1
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Kádková A, Murach J, Østergaard M, Malsam A, Malsam J, Lolicato F, Nickel W, Söllner TH, Sørensen JB. SNAP25 disease mutations change the energy landscape for synaptic exocytosis due to aberrant SNARE interactions. eLife 2024; 12:RP88619. [PMID: 38411501 PMCID: PMC10911398 DOI: 10.7554/elife.88619] [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] [Indexed: 02/28/2024] Open
Abstract
SNAP25 is one of three neuronal SNAREs driving synaptic vesicle exocytosis. We studied three mutations in SNAP25 that cause epileptic encephalopathy: V48F, and D166Y in the synaptotagmin-1 (Syt1)-binding interface, and I67N, which destabilizes the SNARE complex. All three mutations reduced Syt1-dependent vesicle docking to SNARE-carrying liposomes and Ca2+-stimulated membrane fusion in vitro and when expressed in mouse hippocampal neurons. The V48F and D166Y mutants (with potency D166Y > V48F) led to reduced readily releasable pool (RRP) size, due to increased spontaneous (miniature Excitatory Postsynaptic Current, mEPSC) release and decreased priming rates. These mutations lowered the energy barrier for fusion and increased the release probability, which are gain-of-function features not found in Syt1 knockout (KO) neurons; normalized mEPSC release rates were higher (potency D166Y > V48F) than in the Syt1 KO. These mutations (potency D166Y > V48F) increased spontaneous association to partner SNAREs, resulting in unregulated membrane fusion. In contrast, the I67N mutant decreased mEPSC frequency and evoked EPSC amplitudes due to an increase in the height of the energy barrier for fusion, whereas the RRP size was unaffected. This could be partly compensated by positive charges lowering the energy barrier. Overall, pathogenic mutations in SNAP25 cause complex changes in the energy landscape for priming and fusion.
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Affiliation(s)
- Anna Kádková
- Department of Neuroscience, University of CopenhagenCopenhagenDenmark
| | | | - Maiken Østergaard
- Department of Neuroscience, University of CopenhagenCopenhagenDenmark
| | - Andrea Malsam
- Heidelberg University Biochemistry CenterHeidelbergDenmark
| | - Jörg Malsam
- Heidelberg University Biochemistry CenterHeidelbergDenmark
| | - Fabio Lolicato
- Heidelberg University Biochemistry CenterHeidelbergDenmark
- Department of Physics, University of HelsinkiHelsinkiFinland
| | - Walter Nickel
- Heidelberg University Biochemistry CenterHeidelbergDenmark
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2
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Li F, Grushin K, Coleman J, Pincet F, Rothman JE. Diacylglycerol-dependent hexamers of the SNARE-assembling chaperone Munc13-1 cooperatively bind vesicles. Proc Natl Acad Sci U S A 2023; 120:e2306086120. [PMID: 37883433 PMCID: PMC10623011 DOI: 10.1073/pnas.2306086120] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2023] [Accepted: 09/28/2023] [Indexed: 10/28/2023] Open
Abstract
Munc13-1 is essential for vesicle docking and fusion at the active zone of synapses. Here, we report that Munc13-1 self-assembles into molecular clusters within diacylglycerol-rich microdomains present in phospholipid bilayers. Although the copy number of Munc13-1 molecules in these clusters has a broad distribution, a systematic Poisson analysis shows that this is most likely the result of two molecular species: monomers and mainly hexameric oligomers. Each oligomer is able to capture one vesicle independently. Hexamers have also been observed in crystals of Munc13-1 that form between opposed phospholipid bilayers [K. Grushin, R. V. Kalyana Sundaram, C. V. Sindelar, J. E. Rothman, Proc. Natl. Acad. Sci. U.S.A. 119, e2121259119 (2022)]. Mutations targeting the contacts stabilizing the crystallographic hexagons also disrupt the isolated hexamers, suggesting they are identical. Additionally, these mutations also convert vesicle binding from a cooperative to progressive mode. Our study provides an independent approach showing that Munc13-1 can form mainly hexamers on lipid bilayers each capable of vesicle capture.
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Affiliation(s)
- Feng Li
- Department of Cell Biology, School of Medicine, Yale University, New Haven, CT06520
- Nanobiology Institute, School of Medicine, Yale University, West Haven, CT06516
| | - Kirill Grushin
- Department of Cell Biology, School of Medicine, Yale University, New Haven, CT06520
- Nanobiology Institute, School of Medicine, Yale University, West Haven, CT06516
| | - Jeff Coleman
- Department of Cell Biology, School of Medicine, Yale University, New Haven, CT06520
- Nanobiology Institute, School of Medicine, Yale University, West Haven, CT06516
| | - Frederic Pincet
- Department of Cell Biology, School of Medicine, Yale University, New Haven, CT06520
- Nanobiology Institute, School of Medicine, Yale University, West Haven, CT06516
- Laboratoire de Physique de l’Ecole normale supérieure, Département de Physique, Ecole Normale Supérieure, Université Paris Sciences & Lettres CNRS, Sorbonne Université, Université de Paris, ParisF-75005, France
| | - James E. Rothman
- Department of Cell Biology, School of Medicine, Yale University, New Haven, CT06520
- Nanobiology Institute, School of Medicine, Yale University, West Haven, CT06516
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3
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Zhang J, Guan M, Lv M, Liu Y, Zhang H, Zhang Z, Zhang K. Localized Imaging of Programmed Death-Ligand 1 on Individual Tumor-Derived Extracellular Vesicles for Prediction of Immunotherapy Response. ACS NANO 2023; 17:20120-20134. [PMID: 37819165 DOI: 10.1021/acsnano.3c05799] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/13/2023]
Abstract
Programmed death-ligand 1 (PD-L1) on tumor-derived small extracellular vesicles (EVs) is a biomarker for prediction of the immunotherapy response. However, conventional bulk measurement can hardly analyze the expression of PD-L1 on individual tumor-derived EVs. Herein, a method for localized imaging of tumor-derived individual EVs PD-L1 (LITIE) is developed. In this assay, EVs in plasma were directly captured on a biochip. Then the liposome-mediated membrane fusion strategy was used to image miR-21 in EVs to discriminate miR-21-positive EVs from the whole EVs populations. Subsequently, the primer exchange reaction (PER) is applied to generate localized and amplified fluorescent signals for imaging PD-L1 on identified tumor-derived EVs. When applied in clinical sample tests, the LITIE assay could effectively distinguish breast cancer patients from healthy donors or patients with benign tumors. Interestingly, in a mice melanoma model, the LITIE assay showed the ability to predict immunotherapy response even before drug treatment. Thus, we think the strategy of measuring individual tumor-derived EVs PD-L1 could serve as an alternative way for screening clinical responders suitable for immunotherapy.
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Affiliation(s)
- Junli Zhang
- School of Pharmaceutical Sciences, Zhengzhou University, Zhengzhou 450001, China
- Henan Key Laboratory of Targeting Therapy and Diagnosis for Critical Diseases, Zhengzhou 450001, China
| | - Mengting Guan
- School of Pharmaceutical Sciences, Zhengzhou University, Zhengzhou 450001, China
| | - Min Lv
- School of Pharmaceutical Sciences, Zhengzhou University, Zhengzhou 450001, China
| | - Yingying Liu
- School of Pharmaceutical Sciences, Zhengzhou University, Zhengzhou 450001, China
| | - Hongling Zhang
- School of Pharmaceutical Sciences, Zhengzhou University, Zhengzhou 450001, China
- Henan Key Laboratory of Targeting Therapy and Diagnosis for Critical Diseases, Zhengzhou 450001, China
| | - Zhenzhong Zhang
- School of Pharmaceutical Sciences, Zhengzhou University, Zhengzhou 450001, China
- Henan Key Laboratory of Targeting Therapy and Diagnosis for Critical Diseases, Zhengzhou 450001, China
| | - Kaixiang Zhang
- School of Pharmaceutical Sciences, Zhengzhou University, Zhengzhou 450001, China
- Henan Key Laboratory of Targeting Therapy and Diagnosis for Critical Diseases, Zhengzhou 450001, China
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4
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Nishad R, Betancourt-Solis M, Dey H, Heidelberger R, McNew JA. Regulation of Syntaxin3B-Mediated Membrane Fusion by T14, Munc18, and Complexin. Biomolecules 2023; 13:1463. [PMID: 37892145 PMCID: PMC10604575 DOI: 10.3390/biom13101463] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2023] [Revised: 09/22/2023] [Accepted: 09/26/2023] [Indexed: 10/29/2023] Open
Abstract
Retinal neurons that form ribbon-style synapses operate over a wide dynamic range, continuously relaying visual information to their downstream targets. The remarkable signaling abilities of these neurons are supported by specialized presynaptic machinery, one component of which is syntaxin3B. Syntaxin3B is an essential t-SNARE protein of photoreceptors and bipolar cells that is required for neurotransmitter release. It has a light-regulated phosphorylation site in its N-terminal domain at T14 that has been proposed to modulate membrane fusion. However, a direct test of the latter has been lacking. Using a well-controlled in vitro fusion assay, we found that a phosphomimetic T14 syntaxin3B mutation leads to a small but significant enhancement of SNARE-mediated membrane fusion following the formation of the t-SNARE complex. While the addition of Munc18a had only a minimal effect on membrane fusion mediated by SNARE complexes containing wild-type syntaxin3B, a more significant enhancement was observed in the presence of Munc18a when the SNARE complexes contained a syntaxin3B T14 phosphomimetic mutant. Finally, we showed that the retinal-specific complexins (Cpx III and Cpx IV) inhibited membrane fusion mediated by syntaxin3B-containing SNARE complexes in a dose-dependent manner. Collectively, our results establish that membrane fusion mediated by syntaxin3B-containing SNARE complexes is regulated by the T14 residue of syntaxin3B, Munc18a, and Cpxs III and IV.
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Affiliation(s)
- Rajkishor Nishad
- Department of BioSciences, Rice University, 6500 Main Street, MS 601, Houston, TX 77005, USA;
| | - Miguel Betancourt-Solis
- Department of BioSciences, Rice University, 6500 Main Street, MS 601, Houston, TX 77005, USA;
- Lonza Biologics, 14905 Kirby Dr, Houston, TX 77047, USA
| | - Himani Dey
- Department of Neurobiology and Anatomy, McGovern Medical School, The University of Texas Health Science Center, Houston (UTHealth Houston), 6431 Fannin Street, Houston, TX 77030, USA;
| | - Ruth Heidelberger
- Department of Neurobiology and Anatomy, McGovern Medical School, The University of Texas Health Science Center, Houston (UTHealth Houston), 6431 Fannin Street, Houston, TX 77030, USA;
| | - James A. McNew
- Department of BioSciences, Rice University, 6500 Main Street, MS 601, Houston, TX 77005, USA;
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5
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Zhang Z, Feng Z, Zhao X, Jean D, Yu Z, Chapman ER. Functionalization and higher-order organization of liposomes with DNA nanostructures. Nat Commun 2023; 14:5256. [PMID: 37644062 PMCID: PMC10465589 DOI: 10.1038/s41467-023-41013-2] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2023] [Accepted: 08/11/2023] [Indexed: 08/31/2023] Open
Abstract
Small unilamellar vesicles (SUVs) are indispensable model membranes, organelle mimics, and drug and vaccine carriers. However, the lack of robust techniques to functionalize or organize preformed SUVs limits their applications. Here we use DNA nanostructures to coat, cluster, and pattern sub-100-nm liposomes, generating distance-controlled vesicle networks, strings and dimers, among other configurations. The DNA coating also enables attachment of proteins to liposomes, and temporal control of membrane fusion driven by SNARE protein complexes. Such a convenient and versatile method of engineering premade vesicles both structurally and functionally is highly relevant to bottom-up biology and targeted delivery.
