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Bhaskar BR, Yadav L, Sriram M, Sanghrajka K, Gupta M, V BK, Nellikka RK, Das D. Differential SNARE chaperoning by Munc13-1 and Munc18-1 dictates fusion pore fate at the release site. Nat Commun 2024; 15:4132. [PMID: 38755165 PMCID: PMC11099066 DOI: 10.1038/s41467-024-46965-7] [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: 04/21/2023] [Accepted: 03/14/2024] [Indexed: 05/18/2024] Open
Abstract
The regulated release of chemical messengers is crucial for cell-to-cell communication; abnormalities in which impact coordinated human body function. During vesicular secretion, multiple SNARE complexes assemble at the release site, leading to fusion pore opening. How membrane fusion regulators act on heterogeneous SNARE populations to assemble fusion pores in a timely and synchronized manner, is unknown. Here, we demonstrate the role of SNARE chaperones Munc13-1 and Munc18-1 in rescuing individual nascent fusion pores from their diacylglycerol lipid-mediated inhibitory states. At the onset of membrane fusion, Munc13-1 clusters multiple SNARE complexes at the release site and synchronizes release events, while Munc18-1 stoichiometrically interacts with trans-SNARE complexes to enhance N- to C-terminal zippering. When both Munc proteins are present simultaneously, they differentially access dynamic trans-SNARE complexes to regulate pore properties. Overall, Munc proteins' direct action on fusion pore assembly indicates their role in controlling quantal size during vesicular secretion.
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Affiliation(s)
- Bhavya R Bhaskar
- Department of Biological Sciences, Tata Institute of Fundamental Research, Mumbai, 400005, India
| | - Laxmi Yadav
- Department of Biological Sciences, Tata Institute of Fundamental Research, Mumbai, 400005, India
| | - Malavika Sriram
- Department of Biological Sciences, Tata Institute of Fundamental Research, Mumbai, 400005, India
| | - Kinjal Sanghrajka
- Department of Biological Sciences, Tata Institute of Fundamental Research, Mumbai, 400005, India
| | - Mayank Gupta
- Department of Biological Sciences, Tata Institute of Fundamental Research, Mumbai, 400005, India
| | - Boby K V
- Department of Biological Sciences, Tata Institute of Fundamental Research, Mumbai, 400005, India
| | - Rohith K Nellikka
- Department of Biological Sciences, Tata Institute of Fundamental Research, Mumbai, 400005, India
| | - Debasis Das
- Department of Biological Sciences, Tata Institute of Fundamental Research, Mumbai, 400005, India.
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2
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Amini M, Benson JD. Technologies for Vitrification Based Cryopreservation. Bioengineering (Basel) 2023; 10:bioengineering10050508. [PMID: 37237578 DOI: 10.3390/bioengineering10050508] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2023] [Revised: 03/08/2023] [Accepted: 03/30/2023] [Indexed: 05/28/2023] Open
Abstract
Cryopreservation is a unique and practical method to facilitate extended access to biological materials. Because of this, cryopreservation of cells, tissues, and organs is essential to modern medical science, including cancer cell therapy, tissue engineering, transplantation, reproductive technologies, and bio-banking. Among diverse cryopreservation methods, significant focus has been placed on vitrification due to low cost and reduced protocol time. However, several factors, including the intracellular ice formation that is suppressed in the conventional cryopreservation method, restrict the achievement of this method. To enhance the viability and functionality of biological samples after storage, a large number of cryoprotocols and cryodevices have been developed and studied. Recently, new technologies have been investigated by considering the physical and thermodynamic aspects of cryopreservation in heat and mass transfer. In this review, we first present an overview of the physiochemical aspects of freezing in cryopreservation. Secondly, we present and catalog classical and novel approaches that seek to capitalize on these physicochemical effects. We conclude with the perspective that interdisciplinary studies provide pieces of the cryopreservation puzzle to achieve sustainability in the biospecimen supply chain.
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Affiliation(s)
- Mohammad Amini
- Department of Biology, University of Saskatchewan, Saskatoon, SK S7N 5E2, Canada
| | - James D Benson
- Department of Biology, University of Saskatchewan, Saskatoon, SK S7N 5E2, Canada
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3
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Sparse deconvolution improves the resolution of live-cell super-resolution fluorescence microscopy. Nat Biotechnol 2022; 40:606-617. [PMID: 34782739 DOI: 10.1038/s41587-021-01092-2] [Citation(s) in RCA: 79] [Impact Index Per Article: 39.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2020] [Accepted: 09/10/2021] [Indexed: 02/07/2023]
Abstract
A main determinant of the spatial resolution of live-cell super-resolution (SR) microscopes is the maximum photon flux that can be collected. To further increase the effective resolution for a given photon flux, we take advantage of a priori knowledge about the sparsity and continuity of biological structures to develop a deconvolution algorithm that increases the resolution of SR microscopes nearly twofold. Our method, sparse structured illumination microscopy (Sparse-SIM), achieves ~60-nm resolution at a frame rate of up to 564 Hz, allowing it to resolve intricate structures, including small vesicular fusion pores, ring-shaped nuclear pores formed by nucleoporins and relative movements of inner and outer mitochondrial membranes in live cells. Sparse deconvolution can also be used to increase the three-dimensional resolution of spinning-disc confocal-based SIM, even at low signal-to-noise ratios, which allows four-color, three-dimensional live-cell SR imaging at ~90-nm resolution. Overall, sparse deconvolution will be useful to increase the spatiotemporal resolution of live-cell fluorescence microscopy.
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4
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Yang G, Li L, Liu Y, Liang K, Wei L, Chen L. Hyperglycemia-Induced Dysregulated Fusion Intermediates in Insulin-Secreting Cells Visualized by Super-Resolution Microscopy. Front Cell Dev Biol 2021; 9:650167. [PMID: 33937248 PMCID: PMC8083903 DOI: 10.3389/fcell.2021.650167] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2021] [Accepted: 03/15/2021] [Indexed: 11/23/2022] Open
Abstract
Impaired insulin release is a hallmark of type 2 diabetes and is closely related to chronically elevated glucose concentrations, known as “glucotoxicity.” However, the molecular mechanisms by which glucotoxicity impairs insulin secretion remain poorly understood. In addition to known kiss-and-run and kiss-and-stay fusion events in INS-1 cells, ultrafast Hessian structured illumination microscopy (Hessian SIM) enables full fusion to be categorized according to the newly identified structures, such as ring fusion (those with enlarged pores) or dot fusion (those without apparent pores). In addition, we identified four fusion intermediates during insulin exocytosis: initial pore opening, vesicle collapse, enlarged pore formation, and final pore dilation. Long-term incubation in supraphysiological doses of glucose reduced exocytosis in general and increased the occurrence of kiss-and-run events at the expense of reduced full fusion. In addition, hyperglycemia delayed pore opening, vesicle collapse, and enlarged pore formation in full fusion events. It also reduced the size of apparently enlarged pores, all of which contributed to the compromised insulin secretion. These phenotypes were mostly due to the hyperglycemia-induced reduction in syntaxin-1A (Stx-1A) and SNAP-25 protein, since they could be recapitulated by the knockdown of endogenous Stx-1A and SNAP-25. These findings suggest essential roles for the vesicle fusion type and intermediates in regulating insulin secretion from pancreatic beta cells in normal and disease conditions.
