1
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Surma M, Anbarasu K, Das A. Arp2/3 mediated dynamic lamellipodia of the hPSC colony edges promote liposome-based DNA delivery. Stem Cells 2024; 42:607-622. [PMID: 38717908 PMCID: PMC11228622 DOI: 10.1093/stmcls/sxae033] [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: 11/14/2023] [Accepted: 04/19/2024] [Indexed: 05/27/2024]
Abstract
Cationic liposome-mediated delivery of drugs, DNA, or RNA plays a pivotal role in small molecule therapy, gene editing, and immunization. However, our current knowledge regarding the cellular structures that facilitate this process remains limited. Here, we used human pluripotent stem cells (hPSCs), which form compact colonies consisting of dynamically active cells at the periphery and epithelial-like cells at the core. We discovered that cells at the colony edges selectively got transfected by cationic liposomes through actin-related protein 2/3 (Arp2/3) dependent dynamic lamellipodia, which is augmented by myosin II inhibition. Conversely, cells at the core establish tight junctions at their apical surfaces, impeding liposomal access to the basal lamellipodia and thereby inhibiting transfection. In contrast, liposomes incorporating mannosylated lipids are internalized throughout the entire colony via receptor-mediated endocytosis. These findings contribute a novel mechanistic insight into enhancing therapeutic delivery via liposomes, particularly in cell types characterized by dynamic lamellipodia, such as immune cells or those comprising the epithelial layer.
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Affiliation(s)
- Michelle Surma
- Department of Ophthalmology, Eugene and Marilyn Glick Eye Institute, Indiana University, Indianapolis, IN 46202, United States
| | - Kavitha Anbarasu
- Department of Ophthalmology, Eugene and Marilyn Glick Eye Institute, Indiana University, Indianapolis, IN 46202, United States
- Department of Medical and Molecular Genetics, Indiana University, Indianapolis, IN 46202, United States
| | - Arupratan Das
- Department of Ophthalmology, Eugene and Marilyn Glick Eye Institute, Indiana University, Indianapolis, IN 46202, United States
- Department of Medical and Molecular Genetics, Indiana University, Indianapolis, IN 46202, United States
- Stark Neurosciences Research Institute, Indiana University, Indianapolis, IN 46202, United States
- Department of Biochemistry and Molecular Biology, Indiana University, Indianapolis, IN 46202, United States
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2
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Jahn R, Cafiso DC, Tamm LK. Mechanisms of SNARE proteins in membrane fusion. Nat Rev Mol Cell Biol 2024; 25:101-118. [PMID: 37848589 DOI: 10.1038/s41580-023-00668-x] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/06/2023] [Indexed: 10/19/2023]
Abstract
Soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs) are a family of small conserved eukaryotic proteins that mediate membrane fusion between organelles and with the plasma membrane. SNAREs are directly or indirectly anchored to membranes. Prior to fusion, complementary SNAREs assemble between membranes with the aid of accessory proteins that provide a scaffold to initiate SNARE zippering, pulling the membranes together and mediating fusion. Recent advances have enabled the construction of detailed models describing bilayer transitions and energy barriers along the fusion pathway and have elucidated the structures of SNAREs complexed in various states with regulatory proteins. In this Review, we discuss how these advances are yielding an increasingly detailed picture of the SNARE-mediated fusion pathway, leading from first contact between the membranes via metastable non-bilayer intermediates towards the opening and expansion of a fusion pore. We describe how SNARE proteins assemble into complexes, how this assembly is regulated by accessory proteins and how SNARE complexes overcome the free energy barriers that prevent spontaneous membrane fusion.
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Affiliation(s)
- Reinhard Jahn
- Laboratory of Neurobiology, Max-Planck Institute for Multidisciplinary Sciences, Göttingen, Germany.
| | - David C Cafiso
- Department of Chemistry, University of Virginia, Charlottesville, VA, USA
| | - Lukas K Tamm
- Department of Molecular Physiology and Biological Physics, University of Virginia, Charlottesville, VA, USA
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3
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Tror S, Jeon S, Nguyen HT, Huh E, Shin K. A Self-Regenerating Artificial Cell, that is One Step Closer to Living Cells: Challenges and Perspectives. SMALL METHODS 2023; 7:e2300182. [PMID: 37246263 DOI: 10.1002/smtd.202300182] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/12/2023] [Revised: 04/29/2023] [Indexed: 05/30/2023]
Abstract
Controllable, self-regenerating artificial cells (SRACs) can be a vital advancement in the field of synthetic biology, which seeks to create living cells by recombining various biological molecules in the lab. This represents, more importantly, the first step on a long journey toward creating reproductive cells from rather fragmentary biochemical mimics. However, it is still a difficult task to replicate the complex processes involved in cell regeneration, such as genetic material replication and cell membrane division, in artificially created spaces. This review highlights recent advances in the field of controllable, SRACs and the strategies to achieve the goal of creating such cells. Self-regenerating cells start by replicating DNA and transferring it to a location where proteins can be synthesized. Functional but essential proteins must be synthesized for sustained energy generation and survival needs and function in the same liposomal space. Finally, self-division and repeated cycling lead to autonomous, self-regenerating cells. The pursuit of controllable, SRACs will enable authors to make bold advances in understanding life at the cellular level, ultimately providing an opportunity to use this knowledge to understand the nature of life.
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Affiliation(s)
- Seangly Tror
- Department of Chemistry and Institute of Biological Interfaces, Sogang University, Seoul, 04107, Republic of Korea
| | - SeonMin Jeon
- Department of Chemistry and Institute of Biological Interfaces, Sogang University, Seoul, 04107, Republic of Korea
| | - Huong Thanh Nguyen
- Department of Chemistry and Institute of Biological Interfaces, Sogang University, Seoul, 04107, Republic of Korea
| | - Eunjin Huh
- Department of Chemistry and Institute of Biological Interfaces, Sogang University, Seoul, 04107, Republic of Korea
| | - Kwanwoo Shin
- Department of Chemistry and Institute of Biological Interfaces, Sogang University, Seoul, 04107, Republic of Korea
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4
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The Role of α-Synuclein in SNARE-mediated Synaptic Vesicle Fusion. J Mol Biol 2023; 435:167775. [PMID: 35931109 DOI: 10.1016/j.jmb.2022.167775] [Citation(s) in RCA: 14] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2022] [Revised: 07/28/2022] [Accepted: 07/28/2022] [Indexed: 02/04/2023]
Abstract
Neuronal communication depends on exquisitely regulated membrane fusion between synaptic vesicles and presynaptic neurons, which results in neurotransmitter release in precisely timed patterns. Presynaptic dysfunctions are known to occur prior to the onset of neurodegenerative diseases, including Parkinson's disease. Synaptic accumulation of α-synuclein (α-Syn) oligomers has been implicated in the pathway leading to such outcomes. α-Syn oligomers exert aberrant effects on presynaptic fusion machinery through their interactions with synaptic vesicles and proteins. Here, we summarize in vitro bulk and single-vesicle assays for investigating the functions of α-Syn monomers and oligomers in synaptic vesicle fusion and then discuss the current understanding of the roles of α-Syn monomers and oligomers in synaptic vesicle fusion. Finally, we suggest a new therapeutic avenue specifically targeting the mechanisms of α-Syn oligomer toxicity rather than the oligomer itself.
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5
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Andersson A, Fornasier M, Makasewicz K, Pálmadóttir T, Linse S, Sparr E, Jönsson P. Single-vesicle intensity and colocalization fluorescence microscopy to study lipid vesicle fusion, fission, and lipid exchange. Front Mol Neurosci 2022; 15:1007699. [PMID: 36533132 PMCID: PMC9751204 DOI: 10.3389/fnmol.2022.1007699] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2022] [Accepted: 10/18/2022] [Indexed: 12/19/2023] Open
Abstract
Interactions of lipid vesicles play important roles in a large variety of functions and dysfunctions in the human body. Vital for several biochemical functions is the interaction between monomeric proteins and lipid membranes, and the induced phenomena such as fusion between vesicles and cell membranes, lipid exchange between the membranes, or vesicle fission. Identification of single events and their frequency of occurrence would provide valuable information about protein-lipid interactions in both healthy and degenerative pathways. In this work, we present a single-vesicle intensity and colocalization fluorescence microscopy assay with a custom-written MATLAB analysis program. The assay can be used to study lipid exchange as well as vesicle fusion and fission between two vesicle populations labeled with different fluorescent dyes. Vesicles from the two populations are first mixed and docked to a glass surface. The sample is then simultaneously imaged using two separate wavelength channels monitoring intensity changes and colocalization of vesicles from the two populations. The monomeric pre-synaptic protein α-synuclein (α-syn) and small unilamellar vesicles consisting of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), 1,2-dioleoyl-sn-glycero-3-phospho-L-serine, (DOPS), and monosialotetrahexosylganglioside (GM1) were used as a model system to evaluate the method. From our analysis, neither α-syn induced fusion nor lipid exchange was observed for vesicles consisting of DOPC:DOPS (7:3). However, including 10% GM1 in the vesicles resulted in a 91% increase of the number of vesicles within 10 min, combined with a 57% decrease in the average fluorescence intensity per vesicle, indicating that approximately half of the vesicles underwent fission. The method facilitates the study of lipid vesicle fusion, fission, and lipid exchange under controlled conditions. It also allows these events to be studied for systems with more complex composition including exosomes and lipid-based drug carriers, to enable a better understanding of their physicochemical properties.
