1
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Jahn R, Cafiso DC, Tamm LK. Mechanisms of SNARE proteins in membrane fusion. Nat Rev Mol Cell Biol 2024; 25:101-118. [PMID: 37848589 DOI: 10.1038/s41580-023-00668-x] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/06/2023] [Indexed: 10/19/2023]
Abstract
Soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs) are a family of small conserved eukaryotic proteins that mediate membrane fusion between organelles and with the plasma membrane. SNAREs are directly or indirectly anchored to membranes. Prior to fusion, complementary SNAREs assemble between membranes with the aid of accessory proteins that provide a scaffold to initiate SNARE zippering, pulling the membranes together and mediating fusion. Recent advances have enabled the construction of detailed models describing bilayer transitions and energy barriers along the fusion pathway and have elucidated the structures of SNAREs complexed in various states with regulatory proteins. In this Review, we discuss how these advances are yielding an increasingly detailed picture of the SNARE-mediated fusion pathway, leading from first contact between the membranes via metastable non-bilayer intermediates towards the opening and expansion of a fusion pore. We describe how SNARE proteins assemble into complexes, how this assembly is regulated by accessory proteins and how SNARE complexes overcome the free energy barriers that prevent spontaneous membrane fusion.
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Affiliation(s)
- Reinhard Jahn
- Laboratory of Neurobiology, Max-Planck Institute for Multidisciplinary Sciences, Göttingen, Germany.
| | - David C Cafiso
- Department of Chemistry, University of Virginia, Charlottesville, VA, USA
| | - Lukas K Tamm
- Department of Molecular Physiology and Biological Physics, University of Virginia, Charlottesville, VA, USA
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2
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Bu B, Tian Z, Li D, Zhang K, Chen W, Ji B, Diao J. Double-Transmembrane Domain of SNAREs Decelerates the Fusion by Increasing the Protein-Lipid Mismatch. J Mol Biol 2023; 435:168089. [PMID: 37030649 PMCID: PMC10247502 DOI: 10.1016/j.jmb.2023.168089] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2023] [Revised: 04/02/2023] [Accepted: 04/02/2023] [Indexed: 04/10/2023]
Abstract
SNARE is the essential mediator of membrane fusion that highly relies on the molecular structure of SNAREs. For instance, the protein syntaxin-1 involved in neuronal SNAREs, has a single transmembrane domain (sTMD) leading to fast fusion, while the syntaxin 17 has a V-shape double TMDs (dTMDs), taking part in the autophagosome maturation. However, it is not clear how the TMD structure influences the fusion process. Here, we demonstrate that the dTMDs significantly reduce fusion rate compared with the sTMD by using an in vitro reconstitution system. Through theoretical analysis, we reveal that the V-shape dTMDs can significantly increase protein-lipid mismatch, thereby raising the energy barrier of the fusion, and that increasing the number of SNAREs can reduce the energy barrier or protein-lipid mismatch. This study provides a physicochemical mechanistic understanding of SNARE-regulated membrane fusion.
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Affiliation(s)
- Bing Bu
- Institute of Biomedical Engineering and Health Sciences, Changzhou University, Changzhou, Jiangsu 213164, China
| | - Zhiqi Tian
- Department of Cancer Biology, University of Cincinnati College of Medicine, Cincinnati, OH 45267, USA
| | - Dechang Li
- Institute of Applied Mechanics, Department of Engineering Mechanics, Zhejiang University, Hangzhou 310027, China.
| | - Kai Zhang
- Department of Biochemistry, University of Illinois, Urbana-Champaign, Illinois 61801, USA
| | - Wei Chen
- Department of Cell Biology and Department of Cardiology of the Second Affiliated Hospital, Zhejiang University School of Medicine, Zhejiang University, Hangzhou 310058, China
| | - Baohua Ji
- Institute of Applied Mechanics, Department of Engineering Mechanics, Zhejiang University, Hangzhou 310027, China
| | - Jiajie Diao
- Department of Cancer Biology, University of Cincinnati College of Medicine, Cincinnati, OH 45267, USA.
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3
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Hesselbarth J, Schmidt C. Mass spectrometry uncovers intermediates and off-pathway complexes for SNARE complex assembly. Commun Biol 2023; 6:198. [PMID: 36806321 PMCID: PMC9941103 DOI: 10.1038/s42003-023-04548-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2022] [Accepted: 02/01/2023] [Indexed: 02/22/2023] Open
Abstract
The SNARE complex assembles from vesicular Synaptobrevin-2 as well as Syntaxin-1 and SNAP25 both anchored to the presynaptic membrane. It mediates fusion of synaptic vesicles with the presynaptic plasma membrane resulting in exocytosis of neurotransmitters. While the general sequence of SNARE complex formation is well-established, our knowledge on possible intermediates and stable off-pathway complexes is incomplete. We, therefore, follow the stepwise assembly of the SNARE complex and target individual SNAREs, binary sub-complexes, the ternary SNARE complex as well as interactions with Complexin-1. Using native mass spectrometry, we identify the stoichiometry of sub-complexes and monitor oligomerisation of various assemblies. Importantly, we find that interactions with Complexin-1 reduce multimerisation of the ternary SNARE complex. Chemical cross-linking provides detailed insights into these interactions suggesting a role for membrane fusion. In summary, we unravel the stoichiometry of intermediates and off-pathway complexes and compile a road map of SNARE complex assembly including regulation by Complexin-1.
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Affiliation(s)
- Julia Hesselbarth
- Interdisciplinary Research Centre HALOmem, Charles Tanford Protein Centre, Institute of Biochemistry and Biotechnology, Martin Luther University Halle-Wittenberg, Halle, Germany
- Department of Chemistry - Biochemistry, Biocenter II, Johannes Gutenberg University Mainz, Mainz, Germany
| | - Carla Schmidt
- Interdisciplinary Research Centre HALOmem, Charles Tanford Protein Centre, Institute of Biochemistry and Biotechnology, Martin Luther University Halle-Wittenberg, Halle, Germany.
- Department of Chemistry - Biochemistry, Biocenter II, Johannes Gutenberg University Mainz, Mainz, Germany.
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4
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Sharma M, Burré J. α-Synuclein in synaptic function and dysfunction. Trends Neurosci 2023; 46:153-166. [PMID: 36567199 PMCID: PMC9877183 DOI: 10.1016/j.tins.2022.11.007] [Citation(s) in RCA: 31] [Impact Index Per Article: 31.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2022] [Revised: 11/07/2022] [Accepted: 11/29/2022] [Indexed: 12/24/2022]
Abstract
α-Synuclein is a neuronal protein that is enriched in presynaptic terminals. Under physiological conditions, it binds to synaptic vesicle membranes and functions in neurotransmitter release, although the molecular details remain unclear, and it is controversial whether α-synuclein inhibits or facilitates neurotransmitter release. Pathologically, in synucleinopathies including Parkinson's disease (PD), α-synuclein forms aggregates that recruit monomeric α-synuclein and spread throughout the brain, which triggers neuronal dysfunction at molecular, cellular, and organ levels. Here, we present an overview of the effects of α-synuclein on SNARE-complex assembly, neurotransmitter release, and synaptic vesicle pool homeostasis, and discuss how the observed divergent effects of α-synuclein on neurotransmitter release can be reconciled. We also discuss how gain-of-function versus loss-of-function of α-synuclein may contribute to pathogenesis in synucleinopathies.
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Affiliation(s)
- Manu Sharma
- Appel Alzheimer's Disease Research Institute, Brain and Mind Research Institute, Weill Cornell Medicine, New York, NY, USA.
| | - Jacqueline Burré
- Appel Alzheimer's Disease Research Institute, Brain and Mind Research Institute, Weill Cornell Medicine, New York, NY, USA.
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5
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Aliakbarinodehi N, Gallud A, Mapar M, Wesén E, Heydari S, Jing Y, Emilsson G, Liu K, Sabirsh A, Zhdanov VP, Lindfors L, Esbjörner EK, Höök F. Interaction Kinetics of Individual mRNA-Containing Lipid Nanoparticles with an Endosomal Membrane Mimic: Dependence on pH, Protein Corona Formation, and Lipoprotein Depletion. ACS NANO 2022; 16:20163-20173. [PMID: 36511601 PMCID: PMC9798854 DOI: 10.1021/acsnano.2c04829] [Citation(s) in RCA: 18] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/17/2022] [Accepted: 12/06/2022] [Indexed: 06/04/2023]
Abstract
Lipid nanoparticles (LNPs) have emerged as potent carriers for mRNA delivery, but several challenges remain before this approach can offer broad clinical translation of mRNA therapeutics. To improve their efficacy, a better understanding is required regarding how LNPs are trapped and processed at the anionic endosomal membrane prior to mRNA release. We used surface-sensitive fluorescence microscopy with single LNP resolution to investigate the pH dependency of the binding kinetics of ionizable lipid-containing LNPs to a supported endosomal model membrane. A sharp increase of LNP binding was observed when the pH was lowered from 6 to 5, accompanied by stepwise large-scale LNP disintegration. For LNPs preincubated in serum, protein corona formation shifted the onset of LNP binding and subsequent disintegration to lower pH, an effect that was less pronounced for lipoprotein-depleted serum. The LNP binding to the endosomal membrane mimic was observed to eventually become severely limited by suppression of the driving force for the formation of multivalent bonds during LNP attachment or, more specifically, by charge neutralization of anionic lipids in the model membrane due to their association with cationic lipids from earlier attached LNPs upon their disintegration. Cell uptake experiments demonstrated marginal differences in LNP uptake in untreated and lipoprotein-depleted serum, whereas lipoprotein-depleted serum increased mRNA-controlled protein (eGFP) production substantially. This complies with model membrane data and suggests that protein corona formation on the surface of the LNPs influences the nature of the interaction between LNPs and endosomal membranes.
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Affiliation(s)
- Nima Aliakbarinodehi
- Division
of Nano and Biophysics, Department of Physics, Chalmers University of Technology 41296 Göteborg, Sweden
| | - Audrey Gallud
- Division
of Chemical Biology, Department of Biology and Biological Engineering, Chalmers University of Technology, 41296 Göteborg, Sweden
- Advanced
Drug Delivery, Pharmaceutical Sciences,
R&D, AstraZeneca, 43181 Gothenburg, Sweden
| | - Mokhtar Mapar
- Division
of Nano and Biophysics, Department of Physics, Chalmers University of Technology 41296 Göteborg, Sweden
| | - Emelie Wesén
- Division
of Chemical Biology, Department of Biology and Biological Engineering, Chalmers University of Technology, 41296 Göteborg, Sweden
| | - Sahar Heydari
- Division
of Chemical Biology, Department of Biology and Biological Engineering, Chalmers University of Technology, 41296 Göteborg, Sweden
| | - Yujia Jing
- Advanced
Drug Delivery, Pharmaceutical Sciences,
R&D, AstraZeneca, 43181 Gothenburg, Sweden
| | - Gustav Emilsson
- Advanced
Drug Delivery, Pharmaceutical Sciences,
R&D, AstraZeneca, 43181 Gothenburg, Sweden
| | - Kai Liu
- Advanced
Drug Delivery, Pharmaceutical Sciences,
R&D, AstraZeneca, 43181 Gothenburg, Sweden
| | - Alan Sabirsh
- Advanced
Drug Delivery, Pharmaceutical Sciences,
R&D, AstraZeneca, 43181 Gothenburg, Sweden
| | - Vladimir P. Zhdanov
- Division
of Nano and Biophysics, Department of Physics, Chalmers University of Technology 41296 Göteborg, Sweden
- Boreskov
Institute of Catalysis, Russian Academy
of Sciences, Novosibirsk 630090, Russia
| | - Lennart Lindfors
- Advanced
Drug Delivery, Pharmaceutical Sciences,
R&D, AstraZeneca, 43181 Gothenburg, Sweden
| | - Elin K. Esbjörner
- Division
of Chemical Biology, Department of Biology and Biological Engineering, Chalmers University of Technology, 41296 Göteborg, Sweden
| | - Fredrik Höök
- Division
of Nano and Biophysics, Department of Physics, Chalmers University of Technology 41296 Göteborg, Sweden
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6
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Bills BL, Knowles MK. Phosphatidic Acid Accumulates at Areas of Curvature in Tubulated Lipid Bilayers and Liposomes. Biomolecules 2022; 12:1707. [PMID: 36421720 PMCID: PMC9687397 DOI: 10.3390/biom12111707] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2022] [Revised: 11/09/2022] [Accepted: 11/12/2022] [Indexed: 10/24/2023] Open
Abstract
Phosphatidic acid (PA) is a signaling lipid that is produced enzymatically from phosphatidylcholine (PC), lysophosphatidic acid, or diacylglycerol. Compared to PC, PA lacks a choline moiety on the headgroup, making the headgroup smaller than that of PC and PA, and PA has a net negative charge. Unlike the cylindrical geometry of PC, PA, with its small headgroup relative to the two fatty acid tails, is proposed to support negatively curved membranes. Thus, PA is thought to play a role in a variety of biological processes that involve bending membranes, such as the formation of intraluminal vesicles in multivesicular bodies and membrane fusion. Using supported tubulated lipid bilayers (STuBs), the extent to which PA localizes to curved membranes was determined. STuBs were created via liposome deposition with varying concentrations of NaCl (500 mM to 1 M) on glass to form supported bilayers with connected tubules. The location of fluorescently labeled lipids relative to tubules was determined by imaging with total internal reflection or confocal fluorescence microscopy. The accumulation of various forms of PA (with acyl chains of 16:0-6:0, 16:0-12:0, 18:1-12:0) were compared to PC and the headgroup labeled phosphatidylethanolamine (PE), a lipid that has been shown to accumulate at regions of curvature. PA and PE accumulated more at tubules and led to the formation of more tubules than PC. Using large unilamellar liposomes in a dye-quenching assay, the location of the headgroup labeled PE was determined to be mostly on the outer, positively curved leaflet, whereas the tail labeled PA was located more on the inner, negatively curved leaflet. This study demonstrates that PA localizes to regions of negative curvature in liposomes and supports the formation of curved, tubulated membranes. This is one way that PA could be involved with curvature formation during a variety of cell processes.