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Affiliation(s)
- Guoyi Yang
- State Key Laboratory of Membrane Biology, Beijing Key Laboratory of Cardiometabolic Molecular Medicine, Institute of Molecular Medicine, School of Future Technology, Peking University, Beijing, China
| | - Liuju Li
- State Key Laboratory of Membrane Biology, Beijing Key Laboratory of Cardiometabolic Molecular Medicine, Institute of Molecular Medicine, School of Future Technology, Peking University, Beijing, China
| | - Yanmei Liu
- State Key Laboratory of Membrane Biology, Beijing Key Laboratory of Cardiometabolic Molecular Medicine, Institute of Molecular Medicine, School of Future Technology, Peking University, Beijing, China.,Institute for Brain Research and Rehabilitation, Key Laboratory of Brain, Cognition and Education Science, South China Normal University, Guangzhou, China
| | - Kuo Liang
- Department of General Surgery, Xuanwu Hospital, Capital Medical University, Beijing, China
| | - Lisi Wei
- State Key Laboratory of Membrane Biology, Beijing Key Laboratory of Cardiometabolic Molecular Medicine, Institute of Molecular Medicine, School of Future Technology, Peking University, Beijing, China
| | - Liangyi Chen
- State Key Laboratory of Membrane Biology, Beijing Key Laboratory of Cardiometabolic Molecular Medicine, Institute of Molecular Medicine, School of Future Technology, Peking University, Beijing, China.,PKU-IDG/McGovern Institute for Brain Research, Beijing, China.,Beijing Academy of Artificial Intelligence, Beijing, China.,Shenzhen Bay Laboratory, Shenzhen, China
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5
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Holz RW, Zimmerberg J. Dynamic Relationship of the SNARE Complex with a Membrane. Biophys J 2019; 117:627-630. [PMID: 31378313 DOI: 10.1016/j.bpj.2019.07.010] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2019] [Revised: 06/19/2019] [Accepted: 07/09/2019] [Indexed: 11/28/2022] Open
Abstract
Fusion of secretory granules and synaptic vesicles with the plasma membrane is driven by SNARE protein interactions. Intensive investigations in vitro, which include x-ray crystallography, cryoelectron microscopy, and NMR analyses by numerous groups, have elucidated structures relevant to the function of these proteins. Although function depends on the proteins being membrane bound, for experimental reasons, most of the studies have used cytosolic domains, as exemplified by the groundbreaking studies that elucidated the structure of a tetrapeptide helical bundle formed by interaction of the cytosolic domains of syntaxin1A, SNAP25 (two peptides) and synaptobrevin 2. Because the cytosolic fragments were unfettered by membrane attachments, it is likely that the tetrapeptide helical bundle reflects the lowest energy state, such as that found in the "cis" interactions of the SNARE motifs after fusion when they co-localize in the plasma membrane. Much more difficult to study and still poorly understood are critical "trans" interactions between the synaptic vesicle SNARE protein synaptobrevin 2 and the plasma membrane syntaxin1A/SNAP25 complex that initiate the fusion event. In a series of articles from the laboratory of Lukas Tamm, the spontaneous orientation of the SNARE motif of membrane-bound, full-length syntaxin1A with respect to the membrane hosting syntaxin's transmembrane domain was investigated with nanometer precision under a variety of conditions, including those that model aspects of the "trans" configuration. The studies rely on fluorescence interference-contrast microscopy, a technique that utilizes the pattern of constructive and destructive interference arising from incoming and reflected excitation and emission light at the surface of a silicon chip that has been layered with oxidized silicon of varying depths. This Perspective discusses their findings, including the unexpected influence of the degree of lipid unsaturation on the orientation of the SNARE complex.
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Affiliation(s)
- Ronald W Holz
- Department of Pharmacology, University of Michigan Medical School, Ann Arbor, Michigan.
| | - Joshua Zimmerberg
- Division of Basic and Translational Biophysics, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland
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6
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Levin J. The Evolution of Mammalian Platelets. Platelets 2019. [DOI: 10.1016/b978-0-12-813456-6.00001-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/16/2023]
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Abbineni PS, Axelrod D, Holz RW. Visualization of expanding fusion pores in secretory cells. J Gen Physiol 2018; 150:1640-1646. [PMID: 30470717 PMCID: PMC6279363 DOI: 10.1085/jgp.201812186] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2018] [Accepted: 11/06/2018] [Indexed: 11/20/2022] Open
Abstract
Abbineni et al. examine recent imaging work on fusion pores and discuss the dynamics of PI-4,5-P2 accumulation on granule membranes.
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Affiliation(s)
- Prabhodh S Abbineni
- Department of Pharmacology, University of Michigan Medical School, Ann Arbor, MI
| | - Daniel Axelrod
- Department of Pharmacology, University of Michigan Medical School, Ann Arbor, MI .,Department of Physics and LSA Biophysics, University of Michigan Medical School, Ann Arbor, MI
| | - Ronald W Holz
- Department of Pharmacology, University of Michigan Medical School, Ann Arbor, MI
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Álvarez de Toledo G, Montes MÁ, Montenegro P, Borges R. Phases of the exocytotic fusion pore. FEBS Lett 2018; 592:3532-3541. [PMID: 30169901 DOI: 10.1002/1873-3468.13234] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2018] [Revised: 08/25/2018] [Accepted: 08/28/2018] [Indexed: 01/19/2023]
Abstract
Membrane fusion and fission are fundamental processes in living organisms. Membrane fusion occurs through the formation of a fusion pore, which is the structure that connects two lipid membranes during their fusion. Fusion pores can form spontaneously, but cells endow themselves with a set of proteins that make the process of fusion faster and regulatable. The fusion pore starts with a narrow diameter and dilates relatively slowly; it may fluctuate in size or can even close completely, producing a transient vesicle fusion (kiss-and-run), or can finally expand abruptly to release all vesicle contents. A set of proteins control the formation, dilation, and eventual closure of the fusion pore and, therefore, the velocity at which the contents of secretory vesicles are released to the extracellular medium. Thus, the regulation of fusion pore expansion or closure is key to regulate the release of neurotransmitters and hormones. Here, we review the phases of the fusion pore and discuss the implications in the modes of exocytosis.
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Affiliation(s)
| | - María Ángeles Montes
- Dpto. Fisiología Médica y Biofísica, Facultad de Medicina, Universidad de Sevilla, Spain
| | - Pablo Montenegro
- Unidad de Farmacología, Facultad de Medicina, Universidad de La Laguna, Spain
| | - Ricardo Borges
- Unidad de Farmacología, Facultad de Medicina, Universidad de La Laguna, Spain
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9
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Fast, long-term, super-resolution imaging with Hessian structured illumination microscopy. Nat Biotechnol 2018; 36:451-459. [PMID: 29644998 DOI: 10.1038/nbt.4115] [Citation(s) in RCA: 238] [Impact Index Per Article: 39.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2017] [Accepted: 03/01/2018] [Indexed: 01/13/2023]
Abstract
To increase the temporal resolution and maximal imaging time of super-resolution (SR) microscopy, we have developed a deconvolution algorithm for structured illumination microscopy based on Hessian matrixes (Hessian-SIM). It uses the continuity of biological structures in multiple dimensions as a priori knowledge to guide image reconstruction and attains artifact-minimized SR images with less than 10% of the photon dose used by conventional SIM while substantially outperforming current algorithms at low signal intensities. Hessian-SIM enables rapid imaging of moving vesicles or loops in the endoplasmic reticulum without motion artifacts and with a spatiotemporal resolution of 88 nm and 188 Hz. Its high sensitivity allows the use of sub-millisecond excitation pulses followed by dark recovery times to reduce photobleaching of fluorescent proteins, enabling hour-long time-lapse SR imaging of actin filaments in live cells. Finally, we observed the structural dynamics of mitochondrial cristae and structures that, to our knowledge, have not been observed previously, such as enlarged fusion pores during vesicle exocytosis.