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Affiliation(s)
- Zhao Zhang
- Howard Hughes Medical Institute, Department of Neuroscience, University of Wisconsin-Madison, Madison, WI 53705, USA.
| | - Zhaomeng Feng
- Howard Hughes Medical Institute, Department of Neuroscience, University of Wisconsin-Madison, Madison, WI 53705, USA
| | - Xiaowei Zhao
- Howard Hughes Medical Institute, CryoEM Shared Resource, Janelia Research Campus, 19700 Helix Drive, Ashburn, VA 20147, USA
| | - Dominique Jean
- Howard Hughes Medical Institute, CryoEM Shared Resource, Janelia Research Campus, 19700 Helix Drive, Ashburn, VA 20147, USA
| | - Zhiheng Yu
- Howard Hughes Medical Institute, CryoEM Shared Resource, Janelia Research Campus, 19700 Helix Drive, Ashburn, VA 20147, USA
| | - Edwin R Chapman
- Howard Hughes Medical Institute, Department of Neuroscience, University of Wisconsin-Madison, Madison, WI 53705, USA.
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6
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Khvotchev M, Soloviev M. SNARE Modulators and SNARE Mimetic Peptides. Biomolecules 2022; 12:biom12121779. [PMID: 36551207 PMCID: PMC9776023 DOI: 10.3390/biom12121779] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2022] [Revised: 11/22/2022] [Accepted: 11/26/2022] [Indexed: 12/03/2022] Open
Abstract
The soluble N-ethylmaleimide-sensitive factor (NSF) attachment protein (SNAP) receptor (SNARE) proteins play a central role in most forms of intracellular membrane trafficking, a key process that allows for membrane and biocargo shuffling between multiple compartments within the cell and extracellular environment. The structural organization of SNARE proteins is relatively simple, with several intrinsically disordered and folded elements (e.g., SNARE motif, N-terminal domain, transmembrane region) that interact with other SNAREs, SNARE-regulating proteins and biological membranes. In this review, we discuss recent advances in the development of functional peptides that can modify SNARE-binding interfaces and modulate SNARE function. The ability of the relatively short SNARE motif to assemble spontaneously into stable coiled coil tetrahelical bundles has inspired the development of reduced SNARE-mimetic systems that use peptides for biological membrane fusion and for making large supramolecular protein complexes. We evaluate two such systems, based on peptide-nucleic acids (PNAs) and coiled coil peptides. We also review how the self-assembly of SNARE motifs can be exploited to drive on-demand assembly of complex re-engineered polypeptides.
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Affiliation(s)
- Mikhail Khvotchev
- Department of Biochemistry, Center for Neuroscience, Faculty of Science, Mahidol University, Bangkok 10400, Thailand
- Correspondence: (M.K.); (M.S.)
| | - Mikhail Soloviev
- Department of Biological Sciences, Royal Holloway University of London, Egham, Surrey TW20 0EX, UK
- Correspondence: (M.K.); (M.S.)
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7
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Kumar H, Jimah JR, Misal SA, Salinas ND, Fried M, Schlesinger PH, Tolia NH. Implications of conformational flexibility, lipid binding, and regulatory domains in cell traversal-protein CelTOS for apicomplexan migration. J Biol Chem 2022; 298:102241. [PMID: 35809642 PMCID: PMC9400078 DOI: 10.1016/j.jbc.2022.102241] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2022] [Revised: 06/29/2022] [Accepted: 07/05/2022] [Indexed: 12/04/2022] Open
Abstract
Malaria and other apicomplexan-caused diseases affect millions of humans, agricultural animals, and pets. Cell traversal is a common feature used by multiple apicomplexan parasites to migrate through host cells and can be exploited to develop therapeutics against these deadly parasites. Here, we provide insights into the mechanism of the Cell-traversal protein for ookinetes and sporozoites (CelTOS), a conserved cell-traversal protein in apicomplexan parasites and malaria vaccine candidate. CelTOS has previously been shown to form pores in cell membranes to enable traversal of parasites through cells. We establish roles for the distinct protein regions of Plasmodium vivax CelTOS and examine the mechanism of pore formation. We further demonstrate that CelTOS dimer dissociation is required for pore formation, as disulfide bridging between monomers inhibits pore formation, and this inhibition is rescued by disulfide-bridge reduction. We also show that a helix-destabilizing amino acid, Pro127, allows CelTOS to undergo significant conformational changes to assemble into pores. The flexible C terminus of CelTOS is a negative regulator that limits pore formation. Finally, we highlight that lipid binding is a prerequisite for pore assembly as mutation of a phospholipids-binding site in CelTOS resulted in loss of lipid binding and abrogated pore formation. These findings identify critical regions in CelTOS and will aid in understanding the egress mechanism of malaria and other apicomplexan parasites as well as have implications for studying the function of other essential pore-forming proteins.
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Affiliation(s)
- Hirdesh Kumar
- Host-Pathogen Interactions and Structural Vaccinology Section, Laboratory of Malaria Immunology and Vaccinology, National Institute of Allergy and Infectious Disease, National Institutes of Health Bethesda, Maryland
| | - John R Jimah
- Department of Molecular Biology, Princeton University, Princeton, NJ 08544
| | - Santosh A Misal
- Molecular Pathogenesis and Biomarkers Section, Laboratory of Malaria Immunology and Vaccinology, National Institute of Allergy and Infectious Disease, National Institutes of Health Bethesda, Maryland
| | - Nichole D Salinas
- Host-Pathogen Interactions and Structural Vaccinology Section, Laboratory of Malaria Immunology and Vaccinology, National Institute of Allergy and Infectious Disease, National Institutes of Health Bethesda, Maryland
| | - Michal Fried
- Molecular Pathogenesis and Biomarkers Section, Laboratory of Malaria Immunology and Vaccinology, National Institute of Allergy and Infectious Disease, National Institutes of Health Bethesda, Maryland
| | - Paul H Schlesinger
- Department of Cell Biology and Physiology, Washington, University School of Medicine, Saint Louis, United States
| | - Niraj H Tolia
- Host-Pathogen Interactions and Structural Vaccinology Section, Laboratory of Malaria Immunology and Vaccinology, National Institute of Allergy and Infectious Disease, National Institutes of Health Bethesda, Maryland.
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8
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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: 1] [Impact Index Per Article: 0.5] [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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9
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Molecular encoding and synaptic decoding of context during salt chemotaxis in C. elegans. Nat Commun 2022; 13:2928. [PMID: 35624091 PMCID: PMC9142520 DOI: 10.1038/s41467-022-30279-7] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2021] [Accepted: 04/25/2022] [Indexed: 01/21/2023] Open
Abstract
Animals navigate toward favorable locations using various environmental cues. However, the mechanism of how the goal information is encoded and decoded to generate migration toward the appropriate direction has not been clarified. Here, we describe the mechanism of migration towards a learned concentration of NaCl in Caenorhabditis elegans. In the salt-sensing neuron ASER, the difference between the experienced and currently perceived NaCl concentration is encoded as phosphorylation at Ser65 of UNC-64/Syntaxin 1 A through the protein kinase C(PKC-1) signaling pathway. The phosphorylation affects basal glutamate transmission from ASER, inducing the reversal of the postsynaptic response of reorientation-initiating neurons (i.e., from inhibitory to excitatory), guiding the animals toward the experienced concentration. This process, the decoding of the context, is achieved through the differential sensitivity of postsynaptic excitatory and inhibitory receptors. Our results reveal the mechanism of migration based on the synaptic plasticity that conceptually differs from the classical ones. The nematode C. elegans moves around to find an optimal environment. This work demonstrates how it can detect and move towards a previously learned salinity using the salt-sensing neuron ASER.
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10
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Hettich BF, Bader JJ, Leroux J. Encapsulation of Hydrophilic Compounds in Small Extracellular Vesicles: Loading Capacity and Impact on Vesicle Functions. Adv Healthc Mater 2022; 11:e2100047. [PMID: 33951319 DOI: 10.1002/adhm.202100047] [Citation(s) in RCA: 29] [Impact Index Per Article: 14.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2021] [Revised: 03/04/2021] [Indexed: 12/11/2022]
Abstract
Their natural functions in intercellular communication render extracellular vesicles (EV) highly attractive for drug delivery applications. However, the loading efficiency of present methods to incorporate particularly hydrophilic low molecular weight drugs of biomedical interest is largely unexplored, as is the impact these methods may have on the intrinsic structural and biological vesicle properties. Here, different methods are exploited to incorporate hydrophilic non-membrane permeable compounds into stem cell-derived small EV, and to assess the vesicle characteristics after the different loading processes. When comparing several methods head-to-head, the loading capacity increases in the order saponin ≤ sonication < fusion < freeze-thawing ≤ osmotic shock. Interestingly, the structural and biological functions of small EV are dependent on the applied encapsulation process, with the functional properties being altered at a greater extent. Therefore, the importance of including additional characterization parameters to probe alterations of the biological functionality of small EV is clearly demonstrated. Here, freeze-thawing and particularly the osmotic shock have proven to be the most appropriate methods for EV loading, as they achieve a high drug encapsulation and yet preserve the investigated structural and biological vesicle characteristics.
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Affiliation(s)
- Britta Franziska Hettich
- Institute of Pharmaceutical Sciences Department of Chemistry and Applied Biosciences ETH Zurich Zurich 8093 Switzerland
| | - Johannes Josua Bader
- Institute of Pharmaceutical Sciences Department of Chemistry and Applied Biosciences ETH Zurich Zurich 8093 Switzerland
| | - Jean‐Christophe Leroux
- Institute of Pharmaceutical Sciences Department of Chemistry and Applied Biosciences ETH Zurich Zurich 8093 Switzerland
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11
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Xia X, Wang Y, Qin Y, Zhao S, Zheng JC. Exosome: A novel neurotransmission modulator or non-canonical neurotransmitter? Ageing Res Rev 2022; 74:101558. [PMID: 34990846 DOI: 10.1016/j.arr.2021.101558] [Citation(s) in RCA: 27] [Impact Index Per Article: 13.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2021] [Revised: 08/13/2021] [Accepted: 12/30/2021] [Indexed: 02/08/2023]
Abstract
Neurotransmission is the electrical impulse-triggered propagation of signals between neurons or between neurons and other cell types such as skeletal muscle cells. Recent studies point out the involvement of exosomes, a type of small bilipid layer-enclosed extracellular vesicles, in regulating neurotransmission. Through horizontally transferring proteins, lipids, and nucleic acids, exosomes can modulate synaptic activities rapidly by controlling neurotransmitter release or progressively by regulating neural plasticity including synapse formation, neurite growth & removal, and axon guidance & elongation. In this review, we summarize the similarities and differences between exosomes and synaptic vesicles in their biogenesis, contents, and release. We also highlight the recent progress made in demonstrating the biological roles of exosome in regulating neurotransmission, and propose a modified model of neurotransmission, in which exosomes act as novel neurotransmitters. Lastly, we provide a comprehensive discussion of the enlightenment of the current knowledge on neurotransmission to the future directions of exosome research.
