesting an indirect mode of action. As the structural and functional properties of both alpha-synuclein and the SNARE proteins can be modified by arachidonic acid, a common lipid regulator, we analysed this possible tripartite link in detail. Here, we show that the ability of arachidonic acid to stimulate SNARE complex formation and exocytosis can be controlled by alpha-synuclein, both in vitro and in vivo. Alpha-synuclein sequesters arachidonic acid and thereby blocks the activation of SNAREs. Our data provide mechanistic insights into the action of alpha-synuclein in the modulation of neurotransmission.
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21
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Lu B, Song S, Shin YK. Accessory alpha-helix of complexin I can displace VAMP2 locally in the complexin-SNARE quaternary complex. J Mol Biol 2009; 396:602-9. [PMID: 20026076 DOI: 10.1016/j.jmb.2009.12.020] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2009] [Revised: 11/05/2009] [Accepted: 12/11/2009] [Indexed: 10/20/2022]
Abstract
The calcium-triggered neurotransmitter release requires three SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) proteins: synaptobrevin 2 (or vesicle-associated membrane protein 2) on the synaptic vesicle and syntaxin 1 and SNAP-25 (synaptosome-associated protein of 25 kDa) at the presynaptic plasma membrane. This minimal fusion machinery is believed to drive fusion of the vesicle to the presynaptic membrane. Complexin, also known as synaphin, is a neuronal cytosolic protein that acts as a major regulator of synaptic vesicle exocytosis. Stimulatory and inhibitory effects of complexin have both been reported, suggesting the duality of its function. To shed light on the molecular basis of the complexin's dual function, we have performed an EPR investigation of the complexin-SNARE quaternary complex. We found that the accessory alpha-helix (amino acids 27-48) by itself has the capacity to replace the C-terminus of the SNARE motif of vesicle-associated membrane protein 2 in the four-helix bundle and makes the SNARE complex weaker when the N-terminal region of complexin I (amino acids 1-26) is removed. However, the accessory alpha-helix remains detached from the SNARE core when the N-terminal region of complexin I is present. Thus, our data show the possibility that the balance between the activities of the accessory alpha-helix and the N-terminal domain might determine the final outcome of the complexin function, either stimulatory or inhibitory.
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Affiliation(s)
- Bin Lu
- Department of Biochemistry, Biophysics and Molecular Biology, Iowa State University, Ames, IA 50011, USA
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22
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Tadokoro S, Nakanishi M, Hirashima N. Complexin II regulates degranulation in RBL-2H3 cells by interacting with SNARE complex containing syntaxin-3. Cell Immunol 2009; 261:51-6. [PMID: 19932892 DOI: 10.1016/j.cellimm.2009.10.011] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2009] [Revised: 10/17/2009] [Accepted: 10/22/2009] [Indexed: 11/25/2022]
Abstract
Recent studies have revealed that SNARE proteins are involved in the exocytotic release (degranulation) in mast cells. However, the roles of SNARE regulatory proteins are poorly understood. Complexin is one such regulatory protein and it plays a crucial role in exocytotic release. In this study, we characterized the interaction between SNARE complex and complexin II in mast cells by GST pull-down assay and in vitro binding assay. We found that the SNARE complex that interacted with complexin II consisted of syntaxin-3, SNAP-23, and VAMP-2 or -8, whereas syntaxin-4 was not detected. Recombinant syntaxin-3 binds to complexin II by itself, but its affinity to complexin II was enhanced upon addition of VAMP-8 and SNAP-23. Furthermore, the region of complexin II responsible for binding to the SNARE complex, was near the central alpha-helix region. These results suggest that complexin II regulates degranulation by interacting with the SNARE complex containing syntaxin-3.
