1
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Patil SS, Sanghrajka K, Sriram M, Chakraborty A, Majumdar S, Bhaskar BR, Das D. Synaptobrevin2 monomers and dimers differentially engage to regulate the functional trans-SNARE assembly. Life Sci Alliance 2024; 7:e202402568. [PMID: 38238088 PMCID: PMC10796598 DOI: 10.26508/lsa.202402568] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2024] [Revised: 01/12/2024] [Accepted: 01/12/2024] [Indexed: 01/22/2024] Open
Abstract
The precise cell-to-cell communication relies on SNARE-catalyzed membrane fusion. Among ∼70 copies of synaptobrevin2 (syb2) in synaptic vesicles, only ∼3 copies are sufficient to facilitate the fusion process at the presynaptic terminal. It is unclear what dictates the number of SNARE complexes that constitute the fusion pore assembly. The structure-function relation of these dynamic pores is also unknown. Here, we demonstrate that syb2 monomers and dimers differentially engage in regulating the trans-SNARE assembly during membrane fusion. The differential recruitment of two syb2 structures at the membrane fusion site has consequences in regulating individual nascent fusion pore properties. We have identified a few syb2 transmembrane domain residues that control monomer/dimer conversion. Overall, our study indicates that syb2 monomers and dimers are differentially recruited at the release sites for regulating membrane fusion events.
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Affiliation(s)
- Swapnali S Patil
- https://ror.org/03ht1xw27 Department of Biological Sciences, Tata Institute of Fundamental Research, Mumbai, India
| | - Kinjal Sanghrajka
- https://ror.org/03ht1xw27 Department of Biological Sciences, Tata Institute of Fundamental Research, Mumbai, India
| | - Malavika Sriram
- https://ror.org/03ht1xw27 Department of Biological Sciences, Tata Institute of Fundamental Research, Mumbai, India
| | - Aritra Chakraborty
- https://ror.org/03ht1xw27 Department of Biological Sciences, Tata Institute of Fundamental Research, Mumbai, India
| | - Sougata Majumdar
- https://ror.org/03ht1xw27 Department of Biological Sciences, Tata Institute of Fundamental Research, Mumbai, India
| | - Bhavya R Bhaskar
- https://ror.org/03ht1xw27 Department of Biological Sciences, Tata Institute of Fundamental Research, Mumbai, India
| | - Debasis Das
- https://ror.org/03ht1xw27 Department of Biological Sciences, Tata Institute of Fundamental Research, Mumbai, India
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2
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Weisgerber AW, Otruba Z, Knowles MK. Syntaxin clusters and cholesterol affect the mobility of Syntaxin1a. Biophys J 2024:S0006-3495(24)00028-6. [PMID: 38221759 DOI: 10.1016/j.bpj.2024.01.012] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2023] [Revised: 12/02/2023] [Accepted: 01/10/2024] [Indexed: 01/16/2024] Open
Abstract
Syntaxin1a (Syx1a) is essential for stimulated exocytosis in neuroendocrine cells. The vesicle docking process involves the formation of nanoscale Syx1a domains on the plasma membrane and the Syx1a clusters disintegrate during the fusion process. Syx1a nanodomains are static yet Syx1a molecules dynamically enter and leave the domains; the process by which these clusters maintain this balance is unclear. In this work, the dynamics of the Syx1a molecules is elucidated relative to the cluster position through a labeling strategy that allows both the bulk position of the Syx clusters to be visualized concurrent with the trajectories of single Syx1a molecules on the surface of PC12 cells. Single Syx1a molecules were tracked in time relative to cluster positions to decipher how Syx1a moves within a cluster and when clusters are not present. Syx1a is mobile on the plasma membrane, more mobile at the center of clusters, and less mobile near the edges of clusters; this depends on the presence of the N-terminal Habc domain and cholesterol, which are essential for proper exocytosis. Simulations of the dynamics observed at clusters support a model where clusters are maintained by a large cage (r = 100 nm) within which Syx1a remains highly mobile within the cluster (r = 50 nm). The depletion of cholesterol dramatically reduces the mobility of Syx1a within clusters and less so over the rest of the plasma membrane. This suggests that fluidity of Syx1a supramolecular clusters is needed for function.
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Affiliation(s)
- Alan W Weisgerber
- Department of Chemistry and Biochemistry, University of Denver, Denver, Colorado
| | - Zdeněk Otruba
- Department of Chemistry and Biochemistry, University of Denver, Denver, Colorado
| | - Michelle K Knowles
- Department of Chemistry and Biochemistry, University of Denver, Denver, Colorado.
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3
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Fadil SA, Janetopoulos C. The Polarized Redistribution of the Contractile Vacuole to the Rear of the Cell is Critical for Streaming and is Regulated by PI(4,5)P2-Mediated Exocytosis. Front Cell Dev Biol 2022; 9:765316. [PMID: 35928786 PMCID: PMC9344532 DOI: 10.3389/fcell.2021.765316] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2021] [Accepted: 10/20/2021] [Indexed: 12/05/2022] Open
Abstract
Dictyostelium discoideum amoebae align in a head to tail manner during the process of streaming during fruiting body formation. The chemoattractant cAMP is the chemoattractant regulating cell migration during this process and is released from the rear of cells. The process by which this cAMP release occurs has eluded investigators for many decades, but new findings suggest that this release can occur through expulsion during contractile vacuole (CV) ejection. The CV is an organelle that performs several functions inside the cell including the regulation of osmolarity, and discharges its content via exocytosis. The CV localizes to the rear of the cell and appears to be part of the polarity network, with the localization under the influence of the plasma membrane (PM) lipids, including the phosphoinositides (PIs), among those is PI(4,5)P2, the most abundant PI on the PM. Research on D. discoideum and neutrophils have shown that PI(4,5)P2 is enriched at the rear of migrating cells. In several systems, it has been shown that the essential regulator of exocytosis is through the exocyst complex, mediated in part by PI(4,5)P2-binding. This review features the role of the CV complex in D. discoideum signaling with a focus on the role of PI(4,5)P2 in regulating CV exocytosis and localization. Many of the regulators of these processes are conserved during evolution, so the mechanisms controlling exocytosis and membrane trafficking in D. discoideum and mammalian cells will be discussed, highlighting their important functions in membrane trafficking and signaling in health and disease.
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Affiliation(s)
- Sana A. Fadil
- Department of Biological Sciences, University of the Sciences in Philadelphia, Philadelphia, PA, United States
- Department of Natural product, Faculty of Pharmacy, King Abdulaziz University, Saudia Arabia
| | - Chris Janetopoulos
- Department of Biological Sciences, University of the Sciences in Philadelphia, Philadelphia, PA, United States
- The Science Research Institute, Albright College, Reading, PA, United States
- The Department of Cell Biology at Johns Hopkins University School of Medicine, Baltimore, MD, United States
- *Correspondence: Chris Janetopoulos,
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4
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Mion D, Bunel L, Heo P, Pincet F. The beginning and the end of SNARE-induced membrane fusion. FEBS Open Bio 2022; 12:1958-1979. [PMID: 35622519 PMCID: PMC9623537 DOI: 10.1002/2211-5463.13447] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2022] [Revised: 05/11/2022] [Accepted: 05/25/2022] [Indexed: 01/25/2023] Open
Abstract
Membrane fusion is not a spontaneous process. Physiologically, the formation of coiled-coil protein complexes, the SNAREpins, bridges the membrane of a vesicle and a target membrane, brings them in close contact, and provides the energy necessary for their fusion. In this review, we utilize results from in vitro experiments and simple physics and chemistry models to dissect the kinetics and energetics of the fusion process from the encounter of the two membranes to the full expansion of a fusion pore. We find three main energy barriers that oppose the fusion process: SNAREpin initiation, fusion pore opening, and expansion. SNAREpin initiation is inherent to the proteins and makes in vitro fusion kinetic experiments rather slow. The kinetics are physiologically accelerated by effectors. The energy barriers that precede pore opening and pore expansion can be overcome by several SNAREpins acting in concert.
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Affiliation(s)
- Delphine Mion
- Laboratoire de Physique de l'École Normale Supérieure, ENS, Université PSLCNRS, Sorbonne Université, Université Paris CitéFrance
| | - Louis Bunel
- Laboratoire de Physique de l'École Normale Supérieure, ENS, Université PSLCNRS, Sorbonne Université, Université Paris CitéFrance
| | - Paul Heo
- Institute of Psychiatry and Neuroscience of Paris (IPNP)INSERM U1266ParisFrance
| | - Frédéric Pincet
- Laboratoire de Physique de l'École Normale Supérieure, ENS, Université PSLCNRS, Sorbonne Université, Université Paris CitéFrance
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5
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Mertins J, Finke J, Sies R, Rink KM, Hasenauer J, Lang T. The mesoscale organization of syntaxin 1A and SNAP25 is determined by SNARE-SNARE interactions. eLife 2021; 10:69236. [PMID: 34779769 PMCID: PMC8629428 DOI: 10.7554/elife.69236] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2021] [Accepted: 11/14/2021] [Indexed: 01/01/2023] Open
Abstract
SNARE proteins have been described as the effectors of fusion events in the secretory pathway more than two decades ago. The strong interactions between SNARE domains are clearly important in membrane fusion, but it is unclear whether they are involved in any other cellular processes. Here, we analyzed two classical SNARE proteins, syntaxin 1A and SNAP25. Although they are supposed to be engaged in tight complexes, we surprisingly find them largely segregated in the plasma membrane. Syntaxin 1A only occupies a small fraction of the plasma membrane area. Yet, we find it is able to redistribute the far more abundant SNAP25 on the mesoscale by gathering crowds of SNAP25 molecules onto syntaxin clusters in a SNARE-domain-dependent manner. Our data suggest that SNARE domain interactions are not only involved in driving membrane fusion on the nanoscale, but also play an important role in controlling the general organization of proteins on the mesoscale. Further, we propose these mechanisms preserve active syntaxin 1A–SNAP25 complexes at the plasma membrane.
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Affiliation(s)
- Jasmin Mertins
- Departments of Membrane Biochemistry, Life & Medical Sciences (LIMES) Institute, University of Bonn, Bonn, Germany
| | - Jérôme Finke
- Departments of Membrane Biochemistry, Life & Medical Sciences (LIMES) Institute, University of Bonn, Bonn, Germany
| | - Ricarda Sies
- Departments of Membrane Biochemistry, Life & Medical Sciences (LIMES) Institute, University of Bonn, Bonn, Germany
| | - Kerstin M Rink
- Heidelberg University Biochemistry Center (BZH), Heidelberg, Germany
| | - Jan Hasenauer
- Computational Life Sciences, Life & Medical Sciences (LIMES) Institute, University of Bonn, Bonn, Germany.,Interdisciplinary Research Unit Mathematics and Life Sciences, University of Bonn, Bonn, Germany.,Institute of Computational Biology, Helmholtz Center Munich - German Research Center for Environmental Health, Neuherberg, Germany
| | - Thorsten Lang
- Departments of Membrane Biochemistry, Life & Medical Sciences (LIMES) Institute, University of Bonn, Bonn, Germany
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6
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The SNAP-25 Protein Family. Neuroscience 2019; 420:50-71. [DOI: 10.1016/j.neuroscience.2018.09.020] [Citation(s) in RCA: 34] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2018] [Revised: 08/31/2018] [Accepted: 09/14/2018] [Indexed: 01/04/2023]
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7
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Richter KN, Patzelt C, Phan NTN, Rizzoli SO. Antibody-driven capture of synaptic vesicle proteins on the plasma membrane enables the analysis of their interactions with other synaptic proteins. Sci Rep 2019; 9:9231. [PMID: 31239503 PMCID: PMC6592915 DOI: 10.1038/s41598-019-45729-4] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2019] [Accepted: 06/13/2019] [Indexed: 01/07/2023] Open
Abstract
Many organelles from the secretory pathway fuse to the plasma membrane, to exocytose different cargoes. Their proteins are then retrieved from the plasma membrane by endocytosis, and the organelles are re-formed. It is generally unclear whether the organelle proteins colocalize when they are on the plasma membrane, or whether they disperse. To address this, we generated here a new approach, which we tested on synaptic vesicles, organelles that are known to exo- and endocytose frequently. We tagged the synaptotagmin molecules of newly exocytosed vesicles using clusters of primary and secondary antibodies targeted against the luminal domains of these molecules. The antibody clusters are too large for endocytosis, and thus sequestered the synaptotagmin molecules on the plasma membrane. Immunostainings for other synaptic molecules then revealed whether they colocalized with the sequestered synaptotagmin molecules. We suggest that such assays may be in the future extended to other cell types and other organelles.
