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Balasubramaniam B, Topalidou I, Kelley M, Meadows SM, Funk O, Ailion M, Fay DS. Effectors of anterior morphogenesis in C. elegans embryos. Biol Open 2023; 12:bio059982. [PMID: 37345480 PMCID: PMC10339035 DOI: 10.1242/bio.059982] [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: 04/23/2023] [Accepted: 06/19/2023] [Indexed: 06/23/2023] Open
Abstract
During embryogenesis the nascent Caenorhabditis elegans epidermis secretes an apical extracellular matrix (aECM) that serves as an external stabilizer, preventing deformation of the epidermis by mechanical forces exerted during morphogenesis. At present, the factors that contribute to aECM function are mostly unknown, including the aECM components themselves, their posttranslational regulators, and the pathways required for their secretion. Here we showed that two proteins previously linked to aECM function, SYM-3/FAM102A and SYM-4/WDR44, colocalize to intracellular and membrane-associated puncta and likely function in a complex. Proteomics experiments also suggested potential roles for SYM-3/FAM102A and SYM-4/WDR44 family proteins in intracellular trafficking. Nonetheless, we found no evidence to support a critical function for SYM-3 or SYM-4 in the apical deposition of two aECM components, NOAH-1 and FBN-1. Moreover, loss of a key splicing regulator of fbn-1, MEC-8/RBPMS2, had surprisingly little effect on the abundance or deposition of FBN-1. Using a focused screening approach, we identified 32 additional proteins that likely contribute to the structure and function of the embryonic aECM. We also characterized morphogenesis defects in embryos lacking mir-51 microRNA family members, which display a similar phenotype to mec-8; sym double mutants. Collectively, these findings add to our knowledge of factors controlling embryonic morphogenesis.
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Affiliation(s)
- Boopathi Balasubramaniam
- Department of Molecular Biology, College of Agriculture, Life Sciences and Natural Resources, University of Wyoming, Laramie 82071-3944, WY, USA
| | - Irini Topalidou
- Department of Biochemistry, University of Washington, Seattle 98195-7350, WA, USA
| | - Melissa Kelley
- Department of Molecular Biology, College of Agriculture, Life Sciences and Natural Resources, University of Wyoming, Laramie 82071-3944, WY, USA
| | - Sarina M. Meadows
- Department of Molecular Biology, College of Agriculture, Life Sciences and Natural Resources, University of Wyoming, Laramie 82071-3944, WY, USA
| | - Owen Funk
- Department of Molecular Biology, College of Agriculture, Life Sciences and Natural Resources, University of Wyoming, Laramie 82071-3944, WY, USA
| | - Michael Ailion
- Department of Biochemistry, University of Washington, Seattle 98195-7350, WA, USA
| | - David S. Fay
- Department of Molecular Biology, College of Agriculture, Life Sciences and Natural Resources, University of Wyoming, Laramie 82071-3944, WY, USA
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Boopathi B, Topalidou I, Kelley M, Meadows SM, Funk O, Ailion M, Fay DS. Pathways that affect anterior morphogenesis in C. elegans embryos. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.04.23.537986. [PMID: 37163004 PMCID: PMC10168279 DOI: 10.1101/2023.04.23.537986] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/11/2023]
Abstract
During embryogenesis the nascent Caenorhabditis elegans epidermis secretes an apical extracellular matrix (aECM) that serves as an external stabilizer, preventing deformation of the epidermis by mechanical forces exerted during morphogenesis. We showed that two conserved proteins linked to this process, SYM-3/FAM102A and SYM-4/WDR44, colocalize to intracellular and membrane-associated puncta and likely function together in a complex. Proteomics data also suggested potential roles for FAM102A and WDR44 family proteins in intracellular trafficking, consistent with their localization patterns. Nonetheless, we found no evidence to support a clear function for SYM-3 or SYM-4 in the apical deposition of two aECM components, FBN-1 and NOAH. Surprisingly, loss of MEC-8/RBPMS2, a conserved splicing factor and regulator of fbn-1 , had little effect on the abundance or deposition of FBN-1 to the aECM. Using a focused screening approach, we identified 32 additional proteins that likely contribute to the structure and function of the embryonic aECM. Lastly, we examined morphogenesis defects in embryos lacking mir-51 microRNA family members, which display a related embryonic phenotype to mec-8; sym double mutants. Collectively, our findings add to our knowledge of pathways controlling embryonic morphogenesis. SUMMARY STATEMENT We identify new proteins in apical ECM biology in C. elegans and provide evidence that SYM-3/FAM102A and SYM-4/WDR44 function together in trafficking but do not regulate apical ECM protein deposition.
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Affiliation(s)
- Balasubramaniam Boopathi
- Department of Molecular Biology, College of Agriculture, Life Sciences and Natural Resources, University of Wyoming, Laramie, Wyoming, United States of America
| | - Irini Topalidou
- Department of Biochemistry, University of Washington, Seattle, United States of America
| | - Melissa Kelley
- Department of Molecular Biology, College of Agriculture, Life Sciences and Natural Resources, University of Wyoming, Laramie, Wyoming, United States of America
| | - Sarina M Meadows
- Department of Molecular Biology, College of Agriculture, Life Sciences and Natural Resources, University of Wyoming, Laramie, Wyoming, United States of America
| | - Owen Funk
- Department of Molecular Biology, College of Agriculture, Life Sciences and Natural Resources, University of Wyoming, Laramie, Wyoming, United States of America
| | - Michael Ailion
- Department of Biochemistry, University of Washington, Seattle, United States of America
| | - David S Fay
- Department of Molecular Biology, College of Agriculture, Life Sciences and Natural Resources, University of Wyoming, Laramie, Wyoming, United States of America
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Tang X, Yu D, Wang H, Lei Z, Zhai Y, Sun M, Chen S, Wang Y, Liu Z, Hu W, Wang X. Synaptotagmin 1-mediated cell membrane penetration and dopamine release enhancement by latroeggtoxin-VI. Int J Biol Macromol 2022; 216:906-915. [PMID: 35914553 DOI: 10.1016/j.ijbiomac.2022.07.208] [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: 04/03/2022] [Revised: 07/24/2022] [Accepted: 07/25/2022] [Indexed: 11/05/2022]
Abstract
Latroeggtoxin-VI (LETX-VI), a proteinaceous neurotoxin mined from the egg transcriptome of spider L. tredecimguttatus, was previously found to promote the release of dopamine from PC12 cells. However, the relevant molecular mechanism has not been fully clear. Here LETX-VI was demonstrated to rapidly penetrate the plasma membrane of PC12 cells via the vesicle exocytosis/endocytosis cycle, during which vesicular transmembrane protein synaptotagmin 1 (Syt1) functions as a receptor, with its vesicle luminal domain interacting with the C-terminal region of LETX-VI. The C-terminal sequence of LETX-VI is the functional region for both entering cells and promoting dopamine release. After gaining entry into the PC12 cells, LETX-VI down-regulated the phosphorylation levels of Syt1 at T201 and T195, thereby facilitating vesicle fusion with plasma membrane and thus promoting dopamine release. The relevant mechanism analysis indicated that LETX-VI has a protein phosphatase 2A (PP2A) activator activity. The present work has not only probed into the Syt1-mediated action mechanism of LETX-VI, but also revealed the structure-function relationship of the toxin, thus suggesting its potential applications in the drug transmembrane delivery and treatment of the diseases related to dopamine release and PP2A activity deficiency.
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Affiliation(s)
- Xiaochao Tang
- State Key Laboratory of Developmental Biology of Freshwater Fish, Protein Chemistry Laboratory, College of Life Sciences, Hunan Normal University, Changsha 410081, Hunan, China
| | - Dianmei Yu
- State Key Laboratory of Developmental Biology of Freshwater Fish, Protein Chemistry Laboratory, College of Life Sciences, Hunan Normal University, Changsha 410081, Hunan, China
| | - Haiyan Wang
- State Key Laboratory of Developmental Biology of Freshwater Fish, Protein Chemistry Laboratory, College of Life Sciences, Hunan Normal University, Changsha 410081, Hunan, China
| | - Zhixiang Lei
- State Key Laboratory of Developmental Biology of Freshwater Fish, Protein Chemistry Laboratory, College of Life Sciences, Hunan Normal University, Changsha 410081, Hunan, China
| | - Yiwen Zhai
- State Key Laboratory of Developmental Biology of Freshwater Fish, Protein Chemistry Laboratory, College of Life Sciences, Hunan Normal University, Changsha 410081, Hunan, China
| | - Minglu Sun
- State Key Laboratory of Developmental Biology of Freshwater Fish, Protein Chemistry Laboratory, College of Life Sciences, Hunan Normal University, Changsha 410081, Hunan, China
| | - Si Chen
- State Key Laboratory of Developmental Biology of Freshwater Fish, Protein Chemistry Laboratory, College of Life Sciences, Hunan Normal University, Changsha 410081, Hunan, China
| | - Ying Wang
- State Key Laboratory of Developmental Biology of Freshwater Fish, Protein Chemistry Laboratory, College of Life Sciences, Hunan Normal University, Changsha 410081, Hunan, China
| | - Zhen Liu
- State Key Laboratory of Developmental Biology of Freshwater Fish, Protein Chemistry Laboratory, College of Life Sciences, Hunan Normal University, Changsha 410081, Hunan, China
| | - Weijun Hu
- State Key Laboratory of Developmental Biology of Freshwater Fish, Protein Chemistry Laboratory, College of Life Sciences, Hunan Normal University, Changsha 410081, Hunan, China
| | - Xianchun Wang
- State Key Laboratory of Developmental Biology of Freshwater Fish, Protein Chemistry Laboratory, College of Life Sciences, Hunan Normal University, Changsha 410081, Hunan, China.
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Bykhovskaia M. SNARE complex alters the interactions of the Ca 2+ sensor synaptotagmin 1 with lipid bilayers. Biophys J 2021; 120:642-661. [PMID: 33453271 DOI: 10.1016/j.bpj.2020.12.025] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2020] [Revised: 12/19/2020] [Accepted: 12/24/2020] [Indexed: 12/24/2022] Open
Abstract
Release of neuronal transmitters from nerve terminals is triggered by the molecular Ca2+ sensor synaptotagmin 1 (Syt1). Syt1 is a transmembrane protein attached to the synaptic vesicle (SV), and its cytosolic region comprises two domains, C2A and C2B, which are thought to penetrate into lipid bilayers upon Ca2+ binding. Before fusion, SVs become attached to the presynaptic membrane (PM) by the four-helical SNARE complex, which is thought to bind the C2B domain in vivo. To understand how the interactions of Syt1 with lipid bilayers and the SNARE complex trigger fusion, we performed molecular dynamics (MD) simulations at a microsecond scale. We investigated how the isolated C2 modules and the C2AB tandem of Syt1 interact with membranes mimicking either SV or PM. The simulations showed that the C2AB tandem can either bridge SV and PM or insert into PM with its Ca2+-bound tips and that the latter configuration is more favorable. Surprisingly, C2 domains did not cooperate in penetrating into PM but instead mutually hindered their insertion into the bilayer. To test whether the interaction of Syt1 with lipid bilayers could be affected by the C2B-SNARE attachment, we performed systematic conformational analysis of the C2AB-SNARE complex. Notably, we found that the C2B-SNARE interface precludes the coupling of C2 domains and promotes their insertion into PM. We performed the MD simulations of the prefusion protein complex positioned between the lipid bilayers mimicking PM and SV, and our results demonstrated in silico that the presence of the Ca2+ bound C2AB tandem promotes lipid merging. Altogether, our MD simulations elucidated the role of the Syt1-SNARE interactions in the fusion process and produced the dynamic all-atom model of the prefusion protein-lipid complex.