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10
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Liang K, Wei L, Chen L. Exocytosis, Endocytosis, and Their Coupling in Excitable Cells. Front Mol Neurosci 2017; 10:109. [PMID: 28469555 PMCID: PMC5395637 DOI: 10.3389/fnmol.2017.00109] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2017] [Accepted: 03/31/2017] [Indexed: 11/13/2022] Open
Abstract
Evoked exocytosis in excitable cells is fast and spatially confined and must be followed by coupled endocytosis to enable sustained exocytosis while maintaining the balance of the vesicle pool and the plasma membrane. Various types of exocytosis and endocytosis exist in these excitable cells, as those has been found from different types of experiments conducted in different cell types. Correlating these diversified types of exocytosis and endocytosis is problematic. By providing an outline of different exocytosis and endocytosis processes and possible coupling mechanisms here, we emphasize that the endocytic pathway may be pre-determined at the time the vesicle chooses to fuse with the plasma membrane in one specific mode. Therefore, understanding the early intermediate stages of vesicle exocytosis may be instrumental in exploring the mechanism of tailing endocytosis.
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Affiliation(s)
- Kuo Liang
- Department of General Surgery, XuanWu Hospital, Capital Medical UniversityBeijing, China
| | - Lisi Wei
- State Key Laboratory of Membrane Biology, Beijing Key Laboratory of Cardiometabolic Molecular Medicine, Institute of Molecular Medicine, Peking UniversityBeijing, China
| | - Liangyi Chen
- State Key Laboratory of Membrane Biology, Beijing Key Laboratory of Cardiometabolic Molecular Medicine, Institute of Molecular Medicine, Peking UniversityBeijing, China
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11
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Armstrong PB. Comparative Biology of the Pentraxin Protein Family: Evolutionarily Conserved Component of Innate Immune System. INTERNATIONAL REVIEW OF CELL AND MOLECULAR BIOLOGY 2015; 316:1-47. [DOI: 10.1016/bs.ircmb.2015.01.002] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
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12
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Zimmerberg J, Blank PS. It's what's inside that matters. Biophys J 2014; 107:5-7. [PMID: 24988334 DOI: 10.1016/j.bpj.2014.05.032] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2014] [Accepted: 05/06/2014] [Indexed: 10/25/2022] Open
Affiliation(s)
- Joshua Zimmerberg
- Program in Physical Biology, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland.
| | - Paul S Blank
- Program in Physical Biology, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland
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Smith CL, Varoqueaux F, Kittelmann M, Azzam RN, Cooper B, Winters CA, Eitel M, Fasshauer D, Reese TS. Novel cell types, neurosecretory cells, and body plan of the early-diverging metazoan Trichoplax adhaerens. Curr Biol 2014; 24:1565-1572. [PMID: 24954051 DOI: 10.1016/j.cub.2014.05.046] [Citation(s) in RCA: 135] [Impact Index Per Article: 13.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2014] [Revised: 04/03/2014] [Accepted: 05/19/2014] [Indexed: 11/18/2022]
Abstract
BACKGROUND Trichoplax adhaerens is the best-known member of the phylum Placozoa, one of the earliest-diverging metazoan phyla. It is a small disk-shaped animal that glides on surfaces in warm oceans to feed on algae. Prior anatomical studies of Trichoplax revealed that it has a simple three-layered organization with four somatic cell types. RESULTS We reinvestigate the cellular organization of Trichoplax using advanced freezing and microscopy techniques to identify localize and count cells. Six somatic cell types are deployed in stereotyped positions. A thick ventral plate, comprising the majority of the cells, includes ciliated epithelial cells, newly identified lipophil cells packed with large lipid granules, and gland cells. Lipophils project deep into the interior, where they alternate with regularly spaced fiber cells whose branches contact all other cell types, including cells of the dorsal and ventral epithelium. Crystal cells, each containing a birefringent crystal, are arrayed around the rim. Gland cells express several proteins typical of neurosecretory cells, and a subset of them, around the rim, also expresses an FMRFamide-like neuropeptide. CONCLUSIONS Structural analysis of Trichoplax with significantly improved techniques provides an advance in understanding its cell types and their distributions. We find two previously undetected cell types, lipohil and crystal cells, and an organized body plan in which different cell types are arranged in distinct patterns. The composition of gland cells suggests that they are neurosecretory cells and could control locomotor and feeding behavior.
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Affiliation(s)
- Carolyn L Smith
- National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892, USA.
| | - Frédérique Varoqueaux
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, Hermann-Rein-Strasse 3, 37075 Göttingen, Germany; Department of Fundamental Neurosciences, University of Lausanne, Rue du Bugnon 9, 1005 Lausanne, Switzerland
| | - Maike Kittelmann
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, Hermann-Rein-Strasse 3, 37075 Göttingen, Germany
| | - Rita N Azzam
- National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892, USA
| | - Benjamin Cooper
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, Hermann-Rein-Strasse 3, 37075 Göttingen, Germany
| | - Christine A Winters
- National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892, USA
| | - Michael Eitel
- Ecology and Evolution, Institut für Tierökologie und Zellbiologie, TiHo Hannover, Buenteweg 17d, 30559 Hannover, Germany
| | - Dirk Fasshauer
- Department of Fundamental Neurosciences, University of Lausanne, Rue du Bugnon 9, 1005 Lausanne, Switzerland.
| | - Thomas S Reese
- National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892, USA
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Molotkovsky RJ, Akimov SA. Stabilization of a complex of fusion proteins by membrane deformations. Biophysics (Nagoya-shi) 2013. [DOI: 10.1134/s0006350913050096] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
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John BA, Jalal K, Kamaruzzam Y, Zaleha K. Mechanism in the Clot Formation of Horseshoe Crab Blood during Bacterial Endotoxin Invasion. ACTA ACUST UNITED AC 2010. [DOI: 10.3923/jas.2010.1930.1936] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
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18
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Plonsky I, Kingsley DH, Rashtian A, Blank PS, Zimmerberg J. Initial size and dynamics of viral fusion pores are a function of the fusion protein mediating membrane fusion. Biol Cell 2008; 100:377-86. [PMID: 18208404 PMCID: PMC3650648 DOI: 10.1042/bc20070040] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
BACKGROUND INFORMATION Protein-mediated merger of biological membranes, membrane fusion, is an important process. To investigate the role of fusogenic proteins in the initial size and dynamics of the fusion pore (a narrow aqueous pathway, which widens to finalize membrane fusion), two different fusion proteins expressed in the same cell line were investigated: the major glycoprotein of baculovirus Autographa californica (GP64) and the HA (haemagglutinin) of influenza X31. RESULTS The host Sf9 cells expressing these viral proteins, irrespective of protein species, fused to human RBCs (red blood cells) upon acidification of the medium. A high-time-resolution electrophysiological study of fusion pore conductance revealed fundamental differences in (i) the initial pore conductance; pores created by HA were smaller than those created by GP64; (ii) the ability of pores to flicker; only HA-mediated pores flickered; and (iii) the time required for pore formation; HA-mediated pores took much longer to form after acidification. CONCLUSION HA and GP64 have divergent electrophysiological phenotypes even when they fuse identical membranes, and fusion proteins play a crucial role in determining initial fusion pore characteristics. The structure of the initial fusion pore detected by electrical conductance measurements is sensitive to the nature of the fusion protein.
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Affiliation(s)
- Ilya Plonsky
- Laboratory of Cellular and Molecular Biophysics, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892-1855, U.S.A
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Neco P, Fernández-Peruchena C, Navas S, Gutiérrez LM, de Toledo GA, Alés E. Myosin II contributes to fusion pore expansion during exocytosis. J Biol Chem 2008; 283:10949-57. [PMID: 18283106 DOI: 10.1074/jbc.m709058200] [Citation(s) in RCA: 80] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
During exocytosis, the fusion pore expands to allow release of neurotransmitters and hormones to the extracellular space. To understand the process of synaptic transmission, it is of outstanding importance to know the properties of the fusion pore and how these properties affect the release process. Many proteins have been implicated in vesicle fusion; however, there is little evidence for proteins involved in fusion pore expansion. Myosin II has been shown to participate in the transport of vesicles and, surprisingly, in the final phases of exocytosis, affecting the kinetics of catecholamine release in adrenal chromaffin cells as measured by amperometry. Here, we have studied single vesicle exocytosis in chromaffin cells overexpressing an unphosphorylatable form (T18AS19A RLC-GFP) of myosin II that produces an inactive protein by patch amperometry. This method allows direct determination of fusion pore expansion by measuring its conductance, whereas the release of catecholamines is recorded simultaneously by amperometry. Here we demonstrated that the fusion pore is of critical importance to control the release of catecholamines during single vesicle secretion in chromaffin cells. We proved that myosin II acts as a molecular motor on the fusion pore expansion by hindering its dilation when it lacks the phosphorylation sites.