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Affiliation(s)
- Satoshi Tadokoro
- Graduate School of Pharmaceutical Sciences, Nagoya City University, 3-1, Tanabe-dori, Mizuho-ku, Nagoya 467-8603, Japan
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23
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Brunner Y, Schvartz D, Couté Y, Sanchez JC. Proteomics of regulated secretory organelles. MASS SPECTROMETRY REVIEWS 2009; 28:844-867. [PMID: 19301366 DOI: 10.1002/mas.20211] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
Regulated secretory organelles are important subcellular structures of living cells that allow the release in the extracellular space of crucial compounds, such as hormones and neurotransmitters. Therefore, the regulation of biogenesis, trafficking, and exocytosis of regulated secretory organelles has been intensively studied during the last 30 years. However, due to the large number of different regulated secretory organelles, only a few of them have been specifically characterized. New insights into regulated secretory organelles open crucial perspectives for a better comprehension of the mechanisms that govern cell secretion. The combination of subcellular fractionation, protein separation, and mass spectrometry is also possible to study regulated secretory organelles at the proteome level. In this review, we present different strategies used to isolate regulated secretory organelles, separate their protein content, and identify the proteins by mass spectrometry. The biological significance of regulated secretory organelles-proteomic analysis is discussed as well.
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Affiliation(s)
- Yannick Brunner
- Biomedical Proteomics Research Group, University Medical Center, Geneva, Switzerland
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24
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Complexin-I is required for high-fidelity transmission at the endbulb of Held auditory synapse. J Neurosci 2009; 29:7991-8004. [PMID: 19553439 DOI: 10.1523/jneurosci.0632-09.2009] [Citation(s) in RCA: 82] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Complexins (CPXs I-IV) presumably act as regulators of the SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) complex, but their function in the intact mammalian nervous system is not well established. Here, we explored the role of CPXs in the mouse auditory system. Hearing was impaired in CPX I knock-out mice but normal in knock-out mice for CPXs II, III, IV, and III/IV as measured by auditory brainstem responses. Complexins were not detectable in cochlear hair cells but CPX I was expressed in spiral ganglion neurons (SGNs) that give rise to the auditory nerve. Ca(2+)-dependent exocytosis of inner hair cells and sound encoding by SGNs were unaffected in CPX I knock-out mice. In the absence of CPX I, the resting release probability in the endbulb of Held synapses of the auditory nerve fibers with bushy cells in the cochlear nucleus was reduced. As predicted by computational modeling, bushy cells had decreased spike rates at sound onset as well as longer and more variable first spike latencies explaining the abnormal auditory brainstem responses. In addition, we found synaptic transmission to outlast the stimulus at many endbulb of Held synapses in vitro and in vivo, suggesting impaired synchronization of release to stimulus offset. Although sound encoding in the cochlea proceeds in the absence of complexins, CPX I is required for faithful processing of sound onset and offset in the cochlear nucleus.
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25
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Abdulreda MH, Moy VT. Investigation of SNARE-Mediated Membrane Fusion Mechanism Using Atomic Force Microscopy. JAPANESE JOURNAL OF APPLIED PHYSICS (2008) 2009; 48:8JA03-8JA0310. [PMID: 20228892 PMCID: PMC2836841 DOI: 10.1143/jjap.48.08ja03] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
Membrane fusion is driven by specialized proteins that reduce the free energy penalty for the fusion process. In neurons and secretory cells, soluble N-ethylmaleimide-sensitive factor-attachment protein (SNAP) receptors (SNAREs) mediate vesicle fusion with the plasma membrane during vesicular content release. Although, SNAREs have been widely accepted as the minimal machinery for membrane fusion, the specific mechanism for SNARE-mediated membrane fusion remains an active area of research. Here, we summarize recent findings based on force measurements acquired in a novel experimental system that uses atomic force microscope (AFM) force spectroscopy to investigate the mechanism(s) of membrane fusion and the role of SNAREs in facilitating membrane hemifusion during SNARE-mediated fusion. In this system, protein-free and SNARE-reconstituted lipid bilayers are formed on opposite (trans) substrates and the forces required to induce membrane hemifusion and fusion or to unbind single v-/t-SNARE complexes are measured. The obtained results provide evidence for a mechanism by which the pulling force generated by interacting trans-SNAREs provides critical proximity between the membranes and destabilizes the bilayers at fusion sites by broadening the hemifusion energy barrier and consequently making the membranes more prone to fusion.