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12
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Piffoux M, Silva AKA, Gazeau F, Tareste D. Generation of Hybrid Extracellular Vesicles by Fusion with Functionalized Liposomes. Methods Mol Biol 2022; 2473:385-396. [PMID: 35819777 DOI: 10.1007/978-1-0716-2209-4_24] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
Extracellular vesicles (EVs) and liposomes are natural and synthetic drug delivery systems, respectively, with their own advantages and limitations. EV/liposome fusion allows the generation of hybrid EVs that benefit from both the versatility of liposomes (tunable lipid and protein composition, surface functionalization, lumen loading, etc.) and the functionality of EVs (natural targeting properties, low immunogenicity, anti-inflammatory properties, etc.). Here, we describe the methods to (1) produce EVs and liposomes, (2) induce and monitor their fusion, and (3) purify the obtained hybrid EVs.
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Affiliation(s)
- Max Piffoux
- Laboratoire Matières et Systèmes Complexes, CNRS UMR 7057, Université de Paris, Paris, France
- Interaction Cellules Souches-Niches: Physiologie, Tumeurs Et Réparation Tissulaire, Inserm UMR 1197, Université Paris-Saclay, Villejuif, France
- Département d'oncologie Médicale, Centre Léon Bérard, Lyon, France
- Oncology Department, CITOHL, Lyon-Sud Hospital, Cancer Institute of Hospices Civils de Lyon (IC-HCL), Hospices Civils de Lyon, Lyon, France
| | | | - Florence Gazeau
- Laboratoire Matières et Systèmes Complexes, CNRS UMR 7057, Université de Paris, Paris, France
| | - David Tareste
- Institut de Psychiatrie et Neurosciences de Paris, Inserm UMR 1266, Université de Paris, Paris, France.
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13
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François-Martin C, Bacle A, Rothman JE, Fuchs PFJ, Pincet F. Cooperation of Conical and Polyunsaturated Lipids to Regulate Initiation and Processing of Membrane Fusion. Front Mol Biosci 2021; 8:763115. [PMID: 34746239 PMCID: PMC8566721 DOI: 10.3389/fmolb.2021.763115] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2021] [Accepted: 09/23/2021] [Indexed: 12/03/2022] Open
Abstract
The shape of lipids has long been suspected to be a critical determinant for the control of membrane fusion. To experimentally test this assertion, we used conical and malleable lipids and measured their influence on the fusion kinetics. We found that, as previously suspected, both types of lipids accelerate fusion. However, the implicated molecular mechanisms are strikingly different. Malleable lipids, with their ability to change shape with low energy cost, favor fusion by decreasing the overall activation energy. On the other hand, conical lipids, with their small polar head relative to the area occupied by the hydrophobic chains, tend to make fusion less energetically advantageous because they tend to migrate towards the most favorable lipid leaflet, hindering fusion pore opening. They could however facilitate fusion by generating hydrophobic defects on the membranes; this is suggested by the similar trend observed between the experimental rate of fusion nucleation and the surface occupied by hydrophobic defects obtained by molecular simulations. The synergy of dual-process, activation energy and nucleation kinetics, could facilitate membrane fusion regulation in vivo.
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Affiliation(s)
- Claire François-Martin
- Laboratoire de Physique de l'Ecole Normale Supérieure, ENS, CNRS, Université PSL, Sorbonne Université, Université de Paris, Paris, France
| | - Amélie Bacle
- Laboratoire Coopératif "Lipotoxicity and Channelopathies-ConicMeds", Université de Poitiers, Poitiers, France
| | - James E Rothman
- Department of Cell Biology, School of Medicine, Yale University, New Haven, CT, United States.,Nanobiology Institute, Yale School of Medicine, West Haven, CT, United States
| | - Patrick F J Fuchs
- Laboratoire des Biomolécules (LBM), CNRS, Ecole Normale Supérieure, Sorbonne Université, PSL Research University, Paris, France.,UFR Sciences Du Vivant, Université de Paris, Paris, France
| | - Frédéric Pincet
- Laboratoire de Physique de l'Ecole Normale Supérieure, ENS, CNRS, Université PSL, Sorbonne Université, Université de Paris, Paris, France
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14
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Li F, Kalyana Sundaram RV, Gatta AT, Coleman J, Ramakrishnan S, Krishnakumar SS, Pincet F, Rothman JE. Vesicle capture by membrane-bound Munc13-1 requires self-assembly into discrete clusters. FEBS Lett 2021; 595:2185-2196. [PMID: 34227103 DOI: 10.1002/1873-3468.14157] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2021] [Revised: 06/15/2021] [Accepted: 06/29/2021] [Indexed: 12/11/2022]
Abstract
Munc13-1 is a large banana-shaped soluble protein that is involved in the regulation of synaptic vesicle docking and fusion. Recent studies suggest that multiple copies of Munc13-1 form nano-assemblies in active zones of neurons. However, it is not known whether such clustering of Munc13-1 is correlated with multivalent binding to synaptic vesicles or specific plasma membrane domains at docking sites in the active zone. The functional significance of putative Munc13-1 clustering is also unknown. Here, we report that nano-clustering is an inherent property of Munc13-1 and is indeed required for vesicle binding to bilayers containing Munc13-1. Purified Munc13-1 protein reconstituted onto supported lipid bilayers assembled into clusters containing from 2 to ˜ 20 copies as revealed by a combination of quantitative TIRF microscopy and step-wise photobleaching. Surprisingly, only clusters containing a minimum of 6 copies of Munc13-1 were capable of efficiently capturing and retaining small unilamellar vesicles. The C-terminal C2 C domain of Munc13-1 is not required for Munc13-1 clustering, but is required for efficient vesicle capture. This capture is largely due to a combination of electrostatic and hydrophobic interactions between the C2 C domain and the vesicle membrane.
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Affiliation(s)
- Feng Li
- Department of Cell Biology, School of Medicine, Yale University, New Haven, CT, USA
- Nanobiology Institute, Yale School of Medicine, West Haven, CT, USA
| | - Ramalingam Venkat Kalyana Sundaram
- Department of Cell Biology, School of Medicine, Yale University, New Haven, CT, USA
- Nanobiology Institute, Yale School of Medicine, West Haven, CT, USA
| | - Alberto T Gatta
- Department of Cell Biology, School of Medicine, Yale University, New Haven, CT, USA
- Nanobiology Institute, Yale School of Medicine, West Haven, CT, USA
| | - Jeff Coleman
- Department of Cell Biology, School of Medicine, Yale University, New Haven, CT, USA
- Nanobiology Institute, Yale School of Medicine, West Haven, CT, USA
| | - Sathish Ramakrishnan
- Department of Cell Biology, School of Medicine, Yale University, New Haven, CT, USA
- Nanobiology Institute, Yale School of Medicine, West Haven, CT, USA
| | - Shyam S Krishnakumar
- Department of Cell Biology, School of Medicine, Yale University, New Haven, CT, USA
- Nanobiology Institute, Yale School of Medicine, West Haven, CT, USA
| | - Frederic Pincet
- Department of Cell Biology, School of Medicine, Yale University, New Haven, CT, USA
- Nanobiology Institute, Yale School of Medicine, West Haven, CT, USA
- Laboratoire de Physique de l'Ecole normale supérieure, ENS, Université PSL, CNRS, Sorbonne Université, Université de Paris, Paris, France
| | - James E Rothman
- Department of Cell Biology, School of Medicine, Yale University, New Haven, CT, USA
- Nanobiology Institute, Yale School of Medicine, West Haven, CT, USA
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15
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Complexin Suppresses Spontaneous Exocytosis by Capturing the Membrane-Proximal Regions of VAMP2 and SNAP25. Cell Rep 2021; 32:107926. [PMID: 32698012 PMCID: PMC7116205 DOI: 10.1016/j.celrep.2020.107926] [Citation(s) in RCA: 27] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2019] [Revised: 02/28/2020] [Accepted: 06/26/2020] [Indexed: 01/29/2023] Open
Abstract
The neuronal protein complexin contains multiple domains that exert clamping and facilitatory functions to tune spontaneous and action potential-triggered synaptic release. We address the clamping mechanism and show that the accessory helix of complexin arrests assembly of the soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complex that forms the core machinery of intracellular membrane fusion. In a reconstituted fusion assay, site-and stage-specific photo-cross-linking reveals that, prior to fusion, the complexin accessory helix laterally binds the membrane-proximal C-terminal ends of SNAP25 and VAMP2. Corresponding complexin interface mutants selectively increase spontaneous release of neuro-transmitters in living neurons, implying that the accessory helix suppresses final zippering/assembly of the SNARE four-helix bundle by restraining VAMP2 and SNAP25.
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16
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Sorting sub-150-nm liposomes of distinct sizes by DNA-brick-assisted centrifugation. Nat Chem 2021; 13:335-342. [PMID: 33785892 PMCID: PMC8049973 DOI: 10.1038/s41557-021-00667-5] [Citation(s) in RCA: 27] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2020] [Accepted: 02/23/2021] [Indexed: 02/01/2023]
Abstract
In cells, myriad membrane-interacting proteins generate and maintain curved membrane domains with radii of curvature around or below 50 nm. To understand how such highly curved membranes modulate specific protein functions, and vice versa, it is imperative to use small liposomes with precisely defined attributes as model membranes. Here, we report a versatile and scalable sorting technique that uses cholesterol-modified DNA 'nanobricks' to differentiate hetero-sized liposomes by their buoyant densities. This method separates milligrams of liposomes, regardless of their origins and chemical compositions, into six to eight homogeneous populations with mean diameters of 30-130 nm. We show that these uniform, leak-resistant liposomes serve as ideal substrates to study, with an unprecedented resolution, how membrane curvature influences peripheral (ATG3) and integral (SNARE) membrane protein activities. Compared with conventional methods, our sorting technique represents a streamlined process to achieve superior liposome size uniformity, which benefits research in membrane biology and the development of liposomal drug-delivery systems.
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17
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Ruiter M, Kádková A, Scheutzow A, Malsam J, Söllner TH, Sørensen JB. An Electrostatic Energy Barrier for SNARE-Dependent Spontaneous and Evoked Synaptic Transmission. Cell Rep 2020; 26:2340-2352.e5. [PMID: 30811985 DOI: 10.1016/j.celrep.2019.01.103] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2018] [Revised: 11/05/2018] [Accepted: 01/28/2019] [Indexed: 12/22/2022] Open
Abstract
Information transfer across CNS synapses depends on the very low basal vesicle fusion rate and the ability to rapidly upregulate that rate upon Ca2+ influx. We show that local electrostatic repulsion participates in creating an energy barrier, which limits spontaneous synaptic transmission. The barrier amplitude is increased by negative charges and decreased by positive charges on the SNARE-complex surface. Strikingly, the effect of charges on the barrier is additive and this extends to evoked transmission, but with a shallower charge dependence. Action potential-driven synaptic release is equivalent to the abrupt addition of ∼35 positive charges to the fusion machine. Within an electrostatic model for triggering, the Ca2+ sensor synaptotagmin-1 contributes ∼18 charges by binding Ca2+, while also modulating the fusion barrier at rest. Thus, the energy barrier for synaptic vesicle fusion has a large electrostatic component, allowing synaptotagmin-1 to act as an electrostatic switch and modulator to trigger vesicle fusion.