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Affiliation(s)
- Patricia Neco
- Departamento Fisiología Médica y Biofísica, Universidad de Sevilla, Sevilla 41009, Spain
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Iwanaga S, Muta T, Shigenaga T, Seki N, Kawano K, Katsu T, Kawabata S. Structure-function relationships of tachyplesins and their analogues. CIBA FOUNDATION SYMPOSIUM 2007; 186:160-74; discussion 174-5. [PMID: 7768150 DOI: 10.1002/9780470514658.ch10] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Haemocytes of the horseshoe crab (Limulus) contain a new family of arthropodous peptide antibiotics, termed the tachyplesin family. These cationic peptides are composed of 17-18 amino acid residues with a C-terminal arginine alpha-amide. Tachyplesin I takes on a fairly rigid conformation constrained by two disulphide bridges and adopts a conformation consisting of an antiparallel beta-sheet connected by a beta-turn. Isopeptides of tachyplesin I with amino acid replacements, tachyplesins II and III, and polyphemusins I and II have also been found in the haemocytes of the South-East Asian species and Limulus polyphemus. These peptides are present in abundance in the small granules of the haemocytes and inhibit strongly the growth of not only Gram-negative and Gram-positive bacteria but also fungi such as Candida albicans. Tachyplesin exists in the prepro form consisting of 77 residues; this precursor is probably processed by intracellular proteases and an amidation enzyme before incorporation into the small granules of the haemocytes. We examined the mode of action of tachyplesin I on biomembranes, comparing it with that of gramicidin S. Tachyplesin caused an efflux of K+ from Staphylococcus aureus and Escherichia coli cells similar to that caused by gramicidin S. Another antimicrobial substance, anti-LPS factor, has been isolated from haemocytes.
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Affiliation(s)
- S Iwanaga
- Department of Molecular Biology, Graduate School of Medical Science, Kyushu University, Fukuoka, Japan
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Jeftinija S. The story of cell secretion: events leading to the discovery of the 'porosome' - the universal secretory machinery in cells. J Cell Mol Med 2006; 10:273-9. [PMID: 16796798 PMCID: PMC3933120 DOI: 10.1111/j.1582-4934.2006.tb00398.x] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022] Open
Abstract
Cell secretio has come age, and a century old quest has been elegantly solved. We have come a long way since earlier observations of what appeared to be ‘fibrillar regions’ at teh cell plasama membrance, and electrophysological studies suggesting the presence of ‘fusion pores’ at the cell plasma membrane where secretion occurs. Finally, the fusion pore or ‘porosome’ has been discovered, and its morpholgy and dynamics determined at nm resolution and in real time in live secretory cells. The porosome has been isolated, its omposition determined at nm resolution and in real time in live secretory cells. The porosme has been isolated, its composition determmined and it has been jkboth structurally and functionally reconsituted n artificial lipid membrance. The discoversy of the porosome as the univeral secretory machinery in cell and the discovery of the molecular mechaninsm of vesicular content expulsion during cell secretin have fially enabled a clear understanding of this important cellular process. This review outlines the fascinating and exciting joumey leding to the dicovery of the porosme, ultimately solving one of the most difficut, significant, and fundamental cellular process- cell seretion.
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Affiliation(s)
- S Jeftinija
- Department of Biomedical Sciences, College of Veterinary Medicine, Ames, IA 50011-1250, USA.
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Harata NC, Aravanis AM, Tsien RW. Kiss-and-run and full-collapse fusion as modes of exo-endocytosis in neurosecretion. J Neurochem 2006; 97:1546-70. [PMID: 16805768 DOI: 10.1111/j.1471-4159.2006.03987.x] [Citation(s) in RCA: 138] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Neurotransmitters and hormones are released from neurosecretory cells by exocytosis (fusion) of synaptic vesicles, large dense-core vesicles and other types of vesicles or granules. The exocytosis is terminated and followed by endocytosis (retrieval). More than fifty years of research have established full-collapse fusion and clathrin-mediated endocytosis as essential modes of exo-endocytosis. Kiss-and-run and vesicle reuse represent alternative modes, but their prevalence and importance have yet to be elucidated, especially in neurons of the mammalian CNS. Here we examine various modes of exo-endocytosis across a wide range of neurosecretory systems. Full-collapse fusion and kiss-and-run coexist in many systems and play active roles in exocytotic events. In small nerve terminals of CNS, kiss-and-run has an additional role of enabling nerve terminals to conserve scarce vesicular resources and respond to high-frequency inputs. Full-collapse fusion and kiss-and-run will each contribute to maintaining cellular communication over a wide range of frequencies.
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Affiliation(s)
- Nobutoshi C Harata
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, California, USA
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Conrad ML, Pardy RL, Wainwright N, Child A, Armstrong PB. Response of the blood clotting system of the American horseshoe crab, Limulus polyphemus, to a novel form of lipopolysaccharide from a green alga. Comp Biochem Physiol A Mol Integr Physiol 2006; 144:423-8. [PMID: 16707269 DOI: 10.1016/j.cbpa.2006.03.013] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2005] [Revised: 03/17/2006] [Accepted: 03/24/2006] [Indexed: 11/19/2022]
Abstract
Lipopolysaccharide (LPS, endotoxin) is a component of Gram-negative bacteria and is the principal indicator to the innate immune systems of higher animals of a Gram-negative bacterial invasion. LPS activates the blood clotting system of the American horseshoe crab, Limulus polyphemus. By stimulating blood cell degranulation, LPS triggers the release of the proteins of the clotting system from the cells, and by activating a protease cascade that converts coagulogen, a soluble zymogen, to coagulin, the structural protein of the clot, LPS triggers the production of the fibrillar coagulin blood clot. Although originally thought to be restricted to the Gram-negative bacteria and the cyanobacteria, LPS, or a very similar molecule, has recently been described from a eukaryotic green alga, Chlorella. Here we show that, like LPS from Gram-negative bacteria, the algal molecule stimulates exocytosis of the Limulus blood cell and the clotting of coagulin. The coagulin clot efficiently entraps the cells of Chlorella in a network of fibrils. Invasion and erosion of the carapace by green algae is an important cause of mortality of Limulus, and it is suggested that the cellular response to aLPS may contribute to defense against this pathogen.
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Affiliation(s)
- Mara L Conrad
- Marine Biological Laboratory, 7 MBL Street, Woods Hole, MA 02543, USA
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25
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Muys JJ, Alkaisi MM, Melville DOS, Nagase J, Sykes P, Parguez GM, Evans JJ. Cellular transfer and AFM imaging of cancer cells using Bioimprint. J Nanobiotechnology 2006; 4:1. [PMID: 16426461 PMCID: PMC1395325 DOI: 10.1186/1477-3155-4-1] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2005] [Accepted: 01/22/2006] [Indexed: 01/26/2023] Open
Abstract
A technique for permanently capturing a replica impression of biological cells has been developed to facilitate analysis using nanometer resolution imaging tools, namely the atomic force microscope (AFM). The method, termed Bioimprint™, creates a permanent cell 'footprint' in a non-biohazardous Poly (dimethylsiloxane) (PDMS) polymer composite. The transfer of nanometer scale biological information is presented as an alternative imaging technique at a resolution beyond that of optical microscopy. By transferring cell topology into a rigid medium more suited for AFM imaging, many of the limitations associated with scanning of biological specimens can be overcome. Potential for this technique is demonstrated by analyzing Bioimprint™ replicas created from human endometrial cancer cells. The high resolution transfer of this process is further detailed by imaging membrane morphological structures consistent with exocytosis. The integration of soft lithography to replicate biological materials presents an enhanced method for the study of biological systems at the nanoscale.