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Affiliation(s)
| | | | | | | | | | | | - Peter Jönsson
- Department of Chemistry, Lund University, Lund, Sweden
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6
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Rizo J, Sari L, Qi Y, Im W, Lin MM. All-atom molecular dynamics simulations of Synaptotagmin-SNARE-complexin complexes bridging a vesicle and a flat lipid bilayer. eLife 2022; 11:76356. [PMID: 35708237 PMCID: PMC9239685 DOI: 10.7554/elife.76356] [Citation(s) in RCA: 27] [Impact Index Per Article: 13.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2021] [Accepted: 06/15/2022] [Indexed: 12/14/2022] Open
Abstract
Synaptic vesicles are primed into a state that is ready for fast neurotransmitter release upon Ca2+-binding to Synaptotagmin-1. This state likely includes trans-SNARE complexes between the vesicle and plasma membranes that are bound to Synaptotagmin-1 and complexins. However, the nature of this state and the steps leading to membrane fusion are unclear, in part because of the difficulty of studying this dynamic process experimentally. To shed light into these questions, we performed all-atom molecular dynamics simulations of systems containing trans-SNARE complexes between two flat bilayers or a vesicle and a flat bilayer with or without fragments of Synaptotagmin-1 and/or complexin-1. Our results need to be interpreted with caution because of the limited simulation times and the absence of key components, but suggest mechanistic features that may control release and help visualize potential states of the primed Synaptotagmin-1-SNARE-complexin-1 complex. The simulations suggest that SNAREs alone induce formation of extended membrane-membrane contact interfaces that may fuse slowly, and that the primed state contains macromolecular assemblies of trans-SNARE complexes bound to the Synaptotagmin-1 C2B domain and complexin-1 in a spring-loaded configuration that prevents premature membrane merger and formation of extended interfaces, but keeps the system ready for fast fusion upon Ca2+ influx.
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Affiliation(s)
- Josep Rizo
- Department of Biophysics, The University of Texas Southwestern Medical Center, Dallas, United States.,Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, United States.,Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, United States
| | - Levent Sari
- Department of Biophysics, The University of Texas Southwestern Medical Center, Dallas, United States.,Green Center for Systems Biology, The University of Texas Southwestern Medical Center, Dallas, United States
| | - Yife Qi
- Department of Medicinal Chemistry, School of Pharmacy, Fudan University, Shanghai, China
| | - Wonpil Im
- Department of Biological Sciences, Lehigh University, Bethlehem, United States.,Department of Chemistry, Lehigh University, Bethlehem, United States.,Department of Bioengineering, Lehigh University, Bethlehem, United States.,Department of Computer Science and Engineering, Lehigh University, Bethlehem, United States
| | - Milo M Lin
- Department of Biophysics, The University of Texas Southwestern Medical Center, Dallas, United States.,Green Center for Systems Biology, The University of Texas Southwestern Medical Center, Dallas, United States
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7
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Xu B, Ding J, Caliari A, Lu N, Han F, Xia Y, Xu J, Yomo T. Photoinducible Azobenzene trimethylammonium bromide (AzoTAB)-mediated giant vesicle fusion compatible with synthetic protein translation reactions. Biochem Biophys Res Commun 2022; 618:113-118. [PMID: 35717905 DOI: 10.1016/j.bbrc.2022.06.035] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2022] [Revised: 04/21/2022] [Accepted: 06/10/2022] [Indexed: 11/18/2022]
Abstract
Lipid giant vesicles represent a versatile minimal model system to study the physicochemical basis of lipid membrane fusion. Membrane fusion processes are also of interest in synthetic cell research, where cell-mimicking behavior often requires dynamically interacting compartments. For these applications, triggered fusion compatible with transcription-translation systems is key in achieving complexity. Recently, a photosensitive surfactant, azobenzene trimethylammonium bromide (AzoTAB), has been reported to induce membrane fusion by a photoinduced conformational change. Using imaging flow cytometer (IFC) and confocal microscopy we quantitatively investigated photoinduced AzoTAB-mediated fusion of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylcholine vesicles. The IFC analysis result showed that the fusion rate could reach about 40% following AzoTAB addition and UV irradiation in optimized conditions. We confirmed the compatibility between AzoTAB-induced vesicle fusion and a synthetic cell-free protein translation system using green fluorescent protein as reporter. With the techniques presented, cell-sized vesicle fusion can be quantitatively analyzed and optimized, paving the way to controllable synthetic cells with fundamental biological functions like the ability to express proteins from encapsulated plasmids.
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Affiliation(s)
- Boying Xu
- Laboratory of Biology and Information Science, School of Life Sciences, East China Normal University, Shanghai, 200062, PR China; Tongji University Cancer Center, Shanghai Tenth People's Hospital, School of Medicine, Tongji University, Shanghai, 200072, PR China
| | - Jinquan Ding
- School of Software Engineering, East China Normal University, Shanghai, 200062, PR China
| | - Adriano Caliari
- Laboratory of Biology and Information Science, School of Life Sciences, East China Normal University, Shanghai, 200062, PR China
| | - Nan Lu
- Laboratory of Biology and Information Science, School of Life Sciences, East China Normal University, Shanghai, 200062, PR China
| | - Fuhai Han
- Laboratory of Biology and Information Science, School of Life Sciences, East China Normal University, Shanghai, 200062, PR China
| | - Yang Xia
- Laboratory of Biology and Information Science, School of Life Sciences, East China Normal University, Shanghai, 200062, PR China
| | - Jian Xu
- Laboratory of Biology and Information Science, School of Life Sciences, East China Normal University, Shanghai, 200062, PR China.
| | - Tetsuya Yomo
- Laboratory of Biology and Information Science, School of Life Sciences, East China Normal University, Shanghai, 200062, PR China.
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8
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Grothe T, Walla PJ. Fluorescence Lifetime and Cross-correlation Spectroscopy for Observing Membrane Fusion of Liposome Models Containing Synaptic Proteins. Methods Mol Biol 2022; 2417:167-180. [PMID: 35099799 DOI: 10.1007/978-1-0716-1916-2_13] [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: 06/14/2023]
Abstract
Watching events of membrane fusion in real time and distinguishing between intermediate steps of these events is useful for mechanistic insights but at the same time a challenging task. In this chapter, we describe how to use fluorescence cross-correlation spectroscopy and Förster-resonance energy transfer to resolve the tethering and fusion of membranes by SNARE proteins (syntaxin-1, SNAP-25, and synaptobrevin-2) as an example. The given protocols can easily be adapted to other membrane proteins to investigate their ability to tether or even fuse vesicular membrane.
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Affiliation(s)
- Tobias Grothe
- Laboratory of Neurobiology, Max-Planck-Institute for Biophysical Chemistry, Göttingen, Germany
- Department of Biophysical Chemistry, Institute for Physical and Theoretical Chemistry, TU Braunschweig, Braunschweig, Germany
| | - Peter J Walla
- Laboratory of Neurobiology, Max-Planck-Institute for Biophysical Chemistry, Göttingen, Germany.
- Department of Biophysical Chemistry, Institute for Physical and Theoretical Chemistry, TU Braunschweig, Braunschweig, Germany.
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9
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Rawat N, Singla-Pareek SL, Pareek A. Membrane dynamics during individual and combined abiotic stresses in plants and tools to study the same. PHYSIOLOGIA PLANTARUM 2021; 171:653-676. [PMID: 32949408 DOI: 10.1111/ppl.13217] [Citation(s) in RCA: 50] [Impact Index Per Article: 16.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/29/2020] [Revised: 08/25/2020] [Accepted: 09/13/2020] [Indexed: 05/15/2023]
Abstract
The plasma membrane (PM) is possibly the most diverse biological membrane of plant cells; it separates and guards the cell against its external environment. It has an extremely complex structure comprising a mosaic of lipids and proteins. The PM lipids are responsible for maintaining fluidity, permeability and integrity of the membrane and also influence the functioning of membrane proteins. However, the PM is the primary target of environmental stress, which affects its composition, conformation and properties, thereby disturbing the cellular homeostasis. Maintenance of integrity and fluidity of the PM is a prerequisite for ensuring the survival of plants during adverse environmental conditions. The ability of plants to remodel membrane lipid and protein composition plays a crucial role in adaptation towards varying abiotic environmental cues, including high or low temperature, drought, salinity and heavy metals stress. The dynamic changes in lipid composition affect the functioning of membrane transporters and ultimately regulate the physical properties of the membrane. Plant membrane-transport systems play a significant role in stress adaptation by cooperating with the membrane lipidome to maintain the membrane integrity under stressful conditions. The present review provides a holistic view of stress responses and adaptations in plants, especially the changes in the lipidome and proteome of PM under individual or combined abiotic stresses, which cause alterations in the activity of membrane transporters and modifies the fluidity of the PM. The tools to study the varying lipidome and proteome of the PM are also discussed.