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Voleti R, Jaczynska K, Rizo J. Ca 2+-dependent release of synaptotagmin-1 from the SNARE complex on phosphatidylinositol 4,5-bisphosphate-containing membranes. eLife 2020; 9:57154. [PMID: 32808925 PMCID: PMC7498268 DOI: 10.7554/elife.57154] [Citation(s) in RCA: 33] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2020] [Accepted: 08/12/2020] [Indexed: 11/13/2022] Open
Abstract
The Ca2+ sensor synaptotagmin-1 and the SNARE complex cooperate to trigger neurotransmitter release. Structural studies elucidated three distinct synaptotagmin-1-SNARE complex binding modes involving 'polybasic', 'primary' and 'tripartite' interfaces of synaptotagmin-1. We investigated these interactions using NMR and fluorescence spectroscopy. Synaptotagmin-1 binds to the SNARE complex through the polybasic and primary interfaces in solution. Ca2+-free synaptotagmin-1 binds to SNARE complexes anchored on PIP2-containing nanodiscs. R398Q/R399Q and E295A/Y338W mutations at the primary interface, which strongly impair neurotransmitter release, disrupt and enhance synaptotagmin-1-SNARE complex binding, respectively. Ca2+ induces tight binding of synaptotagmin-1 to PIP2-containing nanodiscs, disrupting synaptotagmin-1-SNARE interactions. Specific effects of mutations in the polybasic region on Ca2+-dependent synaptotagmin-1-PIP2-membrane interactions correlate with their effects on release. Our data suggest that synaptotagmin-1 binds to the SNARE complex through the primary interface and that Ca2+ releases this interaction, inducing PIP2/membrane binding and allowing cooperation between synaptotagmin-1 and the SNAREs in membrane fusion to trigger release.
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Affiliation(s)
- Rashmi Voleti
- Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, United States.,Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, United States.,Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, United States
| | - Klaudia Jaczynska
- Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, United States.,Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, United States.,Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, United States
| | - Josep Rizo
- Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, United States.,Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, United States.,Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, United States
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Tible M, Sandelius Å, Höglund K, Brinkmalm A, Cognat E, Dumurgier J, Zetterberg H, Hugon J, Paquet C, Blennow K. Dissection of synaptic pathways through the CSF biomarkers for predicting Alzheimer disease. Neurology 2020; 95:e953-e961. [PMID: 32586895 DOI: 10.1212/wnl.0000000000010131] [Citation(s) in RCA: 47] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2019] [Accepted: 02/15/2020] [Indexed: 11/15/2022] Open
Abstract
OBJECTIVE To assess the ability of a combination of synaptic CSF biomarkers to separate Alzheimer disease (AD) and non-AD disorders and to help in the differential diagnosis between neurocognitive diseases. METHODS This was a retrospective cross-sectional monocentric study. All participants explored with CSF assessments for neurocognitive decline were invited to participate. After complete clinical and imaging evaluations, 243 patients were included. CSF synaptic (GAP-43, neurogranin, SNAP-25 total, SNAP-25aa40, synaptotagmin-1) and AD biomarkers were blindly quantified with ELISA or mass spectrometry. Statistical analysis compared CSF levels between the various groups of AD dementias (n = 81), mild cognitive impairment (MCI)-AD (n = 30), other MCI (n = 49), other dementias (OD) (n = 49), and neurologic controls (n = 35) and their discriminatory powers. RESULTS All synaptic biomarkers were significantly increased in patients with MCI-AD and AD-dementia compared to the other groups. All synaptic biomarkers could efficiently discriminate AD dementias from OD (AUC ≥0.80). All but synaptotagmin were also able to discriminate patients with MCI-AD from controls (area under the curve [AUC] ≥0.85) and those with AD dementias from controls (AUC ≥0.80). Overall, CSF SNAP-25aa40 had the highest discriminative power (AUC 0.93 between patients with AD dementias and controls or OD, AUC 0.90 between those with MCI-AD and controls). Higher levels were associated with 2 alleles of APOE ε4. CONCLUSION All synaptic biomarkers tested had a good discriminatory power to distinguish patients with AD abnormal CSF from those with non-AD disorders. SNAP25aa40 demonstrated the highest power to discriminate AD CSF-positive patients from patients without AD and neurologic controls in this cohort. CLASSIFICATION OF EVIDENCE This retrospective study provides Class II evidence that CSF synaptic biomarkers discriminate patients with AD from those without AD.
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Affiliation(s)
- Marion Tible
- From the Université de Paris INSERM U1144 (M.T., E.C., J.D., J.H., C.P.), France; Clinical Neurochemistry Laboratory (A.S., K.H., A.B., H.Z., K.B.), Sahlgrenska University Hospital; Institute of Neuroscience and Physiology (A.S., K.H., A.B., H.Z., K.B.), Department of Psychiatry and Neurochemistry, Sahlgrenska Academy at the University of Gothenburg, Mölndal, Sweden; and Center of Cognitive Neurology (E.C., J.D., J.H., C.P.), Lariboisière Fernand-Widal Hospital, APHP, Paris, France
| | - Åsa Sandelius
- From the Université de Paris INSERM U1144 (M.T., E.C., J.D., J.H., C.P.), France; Clinical Neurochemistry Laboratory (A.S., K.H., A.B., H.Z., K.B.), Sahlgrenska University Hospital; Institute of Neuroscience and Physiology (A.S., K.H., A.B., H.Z., K.B.), Department of Psychiatry and Neurochemistry, Sahlgrenska Academy at the University of Gothenburg, Mölndal, Sweden; and Center of Cognitive Neurology (E.C., J.D., J.H., C.P.), Lariboisière Fernand-Widal Hospital, APHP, Paris, France
| | - Kina Höglund
- From the Université de Paris INSERM U1144 (M.T., E.C., J.D., J.H., C.P.), France; Clinical Neurochemistry Laboratory (A.S., K.H., A.B., H.Z., K.B.), Sahlgrenska University Hospital; Institute of Neuroscience and Physiology (A.S., K.H., A.B., H.Z., K.B.), Department of Psychiatry and Neurochemistry, Sahlgrenska Academy at the University of Gothenburg, Mölndal, Sweden; and Center of Cognitive Neurology (E.C., J.D., J.H., C.P.), Lariboisière Fernand-Widal Hospital, APHP, Paris, France
| | - Ann Brinkmalm
- From the Université de Paris INSERM U1144 (M.T., E.C., J.D., J.H., C.P.), France; Clinical Neurochemistry Laboratory (A.S., K.H., A.B., H.Z., K.B.), Sahlgrenska University Hospital; Institute of Neuroscience and Physiology (A.S., K.H., A.B., H.Z., K.B.), Department of Psychiatry and Neurochemistry, Sahlgrenska Academy at the University of Gothenburg, Mölndal, Sweden; and Center of Cognitive Neurology (E.C., J.D., J.H., C.P.), Lariboisière Fernand-Widal Hospital, APHP, Paris, France
| | - Emmanuel Cognat
- From the Université de Paris INSERM U1144 (M.T., E.C., J.D., J.H., C.P.), France; Clinical Neurochemistry Laboratory (A.S., K.H., A.B., H.Z., K.B.), Sahlgrenska University Hospital; Institute of Neuroscience and Physiology (A.S., K.H., A.B., H.Z., K.B.), Department of Psychiatry and Neurochemistry, Sahlgrenska Academy at the University of Gothenburg, Mölndal, Sweden; and Center of Cognitive Neurology (E.C., J.D., J.H., C.P.), Lariboisière Fernand-Widal Hospital, APHP, Paris, France
| | - Julien Dumurgier
- From the Université de Paris INSERM U1144 (M.T., E.C., J.D., J.H., C.P.), France; Clinical Neurochemistry Laboratory (A.S., K.H., A.B., H.Z., K.B.), Sahlgrenska University Hospital; Institute of Neuroscience and Physiology (A.S., K.H., A.B., H.Z., K.B.), Department of Psychiatry and Neurochemistry, Sahlgrenska Academy at the University of Gothenburg, Mölndal, Sweden; and Center of Cognitive Neurology (E.C., J.D., J.H., C.P.), Lariboisière Fernand-Widal Hospital, APHP, Paris, France
| | - Henrik Zetterberg
- From the Université de Paris INSERM U1144 (M.T., E.C., J.D., J.H., C.P.), France; Clinical Neurochemistry Laboratory (A.S., K.H., A.B., H.Z., K.B.), Sahlgrenska University Hospital; Institute of Neuroscience and Physiology (A.S., K.H., A.B., H.Z., K.B.), Department of Psychiatry and Neurochemistry, Sahlgrenska Academy at the University of Gothenburg, Mölndal, Sweden; and Center of Cognitive Neurology (E.C., J.D., J.H., C.P.), Lariboisière Fernand-Widal Hospital, APHP, Paris, France
| | - Jacques Hugon
- From the Université de Paris INSERM U1144 (M.T., E.C., J.D., J.H., C.P.), France; Clinical Neurochemistry Laboratory (A.S., K.H., A.B., H.Z., K.B.), Sahlgrenska University Hospital; Institute of Neuroscience and Physiology (A.S., K.H., A.B., H.Z., K.B.), Department of Psychiatry and Neurochemistry, Sahlgrenska Academy at the University of Gothenburg, Mölndal, Sweden; and Center of Cognitive Neurology (E.C., J.D., J.H., C.P.), Lariboisière Fernand-Widal Hospital, APHP, Paris, France
| | - Claire Paquet
- From the Université de Paris INSERM U1144 (M.T., E.C., J.D., J.H., C.P.), France; Clinical Neurochemistry Laboratory (A.S., K.H., A.B., H.Z., K.B.), Sahlgrenska University Hospital; Institute of Neuroscience and Physiology (A.S., K.H., A.B., H.Z., K.B.), Department of Psychiatry and Neurochemistry, Sahlgrenska Academy at the University of Gothenburg, Mölndal, Sweden; and Center of Cognitive Neurology (E.C., J.D., J.H., C.P.), Lariboisière Fernand-Widal Hospital, APHP, Paris, France.
| | - Kaj Blennow
- From the Université de Paris INSERM U1144 (M.T., E.C., J.D., J.H., C.P.), France; Clinical Neurochemistry Laboratory (A.S., K.H., A.B., H.Z., K.B.), Sahlgrenska University Hospital; Institute of Neuroscience and Physiology (A.S., K.H., A.B., H.Z., K.B.), Department of Psychiatry and Neurochemistry, Sahlgrenska Academy at the University of Gothenburg, Mölndal, Sweden; and Center of Cognitive Neurology (E.C., J.D., J.H., C.P.), Lariboisière Fernand-Widal Hospital, APHP, Paris, France
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Abstract
Modulation of neurotransmitter exocytosis by activated Gi/o coupled G-protein coupled receptors (GPCRs) is a universal regulatory mechanism used both to avoid overstimulation and to influence circuitry. One of the known modulation mechanisms is the interaction between Gβγ and the soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNAREs). There are 5 Gβ and 12 Gγ subunits, but specific Gβγs activated by a given GPCR and the specificity to effectors, such as SNARE, in vivo are not known. Although less studied, Gβγ binding to the exocytic fusion machinery (i.e. SNARE) provides a more direct regulatory mechanism for neurotransmitter release. Here, we review some recent insights in the architecture of the synaptic terminal, modulation of synaptic transmission, and implications of G protein modulation of synaptic transmission in diseases. Numerous presynaptic proteins are involved in the architecture of synaptic terminals, particularly the active zone, and their importance in the regulation of exocytosis is still not completely understood. Further understanding of the Gβγ-SNARE interaction and the architecture and mechanisms of exocytosis may lead to the discovery of novel therapeutic targets to help patients with various disorders such as hypertension, attention-deficit/hyperactivity disorder, post-traumatic stress disorder, and acute/chronic pain.