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Affiliation(s)
- JJ Muys
- Department of Electrical and Computer Engineering, University of Canterbury, Private Bag 4800, Christchurch, New Zealand
- MacDiarmid Institute for Advanced Materials and Nanotechnology, University of Canterbury, Private Bag 4800, Christchurch, New Zealand
| | - MM Alkaisi
- Department of Electrical and Computer Engineering, University of Canterbury, Private Bag 4800, Christchurch, New Zealand
- MacDiarmid Institute for Advanced Materials and Nanotechnology, University of Canterbury, Private Bag 4800, Christchurch, New Zealand
| | - DOS Melville
- Department of Electrical and Computer Engineering, University of Canterbury, Private Bag 4800, Christchurch, New Zealand
- MacDiarmid Institute for Advanced Materials and Nanotechnology, University of Canterbury, Private Bag 4800, Christchurch, New Zealand
| | - J Nagase
- Christchurch School of Medicine and Health Sciences, University of Otago, Private Bag 4345, Christchurch, New Zealand
| | - P Sykes
- Christchurch School of Medicine and Health Sciences, University of Otago, Private Bag 4345, Christchurch, New Zealand
| | - GM Parguez
- Department of Electrical and Computer Engineering, University of Canterbury, Private Bag 4800, Christchurch, New Zealand
| | - JJ Evans
- MacDiarmid Institute for Advanced Materials and Nanotechnology, University of Canterbury, Private Bag 4800, Christchurch, New Zealand
- Christchurch School of Medicine and Health Sciences, University of Otago, Private Bag 4345, Christchurch, New Zealand
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Abstract
We have recently proposed a mechanism to describe secretion, a fundamental process in all cells. That hypothesis, called porocytosis, embodies all available data and encompasses both forms of secretion, i.e., vesicular and constitutive. The current accepted view of exocytotic secretion involves the physical fusion of vesicle and plasma membranes; however, that hypothesized mechanism does not fit all available physiological data. Energetics of apposed lipid bilayers do not favor unfacilitated fusion. We consider that calcium ions (e.g., 10(-4) to 10(-3) M calcium in microdomains when elevated for 1 ms or less), whose mobility is restricted in space and time, establish salt bridges among adjacent lipid molecules. This establishes transient pores that span both the vesicle and plasma membrane lipid bilayers; the diameter of this transient pore would be approximately 1 nm (the diameter of a single lipid molecule). The lifetime of the transient pore is completely dependent on the duration of sufficient calcium ion levels. This places the porocytosis hypothesis for secretion squarely in the realm of the physical and physical chemical interactions of calcium and phospholipids and places mass action as the driving force for release of secretory material. The porocytosis hypothesis that we propose satisfies all of the observations and provides a framework to integrate our combined knowledge of vesicular and constitutive secretion.
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Affiliation(s)
- Robert B Silver
- Department of Pharmacology, School of Medicine, Wayne State University, Detroit, MI 48201, USA.
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Conrad M, DeNobile J, Chaikhoutdinov I, Escribano D, Lee KG, Cohen WD. Cytoskeletal organization of limulus amebocytes pre- and post-activation: comparative aspects. THE BIOLOGICAL BULLETIN 2004; 207:56-66. [PMID: 15315943 DOI: 10.2307/1543628] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
One of the major functions of circulating Limulus amebocytes is to effect blood coagulation upon receipt of appropriate signals. However, the hypothesis that Limulus amebocytes are fundamentally similar to vertebrate thrombocytes and platelets has not been tested sufficiently in previous studies of their cytoskeletal organization. Whereas the earlier data were derived from transmission electron microscopy (TEM) of thin sections of a limited number of cells, improved fluorescence labeling methods that retain cell morphology have now enabled us to survey F-actin and microtubule organization in intact individual amebocytes and in large amebocyte populations pre- and post-activation. Anti-tubulin immunofluorescence showed the marginal band (MB) of microtubules to be ellipsoidal in most unactivated cells, with essentially no other microtubules present. However, minor subpopulations of cells with discoidal or pointed shape, containing corresponding arrangements of microtubules suggestive of morphogenetic intermediates, were also observed. Texas-red phalloidin labeled an F-actin-rich cortex in unactivated amebocytes, accounting for MB and granule separation from the plasma membrane as visualized in TEM thin sections, and supporting earlier models for MB maintenance of flattened amebocyte morphology by pressure against a cortical layer. Shape transformation after activation by bacterial lipopolysaccharide was attributable principally to spiky and spreading F-actin in outer cell regions, with the MB changing to twisted, nuclei-associated forms and eventually becoming unrecognizable. These major pre- and post-activation cytoskeletal features resemble those of platelets and non-mammalian vertebrate thrombocytes, supporting recognition of the Limulus amebocyte as a representative evolutionary precursor of more specialized clotting cell types.
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Affiliation(s)
- Mara Conrad
- Department of Biological Sciences, Hunter College, New York, NY 10021, USA
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Heuvingh J, Pincet F, Cribier S. Hemifusion and fusion of giant vesicles induced by reduction of inter-membrane distance. THE EUROPEAN PHYSICAL JOURNAL. E, SOFT MATTER 2004; 14:269-276. [PMID: 15338438 DOI: 10.1140/epje/i2003-10151-2] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Proteins involved in membrane fusion, such as SNARE or influenza virus hemagglutinin, share the common function of pulling together opposing membranes in closer contact. The reduction of inter-membrane distance can be sufficient to induce a lipid transition phase and thus fusion. We have used functionalized lipids bearing DNA bases as head groups incorporated into giant unilamellar vesicles in order to reproduce the reduction of distance between membranes and to trigger fusion in a model system. In our experiments, two vesicles were isolated and brought into adhesion by the mean of micromanipulation; their evolution was monitored by fluorescence microscopy. Actual fusion only occurred in about 5% of the experiments. In most cases, a state of "hemifusion" is observed and quantified. In this state, the outer leaflets of both vesicles' bilayers merged whereas the inner leaflets and the aqueous inner contents remained independent. The kinetics of the lipid probes redistribution is in good agreement with a diffusion model in which lipids freely diffuse at the circumference of the contact zone between the two vesicles. The minimal density of bridging structures, such as stalks, necessary to explain this redistribution kinetics can be estimated.
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Affiliation(s)
- J Heuvingh
- Laboratoire de Physico-Chimie Moléculaire des Membranes Biologiques, URD-CNRS UMR 7099, IBPC, 13 rue Pierre et Marie Curie, 75005 Paris, France.
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29
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Abstract
The secretory process requires many different steps and stages. Vesicles must be formed and transported to the target membrane. They must be tethered or docked at the appropriate sites and must be prepared for fusion (priming). As the last step, a fusion pore is formed and the contents are released. Release of neurotransmitter is an extremely rapid event leading to rise times of the postsynaptic response of less than 100 micro s. The release thus occurs during the initial formation of the exocytotic fusion pore. To understand the process of synaptic transmission, it is thus of outstanding importance to understand the molecular structure of the fusion pore, what are the properties of the initial fusion pore, how these properties affect the release process and what other factors may be limiting the kinetics of release. Here we review the techniques currently employed in fusion pore studies and discuss recent data and opinions on exocytotic fusion pore properties.
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Affiliation(s)
- Manfred Lindau
- School of Applied and Engineering Physics, Cornell University, Ithaca, NY 14850, USA.