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26
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Seiler F, Malsam J, Krause JM, Söllner TH. A role of complexin-lipid interactions in membrane fusion. FEBS Lett 2009; 583:2343-8. [PMID: 19540234 DOI: 10.1016/j.febslet.2009.06.025] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2009] [Revised: 06/10/2009] [Accepted: 06/15/2009] [Indexed: 10/20/2022]
Abstract
Complexins (Cpxs) and synaptotagmins regulate calcium-dependent exocytosis. A central helix in Cpx confers specific binding to the soluble N-ethylmaleimide-sensitive factor-attachment protein receptor (SNARE) fusion machinery. An accessory helix in the amino-terminal region inhibits membrane fusion by blocking SNAREpin zippering. We now show that an amphipathic helix in the carboxy-terminal region of CpxI binds lipid bilayers and affects SNARE-mediated lipid mixing in a liposome fusion assay. The substitution of a hydrophobic amino acid within the helix by a charged residue abolishes the lipid interaction and the stimulatory effect of CpxI in liposome fusion. In contrast, the introduction of the bulky hydrophobic amino acid tryptophan stimulates lipid binding and liposome fusion. This data shows that local Cpx-lipid interactions can play a role in membrane fusion.
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Affiliation(s)
- Florian Seiler
- Heidelberg University Biochemistry Center, Im Neuenheimer Feld 345, 69120 Heidelberg, Germany
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27
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28
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Abdulreda MH, Bhalla A, Rico F, Berggren PO, Chapman ER, Moy VT. Pulling force generated by interacting SNAREs facilitates membrane hemifusion. Integr Biol (Camb) 2009; 1:301-10. [PMID: 20023730 DOI: 10.1039/b900685k] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
In biological systems, membrane fusion is mediated by specialized proteins. Although soluble N-ethylmaleimide-sensitive factor attachment protein (SNAP) receptors (SNAREs) provide the minimal molecular machinery required to drive membrane fusion, the precise mechanism for SNARE-mediated fusion remains to be established. Here, we used atomic force microscope (AFM) spectroscopy to determine whether the pulling force generated by interacting SNAREs is directly coupled to membrane fusion. The mechanical strength of the SNARE binding interaction was determined by single molecule force measurements. It was revealed that the forced unbinding of the SNARE complex formed between opposing (trans) bilayers involves two activation barriers; where the steep inner barrier governs the transition from the bound to an intermediate state and the outer barrier governs the transition between the intermediate and the unbound state. Moreover, truncation of either SNAP-25 or VAMP 2 reduced the slope of the inner barrier significantly and, consequently, reduced the pulling strength of the SNARE complex; thus, suggesting that the inner barrier determines the binding strength of the SNARE complex. In parallel, AFM compression force measurements revealed that truncated SNAREs were less efficient than native SNAREs in facilitating hemifusion of the apposed bilayers. Together, these findings reveal a mechanism by which a pulling force generated by interacting trans-SNAREs reduces the slope of the hemifusion barrier and, subsequently, facilitates hemifusion and makes the membranes more prone to fusion.