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Affiliation(s)
- Yun Young Yim
- Department of Pharmacology, Vanderbilt University, Nashville 37232-6600, TN, United States
| | - Zack Zurawski
- Department of Pharmacology, Vanderbilt University, Nashville 37232-6600, TN, United States
| | - Heidi Hamm
- Department of Pharmacology, Vanderbilt University, Nashville 37232-6600, TN, United States.
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Park Y, Ryu JK. Models of synaptotagmin-1 to trigger Ca 2+ -dependent vesicle fusion. FEBS Lett 2018; 592:3480-3492. [PMID: 30004579 DOI: 10.1002/1873-3468.13193] [Citation(s) in RCA: 39] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2018] [Revised: 07/02/2018] [Accepted: 07/06/2018] [Indexed: 11/08/2022]
Abstract
Vesicles in neurons and neuroendocrine cells store neurotransmitters and peptide hormones, which are released by vesicle fusion in response to Ca2+ -evoking stimuli. Synaptotagmin-1 (Syt1), a Ca2+ sensor, mediates ultrafast exocytosis in neurons and neuroendocrine cells. After vesicle docking, Syt1 has two main groups of binding partners: anionic phospholipids and the SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptors) complex. The molecular mechanisms by which Syt1 triggers vesicle fusion remain controversial. This Review introduces and summarizes six molecular models of Syt1: (a) Syt1 triggers SNARE unclamping by displacing complexin, (b) Syt1 clamps SNARE zippering, (c) Syt1 causes membrane curvature, (d) membrane bridging by Syt1, (e) Syt1 is a vesicle-plasma membrane distance regulator, and (f) Syt1 undergoes circular oligomerization. We discuss important conditions to test Syt1 activity in vitro and attempt to illustrate the possible roles of Syt1.
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Affiliation(s)
- Yongsoo Park
- Department of Molecular Biology and Genetics, Koç University, Istanbul, Turkey
| | - Je-Kyung Ryu
- Department of Bionanoscience, Kavli Institute of Nanoscience Delft, Delft University of Technology, The Netherlands
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MacDougall DD, Lin Z, Chon NL, Jackman SL, Lin H, Knight JD, Anantharam A. The high-affinity calcium sensor synaptotagmin-7 serves multiple roles in regulated exocytosis. J Gen Physiol 2018; 150:783-807. [PMID: 29794152 PMCID: PMC5987875 DOI: 10.1085/jgp.201711944] [Citation(s) in RCA: 34] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2017] [Accepted: 05/07/2018] [Indexed: 12/19/2022] Open
Abstract
MacDougall et al. review the structure and function of the calcium sensor synaptotagmin-7 in exocytosis. Synaptotagmin (Syt) proteins comprise a 17-member family, many of which trigger exocytosis in response to calcium. Historically, most studies have focused on the isoform Syt-1, which serves as the primary calcium sensor in synchronous neurotransmitter release. Recently, Syt-7 has become a topic of broad interest because of its extreme calcium sensitivity and diversity of roles in a wide range of cell types. Here, we review the known and emerging roles of Syt-7 in various contexts and stress the importance of its actions. Unique functions of Syt-7 are discussed in light of recent imaging, electrophysiological, and computational studies. Particular emphasis is placed on Syt-7–dependent regulation of synaptic transmission and neuroendocrine cell secretion. Finally, based on biochemical and structural data, we propose a mechanism to link Syt-7’s role in membrane fusion with its role in subsequent fusion pore expansion via strong calcium-dependent phospholipid binding.
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Affiliation(s)
| | - Zesen Lin
- Department of Pharmacology, University of Michigan, Ann Arbor, MI
| | - Nara L Chon
- Department of Chemistry, University of Colorado, Denver, CO
| | - Skyler L Jackman
- Vollum Institute, Oregon Health & Science University, Portland, OR
| | - Hai Lin
- Department of Chemistry, University of Colorado, Denver, CO
| | | | - Arun Anantharam
- Department of Pharmacology, University of Michigan, Ann Arbor, MI
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Bruinsma S, James DJ, Quintana Serrano M, Esquibel J, Woo SS, Kielar-Grevstad E, Crummy E, Qurashi R, Kowalchyk JA, Martin TFJ. Small molecules that inhibit the late stage of Munc13-4-dependent secretory granule exocytosis in mast cells. J Biol Chem 2018; 293:8217-8229. [PMID: 29615494 PMCID: PMC5971468 DOI: 10.1074/jbc.ra117.001547] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2017] [Revised: 03/30/2018] [Indexed: 01/05/2023] Open
Abstract
Ca2+-dependent secretory granule fusion with the plasma membrane is the final step for the exocytic release of inflammatory mediators, neuropeptides, and peptide hormones. Secretory cells use a similar protein machinery at late steps in the regulated secretory pathway, employing protein isoforms from the Rab, Sec1/Munc18, Munc13/CAPS, SNARE, and synaptotagmin protein families. However, no small-molecule inhibitors of secretory granule exocytosis that target these proteins are currently available but could have clinical utility. Here we utilized a high-throughput screen of a 25,000-compound library that identified 129 small-molecule inhibitors of Ca2+-triggered secretory granule exocytosis in RBL-2H3 mast cells. These inhibitors broadly fell into six different chemical classes, and follow-up permeable cell and liposome fusion assays identified the target for one class of these inhibitors. A family of 2-aminobenzothiazoles (termed benzothiazole exocytosis inhibitors or bexins) was found to inhibit mast cell secretory granule fusion by acting on a Ca2+-dependent, C2 domain–containing priming factor, Munc13-4. Our findings further indicated that bexins interfere with Munc13-4–membrane interactions and thereby inhibit Munc13-4–dependent membrane fusion. We conclude that bexins represent a class of specific secretory pathway inhibitors with potential as therapeutic agents.
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Affiliation(s)
- Stephen Bruinsma
- Department of Biochemistry, University of Wisconsin, Madison Wisconsin 53706
| | - Declan J James
- Department of Biochemistry, University of Wisconsin, Madison Wisconsin 53706
| | | | - Joseph Esquibel
- Department of Biochemistry, University of Wisconsin, Madison Wisconsin 53706
| | - Sang Su Woo
- Department of Biochemistry, University of Wisconsin, Madison Wisconsin 53706
| | | | - Ellen Crummy
- Department of Biochemistry, University of Wisconsin, Madison Wisconsin 53706
| | - Rehan Qurashi
- Department of Biochemistry, University of Wisconsin, Madison Wisconsin 53706
| | - Judy A Kowalchyk
- Department of Biochemistry, University of Wisconsin, Madison Wisconsin 53706
| | - Thomas F J Martin
- Department of Biochemistry, University of Wisconsin, Madison Wisconsin 53706.
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11
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Öhrfelt A, Brinkmalm A, Dumurgier J, Brinkmalm G, Hansson O, Zetterberg H, Bouaziz-Amar E, Hugon J, Paquet C, Blennow K. The pre-synaptic vesicle protein synaptotagmin is a novel biomarker for Alzheimer's disease. ALZHEIMERS RESEARCH & THERAPY 2016; 8:41. [PMID: 27716408 PMCID: PMC5048479 DOI: 10.1186/s13195-016-0208-8] [Citation(s) in RCA: 121] [Impact Index Per Article: 15.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/07/2016] [Accepted: 09/05/2016] [Indexed: 11/22/2022]
Abstract
Background Synaptic degeneration is a central pathogenic event in Alzheimer’s disease that occurs early during the course of disease and correlates with cognitive symptoms. The pre-synaptic vesicle protein synaptotagmin-1 appears to be essential for the maintenance of an intact synaptic transmission and cognitive function. Synaptotagmin-1 in cerebrospinal fluid is a candidate Alzheimer biomarker for synaptic dysfunction that also may correlate with cognitive decline. Methods In this study, a novel mass spectrometry-based assay for measurement of cerebrospinal fluid synaptotagmin-1 was developed, and was evaluated in two independent sample sets of patients and controls. Sample set I included cerebrospinal fluid samples from patients with dementia due to Alzheimer’s disease (N = 17, age 52–86 years), patients with mild cognitive impairment due to Alzheimer’s disease (N = 5, age 62–88 years), and controls (N = 17, age 41–82 years). Sample set II included cerebrospinal fluid samples from patients with dementia due to Alzheimer’s disease (N = 24, age 52–84 years), patients with mild cognitive impairment due to Alzheimer’s disease (N = 18, age 58–83 years), and controls (N = 36, age 43–80 years). Results The reproducibility of the novel method showed coefficients of variation of the measured synaptotagmin-1 peptide 215–223 (VPYSELGGK) and peptide 238–245 (HDIIGEFK) of 14 % or below. In both investigated sample sets, the CSF levels of synaptotagmin-1 were significantly increased in patients with dementia due to Alzheimer’s disease (P ≤ 0.0001) and in patients with mild cognitive impairment due to Alzheimer’s disease (P < 0.001). In addition, in sample set I the synaptotagmin-1 level was significantly higher in patients with mild cognitive impairment due to Alzheimer’s disease compared with patients with dementia due to Alzheimer’s disease (P ≤ 0.05). Conclusions Cerebrospinal fluid synaptotagmin-1 is a promising biomarker to monitor synaptic dysfunction and degeneration in Alzheimer’s disease that may be useful for clinical diagnosis, to monitor effect on synaptic integrity by novel drug candidates, and to explore pathophysiology directly in patients with Alzheimer’s disease. Electronic supplementary material The online version of this article (doi:10.1186/s13195-016-0208-8) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Annika Öhrfelt
- Department of Psychiatry and Neurochemistry, Institute of Neuroscience and Physiology, The Sahlgrenska Academy at the University of Gothenburg, Sahlgrenska University Hospital, Mölndal, SE-431 80, Sweden.
| | - Ann Brinkmalm
- Department of Psychiatry and Neurochemistry, Institute of Neuroscience and Physiology, The Sahlgrenska Academy at the University of Gothenburg, Sahlgrenska University Hospital, Mölndal, SE-431 80, Sweden.,Clinical Neurochemistry Laboratory, Sahlgrenska University Hospital, Mölndal, Sweden
| | - Julien Dumurgier
- Centre Mémoire de Ressources et de Recherche (CMRR) Paris Nord Ile de France, INSERM UMR-S942, Groupe Hospitalier Lariboisière Fernand-Widal Saint-Louis, Paris, France
| | - Gunnar Brinkmalm
- Department of Psychiatry and Neurochemistry, Institute of Neuroscience and Physiology, The Sahlgrenska Academy at the University of Gothenburg, Sahlgrenska University Hospital, Mölndal, SE-431 80, Sweden
| | - Oskar Hansson
- Clinical Memory Research Unit, Department of Clinical Sciences, Lund University, Malmö, Sweden.,Memory Clinic, Skåne University Hospital, Malmö, Sweden
| | - Henrik Zetterberg
- Department of Psychiatry and Neurochemistry, Institute of Neuroscience and Physiology, The Sahlgrenska Academy at the University of Gothenburg, Sahlgrenska University Hospital, Mölndal, SE-431 80, Sweden.,Clinical Neurochemistry Laboratory, Sahlgrenska University Hospital, Mölndal, Sweden.,Department of Molecular Neuroscience, UCL Institute of Neurology, London, UK
| | - Elodie Bouaziz-Amar
- Service de Biochimie, Groupe Hospitalier Lariboisiere FW Saint-Louis, APHP, Université Paris Diderot, 75010, Paris, France
| | - Jacques Hugon
- Centre Mémoire de Ressources et de Recherche (CMRR) Paris Nord Ile de France, INSERM UMR-S942, Groupe Hospitalier Lariboisière Fernand-Widal Saint-Louis, Paris, France
| | - Claire Paquet
- Centre Mémoire de Ressources et de Recherche (CMRR) Paris Nord Ile de France, INSERM UMR-S942, Groupe Hospitalier Lariboisière Fernand-Widal Saint-Louis, Paris, France
| | - Kaj Blennow
- Department of Psychiatry and Neurochemistry, Institute of Neuroscience and Physiology, The Sahlgrenska Academy at the University of Gothenburg, Sahlgrenska University Hospital, Mölndal, SE-431 80, Sweden.,Clinical Neurochemistry Laboratory, Sahlgrenska University Hospital, Mölndal, Sweden
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12
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Synaptotagmin-1 binds to PIP(2)-containing membrane but not to SNAREs at physiological ionic strength. Nat Struct Mol Biol 2015; 22:815-23. [PMID: 26389740 PMCID: PMC4596797 DOI: 10.1038/nsmb.3097] [Citation(s) in RCA: 86] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2015] [Accepted: 08/26/2015] [Indexed: 12/19/2022]
Abstract
The Ca(2+) sensor synaptotagmin-1 is thought to trigger membrane fusion by binding to acidic membrane lipids and SNARE proteins. Previous work has shown that binding is mediated by electrostatic interactions that are sensitive to the ionic environment. However, the influence of divalent or polyvalent ions, at physiological concentrations, on synaptotagmin's binding to membranes or SNAREs has not been explored. Here we show that binding of rat synaptotagmin-1 to membranes containing phosphatidylinositol 4,5-bisphosphate (PIP2) is regulated by charge shielding caused by the presence of divalent cations. Surprisingly, polyvalent ions such as ATP and Mg(2+) completely abrogate synaptotagmin-1 binding to SNAREs regardless of the presence of Ca(2+). Altogether, our data indicate that at physiological ion concentrations Ca(2+)-dependent synaptotagmin-1 binding is confined to PIP2-containing membrane patches in the plasma membrane, suggesting that membrane interaction of synaptotagmin-1 rather than SNARE binding triggers exocytosis of vesicles.