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Affiliation(s)
- Nishtha Rawat
- Stress Physiology and Molecular Biology Laboratory, School of Life Sciences, Jawaharlal Nehru University, New Delhi, 110067, India
| | - Sneh L Singla-Pareek
- Plant Stress Biology, International Centre for Genetic Engineering and Biotechnology, Aruna Asaf Ali Road, New Delhi, 110067, India
| | - Ashwani Pareek
- Stress Physiology and Molecular Biology Laboratory, School of Life Sciences, Jawaharlal Nehru University, New Delhi, 110067, India
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10
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Grothe T, Nowak J, Jahn R, Walla PJ. Selected tools to visualize membrane interactions. EUROPEAN BIOPHYSICS JOURNAL : EBJ 2021; 50:211-222. [PMID: 33787948 PMCID: PMC8071796 DOI: 10.1007/s00249-021-01516-6] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/12/2020] [Revised: 02/19/2021] [Accepted: 03/08/2021] [Indexed: 11/28/2022]
Abstract
In the past decade, we developed various fluorescence-based methods for monitoring membrane fusion, membrane docking, distances between membranes, and membrane curvature. These tools were mainly developed using liposomes as model systems, which allows for the dissection of specific interactions mediated by, for example, fusion proteins. Here, we provide an overview of these methods, including two-photon fluorescence cross-correlation spectroscopy and intramembrane Förster energy transfer, with asymmetric labelling of inner and outer membrane leaflets and the calibrated use of transmembrane energy transfer to determine membrane distances below 10 nm. We discuss their application range and their limitations using examples from our work on protein-mediated vesicle docking and fusion.
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Affiliation(s)
- Tobias Grothe
- Laboratory of Neurobiology, Max-Planck-Institute for Biophysical Chemistry, 37077, Göttingen, Germany
- Department of Biophysical Chemistry, Institute for Physical and Theoretical Chemistry, University of Braunschweig, 38106, Braunschweig, Germany
| | - Julia Nowak
- Department of Biophysical Chemistry, Institute for Physical and Theoretical Chemistry, University of Braunschweig, 38106, Braunschweig, Germany
| | - Reinhard Jahn
- Laboratory of Neurobiology, Max-Planck-Institute for Biophysical Chemistry, 37077, Göttingen, Germany
| | - Peter Jomo Walla
- Laboratory of Neurobiology, Max-Planck-Institute for Biophysical Chemistry, 37077, Göttingen, Germany.
- Department of Biophysical Chemistry, Institute for Physical and Theoretical Chemistry, University of Braunschweig, 38106, Braunschweig, Germany.
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11
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Schmidt CC, Vasic V, Stein A. Doa10 is a membrane protein retrotranslocase in ER-associated protein degradation. eLife 2020; 9:56945. [PMID: 32588820 PMCID: PMC7319771 DOI: 10.7554/elife.56945] [Citation(s) in RCA: 30] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2020] [Accepted: 05/28/2020] [Indexed: 12/17/2022] Open
Abstract
In endoplasmic reticulum-associated protein degradation (ERAD), membrane proteins are ubiquitinated, extracted from the membrane, and degraded by the proteasome. The cytosolic ATPase Cdc48 drives extraction by pulling on polyubiquitinated substrates. How hydrophobic transmembrane (TM) segments are moved from the phospholipid bilayer into cytosol, often together with hydrophilic and folded ER luminal protein parts, is not known. Using a reconstituted system with purified proteins from Saccharomyces cerevisiae, we show that the ubiquitin ligase Doa10 (Teb-4/MARCH6 in animals) is a retrotranslocase that facilitates membrane protein extraction. A substrate’s TM segment interacts with the membrane-embedded domain of Doa10 and then passively moves into the aqueous phase. Luminal substrate segments cross the membrane in an unfolded state. Their unfolding occurs on the luminal side of the membrane by cytoplasmic Cdc48 action. Our results reveal how a membrane-bound retrotranslocase cooperates with the Cdc48 ATPase in membrane protein extraction. The inside of a cell contains many different compartments called organelles, which are separated by membranes. Each organelle is composed of a unique set of proteins and performs specific roles in the cell. The endoplasmic reticulum, or ER for short, is an organelle where many proteins are produced. Most of these proteins are then released from the cell or sorted to other organelles. The ER has a strict quality control system that ensures any faulty proteins are quickly marked for the cell to destroy. However, the destruction process itself does not happen in the ER, so faulty proteins first need to leave this organelle. This is achieved by a group of proteins known as endoplasmic reticulum-associated protein degradation machinery (or ERAD for short). To extract a faulty protein from the ER, proteins of the ER and outside the ER cooperate. First, an ERAD protein called Doa10 attaches a small protein tag called ubiquitin to the faulty proteins to mark them for destruction. Then, outside of the ER, a protein called Cdc48 ‘grabs’ the ubiquitin tag and pulls. But that is only part of the story. Many of the proteins made by the ER have tethers that anchor them firmly to the membrane, making them much harder to remove. To get a better idea of how the extraction works, Schmidt et al. rebuilt the ERAD machinery in a test tube. This involved purifying proteins from yeast and inserting them into artificial membranes, allowing closer study of each part of the process. This revealed that attaching ubiquitin tags to faulty proteins is only one part of Doa10's role; it also participates in the extraction itself. Part of Doa10 resides within the membrane, and this ‘membrane-spanning domain’ can interact with faulty proteins, loosening their membrane anchors. At the same time, Cdc48 pulls from the outside. This pulling force causes the faulty proteins to unfold, allowing them to pass through the membrane. Given these findings, the next step is to find out exactly how Doa10 works by looking at its three-dimensional structure. This could have implications not only for the study of ERAD, but of similar quality control processes in other organelles too. A build-up of faulty proteins can cause diseases like neurodegeneration, so understanding how cells remove faulty proteins could help future medical research.
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Affiliation(s)
- Claudia C Schmidt
- Research Group Membrane Protein Biochemistry, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
| | - Vedran Vasic
- Research Group Membrane Protein Biochemistry, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
| | - Alexander Stein
- Research Group Membrane Protein Biochemistry, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
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12
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A protocell with fusion and division. Biochem Soc Trans 2019; 47:1909-1919. [PMID: 31819942 DOI: 10.1042/bst20190576] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2019] [Revised: 11/12/2019] [Accepted: 11/25/2019] [Indexed: 11/17/2022]
Abstract
A protocell is a synthetic form of cellular life that is constructed from phospholipid vesicles and used to understand the emergence of life from a nonliving chemical network. To be considered 'living', a protocell should be capable of self-proliferation, which includes successive growth and division processes. The growth of protocells can be achieved via vesicle fusion approaches. In this review, we provide a brief overview of recent research on the formation of a protocell, fusion and division processes of the protocell, and encapsulation of a defined chemical network such as the genetic material. We also provide some perspectives on the challenges and future developments of synthetic protocell research.
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13
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Lira RB, Robinson T, Dimova R, Riske KA. Highly Efficient Protein-free Membrane Fusion: A Giant Vesicle Study. Biophys J 2019; 116:79-91. [PMID: 30579564 PMCID: PMC6342729 DOI: 10.1016/j.bpj.2018.11.3128] [Citation(s) in RCA: 60] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2018] [Revised: 11/14/2018] [Accepted: 11/19/2018] [Indexed: 12/18/2022] Open
Abstract
Membrane fusion is a ubiquitous process in biology and is a prerequisite for many intracellular delivery protocols relying on the use of liposomes as drug carriers. Here, we investigate in detail the process of membrane fusion and the role of opposite charges in a protein-free lipid system based on cationic liposomes (LUVs, large unilamellar vesicles) and anionic giant unilamellar vesicles (GUVs) composed of different palmitoyloleoylphosphatidylcholine (POPC)/palmitoyloleoylphosphatidylglycerol (POPG) molar ratios. By using a set of optical-microscopy- and microfluidics-based methods, we show that liposomes strongly dock to GUVs of pure POPC or low POPG fraction (up to 10 mol%) in a process mainly associated with hemifusion and membrane tension increase, commonly leading to GUV rupture. On the other hand, docked LUVs quickly and very efficiently fuse with negative GUVs of POPG fractions at or above 20 mol%, resulting in dramatic GUV area increase in a charge-dependent manner; the vesicle area increase is deduced from GUV electrodeformation. Importantly, both hemifusion and full fusion are leakage-free. Fusion efficiency is quantified by the lipid transfer from liposomes to GUVs using fluorescence resonance energy transfer (FRET), which leads to consistent results when compared to fluorescence-lifetime-based FRET. We develop an approach to deduce the final composition of single GUVs after fusion based on the FRET efficiency. The results suggest that fusion is driven by membrane charge and appears to proceed up to charge neutralization of the acceptor GUV.
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Affiliation(s)
- Rafael B Lira
- Departamento de Biofísica, Universidade Federal de São Paulo, São Paulo, Brazil; Department of Theory and Bio-Systems, Max Planck Institute of Colloids and Interfaces, Potsdam, Germany
| | - Tom Robinson
- Department of Theory and Bio-Systems, Max Planck Institute of Colloids and Interfaces, Potsdam, Germany
| | - Rumiana Dimova
- Department of Theory and Bio-Systems, Max Planck Institute of Colloids and Interfaces, Potsdam, Germany.
| | - Karin A Riske
- Departamento de Biofísica, Universidade Federal de São Paulo, São Paulo, Brazil.
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14
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Biochemical studies of membrane fusion at the single-particle level. Prog Lipid Res 2019; 73:92-100. [PMID: 30611882 DOI: 10.1016/j.plipres.2019.01.001] [Citation(s) in RCA: 34] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2018] [Revised: 01/01/2019] [Accepted: 01/02/2019] [Indexed: 01/21/2023]
Abstract
To study membrane fusion mediated by synaptic proteins, proteoliposomes have been widely used for in vitro ensemble measurements with limited insights into the fusion mechanism. Single-particle techniques have proven to be powerful in overcoming the limitations of traditional ensemble methods. Here, we summarize current single-particle methods in biophysical and biochemical studies of fusion mediated by soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs) and other synaptic proteins, together with their advantages and limitations.