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Affiliation(s)
- Broderick L. Bills
- Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80210, USA
- Molecular and Cellular Biophysics Program, University of Denver, Denver, CO 80210, USA
| | - Michelle K. Knowles
- Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80210, USA
- Molecular and Cellular Biophysics Program, University of Denver, Denver, CO 80210, USA
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7
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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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8
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Szule JA. Hypothesis Relating the Structure, Biochemistry and Function of Active Zone Material Macromolecules at a Neuromuscular Junction. Front Synaptic Neurosci 2022; 13:798225. [PMID: 35069169 PMCID: PMC8766674 DOI: 10.3389/fnsyn.2021.798225] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2021] [Accepted: 12/14/2021] [Indexed: 12/22/2022] Open
Abstract
This report integrates knowledge of in situ macromolecular structures and synaptic protein biochemistry to propose a unified hypothesis for the regulation of certain vesicle trafficking events (i.e., docking, priming, Ca2+-triggering, and membrane fusion) that lead to neurotransmitter secretion from specialized “active zones” of presynaptic axon terminals. Advancements in electron tomography, to image tissue sections in 3D at nanometer scale resolution, have led to structural characterizations of a network of different classes of macromolecules at the active zone, called “Active Zone Material’. At frog neuromuscular junctions, the classes of Active Zone Material macromolecules “top-masts”, “booms”, “spars”, “ribs” and “pins” direct synaptic vesicle docking while “pins”, “ribs” and “pegs” regulate priming to influence Ca2+-triggering and membrane fusion. Other classes, “beams”, “steps”, “masts”, and “synaptic vesicle luminal filaments’ likely help organize and maintain the structural integrity of active zones. Extensive studies on the biochemistry that regulates secretion have led to comprehensive characterizations of the many conserved proteins universally involved in these trafficking events. Here, a hypothesis including a partial proteomic atlas of Active Zone Material is presented which considers the common roles, binding partners, physical features/structure, and relative positioning in the axon terminal of both the proteins and classes of macromolecules involved in the vesicle trafficking events. The hypothesis designates voltage-gated Ca2+ channels and Ca2+-gated K+ channels to ribs and pegs that are connected to macromolecules that span the presynaptic membrane at the active zone. SNARE proteins (Syntaxin, SNAP25, and Synaptobrevin), SNARE-interacting proteins Synaptotagmin, Munc13, Munc18, Complexin, and NSF are designated to ribs and/or pins. Rab3A and Rabphillin-3A are designated to top-masts and/or booms and/or spars. RIM, Bassoon, and Piccolo are designated to beams, steps, masts, ribs, spars, booms, and top-masts. Spectrin is designated to beams. Lastly, the luminal portions of SV2 are thought to form the bulk of the observed synaptic vesicle luminal filaments. The goal here is to help direct future studies that aim to bridge Active Zone Material structure, biochemistry, and function to ultimately determine how it regulates the trafficking events in vivo that lead to neurotransmitter secretion.
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9
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Abbineni PS, Briguglio JS, Chapman ER, Holz RW, Axelrod D. VAMP2 and synaptotagmin mobility in chromaffin granule membranes: implications for regulated exocytosis. Mol Biol Cell 2021; 33:ar53. [PMID: 34851717 PMCID: PMC9265163 DOI: 10.1091/mbc.e21-10-0494] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Granule-plasma membrane docking and fusion can only occur when proteins that enable these reactions are present at the granule-plasma membrane contact. Thus, the mobility of granule membrane proteins may influence docking, and membrane fusion. We measured the mobility of vesicle associated membrane protein 2 (VAMP2), synaptotagmin 1 (Syt1), and synaptotagmin 7 (Syt7) in chromaffin granule membranes in living chromaffin cells. We used a method that is not limited by standard optical resolution. A bright flash of strongly decaying evanescent field produced by total internal reflection (TIR) was used to photobleach GFP-labeled proteins in the granule membrane. Fluorescence recovery occurs as unbleached protein in the granule membrane distal from the glass interface diffuses into the more bleached proximal regions, enabling the measurement of diffusion coefficients. We found that VAMP2-EGFP and Syt7-EGFP are mobile with a diffusion coefficient of approximately 3 × 10-10 cm2/s. Syt1-EGFP mobility was below the detection limit. Utilizing these diffusion parameters, we estimated the time required for these proteins to arrive at docking and nascent fusion sites to be many tens of milliseconds. Our analyses raise the possibility that the diffusion characteristics of VAMP2 and Syt proteins could be a factor that influences the rate of exocytosis.
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Affiliation(s)
- Prabhodh S Abbineni
- Life Sciences Institute, University of Michigan, Ann Arbor, Michigan.,Department of Pharmacology, University of Michigan, Ann Arbor, Michigan
| | - Joseph S Briguglio
- Howard Hughes Medical Institute, Department of Neuroscience, University of Wisconsin, Madison, WI
| | - Edwin R Chapman
- Howard Hughes Medical Institute, Department of Neuroscience, University of Wisconsin, Madison, WI
| | - Ronald W Holz
- Department of Pharmacology, University of Michigan, Ann Arbor, Michigan
| | - Daniel Axelrod
- Department of Pharmacology, University of Michigan, Ann Arbor, Michigan.,Department of Physics, University of Michigan, Ann Arbor, Michigan
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10
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Nikolaus J, Hancock K, Tsemperouli M, Baddeley D, Karatekin E. Optimal Detection of Fusion Pore Dynamics Using Polarized Total Internal Reflection Fluorescence Microscopy. Front Mol Biosci 2021; 8:740408. [PMID: 34859048 PMCID: PMC8631473 DOI: 10.3389/fmolb.2021.740408] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2021] [Accepted: 10/06/2021] [Indexed: 11/13/2022] Open
Abstract
The fusion pore is the initial narrow connection that forms between fusing membranes. During vesicular release of hormones or neurotransmitters, the nanometer-sized fusion pore may open-close repeatedly (flicker) before resealing or dilating irreversibly, leading to kiss-and-run or full-fusion events, respectively. Pore dynamics govern vesicle cargo release and the mode of vesicle recycling, but the mechanisms are poorly understood. This is partly due to a lack of reconstituted assays that combine single-pore sensitivity and high time resolution. Total internal reflection fluorescence (TIRF) microscopy offers unique advantages for characterizing single membrane fusion events, but signals depend on effects that are difficult to disentangle, including the polarization of the excitation electric field, vesicle size, photobleaching, orientation of the excitation dipoles of the fluorophores with respect to the membrane, and the evanescent field depth. Commercial TIRF microscopes do not allow control of excitation polarization, further complicating analysis. To overcome these challenges, we built a polarization-controlled total internal reflection fluorescence (pTIRF) microscope and monitored fusion of proteoliposomes with planar lipid bilayers with single molecule sensitivity and ∼15 ms temporal resolution. Using pTIRF microscopy, we detected docking and fusion of fluorescently labeled small unilamellar vesicles, reconstituted with exocytotic/neuronal v-SNARE proteins (vSUVs), with a supported bilayer containing the cognate t-SNAREs (tSBL). By varying the excitation polarization angle, we were able to identify a dye-dependent optimal polarization at which the fluorescence increase upon fusion was maximal, facilitating event detection and analysis of lipid transfer kinetics. An improved algorithm allowed us to estimate the size of the fusing vSUV and the fusion pore openness (the fraction of time the pore is open) for every event. For most events, lipid transfer was much slower than expected for diffusion through an open pore, suggesting that fusion pore flickering limits lipid release. We find a weak correlation between fusion pore openness and vesicle area. The approach can be used to study mechanisms governing fusion pore dynamics in a wide range of membrane fusion processes.
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Affiliation(s)
- Joerg Nikolaus
- Cellular and Molecular Physiology, Yale University, New Haven, CT, United States
- Nanobiology Institute, Yale University, West Haven, CT, United States
| | - Kasey Hancock
- Cellular and Molecular Physiology, Yale University, New Haven, CT, United States
- Nanobiology Institute, Yale University, West Haven, CT, United States
- Integrated Physical and Engineering Biology Program, Yale University, New Haven, CT, United States
| | - Maria Tsemperouli
- Cellular and Molecular Physiology, Yale University, New Haven, CT, United States
- Nanobiology Institute, Yale University, West Haven, CT, United States
| | - David Baddeley
- Nanobiology Institute, Yale University, West Haven, CT, United States
- Cell Biology, Yale University, New Haven, CT, United States
| | - Erdem Karatekin
- Cellular and Molecular Physiology, Yale University, New Haven, CT, United States
- Nanobiology Institute, Yale University, West Haven, CT, United States
- Molecular Biophysics and Biochemistry, Yale University, New Haven, CT, United States
- Saints-Pères Paris Institute for the Neurosciences (SPPIN), Université de Paris, Centre National de la Recherche Scientifique (CNRS), Paris, France
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11
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Mühlenbrock P, Sari M, Steinem C. In vitro single vesicle fusion assays based on pore-spanning membranes: merits and drawbacks. EUROPEAN BIOPHYSICS JOURNAL : EBJ 2021; 50:239-252. [PMID: 33320298 PMCID: PMC8071798 DOI: 10.1007/s00249-020-01479-0] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/21/2020] [Revised: 11/06/2020] [Accepted: 11/09/2020] [Indexed: 12/22/2022]
Abstract
Neuronal fusion mediated by soluble N-ethylmaleimide-sensitive-factor attachment protein receptors (SNAREs) is a fundamental cellular process by which two initially distinct membranes merge resulting in one interconnected structure to release neurotransmitters into the presynaptic cleft. To get access to the different stages of the fusion process, several in vitro assays have been developed. In this review, we provide a short overview of the current in vitro single vesicle fusion assays. Among those assays, we developed a single vesicle assay based on pore-spanning membranes (PSMs) on micrometre-sized pores in silicon, which might overcome some of the drawbacks associated with the other membrane architectures used for investigating fusion processes. Prepared by spreading of giant unilamellar vesicles with reconstituted t-SNAREs, PSMs provide an alternative tool to supported lipid bilayers to measure single vesicle fusion events by means of fluorescence microscopy. Here, we discuss the diffusive behaviour of the reconstituted membrane components as well as that of the fusing synthetic vesicles with reconstituted synaptobrevin 2 (v-SNARE). We compare our results with those obtained if the synthetic vesicles are replaced by natural chromaffin granules under otherwise identical conditions. The fusion efficiency as well as the different fusion states observable in this assay by means of both lipid mixing and content release are illuminated.
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Affiliation(s)
- Peter Mühlenbrock
- Georg-August-Universität Göttingen, Institute of Organic and Biomolecular Chemistry, Tammannstr. 2, 37077, Göttingen, Germany
| | - Merve Sari
- Georg-August-Universität Göttingen, Institute of Organic and Biomolecular Chemistry, Tammannstr. 2, 37077, Göttingen, Germany
| | - Claudia Steinem
- Georg-August-Universität Göttingen, Institute of Organic and Biomolecular Chemistry, Tammannstr. 2, 37077, Göttingen, Germany.
- Max-Planck-Institute for Dynamics and Self Organization, Am Faßberg 17, 37077, Göttingen, Germany.