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Affiliation(s)
- Katharina N Richter
- Institute for Neuro- and Sensory Physiology, Center for Biostructural Imaging of Neurodegeneration, University Medical Center Göttingen, Göttingen, Germany.
| | - Christina Patzelt
- Institute for Neuro- and Sensory Physiology, Center for Biostructural Imaging of Neurodegeneration, University Medical Center Göttingen, Göttingen, Germany
| | - Nhu T N Phan
- Institute for Neuro- and Sensory Physiology, Center for Biostructural Imaging of Neurodegeneration, University Medical Center Göttingen, Göttingen, Germany
| | - Silvio O Rizzoli
- Institute for Neuro- and Sensory Physiology, Center for Biostructural Imaging of Neurodegeneration, University Medical Center Göttingen, Göttingen, Germany.
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8
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Padmanabhan P, Bademosi AT, Kasula R, Lauwers E, Verstreken P, Meunier FA. Need for speed: Super-resolving the dynamic nanoclustering of syntaxin-1 at exocytic fusion sites. Neuropharmacology 2019; 169:107554. [PMID: 30826343 DOI: 10.1016/j.neuropharm.2019.02.036] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2018] [Revised: 02/21/2019] [Accepted: 02/27/2019] [Indexed: 01/08/2023]
Abstract
Communication between cells relies on regulated exocytosis, a multi-step process that involves the docking, priming and fusion of vesicles with the plasma membrane, culminating in the release of neurotransmitters and hormones. Key proteins and lipids involved in exocytosis are subjected to Brownian movement and constantly switch between distinct motion states which are governed by short-lived molecular interactions. Critical biochemical reactions between exocytic proteins that occur in the confinement of nanodomains underpin the precise sequence of priming steps which leads to the fusion of vesicles. The advent of super-resolution microscopy techniques has provided the means to visualize individual molecules on the plasma membrane with high spatiotemporal resolution in live cells. These techniques are revealing a highly dynamic nature of the nanoscale organization of the exocytic machinery. In this review, we focus on soluble N-ethylmaleimide-sensitive factor attachment receptor (SNARE) syntaxin-1, which mediates vesicular fusion. Syntaxin-1 is highly mobile at the plasma membrane, and its inherent speed allows fast assembly and disassembly of syntaxin-1 nanoclusters which are associated with exocytosis. We reflect on recent studies which have revealed the mechanisms regulating syntaxin-1 nanoclustering on the plasma membrane and draw inferences on the effect of synaptic activity, phosphoinositides, N-ethylmaleimide-sensitive factor (NSF), α-soluble NSF attachment protein (α-SNAP) and SNARE complex assembly on the dynamic nanoscale organization of syntaxin-1. This article is part of the special issue entitled 'Mobility and trafficking of neuronal membrane proteins'.
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Affiliation(s)
- Pranesh Padmanabhan
- Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, The University of Queensland, Queensland, Australia
| | - Adekunle T Bademosi
- Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, The University of Queensland, Queensland, Australia
| | - Ravikiran Kasula
- Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, The University of Queensland, Queensland, Australia
| | - Elsa Lauwers
- VIB-KU Leuven Center for Brain & Disease Research, 3000 Leuven, Belgium; Department of Neurosciences and Leuven Brain Institute, KU Leuven, 3000 Leuven, Belgium
| | - Patrik Verstreken
- VIB-KU Leuven Center for Brain & Disease Research, 3000 Leuven, Belgium; Department of Neurosciences and Leuven Brain Institute, KU Leuven, 3000 Leuven, Belgium
| | - Frédéric A Meunier
- Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, The University of Queensland, Queensland, Australia.
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9
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Abstract
Plasma membrane proteins organize into structures named compartments, microdomains, rafts, phases, crowds, or clusters. These structures are often smaller than 100 nm in diameter. Despite their importance in many cellular functions, little is known about their inner organization. For instance, how densely are molecules packed? Being aware of the protein compaction may contribute to our general understanding of why such structures exist and how they execute their functions. In this study, we have investigated plasma membrane crowds formed by the amyloid precursor protein (APP), a protein well known for its involvement in Alzheimer's disease. By combining biochemical experiments with conventional and super-resolution stimulated emission depletion microscopy, we quantitatively determined the protein packing density within APP crowds. We found that crowds occurring with reasonable frequency contain between 20 and 30 molecules occupying a spherical area with a diameter between 65 and 85 nm. Additionally, we found the vast majority of plasmalemmal APP residing in these crowds. The model suggests a high molecular density of protein material within plasmalemmal APP crowds. This should affect the protein's biochemical accessibility and processing by nonpathological α-secretases. As clustering of APP is a prerequisite for endocytic entry into the pathological processing pathway, elucidation of the packing density also provides a deeper understanding of this part of APP's life cycle.
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10
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Dingjan I, Linders PTA, Verboogen DRJ, Revelo NH, Ter Beest M, van den Bogaart G. Endosomal and Phagosomal SNAREs. Physiol Rev 2018; 98:1465-1492. [PMID: 29790818 DOI: 10.1152/physrev.00037.2017] [Citation(s) in RCA: 51] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
The soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) protein family is of vital importance for organelle communication. The complexing of cognate SNARE members present in both the donor and target organellar membranes drives the membrane fusion required for intracellular transport. In the endocytic route, SNARE proteins mediate trafficking between endosomes and phagosomes with other endosomes, lysosomes, the Golgi apparatus, the plasma membrane, and the endoplasmic reticulum. The goal of this review is to provide an overview of the SNAREs involved in endosomal and phagosomal trafficking. Of the 38 SNAREs present in humans, 30 have been identified at endosomes and/or phagosomes. Many of these SNAREs are targeted by viruses and intracellular pathogens, which thereby reroute intracellular transport for gaining access to nutrients, preventing their degradation, and avoiding their detection by the immune system. A fascinating picture is emerging of a complex transport network with multiple SNAREs being involved in consecutive trafficking routes.
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Affiliation(s)
- Ilse Dingjan
- Department of Tumor Immunology, Radboud Institute for Molecular Life Sciences, Radboud University Medical Center , Nijmegen , The Netherlands ; and Department of Molecular Immunology, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen , Groningen , The Netherlands
| | - Peter T A Linders
- Department of Tumor Immunology, Radboud Institute for Molecular Life Sciences, Radboud University Medical Center , Nijmegen , The Netherlands ; and Department of Molecular Immunology, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen , Groningen , The Netherlands
| | - Danielle R J Verboogen
- Department of Tumor Immunology, Radboud Institute for Molecular Life Sciences, Radboud University Medical Center , Nijmegen , The Netherlands ; and Department of Molecular Immunology, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen , Groningen , The Netherlands
| | - Natalia H Revelo
- Department of Tumor Immunology, Radboud Institute for Molecular Life Sciences, Radboud University Medical Center , Nijmegen , The Netherlands ; and Department of Molecular Immunology, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen , Groningen , The Netherlands
| | - Martin Ter Beest
- Department of Tumor Immunology, Radboud Institute for Molecular Life Sciences, Radboud University Medical Center , Nijmegen , The Netherlands ; and Department of Molecular Immunology, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen , Groningen , The Netherlands
| | - Geert van den Bogaart
- Department of Tumor Immunology, Radboud Institute for Molecular Life Sciences, Radboud University Medical Center , Nijmegen , The Netherlands ; and Department of Molecular Immunology, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen , Groningen , The Netherlands
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11
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Vesicle Docking Is a Key Target of Local PI(4,5)P 2 Metabolism in the Secretory Pathway of INS-1 Cells. Cell Rep 2018; 20:1409-1421. [PMID: 28793264 PMCID: PMC5613661 DOI: 10.1016/j.celrep.2017.07.041] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2017] [Revised: 05/31/2017] [Accepted: 07/14/2017] [Indexed: 12/29/2022] Open
Abstract
Phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) signaling is transient and spatially confined in live cells. How this pattern of signaling regulates transmitter release and hormone secretion has not been addressed. We devised an optogenetic approach to control PI(4,5)P2 levels in time and space in insulin-secreting cells. Combining this approach with total internal reflection fluorescence microscopy, we examined individual vesicle-trafficking steps. Unlike long-term PI(4,5)P2 perturbations, rapid and cell-wide PI(4,5)P2 reduction in the plasma membrane (PM) strongly inhibits secretion and intracellular Ca2+ concentration ([Ca2+]i) responses, but not sytaxin1a clustering. Interestingly, local PI(4,5)P2 reduction selectively at vesicle docking sites causes remarkable vesicle undocking from the PM without affecting [Ca2+]i. These results highlight a key role of local PI(4,5)P2 in vesicle tethering and docking, coordinated with its role in priming and fusion. Thus, different spatiotemporal PI(4,5)P2 signaling regulates distinct steps of vesicle trafficking, and vesicle docking may be a key target of local PI(4,5)P2 signaling in vivo.
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12
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Satnav for cells: Destination membrane fusion. Cell Calcium 2017; 68:14-23. [PMID: 29129204 DOI: 10.1016/j.ceca.2017.10.001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2017] [Revised: 09/20/2017] [Accepted: 10/07/2017] [Indexed: 11/23/2022]
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13
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The L-type Voltage-Gated Calcium Channel co-localizes with Syntaxin 1A in nano-clusters at the plasma membrane. Sci Rep 2017; 7:11350. [PMID: 28900128 PMCID: PMC5595989 DOI: 10.1038/s41598-017-10588-4] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2017] [Accepted: 08/09/2017] [Indexed: 11/25/2022] Open
Abstract
The secretory signal elicited by membrane depolarization traverses from the Ca2+-bound α11.2 pore-forming subunit of the L-type Ca2+-channel (Cav1.2) to syntaxin 1 A (Sx1A) via an intra-membrane signaling mechanism. Here, we report the use of two-color Photo-Activated-Localization-Microscopy (PALM) to determine the relation between Cav1.2 and Sx1A in single-molecule detail. We observed nanoscale co-clusters of PAmCherry-tagged Sx1A and Dronpa-tagged α11.2 at a ~1:1 ratio. PAmCherry-tagged Sx1AC145A, or PAmCherry-tagged Sx2, an inactive Cav1.2 modulator, in which Cys145 is a Ser residue, showed no co-clustering. These results are consistent with the crucial role of the single cytosolic Sx1ACys145 in clustering with Cav1.2. Cav1.2 and the functionally inactive transmembrane-domain double mutant Sx1AC271V/C272V engendered clusters with a ~2:1 ratio. A higher extent of co-clustering, which coincides with compromised depolarization-evoked transmitter-release, was observed also by oxidation of Sx1ACys271 and Cys272. Our super-resolution-imaging results set the stage for studying co-clustering of the channel with other exocytotic proteins at a single-molecule level.