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Kozlovsky Y, Chernomordik LV, Kozlov MM. Lipid intermediates in membrane fusion: formation, structure, and decay of hemifusion diaphragm. Biophys J 2002; 83:2634-51. [PMID: 12414697 PMCID: PMC1302349 DOI: 10.1016/s0006-3495(02)75274-0] [Citation(s) in RCA: 222] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Lipid bilayer fusion is thought to involve formation of a local hemifusion connection, referred to as a fusion stalk. The subsequent fusion stages leading to the opening of a fusion pore remain unknown. The earliest fusion pore could represent a bilayer connection between the membranes and could be formed directly from the stalk. Alternatively, fusion pore can form in a single bilayer, referred to as hemifusion diaphragm (HD), generated by stalk expansion. To analyze the plausibility of stalk expansion, we studied the pathway of hemifusion theoretically, using a recently developed elastic model. We show that the stalk has a tendency to expand into an HD for lipids with sufficiently negative spontaneous splay, (~)J(s)< 0. For different experimentally relevant membrane configurations we find two characteristic values of the spontaneous splay. (~)J*(s) and (~)J**(s), determining HD dimension. The HD is predicted to have a finite equilibrium radius provided that the spontaneous splay is in the range (~)J**(s)< (~)J(s)<(~)J*(s), and to expand infinitely for (~)J(s)<(~)J**(s). In the case of common lipids, which do not fuse spontaneously, an HD forms only under action of an external force pulling the diaphragm rim apart. We calculate the dependence of the HD radius on this force. To address the mechanism of fusion pore formation, we analyze the distribution of the lateral tension emerging in the HD due to the establishment of lateral equilibrium between the deformed and relaxed portions of lipid monolayers. We show that this tension concentrates along the HD rim and reaches high values sufficient to rupture the bilayer and form the fusion pore. Our analysis supports the hypothesis that transition from a hemifusion to a fusion pore involves radial expansion of the stalk.
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Affiliation(s)
- Yonathan Kozlovsky
- Department of Physiology and Pharmacology, Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv 69978, Israel
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31
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Abstract
We studied the interaction of bilayer vesicles and adhesive nanoparticles using a Brownian dynamics simulation. The nanoparticles are simple models of proteins or colloids. The adhering nanoparticle induces the morphological change of the vesicle: budding, formation of two vesicles in which only outer monolayers are connected, and fission. We also show that the nanoparticle promotes the fusion process: fusion-pore opening from a stalk intermediate, a neck-like structure that only connects outer monolayers of two vesicles. The nanoparticle bends the stalk, and induces the pore opening.
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Affiliation(s)
- Hiroshi Noguchi
- Department of Applied Molecular Science, Institute for Molecular Science, Okazaki 444-8585, Japan.
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Chen FS, Markosyan RM, Melikyan GB. The process of membrane fusion: Nipples, hemifusion, pores, and pore growth. PEPTIDE-LIPID INTERACTIONS 2002. [DOI: 10.1016/s1063-5823(02)52020-2] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
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34
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Grinstein S, Vander Meulen J, Furuya W. Possible role of H+-alkali cation countertransport in secretary granule swelling during exocytosis. FEBS Lett 2001. [DOI: 10.1016/0014-5793(82)81230-1] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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Kuzmin PI, Zimmerberg J, Chizmadzhev YA, Cohen FS. A quantitative model for membrane fusion based on low-energy intermediates. Proc Natl Acad Sci U S A 2001; 98:7235-40. [PMID: 11404463 PMCID: PMC34652 DOI: 10.1073/pnas.121191898] [Citation(s) in RCA: 251] [Impact Index Per Article: 10.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2000] [Accepted: 04/18/2001] [Indexed: 11/18/2022] Open
Abstract
The energetics of a fusion pathway is considered, starting from the contact site where two apposed membranes each locally protrude (as "nipples") toward each other. The equilibrium distance between the tips of the two nipples is determined by a balance of physical forces: repulsion caused by hydration and attraction generated by fusion proteins. The energy to create the initial stalk, caused by bending of cis monolayer leaflets, is much less when the stalk forms between nipples rather than parallel flat membranes. The stalk cannot, however, expand by bending deformations alone, because this would necessitate the creation of a hydrophobic void of prohibitively high energy. But small movements of the lipids out of the plane of their monolayers allow transformation of the stalk into a modified stalk. This intermediate, not previously considered, is a low-energy structure that can reconfigure into a fusion pore via an additional intermediate, the prepore. The lipids of this latter structure are oriented as in a fusion pore, but the bilayer is locally compressed. All membrane rearrangements occur in a discrete local region without creation of an extended hemifusion diaphragm. Importantly, all steps of the proposed pathway are energetically feasible.
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Affiliation(s)
- P I Kuzmin
- Frumkin Institute of Electrochemistry, Moscow, Russia 117071
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36
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Samuel ADT, Petersen JD, Reese TS. Envelope structure of Synechococcus sp. WH8113, a nonflagellated swimming cyanobacterium. BMC Microbiol 2001; 1:4. [PMID: 11329361 PMCID: PMC31413 DOI: 10.1186/1471-2180-1-4] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2001] [Accepted: 04/24/2001] [Indexed: 11/28/2022] Open
Abstract
BACKGROUND Many bacteria swim by rotating helical flagellar filaments. Waterbury et al. discovered an exception, strains of the cyanobacterium Synechococcus that swim without flagella or visible changes in shape. Other species of cyanobacteria glide on surfaces. The hypothesis that Synechococcus might swim using traveling surface waves prompted this investigation. RESULTS Using quick-freeze electron microscopy, we have identified a crystalline surface layer that encloses the outer membrane of the motile strain Synechococcus sp. WH8113, the components of which are arranged in a rhomboid lattice. Spicules emerge in profusion from the layer and extend up to 150 nm into the surrounding fluid. These spicules also send extensions inwards to the inner cell membrane where motility is powered by an ion-motive force. CONCLUSION The envelope structure of Synechococcus sp. WH8113 provides new constraints on its motile mechanism. The spicules are well positioned to transduce energy at the cell membrane into mechanical work at the cell surface. One model is that an unidentified motor embedded in the cell membrane utilizes the spicules as oars to generate a traveling wave external to the surface layer in the manner of ciliated eukaryotes.
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Affiliation(s)
- Aravinthan DT Samuel
- Rowland Institute for Science, Cambridge, Massachusetts, USA and Department of Molecular & Cellular Biology, Harvard University, Cambridge, Massachusetts, USA
| | - Jennifer D Petersen
- Laboratory of Neurobiology, NIH, NINDS at the Marine Biological Laboratory, Woods Hole, Massachusetts, USA
| | - Thomas S Reese
- Laboratory of Neurobiology, NIH, NINDS at the Marine Biological Laboratory, Woods Hole, Massachusetts, USA
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Frolov VA, Cho MS, Bronk P, Reese TS, Zimmerberg J. Multiple local contact sites are induced by GPI-linked influenza hemagglutinin during hemifusion and flickering pore formation. Traffic 2000; 1:622-30. [PMID: 11208150 DOI: 10.1034/j.1600-0854.2000.010806.x] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Membrane fusion intermediates induced by the glycosylphosphatidylinositol-linked ectodomain of influenza hemagglutinin (GPI-HA) were investigated by rapid freeze, freeze-substitution, thin section electron microscopy, and with simultaneous recordings of whole-cell admittance and fluorescence. Upon triggering, the previously separated membranes developed numerous hourglass shaped points of membrane contact (approximately 10-130 nm waist) when viewed by electron microscopy. Stereo pairs showed close membrane contact at peaks of complementary protrusions, arising from each membrane. With HA, there were fewer contacts, but wide fusion pores. Physiological measurements showed fast lipid dye mixing between cells after acidification, and either fusion pore formation or the lack thereof (true hemifusion). For the earliest pores, a similar conductance distribution and frequency of flickering pores were detected for both HA and GPI-HA. For GPI-HA, lipid mixing was detected prior to, during, or after pore opening, whereas for HA, lipid mixing is seen only after pore opening. Our findings are consistent with a pathway wherein conformational changes in the ectodomain of HA pull membranes towards each other to form a contact site, then hemifusion and pore formation initiate in a small percentage of these contact sites. Finally, the transmembrane domain of HA is needed to complete membrane fusion for macromolecular content mixing.