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12
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Radhakrishnan A, Li X, Grushin K, Krishnakumar SS, Liu J, Rothman JE. Symmetrical arrangement of proteins under release-ready vesicles in presynaptic terminals. Proc Natl Acad Sci U S A 2021; 118:e2024029118. [PMID: 33468631 PMCID: PMC7865176 DOI: 10.1073/pnas.2024029118] [Citation(s) in RCA: 30] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
Controlled release of neurotransmitters stored in synaptic vesicles (SVs) is a fundamental process that is central to all information processing in the brain. This relies on tight coupling of the SV fusion to action potential-evoked presynaptic Ca2+ influx. This Ca2+-evoked release occurs from a readily releasable pool (RRP) of SVs docked to the plasma membrane (PM). The protein components involved in initial SV docking/tethering and the subsequent priming reactions which make the SV release ready are known. Yet, the supramolecular architecture and sequence of molecular events underlying SV release are unclear. Here, we use cryoelectron tomography analysis in cultured hippocampal neurons to delineate the arrangement of the exocytosis machinery under docked SVs. Under native conditions, we find that vesicles are initially "tethered" to the PM by a variable number of protein densities (∼10 to 20 nm long) with no discernible organization. In contrast, we observe exactly six protein masses, each likely consisting of a single SNAREpin with its bound Synaptotagmins and Complexin, arranged symmetrically connecting the "primed" vesicles to the PM. Our data indicate that the fusion machinery is likely organized into a highly cooperative framework during the priming process which enables rapid SV fusion and neurotransmitter release following Ca2+ influx.
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Affiliation(s)
| | - Xia Li
- Department of Microbial Pathogenesis, Yale University School of Medicine, New Haven, CT 06520
- Microbial Sciences Institute, Yale University School of Medicine, New Haven, CT 06520
| | - Kirill Grushin
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06520
| | - Shyam S Krishnakumar
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06520;
| | - Jun Liu
- Department of Microbial Pathogenesis, Yale University School of Medicine, New Haven, CT 06520;
- Microbial Sciences Institute, Yale University School of Medicine, New Haven, CT 06520
| | - James E Rothman
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06520;
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13
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Li M, Oh TJ, Fan H, Diao J, Zhang K. Syntaxin Clustering and Optogenetic Control for Synaptic Membrane Fusion. J Mol Biol 2020; 432:4773-4782. [PMID: 32682743 DOI: 10.1016/j.jmb.2020.07.005] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2020] [Revised: 07/05/2020] [Accepted: 07/12/2020] [Indexed: 01/01/2023]
Abstract
Membrane fusion during synaptic transmission mediates the trafficking of chemical signals and neuronal communication. The fast kinetics of membrane fusion on the order of millisecond is precisely regulated by the assembly of SNAREs and accessory proteins. It is believed that the formation of the SNARE complex is a key step during membrane fusion. Little is known, however, about the molecular machinery that mediates the formation of a large pre-fusion complex, including multiple SNAREs and accessory proteins. Syntaxin, a transmembrane protein on the plasma membrane, has been observed to undergo oligomerization to form clusters. Whether this clustering plays a critical role in membrane fusion is poorly understood in live cells. Optogenetics is an emerging biotechnology armed with the capacity to precisely modulate protein-protein interaction in time and space. Here, we propose an experimental scheme that combines optogenetics with single-vesicle membrane fusion, aiming to gain a better understanding of the molecular mechanism by which the syntaxin cluster regulates membrane fusion. We envision that newly developed optogenetic tools could facilitate the mechanistic understanding of synaptic transmission in live cells and animals.
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Affiliation(s)
- Miaoling Li
- Key Laboratory of Medical Electrophysiology of Ministry of Education and Medical Electrophysiological Key Laboratory of Sichuan Province, Institute of Cardiovascular Research, Southwest Medical University, Luzhou, Sichuan 646000, China
| | - Teak-Jung Oh
- Department of Biochemistry, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
| | - Huaxun Fan
- Department of Biochemistry, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
| | - Jiajie Diao
- Department of Cancer Biology, University of Cincinnati College of Medicine, Cincinnati, OH 45267, USA.
| | - Kai Zhang
- Department of Biochemistry, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA.
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14
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Fusion Pore Formation Observed during SNARE-Mediated Vesicle Fusion with Pore-Spanning Membranes. Biophys J 2020; 119:151-161. [PMID: 32533941 DOI: 10.1016/j.bpj.2020.05.023] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2020] [Revised: 05/22/2020] [Accepted: 05/26/2020] [Indexed: 12/27/2022] Open
Abstract
Planar pore-spanning membranes (PSMs) have been shown to be a versatile tool to resolve elementary steps of the neuronal fusion process. However, in previous studies, we monitored only lipid mixing between fusing large unilamellar vesicles and PSMs and did not gather information about the formation of fusion pores. To address this important step of the fusion process, we entrapped sulforhodamine B at self-quenching concentrations into large unilamellar vesicles containing the v-SNARE synaptobrevin 2, which were docked and fused with lipid-labeled PSMs containing the t-SNARE acceptor complex ΔN49 prepared on gold-coated porous silicon substrates. By dual-color spinning disk fluorescence microscopy with a time resolution of ∼20 ms, we could unambiguously distinguish between bursting vesicles, which was only rarely observed (<0.01%), and fusion pore formation. From the time-resolved dual-color fluorescence time traces, we were able to identify different fusion pathways, including remaining three-dimensional postfusion structures with released content and transient openings and closings of the fusion pores. Our results on fusion pore formation and lipid diffusion from the PSM into the fusing vesicle let us conclude that the content release, i.e., fusion pore formation after the merger of the two lipid membranes occurs almost simultaneously.
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15
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Controlled Peptide-Mediated Vesicle Fusion Assessed by Simultaneous Dual-Colour Time-Lapsed Fluorescence Microscopy. Sci Rep 2020; 10:3087. [PMID: 32080270 PMCID: PMC7033240 DOI: 10.1038/s41598-020-59926-z] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2019] [Accepted: 01/31/2020] [Indexed: 12/03/2022] Open
Abstract
We have employed a model system, inspired by SNARE proteins, to facilitate membrane fusion between Giant Unilamellar Vesicles (GUVs) and Large Unilamellar Vesicles (LUVs) under physiological conditions. In this system, two synthetic lipopeptide constructs comprising the coiled-coil heterodimer-forming peptides K4, (KIAALKE)4, or E4, (EIAALEK)4, a PEG spacer of variable length, and a cholesterol moiety to anchor the peptides into the liposome membrane replace the natural SNARE proteins. GUVs are functionalized with one of the lipopeptide constructs and the fusion process is triggered by adding LUVs bearing the complementary lipopeptide. Dual-colour time lapse fluorescence microscopy was used to visualize lipid- and content-mixing. Using conventional confocal microscopy, lipid mixing was observed on the lipid bilayer of individual GUVs. In addition to lipid-mixing, content-mixing assays showed a low efficiency due to clustering of K4-functionalized LUVs on the GUVs target membranes. We showed that, through the use of the non-ionic surfactant Tween 20, content-mixing between GUVs and LUVs could be improved, meaning this system has the potential to be employed for drug delivery in biological systems.
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16
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Liu P, Song C, Wang C, Li Y, Su L, Li J, Zhao Q, Wang Z, Shen M, Wang G, Yu Y, Zhang L. Spinal SNAP-25 regulates membrane trafficking of GluA1-containing AMPA receptors in spinal injury-induced neuropathic pain in rats. Neurosci Lett 2020; 715:134616. [PMID: 31705923 DOI: 10.1016/j.neulet.2019.134616] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2019] [Revised: 10/21/2019] [Accepted: 11/04/2019] [Indexed: 12/17/2022]
Abstract
INTRODUCTION Synaptosomal associated proteins of 25 kDa (SNAP-25), as a member of stable soluble N-ethylmaleimide-sensitive factor attachment protein receptor complex, is critical for membrane fusion and required for the release of neurotransmitters. The α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor is implicated in pathologic pain. This study aimed to investigate whether and how SNAP-25 regulated AMPA receptors in neuropathic pain. METHODS Male Sprague-Dawley rats underwent L4 spinal nerve ligation (SNL) or the sham procedure. After assessing mechanical allodynia and thermal sensitivity, the ipsilateral portion of the L4-5 spinal cord was harvested. The expression level of SNAP-25 was analyzed by Western blot analysis and real-time quantitative polymerase chain reaction. SNAP-25 phosphorylation and AMPA receptor membrane trafficking levels were evaluated with Western blot analysis. An association between SNAP-25 and AMPA membrane trafficking was confirmed by SNAP-25 expression or phosphorylation inhibition. RESULTS The SNL procedure induced and maintained mechanical allodynia and thermal hyperalgesia. SNL increased the expression and phosphorylation of SNAP-25 and the membrane trafficking of AMPA receptors in the spinal cord. SNAP-25 expression or phosphorylation inhibition alleviated neuropathic pain and downregulated membrane trafficking of AMPA receptors after SNL. GluA1-containing AMPA receptor inhibition relieved mechanical allodynia and thermal hyperalgesia after SNL. CONCLUSIONS The upregulation of SNAP-25-dependent membrane trafficking of AMPA receptors via SNAP-25 phosphorylation at Ser187 contributed to SNL-induced neuropathic pain. Thus, the inhibition of SNAP-25 expression or phosphorylation might serve as a treatment for neuropathic pain. However, the mechanism of GluA1-containing AMPA receptor membrane trafficking mediated by SNAP-25 phosphorylation in neuropathic pain deserves further exploration.
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Affiliation(s)
- Peng Liu
- Department of General Surgery, Tianjin Medical University General Hospital, Tianjin, 300052, China
| | - Chengcheng Song
- Department of Anesthesiology, Tianjin Medical University General Hospital, Tianjin, 300052, China; Tianjin Research Institute of Anesthesiology, Tianjin, 300052, China
| | - Chunyan Wang
- Department of Anesthesiology, Tianjin Medical University General Hospital, Tianjin, 300052, China; Tianjin Research Institute of Anesthesiology, Tianjin, 300052, China
| | - Yize Li
- Department of Anesthesiology, Tianjin Medical University General Hospital, Tianjin, 300052, China; Tianjin Research Institute of Anesthesiology, Tianjin, 300052, China
| | - Lin Su
- Department of Anesthesiology, Tianjin Medical University General Hospital, Tianjin, 300052, China; Tianjin Research Institute of Anesthesiology, Tianjin, 300052, China
| | - Jing Li
- Department of Anesthesiology, Tianjin Medical University General Hospital, Tianjin, 300052, China; Tianjin Research Institute of Anesthesiology, Tianjin, 300052, China
| | - Qi Zhao
- Department of Anesthesiology, Tianjin Medical University General Hospital, Tianjin, 300052, China; Tianjin Research Institute of Anesthesiology, Tianjin, 300052, China
| | - Zhen Wang
- Department of Anesthesiology, Tianjin Medical University General Hospital, Tianjin, 300052, China; Tianjin Research Institute of Anesthesiology, Tianjin, 300052, China
| | - Mengxi Shen
- Department of Anesthesiology, Tianjin Medical University General Hospital, Tianjin, 300052, China; Tianjin Research Institute of Anesthesiology, Tianjin, 300052, China
| | - Guolin Wang
- Department of Anesthesiology, Tianjin Medical University General Hospital, Tianjin, 300052, China; Tianjin Research Institute of Anesthesiology, Tianjin, 300052, China
| | - Yonghao Yu
- Department of Anesthesiology, Tianjin Medical University General Hospital, Tianjin, 300052, China; Tianjin Research Institute of Anesthesiology, Tianjin, 300052, China
| | - Linlin Zhang
- Department of Anesthesiology, Tianjin Medical University General Hospital, Tianjin, 300052, China; Tianjin Research Institute of Anesthesiology, Tianjin, 300052, China.
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17
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Shen Q, Grome MW, Yang Y, Lin C. Engineering Lipid Membranes with Programmable DNA Nanostructures. ADVANCED BIOSYSTEMS 2020; 4:1900215. [PMID: 31934608 PMCID: PMC6957268 DOI: 10.1002/adbi.201900215] [Citation(s) in RCA: 26] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/03/2019] [Indexed: 12/18/2022]
Abstract
Lipid and DNA are abundant biomolecules with critical functions in cells. The water-insoluble, amphipathic lipid molecules are best known for their roles in energy storage (e.g. as triglyceride), signaling (e.g. as sphingolipid), and compartmentalization (e.g. by forming membrane-enclosed bodies). The soluble, highly negatively charged DNA, which stores cells' genetic information, has proven to be an excellent material for constructing programmable nanostructures in vitro thanks to its self-assembling capabilities. These two seemingly distant molecules make contact within cell nuclei, often via lipidated proteins, with proposed functions of modulating chromatin structures. Carefully formulated lipid/DNA complexes are promising reagents for gene therapy. The past few years saw an emerging research field of interfacing DNA nanostructures with lipid membranes, with an overarching goal of generating DNA/lipid hybrid materials that possess novel and controllable structure, dynamics, and function. An arsenal of DNA-based tools has been created to coat, mold, deform, and penetrate lipid bilayers, affording us the ability to manipulate membranes with nanoscopic precision. These membrane engineering methods not only enable quantitative biophysical studies, but also open new opportunities in synthetic biology (e.g. artificial cells) and therapeutics (e.g. drug delivery).