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Affiliation(s)
- Midhat H Abdulreda
- University of Miami Miller School of Medicine, Physiology & Biophysics Department, 1600 NW 10th Ave., Miami, FL 33136, USA
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29
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Chicka MC, Chapman ER. Concurrent binding of complexin and synaptotagmin to liposome-embedded SNARE complexes. Biochemistry 2009; 48:657-9. [PMID: 19128031 PMCID: PMC2651691 DOI: 10.1021/bi801962d] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/04/2022]
Abstract
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Synaptotagmin and complexin regulate SNARE-mediated synaptic vesicle exocytosis. It has been proposed that complexin clamps membrane fusion and that Ca2+-synaptotagmin displaces complexin from SNARE complexes to relieve this clamping activity. Using a reconstituted system, we demonstrate that complexin and synaptotagmin simultaneously bind to neuronal SNARE complexes and that both apo-synaptotagmin and complexin inhibit SNARE-mediated membrane fusion. Moreover, the clamping ability of apo-synaptotagmin occluded the clamping activity of complexin until the arrival of a Ca2+ trigger, at which point synaptotagmin accelerated fusion while high concentrations of complexin inhibited fusion. Thus, the inhibitory patterns of synaptotagmin and complexin are different, suggesting that SNAREs assemble into distinct states along the fusion pathway. These data also suggest that during synaptotagmin-regulated vesicle−vesicle fusion, complexin does not function as a fusion clamp that is relieved by Ca2+-synaptotagmin.
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Affiliation(s)
- Michael C Chicka
- Department of Physiology and Programs in Cellular and Molecular Biology, University of Wisconsin, 1300 University Avenue, SMI 129, Madison, Wisconsin 53706, USA
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Abstract
Membrane fusion underlies many cellular events, including secretion, exocytosis, endocytosis, organelle reconstitution, transport from endoplasmic reticulum to Golgi and nuclear envelope formation. A large number of investigations into membrane fusion indicate various roles for individual members of the phosphoinositide class of membrane lipids. We first review the phosphoinositides as membrane recognition sites and their regulatory functions in membrane fusion. We then consider how modulation of phosphoinositides and their products may affect the structure and dynamics of natural membranes facilitating fusion. These diverse roles underscore the importance of these phospholipids in the fusion of biological membranes.
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31
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The carboxy-terminal domain of complexin I stimulates liposome fusion. Proc Natl Acad Sci U S A 2009; 106:2001-6. [PMID: 19179400 DOI: 10.1073/pnas.0812813106] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Regulated exocytosis requires tight coupling of the membrane fusion machinery to a triggering signal and a fast response time. Complexins are part of this regulation and, together with synaptotagmins, control calcium-dependent exocytosis. Stimulatory and inhibitory functions have been reported for complexins. To test if complexins directly affect membrane fusion, we analyzed the 4 known mammalian complexin isoforms in a reconstituted fusion assay. In contrast to complexin III (CpxIII) and CpxIV, CpxI and CpxII stimulated soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE)-pin assembly and membrane fusion. This stimulatory effect required a preincubation at low temperature and was specific for neuronal t-SNAREs. Stimulation of membrane fusion was lost when the carboxy-terminal domain of CpxI was deleted or serine 115, a putative phosphorylation site, was mutated. Transfer of the carboxy-terminal domain of CpxI to CpxIII resulted in a stimulatory CpxIII-I chimera. Thus, the carboxy-terminal domains of CpxI and CpxII promote the fusion of high-curvature liposomes.
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Direct interaction of SNARE complex binding protein synaphin/complexin with calcium sensor synaptotagmin 1. ACTA ACUST UNITED AC 2009; 36:173-89. [PMID: 19132534 DOI: 10.1007/s11068-008-9032-9] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2008] [Revised: 07/10/2008] [Accepted: 08/28/2008] [Indexed: 01/10/2023]
Abstract
Although the binding of synaphin (also called complexin) to the soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complex is critical for synaptic vesicle exocytosis, the exact role of synaphin remains unclear. Here, we show that synaphin directly binds to synaptotagmin 1, a major Ca(2+) sensor for fast neurotransmitter release, in a 1:1 stoichiometry. Mapping of the synaphin site involved in synaptotagmin 1 binding revealed that the C-terminal region is essential for the interaction between these two proteins. Binding was sensitive to ionic strength, suggesting the involvement of charged residues in the C-terminus region. Mutation of the seven consecutive glutamic acid residues (residues 108-114) at the C-terminal region of synaphin to alanines or glutamines resulted in a dramatic reduction in synaptotagmin 1 binding activity. Furthermore, a peptide from the C-terminus of synaphin (residues 91-124) blocked the binding of synaptotagmin 1 to synaphin, an effect that was abolished by mutating the consecutive glutamic acid residues to alanine. Immunoprecipitation experiments with brain membrane extracts showed the presence of a complex consisting of synaphin, synaptotagmin 1, and SNAREs. We propose that synaphin recruits synaptotagmin 1 to the SNARE-based fusion complex and synergistically functions with synaptotagmin 1 in mediating fast synaptic vesicle exocytosis.