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Affiliation(s)
- V A Frolov
- Laboratory of Cellular and Molecular Biophysics, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA
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38
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Valentijn K, Valentijn JA, Jamieson JD. Role of actin in regulated exocytosis and compensatory membrane retrieval: insights from an old acquaintance. Biochem Biophys Res Commun 1999; 266:652-61. [PMID: 10603303 DOI: 10.1006/bbrc.1999.1883] [Citation(s) in RCA: 67] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
This review summarizes new insights into the role of the actin cytoskeleton in exocytosis and compensatory membrane retrieval from mammalian regulated secretory cells. Data from our lab and others now indicate that the actin cytoskeleton is involved in exocytosis both as a negative regulator of membrane fusion under resting conditions and as a facilitator of movement of secretory granules to their site of fusion with the apical plasmalemma. Coating of docked secretory granules with actin filaments correlates with the dissociation of secretory-granule-associated rab3D, pointing out a novel role for rab proteins in modulating the actin cytoskeleton during regulated exocytosis. Compensatory membrane retrieval following regulated exocytosis is also critically dependent on the actin cytoskeleton both in initiating the formation of clathrin-coated retrieval vesicles and subsequent trafficking back into the cell. We propose that insertion of secretory granule membrane into the plasmalemma initiates a trigger for membrane retrieval, possibly by exposing sites where proteins involved in compensatory membrane retrieval are assembled. The results summarized in this review were derived primarily from investigations on the pancreatic acinar cell, an old friend who is providing modern wisdom not attainable in other simpler systems.
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Affiliation(s)
- K Valentijn
- Department of Cell Biology, Yale University School of Medicine, New Haven, Connecticut, 60520, USA
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39
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Roberts RL, Barbieri MA, Pryse KM, Chua M, Morisaki JH, Stahl PD. Endosome fusion in living cells overexpressing GFP-rab5. J Cell Sci 1999; 112 ( Pt 21):3667-75. [PMID: 10523503 DOI: 10.1242/jcs.112.21.3667] [Citation(s) in RCA: 128] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
CHO and BHK cells which overexpress either wild-type rab5 or rab5:Q79L, a constitutively active rab5 mutant, develop enlarged cytoplasmic vesicles that exhibit many characteristics of early endosomes including immunoreactivity for rab5 and transferrin receptor. Time-lapse video microscopy shows the enlarged endosomes arise primarily by fusion of smaller vesicles. These fusion events occur mostly by a ‘bridge’ fusion mechanism in which the initial opening between vesicles does not expand; instead, membrane flows slowly and continuously from the smaller to the larger endosome in the fusing pair, through a narrow, barely perceptible membranous ‘bridge’ between them. The unique aspect of rab5 mediated ‘bridge’ fusion is the persistence of a tight constriction at the site where vesicles merge and we hypothesize that this constriction results from the relatively slow disassembly of a putative docking/fusion complex. To determine the relation of rab5 to the fusion ‘bridge’, we used confocal fluorescence microscopy to monitor endosome fusion in cells overexpressing GFP-rab5 fusion proteins. Vesicle docking in these cells is accompanied by recruitment of the GFP-rab5 into a brightly fluorescent spot in the ‘bridge’ region between fusing vesicles that persists throughout the entire length of the fusion event and which often persist for minutes following endosome fusion. Other endosomal membrane markers, including FM4-64, are not concentrated in fusion ‘bridges’. These results support the idea that the GFP-rab5 spots represent the localized accumulation of GFP-rab5 between fusing endosomes and not simply overlap of adjacent membranes. The idea that the GFP-rab5 spots do not represent membrane overlap is further supported by experiments using photobleaching techniques and confocal imaging which show that GFP-rab5 localized in spots between fusion couplets is resistant to diffusion while GFP-rab5 on endosomal membranes away from these spots rapidly diffuses with a rate constant of about 1.0 (+/-0.3) x10(-)(9)cm(2)/second.
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Affiliation(s)
- R L Roberts
- Department of Cell Biology and Physiology and Biochemistry and Molecular Biophysics, Washington University, School of Medicine, St Louis, MO 63110, USA
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40
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Markosyan RM, Melikyan GB, Cohen FS. Tension of membranes expressing the hemagglutinin of influenza virus inhibits fusion. Biophys J 1999; 77:943-52. [PMID: 10423439 PMCID: PMC1300385 DOI: 10.1016/s0006-3495(99)76945-6] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
The effects of membrane tension on fusion between cells expressing the hemagglutinin (HA) of influenza virus and red blood cells were studied by capacitance measurements. Inflation of an HA-expressing cell was achieved by applying a positive hydrostatic pressure to its interior through a patch-clamp pipette in the whole-cell configuration. Inflating cells to the maximum extent possible without lysis created a membrane tension and completely inhibited low-pH-induced fusion at room temperature. Fully inflated cells that were subsequently deflated to normal size resumed the ability to fuse in response to low pH. At the higher temperature of 32 degrees C, fusion conditions were sufficiently optimal that full inflation did not hinder fusion, and once formed, pores enlarged more rapidly than those of never inflated cells. It is suggested that under fusogenic conditions HA causes the formation of a dimple within the membrane in which it resides, and that membrane tension hinders fusion by preventing the formation of dimples. Because dimpling bends the bilayer portion of bound membranes so that they come into intimate contact, the damping of dimpling would suppress this initial step in the fusion process.
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Affiliation(s)
- R M Markosyan
- Rush Medical College, Department of Molecular Biophysics and Physiology, Chicago, Illinois 60612, USA
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41
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Chizmadzhev YA, Kumenko DA, Kuzmin PI, Chernomordik LV, Zimmerberg J, Cohen FS. Lipid flow through fusion pores connecting membranes of different tensions. Biophys J 1999; 76:2951-65. [PMID: 10354423 PMCID: PMC1300267 DOI: 10.1016/s0006-3495(99)77450-3] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022] Open
Abstract
When two membranes fuse, their components mix; this is usually described as a purely diffusional process. However, if the membranes are under different tensions, the material will spread predominantly by convection. We use standard fluid mechanics to rigorously calculate the steady-state convective flux of lipids. A fusion pore is modeled as a toroid shape, connecting two planar membranes. Each of the membrane monolayers is considered separately as incompressible viscous media with the same shear viscosity, etas. The two monolayers interact by sliding past each other, described by an intermonolayer viscosity, etar. Combining a continuity equation with an equation that balances the work provided by the tension difference, Deltasigma, against the energy dissipated by flow in the viscous membrane, yields expressions for lipid velocity, upsilon, and area of lipid flux, Phi. These expressions for upsilon and Phi depend on Deltasigma, etas, etar, and geometrical aspects of a toroidal pore, but the general features of the theory hold for any fusion pore that has a roughly hourglass shape. These expressions are readily applicable to data from any experiments that monitor movement of lipid dye between fused membranes under different tensions. Lipid velocity increases nonlinearly from a small value for small pore radii, rp, to a saturating value at large rp. As a result of velocity saturation, the flux increases linearly with pore radius for large pores. The calculated lipid flux is in agreement with available experimental data for both large and transient fusion pores.