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Affiliation(s)
- Qi Shen
- Department of Cell Biology and Nanobiology Institute, Yale University
| | - Michael W Grome
- Department of Cell Biology and Nanobiology Institute, Yale University
| | - Yang Yang
- Department of Cell Biology and Nanobiology Institute, Yale University
- Institute of Molecular Medicine, Renji Hospital, Shanghai Jiao Tong University School of Medicine
| | - Chenxiang Lin
- Department of Cell Biology and Nanobiology Institute, Yale University
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18
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Dogra N, Balaraman RP, Kohli P. Chemically Engineered Synthetic Lipid Vesicles for Sensing and Visualization of Protein-Bilayer Interactions. Bioconjug Chem 2019; 30:2136-2149. [PMID: 31314501 DOI: 10.1021/acs.bioconjchem.9b00366] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
From pathogen intrusion to immune response, the cell membrane plays an important role in signal transduction. Such signals are important for cellular proliferation and survival. However, measurement of these subtle signals through the lipid membrane scaffold is challenging. We present a chromatic model membrane vesicle system engineered to covalently bind with lysine residues of protein molecules for investigation of cellular interactions and signaling. We discovered that different protein molecules induced differential spectroscopic signals, which is based on the chemical and physical properties of protein interacting at the vesicle surface. The observed chromatic response (CR) for bound protein molecules with higher molecular weight was much larger (∼5-15×) than those for low molecular weight proteins. Through mass spectrometry (MS), we found that only 6 out of 60 (10%) lysine groups present in bovine serum albumin (BSA) were accessible to the membrane of the vesicles. Finally, a "sphere-shell" model representing the protein-vesicle complex was used for evaluating the contribution of van der Waals interactions between proteins and vesicles. Our analysis points to contributions from van der Waals, hydrophobic, and electrostatic interactions toward observed CR signals resulting from molecular interactions at the vesicle membrane surface. Overall, this study provided a convenient, chromatic, semiquantitative method of detecting biomolecules and their interactions with model membranes at sub-nanomolar concentration.
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Affiliation(s)
- Navneet Dogra
- Department of Chemistry and Biochemistry , Southern Illinois University , Carbondale , Illinois 62901 , United States.,IBM T. J. Watson Research Center , Yorktown Heights , New York 10058 , United States.,Department of Genetics and Genomic Sciences , Icahn School of Medicine at Mount Sinai , New York , New York 10029 , United States
| | - Rajesh P Balaraman
- Department of Chemistry and Biochemistry , Southern Illinois University , Carbondale , Illinois 62901 , United States
| | - Punit Kohli
- Department of Chemistry and Biochemistry , Southern Illinois University , Carbondale , Illinois 62901 , United States
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19
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A Nanodisc-Cell Fusion Assay with Single-Pore Sensitivity and Sub-millisecond Time Resolution. Methods Mol Biol 2019; 1860:263-275. [PMID: 30317511 DOI: 10.1007/978-1-4939-8760-3_17] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/13/2023]
Abstract
During exocytosis, vesicles fuse with the plasma membrane and release their contents. The fusion pore is the initial, nanometer-sized connection between the plasma membrane and the cargo-laden vesicle. A growing body of evidence points toward the fusion pore being a regulator of exocytosis, but the shortcomings of current experimental techniques to investigate single-fusion pores make it difficult to study factors governing pore behavior. Here we describe an assay that fuses v-SNARE-reconstituted nanodiscs with cells ectopically expressing "flipped" t-SNAREs to monitor dynamics of single fusion pores in a biochemically defined system using electrical recordings. We also describe a fluorescence microscopy-based approach to monitor nanodisc-cell fusion that is much simpler to employ, but cannot resolve single pores.
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20
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Abstract
Ca2+-dependent secretion is a process by which important signaling molecules that are produced within a cell-including proteins and neurotransmitters-are expelled to the extracellular environment. The cellular mechanism that underlies secretion is referred to as exocytosis. Many years of work have revealed that exocytosis in neurons and neuroendocrine cells is tightly coupled to Ca2+ and orchestrated by a series of protein-protein/protein-lipid interactions. Here, we highlight landmark discoveries that have informed our current understanding of the process. We focus principally on reductionist studies performed using powerful model secretory systems and cell-free reconstitution assays. In recent years, molecular cloning and genetics have implicated the involvement of a sizeable number of proteins in exocytosis. We expect reductionist approaches will be central to attempts to resolve their roles. The Journal of General Physiology will continue to be an outlet for much of this work, befitting its tradition of publishing strongly mechanistic, basic research.
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Affiliation(s)
- Arun Anantharam
- Department of Pharmacology, University of Michigan, Ann Arbor, MI
| | - Alex J B Kreutzberger
- Center for Membrane and Cell Physiology, University of Virginia, Charlottesville, VA
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21
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Jiang X, Zhang Z, Cheng K, Wu Q, Jiang L, Pielak GJ, Liu M, Li C. Membrane-mediated disorder-to-order transition of SNAP25 flexible linker facilitates its interaction with syntaxin-1 and SNARE-complex assembly. FASEB J 2019; 33:7985-7994. [PMID: 30916996 DOI: 10.1096/fj.201802796r] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
The soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complex comprises synaptosome-associated protein of 25 kDa (SNAP25), syntaxin-1a (syx-1), and synaptobrevin 2, which is essential for many physiologic processes requiring membrane fusion. Several studies imply that the loop region of SNAP25 plays important roles in SNARE-complex assembly. However, why and how the flexible loop facilitates the complex assembly remains poorly understood because it is purposely deleted in almost all structural studies. By using NMR spectroscopy and circular dichroism spectropolarimetry, we characterized SNAP25 structure and interactions with other SNAREs in aqueous buffer and in the membrane. We found that the N-terminal of the SNAP25 loop region binds with membrane, and this interaction induced a disorder-to-order conformational change of the loop, resulting in enhanced interaction between the C-terminal of the SNAP25 loop and syx-1. We further proved that SNARE-complex assembly efficiency decreased when we disrupted the electrostatic interaction between C-terminal of the SNAP25 loop and syx-1, suggesting that the SNAP25 loop region facilitates SNARE-complex assembly through promoting prefusion SNARE binary complex formation. Our work elucidates the role of the flexible loop and the membrane environment in SNARE-complex assembly at the residue level, which helps to understand membrane fusion, a fundamental transport and communication process in cells.-Jiang, X., Zhang, Z., Cheng, K., Wu, Q., Jiang, L., Pielak, G. J., Liu, M., Li, C. Membrane-mediated disorder-to-order transition of SNAP25 flexible linker facilitates its interaction with syntaxin-1 and SNARE-complex assembly.
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Affiliation(s)
- Xin Jiang
- Key Laboratory of Magnetic Resonance in Biological Systems, State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, National Center for Magnetic Resonance in Wuhan, Wuhan National Laboratory for Optoelectronics, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan, China.,Graduate University of Chinese Academy of Sciences, Beijing, China
| | - Zeting Zhang
- Key Laboratory of Magnetic Resonance in Biological Systems, State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, National Center for Magnetic Resonance in Wuhan, Wuhan National Laboratory for Optoelectronics, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan, China
| | - Kai Cheng
- Key Laboratory of Magnetic Resonance in Biological Systems, State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, National Center for Magnetic Resonance in Wuhan, Wuhan National Laboratory for Optoelectronics, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan, China
| | - Qiong Wu
- Key Laboratory of Magnetic Resonance in Biological Systems, State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, National Center for Magnetic Resonance in Wuhan, Wuhan National Laboratory for Optoelectronics, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan, China
| | - Ling Jiang
- Key Laboratory of Magnetic Resonance in Biological Systems, State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, National Center for Magnetic Resonance in Wuhan, Wuhan National Laboratory for Optoelectronics, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan, China.,Graduate University of Chinese Academy of Sciences, Beijing, China
| | - Gary J Pielak
- Department of Chemistry and Department of Biochemistry and Biophysics, University of North Carolina-Chapel Hill, Chapel Hill, North Carolina, USA.,Lineberger Comprehensive Cancer Center, University of North Carolina-Chapel Hill, Chapel Hill, North Carolina, USA.,Integrative Program for Biological and Genome Sciences, University of North Carolina-Chapel Hill, Chapel Hill, North Carolina, USA
| | - Maili Liu
- Key Laboratory of Magnetic Resonance in Biological Systems, State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, National Center for Magnetic Resonance in Wuhan, Wuhan National Laboratory for Optoelectronics, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan, China.,Graduate University of Chinese Academy of Sciences, Beijing, China
| | - Conggang Li
- Key Laboratory of Magnetic Resonance in Biological Systems, State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, National Center for Magnetic Resonance in Wuhan, Wuhan National Laboratory for Optoelectronics, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan, China.,Graduate University of Chinese Academy of Sciences, Beijing, China
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22
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Hawk BJD, Khounlo R, Shin YK. Alpha-Synuclein Continues to Enhance SNARE-Dependent Vesicle Docking at Exorbitant Concentrations. Front Neurosci 2019; 13:216. [PMID: 30949020 PMCID: PMC6437117 DOI: 10.3389/fnins.2019.00216] [Citation(s) in RCA: 28] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2019] [Accepted: 02/25/2019] [Indexed: 11/18/2022] Open
Abstract
Recently, Parkinson’s disease-associated α-synuclein (αS) has emerged as an important regulator for SNARE-dependent vesicle fusion. However, it is controversial if excessive accumulation of αS, even in the absence of aggregation, impairs neurotransmission. Here we use a single vesicle fusion assay with ms time resolution capable of dissecting the impact of αS on each step of membrane fusion. Unlike the previous results from various in vitro, cellular, and in vivo studies, we find that non-aggregated αS promotes vesicle merger even at exorbitant concentrations. The enhancement has been seen as much as 13 fold. Delving into the kinetics of the intermediate states for vesicle fusion reveals that αS stimulates vesicle docking without altering the dynamics of bilayer merger (lipid mixing). However, minute amounts of soluble aggregated species abolish SNARE-dependent bilayer merger completely. Thus, the results show that excessive accumulation of non-aggregated αS may not be toxic for neurotransmitter release.
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Affiliation(s)
- Brenden J D Hawk
- Roy J. Carver Department of Biochemistry, Biophysics and Molecular Biology, Iowa State University, Ames, IA, United States
| | - Ryan Khounlo
- Roy J. Carver Department of Biochemistry, Biophysics and Molecular Biology, Iowa State University, Ames, IA, United States
| | - Yeon-Kyun Shin
- Roy J. Carver Department of Biochemistry, Biophysics and Molecular Biology, Iowa State University, Ames, IA, United States
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23
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Li X, Radhakrishnan A, Grushin K, Kasula R, Chaudhuri A, Gomathinayagam S, Krishnakumar SS, Liu J, Rothman JE. Symmetrical organization of proteins under docked synaptic vesicles. FEBS Lett 2019; 593:144-153. [PMID: 30561792 PMCID: PMC6353562 DOI: 10.1002/1873-3468.13316] [Citation(s) in RCA: 28] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2018] [Revised: 12/13/2018] [Accepted: 12/17/2018] [Indexed: 11/11/2022]
Abstract
During calcium‐regulated exocytosis, the constitutive fusion machinery is ‘clamped’ in a partially assembled state until synchronously released by calcium. The protein machinery involved in this process is known, but the supra‐molecular architecture and underlying mechanisms are unclear. Here, we use cryo‐electron tomography analysis in nerve growth factor‐differentiated neuro‐endocrine (PC12) cells to delineate the organization of the release machinery under the docked vesicles. We find that exactly six exocytosis modules, each likely consisting of a single SNAREpin with its bound Synaptotagmins, Complexin, and Munc18 proteins, are symmetrically arranged at the vesicle–PM interface. Mutational analysis suggests that the symmetrical organization is templated by circular oligomers of Synaptotagmin. The observed arrangement, including its precise radial positioning, is in‐line with the recently proposed ‘buttressed ring hypothesis’.