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Inhibition of SNARE-driven neuroexocytosis by plant extracts. Biotechnol Lett 2008; 31:361-9. [PMID: 19023663 DOI: 10.1007/s10529-008-9878-z] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2008] [Revised: 11/03/2008] [Accepted: 11/10/2008] [Indexed: 10/21/2022]
Abstract
Neuronal soluble N-ethylmaleimide-sensitive factor attachment protein (SNAP) receptor (SNARE) proteins mediate membrane fusion between synaptic vesicle and presynaptic membrane, resulting in neurotransmitter release. SNARE proteins are specific substrates of botulinum neurotoxins (BoNT) which are now widely used for therapeutic and cosmetic purposes. While BoNT blocks neuroexocytosis by cleaving SNAREs, inhibiting SNARE assembly process might exert the same effect on neurotransmission. In the present study, some extracts of 100 plants reduced neurotransmitter release by inhibiting SNARE complex formation in neuronal cells. The extracts effectively paralyzed muscle of rat phrenic nerve-hemidiaphragm preparation. Our results raise the possibility that SNARE folding inhibitors from natural resources might replace some special BoNT application fields.
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Tong A, Wu L, Lin Q, Lau QC, Zhao X, Li J, Chen P, Chen L, Tang H, Huang C, Wei YQ. Proteomic analysis of cellular protein alterations using a hepatitis B virus-producing cellular model. Proteomics 2008; 8:2012-23. [PMID: 18491315 DOI: 10.1002/pmic.200700849] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Hepatitis B virus (HBV) is one of the major etiological factors responsible for acute and chronic liver disease and for the development of hepatocellular carcinoma (HCC). To determine the effects of HBV replication on host cell-protein expression, we utilized 2-DE and MS/MS analysis to compare and identify differentially expressed proteins between an HBV-producing cell line HepG2.2.15 and its parental cell line HepG2. Of the 66 spots identified as differentially expressed (+/- over twofold, p <0.05) between the two cell lines, 62 spots (corresponding to 61 unique proteins) were positively identified by MS/MS analysis. These proteins could be clearly divided into three major groups by cluster and metabolic/signaling pathway analysis: proteins involved in retinol metabolism pathway, calcium ion-binding proteins, and proteins associated with protein degradation pathways. Other proteins identified include those that function in diverse biological processes such as signal transduction, immune regulation, molecular chaperone, electron transport/redox regulation, cell proliferation/differentiation, and mRNA splicing. In summary, we profiled proteome alterations between HepG2.2.15 and HepG2 cells. The proteins identified in this study would be useful in revealing the mechanisms underlying HBV-host cell interactions and the development of HCC. This study can also provide some useful clues for antiviral research.