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14
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Merklinger E, Schloetel JG, Weber P, Batoulis H, Holz S, Karnowski N, Finke J, Lang T. The packing density of a supramolecular membrane protein cluster is controlled by cytoplasmic interactions. eLife 2017; 6. [PMID: 28722652 PMCID: PMC5536946 DOI: 10.7554/elife.20705] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2016] [Accepted: 07/17/2017] [Indexed: 01/24/2023] Open
Abstract
Molecule clustering is an important mechanism underlying cellular self-organization. In the cell membrane, a variety of fundamentally different mechanisms drive membrane protein clustering into nanometre-sized assemblies. To date, it is unknown whether this clustering process can be dissected into steps differentially regulated by independent mechanisms. Using clustered syntaxin molecules as an example, we study the influence of a cytoplasmic protein domain on the clustering behaviour. Analysing protein mobility, cluster size and accessibility to myc-epitopes we show that forces acting on the transmembrane segment produce loose clusters, while cytoplasmic protein interactions mediate a tightly packed state. We conclude that the data identify a hierarchy in membrane protein clustering likely being a paradigm for many cellular self-organization processes. DOI:http://dx.doi.org/10.7554/eLife.20705.001
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Affiliation(s)
- Elisa Merklinger
- Membrane Biochemistry, Life and Medical Sciences (LIMES) Institute, University of Bonn, Bonn, Germany
| | - Jan-Gero Schloetel
- Membrane Biochemistry, Life and Medical Sciences (LIMES) Institute, University of Bonn, Bonn, Germany
| | - Pascal Weber
- Membrane Biochemistry, Life and Medical Sciences (LIMES) Institute, University of Bonn, Bonn, Germany
| | - Helena Batoulis
- Membrane Biochemistry, Life and Medical Sciences (LIMES) Institute, University of Bonn, Bonn, Germany
| | - Sarah Holz
- Membrane Biochemistry, Life and Medical Sciences (LIMES) Institute, University of Bonn, Bonn, Germany
| | - Nora Karnowski
- Chemical Biology, Life and Medical Sciences (LIMES) Institute, University of Bonn, Bonn, Germany
| | - Jérôme Finke
- Membrane Biochemistry, Life and Medical Sciences (LIMES) Institute, University of Bonn, Bonn, Germany
| | - Thorsten Lang
- Membrane Biochemistry, Life and Medical Sciences (LIMES) Institute, University of Bonn, Bonn, Germany
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15
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Verboogen DRJ, González Mancha N, Ter Beest M, van den Bogaart G. Fluorescence Lifetime Imaging Microscopy reveals rerouting of SNARE trafficking driving dendritic cell activation. eLife 2017; 6. [PMID: 28524818 PMCID: PMC5473687 DOI: 10.7554/elife.23525] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2016] [Accepted: 05/18/2017] [Indexed: 11/13/2022] Open
Abstract
SNARE proteins play a crucial role in intracellular trafficking by catalyzing membrane fusion, but assigning SNAREs to specific intracellular transport routes is challenging with current techniques. We developed a novel Förster resonance energy transfer-fluorescence lifetime imaging microscopy (FRET-FLIM)-based technique allowing visualization of real-time local interactions of fluorescently tagged SNARE proteins in live cells. We used FRET-FLIM to delineate the trafficking steps underlying the release of the inflammatory cytokine interleukin-6 (IL-6) from human blood-derived dendritic cells. We found that activation of dendritic cells by bacterial lipopolysaccharide leads to increased FRET of fluorescently labeled syntaxin 4 with VAMP3 specifically at the plasma membrane, indicating increased SNARE complex formation, whereas FRET with other tested SNAREs was unaltered. Our results revealed that SNARE complexing is a key regulatory step for cytokine production by immune cells and prove the applicability of FRET-FLIM for visualizing SNARE complexes in live cells with subcellular spatial resolution.
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Affiliation(s)
- Daniëlle Rianne José Verboogen
- Department of Tumor Immunology, Radboud Institute for Molecular Life Sciences, Radboud University Medical Center, Nijmegen, Netherlands
| | - Natalia González Mancha
- Department of Tumor Immunology, Radboud Institute for Molecular Life Sciences, Radboud University Medical Center, Nijmegen, Netherlands
| | - Martin Ter Beest
- Department of Tumor Immunology, Radboud Institute for Molecular Life Sciences, Radboud University Medical Center, Nijmegen, Netherlands
| | - Geert van den Bogaart
- Department of Tumor Immunology, Radboud Institute for Molecular Life Sciences, Radboud University Medical Center, Nijmegen, Netherlands
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16
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Han J, Pluhackova K, Böckmann RA. The Multifaceted Role of SNARE Proteins in Membrane Fusion. Front Physiol 2017; 8:5. [PMID: 28163686 PMCID: PMC5247469 DOI: 10.3389/fphys.2017.00005] [Citation(s) in RCA: 178] [Impact Index Per Article: 25.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2016] [Accepted: 01/04/2017] [Indexed: 12/28/2022] Open
Abstract
Membrane fusion is a key process in all living organisms that contributes to a variety of biological processes including viral infection, cell fertilization, as well as intracellular transport, and neurotransmitter release. In particular, the various membrane-enclosed compartments in eukaryotic cells need to exchange their contents and communicate across membranes. Efficient and controllable fusion of biological membranes is known to be driven by cooperative action of SNARE proteins, which constitute the central components of the eukaryotic fusion machinery responsible for fusion of synaptic vesicles with the plasma membrane. During exocytosis, vesicle-associated v-SNARE (synaptobrevin) and target cell-associated t-SNAREs (syntaxin and SNAP-25) assemble into a core trans-SNARE complex. This complex plays a versatile role at various stages of exocytosis ranging from the priming to fusion pore formation and expansion, finally resulting in the release or exchange of the vesicle content. This review summarizes current knowledge on the intricate molecular mechanisms underlying exocytosis triggered and catalyzed by SNARE proteins. Particular attention is given to the function of the peptidic SNARE membrane anchors and the role of SNARE-lipid interactions in fusion. Moreover, the regulatory mechanisms by synaptic auxiliary proteins in SNARE-driven membrane fusion are briefly outlined.
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Affiliation(s)
- Jing Han
- Department of Biochemistry and Molecular Biology, School of Basic Medical Sciences, Xi'an Jiaotong University Health Science CenterXi'an, China; Computational Biology, Department of Biology, Friedrich-Alexander Universität Erlangen-NürnbergErlangen, Germany
| | - Kristyna Pluhackova
- Computational Biology, Department of Biology, Friedrich-Alexander Universität Erlangen-Nürnberg Erlangen, Germany
| | - Rainer A Böckmann
- Computational Biology, Department of Biology, Friedrich-Alexander Universität Erlangen-Nürnberg Erlangen, Germany
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17
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Dun AR, Lord GJ, Wilson RS, Kavanagh DM, Cialowicz KI, Sugita S, Park S, Yang L, Smyth AM, Papadopulos A, Rickman C, Duncan RR. Navigation through the Plasma Membrane Molecular Landscape Shapes Random Organelle Movement. Curr Biol 2017; 27:408-414. [PMID: 28089515 PMCID: PMC5300901 DOI: 10.1016/j.cub.2016.12.002] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2016] [Revised: 09/05/2016] [Accepted: 12/02/2016] [Indexed: 12/13/2022]
Abstract
Eukaryotic plasma membrane organization theory has long been controversial, in part due to a dearth of suitably high-resolution techniques to probe molecular architecture in situ and integrate information from diverse data streams [1]. Notably, clustered patterning of membrane proteins is a commonly conserved feature across diverse protein families (reviewed in [2]), including the SNAREs [3], SM proteins [4, 5], ion channels [6, 7], and receptors (e.g., [8]). Much effort has gone into analyzing the behavior of secretory organelles [9-13], and understanding the relationship between the membrane and proximal organelles [4, 5, 12, 14] is an essential goal for cell biology as broad concepts or rules may be established. Here we explore the generally accepted model that vesicles at the plasmalemma are guided by cytoskeletal tracks to specific sites on the membrane that have clustered molecular machinery for secretion [15], organized in part by the local lipid composition [16]. To increase our understanding of these fundamental processes, we integrated nanoscopy and spectroscopy of the secretory machinery with organelle tracking data in a mathematical model, iterating with knockdown cell models. We find that repeated routes followed by successive vesicles, the re-use of similar fusion sites, and the apparently distinct vesicle "pools" are all fashioned by the Brownian behavior of organelles overlaid on navigation between non-reactive secretory protein molecular depots patterned at the plasma membrane.
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Affiliation(s)
- Alison R Dun
- Institute of Biological Chemistry, Biophysics and Bioengineering, Heriot-Watt University, Edinburgh EH14 4AS, UK; Edinburgh Super-Resolution Imaging Consortium
| | - Gabriel J Lord
- Department of Mathematics, Maxwell Institute, MACS, Heriot-Watt University, Edinburgh EH14 4AS, UK
| | - Rhodri S Wilson
- Institute of Biological Chemistry, Biophysics and Bioengineering, Heriot-Watt University, Edinburgh EH14 4AS, UK; Edinburgh Super-Resolution Imaging Consortium
| | - Deirdre M Kavanagh
- Institute of Biological Chemistry, Biophysics and Bioengineering, Heriot-Watt University, Edinburgh EH14 4AS, UK; Edinburgh Super-Resolution Imaging Consortium
| | - Katarzyna I Cialowicz
- Institute of Biological Chemistry, Biophysics and Bioengineering, Heriot-Watt University, Edinburgh EH14 4AS, UK; Edinburgh Super-Resolution Imaging Consortium
| | - Shuzo Sugita
- Toronto Western Research Institute, Room 11-432, McLaughlin Wing, 399 Bathurst St., Toronto, ON M5T 2S8, Canada
| | - Seungmee Park
- Toronto Western Research Institute, Room 11-432, McLaughlin Wing, 399 Bathurst St., Toronto, ON M5T 2S8, Canada
| | - Lei Yang
- Institute of Biological Chemistry, Biophysics and Bioengineering, Heriot-Watt University, Edinburgh EH14 4AS, UK; Edinburgh Super-Resolution Imaging Consortium
| | - Annya M Smyth
- Centre for Inflammation Research, University of Edinburgh, The Queen's Medical Research Institute, 47 Little France Crescent, Edinburgh EH16 4TJ, UK
| | - Andreas Papadopulos
- The Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, The University of Queensland, Brisbane, QLD 4072, Australia
| | - Colin Rickman
- Institute of Biological Chemistry, Biophysics and Bioengineering, Heriot-Watt University, Edinburgh EH14 4AS, UK; Edinburgh Super-Resolution Imaging Consortium
| | - Rory R Duncan
- Institute of Biological Chemistry, Biophysics and Bioengineering, Heriot-Watt University, Edinburgh EH14 4AS, UK; Edinburgh Super-Resolution Imaging Consortium.
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18
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Toft-Bertelsen TL, Ziomkiewicz I, Houy S, Pinheiro PS, Sørensen JB. Regulation of Ca2+ channels by SNAP-25 via recruitment of syntaxin-1 from plasma membrane clusters. Mol Biol Cell 2016; 27:3329-3341. [PMID: 27605709 PMCID: PMC5170865 DOI: 10.1091/mbc.e16-03-0184] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2016] [Accepted: 09/01/2016] [Indexed: 12/20/2022] Open
Abstract
SNAP-25 regulates Ca2+ channels in an unknown manner. Endogenous and exogenous SNAP-25 inhibit Ca2+ currents indirectly by recruiting syntaxin-1 from clusters on the plasma membrane, thereby making it available for Ca2+ current inhibition. Thus the cell can regulate Ca2+ influx by expanding or contracting syntaxin-1 clusters. SNAP-25 regulates Ca2+ channels, with potentially important consequences for diseases involving an aberrant SNAP-25 expression level. How this regulation is executed mechanistically remains unknown. We investigated this question in mouse adrenal chromaffin cells and found that SNAP-25 inhibits Ca2+ currents, with the B-isoform being more potent than the A-isoform, but not when syntaxin-1 is cleaved by botulinum neurotoxin C. In contrast, syntaxin-1 inhibits Ca2+ currents independently of SNAP-25. Further experiments using immunostaining showed that endogenous or exogenous SNAP-25 expression recruits syntaxin-1 from clusters on the plasma membrane, thereby increasing the immunoavailability of syntaxin-1 and leading indirectly to Ca2+ current inhibition. Expression of Munc18-1, which recruits syntaxin-1 within the exocytotic pathway, does not modulate Ca2+ channels, whereas overexpression of the syntaxin-binding protein Doc2B or ubMunc13-2 increases syntaxin-1 immunoavailability and concomitantly down-regulates Ca2+ currents. Similar findings were obtained upon chemical cholesterol depletion, leading directly to syntaxin-1 cluster dispersal and Ca2+ current inhibition. We conclude that clustering of syntaxin-1 allows the cell to maintain a high syntaxin-1 expression level without compromising Ca2+ influx, and recruitment of syntaxin-1 from clusters by SNAP-25 expression makes it available for regulating Ca2+ channels. This mechanism potentially allows the cell to regulate Ca2+ influx by expanding or contracting syntaxin-1 clusters.