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15
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Fusion assays for model membranes: a critical review. ADVANCES IN BIOMEMBRANES AND LIPID SELF-ASSEMBLY 2019. [DOI: 10.1016/bs.abl.2019.09.003] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/09/2022]
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16
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Hubrich BE, Kumar P, Neitz H, Grunwald M, Grothe T, Walla PJ, Jahn R, Diederichsen U. PNA-Hybridsequenzen als Erkennungseinheiten in SNARE-Protein-analogen Peptiden. Angew Chem Int Ed Engl 2018. [DOI: 10.1002/ange.201805752] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- Barbara E. Hubrich
- Institut für Organische und Biomolekulare Chemie; Georg-August-Universität Göttingen; Tammannstraße 2 37077 Göttingen Deutschland
| | - Pawan Kumar
- Institut für Organische und Biomolekulare Chemie; Georg-August-Universität Göttingen; Tammannstraße 2 37077 Göttingen Deutschland
| | - Hermann Neitz
- Institut für Organische und Biomolekulare Chemie; Georg-August-Universität Göttingen; Tammannstraße 2 37077 Göttingen Deutschland
| | - Matthias Grunwald
- Abteilung für Neurobiologie; Max-Planck-Institut für Biophysikalische Chemie; Am Fassberg 11 37077 Göttingen Deutschland
| | - Tobias Grothe
- Abteilung für Neurobiologie; Max-Planck-Institut für Biophysikalische Chemie; Am Fassberg 11 37077 Göttingen Deutschland
| | - Peter Jomo Walla
- Abteilung für Neurobiologie; Max-Planck-Institut für Biophysikalische Chemie; Am Fassberg 11 37077 Göttingen Deutschland
- Institut für Physikalische und Theoretische Chemie; Technische Universität Braunschweig; Gaußstraße 17 38106 Braunschweig Deutschland
| | - Reinhard Jahn
- Abteilung für Neurobiologie; Max-Planck-Institut für Biophysikalische Chemie; Am Fassberg 11 37077 Göttingen Deutschland
| | - Ulf Diederichsen
- Institut für Organische und Biomolekulare Chemie; Georg-August-Universität Göttingen; Tammannstraße 2 37077 Göttingen Deutschland
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17
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Hubrich BE, Kumar P, Neitz H, Grunwald M, Grothe T, Walla PJ, Jahn R, Diederichsen U. PNA Hybrid Sequences as Recognition Units in SNARE-Protein-Mimicking Peptides. Angew Chem Int Ed Engl 2018; 57:14932-14936. [PMID: 30129689 DOI: 10.1002/anie.201805752] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2018] [Revised: 08/11/2018] [Indexed: 01/01/2023]
Abstract
Membrane fusion is an essential process in nature and is often accomplished by the specific interaction of SNARE proteins. SNARE model systems, in which SNARE domains are replaced by small artificial units, represent valuable tools to study membrane fusion in vitro. The synthesis and analysis is presented of SNARE model peptides that exhibit a recognition motif composed of two different types of peptide nucleic acid (PNA) sequences. This novel recognition unit is designed to mimic the SNARE zippering mechanism that initiates SNARE-mediated fusion. It contains N-(2-aminoethyl)glycine-PNA (aeg-PNA) and alanyl-PNA, which both recognize the respective complementary strand but differ in duplex topology and duplex formation kinetics. The duplex formation of PNA hybrid oligomers as well as the fusogenicity of the model peptides in lipid-mixing assays were characterized and the peptides were found to induce liposome fusion. As an unexpected discovery, peptides with a recognition unit containing only five aeg-PNA nucleo amino acids were sufficient and most efficient to induce liposome fusion.
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Affiliation(s)
- Barbara E Hubrich
- Institut für Organische und Biomolekulare Chemie, Georg-August-Universität Göttingen, Tammannstraße 2, 37077, Göttingen, Germany
| | - Pawan Kumar
- Institut für Organische und Biomolekulare Chemie, Georg-August-Universität Göttingen, Tammannstraße 2, 37077, Göttingen, Germany
| | - Hermann Neitz
- Institut für Organische und Biomolekulare Chemie, Georg-August-Universität Göttingen, Tammannstraße 2, 37077, Göttingen, Germany
| | - Matthias Grunwald
- Abteilung für Neurobiologie, Max-Planck-Institut für Biophysikalische Chemie, Am Fassberg 11, 37077, Göttingen, Germany
| | - Tobias Grothe
- Abteilung für Neurobiologie, Max-Planck-Institut für Biophysikalische Chemie, Am Fassberg 11, 37077, Göttingen, Germany
| | - Peter Jomo Walla
- Abteilung für Neurobiologie, Max-Planck-Institut für Biophysikalische Chemie, Am Fassberg 11, 37077, Göttingen, Germany.,Institut für Physikalische und Theoretische Chemie, Technische Universität Braunschweig, Gaußstraße 17, 38106, Braunschweig, Germany
| | - Reinhard Jahn
- Abteilung für Neurobiologie, Max-Planck-Institut für Biophysikalische Chemie, Am Fassberg 11, 37077, Göttingen, Germany
| | - Ulf Diederichsen
- Institut für Organische und Biomolekulare Chemie, Georg-August-Universität Göttingen, Tammannstraße 2, 37077, Göttingen, Germany
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18
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Jun YW, Wang T, Hwang S, Kim D, Ma D, Kim KH, Kim S, Jung J, Ahn KH. A Ratiometric Two-Photon Fluorescent Probe for Tracking Lysosomal ATP: Direct In Cellulo Observation of Lysosomal Membrane Fusion Processes. Angew Chem Int Ed Engl 2018. [DOI: 10.1002/ange.201804743] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Affiliation(s)
- Yong Woong Jun
- Department of Chemistry; Pohang University of Science and Technology (POSTECH); 77 Cheongam-Ro, Nam-Gu Pohang 37673 Rep. of Korea
| | - Taejun Wang
- Division of Integrative Biosciences and Biotechnology; Pohang University of Science and Technology (POSTECH); 77 Cheongam-Ro, Nam-Gu Pohang 37673 Rep. of Korea
| | - Sekyu Hwang
- Department of Chemistry; Pohang University of Science and Technology (POSTECH); 77 Cheongam-Ro, Nam-Gu Pohang 37673 Rep. of Korea
| | - Dokyoung Kim
- Department of Anatomy and Neurobiology; College of Medicine; Kyung Hee University; 26 Kyungheedae-Ro, Dongdaemun-Gu Seoul 02447 Rep. of Korea
- Center for Converging Humanities; College of Medicine; Kyung Hee University; 26 Kyungheedae-Ro, Dongdaemun-Gu Seoul 02447 Rep. of Korea
| | - Donghee Ma
- Department of Chemistry; Pohang University of Science and Technology (POSTECH); 77 Cheongam-Ro, Nam-Gu Pohang 37673 Rep. of Korea
| | - Ki Hean Kim
- Division of Integrative Biosciences and Biotechnology; Pohang University of Science and Technology (POSTECH); 77 Cheongam-Ro, Nam-Gu Pohang 37673 Rep. of Korea
| | - Sungjee Kim
- Department of Chemistry; Pohang University of Science and Technology (POSTECH); 77 Cheongam-Ro, Nam-Gu Pohang 37673 Rep. of Korea
| | - Junyang Jung
- Department of Anatomy and Neurobiology; College of Medicine; Kyung Hee University; 26 Kyungheedae-Ro, Dongdaemun-Gu Seoul 02447 Rep. of Korea
| | - Kyo Han Ahn
- Department of Chemistry; Pohang University of Science and Technology (POSTECH); 77 Cheongam-Ro, Nam-Gu Pohang 37673 Rep. of Korea
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19
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Jun YW, Wang T, Hwang S, Kim D, Ma D, Kim KH, Kim S, Jung J, Ahn KH. A Ratiometric Two-Photon Fluorescent Probe for Tracking Lysosomal ATP: Direct In Cellulo Observation of Lysosomal Membrane Fusion Processes. Angew Chem Int Ed Engl 2018; 57:10142-10147. [PMID: 29873167 DOI: 10.1002/anie.201804743] [Citation(s) in RCA: 58] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2018] [Indexed: 11/10/2022]
Abstract
Vesicles exchange their contents through membrane fusion processes, kiss-and-run and full-collapse fusion. Indirect observation of these fusion processes using artificial vesicles enhanced our understanding on the molecular mechanisms involved. Direct observation of the fusion processes in a real biological system, however, remains a challenge owing to many technical obstacles. We report a ratiometric two-photon probe offering real-time tracking of lysosomal ATP with quantitative information for the first time. By applying the probe to two-photon live-cell imaging, the lysosomal membrane fusion process in cells has been directly observed and the concentration of its content, lysosomal ATP, has been measured. Results show that the kiss-and-run process between lysosomes proceeds through repeated transient interactions with gradual content mixing, whereas the full-fusion process occurs at once. Furthermore, it is confirmed that both the fusion processes proceed with conservation of the content. Such a small-molecule probe exerts minimal disturbance and hence has potential for studying various biological processes associated with lysosomal ATP.