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Affiliation(s)
- Marvin Ruiter
- Department of Neuroscience, Faculty of Health and Medical Sciences, 2200 Copenhagen N, University of Copenhagen, Copenhagen, Denmark
| | - Anna Kádková
- Department of Neuroscience, Faculty of Health and Medical Sciences, 2200 Copenhagen N, University of Copenhagen, Copenhagen, Denmark
| | - Andrea Scheutzow
- Heidelberg University Biochemistry Center, 69120 Heidelberg, Germany
| | - Jörg Malsam
- Heidelberg University Biochemistry Center, 69120 Heidelberg, Germany
| | - Thomas H Söllner
- Heidelberg University Biochemistry Center, 69120 Heidelberg, Germany
| | - Jakob B Sørensen
- Department of Neuroscience, Faculty of Health and Medical Sciences, 2200 Copenhagen N, University of Copenhagen, Copenhagen, Denmark.
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18
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Zhang H, Yan H, Shim WB. Fusarium verticillioides SNARE protein FvSyn1 harbours two key functional motifs that play selective roles in fungal development and virulence. MICROBIOLOGY-SGM 2019; 165:1075-1085. [PMID: 31390325 DOI: 10.1099/mic.0.000843] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Fusarium verticillioides is one of the key fungal pathogens responsible for maize stalk rot. While stalk rot pathogens are prevalent worldwide, our understanding of the stalk rot virulence mechanism in pathogenic fungi is still very limited. We previously identified the F. verticillioides FvSYN1 gene, which was demonstrated to play an important role in maize stalk rot virulence. FvSyn1 belongs to a family of soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) proteins that play critical roles in a variety of developmental processes. In this study, we further characterized the cellular features of the FvSyn1 protein, namely how different motifs contribute to development and virulence in F. verticillioides by generating motif-specific deletion mutants. Microscopic observation showed that the ∆Fvsyn1 mutant exhibits rough and hyper-branched hyphae when compared to the wild-type progenitor. Moreover, the ∆Fvsyn1 mutant was sensitive to cell wall stress agents, resulting in vegetative growth reduction. We showed that the FvSyn1::GFP protein is associated with the endomembrane, but this did not clarify why the deletion of FvSyn1 led to stress sensitivity and aberrant hyphal development. Characterization of the FvSyn1 domains indicated that both the syntaxin N-terminus (SynN) domain and the SNARE C-terminus domain play distinct roles in fungal development, but also function collectively in the context of virulence. We also determined that two domains in FvSyn1 are not required for fumonisin production. Interestingly, these two domains were involved in carbon nutrient utilization, including pectin, starch and sorbitol. This study further characterized the role of FvSyn1 domains in hyphal growth, cell wall stress response and virulence in F. verticillioides.
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Affiliation(s)
- Huan Zhang
- Department of Plant Pathology and Microbiology, Texas A&M University, College Station, TX 77843, USA
| | - Huijuan Yan
- Department of Plant Pathology and Microbiology, Texas A&M University, College Station, TX 77843, USA
| | - Won Bo Shim
- Department of Plant Pathology and Microbiology, Texas A&M University, College Station, TX 77843, USA
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19
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Shaaban A, Dhara M, Frisch W, Harb A, Shaib AH, Becherer U, Bruns D, Mohrmann R. The SNAP-25 linker supports fusion intermediates by local lipid interactions. eLife 2019; 8:41720. [PMID: 30883328 PMCID: PMC6422494 DOI: 10.7554/elife.41720] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2018] [Accepted: 03/05/2019] [Indexed: 12/22/2022] Open
Abstract
SNAP-25 is an essential component of SNARE complexes driving fast Ca2+-dependent exocytosis. Yet, the functional implications of the tandem-like structure of SNAP-25 are unclear. Here, we have investigated the mechanistic role of the acylated “linker” domain that concatenates the two SNARE motifs within SNAP-25. Refuting older concepts of an inert connector, our detailed structure-function analysis in murine chromaffin cells demonstrates that linker motifs play a crucial role in vesicle priming, triggering, and fusion pore expansion. Mechanistically, we identify two synergistic functions of the SNAP-25 linker: First, linker motifs support t-SNARE interactions and accelerate ternary complex assembly. Second, the acylated N-terminal linker segment engages in local lipid interactions that facilitate fusion triggering and pore evolution, putatively establishing a favorable membrane configuration by shielding phospholipid headgroups and affecting curvature. Hence, the linker is a functional part of the fusion complex that promotes secretion by SNARE interactions as well as concerted lipid interplay.
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Affiliation(s)
- Ahmed Shaaban
- ZHMB, Saarland University, Homburg, Germany.,Department of Molecular Neurobiology, Max Planck Institute for Experimental Medicine, Göttingen, Germany
| | - Madhurima Dhara
- Institute for Physiology, Center of Integrative Physiology and Molecular Medicine, Saarland University, Homburg, Germany
| | - Walentina Frisch
- Institute for Physiology, Center of Integrative Physiology and Molecular Medicine, Saarland University, Homburg, Germany
| | - Ali Harb
- ZHMB, Saarland University, Homburg, Germany
| | - Ali H Shaib
- Department of Molecular Neurobiology, Max Planck Institute for Experimental Medicine, Göttingen, Germany
| | - Ute Becherer
- Institute for Physiology, Center of Integrative Physiology and Molecular Medicine, Saarland University, Homburg, Germany
| | - Dieter Bruns
- Institute for Physiology, Center of Integrative Physiology and Molecular Medicine, Saarland University, Homburg, Germany
| | - Ralf Mohrmann
- ZHMB, Saarland University, Homburg, Germany.,Institute for Physiology, Otto-von-Guericke University, Magdeburg, Germany.,Center for Behavioral Brain Science, Otto-von-Guericke University, Magdeburg, Germany
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20
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Molecular mechanism of fusion pore formation driven by the neuronal SNARE complex. Proc Natl Acad Sci U S A 2018; 115:12751-12756. [PMID: 30482862 DOI: 10.1073/pnas.1816495115] [Citation(s) in RCA: 38] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Release of neurotransmitters from synaptic vesicles begins with a narrow fusion pore, the structure of which remains unresolved. To obtain a structural model of the fusion pore, we performed coarse-grained molecular dynamics simulations of fusion between a nanodisc and a planar bilayer bridged by four partially unzipped SNARE complexes. The simulations revealed that zipping of SNARE complexes pulls the polar C-terminal residues of the synaptobrevin 2 and syntaxin 1A transmembrane domains to form a hydrophilic core between the two distal leaflets, inducing fusion pore formation. The estimated conductances of these fusion pores are in good agreement with experimental values. Two SNARE protein mutants inhibiting fusion experimentally produced no fusion pore formation. In simulations in which the nanodisc was replaced by a 40-nm vesicle, an extended hemifusion diaphragm formed but a fusion pore did not, indicating that restricted SNARE mobility is required for rapid fusion pore formation. Accordingly, rapid fusion pore formation also occurred in the 40-nm vesicle system when SNARE mobility was restricted by external forces. Removal of the restriction is required for fusion pore expansion.
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21
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Phosphorylation of ULK1 affects autophagosome fusion and links chaperone-mediated autophagy to macroautophagy. Nat Commun 2018; 9:3492. [PMID: 30154410 PMCID: PMC6113293 DOI: 10.1038/s41467-018-05449-1] [Citation(s) in RCA: 110] [Impact Index Per Article: 18.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2016] [Accepted: 04/12/2018] [Indexed: 11/09/2022] Open
Abstract
The Unc-51 like autophagy activating kinase 1 (ULK1) complex plays a central role in the initiation stage of autophagy. However, the function of ULK1 in the late stage of autophagy is unknown. Here, we report that ULK1, a central kinase of the ULK1 complex involved in autophagy initiation, promotes autophagosome–lysosome fusion. PKCα phosphorylates ULK1 and prevents autolysosome formation. PKCα phosphorylation of ULK1 does not change its kinase activity; however, it decreases autophagosome–lysosome fusion by reducing the affinity of ULK1 for syntaxin 17 (STX17). Unphosphorylated ULK1 recruited STX17 and increased STX17′s affinity towards synaptosomal-associated protein 29 (SNAP29). Additionally, phosphorylation of ULK1 enhances its interaction with heat shock cognate 70 kDa protein (HSC70) and increases its degradation through chaperone-mediated autophagy (CMA). Our study unearths a key mechanism underlying autolysosome formation, a process in which the kinase activity of PKCα plays an instrumental role, and reveals the significance of the mutual regulation of macroautophagy and CMA in maintaining the balance of autophagy. The ULK complex plays a well-known role in initiating autophagy, to recycle cellular components in response to nutritional stress. Here, the authors demonstrate a late role for ULK in auotophagosome–lysosome fusion and provide a direct link between macroautophagy and chaperone mediated autophagy.
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22
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Piffoux M, Silva AKA, Wilhelm C, Gazeau F, Tareste D. Modification of Extracellular Vesicles by Fusion with Liposomes for the Design of Personalized Biogenic Drug Delivery Systems. ACS NANO 2018; 12:6830-6842. [PMID: 29975503 DOI: 10.1021/acsnano.8b02053] [Citation(s) in RCA: 244] [Impact Index Per Article: 40.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/12/2023]
Abstract
Extracellular vesicles (EVs) are recognized as nature's own carriers to transport macromolecules throughout the body. Hijacking this endogenous communication system represents an attractive strategy for advanced drug delivery. However, efficient and reproducible loading of EVs with therapeutic or imaging agents still represents a bottleneck for their use as a drug delivery system. Here, we developed a method for modifying cell-derived EVs through their fusion with liposomes containing both membrane and soluble cargoes. The fusion of EVs with functionalized liposomes was triggered by polyethylene glycol (PEG) to create smart biosynthetic hybrid vectors. This versatile method proved to be efficient to enrich EVs with exogenous lipophilic or hydrophilic compounds, while preserving their intrinsic content and biological properties. Hybrid EVs improved cellular delivery efficiency of a chemotherapeutic compound by a factor of 3-4, as compared to the free drug or the drug-loaded liposome precursor. On one side, this method allows the biocamouflage of liposomes by enriching their lipid bilayer and inner compartment with biogenic molecules. On the other side, the proposed fusion strategy enables efficient EV loading, and the pharmaceutical development of EVs with adaptable activity and drug delivery property.