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Affiliation(s)
- Xia Li
- Department of Microbial Pathogenesis, Yale University School of Medicine, New Haven, CT, USA.,Institute of Nautical Medicine, Co-innovation Center of Neuroregeneration, Nantong University, China
| | | | - Kirill Grushin
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT, USA
| | - Ravikiran Kasula
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT, USA
| | - Arunima Chaudhuri
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT, USA
| | | | - Shyam S Krishnakumar
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT, USA.,Department of Clinical and Experimental Epilepsy, UCL Queen Square Institute of Neurology, London, UK
| | - Jun Liu
- Department of Microbial Pathogenesis, Yale University School of Medicine, New Haven, CT, USA.,Department of Cell Biology, Yale University School of Medicine, New Haven, CT, USA
| | - James E Rothman
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT, USA.,Department of Clinical and Experimental Epilepsy, UCL Queen Square Institute of Neurology, London, UK
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24
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Lira RB, Robinson T, Dimova R, Riske KA. Highly Efficient Protein-free Membrane Fusion: A Giant Vesicle Study. Biophys J 2019; 116:79-91. [PMID: 30579564 PMCID: PMC6342729 DOI: 10.1016/j.bpj.2018.11.3128] [Citation(s) in RCA: 60] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2018] [Revised: 11/14/2018] [Accepted: 11/19/2018] [Indexed: 12/18/2022] Open
Abstract
Membrane fusion is a ubiquitous process in biology and is a prerequisite for many intracellular delivery protocols relying on the use of liposomes as drug carriers. Here, we investigate in detail the process of membrane fusion and the role of opposite charges in a protein-free lipid system based on cationic liposomes (LUVs, large unilamellar vesicles) and anionic giant unilamellar vesicles (GUVs) composed of different palmitoyloleoylphosphatidylcholine (POPC)/palmitoyloleoylphosphatidylglycerol (POPG) molar ratios. By using a set of optical-microscopy- and microfluidics-based methods, we show that liposomes strongly dock to GUVs of pure POPC or low POPG fraction (up to 10 mol%) in a process mainly associated with hemifusion and membrane tension increase, commonly leading to GUV rupture. On the other hand, docked LUVs quickly and very efficiently fuse with negative GUVs of POPG fractions at or above 20 mol%, resulting in dramatic GUV area increase in a charge-dependent manner; the vesicle area increase is deduced from GUV electrodeformation. Importantly, both hemifusion and full fusion are leakage-free. Fusion efficiency is quantified by the lipid transfer from liposomes to GUVs using fluorescence resonance energy transfer (FRET), which leads to consistent results when compared to fluorescence-lifetime-based FRET. We develop an approach to deduce the final composition of single GUVs after fusion based on the FRET efficiency. The results suggest that fusion is driven by membrane charge and appears to proceed up to charge neutralization of the acceptor GUV.
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Affiliation(s)
- Rafael B Lira
- Departamento de Biofísica, Universidade Federal de São Paulo, São Paulo, Brazil; Department of Theory and Bio-Systems, Max Planck Institute of Colloids and Interfaces, Potsdam, Germany
| | - Tom Robinson
- Department of Theory and Bio-Systems, Max Planck Institute of Colloids and Interfaces, Potsdam, Germany
| | - Rumiana Dimova
- Department of Theory and Bio-Systems, Max Planck Institute of Colloids and Interfaces, Potsdam, Germany.
| | - Karin A Riske
- Departamento de Biofísica, Universidade Federal de São Paulo, São Paulo, Brazil.
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25
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Biochemical studies of membrane fusion at the single-particle level. Prog Lipid Res 2019; 73:92-100. [PMID: 30611882 DOI: 10.1016/j.plipres.2019.01.001] [Citation(s) in RCA: 34] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2018] [Revised: 01/01/2019] [Accepted: 01/02/2019] [Indexed: 01/21/2023]
Abstract
To study membrane fusion mediated by synaptic proteins, proteoliposomes have been widely used for in vitro ensemble measurements with limited insights into the fusion mechanism. Single-particle techniques have proven to be powerful in overcoming the limitations of traditional ensemble methods. Here, we summarize current single-particle methods in biophysical and biochemical studies of fusion mediated by soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs) and other synaptic proteins, together with their advantages and limitations.
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26
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Hubrich R, Park Y, Mey I, Jahn R, Steinem C. SNARE-Mediated Fusion of Single Chromaffin Granules with Pore-Spanning Membranes. Biophys J 2018; 116:308-318. [PMID: 30598283 DOI: 10.1016/j.bpj.2018.11.3138] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2018] [Revised: 11/15/2018] [Accepted: 11/29/2018] [Indexed: 01/09/2023] Open
Abstract
Pore-spanning membranes (PSMs) composed of supported membrane parts as well as freestanding membrane parts are shown to be very versatile to investigate SNARE-mediated fusion on the single-particle level. They provide a planar geometry readily accessible by confocal fluorescence microscopy, which enabled us for the first time, to our knowledge, to investigate the fusion of individual natural secretory granules (i.e., chromaffin granules (CGs)) on the single-particle level by two-color fluorescence microscopy in a time-resolved manner. The t-SNARE acceptor complex ΔN49 was reconstituted into PSMs containing 2 mol % 1,2-dipalmitoyl-sn-glycero-3-phosphatidylinositol-4,5-bisphosphate and Atto488-1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine, and CGs were fluorescently labeled with 2-((1E,3E)-5-((Z)-3,3-dimethyl-1-octadecylindolin-2-ylidene)penta-1,3-dien-1-yl)-3,3-dimethyl-1-octadecyl-3H-indol-1-ium perchlorate. We compared the dynamics of docked and hemifused CGs as well as their fusion efficacy and kinetics with the results obtained for synthetic synaptobrevin 2-doped vesicles fusing with PSMs of the same composition. Whereas the synthetic vesicles were fully immobile on supported PSMs, docked as well as hemifused CGs were mobile on both PSM parts, which suggests that this system resembles more closely the natural situation. The fusion process of CGs proceeded through three-dimensional post-lipid-mixing structures, which were readily resolved on the gold-covered pore rims of the PSMs and which are discussed in the context of intermediate states observed in live cells.
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Affiliation(s)
- Raphael Hubrich
- Institute of Organic and Biomolecular Chemistry, University of Göttingen, Göttingen, Germany
| | - Yongsoo Park
- Max-Planck Institute for Biophysical Chemistry, Göttingen, Germany; Department of Molecular Biology and Genetics, Koc University, Sarıyer, Istanbul, Turkey
| | - Ingo Mey
- Institute of Organic and Biomolecular Chemistry, University of Göttingen, Göttingen, Germany
| | - Reinhard Jahn
- Max-Planck Institute for Biophysical Chemistry, Göttingen, Germany
| | - Claudia Steinem
- Institute of Organic and Biomolecular Chemistry, University of Göttingen, Göttingen, Germany; Max-Planck Institute for Dynamics and Self-Organization, Göttingen, Germany.
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27
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McDargh ZA, Polley A, O'Shaughnessy B. SNARE-mediated membrane fusion is a two-stage process driven by entropic forces. FEBS Lett 2018; 592:3504-3515. [PMID: 30346036 DOI: 10.1002/1873-3468.13277] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2018] [Revised: 10/17/2018] [Accepted: 10/18/2018] [Indexed: 11/08/2022]
Abstract
SNARE proteins constitute the core of the exocytotic membrane fusion machinery. Fusion occurs when vesicle-associated and target membrane-associated SNAREs zipper into trans-SNARE complexes ('SNAREpins'), but the number required is controversial and the mechanism of cooperative fusion is poorly understood. We developed a highly coarse-grained molecular dynamics simulation to access the long fusion timescales, which revealed a two-stage process. First, zippering energy was dissipated and cooperative entropic forces assembled the SNAREpins into a ring; second, entropic forces expanded the ring, pressing membranes together and catalyzing fusion. We predict that any number of SNAREs fuses membranes, but fusion is faster with more SNAREs.
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Affiliation(s)
- Zachary A McDargh
- Department of Chemical Engineering, Columbia University, New York City, NY, USA
| | - Anirban Polley
- Department of Chemical Engineering, Columbia University, New York City, NY, USA
| | - Ben O'Shaughnessy
- Department of Chemical Engineering, Columbia University, New York City, NY, USA
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28
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Karatekin E. Toward a unified picture of the exocytotic fusion pore. FEBS Lett 2018; 592:3563-3585. [PMID: 30317539 PMCID: PMC6353554 DOI: 10.1002/1873-3468.13270] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2018] [Revised: 09/30/2018] [Accepted: 10/10/2018] [Indexed: 11/07/2022]
Abstract
Neurotransmitter and hormone release involve calcium-triggered fusion of a cargo-loaded vesicle with the plasma membrane. The initial connection between the fusing membranes, called the fusion pore, can evolve in various ways, including rapid dilation to allow full cargo release, slow expansion, repeated opening-closing and resealing. Pore dynamics determine the kinetics of cargo release and the mode of vesicle recycling, but how these processes are controlled is poorly understood. Previous reconstitutions could not monitor single pores, limiting mechanistic insight they could provide. Recently developed nanodisc-based fusion assays allow reconstitution and monitoring of single pores with unprecedented detail and hold great promise for future discoveries. They recapitulate various aspects of exocytotic fusion pores, but comparison is difficult because different approaches suggested very different exocytotic fusion pore properties, even for the same cell type. In this Review, I discuss how most of the data can be reconciled, by recognizing how different methods probe different aspects of the same fusion process. The resulting picture is that fusion pores have broadly distributed properties arising from stochastic processes which can be modulated by physical constraints imposed by proteins, lipids and membranes.
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Affiliation(s)
- Erdem Karatekin
- Department of Cellular and Molecular Physiology, Yale University, New Haven, CT, USA
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT, USA
- Nanobiology Institute, Yale University, West Haven, CT, USA
- Centre National de la Recherche Scientifique (CNRS), Paris, France
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29
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Ramakrishnan S, Gohlke A, Li F, Coleman J, Xu W, Rothman JE, Pincet F. High-Throughput Monitoring of Single Vesicle Fusion Using Freestanding Membranes and Automated Analysis. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2018; 34:5849-5859. [PMID: 29694054 DOI: 10.1021/acs.langmuir.8b00116] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
In vivo membrane fusion primarily occurs between highly curved vesicles and planar membranes. A better understanding of fusion entails an accurate in vitro reproduction of the process. To date, supported bilayers have been commonly used to mimic the planar membranes. Soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) proteins that induce membrane fusion usually have limited fluidity when embedded in supported bilayers. This alters the kinetics and prevents correct reconstitution of the overall fusion process. Also, observing content release across the membrane is hindered by the lack of a second aqueous compartment. Recently, a step toward resolving these issues was achieved by using membranes spread on holey substrates. The mobility of proteins was preserved but vesicles were prone to bind to the substrate when reaching the edge of the hole, preventing the observation of many fusion events over the suspended membrane. Building on this recent advance, we designed a method for the formation of pore-spanning lipid bilayers containing t-SNARE proteins on Si/SiO2 holey chips, allowing the observation of many individual vesicle fusion events by both lipid mixing and content release. With this setup, proteins embedded in the suspended membrane bounced back when they reached the edge of the hole which ensured vesicles did not bind to the substrate. We observed SNARE-dependent membrane fusion with the freestanding bilayer of about 500 vesicles. The time between vesicle docking and fusion is ∼1 s. We also present a new multimodal open-source software, Fusion Analyzer Software, which is required for fast data analysis.
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Affiliation(s)
- Sathish Ramakrishnan
- Laboratoire de Physique Statistique, Ecole Normale Supérieure , PSL Research University, Université Paris Diderot Sorbonne Paris Cité, Sorbonne Universités UPMC Univ Paris 06, CNRS , Paris 75005 , France
- Department of Cell Biology , Yale School of Medicine , New Haven , 333 Cedar Street , Connecticut 06510 , United States
- Nanobiology Institute , 850 West Campus Drive , West Haven , Connecticut 06516 , United States
| | - Andrea Gohlke
- Laboratoire de Physique Statistique, Ecole Normale Supérieure , PSL Research University, Université Paris Diderot Sorbonne Paris Cité, Sorbonne Universités UPMC Univ Paris 06, CNRS , Paris 75005 , France
- Department of Cell Biology , Yale School of Medicine , New Haven , 333 Cedar Street , Connecticut 06510 , United States
- Nanobiology Institute , 850 West Campus Drive , West Haven , Connecticut 06516 , United States
| | - Feng Li
- Department of Cell Biology , Yale School of Medicine , New Haven , 333 Cedar Street , Connecticut 06510 , United States
- Nanobiology Institute , 850 West Campus Drive , West Haven , Connecticut 06516 , United States
| | - Jeff Coleman
- Department of Cell Biology , Yale School of Medicine , New Haven , 333 Cedar Street , Connecticut 06510 , United States
- Nanobiology Institute , 850 West Campus Drive , West Haven , Connecticut 06516 , United States
| | - Weiming Xu
- Department of Cell Biology , Yale School of Medicine , New Haven , 333 Cedar Street , Connecticut 06510 , United States
- Nanobiology Institute , 850 West Campus Drive , West Haven , Connecticut 06516 , United States
| | - James E Rothman
- Department of Cell Biology , Yale School of Medicine , New Haven , 333 Cedar Street , Connecticut 06510 , United States
- Nanobiology Institute , 850 West Campus Drive , West Haven , Connecticut 06516 , United States
| | - Frederic Pincet
- Laboratoire de Physique Statistique, Ecole Normale Supérieure , PSL Research University, Université Paris Diderot Sorbonne Paris Cité, Sorbonne Universités UPMC Univ Paris 06, CNRS , Paris 75005 , France
- Department of Cell Biology , Yale School of Medicine , New Haven , 333 Cedar Street , Connecticut 06510 , United States
- Nanobiology Institute , 850 West Campus Drive , West Haven , Connecticut 06516 , United States
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30
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Singh P, Hui CY. Hydrodynamics govern the pre-fusion docking time of synaptic vesicles. J R Soc Interface 2018; 15:rsif.2017.0818. [PMID: 29386403 DOI: 10.1098/rsif.2017.0818] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2017] [Accepted: 01/09/2018] [Indexed: 11/12/2022] Open
Abstract
Synaptic vesicle fusion is a crucial step in the neurotransmission process. Neurotransmitter-filled vesicles are pre-docked at the synapse by the mediation of ribbon structures and SNARE proteins at the ribbon synapses. An electrical impulse triggers the fusion process of pre-docked vesicles, leading to the formation of a fusion pore and subsequently resulting in the release of neurotransmitter into the synaptic cleft. In this study, a continuum model of lipid membrane along with lubrication theory is used to determine the traverse time of the synaptic vesicle under the influence of hydrodynamic forces. We find that the traverse time is strongly dependent on how fast the driving force decays or grows with closure of the gap between the vesicle and the plasma membrane. If the correct behaviour is chosen, the traverse time obtained is of the order of a few hundred milliseconds and lies within the experimentally obtained value of approximately 250 ms (Zenisek D, Steyer JA, Almers W. 2000 Nature406, 849-854 (doi:10.1038/35022500)). We hypothesize that there are two different force behaviours, which complies with the experimental findings of pre-fusion docking of synaptic vesicles at the ribbon synapses. The common theme in the proposed force models is that the driving force has to very rapidly increase or decrease with the amount of clamping.