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Affiliation(s)
- Aiping Tong
- The State Key Laboratory of Biotherapy, West China Hospital, College of Life Science, Sichuan University, Chengdu, People's Republic of China
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Giraudo CG, Garcia-Diaz A, Eng WS, Yamamoto A, Melia TJ, Rothman JE. Distinct domains of complexins bind SNARE complexes and clamp fusion in vitro. J Biol Chem 2008; 283:21211-9. [PMID: 18499660 PMCID: PMC2475712 DOI: 10.1074/jbc.m803478200] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2008] [Indexed: 12/29/2022] Open
Abstract
In regulated exocytosis, the core membrane fusion machinery proteins, the SNARE proteins, are assisted by a group of regulatory factors in order to couple membrane fusion to an increase of intracellular calcium ion (Ca(2+)) concentration. Complexin-I and synaptotagmin-I have been shown to be key elements for this tightly regulated process. Many studies suggest that complexin-I can arrest the fusion reaction and that synaptotagmin-I can release the complexin-I blockage in a calcium-dependent manner. Although the actual molecular mechanism by which they exert their function is still unknown, recent in vivo experiments postulate that domains of complexin-I produce different effects on neurotransmitter release. Herein, by using an in vitro flipped SNARE cell fusion assay, we have identified and characterized the minimal functional domains of complexin-I necessary to couple calcium and synaptotagmin-I to membrane fusion. Moreover, we provide evidence that other isoforms of complexin, complexin-II, -III, and -IV, can also be functionally coupled to synaptotagmin-I and calcium. These correspond closely to results from in vivo experiments, providing further validation of the physiological relevance of the flipped SNARE system.
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Affiliation(s)
- Claudio G. Giraudo
- Department of Physiology and
Cellular Biophysics, Columbia University, College of Physicians and Surgeons,
New York, New York 10032 and the
Department of Neurology, Columbia
University, New York, New York 10032
| | - Alejandro Garcia-Diaz
- Department of Physiology and
Cellular Biophysics, Columbia University, College of Physicians and Surgeons,
New York, New York 10032 and the
Department of Neurology, Columbia
University, New York, New York 10032
| | - William S. Eng
- Department of Physiology and
Cellular Biophysics, Columbia University, College of Physicians and Surgeons,
New York, New York 10032 and the
Department of Neurology, Columbia
University, New York, New York 10032
| | - Ai Yamamoto
- Department of Physiology and
Cellular Biophysics, Columbia University, College of Physicians and Surgeons,
New York, New York 10032 and the
Department of Neurology, Columbia
University, New York, New York 10032
| | - Thomas J. Melia
- Department of Physiology and
Cellular Biophysics, Columbia University, College of Physicians and Surgeons,
New York, New York 10032 and the
Department of Neurology, Columbia
University, New York, New York 10032
| | - James E. Rothman
- Department of Physiology and
Cellular Biophysics, Columbia University, College of Physicians and Surgeons,
New York, New York 10032 and the
Department of Neurology, Columbia
University, New York, New York 10032
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Complexin and Ca2+ stimulate SNARE-mediated membrane fusion. Nat Struct Mol Biol 2008; 15:707-13. [PMID: 18552825 PMCID: PMC2493294 DOI: 10.1038/nsmb.1446] [Citation(s) in RCA: 94] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2008] [Accepted: 05/15/2008] [Indexed: 11/29/2022]
Abstract
Ca2+-triggered, synchronized synaptic vesicle fusion underlies interneuronal communication. Complexin is a major binding partner of the SNARE complex, the core fusion machinery at the presynapse. The physiological data on complexin, however, have been at odds with each other, making delineation of its molecular function difficult. Here we report direct observation of two-faceted functions of complexin using the single-vesicle fluorescence fusion assay and EPR. We show that complexin I has two opposing effects on trans-SNARE assembly: inhibition of SNARE complex formation and stabilization of assembled SNARE complexes. Of note, SNARE-mediated fusion is markedly stimulated by complexin, and it is further accelerated by two orders of magnitude in response to an externally applied Ca2+ wave. We suggest that SNARE complexes, complexins and phospholipids collectively form a complex substrate for Ca2+ and Ca2+-sensing fusion effectors in neurotransmitter release.