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Affiliation(s)
- Max Piffoux
- Laboratoire Matière et Systèmes Complexes , Université Paris Diderot, Sorbonne Paris Cité , CNRS UMR 7057, F-75013 Paris , France
| | - Amanda K A Silva
- Laboratoire Matière et Systèmes Complexes , Université Paris Diderot, Sorbonne Paris Cité , CNRS UMR 7057, F-75013 Paris , France
| | - Claire Wilhelm
- Laboratoire Matière et Systèmes Complexes , Université Paris Diderot, Sorbonne Paris Cité , CNRS UMR 7057, F-75013 Paris , France
| | - Florence Gazeau
- Laboratoire Matière et Systèmes Complexes , Université Paris Diderot, Sorbonne Paris Cité , CNRS UMR 7057, F-75013 Paris , France
| | - David Tareste
- Institut Jacques Monod , Université Paris Diderot, Sorbonne Paris Cité , CNRS UMR 7592, F-75013 Paris , France
- Centre de Psychiatrie et Neurosciences , Université Paris Descartes, Sorbonne Paris Cité , INSERM UMR 894, F-75014 Paris , France
- Membrane Traffic in Health and Disease , Université Paris Descartes, Sorbonne Paris Cité , INSERM ERL U950, F-75014 Paris , France
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23
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Daste F, Sauvanet C, Bavdek A, Baye J, Pierre F, Le Borgne R, David C, Rojo M, Fuchs P, Tareste D. The heptad repeat domain 1 of Mitofusin has membrane destabilization function in mitochondrial fusion. EMBO Rep 2018; 19:embr.201643637. [PMID: 29661855 DOI: 10.15252/embr.201643637] [Citation(s) in RCA: 32] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2016] [Revised: 03/07/2018] [Accepted: 03/16/2018] [Indexed: 12/31/2022] Open
Abstract
Mitochondria are double-membrane-bound organelles that constantly change shape through membrane fusion and fission. Outer mitochondrial membrane fusion is controlled by Mitofusin, whose molecular architecture consists of an N-terminal GTPase domain, a first heptad repeat domain (HR1), two transmembrane domains, and a second heptad repeat domain (HR2). The mode of action of Mitofusin and the specific roles played by each of these functional domains in mitochondrial fusion are not fully understood. Here, using a combination of in situ and in vitro fusion assays, we show that HR1 induces membrane fusion and possesses a conserved amphipathic helix that folds upon interaction with the lipid bilayer surface. Our results strongly suggest that HR1 facilitates membrane fusion by destabilizing the lipid bilayer structure, notably in membrane regions presenting lipid packing defects. This mechanism for fusion is thus distinct from that described for the heptad repeat domains of SNARE and viral proteins, which assemble as membrane-bridging complexes, triggering close membrane apposition and fusion, and is more closely related to that of the C-terminal amphipathic tail of the Atlastin protein.
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Affiliation(s)
- Frédéric Daste
- Membrane Traffic in Health & Disease, INSERM ERL U950, Sorbonne Paris Cité, Université Paris Descartes, Paris, France.,Institut Jacques Monod, CNRS UMR 7592, Sorbonne Paris Cité, Université Paris Diderot, Paris, France
| | - Cécile Sauvanet
- Institut de Biochimie et Génétique Cellulaires, CNRS UMR 5095, Université de Bordeaux, Bordeaux, France
| | - Andrej Bavdek
- Membrane Traffic in Health & Disease, INSERM ERL U950, Sorbonne Paris Cité, Université Paris Descartes, Paris, France.,Institut Jacques Monod, CNRS UMR 7592, Sorbonne Paris Cité, Université Paris Diderot, Paris, France
| | - James Baye
- Membrane Traffic in Health & Disease, INSERM ERL U950, Sorbonne Paris Cité, Université Paris Descartes, Paris, France.,Institut Jacques Monod, CNRS UMR 7592, Sorbonne Paris Cité, Université Paris Diderot, Paris, France
| | - Fabienne Pierre
- Membrane Traffic in Health & Disease, INSERM ERL U950, Sorbonne Paris Cité, Université Paris Descartes, Paris, France.,Institut Jacques Monod, CNRS UMR 7592, Sorbonne Paris Cité, Université Paris Diderot, Paris, France.,Centre de Psychiatrie et Neurosciences, INSERM UMR 894, Sorbonne Paris Cité, Université Paris Descartes, Paris, France
| | - Rémi Le Borgne
- Institut Jacques Monod, CNRS UMR 7592, Sorbonne Paris Cité, Université Paris Diderot, Paris, France
| | - Claudine David
- Institut de Biochimie et Génétique Cellulaires, CNRS UMR 5095, Université de Bordeaux, Bordeaux, France
| | - Manuel Rojo
- Institut de Biochimie et Génétique Cellulaires, CNRS UMR 5095, Université de Bordeaux, Bordeaux, France
| | - Patrick Fuchs
- Institut Jacques Monod, CNRS UMR 7592, Sorbonne Paris Cité, Université Paris Diderot, Paris, France
| | - David Tareste
- Membrane Traffic in Health & Disease, INSERM ERL U950, Sorbonne Paris Cité, Université Paris Descartes, Paris, France .,Institut Jacques Monod, CNRS UMR 7592, Sorbonne Paris Cité, Université Paris Diderot, Paris, France.,Centre de Psychiatrie et Neurosciences, INSERM UMR 894, Sorbonne Paris Cité, Université Paris Descartes, Paris, France
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24
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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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25
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François-Martin C, Pincet F. Actual fusion efficiency in the lipid mixing assay - Comparison between nanodiscs and liposomes. Sci Rep 2017; 7:43860. [PMID: 28266607 PMCID: PMC5339690 DOI: 10.1038/srep43860] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2016] [Accepted: 01/31/2017] [Indexed: 01/19/2023] Open
Abstract
Lipid exchange occurs between membranes during fusion or active lipid transfer. These processes are necessary in vivo for the homeostasis of the cell at the level of the membranes, the organelles and the cell itself. They are also used by the cell to interact with the surrounding medium. Several assays have been developed to characterize in vitro these processes on model systems. The most common one, relying on fluorescence dequenching, measures lipid mixing between small membranes such as liposomes or nanodiscs in bulk. Usually, relative comparisons of the rate of lipid exchange are made between measurements performed in parallel. Here, we establish a quantitative standardization of this assay to avoid any bias resulting from the temperatures, the chosen fluorescent lipid fractions and from the various detergents used to normalize the measurements. We used this standardization to quantitatively compare the efficiency of SNARE-induced fusion in liposome-liposome and liposome-nanodisc configurations having similar collision frequency. We found that the initial yield of fusion is comparable in both cases, 1 per 2-3 million collisions in spite of a much larger dequenching signal with nanodiscs. Also, the long-term actual fusion rate is slightly lower with nanodiscs than in the liposome-liposome assay.
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Affiliation(s)
- Claire François-Martin
- Laboratoire de Physique Statistique, Ecole Normale Supérieure, Paris Sciences et Lettres Research University, 75005, Paris, France.,Laboratoire de Physique Statistique, Université Paris Diderot Sorbonne Paris Cité, 75005, Paris, France.,Laboratoire de Physique Statistique, Sorbonne Universités, Université Pierre et Marie Curie, Univ Paris 06, CNRS, 75005, Paris, France.,Laboratoire de Physique Statistique, Ecole Normale Supérieure, Paris Sciences et Lettres Research University, 75005, Paris, France
| | - Frédéric Pincet
- Laboratoire de Physique Statistique, Ecole Normale Supérieure, Paris Sciences et Lettres Research University, 75005, Paris, France.,Laboratoire de Physique Statistique, Université Paris Diderot Sorbonne Paris Cité, 75005, Paris, France.,Laboratoire de Physique Statistique, Sorbonne Universités, Université Pierre et Marie Curie, Univ Paris 06, CNRS, 75005, Paris, France.,Laboratoire de Physique Statistique, Ecole Normale Supérieure, Paris Sciences et Lettres Research University, 75005, Paris, France
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26
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Abstract
Membrane fusion is the cell's delivery process, enabling its many compartments to receive cargo and machinery for cell growth and intercellular communication. The overall activation energy of the process must be large enough to prevent frequent and nonspecific spontaneous fusion events, yet must be low enough to allow it to be overcome upon demand by specific fusion proteins [such as soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs)]. Remarkably, to the best of our knowledge, the activation energy for spontaneous bilayer fusion has never been measured. Multiple models have been developed and refined to estimate the overall activation energy and its component parts, and they span a very broad range from 20 kBT to 150 kBT, depending on the assumptions. In this study, using a bulk lipid-mixing assay at various temperatures, we report that the activation energy of complete membrane fusion is at the lowest range of these theoretical values. Typical lipid vesicles were found to slowly and spontaneously fully fuse with activation energies of ∼30 kBT Our data demonstrate that the merging of membranes is not nearly as energy consuming as anticipated by many models and is ideally positioned to minimize spontaneous fusion while enabling rapid, SNARE-dependent fusion upon demand.
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Yue P, Zhang Y, Mei K, Wang S, Lesigang J, Zhu Y, Dong G, Guo W. Sec3 promotes the initial binary t-SNARE complex assembly and membrane fusion. Nat Commun 2017; 8:14236. [PMID: 28112172 PMCID: PMC5267525 DOI: 10.1038/ncomms14236] [Citation(s) in RCA: 57] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2015] [Accepted: 12/12/2016] [Indexed: 01/04/2023] Open
Abstract
The soluble N-ethylmaleimide-sensitive factor-attachment protein receptors (SNAREs) constitute the core machinery for membrane fusion during eukaryotic cell vesicular trafficking. However, how the assembly of the SNARE complex is initiated is unknown. Here we report that Sec3, a component of the exocyst complex that mediates vesicle tethering during exocytosis, directly interacts with the t-SNARE protein Sso2. This interaction promotes the formation of an Sso2-Sec9 'binary' t-SNARE complex, the early rate-limiting step in SNARE complex assembly, and stimulates membrane fusion. The crystal structure of the Sec3-Sso2 complex suggests that Sec3 binding induces conformational changes of Sso2 that are crucial for the relief of its auto-inhibition. Interestingly, specific disruption of the Sec3-Sso2 interaction in cells blocks exocytosis without affecting the function of Sec3 in vesicle tethering. Our study reveals an activation mechanism for SNARE complex assembly, and uncovers a role of the exocyst in promoting membrane fusion in addition to vesicle tethering.
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Affiliation(s)
- Peng Yue
- Department of Biology, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
| | - Yubo Zhang
- Department of Medical Biochemistry, Max F. Perutz Laboratories, Medical University of Vienna, 1030 Vienna, Austria
| | - Kunrong Mei
- Department of Biology, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
| | - Shaoxiao Wang
- Department of Biology, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
| | - Johannes Lesigang
- Department of Medical Biochemistry, Max F. Perutz Laboratories, Medical University of Vienna, 1030 Vienna, Austria
| | - Yueyao Zhu
- Department of Biology, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
| | - Gang Dong
- Department of Medical Biochemistry, Max F. Perutz Laboratories, Medical University of Vienna, 1030 Vienna, Austria
| | - Wei Guo
- Department of Biology, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
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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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Motta I, Gohlke A, Adrien V, Li F, Gardavot H, Rothman JE, Pincet F. Formation of Giant Unilamellar Proteo-Liposomes by Osmotic Shock. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2015; 31:7091-7099. [PMID: 26038815 PMCID: PMC4950989 DOI: 10.1021/acs.langmuir.5b01173] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
Giant unilamellar vesicles (GUVs), composed of a phospholipid bilayer, are often used as a model system for cell membranes. However, the study of proteo-membrane interactions in this system is limited as the incorporation of integral and lipid-anchored proteins into GUVs remains challenging. Here, we present a simple generic method to incorporate proteins into GUVs. The basic principle is to break proteo-liposomes with an osmotic shock. They subsequently reseal into larger vesicles which, if necessary, can endure the same to obtain even larger proteo-GUVs. This process does not require specific lipids or reagents, works under physiological conditions with high concentrations of protein, the proteins remains functional after incorporation. The resulting proteo-GUVs can be micromanipulated. Moreover, our protocol is valid for a wide range of protein substrates. We have successfully reconstituted three structurally different proteins, two trans-membrane proteins (TolC and the neuronal t-SNARE), and one lipid-anchored peripheral protein (GABARAP-Like 1 (GL1)). In each case, we verified that the protein remains active after incorporation and in its correctly folded state. We also measured their mobility by performing diffusion measurements via fluorescence recovery after photobleaching (FRAP) experiments on micromanipulated single GUVs. The diffusion coefficients are in agreement with previous data.