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13
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Dynamic binding mode of a Synaptotagmin-1-SNARE complex in solution. Nat Struct Mol Biol 2015; 22:555-64. [PMID: 26030874 PMCID: PMC4496268 DOI: 10.1038/nsmb.3035] [Citation(s) in RCA: 115] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2015] [Accepted: 04/27/2015] [Indexed: 12/21/2022]
Abstract
Rapid neurotransmitter release depends on the Ca2+-sensor Synaptotagmin-1 and the SNARE complex formed by synaptobrevin, syntaxin-1 and SNAP-25. How Synaptotagmin-1 triggers release remains unclear, in part because elucidating high-resolution structures of Synaptotagmin-1-SNARE complexes has been challenging. An NMR approach based on lanthanide-induced pseudocontact shifts now reveals a dynamic binding mode where basic residues in the concave side of the Synaptotagmin-1 C2B domain β-sandwich interact with a polyacidic region of the SNARE complex formed by syntaxin-1 and SNAP-25. The physiological relevance of this dynamic structural model is supported by mutations in basic residues of Synaptotagmin-1 that markedly impair SNARE-complex binding in vitro and Synaptotagmin-1 function in neurons. Mutations with milder effects on binding have correspondingly milder effects on Synaptotagmin-1 function. Our results support a model whereby their dynamic interaction facilitates cooperation between synaptotagmin-1 and the SNAREs in inducing membrane fusion.
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14
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Martin TFJ. PI(4,5)P₂-binding effector proteins for vesicle exocytosis. Biochim Biophys Acta Mol Cell Biol Lipids 2014; 1851:785-93. [PMID: 25280637 DOI: 10.1016/j.bbalip.2014.09.017] [Citation(s) in RCA: 97] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2014] [Revised: 09/20/2014] [Accepted: 09/23/2014] [Indexed: 12/27/2022]
Abstract
PI(4,5)P₂participates directly in priming and possibly in fusion steps of Ca²⁺-triggered vesicle exocytosis. High concentration nanodomains of PI(4,5)P₂reside on the plasma membrane of neuroendocrine cells. A subset of vesicles that co-localize with PI(4,5)P₂ domains appear to undergo preferential exocytosis in stimulated cells. PI(4,5)P₂directly regulates vesicle exocytosis by recruiting and activating PI(4,5)P₂-binding proteins that regulate SNARE protein function including CAPS, Munc13-1/2, synaptotagmin-1, and other C2 domain-containing proteins. These PI(4,5)P₂effector proteins are coincidence detectors that engage in multiple interactions at vesicle exocytic sites. The SNARE protein syntaxin-1 also binds to PI(4,5)P₂, which promotes clustering, but an activating role for PI(4,5)P₂in syntaxin-1 function remains to be fully characterized. Similar principles underlie polarized constitutive vesicle fusion mediated in part by the PI(4,5)P₂-binding subunits of the exocyst complex (Sec3, Exo70). Overall, focal vesicle exocytosis occurs at sites landmarked by PI(4,5)P2, which serves to recruit and/or activate multifunctional PI(4,5)P₂-binding proteins. This article is part of a Special Issue entitled Phosphoinositides.
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Affiliation(s)
- Thomas F J Martin
- Biochemistry Department, University of Wisconsin, 433 Babcock Drive, Madison, WI 53706, USA.
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15
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Jayanthi S, Kathir KM, Rajalingam D, Furr M, Daily A, Thurman R, Rutherford L, Chandrashekar R, Adams P, Prudovsky I, Kumar TKS. Copper binding affinity of the C2B domain of synaptotagmin-1 and its potential role in the nonclassical secretion of acidic fibroblast growth factor. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2014; 1844:2155-63. [PMID: 25224745 DOI: 10.1016/j.bbapap.2014.09.008] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/03/2014] [Revised: 08/20/2014] [Accepted: 09/07/2014] [Indexed: 01/27/2023]
Abstract
Fibroblast growth factor 1 (FGF1) is a heparin-binding proangiogenic protein. FGF1 lacks the conventional N-terminal signal peptide required for secretion through the endoplasmic reticulum (ER)-Golgi secretory pathway. FGF1 is released through a Cu(2+)-mediated nonclassical secretion pathway. The secretion of FGF1 involves the formation of a Cu(2+)-mediated multiprotein release complex (MRC) including FGF1, S100A13 (a calcium-binding protein) and p40 synaptotagmin (Syt1). It is believed that the binding of Cu(2+) to the C2B domain is important for the release of FGF1 into the extracellular medium. In this study, using a variety of biophysical studies, Cu(2+) and lipid interactions of the C2B domain of Syt1 were characterized. Isothermal titration calorimetry (ITC) experiments reveal that the C2B domain binds to Cu(2+) in a biphasic manner involving an initial endothermic and a subsequent exothermic phase. Fluorescence energy transfer experiments using Tb(3+) show that there are two Cu(2+)-binding pockets on the C2B domain, and one of these is also a Ca(2+)-binding site. Lipid-binding studies using ITC demonstrate that the C2B domain preferentially binds to small unilamellar vesicles of phosphatidyl serine (PS). Results of the differential scanning calorimetry and limited trypsin digestion experiments suggest that the C2B domain is marginally destabilized upon binding to PS vesicles. These results, for the first time, suggest that the main role of the C2B domain of Syt1 is to serve as an anchor for the FGF1 MRC on the membrane bilayer. In addition, the binding of the C2B domain to the lipid bilayer is shown to significantly decrease the binding affinity of the protein to Cu(2+). The study provides valuable insights on the sequence of structural events that occur in the nonclassical secretion of FGF1.
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Affiliation(s)
- Srinivas Jayanthi
- Department of Chemistry and Biochemistry, University of Arkansas, Fayetteville, AR 72701, USA.
| | | | | | - Mercede Furr
- Department of Chemistry and Biochemistry, University of Arkansas, Fayetteville, AR 72701, USA.
| | - Anna Daily
- Department of Chemistry and Biochemistry, University of Arkansas, Fayetteville, AR 72701, USA.
| | - Ryan Thurman
- Department of Chemistry and Biochemistry, University of Arkansas, Fayetteville, AR 72701, USA.
| | - Lindsay Rutherford
- Department of Chemistry and Biochemistry, University of Arkansas, Fayetteville, AR 72701, USA.
| | - Reena Chandrashekar
- Department of Chemistry and Biochemistry, University of Arkansas, Fayetteville, AR 72701, USA.
| | - Paul Adams
- Department of Chemistry and Biochemistry, University of Arkansas, Fayetteville, AR 72701, USA.
| | - Igor Prudovsky
- Maine Medical Center Research Institute, Scarborough, ME 04074, USA.
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16
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Ma J, Kelly L, Ingram J, Price TJ, Meriney SD, Dittrich M. New insights into short-term synaptic facilitation at the frog neuromuscular junction. J Neurophysiol 2014; 113:71-87. [PMID: 25210157 DOI: 10.1152/jn.00198.2014] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Short-term synaptic facilitation occurs during high-frequency stimulation, is known to be dependent on presynaptic calcium ions, and persists for tens of milliseconds after a presynaptic action potential. We have used the frog neuromuscular junction as a model synapse for both experimental and computer simulation studies aimed at testing various mechanistic hypotheses proposed to underlie short-term synaptic facilitation. Building off our recently reported excess-calcium-binding-site model of synaptic vesicle release at the frog neuromuscular junction (Dittrich M, Pattillo JM, King JD, Cho S, Stiles JR, Meriney SD. Biophys J 104: 2751-2763, 2013), we have investigated several mechanisms of short-term facilitation at the frog neuromuscular junction. Our studies place constraints on previously proposed facilitation mechanisms and conclude that the presence of a second class of calcium sensor proteins distinct from synaptotagmin can explain known properties of facilitation observed at the frog neuromuscular junction. We were further able to identify a novel facilitation mechanism, which relied on the persistent binding of calcium-bound synaptotagmin molecules to lipids of the presynaptic membrane. In a real physiological context, both mechanisms identified in our study (and perhaps others) may act simultaneously to cause the experimentally observed facilitation. In summary, using a combination of computer simulations and physiological recordings, we have developed a stochastic computer model of synaptic transmission at the frog neuromuscular junction, which sheds light on the facilitation mechanisms in this model synapse.
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Affiliation(s)
- Jun Ma
- Biomedical Applications Group, Pittsburgh Supercomputing Center, Carnegie Mellon University, Pittsburgh, Pennsylvania; Joint Carnegie Mellon-University of Pittsburgh PhD Program in Computational Biology, School of Computer Science, Carnegie Mellon University, Pittsburgh, Pennsylvania
| | - Lauren Kelly
- Department of Neuroscience, University of Pittsburgh, Pittsburgh, Pennsylvania; and
| | - Justin Ingram
- Department of Neuroscience, University of Pittsburgh, Pittsburgh, Pennsylvania; and
| | - Thomas J Price
- Department of Neuroscience, University of Pittsburgh, Pittsburgh, Pennsylvania; and
| | - Stephen D Meriney
- Department of Neuroscience, University of Pittsburgh, Pittsburgh, Pennsylvania; and
| | - Markus Dittrich
- Biomedical Applications Group, Pittsburgh Supercomputing Center, Carnegie Mellon University, Pittsburgh, Pennsylvania; Department of Neuroscience, University of Pittsburgh, Pittsburgh, Pennsylvania; and Department of Computational and Systems Biology, University of Pittsburgh, Pittsburgh, Pennsylvania
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17
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Identification of Differentially Expressed Gene after Femoral Fracture via Microarray Profiling. Int J Genomics 2014; 2014:208751. [PMID: 25110652 PMCID: PMC4119616 DOI: 10.1155/2014/208751] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2014] [Revised: 05/08/2014] [Accepted: 05/18/2014] [Indexed: 11/28/2022] Open
Abstract
We aimed to investigate differentially expressed genes (DEGs) in different stages after femoral fracture based on rat models, providing the basis for the treatment of sport-related fractures. Gene expression data GSE3298 was downloaded from Gene Expression Omnibus (GEO), including 16 chips. All femoral fracture samples were classified into earlier fracture stage and later fracture stage. Total 87 DEGs simultaneously occurred in two stages, of which 4 genes showed opposite expression tendency. Out of the 4 genes, Rest and Cst8 were hub nodes in protein-protein interaction (PPI) network. The GO (Gene Ontology) function enrichment analysis verified that nutrition supply related genes were enriched in the earlier stage and neuron growth related genes were enriched in the later stage. Calcium signaling pathway was the most significant pathway in earlier stage; in later stage, DEGs were enriched into 2 neurodevelopment-related pathways. Analysis of Pearson's correlation coefficient showed that a total of 3,300 genes were significantly associated with fracture time, none of which was overlapped with identified DEGs. This study suggested that Rest and Cst8 might act as potential indicators for fracture healing. Calcium signaling pathway and neurodevelopment-related pathways might be deeply involved in bone healing after femoral fracture.