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Affiliation(s)
- Trine Lisberg Toft-Bertelsen
- Neurosecretion Group, Department of Neuroscience and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, DK-2200 Copenhagen N, Denmark
| | - Iwona Ziomkiewicz
- Neurosecretion Group, Department of Neuroscience and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, DK-2200 Copenhagen N, Denmark
| | - Sébastien Houy
- Neurosecretion Group, Department of Neuroscience and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, DK-2200 Copenhagen N, Denmark
| | - Paulo S Pinheiro
- Neurosecretion Group, Department of Neuroscience and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, DK-2200 Copenhagen N, Denmark
| | - Jakob B Sørensen
- Neurosecretion Group, Department of Neuroscience and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, DK-2200 Copenhagen N, Denmark
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19
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Milovanovic D, Platen M, Junius M, Diederichsen U, Schaap IAT, Honigmann A, Jahn R, van den Bogaart G. Calcium Promotes the Formation of Syntaxin 1 Mesoscale Domains through Phosphatidylinositol 4,5-Bisphosphate. J Biol Chem 2016; 291:7868-76. [PMID: 26884341 PMCID: PMC4824995 DOI: 10.1074/jbc.m116.716225] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2016] [Indexed: 12/21/2022] Open
Abstract
Phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) is a minor component of total plasma membrane lipids, but it has a substantial role in the regulation of many cellular functions, including exo- and endocytosis. Recently, it was shown that PI(4,5)P2and syntaxin 1, a SNARE protein that catalyzes regulated exocytosis, form domains in the plasma membrane that constitute recognition sites for vesicle docking. Also, calcium was shown to promote syntaxin 1 clustering in the plasma membrane, but the molecular mechanism was unknown. Here, using a combination of superresolution stimulated emission depletion microscopy, FRET, and atomic force microscopy, we show that Ca(2+)acts as a charge bridge that specifically and reversibly connects multiple syntaxin 1/PI(4,5)P2complexes into larger mesoscale domains. This transient reorganization of the plasma membrane by physiological Ca(2+)concentrations is likely to be important for Ca(2+)-regulated secretion.
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Affiliation(s)
- Dragomir Milovanovic
- From the Department of Neurobiology, Max Planck Institute for Biophysical Chemistry, 37077 Göttingen, Germany, the Department of Neuroscience, Program in Cellular Neuroscience, Neurodegeneration, and Repair, Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, Connecticut 06511
| | - Mitja Platen
- the Third Institute of Physics, Faculty of Physics
| | - Meike Junius
- Institute for Organic and Biomolecular Chemistry, Georg August University, 37077 Göttingen, Germany
| | - Ulf Diederichsen
- Institute for Organic and Biomolecular Chemistry, Georg August University, 37077 Göttingen, Germany
| | - Iwan A T Schaap
- the Third Institute of Physics, Faculty of Physics, the School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh EH14 4AS, United Kingdom
| | - Alf Honigmann
- the Max Planck Institute for Molecular Cell Biology and Genetics, 01307 Dresden, Germany, and
| | - Reinhard Jahn
- From the Department of Neurobiology, Max Planck Institute for Biophysical Chemistry, 37077 Göttingen, Germany,
| | - Geert van den Bogaart
- From the Department of Neurobiology, Max Planck Institute for Biophysical Chemistry, 37077 Göttingen, Germany, the Department of Tumor Immunology, Radboud University Medical Center, 6525 GA Nijmegen, The Netherlands
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20
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Destainville N, Schmidt TH, Lang T. Where Biology Meets Physics--A Converging View on Membrane Microdomain Dynamics. CURRENT TOPICS IN MEMBRANES 2015; 77:27-65. [PMID: 26781829 DOI: 10.1016/bs.ctm.2015.10.004] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
For several decades, the phenomenon of membrane component segregation into microdomains has been a well-known and highly debated subject, and varying concepts including the raft hypothesis, the fence-and-picket model, hydrophobic-mismatch, and specific protein-protein interactions have been offered as explanations. Here, we review the level of insight into the molecular architecture of membrane domains one is capable of obtaining through biological experimentation. Using SNARE proteins as a paradigm, comprehensive data suggest that several dozens of molecules crowd together into almost circular spots smaller than 100 nm. Such clusters are highly dynamical as they constantly capture and lose molecules. The organization has a strong influence on the functional availability of proteins and likely provides a molecular scaffold for more complex protein networks. Despite this high level of insight, fundamental open questions remain, applying not only to SNARE protein domains but more generally to all types of membrane domains. In this context, we explain the view of physical models and how they are beneficial in advancing our concept of micropatterning. While biological models generally remain qualitative and descriptive, physics aims towards making them quantitative and providing reproducible numbers, in order to discriminate between different mechanisms which have been proposed to account for experimental observations. Despite the fundamental differences in biological and physical approaches as far as cell membrane microdomains are concerned, we are able to show that convergence on common points of views is in reach.
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Affiliation(s)
- Nicolas Destainville
- Laboratoire de Physique Theorique (IRSAMC), Universite Toulouse 3-Paul Sabatier, UPS/CNRS, Toulouse, France
| | - Thomas H Schmidt
- Department of Membrane Biochemistry, Life & Medical Sciences (LIMES) Institute, University of Bonn, Bonn, Germany
| | - Thorsten Lang
- Department of Membrane Biochemistry, Life & Medical Sciences (LIMES) Institute, University of Bonn, Bonn, Germany
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21
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Vreja IC, Nikić I, Göttfert F, Bates M, Kröhnert K, Outeiro TF, Hell SW, Lemke EA, Rizzoli SO. Super-resolution Microscopy of Clickable Amino Acids Reveals the Effects of Fluorescent Protein Tagging on Protein Assemblies. ACS NANO 2015; 9:11034-11041. [PMID: 26498474 DOI: 10.1021/acsnano.5b04434] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
The advent of super-resolution microscopy (nanoscopy) has set high standards for fluorescence tagging. Fluorescent proteins (FPs) are convenient tags in conventional imaging, but their use in nanoscopy has been questioned due to their relatively large size and propensity to form multimers. Here, we compared the nanoscale organization of proteins with or without FP tags by introducing the unnatural amino acid propargyl-L-lysine (PRK) in 26 proteins known to form multimolecular arrangements and into their FP-tagged variants. We revealed the proteins by coupling synthetic fluorophores to PRK via click chemistry and visualized them using ground-state depletion microscopy followed by individual molecule return, as well as stimulated emission depletion microscopy. The arrangements formed by the FP-tagged and nontagged proteins were similar. Mild, but statistically significant differences were observed for only six proteins (23% of all proteins tested). This suggests that FP-based nanoscopy is generally reliable. Unnatural amino acids should be a reliable alternative for the few proteins that are sensitive to FP tagging.
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Affiliation(s)
- Ingrid C Vreja
- International Max Planck Research School for Molecular Biology , Göttingen, Germany
| | - Ivana Nikić
- Structural and Computational Biology Unit, EMBL , 69117 Heidelberg, Germany
| | - Fabian Göttfert
- Department of Nanobiophotonics, Max Planck Institute for Biophysical Chemistry , 37077 Göttingen, Germany
| | - Mark Bates
- Department of Nanobiophotonics, Max Planck Institute for Biophysical Chemistry , 37077 Göttingen, Germany
| | | | | | - Stefan W Hell
- Department of Nanobiophotonics, Max Planck Institute for Biophysical Chemistry , 37077 Göttingen, Germany
| | - Edward A Lemke
- Structural and Computational Biology Unit, EMBL , 69117 Heidelberg, Germany
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22
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Takahashi N, Sawada W, Noguchi J, Watanabe S, Ucar H, Hayashi-Takagi A, Yagishita S, Ohno M, Tokumaru H, Kasai H. Two-photon fluorescence lifetime imaging of primed SNARE complexes in presynaptic terminals and β cells. Nat Commun 2015; 6:8531. [PMID: 26439845 PMCID: PMC4600761 DOI: 10.1038/ncomms9531] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2015] [Accepted: 08/30/2015] [Indexed: 12/30/2022] Open
Abstract
It remains unclear how readiness for Ca(2+)-dependent exocytosis depends on varying degrees of SNARE complex assembly. Here we directly investigate the SNARE assembly using two-photon fluorescence lifetime imaging (FLIM) of Förster resonance energy transfer (FRET) between three pairs of neuronal SNAREs in presynaptic boutons and pancreatic β cells in the islets of Langerhans. These FRET probes functionally rescue their endogenous counterparts, supporting ultrafast exocytosis. We show that trans-SNARE complexes accumulated in the active zone, and estimate the number of complexes associated with each docked vesicle. In contrast, SNAREs were unassembled in resting state, and assembled only shortly prior to insulin exocytosis, which proceeds slowly. We thus demonstrate that distinct states of fusion readiness are associated with SNARE complex formation. Our FRET/FLIM approaches enable optical imaging of fusion readiness in both live and chemically fixed tissues.
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Affiliation(s)
- Noriko Takahashi
- Faculty of Medicine, Laboratory of Structural Physiology, Center for Disease Biology and Integrative Medicine, University of Tokyo, Bunkyo-ku, Tokyo 113-0033, Japan.,CREST, Japan Science and Technology Agency, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan
| | - Wakako Sawada
- Faculty of Medicine, Laboratory of Structural Physiology, Center for Disease Biology and Integrative Medicine, University of Tokyo, Bunkyo-ku, Tokyo 113-0033, Japan.,CREST, Japan Science and Technology Agency, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan
| | - Jun Noguchi
- Faculty of Medicine, Laboratory of Structural Physiology, Center for Disease Biology and Integrative Medicine, University of Tokyo, Bunkyo-ku, Tokyo 113-0033, Japan.,CREST, Japan Science and Technology Agency, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan
| | - Satoshi Watanabe
- Faculty of Medicine, Laboratory of Structural Physiology, Center for Disease Biology and Integrative Medicine, University of Tokyo, Bunkyo-ku, Tokyo 113-0033, Japan.,CREST, Japan Science and Technology Agency, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan
| | - Hasan Ucar
- Faculty of Medicine, Laboratory of Structural Physiology, Center for Disease Biology and Integrative Medicine, University of Tokyo, Bunkyo-ku, Tokyo 113-0033, Japan.,CREST, Japan Science and Technology Agency, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan
| | - Akiko Hayashi-Takagi
- Faculty of Medicine, Laboratory of Structural Physiology, Center for Disease Biology and Integrative Medicine, University of Tokyo, Bunkyo-ku, Tokyo 113-0033, Japan.,PRESTO, Japan Science and Technology Agency, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan
| | - Sho Yagishita
- Faculty of Medicine, Laboratory of Structural Physiology, Center for Disease Biology and Integrative Medicine, University of Tokyo, Bunkyo-ku, Tokyo 113-0033, Japan.,CREST, Japan Science and Technology Agency, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan
| | - Mitsuyo Ohno
- Faculty of Medicine, Laboratory of Structural Physiology, Center for Disease Biology and Integrative Medicine, University of Tokyo, Bunkyo-ku, Tokyo 113-0033, Japan
| | - Hiroshi Tokumaru
- Faculty of Pharmaceutical Sciences at Kagawa, Tokushima Bunri University, Kagawa 769-2193, Japan
| | - Haruo Kasai
- Faculty of Medicine, Laboratory of Structural Physiology, Center for Disease Biology and Integrative Medicine, University of Tokyo, Bunkyo-ku, Tokyo 113-0033, Japan.,CREST, Japan Science and Technology Agency, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan
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23
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Ji C, Zhang Y, Xu P, Xu T, Lou X. Nanoscale Landscape of Phosphoinositides Revealed by Specific Pleckstrin Homology (PH) Domains Using Single-molecule Superresolution Imaging in the Plasma Membrane. J Biol Chem 2015; 290:26978-26993. [PMID: 26396197 DOI: 10.1074/jbc.m115.663013] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2015] [Indexed: 11/06/2022] Open
Abstract
Both phosphatidylinositol 4-phosphate (PI4P) and phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) are independent plasma membrane (PM) determinant lipids that are essential for multiple cellular functions. However, their nanoscale spatial organization in the PM remains elusive. Using single-molecule superresolution microscopy and new photoactivatable fluorescence probes on the basis of pleckstrin homology domains that specifically recognize phosphatidylinositides in insulin-secreting INS-1 cells, we report that the PI(4,5)P2 probes exhibited a remarkably uniform distribution in the major regions of the PM, with some sparse PI(4,5)P2-enriched membrane patches/domains of diverse sizes (383 ± 14 nm on average). Quantitative analysis revealed a modest concentration gradient that was much less steep than previously thought, and no densely packed PI(4,5)P2 nanodomains were observed. Live-cell superresolution imaging further demonstrated the dynamic structural changes of those domains in the flat PM and membrane protrusions. PI4P and phosphatidylinositol (3,4,5)-trisphosphate (PI(3,4,5)P3) showed similar spatial distributions as PI(4,5)P2. These data reveal the nanoscale landscape of key inositol phospholipids in the native PM and imply a framework for local cellular signaling and lipid-protein interactions at a nanometer scale.