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Affiliation(s)
- Yong Woong Jun
- Department of Chemistry, Pohang University of Science and Technology (POSTECH), 77 Cheongam-Ro, Nam-Gu, Pohang, 37673, Rep. of Korea
| | - Taejun Wang
- Division of Integrative Biosciences and Biotechnology, Pohang University of Science and Technology (POSTECH), 77 Cheongam-Ro, Nam-Gu, Pohang, 37673, Rep. of Korea
| | - Sekyu Hwang
- Department of Chemistry, Pohang University of Science and Technology (POSTECH), 77 Cheongam-Ro, Nam-Gu, Pohang, 37673, Rep. of Korea
| | - Dokyoung Kim
- Department of Anatomy and Neurobiology, College of Medicine, Kyung Hee University, 26 Kyungheedae-Ro, Dongdaemun-Gu, Seoul, 02447, Rep. of Korea.,Center for Converging Humanities, College of Medicine, Kyung Hee University, 26 Kyungheedae-Ro, Dongdaemun-Gu, Seoul, 02447, Rep. of Korea
| | - Donghee Ma
- Department of Chemistry, Pohang University of Science and Technology (POSTECH), 77 Cheongam-Ro, Nam-Gu, Pohang, 37673, Rep. of Korea
| | - Ki Hean Kim
- Division of Integrative Biosciences and Biotechnology, Pohang University of Science and Technology (POSTECH), 77 Cheongam-Ro, Nam-Gu, Pohang, 37673, Rep. of Korea
| | - Sungjee Kim
- Department of Chemistry, Pohang University of Science and Technology (POSTECH), 77 Cheongam-Ro, Nam-Gu, Pohang, 37673, Rep. of Korea
| | - Junyang Jung
- Department of Anatomy and Neurobiology, College of Medicine, Kyung Hee University, 26 Kyungheedae-Ro, Dongdaemun-Gu, Seoul, 02447, Rep. of Korea
| | - Kyo Han Ahn
- Department of Chemistry, Pohang University of Science and Technology (POSTECH), 77 Cheongam-Ro, Nam-Gu, Pohang, 37673, Rep. of Korea
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20
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Yavuz H, Kattan I, Hernandez JM, Hofnagel O, Witkowska A, Raunser S, Walla PJ, Jahn R. Arrest of trans-SNARE zippering uncovers loosely and tightly docked intermediates in membrane fusion. J Biol Chem 2018; 293:8645-8655. [PMID: 29666192 PMCID: PMC5986196 DOI: 10.1074/jbc.ra118.003313] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2018] [Indexed: 12/03/2022] Open
Abstract
Soluble N-ethylmaleimide–sensitive factor attachment protein receptor (SNARE) proteins mediate intracellular membrane fusion in the secretory pathway. They contain conserved regions, termed SNARE motifs, that assemble between opposing membranes directionally from their N termini to their membrane-proximal C termini in a highly exergonic reaction. However, how this energy is utilized to overcome the energy barriers along the fusion pathway is still under debate. Here, we have used mutants of the SNARE synaptobrevin to arrest trans-SNARE zippering at defined stages. We have uncovered two distinct vesicle docking intermediates where the membranes are loosely and tightly connected, respectively. The tightly connected state is irreversible and independent of maintaining assembled SNARE complexes. Together, our results shed new light on the intermediate stages along the pathway of membrane fusion.
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Affiliation(s)
| | - Iman Kattan
- Biomolecular Spectroscopy and Single-Molecule Detection Research Group, Max Planck Institute for Biophysical Chemistry, 37077 Göttingen, Germany
| | - Javier M Hernandez
- Department of Structural Biochemistry, Max Planck Institute of Molecular Physiology, 44227 Dortmund, Germany
| | - Oliver Hofnagel
- Department of Structural Biochemistry, Max Planck Institute of Molecular Physiology, 44227 Dortmund, Germany
| | | | - Stefan Raunser
- Department of Structural Biochemistry, Max Planck Institute of Molecular Physiology, 44227 Dortmund, Germany
| | - Peter J Walla
- Biomolecular Spectroscopy and Single-Molecule Detection Research Group, Max Planck Institute for Biophysical Chemistry, 37077 Göttingen, Germany.,Biomolecular Spectroscopy and Single-Molecule Detection Research Group, Max Planck Institute for Biophysical Chemistry, 37077 Göttingen, Germany
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21
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Jumeaux C, Wahlsten O, Block S, Kim E, Chandrawati R, Howes PD, Höök F, Stevens MM. MicroRNA Detection by DNA-Mediated Liposome Fusion. Chembiochem 2018; 19:434-438. [PMID: 29333674 PMCID: PMC5861668 DOI: 10.1002/cbic.201700592] [Citation(s) in RCA: 26] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2017] [Indexed: 12/17/2022]
Abstract
Membrane fusion is a process of fundamental importance in biological systems that involves highly selective recognition mechanisms for the trafficking of molecular and ionic cargos. Mimicking natural membrane fusion mechanisms for the purpose of biosensor development holds great potential for amplified detection because relatively few highly discriminating targets lead to fusion and an accompanied engagement of a large payload of signal-generating molecules. In this work, sequence-specific DNA-mediated liposome fusion is used for the highly selective detection of microRNA. The detection of miR-29a, a known flu biomarker, is demonstrated down to 18 nm within 30 min with high specificity by using a standard laboratory microplate reader. Furthermore, one order of magnitude improvement in the limit of detection is demonstrated by using a novel imaging technique combined with an intensity fluctuation analysis, which is coined two-color fluorescence correlation microscopy.
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Affiliation(s)
- Coline Jumeaux
- Department of MaterialsDepartment of Bioengineering, and Institute of Biomedical EngineeringImperial College LondonExhibition RoadLondonSW7 2AZUK
| | - Olov Wahlsten
- Department of PhysicsChalmers University of Technology41296GöteborgSweden
| | - Stephan Block
- Department of PhysicsChalmers University of Technology41296GöteborgSweden
- Present address: Department of Chemistry and BiochemistryFreie Universität Berlin14195BerlinGermany
| | - Eunjung Kim
- Department of MaterialsDepartment of Bioengineering, and Institute of Biomedical EngineeringImperial College LondonExhibition RoadLondonSW7 2AZUK
| | - Rona Chandrawati
- Department of MaterialsDepartment of Bioengineering, and Institute of Biomedical EngineeringImperial College LondonExhibition RoadLondonSW7 2AZUK
- Present address: School of Chemical and Biomolecular EngineeringThe University of SydneySydneyNSW2006Australia
| | - Philip D. Howes
- Department of MaterialsDepartment of Bioengineering, and Institute of Biomedical EngineeringImperial College LondonExhibition RoadLondonSW7 2AZUK
| | - Fredrik Höök
- Department of PhysicsChalmers University of Technology41296GöteborgSweden
| | - Molly M. Stevens
- Department of MaterialsDepartment of Bioengineering, and Institute of Biomedical EngineeringImperial College LondonExhibition RoadLondonSW7 2AZUK
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22
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Krüger D, Ebenhan J, Werner S, Bacia K. Measuring Protein Binding to Lipid Vesicles by Fluorescence Cross-Correlation Spectroscopy. Biophys J 2017; 113:1311-1320. [PMID: 28697897 DOI: 10.1016/j.bpj.2017.06.023] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2017] [Revised: 05/21/2017] [Accepted: 06/08/2017] [Indexed: 11/26/2022] Open
Abstract
Fluorescence correlation spectroscopy has been previously used to investigate peptide and protein binding to lipid membranes, as it allows for very low amounts of sample, short measurement times and equilibrium binding conditions. Labeling only one of the binding partners, however, comes with certain drawbacks, as it relies on identifying binding events by a change in diffusion coefficient. Since peptide and protein aggregation can obscure specific binding, and since non-stoichiometric binding necessitates the explicit choice of a statistical distribution for the number of bound ligands, we additionally label the liposomes and perform dual-color fluorescence cross-correlation spectroscopy (dcFCCS). We develop a theoretical framework showing that dcFCCS amplitudes allow calculation of the degree of ligand binding and the concentration of unbound ligand, leading to a model-independent binding curve. As the degree of labeling of the ligands does not factor into the measured quantities, it is permissible to mix labeled and unlabeled ligand, thereby extending the range of usable protein concentrations and accessible dissociation constants, KD. The total protein concentration, but not the fraction of labeled protein, needs to be known. In this work, we apply our dcFCCS analysis scheme to Sar1p, a protein of the COPII complex, which binds "major-minor-mix" liposomes. A Langmuir isotherm model yields KD=(2.1±1.1)μM as the single-site dissociation constant. The dcFCCS framework presented here is highly versatile for biophysical analysis of binding interactions. It may be applied to many types of fluorescently labeled ligands and small diffusing particles, including nanodiscs and liposomes containing membrane protein receptors.
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Affiliation(s)
- Daniela Krüger
- Institut für Chemie, Martin-Luther-Universität Halle-Wittenberg, Halle (Saale), Germany
| | - Jan Ebenhan
- Institut für Chemie, Martin-Luther-Universität Halle-Wittenberg, Halle (Saale), Germany
| | - Stefan Werner
- Institut für Chemie, Martin-Luther-Universität Halle-Wittenberg, Halle (Saale), Germany
| | - Kirsten Bacia
- Institut für Chemie, Martin-Luther-Universität Halle-Wittenberg, Halle (Saale), Germany.