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18
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Synaptotagmin interaction with SNAP-25 governs vesicle docking, priming, and fusion triggering. J Neurosci 2013; 33:14417-30. [PMID: 24005294 DOI: 10.1523/jneurosci.1236-13.2013] [Citation(s) in RCA: 59] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023] Open
Abstract
SNARE complex assembly constitutes a key step in exocytosis that is rendered Ca(2+)-dependent by interactions with synaptotagmin-1. Two putative sites for synaptotagmin binding have recently been identified in SNAP-25 using biochemical methods: one located around the center and another at the C-terminal end of the SNARE bundle. However, it is still unclear whether and how synaptotagmin-1 × SNARE interactions at these sites are involved in regulating fast neurotransmitter release. Here, we have used electrophysiological techniques with high time-resolution to directly investigate the mechanistic ramifications of proposed SNAP-25 × synaptotagmin-1 interaction in mouse chromaffin cells. We demonstrate that the postulated central binding domain surrounding layer zero covers both SNARE motifs of SNAP-25 and is essential for vesicle docking, priming, and fast fusion-triggering. Mutation of this site caused no further functional alterations in synaptotagmin-1-deficient cells, indicating that the central acidic patch indeed constitutes a mechanistically relevant synaptotagmin-1 interaction site. Moreover, our data show that the C-terminal binding interface only plays a subsidiary role in triggering but is required for the full size of the readily releasable pool. Intriguingly, we also found that mutation of synaptotagmin-1 interaction sites led to more pronounced phenotypes in the context of the adult neuronal isoform SNAP-25B than in the embryonic isoform SNAP-25A. Further experiments demonstrated that stronger synaptotagmin-1 × SNAP-25B interactions allow for the larger primed vesicle pool supported by SNAP-25 isoform B. Thus, synaptotagmin-1 × SNARE interactions are not only required for multiple mechanistic steps en route to fusion but also underlie the developmental control of the releasable vesicle pool.
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19
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Giladi M, Michaeli L, Almagor L, Bar-On D, Buki T, Ashery U, Khananshvili D, Hirsch JA. The C2B domain is the primary Ca2+ sensor in DOC2B: a structural and functional analysis. J Mol Biol 2013; 425:4629-41. [PMID: 23994332 DOI: 10.1016/j.jmb.2013.08.017] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2013] [Revised: 08/12/2013] [Accepted: 08/21/2013] [Indexed: 12/21/2022]
Abstract
DOC2B (double-C2 domain) protein is thought to be a high-affinity Ca(2+) sensor for spontaneous and asynchronous neurotransmitter release. To elucidate the molecular features underlying its physiological role, we determined the crystal structures of its isolated C2A and C2B domains and examined their Ca(2+)-binding properties. We further characterized the solution structure of the tandem domains (C2AB) using small-angle X-ray scattering. In parallel, we tested structure-function correlates with live cell imaging tools. We found that, despite striking structural similarity, C2B binds Ca(2+) with considerably higher affinity than C2A. The C2AB solution structure is best modeled as two domains with a highly flexible orientation and no difference in the presence or absence of Ca(2+). In addition, kinetic studies of C2AB demonstrate that, in the presence of unilamellar vesicles, Ca(2+) binding is stabilized, as reflected by the ~10-fold slower rate of Ca(2+) dissociation than in the absence of vesicles. In cells, isolated C2B translocates to the plasma membrane (PM) with an EC50 of 400 nM while the C2A does not translocate at submicromolar Ca(2+) concentrations, supporting the biochemical observations. Nevertheless, C2AB translocates to the PM with an ~2-fold lower EC50 and to a greater extent than C2B. Our results, together with previous studies, reveal that the C2B is the primary Ca(2+) sensing unit in DOC2B, whereas C2A enhances the interaction of C2AB with the PM.
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Affiliation(s)
- Moshe Giladi
- Department of Physiology and Pharmacology, Sackler School of Medicine, Tel-Aviv University, Ramat-Aviv 69978, Israel
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20
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Zhou A, Brewer KD, Rizo J. Analysis of SNARE complex/synaptotagmin-1 interactions by one-dimensional NMR spectroscopy. Biochemistry 2013; 52:3446-56. [PMID: 23617808 DOI: 10.1021/bi400230u] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Neurotransmitter release depends critically on the Ca(2+) sensor synaptotagmin-1 and the SNARE proteins syntaxin-1, synaptobrevin, and SNAP-25, which mediate membrane fusion by forming tight SNARE complexes that bridge the synaptic vesicle and plasma membranes. Interactions between the SNARE complex and the two C2 domains of synaptotagmin-1 (the C2A and C2B domains) are believed to play a key role in coupling Ca(2+) sensing to membrane fusion, but the nature of these interactions is unclear, in part because of a paucity of data obtained by quantitative biophysical methods. Here we have analyzed synaptotagmin-1/SNARE complex interactions by monitoring the decrease in the intensities of one-dimensional (13)C-edited (1)H NMR spectra of (13)C-labeled fragments of synaptotagmin-1 upon binding to unlabeled SNARE complex. Our results indicate that there is a primary binding mode between synaptotagmin-1 and the SNARE complex that involves a polybasic region in the C2B domain and has a sub-micromolar affinity. Our NMR data, combined with precipitation assays, show that there are additional SNARE complex/synaptotagmin-1 interactions that lead to aggregation and that involve in part two arginines at the bottom of the C2B domain. Overall, this study shows the importance of disentangling the contributions of different types of interactions to SNARE complex/synaptotagmin-1 binding and illustrates the usefulness of one-dimensional NMR methods to analyze intricate protein interactions.
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Affiliation(s)
- Amy Zhou
- Departments of Biophysics, Biochemistry and Pharmacology, University of Texas Southwestern Medical Center , 6000 Harry Hines Boulevard, Dallas, Texas 75390, United States
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21
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Yeo H, Kim HW, Mo J, Lee D, Han S, Hong S, Koh MJ, Sun W, Choi S, Rhyu IJ, Kim H, Lee HW. Developmental expression and subcellular distribution of synaptotagmin 11 in rat hippocampus. Neuroscience 2012; 225:35-43. [PMID: 22960622 DOI: 10.1016/j.neuroscience.2012.08.062] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2012] [Revised: 08/21/2012] [Accepted: 08/29/2012] [Indexed: 11/18/2022]
Abstract
Synaptotagmins are required for Ca(2+)-dependent membrane-trafficking in either neuronal synaptic vesicles or cellular membranes. Previous reports suggested that the synaptotagmin 11 (syt11) gene is involved in the development of schizophrenia based on the genomic analysis of patients. Parkin protein binds to the C2 domains of Syt11 which leads to the polyubiquitination of Syt11. However, where and how Syt11 performs its role in the brain is largely unknown. Here, we report that Syt11 is expressed mainly in the brain. In addition, exogenously expressed Syt11 in HEK293 cells can form higher molecular weight complex via its transmembrane domain. Also, Syt11 is targeted to both dendrite and axon compartments. Immunocytochemistry showed that Syt11 is juxtaposed to postsynaptic markers in both excitatory and inhibitory synapses. Both neuroligin 1 and 2, which are postsynaptic cell adhesion molecules and differentially induce excitatory and inhibitory presynapses, respectively, recruit Syt11 in neuron coculture. Immunogold electron microscopy analysis revealed that Syt11 exists mainly in presynaptic neurotransmitter vesicles and plasma membrane, and rarely in postsynaptic sites. These results suggest that Syt11 may contribute to the regulation of neurotransmitter release in the excitatory and inhibitory presynapses, and postsynapse-targeted membrane trafficking in dendrites.
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Affiliation(s)
- H Yeo
- Department of Anatomy and Division of Brain Korea 21 Biomedical Science, College of Medicine, Korea University, 126-1, 5-Ka, Anam-Dong, Seongbuk-Gu, Seoul 136-705, Republic of Korea
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Boswell KL, James DJ, Esquibel JM, Bruinsma S, Shirakawa R, Horiuchi H, Martin TFJ. Munc13-4 reconstitutes calcium-dependent SNARE-mediated membrane fusion. ACTA ACUST UNITED AC 2012; 197:301-12. [PMID: 22508512 PMCID: PMC3328385 DOI: 10.1083/jcb.201109132] [Citation(s) in RCA: 70] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Munc13-4 is a Ca2+-dependent membrane- and SNARE-binding protein that promotes membrane fusion. Munc13-4 is a widely expressed member of the CAPS/Munc13 protein family proposed to function in priming secretory granules for exocytosis. Munc13-4 contains N- and C-terminal C2 domains (C2A and C2B) predicted to bind Ca2+, but Ca2+-dependent regulation of Munc13-4 activity has not been described. The C2 domains bracket a predicted SNARE-binding domain, but whether Munc13-4 interacts with SNARE proteins is unknown. We report that Munc13-4 bound Ca2+ and restored Ca2+-dependent granule exocytosis to permeable cells (platelets, mast, and neuroendocrine cells) dependent on putative Ca2+-binding residues in C2A and C2B. Munc13-4 exhibited Ca2+-stimulated SNARE interactions dependent on C2A and Ca2+-dependent membrane binding dependent on C2B. In an apparent coupling of membrane and SNARE binding, Munc13-4 stimulated SNARE-dependent liposome fusion dependent on putative Ca2+-binding residues in both C2A and C2B domains. Munc13-4 is the first priming factor shown to promote Ca2+-dependent SNARE complex formation and SNARE-mediated liposome fusion. These properties of Munc13-4 suggest its function as a Ca2+ sensor at rate-limiting priming steps in granule exocytosis.
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Affiliation(s)
- Kristin L Boswell
- Department of Biochemistry, University of Wisconsin, Madison, WI 53706, USA
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Kim JY, Choi BK, Choi MG, Kim SA, Lai Y, Shin YK, Lee NK. Solution single-vesicle assay reveals PIP2-mediated sequential actions of synaptotagmin-1 on SNAREs. EMBO J 2012; 31:2144-55. [PMID: 22407297 DOI: 10.1038/emboj.2012.57] [Citation(s) in RCA: 63] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2011] [Accepted: 02/08/2012] [Indexed: 12/20/2022] Open
Abstract
Synaptotagmin-1 (Syt1) is a major Ca(2+) sensor for synchronous neurotransmitter release, which requires vesicle fusion mediated by SNAREs (soluble N-ethylmaleimide-sensitive factor attachment protein receptors). Syt1 utilizes its diverse interactions with target membrane (t-) SNARE, SNAREpin, and phospholipids, to regulate vesicle fusion. To dissect the functions of Syt1, we apply a single-molecule technique, alternating-laser excitation (ALEX), which is capable of sorting out subpopulations of fusion intermediates and measuring their kinetics in solution. The results show that Syt1 undergoes at least three distinct steps prior to lipid mixing. First, without Ca(2+), Syt1 mediates vesicle docking by directly binding to t-SNARE/phosphatidylinositol 4,5-biphosphate (PIP(2)) complex and increases the docking rate by 10(3) times. Second, synaptobrevin-2 binding to t-SNARE displaces Syt1 from SNAREpin. Third, with Ca(2+), Syt1 rebinds to SNAREpin, which again requires PIP(2). Thus without Ca(2+), Syt1 may bring vesicles to the plasma membrane in proximity via binding to t-SNARE/PIP(2) to help SNAREpin formation and then, upon Ca(2+) influx, it may rebind to SNAREpin, which may trigger synchronous fusion. The results show that ALEX is a powerful method to dissect multiple kinetic steps in the vesicle fusion pathway.