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Affiliation(s)
- Chen Ji
- Department of Neuroscience, School of Medicine and Public Health, University of Wisconsin-Madison, Madison, Wisconsin 53705 and
| | - Yongdeng Zhang
- the National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China
| | - Pingyong Xu
- the National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China
| | - Tao Xu
- the National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China
| | - Xuelin Lou
- Department of Neuroscience, School of Medicine and Public Health, University of Wisconsin-Madison, Madison, Wisconsin 53705 and.
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24
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Ullrich A, Böhme MA, Schöneberg J, Depner H, Sigrist SJ, Noé F. Dynamical Organization of Syntaxin-1A at the Presynaptic Active Zone. PLoS Comput Biol 2015; 11:e1004407. [PMID: 26367029 PMCID: PMC4569342 DOI: 10.1371/journal.pcbi.1004407] [Citation(s) in RCA: 51] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2014] [Accepted: 06/15/2015] [Indexed: 01/10/2023] Open
Abstract
Synaptic vesicle fusion is mediated by SNARE proteins forming in between synaptic vesicle (v-SNARE) and plasma membrane (t-SNARE), one of which is Syntaxin-1A. Although exocytosis mainly occurs at active zones, Syntaxin-1A appears to cover the entire neuronal membrane. By using STED super-resolution light microscopy and image analysis of Drosophila neuro-muscular junctions, we show that Syntaxin-1A clusters are more abundant and have an increased size at active zones. A computational particle-based model of syntaxin cluster formation and dynamics is developed. The model is parametrized to reproduce Syntaxin cluster-size distributions found by STED analysis, and successfully reproduces existing FRAP results. The model shows that the neuronal membrane is adjusted in a way to strike a balance between having most syntaxins stored in large clusters, while still keeping a mobile fraction of syntaxins free or in small clusters that can efficiently search the membrane or be traded between clusters. This balance is subtle and can be shifted toward almost no clustering and almost complete clustering by modifying the syntaxin interaction energy on the order of only 1 kBT. This capability appears to be exploited at active zones. The larger active-zone syntaxin clusters are more stable and provide regions of high docking and fusion capability, whereas the smaller clusters outside may serve as flexible reserve pool or sites of spontaneous ectopic release.
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Affiliation(s)
- Alexander Ullrich
- Department of Mathematics, Freie Universität Berlin, Berlin, Germany
| | - Mathias A. Böhme
- Institute for Biology/Genetics, Freie Universität Berlin, Berlin, Germany
- NeuroCure Cluster of Excellence, Charité Berlin, Berlin, Germany
| | | | - Harald Depner
- Institute for Biology/Genetics, Freie Universität Berlin, Berlin, Germany
| | - Stephan J. Sigrist
- Institute for Biology/Genetics, Freie Universität Berlin, Berlin, Germany
- NeuroCure Cluster of Excellence, Charité Berlin, Berlin, Germany
| | - Frank Noé
- Department of Mathematics, Freie Universität Berlin, Berlin, Germany
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25
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Milovanovic D, Jahn R. Organization and dynamics of SNARE proteins in the presynaptic membrane. Front Physiol 2015; 6:89. [PMID: 25852575 PMCID: PMC4365744 DOI: 10.3389/fphys.2015.00089] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2015] [Accepted: 03/05/2015] [Indexed: 01/19/2023] Open
Abstract
Our view of the lateral organization of lipids and proteins in the plasma membrane has evolved substantially in the last few decades. It is widely accepted that many, if not all, plasma membrane proteins and lipids are organized in specific domains. These domains vary widely in size, composition, and stability, and they represent platforms governing diverse cell functions. The presynaptic plasma membrane is a well-studied example of a membrane which undergoes rearrangements, especially during exo- and endocytosis. Many proteins and lipids involved in presynaptic function are known, and major efforts have been made to understand their spatial organization and dynamics. Here, we focus on the mechanisms underlying the organization of SNAREs, the key proteins of the fusion machinery, in distinct domains, and we discuss the functional significance of these clusters.
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Affiliation(s)
- Dragomir Milovanovic
- Department of Neurobiology, Max Planck Institute for Biophysical Chemistry Göttingen, Germany
| | - Reinhard Jahn
- Department of Neurobiology, Max Planck Institute for Biophysical Chemistry Göttingen, Germany
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26
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Hydrophobic mismatch sorts SNARE proteins into distinct membrane domains. Nat Commun 2015; 6:5984. [PMID: 25635869 PMCID: PMC4313621 DOI: 10.1038/ncomms6984] [Citation(s) in RCA: 107] [Impact Index Per Article: 11.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2014] [Accepted: 11/28/2014] [Indexed: 12/12/2022] Open
Abstract
The clustering of proteins and lipids in distinct microdomains is emerging as an important principle for the spatial patterning of biological membranes. Such domain formation can be the result of hydrophobic and ionic interactions with membrane lipids as well as of specific protein–protein interactions. Here using plasma membrane-resident SNARE proteins as model, we show that hydrophobic mismatch between the length of transmembrane domains (TMDs) and the thickness of the lipid membrane suffices to induce clustering of proteins. Even when the TMDs differ in length by only a single residue, hydrophobic mismatch can segregate structurally closely homologous membrane proteins in distinct membrane domains. Domain formation is further fine-tuned by interactions with polyanionic phosphoinositides and homo and heterotypic protein interactions. Our findings demonstrate that hydrophobic mismatch contributes to the structural organization of membranes. Clustering of proteins in the plasma membrane plays an important role in the regulation of both cellular signalling and membrane remodelling. Milovanovic et al. demonstrate that mismatch between transmembrane domain length and the lipid bilayer thickness is sufficient to drive clustering of SNARE proteins.
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27
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Kavanagh DM, Smyth AM, Martin KJ, Dun A, Brown ER, Gordon S, Smillie KJ, Chamberlain LH, Wilson RS, Yang L, Lu W, Cousin MA, Rickman C, Duncan RR. A molecular toggle after exocytosis sequesters the presynaptic syntaxin1a molecules involved in prior vesicle fusion. Nat Commun 2014; 5:5774. [PMID: 25517944 PMCID: PMC4284649 DOI: 10.1038/ncomms6774] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2014] [Accepted: 11/06/2014] [Indexed: 01/05/2023] Open
Abstract
Neuronal synapses are among the most scrutinized of cellular systems, serving as a model for all membrane trafficking studies. Despite this, synaptic biology has proven difficult to interrogate directly in situ due to the small size and dynamic nature of central synapses and the molecules within them. Here we determine the spatial and temporal interaction status of presynaptic proteins, imaging large cohorts of single molecules inside active synapses. Measuring rapid interaction dynamics during synaptic depolarization identified the small number of syntaxin1a and munc18-1 protein molecules required to support synaptic vesicle exocytosis. After vesicle fusion and subsequent SNARE complex disassembly, a prompt switch in syntaxin1a and munc18-1-binding mode, regulated by charge alteration on the syntaxin1a N-terminal, sequesters monomeric syntaxin1a from other disassembled fusion complex components, preventing ectopic SNARE complex formation, readying the synapse for subsequent rounds of neurotransmission.
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Affiliation(s)
- Deirdre M. Kavanagh
- Institute of Biological Chemistry, Biophysics and Bioengineering, Heriot Watt University, Edinburgh EH14 4AS, UK
- Edinburgh Super-Resolution Imaging Consortium, www.esric.org
| | - Annya M. Smyth
- Institute of Biological Chemistry, Biophysics and Bioengineering, Heriot Watt University, Edinburgh EH14 4AS, UK
- Edinburgh Super-Resolution Imaging Consortium, www.esric.org
- Centre for Integrative Physiology, University of Edinburgh, George Square, Edinburgh EH8 9XD, UK
| | - Kirsty J. Martin
- Institute of Biological Chemistry, Biophysics and Bioengineering, Heriot Watt University, Edinburgh EH14 4AS, UK
- Edinburgh Super-Resolution Imaging Consortium, www.esric.org
| | - Alison Dun
- Institute of Biological Chemistry, Biophysics and Bioengineering, Heriot Watt University, Edinburgh EH14 4AS, UK
- Edinburgh Super-Resolution Imaging Consortium, www.esric.org
| | - Euan R. Brown
- Institute of Biological Chemistry, Biophysics and Bioengineering, Heriot Watt University, Edinburgh EH14 4AS, UK
- Edinburgh Super-Resolution Imaging Consortium, www.esric.org
| | - Sarah Gordon
- Centre for Integrative Physiology, University of Edinburgh, George Square, Edinburgh EH8 9XD, UK
| | - Karen J. Smillie
- Centre for Integrative Physiology, University of Edinburgh, George Square, Edinburgh EH8 9XD, UK
| | - Luke H. Chamberlain
- Strathclyde Institute of Pharmacy and Biomedical Sciences, 161 Cathedral Street, Glasgow G4 0RE, UK
| | - Rhodri S. Wilson
- Institute of Biological Chemistry, Biophysics and Bioengineering, Heriot Watt University, Edinburgh EH14 4AS, UK
- Edinburgh Super-Resolution Imaging Consortium, www.esric.org
| | - Lei Yang
- Institute of Biological Chemistry, Biophysics and Bioengineering, Heriot Watt University, Edinburgh EH14 4AS, UK
- Edinburgh Super-Resolution Imaging Consortium, www.esric.org
| | - Weiping Lu
- Institute of Biological Chemistry, Biophysics and Bioengineering, Heriot Watt University, Edinburgh EH14 4AS, UK
- Edinburgh Super-Resolution Imaging Consortium, www.esric.org
| | - Michael A. Cousin
- Centre for Integrative Physiology, University of Edinburgh, George Square, Edinburgh EH8 9XD, UK
| | - Colin Rickman
- Institute of Biological Chemistry, Biophysics and Bioengineering, Heriot Watt University, Edinburgh EH14 4AS, UK
- Edinburgh Super-Resolution Imaging Consortium, www.esric.org
| | - Rory R. Duncan
- Institute of Biological Chemistry, Biophysics and Bioengineering, Heriot Watt University, Edinburgh EH14 4AS, UK
- Edinburgh Super-Resolution Imaging Consortium, www.esric.org
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28
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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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29
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Xie L, Liang T, Kang Y, Lin X, Sobbi R, Xie H, Chao C, Backx P, Feng ZP, Shyng SL, Gaisano HY. Phosphatidylinositol 4,5-biphosphate (PIP2) modulates syntaxin-1A binding to sulfonylurea receptor 2A to regulate cardiac ATP-sensitive potassium (KATP) channels. J Mol Cell Cardiol 2014; 75:100-10. [DOI: 10.1016/j.yjmcc.2014.07.012] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/06/2014] [Revised: 07/15/2014] [Accepted: 07/18/2014] [Indexed: 11/15/2022]
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Saka SK, Honigmann A, Eggeling C, Hell SW, Lang T, Rizzoli SO. Multi-protein assemblies underlie the mesoscale organization of the plasma membrane. Nat Commun 2014; 5:4509. [PMID: 25060237 PMCID: PMC4124874 DOI: 10.1038/ncomms5509] [Citation(s) in RCA: 133] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2014] [Accepted: 06/25/2014] [Indexed: 02/07/2023] Open
Abstract
Most proteins have uneven distributions in the plasma membrane. Broadly speaking, this may be caused by mechanisms specific to each protein, or may be a consequence of a general pattern that affects the distribution of all membrane proteins. The latter hypothesis has been difficult to test in the past. Here, we introduce several approaches based on click chemistry, through which we study the distribution of membrane proteins in living cells, as well as in membrane sheets. We found that the plasma membrane proteins form multi-protein assemblies that are long lived (minutes), and in which protein diffusion is restricted. The formation of the assemblies is dependent on cholesterol. They are separated and anchored by the actin cytoskeleton. Specific proteins are preferentially located in different regions of the assemblies, from their cores to their edges. We conclude that the assemblies constitute a basic mesoscale feature of the membrane, which affects the patterning of most membrane proteins, and possibly also their activity. Although many proteins adopt uneven distributions in the plasma membrane, it is not clear how these nanoscale heterogeneities relate to the general protein patterning of the membrane. Saka et al. use click chemistry to reveal the mesoscale organization of membrane proteins into multi-protein assemblies.