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Wright J, Morales MM, Sousa-Menzes J, Ornellas D, Sipes J, Cui Y, Cui I, Hulamm P, Cebotaru V, Cebotaru L, Guggino WB, Guggino SE. Transcriptional adaptation to Clcn5 knockout in proximal tubules of mouse kidney. Physiol Genomics 2008; 33:341-54. [DOI: 10.1152/physiolgenomics.00024.2008] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Dent disease has multiple defects attributed to proximal tubule malfunction including low-molecular-weight proteinuria, aminoaciduria, phosphaturia, and glycosuria. To understand the changes in kidney function of the Clc5 chloride/proton exchanger gene knockout mouse model of Dent disease, we examined gene expression profiles from proximal S1 and S2 tubules of mouse kidneys. We found many changes in gene expression not known previously to be altered in this disease. Genes involved in lipid metabolism, organ development, and organismal physiological processes had the greatest number of significantly changed transcripts. In addition, genes of catalytic activity and transporter activity also had a great number of changed transcripts. Overall, 720 genes are expressed differentially in the proximal tubules of the Dent Clcn5 knockout mouse model compared with those of control wild-type mice. The fingerprint of these gene changes may help us to understand the phenotype of Dent disease.
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Affiliation(s)
- Jerry Wright
- Department of Physiology, Johns Hopkins School of Medicine, Johns Hopkins University, Baltimore, Maryland
| | - Marcelo M. Morales
- Instituto de Biophysica Carlos Chagas, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
| | - Jackson Sousa-Menzes
- Instituto de Biophysica Carlos Chagas, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
| | - Debora Ornellas
- Instituto de Biophysica Carlos Chagas, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
| | - Jennifer Sipes
- Department of Medicine, Johns Hopkins School of Medicine, Johns Hopkins University, Baltimore, Maryland
| | - Yan Cui
- Department of Medicine, Johns Hopkins School of Medicine, Johns Hopkins University, Baltimore, Maryland
| | - Isabelle Cui
- Department of Medicine, Johns Hopkins School of Medicine, Johns Hopkins University, Baltimore, Maryland
| | - Phuson Hulamm
- Department of Medicine, Johns Hopkins School of Medicine, Johns Hopkins University, Baltimore, Maryland
| | - Valeriu Cebotaru
- Department of Medicine, Johns Hopkins School of Medicine, Johns Hopkins University, Baltimore, Maryland
| | - Liudmila Cebotaru
- Department of Medicine, Johns Hopkins School of Medicine, Johns Hopkins University, Baltimore, Maryland
| | - William B. Guggino
- Instituto de Biophysica Carlos Chagas, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
| | - Sandra E. Guggino
- Department of Medicine, Johns Hopkins School of Medicine, Johns Hopkins University, Baltimore, Maryland
- Department of Physiology, Johns Hopkins School of Medicine, Johns Hopkins University, Baltimore, Maryland
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Abstract
In contrast to constitutive secretion, SNARE-mediated synaptic vesicle fusion is controlled by multiple regulatory proteins, which determine the Ca(2+) sensitivity of the vesicle fusion process and the speed of excitation-secretion coupling. Complexins are among the best characterized SNARE regulators known to date. They operate by binding to trimeric SNARE complexes consisting of the vesicle protein synaptobrevin and the plasma membrane proteins syntaxin and SNAP-25. The question as to whether complexins facilitate or inhibit SNARE-mediated fusion processes is currently a matter of significant controversy. This is mainly because of the fact that biochemical experiments in vitro and studies on vertebrate complexins in vivo have yielded apparently contradictory results. In this review, I provide a summary of available data on the role of complexins in SNARE-mediated vesicle fusion and attempt to define a model of complexin function that incorporates evidence for both facilitatory and inhibitory roles of complexins in SNARE-mediated fusion.
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Affiliation(s)
- Nils Brose
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, Göttingen, Germany.