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23
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Witkowska A, Jahn R. Rapid SNARE-Mediated Fusion of Liposomes and Chromaffin Granules with Giant Unilamellar Vesicles. Biophys J 2017; 113:1251-1259. [PMID: 28400045 PMCID: PMC5607038 DOI: 10.1016/j.bpj.2017.03.010] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2016] [Revised: 03/12/2017] [Accepted: 03/13/2017] [Indexed: 11/03/2022] Open
Abstract
Soluble N-ethylmaleimide-sensitive factor activating protein receptor (SNARE) proteins are the main catalysts for membrane fusion in the secretory pathway of eukaryotic cells. In vitro, SNAREs are sufficient to mediate effective fusion of both native and artificial membranes. Here we have established, to our knowledge, a new platform for monitoring SNARE-mediated docking and fusion between giant unilamellar vesicles (GUVs) and smaller liposomes or purified secretory granules with high temporal and spatial resolution. Analysis of fusion is restricted to the free-standing part of the GUV-membrane exhibiting low curvature and a lack of surface contact, thus avoiding adhesion-mediated interference with the fusion reaction as in fusion with supported bilayers or surface-immobilized small vesicles. Our results show that liposomes and chromaffin granules fuse with GUVs containing activated SNAREs with only few milliseconds delay between docking and fusion. We conclude that after initial contact in trans, SNAREs alone can complete fusion at a rate close to fast neuronal exocytosis.
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Affiliation(s)
- Agata Witkowska
- Department of Neurobiology, Max-Planck-Institute for Biophysical Chemistry, Göttingen, Germany; International Max Planck Research School for Molecular Biology at the University of Göttingen, Göttingen, Germany
| | - Reinhard Jahn
- Department of Neurobiology, Max-Planck-Institute for Biophysical Chemistry, Göttingen, Germany.
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24
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Abstract
SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptors) proteins are a highly regulated class of membrane proteins lying in the center of membrane fusion. In conjunction with accessory proteins, SNAREs drive efficient merger of two distinct lipid bilayers into one interconnected structure. This chapter describes our fluorescence resonance energy transfer (FRET)-based proteoliposome fusion assays for the roles of various SNARE proteins, accessory proteins, and effects of different lipid compositions on membrane fusion involved in autophagy.
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Affiliation(s)
- J Diao
- University of Cincinnati College of Medicine, Cincinnati, OH, United States.
| | - L Li
- Center for Autophagy Research, University of Texas Southwestern Medical Center, Dallas, TX, United States; University of Texas Southwestern Medical Center, Dallas, TX, United States
| | - Y Lai
- Stanford University, Stanford, CA, United States
| | - Q Zhong
- Center for Autophagy Research, University of Texas Southwestern Medical Center, Dallas, TX, United States; University of Texas Southwestern Medical Center, Dallas, TX, United States.
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25
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Li X, Xing J, Qiu Z, He Q, Lin J. Quantification of Membrane Protein Dynamics and Interactions in Plant Cells by Fluorescence Correlation Spectroscopy. MOLECULAR PLANT 2016; 9:1229-1239. [PMID: 27381442 DOI: 10.1016/j.molp.2016.06.017] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/03/2016] [Revised: 06/25/2016] [Accepted: 06/27/2016] [Indexed: 05/25/2023]
Abstract
Deciphering the dynamics of protein and lipid molecules on appropriate spatial and temporal scales may shed light on protein function and membrane organization. However, traditional bulk approaches cannot unambiguously quantify the extremely diverse mobility and interactions of proteins in living cells. Fluorescence correlation spectroscopy (FCS) is a powerful technique to describe events that occur at the single-molecule level and on the nanosecond to second timescales; therefore, FCS can provide data on the heterogeneous organization of membrane systems. FCS can also be combined with other microscopy techniques, such as super-resolution techniques. More importantly, FCS is minimally invasive, which makes it an ideal approach to detect the heterogeneous distribution and dynamics of key proteins during development. In this review, we give a brief introduction about the development of FCS and summarize the significant contributions of FCS in understanding the organization of plant cell membranes and the dynamics and interactions of membrane proteins. We also discuss the potential applications of this technique in plant biology.
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Affiliation(s)
- Xiaojuan Li
- College of Biological Sciences and Biotechnology, Beijing Forestry University, Beijing 100083, China
| | - Jingjing Xing
- Key Laboratory of Plant Resources, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China; University of Chinese Academy of Sciences, Beijing 10049, China
| | - Zongbo Qiu
- College of Life Sciences, Henan Normal University, Xinxiang 453007, China
| | - Qihua He
- The Health Science Center, Peking University, Beijing 100191, China
| | - Jinxing Lin
- College of Biological Sciences and Biotechnology, Beijing Forestry University, Beijing 100083, China.
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26
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Van Koninckxloo A, Henoumont C, Laurent S, Muller RN, Vander Elst L. (1) H-NMR relaxometric studies of interaction between apoptosis specific MRI paramagnetic contrast agents and micellar models of apoptotic cells. MAGNETIC RESONANCE IN CHEMISTRY : MRC 2016; 54:568-574. [PMID: 26647764 DOI: 10.1002/mrc.4397] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/18/2015] [Revised: 10/02/2015] [Accepted: 11/11/2015] [Indexed: 06/05/2023]
Abstract
(1) H-NMR was previously used to analyze the interaction between peptides (E3 and R826) selected by phage display to target apoptotic cells and phospholipidic models of these cells. In order to avoid the use of apoptotic cells and to obtain a fast evaluation of the efficiency of the potential MRI contrast agents obtained by grafting these peptides and their scramble analogs on a paramagnetic gadolinium complex, their proton relaxometric behavior was investigated in the presence of micelles mimicking healthy and apoptotic cells. Their preferential interaction with 1,2-dipalmitoyl-sn-glycero-3-phospho-l-serine micelles mimicking apoptotic cells as compared with 1,2-dipalmitoyl-sn-glycero-3-phosphocholine micelles modeling healthy cells was shown by nuclear magnetic relaxation dispersion profiles and the enhancement of the transverse proton relaxation rates at 60 MHz. The association constant values confirm the stronger interaction of the selected conjugated peptides (Ka Gd-PMN-E3(gadolinium 2,2',2'',2'''-[((4-carboxy)pyridine-2,6-diyl)bis(methylenenitrilo)]-tetrakis acetate) grafted with E3 peptide): 2.43 10(4) m(-1) ; Ka Gd-DTPA-R826(gadolinium ((1-p-isothiocyanatobenzyl)-diethylenetriaminepentaacetate) grafted with R826 peptide): 2.91 10(4) m(-1) ) as compared with their conjugated scrambles (Ka Gd-PMN-E3sc(gadolinium 2,2',2'',2'''-[((4-carboxy)pyridine-2,6-diyl)bis(methylenenitrilo)]-tetrakis acetate) grafted with E3 scramble peptide): 0.18 10(4) m(-1) ; Ka Gd-DTPA-R826sc(gadolinium ((1-p-isothiocyanatobenzyl)-diethylenetriaminepentaacetate) grafted with R826 scramble peptide): 0.32 10(4) m(-1) ) even if the conjugation of E3 and R826 seems to decrease their interaction. Copyright © 2015 John Wiley & Sons, Ltd.
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Affiliation(s)
- Aurore Van Koninckxloo
- Department of General, Organic and Biomedical Chemistry, NMR and Molecular Imaging Laboratory, University of Mons, 7000, Mons, Belgium
| | - Céline Henoumont
- Department of General, Organic and Biomedical Chemistry, NMR and Molecular Imaging Laboratory, University of Mons, 7000, Mons, Belgium
| | - Sophie Laurent
- Department of General, Organic and Biomedical Chemistry, NMR and Molecular Imaging Laboratory, University of Mons, 7000, Mons, Belgium
- CMMI - Center for Microscopy and Molecular Imaging, 6041, Gosselies, Belgium
| | - Robert N Muller
- Department of General, Organic and Biomedical Chemistry, NMR and Molecular Imaging Laboratory, University of Mons, 7000, Mons, Belgium
- CMMI - Center for Microscopy and Molecular Imaging, 6041, Gosselies, Belgium
| | - Luce Vander Elst
- Department of General, Organic and Biomedical Chemistry, NMR and Molecular Imaging Laboratory, University of Mons, 7000, Mons, Belgium
- CMMI - Center for Microscopy and Molecular Imaging, 6041, Gosselies, Belgium
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27
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Braun T, Kleusch C, Naumovska E, Merkel R, Csiszár A. A bioanalytical assay to distinguish cellular uptake routes for liposomes. Cytometry A 2015; 89:301-8. [DOI: 10.1002/cyto.a.22792] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2015] [Revised: 09/17/2015] [Accepted: 10/05/2015] [Indexed: 12/13/2022]
Affiliation(s)
- Tobias Braun
- ICS-7: Biomechanics; Forschungszentrum Jülich GmbH, Institute of Complex Systems; Jülich 52425 Germany
| | - Christian Kleusch
- ICS-7: Biomechanics; Forschungszentrum Jülich GmbH, Institute of Complex Systems; Jülich 52425 Germany
| | - Elena Naumovska
- ICS-7: Biomechanics; Forschungszentrum Jülich GmbH, Institute of Complex Systems; Jülich 52425 Germany
| | - Rudolf Merkel
- ICS-7: Biomechanics; Forschungszentrum Jülich GmbH, Institute of Complex Systems; Jülich 52425 Germany
| | - Agnes Csiszár
- ICS-7: Biomechanics; Forschungszentrum Jülich GmbH, Institute of Complex Systems; Jülich 52425 Germany
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28
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Synaptotagmin-1 binds to PIP(2)-containing membrane but not to SNAREs at physiological ionic strength. Nat Struct Mol Biol 2015; 22:815-23. [PMID: 26389740 PMCID: PMC4596797 DOI: 10.1038/nsmb.3097] [Citation(s) in RCA: 86] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2015] [Accepted: 08/26/2015] [Indexed: 12/19/2022]
Abstract
The Ca(2+) sensor synaptotagmin-1 is thought to trigger membrane fusion by binding to acidic membrane lipids and SNARE proteins. Previous work has shown that binding is mediated by electrostatic interactions that are sensitive to the ionic environment. However, the influence of divalent or polyvalent ions, at physiological concentrations, on synaptotagmin's binding to membranes or SNAREs has not been explored. Here we show that binding of rat synaptotagmin-1 to membranes containing phosphatidylinositol 4,5-bisphosphate (PIP2) is regulated by charge shielding caused by the presence of divalent cations. Surprisingly, polyvalent ions such as ATP and Mg(2+) completely abrogate synaptotagmin-1 binding to SNAREs regardless of the presence of Ca(2+). Altogether, our data indicate that at physiological ion concentrations Ca(2+)-dependent synaptotagmin-1 binding is confined to PIP2-containing membrane patches in the plasma membrane, suggesting that membrane interaction of synaptotagmin-1 rather than SNARE binding triggers exocytosis of vesicles.