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42
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Abstract
We have inflated patch-clamped mast cells by 3.8 +/- 1.6 times their volume by applying a hydrostatic pressure of 5-15 cm H2O to the interior of the patch pipette. Inflation did not cause changes in the cell membrane conductance and caused only a small reversible change in the cell membrane capacitance (36 +/- 5 fF/cm H2O). The specific cell membrane capacitance of inflated cells was found to be 0.5 microF/cm2. High-resolution capacitance recordings showed that inflation reduced the frequency of exocytotic fusion events by approximately 70-fold, with the remaining fusion events showing an unusual time course. Shortly after the pressure was returned to 0 cm H2O, mast cells regained their normal size and appearance and degranulated completely, even after remaining inflated for up to 60 min. We interpret these observations as an indication that inflated mast cells reversibly disassemble the structures that regulate exocytotic fusion. Upon returning to its normal size, the cell cytosol reassembles the fusion pore scaffolds and allows exocytosis to proceed, suggesting that exocytotic fusion does not require soluble proteins. Reassembly of the fusion pore can be prevented by inflating the cells with solutions containing the protease pronase, which completely blocked exocytosis. We also interpret these results as evidence that the activity of the fusion pore is sensitive to the tension of the plasma membrane.
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Affiliation(s)
- C Solsona
- Department of Cell Biology, Medical School, University of Barcelona, Spain
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43
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Akisaka T, Miyaji T, Yoshida H, Inoue M. Ultrastructure of quick-frozen and freeze-substituted chick osteoclasts. J Anat 1997; 190 ( Pt 3):433-45. [PMID: 9147229 PMCID: PMC1467623 DOI: 10.1046/j.1469-7580.1997.19030433.x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
For comparison with chemically fixed osteoclasts, we prepared chick osteoclasts by quick freezing followed by freeze-substitution. In spite of technical difficulties this demonstrated that osteoclasts can be satisfactorily frozen in situ by the metal contact method. Ultrastructural differences were revealed between conventional fixation and quick freezing. Compared with conventional fixation, the quick freezing method appeared to improve preservation: (1) a discrete trilaminar plasma membrane and other intracellular membranes showed a smooth profile without undulation or rupture; (2) cytoskeletal components appeared to be clearer, straighter, and more numerous; (3) the interior of the ruffled finger contained interconnected lattice structures whereas highly organised microfilaments were seen in the clear zone; (4) well developed tubulovesicular structures (TVSs) that branched or anastomosed with each other were revealed in the cytoplasm; (5) the contents of intracellular membrane systems including the nuclear envelope, endoplasmic reticulum, and Golgi complex were stained to a various extent; (6) vesicles and vacuoles were much smaller, round and well-defined with electron-dense contents; (7) crystalline structures were seen at the extracellular channels of the ruffled border, in the lumen of TVSs, and in vesicles; (8) in some instances mitochondrial granules were visible; (9) within the resorptive lacuna, osteoclasts adhered to the degraded bone matrix without any intervening empty space.
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Affiliation(s)
- T Akisaka
- Department of Anatomy, Asahi University School of Dentistry, Gifu, Japan
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44
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Fernandez JM. Cellular and molecular mechanics by atomic force microscopy: capturing the exocytotic fusion pore in vivo? Proc Natl Acad Sci U S A 1997; 94:9-10. [PMID: 8990151 PMCID: PMC33650 DOI: 10.1073/pnas.94.1.9] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Affiliation(s)
- J M Fernandez
- Department of Physiology and Biophysics, Mayo Clinic, Rochester, MN 55905, USA
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45
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The mechanism of diatom locomotion. I. An ultrastructural study of the motility apparatus. ACTA ACUST UNITED AC 1997. [DOI: 10.1098/rspb.1983.0042] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Observations of raphe-associated cell structure of the diatomNavicula cuspidatasuggest the involvement in cell locomotion of secretory vesicles, the locally specialized plasmalemma opposite the raphe, microfilamentous bundles and strands of mucilage in the raphe. It is proposed th at diatoms are propelled by the flow of adhesive strands of mucilage that project from the raphe, powered and controlled by a membrane-associated microfilamentous system.
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46
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Abstract
Membrane fusion occurs as part of processes as different as synaptic neurotransmitter transmission and infection with influenza virus. Recent evidence paints a picture in which the organization of proteins into a macromolecular scaffold brings the two fusing membranes together and induces hemifusion, that is, the fusion of the apposing leaflets of the two membranes to form a common bilayer. A small dynamic fusion pore forms in the common bilayer and usually expands to allow complete membrane merging. The mechanisms of fusion appear to be remarkably similar in exocytosis and virus-induced fusion. During exocytotic fusion, there is an additional twist to the mechanism, as sometimes the fusion pores close after release of small non-quantal amounts of secretory products.
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Affiliation(s)
- J R Monck
- Department of Physiology, University of California at Los Angeles School of Medicine, 90024, USA.
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47
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Abstract
Disparate biological fusion reactions and fusion of purely lipid bilayers are similarly influenced by 'non-bilayer' lipids (lipids which do not form lipid bilayers in water by themselves). Lipid composition of membranes affects biological fusion at a stage downstream of activation of fusion proteins and prior to fusion pore formation. These data suggest that actual merger of membrane lipid bilayers in different fusion reactions proceeds via the same pathway. The effects of non-bilayer lipids specifically correlate with their ability to bend lipid monolayers in different directions, and appear to be consistent with the specific hypothesis of membrane fusion suggesting that fusion proceeds through highly bent intermediates--stalks, local connections between contacting monolayers of fusing membranes.
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Affiliation(s)
- L Chernomordik
- Laboratory of Theoretical and Physical Biology, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892-1855, USA.
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48
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Moreira JE, Reese TS, Kachar B. Freeze-substitution as a preparative technique for immunoelectronmicroscopy: evaluation by atomic force microscopy. Microsc Res Tech 1996; 33:251-61. [PMID: 8652883 DOI: 10.1002/(sici)1097-0029(19960215)33:3<251::aid-jemt2>3.0.co;2-t] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
Cryofixation followed by freeze substitution in osmium tetroxide was evaluated as a method for preparing biological specimens for immunoelectronmicroscopy. Samples were rapidly frozen by impact onto a sapphire block cooled with liquid nitrogen, substituted at -80 degrees C in acetone containing osmium tetroxide, and embedded in epoxy resin. With this protocol, excellent ultrastructure can be combined with localization of antigens that otherwise would be inactivated by the osmium, but labeling may need to be enhanced by chemically etching the sections prior to staining. The effects of etching on various structures in the sections were investigated by examining the sections with atomic force microscopy, an approach that yields three-dimensional views of the surface of the section. A considerable part of the section was removed or collapsed by the etching, and these effects occurred differentially in several components of the tissue and with different etching protocols. Nevertheless, the results suggest that the partial removal of the plastic by etching of freeze-substituted tissue can be explored as a method for exposing fine biological structures for observation with atomic force microscopy.
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Affiliation(s)
- J E Moreira
- National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland 20892, USA
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49
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Affiliation(s)
- S Srimal
- Molecular Biophysics Unit, Indian Institute of Science, Bangalore, India
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50
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Chernomordik L, Chanturiya A, Green J, Zimmerberg J. The hemifusion intermediate and its conversion to complete fusion: regulation by membrane composition. Biophys J 1995; 69:922-9. [PMID: 8519992 PMCID: PMC1236321 DOI: 10.1016/s0006-3495(95)79966-0] [Citation(s) in RCA: 210] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
To fuse, membranes must bend. The energy of each lipid monolayer with respect to bending is minimized at the spontaneous curvature of the monolayer. Two lipids known to promote opposite spontaneous curvatures, lysophosphatidylcholine and arachidonic acid, were added to different sides of planar phospholipid membranes. Lysophosphatidylcholine added to the contacting monolayers of fusing membranes inhibited the hemifusion we observed between lipid vesicles and planar membranes. In contrast, fusion pore formation depended upon the distal monolayer of the planar membrane; lysophosphatidylcholine promoted and arachidonic acid inhibited. Thus, the intermediates of hemifusion and fusion pores in phospholipid membranes involve different membrane monolayers and may have opposite net curvatures, Biological fusion may proceed through similar intermediates.
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Affiliation(s)
- L Chernomordik
- Laboratory of Theoretical and Physical Biology, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892, USA
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