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Affiliation(s)
- Isabelle Motta
- 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
| | - Andrea Gohlke
- 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
- Department of Cell Biology, Nanobiology Institute, School of Medicine, Yale University, 333 Cedar Street, New Haven, CT 06520, USA
| | - Vladimir Adrien
- 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
- Laboratoire de Cristallographie et RMN Biologiques, Université Paris Descartes, CNRS, UMR 8015, Paris, France
| | - Feng Li
- Department of Cell Biology, Nanobiology Institute, School of Medicine, Yale University, 333 Cedar Street, New Haven, CT 06520, USA
| | - Hélène Gardavot
- 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
| | - James E. Rothman
- Department of Cell Biology, Nanobiology Institute, School of Medicine, Yale University, 333 Cedar Street, New Haven, CT 06520, USA
| | - 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
- Department of Cell Biology, Nanobiology Institute, School of Medicine, Yale University, 333 Cedar Street, New Haven, CT 06520, USA
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Beales PA, Ciani B, Cleasby AJ. Nature's lessons in design: nanomachines to scaffold, remodel and shape membrane compartments. Phys Chem Chem Phys 2015; 17:15489-507. [DOI: 10.1039/c5cp00480b] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Our understanding of the membrane sculpting capabilities of proteins from experimental model systems could be used to construct functional compartmentalised architectures for the engineering of synthetic cells.
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Affiliation(s)
- Paul A. Beales
- School of Chemistry and Astbury Centre for Structural Molecular Biology
- University of Leeds
- Leeds LS2 9JT
- UK
| | - Barbara Ciani
- Centre for Membrane Interaction and Dynamics
- Department of Chemistry
- University of Sheffield
- Sheffield S3 7HF
- UK
| | - Alexa J. Cleasby
- Centre for Membrane Interaction and Dynamics
- Department of Chemistry
- University of Sheffield
- Sheffield S3 7HF
- UK
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31
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Ronzone E, Wesolowski J, Bauler LD, Bhardwaj A, Hackstadt T, Paumet F. An α-helical core encodes the dual functions of the chlamydial protein IncA. J Biol Chem 2014; 289:33469-80. [PMID: 25324548 DOI: 10.1074/jbc.m114.592063] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023] Open
Abstract
Chlamydia is an intracellular bacterium that establishes residence within parasitophorous compartments (inclusions) inside host cells. Chlamydial inclusions are uncoupled from the endolysosomal pathway and undergo fusion with cellular organelles and with each other. To do so, Chlamydia expresses proteins on the surface of the inclusion using a Type III secretion system. These proteins, termed Incs, are located at the interface between host and pathogen and carry out the functions necessary for Chlamydia survival. Among these Incs, IncA plays a critical role in both protecting the inclusion from lysosomal fusion and inducing the homotypic fusion of inclusions. Within IncA are two regions homologous to eukaryotic SNARE (soluble N-ethylmaleimide-sensitive factor attachment receptor) domains referred to as SNARE-like domain 1 (SLD1) and SNARE-like domain 2 (SLD2). Using a multidisciplinary approach, we have discovered the functional core of IncA that retains the ability to both inhibit SNARE-mediated fusion and promote the homotypic fusion of Chlamydia inclusions. Circular dichroism and analytical ultracentrifugation experiments show that this core region is composed almost entirely of α-helices and assembles into stable homodimers in solution. Altogether, we propose that both IncA functions are encoded in a structured core domain that encompasses SLD1 and part of SLD2.
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Affiliation(s)
- Erik Ronzone
- From the Departments of Microbiology and Immunology and
| | | | - Laura D Bauler
- the Host-Parasite Interactions Section, Laboratory of Intracellular Parasites, Rocky Mountain Laboratories, NIAID, National Institutes of Health, Hamilton, Montana 59840
| | - Anshul Bhardwaj
- Biochemistry and Molecular Biology, Thomas Jefferson University, Philadelphia, Pennsylvania 19107 and
| | - Ted Hackstadt
- the Host-Parasite Interactions Section, Laboratory of Intracellular Parasites, Rocky Mountain Laboratories, NIAID, National Institutes of Health, Hamilton, Montana 59840
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Abstract
The soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complex drives the majority of intracellular and exocytic membrane fusion events. Whether and how SNAREs cooperate to mediate fusion has been a subject of intense study, with estimates ranging from a single SNARE complex to 15. Here we show that there is no universally conserved number of SNARE complexes involved as revealed by our observation that this varies greatly depending on membrane curvature. When docking rates of small (∼40 nm) and large (∼100 nm) liposomes reconstituted with different synaptobrevin (the SNARE present in synaptic vesicles) densities are taken into account, the lipid mixing efficiency was maximal with small liposomes with only one synaptobrevin, whereas 23-30 synaptobrevins were necessary for efficient lipid mixing in large liposomes. Our results can be rationalized in terms of strong and weak cooperative coupling of SNARE complex assembly where each mode implicates different intermediate states of fusion that have been recently identified by electron microscopy. We predict that even higher variability in cooperativity is present in different physiological scenarios of fusion, and we further hypothesize that plasticity of SNAREs to engage in different coupling modes is an important feature of the biologically ubiquitous SNARE-mediated fusion reactions.
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33
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Meriney SD, Umbach JA, Gundersen CB. Fast, Ca2+-dependent exocytosis at nerve terminals: shortcomings of SNARE-based models. Prog Neurobiol 2014; 121:55-90. [PMID: 25042638 DOI: 10.1016/j.pneurobio.2014.07.001] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2013] [Revised: 04/14/2014] [Accepted: 07/03/2014] [Indexed: 11/30/2022]
Abstract
Investigations over the last two decades have made major inroads in clarifying the cellular and molecular events that underlie the fast, synchronous release of neurotransmitter at nerve endings. Thus, appreciable progress has been made in establishing the structural features and biophysical properties of the calcium (Ca2+) channels that mediate the entry into nerve endings of the Ca2+ ions that trigger neurotransmitter release. It is now clear that presynaptic Ca2+ channels are regulated at many levels and the interplay of these regulatory mechanisms is just beginning to be understood. At the same time, many lines of research have converged on the conclusion that members of the synaptotagmin family serve as the primary Ca2+ sensors for the action potential-dependent release of neurotransmitter. This identification of synaptotagmins as the proteins which bind Ca2+ and initiate the exocytotic fusion of synaptic vesicles with the plasma membrane has spurred widespread efforts to reveal molecular details of synaptotagmin's action. Currently, most models propose that synaptotagmin interfaces directly or indirectly with SNARE (soluble, N-ethylmaleimide sensitive factor attachment receptors) proteins to trigger membrane fusion. However, in spite of intensive efforts, the field has not achieved consensus on the mechanism by which synaptotagmins act. Concurrently, the precise sequence of steps underlying SNARE-dependent membrane fusion remains controversial. This review considers the pros and cons of the different models of SNARE-mediated membrane fusion and concludes by discussing a novel proposal in which synaptotagmins might directly elicit membrane fusion without the intervention of SNARE proteins in this final fusion step.
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Affiliation(s)
- Stephen D Meriney
- Department of Neuroscience, Center for Neuroscience, University of Pittsburgh, Pittsburgh, PA 15260, USA
| | - Joy A Umbach
- Department of Molecular and Medical Pharmacology, UCLA David Geffen School of Medicine, Los Angeles, CA 90095, USA
| | - Cameron B Gundersen
- Department of Molecular and Medical Pharmacology, UCLA David Geffen School of Medicine, Los Angeles, CA 90095, USA.
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34
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Li F, Kümmel D, Coleman J, Reinisch KM, Rothman JE, Pincet F. A half-zippered SNARE complex represents a functional intermediate in membrane fusion. J Am Chem Soc 2014; 136:3456-64. [PMID: 24533674 PMCID: PMC3985920 DOI: 10.1021/ja410690m] [Citation(s) in RCA: 53] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
![]()
SNARE
(soluble N-ethylmaleimide-sensitive factor
attachment protein receptor) proteins mediate fusion by pulling biological
membranes together via a zippering mechanism. Recent biophysical studies
have shown that t- and v-SNAREs can assemble in multiple stages from
the N-termini toward the C-termini. Here we show that functionally,
membrane fusion requires a sequential, two-step folding pathway and
assign specific and distinct functions for each step. First, the N-terminal
domain (NTD) of the v-SNARE docks to the t-SNARE, which leads to a
conformational rearrangement into an activated half-zippered SNARE
complex. This partially assembled SNARE complex locks the C-terminal
(CTD) portion of the t-SNARE into the same structure as in the postfusion
4-helix bundle, thereby creating the binding site for the CTD of the
v-SNARE and enabling fusion. Then zippering of the remaining CTD,
the membrane-proximal linker (LD), and transmembrane (TMD) domains
is required and sufficient to trigger fusion. This intrinsic property
of the SNAREs fits well with the action of physiologically vital regulators
such as complexin. We also report that NTD assembly is the rate-limiting
step. Our findings provide a refined framework for delineating the
molecular mechanism of SNARE-mediated membrane fusion and action of
regulatory proteins.
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Affiliation(s)
- Feng Li
- Department of Cell Biology, School of Medicine, Yale University , 333 Cedar Street, New Haven, Connecticut 06520, United States
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35
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Insulin stimulates syntaxin4 SNARE complex assembly via a novel regulatory mechanism. Mol Cell Biol 2014; 34:1271-9. [PMID: 24469400 DOI: 10.1128/mcb.01203-13] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
Insulin stimulates glucose transport into fat and muscle cells by increasing the exocytic trafficking rate of the GLUT4 facilitative glucose transporter from intracellular stores to the plasma membrane. Delivery of GLUT4 to the plasma membrane is mediated by formation of functional SNARE complexes containing syntaxin4, SNAP23, and VAMP2. Here we have used an in situ proximity ligation assay to integrate these two observations by demonstrating for the first time that insulin stimulation causes an increase in syntaxin4-containing SNARE complex formation in adipocytes. Furthermore, we demonstrate that insulin brings about this increase in SNARE complex formation by mobilizing a pool of syntaxin4 held in an inactive state under basal conditions. Finally, we have identified phosphorylation of the regulatory protein Munc18c, a direct target of the insulin receptor, as a molecular switch to coordinate this process. Hence, this report provides molecular detail of how the cell alters membrane traffic in response to an external stimulus, in this case, insulin.
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36
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Pähler G, Panse C, Diederichsen U, Janshoff A. Coiled-coil formation on lipid bilayers--implications for docking and fusion efficiency. Biophys J 2013; 103:2295-303. [PMID: 23283228 DOI: 10.1016/j.bpj.2012.08.053] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2012] [Revised: 07/31/2012] [Accepted: 08/15/2012] [Indexed: 11/26/2022] Open
Abstract
Coiled-coil formation of four different oligopeptides was characterized in solution, on hydrogels, and on membranes by employing circular dichroism spectroscopy, surface plasmon resonance spectroscopy, attenuated total reflection infrared spectroscopy, and ellipsometry. Peptide sequences rich in either glutamic acid (E: E3Cys, i-E3Cys) or lysine (K: K3Cys, i-K3Cys) were used to represent minimal mimics of eukaryotic SNARE motifs. Half of the peptides were synthesized in reverse sequence, so that parallel and antiparallel heptad coiled-coil structures were formed. Either E-peptides or K-peptides were attached covalently to phospholipid anchors via maleimide chemistry, and served as receptors for the recognition of the corresponding binding partners added to solution. Attenuated total reflection infrared spectroscopy of single bilayers confirmed the formation of coiled-coil complexes at the membrane interface. Coiled-coil formation in solution, as compared with association at the membrane surface, displays considerably larger binding constants that are largely attributed to loss of translational entropy at the interface. Finally, the fusogenicity of the various coiled-coil motifs was explored, and the results provide clear evidence that hemifusion followed by full fusion requires a parallel orientation of α-helices, whereas antiparallel oriented coiled-coil motifs display only docking.