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Affiliation(s)
- Pankaj Singh
- Department of Theoretical and Applied Mechanics, Cornell University, Ithaca, NY 14853, USA
| | - Chung-Yuen Hui
- Department of Mechanical and Aerospace Engineering, Cornell University, Ithaca, NY 14853, USA
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31
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Kim J, Shin YK. Productive and Non-productive Pathways for Synaptotagmin 1 to Support Ca 2+-Triggered Fast Exocytosis. Front Mol Neurosci 2017; 10:380. [PMID: 29187811 PMCID: PMC5695160 DOI: 10.3389/fnmol.2017.00380] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2017] [Accepted: 11/01/2017] [Indexed: 12/17/2022] Open
Abstract
Ca2+-triggered SNARE-mediated membrane fusion is essential for neuronal communication. The speed of this process is of particular importance because it sets a time limit to cognitive and physical activities. In this work, we expand the proteoliposome-to-supported bilayer (SBL) fusion assay by successfully incorporating synaptotagmin 1 (Syt1), a major Ca2+ sensor. We report that Syt1 and Ca2+ together can elicit more than a 50-fold increase in the number of membrane fusion events when compared with membrane fusion mediated by SNAREs only. What is remarkable is that ~55% of all vesicle fusion events occurs within 20 ms upon vesicle docking. Furthermore, pre-binding of Syt1 to SNAREs prior to Ca2+ inhibits spontaneous fusion, but intriguingly, this leads to a complete loss of the Ca2+ responsiveness. Thus, our results suggest that there is a productive and a non-productive pathway for Syt1, depending on whether there is a premature interaction between Syt1 and SNAREs. Our results show that Ca2+ binding to Syt1 prior to Syt1's binding to SNAREs may be a prerequisite for the productive pathway. The successful reconstitution of Syt1 activities in the physiological time scale provides new opportunities to test the current mechanistic models for Ca2+-triggered exocytosis.
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Affiliation(s)
| | - Yeon-Kyun Shin
- Roy J. Carver Department of Biochemistry, Biophysics and Molecular Biology, Iowa State University, Ames, IA, United States
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32
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Wang T, Li L, Hong W. SNARE proteins in membrane trafficking. Traffic 2017; 18:767-775. [PMID: 28857378 DOI: 10.1111/tra.12524] [Citation(s) in RCA: 100] [Impact Index Per Article: 14.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2017] [Revised: 08/25/2017] [Accepted: 08/25/2017] [Indexed: 12/25/2022]
Abstract
SNAREs are the core machinery mediating membrane fusion. In this review, we provide an update on the recent progress on SNAREs regulating membrane fusion events, especially the more detailed fusion processes dissected by well-developed biophysical methods and in vitro single molecule analysis approaches. We also briefly summarize the relevant research from Chinese laboratories and highlight the significant contributions on our understanding of SNARE-mediated membrane trafficking from scientists in China.
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Affiliation(s)
- Tuanlao Wang
- School of Pharmaceutical Sciences, State Key Laboratory of Cellular Stress Biology, Xiamen University, Xiamen, China
| | - Liangcheng Li
- School of Pharmaceutical Sciences, State Key Laboratory of Cellular Stress Biology, Xiamen University, Xiamen, China
| | - Wanjin Hong
- School of Pharmaceutical Sciences, State Key Laboratory of Cellular Stress Biology, Xiamen University, Xiamen, China.,Institute of Molecular and Cell Biology, A*STAR (Agency for Science, Technology and Research), Singapore, Singapore
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33
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Kuhlmann JW, Junius M, Diederichsen U, Steinem C. SNARE-Mediated Single-Vesicle Fusion Events with Supported and Freestanding Lipid Membranes. Biophys J 2017; 112:2348-2356. [PMID: 28591607 DOI: 10.1016/j.bpj.2017.04.032] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2016] [Revised: 04/24/2017] [Accepted: 04/24/2017] [Indexed: 10/19/2022] Open
Abstract
In vitro single-vesicle fusion assays are important tools to analyze the details of SNARE-mediated fusion processes. In this study, we employed planar pore-spanning membranes (PSMs) prepared on porous silicon substrates with large pore diameters of 5 μm, allowing us to compare the process of vesicle docking and fusion on the supported parts of the PSMs (s-PSMs) with that on the freestanding membrane parts (f-PSM) under the exact same experimental conditions. The PSMs harbor the t-SNARE ΔN49-complex to investigate the dynamics and fusogenicity of single large unilamellar vesicles doped with the v-SNARE synaptobrevin 2 by means of spinning-disc confocal microscopy with a time resolution of 10 ms. Our results demonstrate that vesicles docked to the s-PSM were fully immobile, whereas those docked to the f-PSM were mobile with a mean diffusion coefficient of 0.42 μm2/s. Despite the different dynamics of the vesicles on the two membrane types, similar fusion kinetics were observed, giving rise to a common fusion mechanism. Further investigations of individual lipid mixing events on the s-PSMs revealed semi-stable post-fusion structures.
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Affiliation(s)
- Jan W Kuhlmann
- Institute of Organic and Biomolecular Chemistry, University of Göttingen, Göttingen, Germany
| | - Meike Junius
- Institute of Organic and Biomolecular Chemistry, University of Göttingen, Göttingen, Germany
| | - Ulf Diederichsen
- Institute of Organic and Biomolecular Chemistry, University of Göttingen, Göttingen, Germany
| | - Claudia Steinem
- Institute of Organic and Biomolecular Chemistry, University of Göttingen, Göttingen, Germany.
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34
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Abstract
Fusion between two lipid bilayers is one of the central processes in cell biology, playing a key role in endocytosis, exocytosis, and vesicle transport. We have previously developed a model system that uses the hybridization of complementary DNA strands to model the formation of the SNARE four-helix bundle that mediates synaptic vesicle fusion and used it to study vesicle fusion to a tethered lipid bilayer. Using single vesicle assays, 70% of observed fusion events in the DNA-lipid system are arrested at the hemifusion stage, whereas only 5% eventually go to full fusion. This may be because the diglycerol ether that anchors the DNA in the membrane spans only half the bilayer: upon hemifusion and mixing of the outer leaflets, the DNA-lipid is free to diffuse into the target membrane and away from the vesicle. Here, we test the hypothesis that the length of the membrane anchor may impact the outcome by comparing single leaflet-spanning DNA-lipid mediated vesicle fusion with fusion mediated by DNA anchored by solanesol, a C45 isoprenoid of sufficient length to span the bilayer. When the solanesol anchor was present on the incoming vesicles, target membrane, or both, ∼2-3 times as much full fusion was observed as in the DNA-lipid mediated system, as measured by lipid mixing or content transfer. These results indicate that a transmembrane anchor increases the efficiency of full fusion.
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Affiliation(s)
| | - Steven G Boxer
- Department of Chemistry, Stanford University, Stanford, California.
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35
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Entropic forces drive self-organization and membrane fusion by SNARE proteins. Proc Natl Acad Sci U S A 2017; 114:5455-5460. [PMID: 28490503 DOI: 10.1073/pnas.1611506114] [Citation(s) in RCA: 43] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
SNARE proteins are the core of the cell's fusion machinery and mediate virtually all known intracellular membrane fusion reactions on which exocytosis and trafficking depend. Fusion is catalyzed when vesicle-associated v-SNAREs form trans-SNARE complexes ("SNAREpins") with target membrane-associated t-SNAREs, a zippering-like process releasing ∼65 kT per SNAREpin. Fusion requires several SNAREpins, but how they cooperate is unknown and reports of the number required vary widely. To capture the collective behavior on the long timescales of fusion, we developed a highly coarse-grained model that retains key biophysical SNARE properties such as the zippering energy landscape and the surface charge distribution. In simulations the ∼65-kT zippering energy was almost entirely dissipated, with fully assembled SNARE motifs but uncomplexed linker domains. The SNAREpins self-organized into a circular cluster at the fusion site, driven by entropic forces that originate in steric-electrostatic interactions among SNAREpins and membranes. Cooperative entropic forces expanded the cluster and pulled the membranes together at the center point with high force. We find that there is no critical number of SNAREs required for fusion, but instead the fusion rate increases rapidly with the number of SNAREpins due to increasing entropic forces. We hypothesize that this principle finds physiological use to boost fusion rates to meet the demanding timescales of neurotransmission, exploiting the large number of v-SNAREs available in synaptic vesicles. Once in an unfettered cluster, we estimate ≥15 SNAREpins are required for fusion within the ∼1-ms timescale of neurotransmitter release.
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36
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Witkowska A, Jahn R. Rapid SNARE-Mediated Fusion of Liposomes and Chromaffin Granules with Giant Unilamellar Vesicles. Biophys J 2017; 113:1251-1259. [PMID: 28400045 PMCID: PMC5607038 DOI: 10.1016/j.bpj.2017.03.010] [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: 10/07/2016] [Revised: 03/12/2017] [Accepted: 03/13/2017] [Indexed: 11/03/2022] Open
Abstract
Soluble N-ethylmaleimide-sensitive factor activating protein receptor (SNARE) proteins are the main catalysts for membrane fusion in the secretory pathway of eukaryotic cells. In vitro, SNAREs are sufficient to mediate effective fusion of both native and artificial membranes. Here we have established, to our knowledge, a new platform for monitoring SNARE-mediated docking and fusion between giant unilamellar vesicles (GUVs) and smaller liposomes or purified secretory granules with high temporal and spatial resolution. Analysis of fusion is restricted to the free-standing part of the GUV-membrane exhibiting low curvature and a lack of surface contact, thus avoiding adhesion-mediated interference with the fusion reaction as in fusion with supported bilayers or surface-immobilized small vesicles. Our results show that liposomes and chromaffin granules fuse with GUVs containing activated SNAREs with only few milliseconds delay between docking and fusion. We conclude that after initial contact in trans, SNAREs alone can complete fusion at a rate close to fast neuronal exocytosis.
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Affiliation(s)
- Agata Witkowska
- Department of Neurobiology, Max-Planck-Institute for Biophysical Chemistry, Göttingen, Germany; International Max Planck Research School for Molecular Biology at the University of Göttingen, Göttingen, Germany
| | - Reinhard Jahn
- Department of Neurobiology, Max-Planck-Institute for Biophysical Chemistry, Göttingen, Germany.
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37
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Wu Z, Bello OD, Thiyagarajan S, Auclair SM, Vennekate W, Krishnakumar SS, O'Shaughnessy B, Karatekin E. Dilation of fusion pores by crowding of SNARE proteins. eLife 2017; 6. [PMID: 28346138 PMCID: PMC5404929 DOI: 10.7554/elife.22964] [Citation(s) in RCA: 48] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2016] [Accepted: 03/26/2017] [Indexed: 01/29/2023] Open
Abstract
Hormones and neurotransmitters are released through fluctuating exocytotic fusion pores that can flicker open and shut multiple times. Cargo release and vesicle recycling depend on the fate of the pore, which may reseal or dilate irreversibly. Pore nucleation requires zippering between vesicle-associated v-SNAREs and target membrane t-SNAREs, but the mechanisms governing the subsequent pore dilation are not understood. Here, we probed the dilation of single fusion pores using v-SNARE-reconstituted ~23-nm-diameter discoidal nanolipoprotein particles (vNLPs) as fusion partners with cells ectopically expressing cognate, 'flipped' t-SNAREs. Pore nucleation required a minimum of two v-SNAREs per NLP face, and further increases in v-SNARE copy numbers did not affect nucleation rate. By contrast, the probability of pore dilation increased with increasing v-SNARE copies and was far from saturating at 15 v-SNARE copies per face, the NLP capacity. Our experimental and computational results suggest that SNARE availability may be pivotal in determining whether neurotransmitters or hormones are released through a transient ('kiss and run') or an irreversibly dilating pore (full fusion).