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Affiliation(s)
- Sinem K Saka
- 1] Department of Neuro- and Sensory Physiology, University of Göttingen Medical Centre, and Centre for Nanoscale Microscopy and Molecular Physiology of the Brain (CNMPB), 37075 Göttingen, Germany [2] International Max Planck Research School Molecular Biology, 37077 Göttingen, Germany
| | - Alf Honigmann
- Department of Nanobiophotonics, Max Planck Institute for Biophysical Chemistry, 37077 Göttingen, Germany
| | - Christian Eggeling
- MRC Human Immunology Unit, Weatherall Institute of Molecular Medicine, Oxford OX3 9DS, UK
| | - Stefan W Hell
- Department of Nanobiophotonics, Max Planck Institute for Biophysical Chemistry, 37077 Göttingen, Germany
| | - Thorsten Lang
- Department of Membrane Biochemistry, Life and Medical Sciences (LIMES) Institute, University of Bonn, 53115 Bonn, Germany
| | - Silvio O Rizzoli
- Department of Neuro- and Sensory Physiology, University of Göttingen Medical Centre, and Centre for Nanoscale Microscopy and Molecular Physiology of the Brain (CNMPB), 37075 Göttingen, Germany
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Abstract
The failure of pancreatic β‐cells to supply insulin in quantities sufficient to maintain euglycemia is a hallmark of type 2 diabetes. Perturbation of β‐cell cholesterol homeostasis, culminating in elevated intracellular cholesterol levels, impairs insulin secretion and has therefore been proposed as a mechanism contributing to β‐cell dysfunction. The manner in which this occurs, however, is unclear. Cholesterol is an essential lipid, as well as a major component of membrane rafts, and numerous proteins critical for the regulation of insulin secretion have been reported to associate with these domains. Although this suggests that alterations in membrane rafts could partially account for the reduction in insulin secretion observed when β‐cell cholesterol accumulates, this has not yet been demonstrated. In this review, we provide a brief overview of recent work implicating membrane rafts in some of the basic molecular mechanisms of insulin secretion, and discuss the insight it provides into the β‐cell dysfunction characteristic of type 2 diabetes. (J Diabetes Invest, doi: 10.1111/j.2040‐1124.2012.00200.x, 2012)
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Affiliation(s)
- Ronald Dirkx
- Molecular Diabetology, Paul Langerhans Institute Dresden, School of Medicine and University Clinic "Carl Gustav Carus", Dresden University of Technology
| | - Michele Solimena
- Molecular Diabetology, Paul Langerhans Institute Dresden, School of Medicine and University Clinic "Carl Gustav Carus", Dresden University of Technology ; Max Planck Institute of Molecular Cell Biology and Genetics, Dresden, Germany
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Gandasi NR, Barg S. Contact-induced clustering of syntaxin and munc18 docks secretory granules at the exocytosis site. Nat Commun 2014; 5:3914. [PMID: 24835618 DOI: 10.1038/ncomms4914] [Citation(s) in RCA: 90] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2013] [Accepted: 04/17/2014] [Indexed: 02/06/2023] Open
Abstract
Docking of secretory vesicles at the plasma membrane is a poorly understood prerequisite for exocytosis. Current models propose raft-like clusters containing syntaxin as docking receptor, but direct evidence for this is lacking. Here we provide quantitative measurements of several exocytosis proteins (syntaxin, SNAP25, munc18, munc13 and rab3) at the insulin granule release site and show that docking coincides with rapid de novo formation of syntaxin1/munc18 clusters at the nascent docking site. Formation of such clusters prevents undocking and is not observed during failed docking attempts. Overexpression of syntaxins' N-terminal Habc-domain competitively interferes with both cluster formation and successful docking. SNAP25 and munc13 are recruited to the docking site more than a minute later, consistent with munc13's reported role in granule priming rather than docking. We conclude that secretory vesicles dock by inducing syntaxin1/munc18 clustering in the target membrane, and find no evidence for preformed docking receptors.
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Affiliation(s)
- Nikhil R Gandasi
- Department of Medical Cell Biology, Uppsala University, BMC 571, 75123 Uppsala, Sweden
| | - Sebastian Barg
- Department of Medical Cell Biology, Uppsala University, BMC 571, 75123 Uppsala, Sweden
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33
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Bost A, Pasche M, Schirra C, Becherer U. Super-resolution microscopy in studying neuroendocrine cell function. Front Neurosci 2013; 7:222. [PMID: 24324394 PMCID: PMC3839409 DOI: 10.3389/fnins.2013.00222] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2013] [Accepted: 11/04/2013] [Indexed: 12/13/2022] Open
Abstract
The last two decades have seen a tremendous development in high resolution microscopy techniques giving rise to acronyms such as TIRFM, SIM, PALM, STORM, and STED. The goal of all these techniques is to overcome the physical resolution barrier of light microscopy in order to resolve precise protein localization and possibly their interaction in cells. Neuroendocrine cell function is to secrete hormones and peptides on demand. This fine-tuned multi-step process is mediated by a large array of proteins. Here, we review the new microscopy techniques used to obtain high resolution and how they have been applied to increase our knowledge of the molecular mechanisms involved in neuroendocrine cell secretion. Further the limitations of these methods are discussed and insights in possible new applications are provided.
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Affiliation(s)
- Anneka Bost
- Physiologisches Institut, Universität des Saarlandes Homburg/Saar, Germany
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34
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Martin S, Tomatis VM, Papadopulos A, Christie MP, Malintan NT, Gormal RS, Sugita S, Martin JL, Collins BM, Meunier FA. The Munc18-1 domain 3a loop is essential for neuroexocytosis but not for syntaxin-1A transport to the plasma membrane. J Cell Sci 2013; 126:2353-60. [PMID: 23761923 DOI: 10.1242/jcs.126813] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Munc18-1 plays a dual role in transporting syntaxin-1A (Sx1a) to the plasma membrane and regulating SNARE-mediated membrane fusion. As impairment of either function leads to a common exocytic defect, assigning specific roles for various Munc18-1 domains has proved difficult. Structural analyses predict that a loop region in Munc18-1 domain 3a could catalyse the conversion of Sx1a from a 'closed', fusion-incompetent to an 'open', fusion-competent conformation. As this conversion occurs at the plasma membrane, mutations in this loop could potentially separate the chaperone and exocytic functions of Munc18-1. Expression of a Munc18-1 deletion mutant lacking 17 residues of the domain 3a loop (Munc18-1(Δ317-333)) in PC12 cells deficient in endogenous Munc18 (DKD-PC12 cells) fully rescued transport of Sx1a to the plasma membrane, but not exocytic secretory granule fusion. In vitro binding of Munc18-1(Δ317-333) to Sx1a was indistinguishable from that of full-length Munc18-1, consistent with the critical role of the closed conformation in Sx1a transport. However, in DKD-PC12 cells, Munc18-1(Δ317-333) binding to Sx1a was greatly reduced compared to that of full-length Munc18-1, suggesting that closed conformation binding contributes little to the overall interaction at the cell surface. Furthermore, we found that Munc18-1(Δ317-333) could bind SNARE complexes in vitro, suggesting that additional regulatory factors underpin the exocytic function of Munc18-1 in vivo. Together, these results point to a defined role for Munc18-1 in facilitating exocytosis linked to the loop region of domain 3a that is clearly distinct from its function in Sx1a transport.
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Affiliation(s)
- Sally Martin
- Queensland Brain Institute, The University of Queensland, Brisbane QLD 4072, Australia
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35
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Abstract
Exocytosis, the process in which material is transported from the cell interior to the extracellular space, proceeds through a complex mechanism. Defects in this process are linked to a number of serious illnesses including diabetes, cancer, and a range of neuropathologies. In neuroendocrine cells, exocytosis involves the fusion of secretory vesicles, carrying signaling molecules, with the plasma membrane through the coordinated interplay of proteins, lipids, and small molecules. This process is highly regulated and occurs in a complex three-dimensional environment within the cell precisely coupled to the stimulus. The study of exocytosis poses significant challenges, involving rapidly changing, nano-scale, protein-protein, and protein-lipid interactions, at specialized sites in the cell. Over the last decade our understanding of neuroendocrine exocytosis has been greatly enhanced by developments in fluorescence microscopy. Modern microscopy encompasses a toolbox of advanced techniques, pushing the limits of sensitivity and resolution, to probe different properties of exocytosis. In more recent years, the development of super-resolution microscopy techniques, side-stepping the limits of optical resolution imposed by the physical properties of light, have started to provide an unparalleled view of exocytosis. In this review we will discuss how advances in fluorescence microscopy are shedding light on the spatial and temporal organization of the exocytotic machinery.
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Affiliation(s)
- Alicja Graczyk
- Institute of Biological Chemistry, Biophysics and Bioengineering, School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh, UK
| | - Colin Rickman
- Institute of Biological Chemistry, Biophysics and Bioengineering, School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh, UK
- *Correspondence: Colin Rickman, Institute of Biological Chemistry, Biophysics and Bioengineering, School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh EH14 4AS, UK e-mail:
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36
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Molino D, Galli T. Biogenesis and transport of membrane domains-potential implications in brain pathologies. Biochimie 2013; 96:75-84. [PMID: 24075975 DOI: 10.1016/j.biochi.2013.09.014] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2013] [Accepted: 09/12/2013] [Indexed: 11/28/2022]
Abstract
Lipids in biological membranes show astonishing chemical diversity, but they also show some key conserved structures in different organisms. In addition, some of their biophysical properties have been related to specific functions. In this review, we aim to discuss the role of sphingolipids- and cholesterol-rich micro- and nano-membrane domains (MD) and highlight their pivotal role in lipid-protein clustering processes, vesicle biogenesis and membrane fusion. We further review potential connections between human pathologies and defects in MD biosynthesis, recycling and homeostasis. Brain, which is second only to the adipose tissues in term of lipid abundance, is particularly affected by MD defects which are linked to neurodegenerative disorders. Finally we propose a potential connection between MD and several nutrient-related processes and envision how diet and autophagy could bring insights towards understanding the impact of global lipid homeostasis on human health and disease.
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Affiliation(s)
- Diana Molino
- Institut Jacques Monod, UMR 7592, CNRS, Université Paris Diderot, Sorbonne Paris Cité, F-75205 Paris, France; INSERM ERL U950, Membrane Traffic in Neuronal and Epithelial Morphogenesis, F-75013 Paris, France.