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SNAREpin/Munc18 promotes adhesion and fusion of large vesicles to giant membranes. Proc Natl Acad Sci U S A 2008; 105:2380-5. [PMID: 18268324 DOI: 10.1073/pnas.0712125105] [Citation(s) in RCA: 87] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Exocytic vesicle fusion requires both the SNARE family of fusion proteins and a closely associated regulatory subunit of the Sec1/Munc18 (SM) family. In principle, SM proteins could act at an early SNARE assembly step to promote vesicle-plasma membrane adhesion or at a late step to overcome the energetic barrier for fusion. Here, we use the neuronal cognates of each of these protein families to recapitulate, and distinguish, membrane adhesion and fusion on a novel lipidic platform suitable for imaging by fluorescence microscopy. Vesicle SNARE (v-SNARE) proteins reconstituted into giant vesicles ( approximately 10 mum) are fully mobile and functional. Through confocal microscopy, we observe that large vesicles ( approximately 100 nm) carrying target membrane SNAREs (t-SNAREs) both adhere to and freely move on the surface of the v-SNARE giant vesicle. Under conditions where the intrinsic ability of SNAREs to drive fusion is minimized, Munc18 stimulates both SNARE-dependent stable adhesion and fusion. Furthermore, mutation of a critical Munc18-binding residue on the N terminus of the t-SNARE syntaxin uncouples Munc18-stimulated vesicle adhesion from membrane fusion. We expect that the study of SNARE-mediated fusion with giant membranes will find wide applicability in distinguishing adhesion- and fusion-directed SNARE regulatory factors.
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Cohen R, Marom M, Atlas D. Depolarization-evoked secretion requires two vicinal transmembrane cysteines of syntaxin 1A. PLoS One 2007; 2:e1273. [PMID: 18060067 PMCID: PMC2094736 DOI: 10.1371/journal.pone.0001273] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2007] [Accepted: 11/14/2007] [Indexed: 11/24/2022] Open
Abstract
Background The interactions of the voltage-gated Ca2+ channel (VGCC) with syntaxin 1A (Sx 1A), Synaptosome-associated protein of 25 kD (SNAP-25), and synaptotagmin, couple electrical excitation to evoked secretion. Two vicinal Cys residues, Cys 271 and Cys 272 in the Sx 1A transmembrane domain, are highly conserved and participate in modulating channel kinetics. Each of the Sx1A Cys mutants, differently modify the kinetics of Cav1.2, and neuronal Cav2.2 calcium channel. Methodology/Principle Findings We examined the effects of various Sx1A Cys mutants and the syntaxin isoforms 2, 3, and 4 each of which lack vicinal Cys residues, on evoked secretion, monitoring capacitance transients in a functional release assay. Membrane capacitance in Xenopus oocytes co-expressing Cav1.2, Sx1A, SNAP-25 and synaptotagmin, which is Bot C- and Bot A-sensitive, was elicited by a double 500 ms depolarizing pulse to 0 mV. The evoked-release was obliterated when a single Cys Sx1A mutant or either one of the Sx isoforms were substituted for Sx 1A, demonstrating the essential role of vicinal Cys residues in the depolarization mediated process. Protein expression and confocal imaging established the level of the mutated proteins in the cell and their targeting to the plasma membrane. Conclusions/Significance We propose a model whereby the two adjacent transmembranal Cys residues of Sx 1A, lash two calcium channels. Consistent with the necessity of a minimal fusion complex termed the excitosome, each Sx1A is in a complex with SNAP-25, Syt1, and the Ca2+ channel. A Hill coefficient >2 imply that at least three excitosome complexes are required for generating a secreting hetero-oligomer protein complex. This working model suggests that a fusion pore that opens during membrane depolarization could be lined by alternating transmembrane segments of Sx1A and VGCC. The functional coupling of distinct amino acids of Sx 1A with VGCC appears to be essential for depolarization-evoked secretion.
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Affiliation(s)
- Roy Cohen
- Department of Biological Chemistry, The Alexander Silberman Institute of Life Sciences, The Hebrew University of Jerusalem, Jerusalem, Israel
| | - Merav Marom
- Department of Biological Chemistry, The Alexander Silberman Institute of Life Sciences, The Hebrew University of Jerusalem, Jerusalem, Israel
| | - Daphne Atlas
- Department of Biological Chemistry, The Alexander Silberman Institute of Life Sciences, The Hebrew University of Jerusalem, Jerusalem, Israel
- * To whom correspondence should be addressed. E-mail:
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