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Affiliation(s)
- Gesa Pähler
- Institute of Physical Chemistry, Georg August University, Göttingen, Germany
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37
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Ma C, Su L, Seven AB, Xu Y, Rizo J. Reconstitution of the vital functions of Munc18 and Munc13 in neurotransmitter release. Science 2012; 339:421-5. [PMID: 23258414 DOI: 10.1126/science.1230473] [Citation(s) in RCA: 289] [Impact Index Per Article: 24.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
Neurotransmitter release depends critically on Munc18-1, Munc13, the Ca(2+) sensor synaptotagmin-1, and the soluble N-ethylmaleimide-sensitive factor (NSF) attachment protein (SNAP) receptors (SNAREs) syntaxin-1, synaptobrevin, and SNAP-25. In vitro reconstitutions have shown that syntaxin-1-SNAP-25 liposomes fuse efficiently with synaptobrevin liposomes in the presence of synaptotagmin-1-Ca(2+), but neurotransmitter release also requires Munc18-1 and Munc13 in vivo. We found that Munc18-1 could displace SNAP-25 from syntaxin-1 and that fusion of syntaxin-1-Munc18-1 liposomes with synaptobrevin liposomes required Munc13, in addition to SNAP-25 and synaptotagmin-1-Ca(2+). Moreover, when starting with syntaxin-1-SNAP-25 liposomes, NSF-α-SNAP disassembled the syntaxin-1-SNAP-25 heterodimers and abrogated fusion, which then required Munc18-1 and Munc13. We propose that fusion does not proceed through syntaxin-1-SNAP-25 heterodimers but starts with the syntaxin-1-Munc18-1 complex; Munc18-1 and Munc13 then orchestrate membrane fusion together with the SNAREs and synaptotagmin-1-Ca(2+) in an NSF- and SNAP-resistant manner.
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Affiliation(s)
- Cong Ma
- Key Laboratory of Molecular Biophysics, Ministry of Education, and Institute of Biophysics and Biochemistry, Huazhong University of Science and Technology, Wuhan 430074, China.
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Kasai H, Takahashi N, Tokumaru H. Distinct Initial SNARE Configurations Underlying the Diversity of Exocytosis. Physiol Rev 2012; 92:1915-64. [DOI: 10.1152/physrev.00007.2012] [Citation(s) in RCA: 120] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
The dynamics of exocytosis are diverse and have been optimized for the functions of synapses and a wide variety of cell types. For example, the kinetics of exocytosis varies by more than five orders of magnitude between ultrafast exocytosis in synaptic vesicles and slow exocytosis in large dense-core vesicles. However, in all cases, exocytosis is mediated by the same fundamental mechanism, i.e., the assembly of soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) proteins. It is often assumed that vesicles need to be docked at the plasma membrane and SNARE proteins must be preassembled before exocytosis is triggered. However, this model cannot account for the dynamics of exocytosis recently reported in synapses and other cells. For example, vesicles undergo exocytosis without prestimulus docking during tonic exocytosis of synaptic vesicles in the active zone. In addition, epithelial and hematopoietic cells utilize cAMP and kinases to trigger slow exocytosis of nondocked vesicles. In this review, we summarize the manner in which the diversity of exocytosis reflects the initial configurations of SNARE assembly, including trans-SNARE, binary-SNARE, unitary-SNARE, and cis-SNARE configurations. The initial SNARE configurations depend on the particular SNARE subtype (syntaxin, SNAP25, or VAMP), priming proteins (Munc18, Munc13, CAPS, complexin, or snapin), triggering proteins (synaptotagmins, Doc2, and various protein kinases), and the submembraneous cytomatrix, and they are the key to determining the kinetics of subsequent exocytosis. These distinct initial configurations will help us clarify the common SNARE assembly processes underlying exocytosis and membrane trafficking in eukaryotic cells.
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Affiliation(s)
- Haruo Kasai
- Laboratory of Structural Physiology, Center for Disease Biology and Integrative Medicine, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan; and Faculty of Pharmaceutical Sciences at Kagawa, Tokushima Bunri University, Kagawa, Japan
| | - Noriko Takahashi
- Laboratory of Structural Physiology, Center for Disease Biology and Integrative Medicine, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan; and Faculty of Pharmaceutical Sciences at Kagawa, Tokushima Bunri University, Kagawa, Japan
| | - Hiroshi Tokumaru
- Laboratory of Structural Physiology, Center for Disease Biology and Integrative Medicine, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan; and Faculty of Pharmaceutical Sciences at Kagawa, Tokushima Bunri University, Kagawa, Japan
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Gao Y, Zorman S, Gundersen G, Xi Z, Ma L, Sirinakis G, Rothman JE, Zhang Y. Single reconstituted neuronal SNARE complexes zipper in three distinct stages. Science 2012; 337:1340-3. [PMID: 22903523 DOI: 10.1126/science.1224492] [Citation(s) in RCA: 298] [Impact Index Per Article: 24.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) proteins drive membrane fusion by assembling into a four-helix bundle in a zippering process. Here, we used optical tweezers to observe in a cell-free reconstitution experiment in real time a long-sought SNARE assembly intermediate in which only the membrane-distal amino-terminal half of the bundle is assembled. Our findings support the zippering hypothesis, but suggest that zippering proceeds through three sequential binary switches, not continuously, in the amino- and carboxyl-terminal halves of the bundle and the linker domain. The half-zippered intermediate was stabilized by externally applied force that mimicked the repulsion between apposed membranes being forced to fuse. This intermediate then rapidly and forcefully zippered, delivering free energy of 36 k(B)T (where k(B) is Boltzmann's constant and T is temperature) to mediate fusion.
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Affiliation(s)
- Ying Gao
- Department of Cell Biology, Yale University School of Medicine, 333 Cedar Street, New Haven, CT 06520, USA
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Abstract
The platelet release reaction plays a critical role in thrombosis and contributes to the events that follow hemostasis. Previous studies have shown that platelet secretion is mediated by Soluble NSF Attachment Protein Receptor (SNARE) proteins from granule and plasma membranes. The SNAREs form transmembrane complexes that mediate membrane fusion and granule cargo release. Although VAMP-8 (v-SNARE) and SNAP-23 (a t-SNARE class) are important for platelet secretion, the identity of the functional syntaxin (another t-SNARE class) has been controversial. Previous studies using anti-syntaxin Abs in permeabilized platelets have suggested roles for both syntaxin-2 and syntaxin-4. In the present study, we tested these conclusions using platelets from syntaxin-knockout mouse strains and from a Familial Hemophagocytic Lymphohistiocytosis type 4 (FHL4) patient. Platelets from syntaxin-2 and syntaxin-4 single- or double-knockout mice had no secretion defect. Platelets from a FHL4 patient deficient in syntaxin-11 had a robust defect in agonist-induced secretion although their morphology, activation, and cargo levels appeared normal. Semiquantitative Western blotting showed that syntaxin-11 is the more abundant syntaxin in both human and murine platelets. Coimmunoprecipitation experiments showed that syntaxin-11 can form SNARE complexes with both VAMP-8 and SNAP-23. The results of the present study indicate that syntaxin-11, but not syntaxin-2 or syntaxin-4, is required for platelet exocytosis.
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Xia T, Tong J, Rathore SS, Gu X, Dickerson JA. Network motif comparison rationalizes Sec1/Munc18-SNARE regulation mechanism in exocytosis. BMC SYSTEMS BIOLOGY 2012; 6:19. [PMID: 22423977 PMCID: PMC3439672 DOI: 10.1186/1752-0509-6-19] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/23/2011] [Accepted: 03/16/2012] [Indexed: 11/10/2022]
Abstract
BACKGROUND Network motifs, recurring subnetwork patterns, provide significant insight into the biological networks which are believed to govern cellular processes. METHODS We present a comparative network motif experimental approach, which helps to explain complex biological phenomena and increases the understanding of biological functions at the molecular level by exploring evolutionary design principles of network motifs. RESULTS Using this framework to analyze the SM (Sec1/Munc18)-SNARE (N-ethylmaleimide-sensitive factor activating protein receptor) system in exocytic membrane fusion in yeast and neurons, we find that the SM-SNARE network motifs of yeast and neurons show distinct dynamical behaviors. We identify the closed binding mode of neuronal SM (Munc18-1) and SNARE (syntaxin-1) as the key factor leading to mechanistic divergence of membrane fusion systems in yeast and neurons. We also predict that it underlies the conflicting observations in SM overexpression experiments. Furthermore, hypothesis-driven lipid mixing assays validated the prediction. CONCLUSION Therefore this study provides a new method to solve the discrepancies and to generalize the functional role of SM proteins.
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Affiliation(s)
- Tian Xia
- Biomedical Informatics Center, Northwestern University, Chicago, IL 60611, USA.
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Dutta D, Pulsipher A, Luo W, Mak H, Yousaf MN. Engineering cell surfaces via liposome fusion. Bioconjug Chem 2011; 22:2423-33. [PMID: 22054009 DOI: 10.1021/bc200236m] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
In this study, we have rewired cell surfaces with ketone and oxyamine molecules based on liposome fusion for applications in cell-surface engineering. Lipid vesicles, functionalized with ketone and oxyamine molecules, display complementary chemistry and undergo recognition, docking, and subsequent fusion upon covalent oxime bond formation. Liposome fusion was characterized by several techniques including matrix-assisted laser-desorption/ionization mass spectrometry (MALDI-MS), light scattering, fluorescence resonance energy transfer (FRET), and transmission electron microscopy (TEM). When cultured with cells, ketone- and oxyamine-containing liposomes undergo spontaneous membrane fusion to present the respective molecules from cell surfaces. Ketone-functionalized cell surfaces serve as sites for chemoselective ligation with oxyamine-conjugated molecules. We tailored and fluorescently labeled cell surfaces with an oxyamine-conjugated rhodamine dye. As an application of this cell-surface engineering strategy, ketone- and oxyamine-functionalized cells were patterned on oxyamine- and ketone-presenting surfaces, respectively. Cells adhered, spread, and proliferated in the patterned regions via interfacial oxime linkage. The number of ketone molecules on the cell surface was also quantified by flow cytometry.