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Affiliation(s)
- Jae-Yeol Kim
- Department of Physics, Pohang University of Science and Technology, Pohang, Korea
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24
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Li B, Takahashi D, Kawamura Y, Uemura M. Comparison of plasma membrane proteomic changes of Arabidopsis suspension-cultured cells (T87 Line) after cold and ABA treatment in association with freezing tolerance development. PLANT & CELL PHYSIOLOGY 2012; 53:543-54. [PMID: 22318864 DOI: 10.1093/pcp/pcs010] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
The plasma membrane (PM) is the primary site of freezing injury in plants. To determine global changes in PM protein profiles in association with freezing tolerance development, proteome analysis of the purified PM of Arabidopsis suspension-cultured cells (T87 line) was conducted with label-free protein quantification technology. Freezing tolerance of Arabidopsis cells at the lag growth phase (8 d old) increased after cold acclimation (CA) or ABA treatment. Proteome analysis assigned 658 proteins in the PM in total, of which 45.3% (298 proteins) were predicted to have transmembrane domains. They were classified into several functional categories, with the primary categories being proteins in transporters, signal transduction, protein destination and storage, and cell structure. After CA, 271 proteins increased and 111 proteins decreased. ABA treatment resulted in 185 increased and 56 decreased proteins. Of these, 139 increased and 49 decreased proteins were identified in common after both CA and ABA treatment. In addition, there were proteins specifically expressed in cold- (132 increased and 62 decreased) or ABA- (46 increased and 7 decreased) treated cells. Collectively, our results clearly show that (i) responses of the PM proteome to CA and ABA treatment overlap substantially but, at the same time, some proteins exhibited different response patterns in each treatment; and (ii) the majority of ABA-responsive proteins are CA-responsive proteins but not vice versa, suggesting complex interactions of CA and ABA signaling pathways in the PM proteome responses.
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Affiliation(s)
- Bin Li
- The United Graduate School of Agricultural Sciences, Iwate University, Morioka, 020-8550 Japan
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25
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Koch M, Holt M. Coupling exo- and endocytosis: an essential role for PIP₂ at the synapse. Biochim Biophys Acta Mol Cell Biol Lipids 2012; 1821:1114-32. [PMID: 22387937 DOI: 10.1016/j.bbalip.2012.02.008] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2011] [Revised: 02/12/2012] [Accepted: 02/13/2012] [Indexed: 12/24/2022]
Abstract
Chemical synapses are specialist points of contact between two neurons, where information transfer takes place. Communication occurs through the release of neurotransmitter substances from small synaptic vesicles in the presynaptic terminal, which fuse with the presynaptic plasma membrane in response to neuronal stimulation. However, as neurons in the central nervous system typically only possess ~200 vesicles, high levels of release would quickly lead to a depletion in the number of vesicles, as well as leading to an increase in the area of the presynaptic plasma membrane (and possible misalignment with postsynaptic structures). Hence, synaptic vesicle fusion is tightly coupled to a local recycling of synaptic vesicles. For a long time, however, the exact molecular mechanisms coupling fusion and subsequent recycling remained unclear. Recent work now indicates a unique role for the plasma membrane lipid phosphatidylinositol 4,5-bisphosphate (PIP(2)), acting together with the vesicular protein synaptotagmin, in coupling these two processes. In this work, we review the evidence for such a mechanism and discuss both the possible advantages and disadvantages for vesicle recycling (and hence signal transduction) in the nervous system. This article is part of a Special Issue entitled Lipids and Vesicular Transport.
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Affiliation(s)
- Marta Koch
- Laboratory of Neurogenetics, VIB Center for the Biology of Disease and K.U. Leuven Center for Human Genetics, O&N4 Herestraat 49, 3000 Leuven, Belgium
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26
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Betke KM, Wells CA, Hamm HE. GPCR mediated regulation of synaptic transmission. Prog Neurobiol 2012; 96:304-21. [PMID: 22307060 DOI: 10.1016/j.pneurobio.2012.01.009] [Citation(s) in RCA: 76] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2011] [Revised: 01/12/2012] [Accepted: 01/20/2012] [Indexed: 02/06/2023]
Abstract
Synaptic transmission is a finely regulated mechanism of neuronal communication. The release of neurotransmitter at the synapse is not only the reflection of membrane depolarization events, but rather, is the summation of interactions between ion channels, G protein coupled receptors, second messengers, and the exocytotic machinery itself which exposes the components within a synaptic vesicle to the synaptic cleft. The focus of this review is to explore the role of G protein signaling as it relates to neurotransmission, as well as to discuss the recently determined inhibitory mechanism of Gβγ dimers acting directly on the exocytotic machinery proteins to inhibit neurotransmitter release.
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Affiliation(s)
- Katherine M Betke
- Vanderbilt University Medical Center, 442 Robinson Research Building, 23rd Ave. South @ Pierce, Nashville, TN 37232-6600, USA.
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Jackson MB. Inferring structures of kinetic intermediates in Ca(2+)-triggered exocytosis. CURRENT TOPICS IN MEMBRANES 2012; 68:185-208. [PMID: 21771500 DOI: 10.1016/b978-0-12-385891-7.00008-8] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/24/2023]
Affiliation(s)
- Meyer B Jackson
- Department of Neuroscience, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, USA
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Walter AM, Groffen AJ, Sørensen JB, Verhage M. Multiple Ca2+ sensors in secretion: teammates, competitors or autocrats? Trends Neurosci 2011; 34:487-97. [PMID: 21831459 DOI: 10.1016/j.tins.2011.07.003] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2011] [Revised: 06/21/2011] [Accepted: 07/05/2011] [Indexed: 12/25/2022]
Abstract
Regulated neurotransmitter secretion depends on Ca(2+) sensors, C2 domain proteins that associate with phospholipids and soluble N-ethylmaleimide-sensitive fusion attachment protein receptor (SNARE) complexes to trigger release upon Ca(2+) binding. Ca(2+) sensors are thought to prevent spontaneous fusion at rest (clamping) and to promote fusion upon Ca(2+) activation. At least eight, often coexpressed, Ca(2+) sensors have been identified in mammals. Accumulating evidence suggests that multiple Ca(2+) sensors interact, rather than work autonomously, to produce the complex secretory response observed in neurons and secretory cells. In this review, we present several working models to describe how different sensors might be arranged to mediate synchronous, asynchronous and spontaneous neurotransmitter release. We discuss the scenario that different Ca(2+) sensors typically act on one shared vesicle pool and compete for binding the multiple SNARE complexes that are likely to assemble at single vesicles, to exert both clamping and fusion-promoting functions.
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Affiliation(s)
- Alexander M Walter
- Department of Functional Genomics, Center for Neurogenomics and Cognitive Research, Neuroscience Campus Amsterdam, Vrije Universiteit Amsterdam and VU Medical Center, 1081 HV Amsterdam, The Netherlands
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Falkowski MA, Thomas DDH, Messenger SW, Martin TF, Groblewski GE. Expression, localization, and functional role for synaptotagmins in pancreatic acinar cells. Am J Physiol Gastrointest Liver Physiol 2011; 301:G306-16. [PMID: 21636530 PMCID: PMC3154608 DOI: 10.1152/ajpgi.00108.2011] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/21/2011] [Accepted: 06/01/2011] [Indexed: 01/31/2023]
Abstract
Secretagogue-induced changes in intracellular Ca(2+) play a pivotal role in secretion in pancreatic acini yet the molecules that respond to Ca(2+) are uncertain. Zymogen granule (ZG) exocytosis is regulated by soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complexes. In nerve and endocrine cells, Ca(2+)-stimulated exocytosis is regulated by the SNARE-associated family of proteins termed synaptotagmins. This study examined a potential role for synaptotagmins in acinar secretion. RT-PCR revealed that synaptotagmin isoforms 1, 3, 6, and 7 are present in isolated acini. Immunoblotting and immunofluorescence using three different antibodies demonstrated synaptotagmin 1 immunoreactivity in apical cytoplasm and ZG fractions of acini, where it colocalized with vesicle-associated membrane protein 2. Synaptotagmin 3 immunoreactivity was detected in membrane fractions and colocalized with an endolysosomal marker. A potential functional role for synaptotagmin 1 in secretion was indicated by results that introduction of synaptotagmin 1 C2AB domain into permeabilized acini inhibited Ca(2+)-dependent exocytosis by 35%. In contrast, constructs of synaptotagmin 3 had no effect. Confirmation of these findings was achieved by incubating intact acini with an antibody specific to the intraluminal domain of synaptotagmin 1, which is externalized following exocytosis. Externalized synaptotagmin 1 was detected exclusively along the apical membrane. Treatment with CCK-8 (100 pM, 5 min) enhanced immunoreactivity by fourfold, demonstrating that synaptotagmin is inserted into the apical membrane during ZG fusion. Collectively, these data indicate that acini express synaptotagmin 1 and support that it plays a functional role in secretion whereas synaptotagmin 3 has an alternative role in endolysosomal membrane trafficking.
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30
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Vashist SK, Zhang B, Zheng D, Al-Rubeaan K, Luong JHT, Sheu FS. Sulfo-N-hydroxysuccinimide interferes with bicinchoninic acid protein assay. Anal Biochem 2011; 417:156-8. [PMID: 21704014 DOI: 10.1016/j.ab.2011.05.045] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2011] [Revised: 05/30/2011] [Accepted: 05/31/2011] [Indexed: 10/18/2022]
Abstract
This study revealed a major interference from sulfo-N-hydroxysuccinimide (sulfo-NHS) in the bicinchoninic acid (BCA) protein assay. Sulfo-NHS, a common reagent used in bioconjugation and analytical biochemistry, exhibited absorbance signals and absorbance peaks at 562 nm, comparable to bovine serum albumin (BSA). However, the combined absorbance of sulfo-NHS and BSA was not strictly additive. The sulfo-NHS interference was suggested to be caused by the reduction of Cu(2+) in the BCA Kit's reagent B (4% cupric sulfate) in a manner similar to that of the protein.
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31
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van den Bogaart G, Thutupalli S, Risselada JH, Meyenberg K, Holt M, Riedel D, Diederichsen U, Herminghaus S, Grubmüller H, Jahn R. Synaptotagmin-1 may be a distance regulator acting upstream of SNARE nucleation. Nat Struct Mol Biol 2011; 18:805-12. [PMID: 21642968 PMCID: PMC3130798 DOI: 10.1038/nsmb.2061] [Citation(s) in RCA: 112] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2010] [Accepted: 03/17/2011] [Indexed: 12/16/2022]
Abstract
Synaptotagmin-1 triggers Ca2+-sensitive, rapid neurotransmitter release by promoting the interaction of SNARE proteins between the synaptic vesicles and the plasma membrane. How synaptotagmin-1 promotes this interaction is controversial, and the massive increase in membrane fusion efficiency of Ca2+-synaptotagmin-1 has not been reproduced in vitro. However, previous experiments have been performed at relatively high salt concentrations, screening potentially important electrostatic interactions. Using functional reconstitution in liposomes, we show here that at low ionic strength SNARE-mediated membrane fusion becomes strictly dependent on both Ca2+ and synaptotagmin-1. Under these conditions, synaptotagmin-1 functions as a distance regulator: tethering the liposomes too far for SNARE nucleation in the absence of Ca2+, but brings the liposomes close enough for membrane fusion in the presence of Ca2+. These results may explain how the relatively weak electrostatic interactions of synaptotagmin-1 with membranes substantially accelerate fusion.