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Schwenen LLG, Hubrich R, Milovanovic D, Geil B, Yang J, Kros A, Jahn R, Steinem C. Resolving single membrane fusion events on planar pore-spanning membranes. Sci Rep 2015; 5:12006. [PMID: 26165860 PMCID: PMC4499801 DOI: 10.1038/srep12006] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2015] [Accepted: 06/15/2015] [Indexed: 12/15/2022] Open
Abstract
Even though a number of different in vitro fusion assays have been developed to analyze protein mediated fusion, they still only partially capture the essential features of the in vivo situation. Here we established an in vitro fusion assay that mimics the fluidity and planar geometry of the cellular plasma membrane to be able to monitor fusion of single protein-containing vesicles. As a proof of concept, planar pore-spanning membranes harboring SNARE-proteins were generated on highly ordered functionalized 1.2 μm-sized pore arrays in Si3N4. Full mobility of the membrane components was demonstrated by fluorescence correlation spectroscopy. Fusion was analyzed by two color confocal laser scanning fluorescence microscopy in a time resolved manner allowing to readily distinguish between vesicle docking, intermediate states such as hemifusion and full fusion. The importance of the membrane geometry on the fusion process was highlighted by comparing SNARE-mediated fusion with that of a minimal SNARE fusion mimetic.
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Affiliation(s)
- Lando L G Schwenen
- Institute for Organic and Biomolecular Chemistry, University of Göttingen, Tammannstr. 2, 37077 Göttingen, Germany
| | - Raphael Hubrich
- Institute for Organic and Biomolecular Chemistry, University of Göttingen, Tammannstr. 2, 37077 Göttingen, Germany
| | - Dragomir Milovanovic
- Max-Planck-Institute for Biophysical Chemistry, Am Fassberg 11, 37077 Göttingen, Germany
| | - Burkhard Geil
- Institute for Physical Chemistry, University of Göttingen, Tammannstr. 6, 37077 Göttingen, Germany
| | - Jian Yang
- Leiden Institute of Chemistry - Supramolecular and Biomaterials Chemistry, Leiden University, Einsteinweg 55, 2333 CC Leiden, The Netherlands
| | - Alexander Kros
- Leiden Institute of Chemistry - Supramolecular and Biomaterials Chemistry, Leiden University, Einsteinweg 55, 2333 CC Leiden, The Netherlands
| | - Reinhard Jahn
- Max-Planck-Institute for Biophysical Chemistry, Am Fassberg 11, 37077 Göttingen, Germany
| | - Claudia Steinem
- Institute for Organic and Biomolecular Chemistry, University of Göttingen, Tammannstr. 2, 37077 Göttingen, Germany
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30
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Two-Photon Correlation Spectroscopy in Single Dendritic Spines Reveals Fast Actin Filament Reorganization during Activity-Dependent Growth. PLoS One 2015; 10:e0128241. [PMID: 26020927 PMCID: PMC4447372 DOI: 10.1371/journal.pone.0128241] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2014] [Accepted: 04/24/2015] [Indexed: 11/19/2022] Open
Abstract
Two-photon fluorescence correlation spectroscopy (2P-FCS) within single dendritic spines of living hippocampal pyramidal neurons was used to resolve various subpopulations of mobile F-actin during activity-dependent structural changes such as potentiation induced spine head growth. Two major classes of mobile F-actin were discovered: very dynamic and about a hundred times less dynamic F-actin. Spine head enlargement upon application of Tetraethylammonium (TEA), a protocol previously used for the chemical induction of long-term potentiation (cLTP) strictly correlated to changes in the dynamics and filament numbers in the different actin filament fractions. Our observations suggest that spine enlargement is governed by a mechanism in which longer filaments are first cut into smaller filaments that cooperate with the second, increasingly dynamic shorter actin filament population to quickly reorganize and expand the actin cytoskeleton within the spine head. This process would allow a fast and efficient spine head enlargement using a major fraction of the actin filament population that was already present before spine head growth.
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31
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Brunger AT, Cipriano DJ, Diao J. Towards reconstitution of membrane fusion mediated by SNAREs and other synaptic proteins. Crit Rev Biochem Mol Biol 2015; 50:231-41. [PMID: 25788028 PMCID: PMC4673598 DOI: 10.3109/10409238.2015.1023252] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
Proteoliposomes have been widely used for in vitro studies of membrane fusion mediated by synaptic proteins. Initially, such studies were made with large unsynchronized ensembles of vesicles. Such ensemble assays limited the insights into the SNARE-mediated fusion mechanism that could be obtained from them. Single particle microscopy experiments can alleviate many of these limitations but they pose significant technical challenges. Here we summarize various approaches that have enabled studies of fusion mediated by SNAREs and other synaptic proteins at a single-particle level. Currently available methods are described and their advantages and limitations are discussed.
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32
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Zhang Y, Diao J, Colbert KN, Lai Y, Pfuetzner RA, Padolina MS, Vivona S, Ressl S, Cipriano DJ, Choi UB, Shah N, Weis WI, Brunger AT. Munc18a does not alter fusion rates mediated by neuronal SNAREs, synaptotagmin, and complexin. J Biol Chem 2015; 290:10518-34. [PMID: 25716318 PMCID: PMC4400359 DOI: 10.1074/jbc.m114.630772] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2014] [Indexed: 01/25/2023] Open
Abstract
Sec1/Munc18 (SM) proteins are essential for membrane trafficking, but their molecular mechanism remains unclear. Using a single vesicle-vesicle content-mixing assay with reconstituted neuronal SNAREs, synaptotagmin-1, and complexin-1, we show that the neuronal SM protein Munc18a/nSec1 has no effect on the intrinsic kinetics of both spontaneous fusion and Ca2+-triggered fusion between vesicles that mimic synaptic vesicles and the plasma membrane. However, wild type Munc18a reduced vesicle association ∼50% when the vesicles bearing the t-SNAREs syntaxin-1A and SNAP-25 were preincubated with Munc18 for 30 min. Single molecule experiments with labeled SNAP-25 indicate that the reduction of vesicle association is a consequence of sequestration of syntaxin-1A by Munc18a and subsequent release of SNAP-25 (i.e. Munc18a captures syntaxin-1A via its high affinity interaction). Moreover, a phosphorylation mimic mutant of Munc18a with reduced affinity to syntaxin-1A results in less reduction of vesicle association. In summary, Munc18a does not directly affect fusion, although it has an effect on the t-SNARE complex, depending on the presence of other factors and experimental conditions. Our results suggest that Munc18a primarily acts at the prefusion stage.
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Affiliation(s)
- Yunxiang Zhang
- From the Departments of Molecular and Cellular Physiology, Neurology and Neurological Sciences, Structural Biology, and Photon Science and
| | - Jiajie Diao
- From the Departments of Molecular and Cellular Physiology, Neurology and Neurological Sciences, Structural Biology, and Photon Science and the Howard Hughes Medical Institute, Stanford University, Stanford, California 94305
| | - Karen N Colbert
- From the Departments of Molecular and Cellular Physiology, Structural Biology, and
| | - Ying Lai
- From the Departments of Molecular and Cellular Physiology, Neurology and Neurological Sciences, Structural Biology, and Photon Science and
| | - Richard A Pfuetzner
- From the Departments of Molecular and Cellular Physiology, Neurology and Neurological Sciences, Structural Biology, and Photon Science and the Howard Hughes Medical Institute, Stanford University, Stanford, California 94305
| | - Mark S Padolina
- From the Departments of Molecular and Cellular Physiology, Neurology and Neurological Sciences, Structural Biology, and Photon Science and the Howard Hughes Medical Institute, Stanford University, Stanford, California 94305
| | - Sandro Vivona
- From the Departments of Molecular and Cellular Physiology, Neurology and Neurological Sciences, Structural Biology, and Photon Science and
| | - Susanne Ressl
- From the Departments of Molecular and Cellular Physiology, Neurology and Neurological Sciences, Structural Biology, and Photon Science and
| | - Daniel J Cipriano
- From the Departments of Molecular and Cellular Physiology, Neurology and Neurological Sciences, Structural Biology, and Photon Science and the Howard Hughes Medical Institute, Stanford University, Stanford, California 94305
| | - Ucheor B Choi
- From the Departments of Molecular and Cellular Physiology, Neurology and Neurological Sciences, Structural Biology, and Photon Science and the Howard Hughes Medical Institute, Stanford University, Stanford, California 94305
| | | | - William I Weis
- From the Departments of Molecular and Cellular Physiology, Structural Biology, and Photon Science and
| | - Axel T Brunger
- From the Departments of Molecular and Cellular Physiology, Neurology and Neurological Sciences, Structural Biology, and Photon Science and the Howard Hughes Medical Institute, Stanford University, Stanford, California 94305
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Lin CC, Seikowski J, Pérez-Lara A, Jahn R, Höbartner C, Walla PJ. Control of membrane gaps by synaptotagmin-Ca2+ measured with a novel membrane distance ruler. Nat Commun 2014; 5:5859. [PMID: 25500905 PMCID: PMC4275583 DOI: 10.1038/ncomms6859] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2014] [Accepted: 11/14/2014] [Indexed: 11/09/2022] Open
Abstract
Fast synchronous neurotransmitter release is triggered by calcium that activates synaptotagmin-1 (syt-1), resulting in fusion of synaptic vesicles with the presynaptic membrane. Syt-1 possesses two Ca(2+)-binding C2 domains that tether membranes via interactions with anionic phospholipids. It is capable of crosslinking membranes and has recently been speculated to trigger fusion by decreasing the gap between them. As quantitative information on membrane gaps is key to understanding general cellular mechanisms, including the role of syt-1, we developed a fluorescence-lifetime based inter-membrane distance ruler using membrane-anchored DNAs of various lengths as calibration standards. Wild-type and mutant data provide evidence that full-length syt-1 indeed regulates membrane gaps: without Ca(2+), syt-1 maintains membranes at distances of ~7-8 nm. Activation with 100 μM Ca(2+) decreases the distance to ~5 nm by binding the C2 domains to opposing membranes, respectively. These values reveal that activated syt-1 adjusts membrane distances to the level that promotes SNARE complex assembly.