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37
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Ammar MR, Kassas N, Chasserot-Golaz S, Bader MF, Vitale N. Lipids in Regulated Exocytosis: What are They Doing? Front Endocrinol (Lausanne) 2013; 4:125. [PMID: 24062727 PMCID: PMC3775428 DOI: 10.3389/fendo.2013.00125] [Citation(s) in RCA: 79] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/18/2013] [Accepted: 08/31/2013] [Indexed: 12/27/2022] Open
Abstract
The regulated secretory pathway in neuroendocrine cells ends with the release of hormones and neurotransmitters following a rise in cytosolic calcium. This process known as regulated exocytosis involves the assembly of soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) proteins, the synaptic vesicle VAMP (synaptobrevin), and the plasma membrane proteins syntaxin and SNAP-25. Although there is much evidence suggesting that SNARE proteins play a key role in the fusion machinery, other cellular elements regulating the kinetics, the extent of fusion, and the preparation of vesicle for release have received less attention. Among those factors, lipids have also been proposed to play important functions both at the level of secretory vesicle recruitment and late membrane fusion steps. Here, we will review the latest evidence supporting the concept of the fusogenic activity of lipids, and also discuss how this may be achieved. These possibilities include the recruitment and sequestration of the components of the exocytotic machinery, regulation of protein function, and direct effects on membrane topology.
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Affiliation(s)
- Mohamed Raafet Ammar
- Institut des Neurosciences Cellulaires et Intégratives (INCI), UPR-3212 Centre National de la Recherche Scientifique, Université de Strasbourg, Strasbourg, France
| | - Nawal Kassas
- Institut des Neurosciences Cellulaires et Intégratives (INCI), UPR-3212 Centre National de la Recherche Scientifique, Université de Strasbourg, Strasbourg, France
| | - Sylvette Chasserot-Golaz
- Institut des Neurosciences Cellulaires et Intégratives (INCI), UPR-3212 Centre National de la Recherche Scientifique, Université de Strasbourg, Strasbourg, France
| | - Marie-France Bader
- Institut des Neurosciences Cellulaires et Intégratives (INCI), UPR-3212 Centre National de la Recherche Scientifique, Université de Strasbourg, Strasbourg, France
| | - Nicolas Vitale
- Institut des Neurosciences Cellulaires et Intégratives (INCI), UPR-3212 Centre National de la Recherche Scientifique, Université de Strasbourg, Strasbourg, France
- *Correspondence: Nicolas Vitale, Institut des Neurosciences Cellulaires et Intégratives (INCI), UPR-3212 Centre National de la Recherche Scientifique, Université de Strasbourg, 5 rue Blaise Pascal, 67084 Strasbourg, France e-mail:
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38
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Hiersemenzel K, Brown ER, Duncan RR. Imaging large cohorts of single ion channels and their activity. Front Endocrinol (Lausanne) 2013; 4:114. [PMID: 24027557 PMCID: PMC3762133 DOI: 10.3389/fendo.2013.00114] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/30/2013] [Accepted: 08/16/2013] [Indexed: 01/16/2023] Open
Abstract
As calcium is the most important signaling molecule in neurons and secretory cells, amongst many other cell types, it follows that an understanding of calcium channels and their regulation of exocytosis is of vital importance. Calcium imaging using calcium dyes such as Fluo3, or FRET-based dyes that have been used widely has provided invaluable information, which combined with modeling has estimated the subtypes of channels responsible for triggering the exocytotic machinery as well as inferences about the relative distances away from vesicle fusion sites these molecules adopt. Importantly, new super-resolution microscopy techniques, combined with novel Ca(2+) indicators and imaginative imaging approaches can now define directly the nano-scale locations of very large cohorts of single channel molecules in relation to single vesicles. With combinations of these techniques the activity of individual channels can be visualized and quantified using novel Ca(2+) indicators. Fluorescently labeled specific channel toxins can also be used to localize endogenous assembled channel tetramers. Fluorescence lifetime imaging microscopy and other single-photon-resolution spectroscopic approaches offer the possibility to quantify protein-protein interactions between populations of channels and the SNARE protein machinery for the first time. Together with simultaneous electrophysiology, this battery of quantitative imaging techniques has the potential to provide unprecedented detail describing the locations, dynamic behaviors, interactions, and conductance activities of many thousands of channel molecules and vesicles in living cells.
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Affiliation(s)
- Katia Hiersemenzel
- Edinburgh Super-Resolution Imaging Consortium (ESRIC), Institute of Biological Chemistry, Biophysics and Bioengineering, School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh, UK
| | - Euan R. Brown
- Edinburgh Super-Resolution Imaging Consortium (ESRIC), Institute of Biological Chemistry, Biophysics and Bioengineering, School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh, UK
| | - Rory R. Duncan
- Edinburgh Super-Resolution Imaging Consortium (ESRIC), Institute of Biological Chemistry, Biophysics and Bioengineering, School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh, UK
- *Correspondence: Rory R. Duncan, Edinburgh Super-Resolution Imaging Consortium (ESRIC), Institute of Biological Chemistry, Biophysics and Bioengineering, School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh EH14 4AS, UK e-mail:
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39
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40
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Smyth AM, Yang L, Martin KJ, Hamilton C, Lu W, Cousin MA, Rickman C, Duncan RR. Munc18-1 protein molecules move between membrane molecular depots distinct from vesicle docking sites. J Biol Chem 2012; 288:5102-13. [PMID: 23223447 PMCID: PMC3576115 DOI: 10.1074/jbc.m112.407585] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Four evolutionarily conserved proteins are required for mammalian regulated exocytosis: three SNARE proteins, syntaxin, SNAP-25, and synaptobrevin, and the SM protein, Munc18-1. Here, using single-molecule imaging, we measured the spatial distribution of large cohorts of single Munc18-1 molecules correlated with the positions of single secretory vesicles in a functionally rescued Munc18-1-null cellular model. Munc18-1 molecules were nonrandomly distributed across the plasma membrane in a manner not directed by mode of interaction with syntaxin1, with a small mean number of molecules observed to reside under membrane resident vesicles. Surprisingly, we found that the majority of vesicles in fully secretion-competent cells had no Munc18-1 associated within distances relevant to plasma membrane-vesicle SNARE interactions. Live cell imaging of Munc18-1 molecule dynamics revealed that the density of Munc18-1 molecules at the plasma membrane anticorrelated with molecular speed, with single Munc18-1 molecules displaying directed motion between membrane hotspots enriched in syntaxin1a. Our findings demonstrate that Munc18-1 molecules move between membrane depots distinct from vesicle morphological docking sites.
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Affiliation(s)
- Annya M Smyth
- Life-Physical Sciences Interface Laboratory, Institute of Biological Chemistry, Biophysics and Bioengineering, School of Engineering and Physical Sciences, Heriot Watt University, Edinburgh EH14 4AS, Scotland, United Kingdom
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41
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Yang L, Dun AR, Martin KJ, Qiu Z, Dunn A, Lord GJ, Lu W, Duncan RR, Rickman C. Secretory vesicles are preferentially targeted to areas of low molecular SNARE density. PLoS One 2012; 7:e49514. [PMID: 23166692 PMCID: PMC3499460 DOI: 10.1371/journal.pone.0049514] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2012] [Accepted: 10/10/2012] [Indexed: 12/30/2022] Open
Abstract
Intercellular communication is commonly mediated by the regulated fusion, or exocytosis, of vesicles with the cell surface. SNARE (soluble N-ethymaleimide sensitive factor attachment protein receptor) proteins are the catalytic core of the secretory machinery, driving vesicle and plasma membrane merger. Plasma membrane SNAREs (tSNAREs) are proposed to reside in dense clusters containing many molecules, thus providing a concentrated reservoir to promote membrane fusion. However, biophysical experiments suggest that a small number of SNAREs are sufficient to drive a single fusion event. Here we show, using molecular imaging, that the majority of tSNARE molecules are spatially separated from secretory vesicles. Furthermore, the motilities of the individual tSNAREs are constrained in membrane micro-domains, maintaining a non-random molecular distribution and limiting the maximum number of molecules encountered by secretory vesicles. Together our results provide a new model for the molecular mechanism of regulated exocytosis and demonstrate the exquisite organization of the plasma membrane at the level of individual molecular machines.
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Affiliation(s)
- Lei Yang
- Institute of Biological Chemistry, Biophysics and Bioengineering, Heriot-Watt University, Edinburgh, United Kingdom
| | - Alison R. Dun
- Institute of Biological Chemistry, Biophysics and Bioengineering, Heriot-Watt University, Edinburgh, United Kingdom
| | - Kirsty J. Martin
- Institute of Biological Chemistry, Biophysics and Bioengineering, Heriot-Watt University, Edinburgh, United Kingdom
| | - Zhen Qiu
- Institute of Biological Chemistry, Biophysics and Bioengineering, Heriot-Watt University, Edinburgh, United Kingdom
| | - Andrew Dunn
- Institute of Biological Chemistry, Biophysics and Bioengineering, Heriot-Watt University, Edinburgh, United Kingdom
| | - Gabriel J. Lord
- Mathematical and Computer Sciences, Heriot-Watt University, Edinburgh, United Kingdom
| | - Weiping Lu
- Institute of Biological Chemistry, Biophysics and Bioengineering, Heriot-Watt University, Edinburgh, United Kingdom
| | - Rory R. Duncan
- Institute of Biological Chemistry, Biophysics and Bioengineering, Heriot-Watt University, Edinburgh, United Kingdom
| | - Colin Rickman
- Institute of Biological Chemistry, Biophysics and Bioengineering, Heriot-Watt University, Edinburgh, United Kingdom
- * E-mail:
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Kasai H, Takahashi N, Tokumaru H. Distinct Initial SNARE Configurations Underlying the Diversity of Exocytosis. Physiol Rev 2012; 92:1915-64. [DOI: 10.1152/physrev.00007.2012] [Citation(s) in RCA: 120] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
The dynamics of exocytosis are diverse and have been optimized for the functions of synapses and a wide variety of cell types. For example, the kinetics of exocytosis varies by more than five orders of magnitude between ultrafast exocytosis in synaptic vesicles and slow exocytosis in large dense-core vesicles. However, in all cases, exocytosis is mediated by the same fundamental mechanism, i.e., the assembly of soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) proteins. It is often assumed that vesicles need to be docked at the plasma membrane and SNARE proteins must be preassembled before exocytosis is triggered. However, this model cannot account for the dynamics of exocytosis recently reported in synapses and other cells. For example, vesicles undergo exocytosis without prestimulus docking during tonic exocytosis of synaptic vesicles in the active zone. In addition, epithelial and hematopoietic cells utilize cAMP and kinases to trigger slow exocytosis of nondocked vesicles. In this review, we summarize the manner in which the diversity of exocytosis reflects the initial configurations of SNARE assembly, including trans-SNARE, binary-SNARE, unitary-SNARE, and cis-SNARE configurations. The initial SNARE configurations depend on the particular SNARE subtype (syntaxin, SNAP25, or VAMP), priming proteins (Munc18, Munc13, CAPS, complexin, or snapin), triggering proteins (synaptotagmins, Doc2, and various protein kinases), and the submembraneous cytomatrix, and they are the key to determining the kinetics of subsequent exocytosis. These distinct initial configurations will help us clarify the common SNARE assembly processes underlying exocytosis and membrane trafficking in eukaryotic cells.