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Affiliation(s)
- Debjit Dutta
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-3290, United States
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43
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Interactions among the SNARE proteins and complexin analyzed by a yeast four-hybrid assay. Anal Biochem 2011; 416:107-11. [DOI: 10.1016/j.ab.2011.05.010] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2011] [Accepted: 05/06/2011] [Indexed: 11/23/2022]
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Smith EA, Weisshaar JC. Docking, not fusion, as the rate-limiting step in a SNARE-driven vesicle fusion assay. Biophys J 2011; 100:2141-50. [PMID: 21539781 DOI: 10.1016/j.bpj.2011.03.015] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2010] [Revised: 03/09/2011] [Accepted: 03/14/2011] [Indexed: 10/18/2022] Open
Abstract
In vitro vesicle fusion assays that monitor lipid mixing between t-SNARE and v-SNARE vesicles in bulk solution exhibit remarkably slow fusion on the nonphysiological timescale of tens of minutes to several hours. Here, single-vesicle, fluorescence resonance energy transfer-based assays cleanly separate docking and fusion steps for individual vesicle pairs containing full-length SNAREs. Docking is extremely inefficient and is the rate-limiting step. Of importance, the docking and fusion kinetics are comparable in the two assays (one with v-SNARE vesicles tethered to a surface and the other with v-SNARE vesicles free in solution). Addition of the V(C) peptide synaptobrevin-2 (syb(57-92)) increases the docking efficiency by a factor of ∼30, but docking remains rate-limiting. In the presence of V(C) peptide, the fusion step occurs on a timescale of ∼10 s. In previous experiments involving bulk fusion assays in which the addition of synaptotagmin/Ca(2+), Munc-18, or complexin accelerated the observed lipid-mixing rate, the enhancement may have arisen from the docking step rather than the fusion step.
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Affiliation(s)
- Elizabeth A Smith
- Graduate Program in Molecular Biophysics, University of Wisconsin, Madison, Wisconsin, USA
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Khodthong C, Kabachinski G, James DJ, Martin TFJ. Munc13 homology domain-1 in CAPS/UNC31 mediates SNARE binding required for priming vesicle exocytosis. Cell Metab 2011; 14:254-63. [PMID: 21803295 PMCID: PMC3148490 DOI: 10.1016/j.cmet.2011.07.002] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/17/2010] [Revised: 04/09/2011] [Accepted: 06/21/2011] [Indexed: 01/11/2023]
Abstract
Neuropeptide and peptide hormone secretion from neural and endocrine cells occurs by Ca(2+)-triggered dense-core vesicle exocytosis. The membrane fusion machinery consisting of vesicle and plasma membrane SNARE proteins needs to be assembled for Ca(2+)-triggered vesicle exocytosis. The related Munc13 and CAPS/UNC31 proteins that prime vesicle exocytosis are proposed to promote SNARE complex assembly. CAPS binds SNARE proteins and stimulates SNARE complex formation on liposomes, but the relevance of SNARE binding to CAPS function in cells had not been determined. Here we identify a core SNARE-binding domain in CAPS as corresponding to Munc13 homology domain-1 (MHD1). CAPS lacking a single helix in MHD1 was unable to bind SNARE proteins or to support the Ca(2+)-triggered exocytosis of either docked or newly arrived dense-core vesicles. The results show that MHD1 is a SNARE-binding domain and that SNARE protein binding is essential for CAPS function in dense-core vesicle exocytosis.
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Xu Y, Seven AB, Su L, Jiang QX, Rizo J. Membrane bridging and hemifusion by denaturated Munc18. PLoS One 2011; 6:e22012. [PMID: 21765933 PMCID: PMC3130787 DOI: 10.1371/journal.pone.0022012] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2011] [Accepted: 06/10/2011] [Indexed: 11/19/2022] Open
Abstract
Neuronal Munc18-1 and members of the Sec1/Munc18 (SM) protein family play a critical function(s) in intracellular membrane fusion together with SNARE proteins, but the mechanism of action of SM proteins remains highly enigmatic. During experiments designed to address this question employing a 7-nitrobenz-2-oxa-1,3-diazole (NBD) fluorescence de-quenching assay that is widely used to study lipid mixing between reconstituted proteoliposomes, we observed that Munc18-1 from squid (sMunc18-1) was able to increase the apparent NBD fluorescence emission intensity even in the absence of SNARE proteins. Fluorescence emission scans and dynamic light scattering experiments show that this phenomenon arises at least in part from increased light scattering due to sMunc18-1-induced liposome clustering. Nuclear magnetic resonance and circular dichroism data suggest that, although native sMunc18-1 does not bind significantly to lipids, sMunc18-1 denaturation at 37°C leads to insertion into membranes. The liposome clustering activity of sMunc18-1 can thus be attributed to its ability to bridge two membranes upon (perhaps partial) denaturation; correspondingly, this activity is hindered by addition of glycerol. Cryo-electron microscopy shows that liposome clusters induced by sMunc18-1 include extended interfaces where the bilayers of two liposomes come into very close proximity, and clear hemifusion diaphragms. Although the physiological relevance of our results is uncertain, they emphasize the necessity of complementing fluorescence de-quenching assays with alternative experiments in studies of membrane fusion, as well as the importance of considering the potential effects of protein denaturation. In addition, our data suggest a novel mechanism of membrane hemifusion induced by amphipathic macromolecules that does not involve formation of a stalk intermediate.
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Affiliation(s)
- Yi Xu
- Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, Texas, United States of America
- Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, Texas, United States of America
| | - Alpay B. Seven
- Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, Texas, United States of America
- Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, Texas, United States of America
| | - Lijing Su
- Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, Texas, United States of America
- Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, Texas, United States of America
| | - Qiu-Xing Jiang
- Department of Cell Biology, University of Texas Southwestern Medical Center, Dallas, Texas, United States of America
| | - Josep Rizo
- Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, Texas, United States of America
- Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, Texas, United States of America
- * E-mail:
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Schollmeier Y, Krause JM, Kreye S, Malsam J, Söllner TH. Resolving the function of distinct Munc18-1/SNARE protein interaction modes in a reconstituted membrane fusion assay. J Biol Chem 2011; 286:30582-30590. [PMID: 21730064 DOI: 10.1074/jbc.m111.269886] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Sec1p/Munc18 proteins and SNAP receptors (SNAREs) are key components of the intracellular membrane fusion machinery. Compartment-specific v-SNAREs on a transport vesicle pair with their cognate t-SNAREs on the target membrane and drive lipid bilayer fusion. In a reconstituted assay that dissects the sequential assembly of t-SNARE (syntaxin 1·SNAP-25) and v-/t-SNARE (VAMP2·syntaxin 1·SNAP-25) complexes, and finally measures lipid bilayer merger, we resolved the inhibitory and stimulatory functions of the Sec1p/Munc18 protein Munc18-1 at the molecular level. Inhibition of membrane fusion by Munc18-1 requires a closed conformation of syntaxin 1. Remarkably, the concurrent preincubation of Munc18-1-inhibited syntaxin 1 liposomes with both VAMP2 liposomes and SNAP-25 at low temperature releases the inhibition and effectively stimulates membrane fusion. VAMP8 liposomes can neither release the inhibition nor exert the stimulatory effect, demonstrating the need for a specific Munc18-1/VAMP2 interaction. In addition, Munc18-1 binds to the N-terminal peptide of syntaxin 1, which is obligatory for a robust stimulation of membrane fusion. In contrast, this interaction is neither required for the inhibitory function of Munc18-1 nor for the release of this block. These results indicate that Munc18-1 and the neuronal SNAREs already have the inherent capability to function as a basic stage-specific off/on switch to control membrane fusion.
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Affiliation(s)
| | | | - Susanne Kreye
- Heidelberg University Biochemistry Center, 69120 Heidelberg, Germany
| | - Jörg Malsam
- Heidelberg University Biochemistry Center, 69120 Heidelberg, Germany
| | - Thomas H Söllner
- Heidelberg University Biochemistry Center, 69120 Heidelberg, Germany.
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van den Bogaart G, Thutupalli S, Risselada JH, Meyenberg K, Holt M, Riedel D, Diederichsen U, Herminghaus S, Grubmüller H, Jahn R. Synaptotagmin-1 may be a distance regulator acting upstream of SNARE nucleation. Nat Struct Mol Biol 2011; 18:805-12. [PMID: 21642968 PMCID: PMC3130798 DOI: 10.1038/nsmb.2061] [Citation(s) in RCA: 112] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2010] [Accepted: 03/17/2011] [Indexed: 12/16/2022]
Abstract
Synaptotagmin-1 triggers Ca2+-sensitive, rapid neurotransmitter release by promoting the interaction of SNARE proteins between the synaptic vesicles and the plasma membrane. How synaptotagmin-1 promotes this interaction is controversial, and the massive increase in membrane fusion efficiency of Ca2+-synaptotagmin-1 has not been reproduced in vitro. However, previous experiments have been performed at relatively high salt concentrations, screening potentially important electrostatic interactions. Using functional reconstitution in liposomes, we show here that at low ionic strength SNARE-mediated membrane fusion becomes strictly dependent on both Ca2+ and synaptotagmin-1. Under these conditions, synaptotagmin-1 functions as a distance regulator: tethering the liposomes too far for SNARE nucleation in the absence of Ca2+, but brings the liposomes close enough for membrane fusion in the presence of Ca2+. These results may explain how the relatively weak electrostatic interactions of synaptotagmin-1 with membranes substantially accelerate fusion.
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Affiliation(s)
- Geert van den Bogaart
- Department of Neurobiology, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
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49
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Moss TJ, Daga A, McNew JA. Fusing a lasting relationship between ER tubules. Trends Cell Biol 2011; 21:416-23. [PMID: 21550242 DOI: 10.1016/j.tcb.2011.03.009] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2010] [Revised: 03/31/2011] [Accepted: 03/31/2011] [Indexed: 11/18/2022]
Abstract
Atlastin is an integral membrane GTPase localized to the endoplasmic reticulum (ER). In vitro and in vivo analyses indicate that atlastin is a membrane fusogen capable of driving membrane fusion, suggesting a role in ER structure and maintenance. Interestingly, mutations in the human atlastin-1 gene, SPG3A, cause a form of autosomal dominant hereditary spastic paraplegia (HSP). The etiology of HSP is unclear, but two predominant forms of the disorder are caused by mutant proteins that affect ER structure, formation and maintenance in motor neurons. In this review, we describe the current knowledge about the molecular mechanism of atlastin function and its potential role in HSP. Greater understanding of the function of atlastin and associated proteins should provide important insight into normal ER biogenesis and maintenance, as well as the pathology of disease.
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Affiliation(s)
- Tyler J Moss
- Department of Biochemistry and Cell Biology, Rice University, MS601, Houston, TX 77005, USA
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50
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Wesolowski J, Paumet F. SNARE motif: a common motif used by pathogens to manipulate membrane fusion. Virulence 2011; 1:319-24. [PMID: 21178463 DOI: 10.4161/viru.1.4.12195] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
To penetrate host cells through their membranes, pathogens use a variety of molecular components in which the presence of heptad repeat motifs seems to be a prevailing element. Heptad repeats are characterized by a pattern of seven, generally hydrophobic, residues. In order to initiate membrane fusion, viruses use glycoproteins-containing heptad repeats. These proteins are structurally and functionally similar to the SNARE proteins known to be involved in eukaryotic membrane fusion. SNAREs also display a heptad repeat motif called the "SNARE motif". As bacterial genomes are being sequenced, microorganisms also appear to be carrying membrane proteins resembling eukaryotic SNAREs. This category of SNARE-like proteins might share similar functions and could be used by microorganisms to either promote or block membrane fusion. Such a recurrence across pathogenic organisms suggests that this architectural motif was evolutionarily selected because it most effectively ensures the survival of pathogens within the eukaryotic environment.
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Affiliation(s)
- Jordan Wesolowski
- Department of Microbiology and Immunology, Thomas Jefferson University, Philadelphia, PA, USA
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