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Affiliation(s)
- Geert van den Bogaart
- Department of Neurobiology, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
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Hui E, Gaffaney JD, Wang Z, Johnson CP, Evans CS, Chapman ER. Mechanism and function of synaptotagmin-mediated membrane apposition. Nat Struct Mol Biol 2011; 18:813-21. [PMID: 21642967 PMCID: PMC3130839 DOI: 10.1038/nsmb.2075] [Citation(s) in RCA: 62] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2010] [Accepted: 04/28/2011] [Indexed: 11/09/2022]
Abstract
Synaptotagmin-I (syt) is a Ca2+ sensor that triggers synchronous neurotransmitter release. The first documented biochemical property of syt was its ability to aggregate membranes in response to Ca2+. However, the mechanism and function of syt-mediated membrane aggregation are poorly understood. Here, we demonstrate that syt-mediated vesicle aggregation is driven by trans interactions between syt molecules bound to different membranes. We observed a strong correlation between the ability of Ca2+-syt to aggregate vesicles and to stimulate SNARE-mediated membrane fusion. Moreover, artificial aggregation of membranes - using non-syt proteins - also efficiently promoted fusion of SNARE-bearing liposomes. Finally, using a modified fusion assay, we observed that syt drives the assembly of otherwise non-fusogenic individual t-SNARE proteins into fusion competent heterodimers, in an aggregation-independent manner. Thus, membrane aggregation and t-SNARE assembly appear to be two key aspects of Ca2+-syt-regulated, SNARE-catalyzed fusion reactions.
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Affiliation(s)
- Enfu Hui
- Howard Hughes Medical Institute and Department of Neuroscience, University of Wisconsin, Madison, Wisconsin, USA
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Membrane penetration by synaptotagmin is required for coupling calcium binding to vesicle fusion in vivo. J Neurosci 2011; 31:2248-57. [PMID: 21307261 DOI: 10.1523/jneurosci.3153-09.2011] [Citation(s) in RCA: 64] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The vesicle protein synaptotagmin I is the Ca(2+) sensor that triggers fast, synchronous release of neurotransmitter. Specifically, Ca(2+) binding by the C(2)B domain of synaptotagmin is required at intact synapses, yet the mechanism whereby Ca(2+) binding results in vesicle fusion remains controversial. Ca(2+)-dependent interactions between synaptotagmin and SNARE (soluble N-ethylmaleimide-sensitive fusion protein attachment receptor) complexes and/or anionic membranes are possible effector interactions. However, no effector-interaction mutations to date impact synaptic transmission as severely as mutation of the C(2)B Ca(2+)-binding motif, suggesting that these interactions are facilitatory rather than essential. Here we use Drosophila to show the functional role of a highly conserved, hydrophobic residue located at the tip of each of the two Ca(2+)-binding pockets of synaptotagmin. Mutation of this residue in the C(2)A domain (F286) resulted in a ∼50% decrease in evoked transmitter release at an intact synapse, again indicative of a facilitatory role. Mutation of this hydrophobic residue in the C(2)B domain (I420), on the other hand, blocked all locomotion, was embryonic lethal even in syt I heterozygotes, and resulted in less evoked transmitter release than that in syt(null) mutants, which is more severe than the phenotype of C(2)B Ca(2+)-binding mutants. Thus, mutation of a single, C(2)B hydrophobic residue required for Ca(2+)-dependent penetration of anionic membranes results in the most severe disruption of synaptotagmin function in vivo to date. Our results provide direct support for the hypothesis that plasma membrane penetration, specifically by the C(2)B domain of synaptotagmin, is the critical effector interaction for coupling Ca(2+) binding with vesicle fusion.
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Affiliation(s)
- Sascha Martens
- Max F. Perutz Laboratories, University of Vienna, Vienna, Austria
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Lai AL, Huang H, Herrick DZ, Epp N, Cafiso DS. Synaptotagmin 1 and SNAREs form a complex that is structurally heterogeneous. J Mol Biol 2010; 405:696-706. [PMID: 21087613 DOI: 10.1016/j.jmb.2010.11.015] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2010] [Revised: 10/14/2010] [Accepted: 11/05/2010] [Indexed: 01/08/2023]
Abstract
Synaptotagmin 1 (syt1) functions as a Ca(2+)-sensor for neuronal exocytosis. Here, site-directed spin labeling was used to examine the complex formed between a soluble fragment of syt1, which contains its two C2 domains, and the neuronal core soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complex. Changes in electron paramagnetic resonance lineshape and accessibility for spin-labeled syt1 mutants indicate that in solution, the assembled core SNARE complex contacts syt1 in several regions. For the C2B domain, contact occurs in the polybasic face and sites opposite the Ca(2+)-binding loops. For the C2A domain, contact is seen with the SNARE complex in a region near loop 2. Double electron-electron resonance was used to estimate distances between the two C2 domains of syt1. These distances have broad distributions in solution, which do not significantly change when syt1 is fully associated with the core SNARE complex. The broad distance distributions indicate that syt1 is structurally heterogeneous when bound to the SNAREs and does not assume a well-defined structure. Simulated annealing using electron paramagnetic resonance-derived distance restraints produces a family of syt1 structures where the Ca(2+)-binding regions of each domain face in roughly opposite directions. The results suggest that when associated with the SNAREs, syt1 is configured to bind opposing bilayers, but that the syt1/SNARE complex samples multiple conformational states.
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Affiliation(s)
- Alex L Lai
- Department of Chemistry, Biophysics Program and Center for Membrane Biology at the University of Virginia, Charlottesville, VA 22904-4319, USA
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López-Font I, Torregrosa-Hetland CJ, Villanueva J, Gutiérrez LM. t-SNARE cluster organization and dynamics in chromaffin cells. J Neurochem 2010; 114:1550-6. [DOI: 10.1111/j.1471-4159.2010.06872.x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Differential regulation of synchronous versus asynchronous neurotransmitter release by the C2 domains of synaptotagmin 1. Proc Natl Acad Sci U S A 2010; 107:14869-74. [PMID: 20679236 DOI: 10.1073/pnas.1000606107] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Synaptic vesicle fusion at many synapses has been kinetically separated into two distinct Ca(2+)-dependent temporal components consisting of a rapid synchronous phase followed by a slower asynchronous component. Mutations in the synaptic vesicle Ca(2+) sensor Synaptotagmin 1 (Syt 1) reduce synchronous neurotransmission while enhancing the slower asynchronous phase of release. Syt 1 regulation of vesicle fusion requires interactions mediated by its tandem cytoplasmic C2 domains (C2A and C2B). Although Ca(2+) binding by Syt 1 is predicted to drive synchronous release, it is unknown if Ca(2+) interactions with either C2 domain is required for suppression of asynchronous release. To determine if Ca(2+) binding by Syt 1 regulates these two phases of release independently, we performed electrophysiological analysis of transgenically expressed Syt 1 mutated at Ca(2+) binding sites in C2A or C2B in the background of Drosophila Syt 1-null mutants. Transgenic animals expressing mutations that disrupt Ca(2+) binding to C2A fully restored the synchronous phase of neurotransmitter release, whereas the asynchronous component was not suppressed. In contrast, rescue with Ca(2+)-binding mutants in C2B displayed little rescue of the synchronous release component, but reduced asynchronous release. These results suggest that the tandem C2 domains of Syt 1 play independent roles in neurotransmission, as Ca(2+) binding to C2A suppresses asynchronous release, whereas Ca(2+) binding to C2B mediates synchronous fusion.
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Abstract
Neurotransmitter release is mediated by the fusion of synaptic vesicles with the presynaptic plasma membrane. Fusion is triggered by a rise in the intracellular calcium concentration and is dependent on the neuronal SNARE (soluble N-ethylmaleimide-sensitive fusion protein-attachment protein receptor) complex. A plethora of molecules such as members of the MUNC13, MUNC18, complexin and synaptotagmin families act along with the SNARE complex to enable calcium-regulated synaptic vesicle exocytosis. The synaptotagmins are localized to synaptic vesicles by an N-terminal transmembrane domain and contain two cytoplasmic C2 domains. Members of the synaptotagmin family are thought to translate the rise in intracellular calcium concentration into synaptic vesicle fusion. The C2 domains of synaptotagmin-1 bind membranes in a calcium-dependent manner and in response induce a high degree of membrane curvature, which is required for its ability to trigger membrane fusion in vitro and in vivo. Furthermore, members of the soluble DOC2 (double-C2 domain) protein family have similar properties. Taken together, these results suggest that C2 domain proteins such as the synaptotagmins and DOC2s promote membrane fusion by the induction of membrane curvature in the vicinity of the SNARE complex. Given the widespread expression of C2 domain proteins in secretory cells, it is proposed that promotion of SNARE-dependent membrane fusion by the induction of membrane curvature is a widespread phenomenon.
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Musch MW, Arvans DL, Wang Y, Nakagawa Y, Solomaha E, Chang EB. Cyclic AMP-mediated endocytosis of intestinal epithelial NHE3 requires binding to synaptotagmin 1. Am J Physiol Gastrointest Liver Physiol 2010; 298:G203-11. [PMID: 19926819 PMCID: PMC2822502 DOI: 10.1152/ajpgi.00379.2009] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
The apical membrane Na(+)-H(+) exchanger (NHE)3 is regulated by cAMP-dependent phosphorylation, which inhibits its activity through membrane endocytosis. The clathrin complex adaptor protein synaptotagmin 1 (Syt 1) appears to be essential to this process, but little is known about its expression in intestinal epithelial cells or interaction with NHE3. The intestinal epithelial expression and apical location of Syt 1 were determined by Syt 1 mRNA profiling and immunolocalization. Tandem mass spectrometry was used for protein identification. Bis(sulfosuccinimidyl) suberate (BS(3)) cross linking suggested that NHE3 and Syt 1 were in a membrane complex following cAMP stimulation of Caco2BBE (Brush Border Expressions) cells. To investigate the regulation of NHE3 appearance in a Syt 1-containing membrane compartment, doxycycline-inducible hemaglutinin (HA)-tagged NHE3 was expressed in Caco2BBE cells. HA-NHE3 correctly targeted to the apical membrane, where, upon cAMP stimulation, it was internalized with a Syt 1-containing compartment. Site-directed mutagenesis of NHE3 showed that serine 605 (S605) was pivotal to NHE3 and Syt 1 association and internalization. Direct Syt 1 interaction with NHE3 was suggested by fluorescence resonance energy transfer (FRET) analysis. The physiological role of S552 was less clear. By FRET, this serine residue appeared to be involved in cAMP-induced Syt 1 binding of NHE3. However, when HA-tagged NHE3 S552A was expressed in Caco2 cells, the mutated construct was not inserted into the apical membrane. We conclude that intestinal epithelial Syt 1 plays an important role in cAMP-stimulated endocytosis of apical NHE3 through cAMP-dependent phosphorylation of S605 that is required for NHE3 and Syt 1 association.