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Affiliation(s)
- Zhenyong Wu
- Department of Cellular and Molecular Physiology, School of Medicine, Yale University, New Haven, United States.,Nanobiology Institute, Yale University, West Haven, United States
| | - Oscar D Bello
- Nanobiology Institute, Yale University, West Haven, United States.,Department of Cell Biology, School of Medicine, Yale University, New Haven, United States
| | | | - Sarah Marie Auclair
- Nanobiology Institute, Yale University, West Haven, United States.,Department of Cell Biology, School of Medicine, Yale University, New Haven, United States
| | - Wensi Vennekate
- Department of Cellular and Molecular Physiology, School of Medicine, Yale University, New Haven, United States.,Nanobiology Institute, Yale University, West Haven, United States
| | - Shyam S Krishnakumar
- Nanobiology Institute, Yale University, West Haven, United States.,Department of Cell Biology, School of Medicine, Yale University, New Haven, United States
| | - Ben O'Shaughnessy
- Department of Chemical Engineering, Columbia University, New York, United States
| | - Erdem Karatekin
- Department of Cellular and Molecular Physiology, School of Medicine, Yale University, New Haven, United States.,Nanobiology Institute, Yale University, West Haven, United States.,Molecular Biophysics and Biochemistry, Yale University, New Haven, United States.,Laboratoire de Neurophotonique, Université Paris Descartes, Faculté des Sciences Fondamentales et Biomédicales, Centre National de la Recherche Scientifique, Paris, France
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38
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A stochastic model of active zone material mediated synaptic vesicle docking and priming at resting active zones. Sci Rep 2017; 7:278. [PMID: 28325932 PMCID: PMC5428245 DOI: 10.1038/s41598-017-00360-z] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2016] [Accepted: 02/21/2017] [Indexed: 11/09/2022] Open
Abstract
Synaptic vesicles (SVs) fuse with the presynaptic membrane (PM) at specialized regions called active zones for synaptic transmission. SVs are associated with dense aggregates of macromolecules called active zone material (AZM) that has been thought to be involved in SV release. However, its role has recently begun to be elucidated. Several morphological studies proposed distinctively different AZM mediated SV docking and priming models: sequential and concurrent SV docking/priming. To explore ways to reconcile the contradictory models we develop a stochastic AZM mediated SV docking and priming model. We assume that the position of each connection site of the AZM macromolecules on their SV, directly linking the SV with the PM, varies by random shortening and lengthening of the macromolecules at resting active zones. We also perform computer simulations of SVs near the PM at resting active zones, and the results show that the distribution of the AZM connection sites can significantly affect the SV's docking efficiency and distribution of its contact area with the PM, thus priming and that the area correlates with the shape of the SVs providing a way to account for seemingly irreconcilable observations reported about the spatial relationship of SVs with the PM at active zones.
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39
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Kiessling V, Liang B, Kreutzberger AJB, Tamm LK. Planar Supported Membranes with Mobile SNARE Proteins and Quantitative Fluorescence Microscopy Assays to Study Synaptic Vesicle Fusion. Front Mol Neurosci 2017; 10:72. [PMID: 28360838 PMCID: PMC5352703 DOI: 10.3389/fnmol.2017.00072] [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: 01/23/2017] [Accepted: 03/03/2017] [Indexed: 12/31/2022] Open
Abstract
Synaptic vesicle membrane fusion, the process by which neurotransmitter gets released at the presynaptic membrane is mediated by a complex interplay between proteins and lipids. The realization that the lipid bilayer is not just a passive environment where other molecular players like SNARE proteins act, but is itself actively involved in the process, makes the development of biochemical and biophysical assays particularly challenging. We summarize in vitro assays that use planar supported membranes and fluorescence microscopy to address some of the open questions regarding the molecular mechanisms of SNARE-mediated membrane fusion. Most of the assays discussed in this mini-review were developed in our lab over the last 15 years. We emphasize the sample requirements that we found are important for the successful application of these methods.
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Affiliation(s)
- Volker Kiessling
- Center for Membrane and Cell Physiology, University of VirginiaCharlottesville, VA, USA; Department of Molecular Physiology and Biological Physics, University of VirginiaCharlottesville, VA, USA
| | - Binyong Liang
- Center for Membrane and Cell Physiology, University of VirginiaCharlottesville, VA, USA; Department of Molecular Physiology and Biological Physics, University of VirginiaCharlottesville, VA, USA
| | - Alex J B Kreutzberger
- Center for Membrane and Cell Physiology, University of VirginiaCharlottesville, VA, USA; Department of Molecular Physiology and Biological Physics, University of VirginiaCharlottesville, VA, USA
| | - Lukas K Tamm
- Center for Membrane and Cell Physiology, University of VirginiaCharlottesville, VA, USA; Department of Molecular Physiology and Biological Physics, University of VirginiaCharlottesville, VA, USA
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40
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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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Cholesterol Increases the Openness of SNARE-Mediated Flickering Fusion Pores. Biophys J 2016; 110:1538-1550. [PMID: 27074679 DOI: 10.1016/j.bpj.2016.02.019] [Citation(s) in RCA: 51] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2014] [Revised: 02/03/2016] [Accepted: 02/04/2016] [Indexed: 11/22/2022] Open
Abstract
Flickering of fusion pores during exocytotic release of hormones and neurotransmitters is well documented, but without assays that use biochemically defined components and measure single-pore dynamics, the mechanisms remain poorly understood. We used total internal reflection fluorescence microscopy to quantify fusion-pore dynamics in vitro and to separate the roles of soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) proteins and lipid bilayer properties. When small unilamellar vesicles bearing neuronal v-SNAREs fused with planar bilayers reconstituted with cognate t-SNARES, lipid and soluble cargo transfer rates were severely reduced, suggesting that pores flickered. From the lipid release times we computed pore openness, the fraction of time the pore is open, which increased dramatically with cholesterol. For most lipid compositions tested, SNARE-mediated and nonspecifically nucleated pores had similar openness, suggesting that pore flickering was controlled by lipid bilayer properties. However, with physiological cholesterol levels, SNAREs substantially increased the fraction of fully open pores and fusion was so accelerated that there was insufficient time to recruit t-SNAREs to the fusion site, consistent with t-SNAREs being preclustered by cholesterol into functional docking and fusion platforms. Our results suggest that cholesterol opens pores directly by reducing the fusion-pore bending energy, and indirectly by concentrating several SNAREs into individual fusion events.
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42
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Sasmal DK, Pulido LE, Kasal S, Huang J. Single-molecule fluorescence resonance energy transfer in molecular biology. NANOSCALE 2016; 8:19928-19944. [PMID: 27883140 PMCID: PMC5145784 DOI: 10.1039/c6nr06794h] [Citation(s) in RCA: 61] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/19/2023]
Abstract
Single-molecule fluorescence resonance energy transfer (smFRET) is a powerful technique for studying the conformation dynamics and interactions of individual biomolecules. In this review, we describe the concept and principle of smFRET, illustrate general instrumentation and microscopy settings for experiments, and discuss the methods and algorithms for data analysis. Subsequently, we review applications of smFRET in protein conformational changes, ion channel open-close properties, receptor-ligand interactions, nucleic acid structure regulation, vesicle fusion, and force induced conformational dynamics. Finally, we discuss the main limitations of smFRET in molecular biology.
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Affiliation(s)
- Dibyendu K Sasmal
- The Institute for Molecular Engineering, The University of Chicago, Chicago, IL 60637, USA.
| | - Laura E Pulido
- The Institute for Molecular Engineering, The University of Chicago, Chicago, IL 60637, USA.
| | - Shan Kasal
- The Institute for Molecular Engineering, The University of Chicago, Chicago, IL 60637, USA.
| | - Jun Huang
- The Institute for Molecular Engineering, The University of Chicago, Chicago, IL 60637, USA.
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43
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Nikolaus J, Karatekin E. SNARE-mediated Fusion of Single Proteoliposomes with Tethered Supported Bilayers in a Microfluidic Flow Cell Monitored by Polarized TIRF Microscopy. J Vis Exp 2016. [PMID: 27585113 DOI: 10.3791/54349] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
In the ubiquitous process of membrane fusion the opening of a fusion pore establishes the first connection between two formerly separate compartments. During neurotransmitter or hormone release via exocytosis, the fusion pore can transiently open and close repeatedly, regulating cargo release kinetics. Pore dynamics also determine the mode of vesicle recycling; irreversible resealing results in transient, "kiss-and-run" fusion, whereas dilation leads to full fusion. To better understand what factors govern pore dynamics, we developed an assay to monitor membrane fusion using polarized total internal reflection fluorescence (TIRF) microscopy with single molecule sensitivity and ~15 msec time resolution in a biochemically well-defined in vitro system. Fusion of fluorescently labeled small unilamellar vesicles containing v-SNARE proteins (v-SUVs) with a planar bilayer bearing t-SNAREs, supported on a soft polymer cushion (t-SBL, t-supported bilayer), is monitored. The assay uses microfluidic flow channels that ensure minimal sample consumption while supplying a constant density of SUVs. Exploiting the rapid signal enhancement upon transfer of lipid labels from the SUV to the SBL during fusion, kinetics of lipid dye transfer is monitored. The sensitivity of TIRF microscopy allows tracking single fluorescent lipid labels, from which lipid diffusivity and SUV size can be deduced for every fusion event. Lipid dye release times can be much longer than expected for unimpeded passage through permanently open pores. Using a model that assumes retardation of lipid release is due to pore flickering, a pore "openness", the fraction of time the pore remains open during fusion, can be estimated. A soluble marker can be encapsulated in the SUVs for simultaneous monitoring of lipid and soluble cargo release. Such measurements indicate some pores may reseal after losing a fraction of the soluble cargo.
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Affiliation(s)
- Joerg Nikolaus
- Department of Cellular and Molecular Physiology, Yale University School of Medicine; Nanobiology Institute, Yale University
| | - Erdem Karatekin
- Department of Cellular and Molecular Physiology, Yale University School of Medicine; Nanobiology Institute, Yale University; Department of Molecular Biophysics and Biochemistry, Yale University; Laboratoire de Neurophotonique, Université Paris Descartes, Faculté des Sciences Fondamentales et Biomédicales, Centre National de la Recherche Scientifique (CNRS);
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44
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Tarafdar PK, Chakraborty H, Bruno MJ, Lentz BR. Phosphatidylserine-Dependent Catalysis of Stalk and Pore Formation by Synaptobrevin JMR-TMD Peptide. Biophys J 2016; 109:1863-72. [PMID: 26536263 DOI: 10.1016/j.bpj.2015.08.051] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2014] [Revised: 08/16/2015] [Accepted: 08/26/2015] [Indexed: 12/18/2022] Open
Abstract
Although the importance of a SNARE complex in neurotransmitter release is widely accepted, there exist different views on how the complex promotes fusion. One hypothesis is that the SNARE complex's ability to bring membranes into contact is sufficient for fusion, another points to possible roles of juxtamembrane regions (JMRs) and transmembrane domains (TMDs) in catalyzing lipid rearrangement, and another notes the complex's presumed ability to bend membranes near the point of contact. Here, we performed experiments with highly curved vesicles brought into contact using low concentrations of polyethylene glycol (PEG) to investigate the influence of the synaptobrevin (SB) TMD with an attached JMR (SB-JMR-TMD) on the rates of stalk and pore formation during vesicle fusion. SB-JMR-TMD enhanced the rates of stalk and fusion pore (FP) formation in a sharply sigmoidal fashion. We observed an optimal influence at an average of three peptides per vesicle, but only with phosphatidylserine (PS)-containing vesicles. Approximately three SB-JMR-TMDs per vesicle optimally ordered the bilayer interior and excluded water in a similar sigmoidal fashion. The catalytic influences of hexadecane and SB-JMR-TMD on fusion kinetics showed little in common, suggesting different mechanisms. Both kinetic and membrane structure measurements support the hypotheses that SB-JMR-TMD 1) catalyzes initial intermediate formation as a result of its basic JMR disrupting ordered interbilayer water and permitting closer interbilayer approach, and 2) catalyzes pore formation by forming a membrane-spanning complex that increases curvature stress at the circumference of the hemifused diaphragm of the prepore intermediate state.