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Affiliation(s)
- Haruo Kasai
- Laboratory of Structural Physiology, Center for Disease Biology and Integrative Medicine, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan; and Faculty of Pharmaceutical Sciences at Kagawa, Tokushima Bunri University, Kagawa, Japan
| | - Noriko Takahashi
- Laboratory of Structural Physiology, Center for Disease Biology and Integrative Medicine, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan; and Faculty of Pharmaceutical Sciences at Kagawa, Tokushima Bunri University, Kagawa, Japan
| | - Hiroshi Tokumaru
- Laboratory of Structural Physiology, Center for Disease Biology and Integrative Medicine, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan; and Faculty of Pharmaceutical Sciences at Kagawa, Tokushima Bunri University, Kagawa, Japan
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Bar-On D, Wolter S, van de Linde S, Heilemann M, Nudelman G, Nachliel E, Gutman M, Sauer M, Ashery U. Super-resolution imaging reveals the internal architecture of nano-sized syntaxin clusters. J Biol Chem 2012; 287:27158-67. [PMID: 22700970 DOI: 10.1074/jbc.m112.353250] [Citation(s) in RCA: 101] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
Key synaptic proteins from the soluble SNARE (N-ethylmaleimide-sensitive factor attachment protein receptor) family, among many others, are organized at the plasma membrane of cells as clusters containing dozens to hundreds of protein copies. However, the exact membranal distribution of proteins into clusters or as single molecules, the organization of molecules inside the clusters, and the clustering mechanisms are unclear due to limitations of the imaging and analytical tools. Focusing on syntaxin 1 and SNAP-25, we implemented direct stochastic optical reconstruction microscopy together with quantitative clustering algorithms to demonstrate a novel approach to explore the distribution of clustered and nonclustered molecules at the membrane of PC12 cells with single-molecule precision. Direct stochastic optical reconstruction microscopy images reveal, for the first time, solitary syntaxin/SNAP-25 molecules and small clusters as well as larger clusters. The nonclustered syntaxin or SNAP-25 molecules are mostly concentrated in areas adjacent to their own clusters. In the clusters, the density of the molecules gradually decreases from the dense cluster core to the periphery. We further detected large clusters that contain several density gradients. This suggests that some of the clusters are formed by unification of several clusters that preserve their original organization or reorganize into a single unit. Although syntaxin and SNAP-25 share some common distributional features, their clusters differ markedly from each other. SNAP-25 clusters are significantly larger, more elliptical, and less dense. Finally, this study establishes methodological tools for the analysis of single-molecule-based super-resolution imaging data and paves the way for revealing new levels of membranal protein organization.
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Affiliation(s)
- Dana Bar-On
- Laser Laboratory for Fast Reactions in Biology, Department of Biochemistry, Tel Aviv University, Tel Aviv 69978, Israel
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Mohrmann R, Sørensen JB. SNARE requirements en route to exocytosis: from many to few. J Mol Neurosci 2012; 48:387-94. [PMID: 22427188 DOI: 10.1007/s12031-012-9744-2] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2011] [Accepted: 02/29/2012] [Indexed: 12/30/2022]
Abstract
Although it has been known for almost two decades that the ternary complex of N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs) constitutes the functional unit driving membrane fusion, our knowledge about the dynamical arrangement and organization of SNARE proteins and their complexes before and during vesicle exocytosis is still limited. Here, we review recent progress in this expanding field with emphasis on the question of fusion complex stoichiometry, i.e., how many SNARE proteins and complexes are needed for the fusion of a vesicle with the plasma membrane.
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Affiliation(s)
- Ralf Mohrmann
- Department of Physiology, University of Saarland, Homburg, Germany.
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Keighron JD, Ewing AG, Cans AS. Analytical tools to monitor exocytosis: a focus on new fluorescent probes and methods. Analyst 2012; 137:1755-63. [DOI: 10.1039/c2an15901e] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Kruit JK, Wijesekara N, Fox JEM, Dai XQ, Brunham LR, Searle GJ, Morgan GP, Costin AJ, Tang R, Bhattacharjee A, Johnson JD, Light PE, Marsh BJ, MacDonald PE, Verchere CB, Hayden MR. Islet cholesterol accumulation due to loss of ABCA1 leads to impaired exocytosis of insulin granules. Diabetes 2011; 60:3186-96. [PMID: 21998401 PMCID: PMC3219942 DOI: 10.2337/db11-0081] [Citation(s) in RCA: 90] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
OBJECTIVE The ATP-binding cassette transporter A1 (ABCA1) is essential for normal insulin secretion from β-cells. The aim of this study was to elucidate the mechanisms underlying the impaired insulin secretion in islets lacking β-cell ABCA1. RESEARCH DESIGN AND METHODS Calcium imaging, patch clamp, and membrane capacitance were used to assess the effect of ABCA1 deficiency on calcium flux, ion channel function, and exocytosis in islet cells. Electron microscopy was used to analyze β-cell ultrastructure. The quantity and distribution of proteins involved in insulin-granule exocytosis were also investigated. RESULTS We show that a lack of β-cell ABCA1 results in impaired depolarization-induced exocytotic fusion of insulin granules. We observed disturbances in membrane microdomain organization and Golgi and insulin granule morphology in β-cells as well as elevated fasting plasma proinsulin levels in mice in the absence of β-cell ABCA1. Acute cholesterol depletion rescued the exocytotic defect in β-cells lacking ABCA1, indicating that elevated islet cholesterol accumulation directly impairs granule fusion and insulin secretion. CONCLUSIONS Our data highlight a crucial role of ABCA1 and cellular cholesterol in β-cells that is necessary for regulated insulin granule fusion events. These data suggest that abnormalities of cholesterol metabolism may contribute to the impaired β-cell function in diabetes.
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Affiliation(s)
- Janine K. Kruit
- Departments of Medical Genetics, Centre for Molecular Medicine, and Therapeutics, Child and Family Research Institute, University of British Columbia, Vancouver, British Columbia, Canada
| | - Nadeeja Wijesekara
- Departments of Medical Genetics, Centre for Molecular Medicine, and Therapeutics, Child and Family Research Institute, University of British Columbia, Vancouver, British Columbia, Canada
| | - Jocelyn E. Manning Fox
- Department of Pharmacology, Alberta Diabetes Institute, University of Alberta, Edmonton, Alberta, Canada
| | - Xiao-Qing Dai
- Department of Pharmacology, Alberta Diabetes Institute, University of Alberta, Edmonton, Alberta, Canada
| | - Liam R. Brunham
- Departments of Medical Genetics, Centre for Molecular Medicine, and Therapeutics, Child and Family Research Institute, University of British Columbia, Vancouver, British Columbia, Canada
| | - Gavin J. Searle
- Department of Pharmacology, Alberta Diabetes Institute, University of Alberta, Edmonton, Alberta, Canada
| | - Garry P. Morgan
- Institute for Molecular Bioscience, The University of Queensland, Brisbane, Queensland, Australia
| | - Adam J. Costin
- Institute for Molecular Bioscience, The University of Queensland, Brisbane, Queensland, Australia
| | - Renmei Tang
- Departments of Medical Genetics, Centre for Molecular Medicine, and Therapeutics, Child and Family Research Institute, University of British Columbia, Vancouver, British Columbia, Canada
| | - Alpana Bhattacharjee
- Departments of Medical Genetics, Centre for Molecular Medicine, and Therapeutics, Child and Family Research Institute, University of British Columbia, Vancouver, British Columbia, Canada
| | - James D. Johnson
- Department of Cellular and Physiological Sciences, University of British Columbia, Vancouver, British Columbia, Canada
| | - Peter E. Light
- Department of Pharmacology, Alberta Diabetes Institute, University of Alberta, Edmonton, Alberta, Canada
| | - Brad J. Marsh
- Institute for Molecular Bioscience, The University of Queensland, Brisbane, Queensland, Australia
| | - Patrick E. MacDonald
- Department of Pharmacology, Alberta Diabetes Institute, University of Alberta, Edmonton, Alberta, Canada
| | - C. Bruce Verchere
- Departments of Pathology & Laboratory Medicine and Surgery, Child and Family Research Institute, University of British Columbia, Vancouver, British Columbia, Canada
| | - Michael R. Hayden
- Departments of Medical Genetics, Centre for Molecular Medicine, and Therapeutics, Child and Family Research Institute, University of British Columbia, Vancouver, British Columbia, Canada
- Corresponding author: Michael R. Hayden,
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Abstract
All cells complete cell division by the process of cytokinesis. At the end of mitosis, eukaryotic cells accurately mark the site of division between the replicated genetic material and assemble a contractile ring comprised of myosin II, actin filaments and other proteins, which is attached to the plasma membrane. The myosin-actin interaction drives constriction of the contractile ring, forming a cleavage furrow (the so-called 'purse-string' model of cytokinesis). After furrowing is completed, the cells remain attached by a thin cytoplasmic bridge, filled with two anti-parallel arrays of microtubules with their plus-ends interdigitating in the midbody region. The cell then assembles the abscission machinery required for cleavage of the intercellular bridge, and so forms two genetically identical daughter cells. We now know much of the molecular detail of cytokinesis, including a list of potential genes/proteins involved, analysis of the function of some of these proteins, and the temporal order of their arrival at the cleavage site. Such studies reveal that membrane trafficking and/or remodelling appears to play crucial roles in both furrowing and abscission. In the present review, we assess studies of vesicular trafficking during cytokinesis, discuss the role of the lipid components of the plasma membrane and endosomes and their role in cytokinesis, and describe some novel molecules implicated in cytokinesis. The present review covers experiments performed mainly on tissue culture cells. We will end by considering how this mechanistic insight may be related to cytokinesis in other systems, and how other forms of cytokinesis may utilize similar aspects of the same machinery.
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Roder F, Waichman S, Paterok D, Schubert R, Richter C, Liedberg B, Piehler J. Reconstitution of Membrane Proteins into Polymer-Supported Membranes for Probing Diffusion and Interactions by Single Molecule Techniques. Anal Chem 2011; 83:6792-9. [DOI: 10.1021/ac201294v] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Affiliation(s)
| | - Sharon Waichman
- Division of Biophysics, University of Osnabrück, Germany
- Division of Molecular Physics, Linköping University, Sweden
| | - Dirk Paterok
- Division of Biophysics, University of Osnabrück, Germany
| | - Robin Schubert
- Division of Biophysics, University of Osnabrück, Germany
| | | | - Bo Liedberg
- Division of Molecular Physics, Linköping University, Sweden
| | - Jacob Piehler
- Division of Biophysics, University of Osnabrück, Germany
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Ca2+ induces clustering of membrane proteins in the plasma membrane via electrostatic interactions. EMBO J 2011; 30:1209-20. [PMID: 21364530 DOI: 10.1038/emboj.2011.53] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2010] [Accepted: 02/02/2011] [Indexed: 12/23/2022] Open
Abstract
Membrane proteins and membrane lipids are frequently organized in submicron-sized domains within cellular membranes. Factors thought to be responsible for domain formation include lipid-lipid interactions, lipid-protein interactions and protein-protein interactions. However, it is unclear whether the domain structure is regulated by other factors such as divalent cations. Here, we have examined in native plasma membranes and intact cells the role of the second messenger Ca(2+) in membrane protein organization. We find that Ca(2+) at low micromolar concentrations directly redistributes a structurally diverse array of membrane proteins via electrostatic effects. Redistribution results in a more clustered pattern, can be rapid and triggered by Ca(2+) influx through voltage-gated calcium channels and is reversible. In summary, the data demonstrate that the second messenger Ca(2+) strongly influences the organization of membrane proteins, thus adding a novel and unexpected factor that may control the domain structure of biological membranes.
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Dalgarno HIC, Dalgarno PA, Dada AC, Towers CE, Gibson GJ, Parton RM, Davis I, Warburton RJ, Greenaway AH. Nanometric depth resolution from multi-focal images in microscopy. J R Soc Interface 2011; 8:942-51. [PMID: 21247948 PMCID: PMC3104330 DOI: 10.1098/rsif.2010.0508] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
We describe a method for tracking the position of small features in three dimensions from images recorded on a standard microscope with an inexpensive attachment between the microscope and the camera. The depth-measurement accuracy of this method is tested experimentally on a wide-field, inverted microscope and is shown to give approximately 8 nm depth resolution, over a specimen depth of approximately 6 µm, when using a 12-bit charge-coupled device (CCD) camera and very bright but unresolved particles. To assess low-flux limitations a theoretical model is used to derive an analytical expression for the minimum variance bound. The approximations used in the analytical treatment are tested using numerical simulations. It is concluded that approximately 14 nm depth resolution is achievable with flux levels available when tracking fluorescent sources in three dimensions in live-cell biology and that the method is suitable for three-dimensional photo-activated localization microscopy resolution. Sub-nanometre resolution could be achieved with photon-counting techniques at high flux levels.
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Affiliation(s)
- Heather I C Dalgarno
- Physics, SUPA/IIS, School of Engineering and Physical Sciences, Heriot-Watt University, , Edinburgh EH14 4AS, UK
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