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Affiliation(s)
| | | | - Yunwei Wang
- 1Martin Boyer Laboratories, Department of Medicine;
| | | | - Elena Solomaha
- 2Biophysical Research Core Facility, Divisions of Biological and Physical Sciences, University of Chicago, Chicago, Illinois
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Plattner H. Membrane Trafficking in Protozoa. INTERNATIONAL REVIEW OF CELL AND MOLECULAR BIOLOGY 2010; 280:79-184. [DOI: 10.1016/s1937-6448(10)80003-6] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
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Yokotani N, Ichikawa T, Kondou Y, Maeda S, Iwabuchi M, Mori M, Hirochika H, Matsui M, Oda K. Overexpression of a rice gene encoding a small C2 domain protein OsSMCP1 increases tolerance to abiotic and biotic stresses in transgenic Arabidopsis. PLANT MOLECULAR BIOLOGY 2009; 71:391-402. [PMID: 19653105 DOI: 10.1007/s11103-009-9530-x] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/19/2009] [Accepted: 07/16/2009] [Indexed: 05/26/2023]
Abstract
Plant growth and crop production are limited by environmental stress. We used a large population of transgenic Arabidopsis expressing rice full-length cDNAs to isolate the rice genes that improve the tolerance of plants to environmental stress. By sowing T2 seeds of the transgenic lines under conditions of salinity stress, the salt-tolerant line R07047 was isolated. It expressed a rice gene, OsSMCP1, which encodes a small protein with a single C2 domain, a Ca(2+)-dependent membrane-targeting domain. Retransformation of wild-type Arabidopsis revealed that OsSMCP1 is responsible for conferring the salt tolerance. It is particularly interesting that R07047 and newly constructed OsSMCP1-overexpressing Arabidopsis showed enhanced tolerance not only to high salinity but also to osmotic, dehydrative, and oxidative stresses. Furthermore, R07047 showed improved resistance to Pseudomonas syringae. The OsSMCP1 expression in rice is constitutive. Particle-bombardment-mediated transient expression analysis revealed that OsSMCP1 is targeted to plastids in rice epidermal cells. It induced overexpression of several nuclear encoded genes, including the stress-associated genes, in transgenic Arabidopsis. No marked morphological change or growth retardation was observed in R07047 or retransformants. For molecular breeding to improve the tolerance of crops against environmental stress, OsSMCP1 is a promising candidate.
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Affiliation(s)
- Naoki Yokotani
- Research Institute for Biological Sciences Okayama, 7549-1 Yoshikawa, Kibichuo, Okayama 716-1241, Japan
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Affiliation(s)
- Jakob B. Sørensen
- Department of Neuroscience and Pharmacology, Faculty of Health Sciences, University of Copenhagen, 2200 Copenhagen N, Denmark;
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de Wit H, Walter AM, Milosevic I, Gulyás-Kovács A, Riedel D, Sørensen JB, Verhage M. Synaptotagmin-1 docks secretory vesicles to syntaxin-1/SNAP-25 acceptor complexes. Cell 2009; 138:935-46. [PMID: 19716167 DOI: 10.1016/j.cell.2009.07.027] [Citation(s) in RCA: 208] [Impact Index Per Article: 13.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2009] [Revised: 06/02/2009] [Accepted: 07/16/2009] [Indexed: 10/20/2022]
Abstract
Docking, the initial association of secretory vesicles with the plasma membrane, precedes formation of the SNARE complex, which drives membrane fusion. For many years, the molecular identity of the docked state, and especially the vesicular docking protein, has been unknown, as has the link to SNARE complex assembly. Here, using adrenal chromaffin cells, we identify the vesicular docking partner as synaptotagmin-1, the calcium sensor for exocytosis, and SNAP-25 as an essential plasma membrane docking factor, which, together with the previously known docking factors Munc18-1 and syntaxin, form the minimal docking machinery. Moreover, we show that the requirement for Munc18-1 in docking, but not fusion, can be overcome by stabilizing syntaxin/SNAP-25 acceptor complexes. These findings, together with cross-rescue, double-knockout, and electrophysiological data, lead us to propose that vesicles dock when synaptotagmin-1 binds to syntaxin/SNAP-25 acceptor complexes, whereas Munc18-1 is required for the downstream association of synaptobrevin to form fusogenic SNARE complexes.
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Affiliation(s)
- Heidi de Wit
- Department of Functional Genomics, Center for Neurogenomics and Cognitive Research, Neuroscience Campus Amsterdam, Vrije Universiteit Amsterdam and VU Medical Center, 1081 HV Amsterdam, the Netherlands
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Huang H, Cafiso DS. Conformation and membrane position of the region linking the two C2 domains in synaptotagmin 1 by site-directed spin labeling. Biochemistry 2009; 47:12380-8. [PMID: 18956883 DOI: 10.1021/bi801470m] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Synaptotagmin 1 (syt1) is an integral membrane protein localized on the synaptic vesicle that acts as the Ca(2+) sensor for neuronal exocytosis. Synaptotagmin 1 contains two C2 domains, C2A and C2B, which bind Ca(2+) ions, membranes, and SNAREs. Here, site-directed spin labeling (SDSL) was used to determine the position and dynamics of the region that links the two C2 domains in a water soluble construct encompassing the two C2 domains (syt1C2AB). An analysis of the EPR line shapes from this region indicates that the linker is flexible and unstructured when syt1 is in solution or bound to lipid bilayers. The nanosecond dynamics of the linker does not change, in the presence or absence of Ca(2+), suggesting that there is no Ca(2+)-dependent intramolecular association between the two domains. When syt1C2AB is membrane-bound, the position of the linker relative to the membrane interface was determined by measuring parameters for the collision of the spin-labeled syt1C2AB mutants with both soluble and membrane-bound Ni(II) chelates. These data indicate that the linker does not penetrate the membrane surface but lies approximately 7-10 A from the bilayer surface. In addition, the linker remains flexible when syt1C2AB binds to the SNARE complex, indicating that direct interactions between this linker and the SNAREs do not mediate association. These data suggest that the two C2 domains of syt1 interact independently on the membrane interface, or when bound to SNAREs.
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Affiliation(s)
- Hao Huang
- Department of Chemistry and Biophysics Program, University of Virginia, Charlottesville, Virginia 22904-4319, USA
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Fuson KL, Ma L, Sutton RB, Oberhauser AF. The c2 domains of human synaptotagmin 1 have distinct mechanical properties. Biophys J 2009; 96:1083-90. [PMID: 19186144 PMCID: PMC2716670 DOI: 10.1016/j.bpj.2008.10.025] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2008] [Accepted: 10/09/2008] [Indexed: 10/21/2022] Open
Abstract
Synaptotagmin 1 (Syt1) is the Ca(+2) receptor for fast, synchronous vesicle fusion in neurons. Because membrane fusion is an inherently mechanical, force-driven event, Syt1 must be able to adapt to the energetics of the fusion apparatus. Syt1 contains two C2 domains (C2A and C2B) that are homologous in sequence and three-dimensional in structure; yet, a number of observations have suggested that they have distinct biochemical and biological properties. In this study, we analyzed the mechanical stability of the C2A and C2B domains of human Syt1 using single-molecule atomic force microscopy. We found that stretching the C2AB domains of Syt1 resulted in two distinct unfolding force peaks. The larger force peak of approximately 100 pN was identified as C2B and the second peak of approximately 50 pN as C2A. Furthermore, a significant fraction of C2A domains unfolded through a low force intermediate that was not observed in C2B. We conclude that these domains have different mechanical properties. We hypothesize that a relatively small stretching force may be sufficient to deform the effector-binding regions of the C2A domain and modulate the affinity for soluble N-ethylmaleimide-sensitive factor (NSF) attachment protein receptors (SNAREs), phospholipids, and Ca(+2).
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Affiliation(s)
- Kerry L. Fuson
- Department of Biochemistry and Molecular Biology, Sealy Center for Structural Biology and Molecular Biophysics, University of Texas Medical Branch, Galveston, Texas 77555
| | - Liang Ma
- Department of Neuroscience and Cell Biology, Sealy Center for Structural Biology and Molecular Biophysics, University of Texas Medical Branch, Galveston, Texas 77555
| | - R. Bryan Sutton
- Department of Neuroscience and Cell Biology, Sealy Center for Structural Biology and Molecular Biophysics, University of Texas Medical Branch, Galveston, Texas 77555
| | - Andres F. Oberhauser
- Department of Neuroscience and Cell Biology, Sealy Center for Structural Biology and Molecular Biophysics, University of Texas Medical Branch, Galveston, Texas 77555
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López I, Ortiz JA, Villanueva J, Torres V, Torregrosa-Hetland CJ, del Mar Francés M, Viniegra S, Gutiérrez LM. Vesicle Motion and Fusion are Altered in Chromaffin Cells with Increased SNARE Cluster Dynamics. Traffic 2009; 10:172-85. [DOI: 10.1111/j.1600-0854.2008.00861.x] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Hagalili Y, Bachnoff N, Atlas D. The Voltage-Gated Ca2+ Channel Is the Ca2+ Sensor Protein of Secretion. Biochemistry 2008; 47:13822-30. [DOI: 10.1021/bi801619f] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Yamit Hagalili
- Department of Biological Chemistry, The Institute of Life Sciences, The Hebrew University of Jerusalem, Jerusalem, 91904 Israel
| | - Niv Bachnoff
- Department of Biological Chemistry, The Institute of Life Sciences, The Hebrew University of Jerusalem, Jerusalem, 91904 Israel
| | - Daphne Atlas
- Department of Biological Chemistry, The Institute of Life Sciences, The Hebrew University of Jerusalem, Jerusalem, 91904 Israel
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Yamazaki T, Kawamura Y, Minami A, Uemura M. Calcium-dependent freezing tolerance in Arabidopsis involves membrane resealing via synaptotagmin SYT1. THE PLANT CELL 2008; 20:3389-404. [PMID: 19088330 PMCID: PMC2630449 DOI: 10.1105/tpc.108.062679] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/24/2008] [Revised: 10/31/2008] [Accepted: 11/30/2008] [Indexed: 05/18/2023]
Abstract
Plant freezing tolerance involves the prevention of lethal freeze-induced damage to the plasma membrane. We hypothesized that plant freezing tolerance involves membrane resealing, which, in animal cells, is accomplished by calcium-dependent exocytosis following mechanical disruption of the plasma membrane. In Arabidopsis thaliana protoplasts, extracellular calcium enhanced not only freezing tolerance but also tolerance to electroporation, which typically punctures the plasma membrane. However, calcium did not enhance survival when protoplasts were exposed to osmotic stress that mimicked freeze-induced dehydration. Calcium-dependent freezing tolerance was also detected with leaf sections in which ice crystals intruded into tissues. Interestingly, calcium-dependent freezing tolerance was inhibited by extracellular addition of an antibody against the cytosolic region of SYT1, a homolog of synaptotagmin known to be a calcium sensor that initiates exocytosis. This inhibition indicates that the puncture allowing the antibody to flow into the cytoplasm occurs during freeze/thawing. Thus, we propose that calcium-dependent freezing tolerance results from resealing of the punctured site. Protoplasts or leaf sections isolated from Arabidopsis SYT1-RNA interference (RNAi) plants lost calcium-dependent freezing tolerance, and intact SYT1-RNAi plants had lower freezing tolerance than control plants. Taken together, these findings suggest that calcium-dependent freezing tolerance results from membrane resealing and that this mechanism involves SYT1 function.
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Affiliation(s)
- Tomokazu Yamazaki
- The 21st Century Center of Excellence Program, Iwate University, Morioka, Iwate 020-8550, Japan
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Abstract
Plasma insulin levels are determined mainly by the rate of exocytosis of the insulin-containing large dense core vesicles (LDCVs) of pancreatic islet beta-cells. This process involves the recruitment of LDCVs to the plasma membrane, where they are docked by the assembly of multiprotein SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) complexes. However, fusion of the two membranes will proceed only in the presence of Ca(2+) ions, implicating a Ca(2+) sensor protein. The synaptotagmin gene family, comprising 15 members, was proposed to act as such Ca(2+) sensor in regulated exocytosis in neurons and neuroendocrine and endocrine cells. Herein, we review the physiological function of the various synaptotagmins with reference to their impact on insulin exocytosis. Cumulating evidence emphasizes the crucial role of synaptotagmin VII and IX as mediators of glucose-induced insulin secretion.
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Affiliation(s)
- Benoit R Gauthier
- Dept. of Cell Physiology and Metabolism, University Medical Center, 1211 Geneva 4, Switzerland.
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