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Affiliation(s)
- Pradip K Tarafdar
- Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina; Molecular and Cellular Biophysics Program, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina
| | - Hirak Chakraborty
- Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina; Molecular and Cellular Biophysics Program, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina
| | - Michael J Bruno
- Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina; Molecular and Cellular Biophysics Program, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina
| | - Barry R Lentz
- Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina; Molecular and Cellular Biophysics Program, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina.
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Xing P, Wang Y, Yang M, Zhang Y, Wang B, Hao A. Selective Metal-Ion-Mediated Vesicle Adhesion Based on Dynamic Self-Organization of a Pyrene-Appended Glutamic Acid. ACS APPLIED MATERIALS & INTERFACES 2016; 8:17676-17684. [PMID: 27323796 DOI: 10.1021/acsami.6b04279] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Vesicles with dynamic membranes provide an ideal model system for investigating biological membrane activities, whereby vesicle aggregation behaviors including adhesion, fusion, fission, and membrane contraction/extension have attracted much attention. In this work we utilize an aromatic amino acid (pyrene-appended glutamic acid, PGlu) to prepare nanovesicles that aggregate to form vesicle clusters selectively induced by Fe(3+) or Cu(2+), and the vesicles transform into irregular nano-objects when interacting with Al(3+). Vesicle clusters have better stability than pristine vesicles, which hinders the spontaneous morphological transformation from vesicles into lamellar nanosheets with long incubation period. The difference between complexation of Fe(3+) and Al(3+) with vesicles was studied by various techniques. On the basis of metal ion-vesicle interactions, this self-assembled nanovesicle system also behaves as an effective fluorescent sensor for Fe(3+) and Al(3+), which cause fluorescence quenching and enhanced excimer emission, respectively.
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Affiliation(s)
- Pengyao Xing
- Key Laboratory of Colloid and Interface Chemistry, Ministry of Education, and School of Chemistry and Chemical Engineering, Shandong University , Jinan 250100, People's Republic of China
| | - Yajie Wang
- Key Laboratory of Colloid and Interface Chemistry, Ministry of Education, and School of Chemistry and Chemical Engineering, Shandong University , Jinan 250100, People's Republic of China
| | - Minmin Yang
- Key Laboratory of Colloid and Interface Chemistry, Ministry of Education, and School of Chemistry and Chemical Engineering, Shandong University , Jinan 250100, People's Republic of China
| | - Yimeng Zhang
- Key Laboratory of Colloid and Interface Chemistry, Ministry of Education, and School of Chemistry and Chemical Engineering, Shandong University , Jinan 250100, People's Republic of China
| | - Bo Wang
- Key Laboratory of Colloid and Interface Chemistry, Ministry of Education, and School of Chemistry and Chemical Engineering, Shandong University , Jinan 250100, People's Republic of China
| | - Aiyou Hao
- Key Laboratory of Colloid and Interface Chemistry, Ministry of Education, and School of Chemistry and Chemical Engineering, Shandong University , Jinan 250100, People's Republic of China
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46
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Nanodisc-cell fusion: control of fusion pore nucleation and lifetimes by SNARE protein transmembrane domains. Sci Rep 2016; 6:27287. [PMID: 27264104 PMCID: PMC4893671 DOI: 10.1038/srep27287] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2016] [Accepted: 05/13/2016] [Indexed: 12/26/2022] Open
Abstract
The initial, nanometer-sized connection between the plasma membrane and a hormone- or neurotransmitter-filled vesicle –the fusion pore– can flicker open and closed repeatedly before dilating or resealing irreversibly. Pore dynamics determine release and vesicle recycling kinetics, but pore properties are poorly known because biochemically defined single-pore assays are lacking. We isolated single flickering pores connecting v-SNARE-reconstituted nanodiscs to cells ectopically expressing cognate, “flipped” t-SNAREs. Conductance through single, voltage-clamped fusion pores directly reported sub-millisecond pore dynamics. Pore currents fluctuated, transiently returned to baseline multiple times, and disappeared ~6 s after initial opening, as if the fusion pore fluctuated in size, flickered, and resealed. We found that interactions between v- and t-SNARE transmembrane domains (TMDs) promote, but are not essential for pore nucleation. Surprisingly, TMD modifications designed to disrupt v- and t-SNARE TMD zippering prolonged pore lifetimes dramatically. We propose that the post-fusion geometry of the proteins contribute to pore stability.
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47
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Han J, Pluhackova K, Böckmann RA. Exploring the Formation and the Structure of Synaptobrevin Oligomers in a Model Membrane. Biophys J 2016; 110:2004-15. [PMID: 27166808 PMCID: PMC4939486 DOI: 10.1016/j.bpj.2016.04.006] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2015] [Revised: 03/03/2016] [Accepted: 04/06/2016] [Indexed: 11/28/2022] Open
Abstract
SNARE complexes have been shown to act cooperatively to enable the synaptic vesicle fusion in neuronal transmission at millisecond timescale. It has previously been suggested that the oligomerization of SNARE complexes required for cooperative action in fusion is mediated by interactions between transmembrane domains (TMDs). We study the oligomerization of synaptobrevin TMD using ensembles of molecular dynamics (MD) simulations at coarse-grained resolution for both the wild-type (WT) and selected mutants. Trimerization and tetramerization of the sybII WT and mutants displayed distinct kinetics depending both on the rate of dimerization and the availability of alternative binding interfaces. Interestingly, the tetramerization kinetics and propensity for the sybII W89A-W90A mutant was significantly increased as compared with the WT; the tryptophans in WT sybII impose sterical restraints on oligomer packing, thereby maintaining an appropriate plasticity and accessibility of sybII to the binding of its cognate SNARE partners during membrane fusion. Higher-order oligomeric models (ranging from pentamer to octamer), built by incremental addition of peptides to smaller oligomers, revealed substantial stability and high compactness. These larger sybII oligomers may induce membrane deformation, thereby possibly facilitating fast fusion exocytosis.
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Affiliation(s)
- Jing Han
- Computational Biology, Department of Biology, Friedrich-Alexander Universität Erlangen-Nürnberg, Erlangen, 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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48
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Xu W, Nathwani B, Lin C, Wang J, Karatekin E, Pincet F, Shih W, Rothman JE. A Programmable DNA Origami Platform to Organize SNAREs for Membrane Fusion. J Am Chem Soc 2016; 138:4439-47. [PMID: 26938705 DOI: 10.1021/jacs.5b13107] [Citation(s) in RCA: 67] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
Soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complexes are the core molecular machinery of membrane fusion, a fundamental process that drives inter- and intracellular communication and trafficking. One of the questions that remains controversial has been whether and how SNAREs cooperate. Here we show the use of self-assembled DNA-nanostructure rings to template uniform-sized small unilamellar vesicles containing predetermined maximal number of externally facing SNAREs to study the membrane-fusion process. We also incorporated lipid-conjugated complementary ssDNA as tethers into vesicle and target membranes, which enabled bypass of the rate-limiting docking step of fusion reactions and allowed direct observation of individual membrane-fusion events at SNARE densities as low as one pair per vesicle. With this platform, we confirmed at the single event level that, after docking of the templated-SUVs to supported lipid bilayers (SBL), one to two pairs of SNAREs are sufficient to drive fast lipid mixing. Modularity and programmability of this platform makes it readily amenable to studying more complicated systems where auxiliary proteins are involved.
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Affiliation(s)
| | - Bhavik Nathwani
- Wyss Institute for Biologically Inspired Engineering and Biological Chemistry and Molecular Pharmacology, Harvard Medical School, and Department of Cancer Biology, Dana Farber Cancer Institute , Boston, Massachusetts 02115, United States
| | - Chenxiang Lin
- Wyss Institute for Biologically Inspired Engineering and Biological Chemistry and Molecular Pharmacology, Harvard Medical School, and Department of Cancer Biology, Dana Farber Cancer Institute , Boston, Massachusetts 02115, United States
| | | | - Erdem Karatekin
- Laboratoire de Neurophotonique, Université Paris Descartes, Faculté des Sciences Fondamentales et Biomédicales, Centre National de la Recherche Scientifique (CNRS) UMR8250, 45, rue des Saints Pères, 75270 Cedex 06 Paris, France
| | - Frederic Pincet
- Laboratoire de Physique Statistique, Ecole Normale Supérieure de Paris, Université Pierre et Marie Curie, Université Paris Diderot, Centre National de la Recherche Scientifique, UMR 8550, 24 rue Lhomond, 75005 Paris, France
| | - William Shih
- Wyss Institute for Biologically Inspired Engineering and Biological Chemistry and Molecular Pharmacology, Harvard Medical School, and Department of Cancer Biology, Dana Farber Cancer Institute , Boston, Massachusetts 02115, United States
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49
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Fortoul N, Singh P, Hui CY, Bykhovskaia M, Jagota A. Coarse-Grained Model of SNARE-Mediated Docking. Biophys J 2016; 108:2258-69. [PMID: 25954883 DOI: 10.1016/j.bpj.2015.03.053] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2014] [Revised: 03/24/2015] [Accepted: 03/24/2015] [Indexed: 12/11/2022] Open
Abstract
Synaptic transmission requires that vesicles filled with neurotransmitter molecules be docked to the plasma membrane by the SNARE protein complex. The SNARE complex applies attractive forces to overcome the long-range repulsion between the vesicle and membrane. To understand how the balance between the attractive and repulsive forces defines the equilibrium docked state we have developed a model that combines the mechanics of vesicle/membrane deformation with an apparently new coarse-grained model of the SNARE complex. The coarse-grained model of the SNARE complex is calibrated by comparison with all-atom molecular dynamics simulations as well as by force measurements in laser tweezer experiments. The model for vesicle/membrane interactions includes the forces produced by membrane deformation and hydration or electrostatic repulsion. Combining these two parts, the coarse-grained model of the SNARE complex with membrane mechanics, we study how the equilibrium docked state varies with the number of SNARE complexes. We find that a single SNARE complex is able to bring a typical synaptic vesicle to within a distance of ∼ 3 nm from the membrane. Further addition of SNARE complexes shortens this distance, but an overdocked state of >4-6 SNAREs actually increases the equilibrium distance.
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Affiliation(s)
- Nicole Fortoul
- Department of Chemical and Biomolecular Engineering, Lehigh University, Bethlehem, Pennsylvania
| | - Pankaj Singh
- Department of Mechanical & Aerospace Engineering, Cornell University, Ithaca, New York
| | - Chung-Yuen Hui
- Department of Mechanical & Aerospace Engineering, Cornell University, Ithaca, New York
| | - Maria Bykhovskaia
- Neuroscience Department, Universidad Central del Caribe, Bayamon, Puerto Rico
| | - Anand Jagota
- Department of Chemical and Biomolecular Engineering, Lehigh University, Bethlehem, Pennsylvania; Bioengineering Program, Lehigh University, Bethlehem, Pennsylvania.
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50
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Kabachinski G, Kielar-Grevstad DM, Zhang X, James DJ, Martin TFJ. Resident CAPS on dense-core vesicles docks and primes vesicles for fusion. Mol Biol Cell 2016; 27:654-68. [PMID: 26700319 PMCID: PMC4750925 DOI: 10.1091/mbc.e15-07-0509] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2015] [Revised: 12/12/2015] [Accepted: 12/18/2015] [Indexed: 11/11/2022] Open
Abstract
The Ca(2+)-dependent exocytosis of dense-core vesicles in neuroendocrine cells requires a priming step during which SNARE protein complexes assemble. CAPS (aka CADPS) is one of several factors required for vesicle priming; however, the localization and dynamics of CAPS at sites of exocytosis in live neuroendocrine cells has not been determined. We imaged CAPS before, during, and after single-vesicle fusion events in PC12 cells by TIRF micro-scopy. In addition to being a resident on cytoplasmic dense-core vesicles, CAPS was present in clusters of approximately nine molecules near the plasma membrane that corresponded to docked/tethered vesicles. CAPS accompanied vesicles to the plasma membrane and was present at all vesicle exocytic events. The knockdown of CAPS by shRNA eliminated the VAMP-2-dependent docking and evoked exocytosis of fusion-competent vesicles. A CAPS(ΔC135) protein that does not localize to vesicles failed to rescue vesicle docking and evoked exocytosis in CAPS-depleted cells, showing that CAPS residence on vesicles is essential. Our results indicate that dense-core vesicles carry CAPS to sites of exocytosis, where CAPS promotes vesicle docking and fusion competence, probably by initiating SNARE complex assembly.
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Affiliation(s)
- Greg Kabachinski
- Department of Biochemistry, University of Wisconsin, Madison, WI 53706
| | | | - Xingmin Zhang
- Department of Biochemistry, University of Wisconsin, Madison, WI 53706
| | - Declan J James
- Department of Biochemistry, University of Wisconsin, Madison, WI 53706
| | - Thomas F J Martin
- Department of Biochemistry, University of Wisconsin, Madison, WI 53706
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