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Affiliation(s)
- Chao-Chen Lin
- Research Group Biomolecular Spectroscopy and Single-Molecule Detection, Max Planck Institute for Biophysical Chemistry, Am Faßberg 11, 37077 Göttingen, Germany
| | - Jan Seikowski
- Research Group Nucleic Acid Chemistry, Max Planck Institute for Biophysical Chemistry, Am Faßberg 11, 37077 Göttingen, Germany
| | - Angel Pérez-Lara
- Department of Neurobiology, Max Planck Institute for Biophysical Chemistry, Am Faßberg 11, 37077 Göttingen, Germany
| | - Reinhard Jahn
- Department of Neurobiology, Max Planck Institute for Biophysical Chemistry, Am Faßberg 11, 37077 Göttingen, Germany
| | - Claudia Höbartner
- 1] Research Group Nucleic Acid Chemistry, Max Planck Institute for Biophysical Chemistry, Am Faßberg 11, 37077 Göttingen, Germany [2] Institute for Organic and Biomolecular Chemistry, Georg August University Göttingen, Tammannstraße 2, 37077 Göttingen, Germany
| | - Peter Jomo Walla
- 1] Research Group Biomolecular Spectroscopy and Single-Molecule Detection, Max Planck Institute for Biophysical Chemistry, Am Faßberg 11, 37077 Göttingen, Germany [2] Department of Biophysical Chemistry, Institute for Physical and Theoretical Chemistry, University of Braunschweig, Hans-Sommer-Straße 10, 38106 Braunschweig, Germany
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Van Koninckxloo A, Henoumont C, Laurent S, Muller RN, Vander Elst L. NMR chemical shift study of the interaction of selected peptides with liposomal and micellar models of apoptotic cells. J Biol Inorg Chem 2014; 19:1367-76. [PMID: 25287364 DOI: 10.1007/s00775-014-1195-5] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2014] [Accepted: 09/12/2014] [Indexed: 11/30/2022]
Abstract
The interaction between two peptides previously selected by phage display to target apoptotic cells and phospholipidic models of these cells (liposomes or micelles made of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and/or 1,2-dipalmitoyl-sn-glycero-3-phospho-L-serine (DPPS, phosphatidylserine analog) was studied by the simple analysis of the changes induced on the proton NMR chemical shifts of the peptides. Our approach which does not need healthy and/or apoptotic cells for assessing the affinity of different peptides is fast and efficient and requires small amounts of peptide to determine the association constant, the interacting protons, and the number of interaction sites. The micellar model gave more reliable results than the liposomal one. The preferential interaction of the peptide with DPPS was evidenced by the change of the chemical shifts of specific amino acids of the peptides. Our micellar model is thus well suited to mimic apoptotic cells.
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Affiliation(s)
- Aurore Van Koninckxloo
- Department of General, Organic and Biomedical Chemistry, NMR and Molecular Imaging Laboratory, University of Mons, 7000, Mons, Belgium
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35
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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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36
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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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Lai Y, Kim S, Varkey J, Lou X, Song JK, Diao J, Langen R, Shin YK. Nonaggregated α-synuclein influences SNARE-dependent vesicle docking via membrane binding. Biochemistry 2014; 53:3889-96. [PMID: 24884175 PMCID: PMC4075992 DOI: 10.1021/bi5002536] [Citation(s) in RCA: 58] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
![]()
α-Synuclein
(α-Syn), a major component of Lewy body
that is considered as the hallmark of Parkinson’s disease (PD),
has been implicated in neuroexocytosis. Overexpression of α-Syn
decreases the neurotransmitter release. However, the mechanism by
which α-Syn buildup inhibits the neurotransmitter release is
still unclear. Here, we investigated the effect of nonaggregated α-Syn
on SNARE-dependent liposome fusion using fluorescence methods. In
ensemble in vitro assays, α-Syn reduces lipid mixing mediated
by SNAREs. Furthermore, with the more advanced single-vesicle assay
that can distinguish vesicle docking from fusion, we found that α-Syn
specifically inhibits vesicle docking, without interfering with the
fusion. The inhibition in vesicle docking requires α-Syn binding
to acidic lipid containing membranes. Thus, these results imply the
existence of at least two mechanisms of inhibition of SNARE-dependent
membrane fusion: at high concentrations, nonaggregated α-Syn
inhibits docking by binding acidic lipids but not v-SNARE; on the
other hand, at much lower concentrations, large α-Syn oligomers
inhibit via a mechanism that requires v-SNARE interaction [Choi et al. Proc. Natl. Acad. Sci.
U. S. A.2013, 110 (10), 4087−409223431141].
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Affiliation(s)
- Ying Lai
- Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University , Ames, Iowa 50011, United States
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Park Y, Vennekate W, Yavuz H, Preobraschenski J, Hernandez JM, Riedel D, Walla PJ, Jahn R. α-SNAP interferes with the zippering of the SNARE protein membrane fusion machinery. J Biol Chem 2014; 289:16326-35. [PMID: 24778182 DOI: 10.1074/jbc.m114.556803] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Neuronal exocytosis is mediated by soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) proteins. Before fusion, SNARE proteins form complexes bridging the membrane followed by assembly toward the C-terminal membrane anchors, thus initiating membrane fusion. After fusion, the SNARE complex is disassembled by the AAA-ATPase N-ethylmaleimide-sensitive factor that requires the cofactor α-SNAP to first bind to the assembled SNARE complex. Using chromaffin granules and liposomes we now show that α-SNAP on its own interferes with the zippering of membrane-anchored SNARE complexes midway through the zippering reaction, arresting SNAREs in a partially assembled trans-complex and preventing fusion. Intriguingly, the interference does not result in an inhibitory effect on synaptic vesicles, suggesting that membrane properties also influence the final outcome of α-SNAP interference with SNARE zippering. We suggest that binding of α-SNAP to the SNARE complex affects the ability of the SNARE complex to harness energy or transmit force to the membrane.
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Affiliation(s)
| | - Wensi Vennekate
- From the Department of Neurobiology, the AG Biomolecular Spectroscopy and Single-Molecule Detection, and
| | | | | | | | - Dietmar Riedel
- the Facility for Electron Microscopy, Max-Planck-Institute for Biophysical Chemistry, 37077 Göttingen and
| | - Peter Jomo Walla
- the AG Biomolecular Spectroscopy and Single-Molecule Detection, and the Department of Biophysical Chemistry, Institute for Physical and Theoretical Chemistry, Technical University of Braunschweig, 38106 Braunschweig, Germany
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Phospho-NHE3 forms membrane patches and interacts with beta-actin to sense and maintain constant direction during cell migration. Exp Cell Res 2014; 324:13-29. [PMID: 24657527 DOI: 10.1016/j.yexcr.2014.03.005] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2013] [Revised: 02/28/2014] [Accepted: 03/02/2014] [Indexed: 01/14/2023]
Abstract
The Na(+)/H(+) exchanger NHE3 colocalizes with beta-actin at the leading edge of directionally migrating cells. Using human osteosarcoma cells (SaOS-2), rat osteoblasts (calvaria), and human embryonic kidney (HEK) cells, we identified a novel role for NHE3 via beta-actin in anode and cathode directed motility, during electrotaxis. NHE3 knockdown by RNAi revealed that NHE3 expression is required to achieve constant directionality and polarity in migrating cells. Phosphorylated NHE3 (pNHE3) and beta-actin complex formation was impaired by the NHE3 inhibitor S3226 (IC50 0.02µM). Fluorescence cross-correlation spectroscopy (FCCS) revealed that the molecular interactions between NHE3 and beta-actin in membrane protrusions increased 1.7-fold in the presence of a directional cue and decreased 3.3-fold in the presence of cytochalasin D. Data from flow cytometric analysis showed that membrane potential of cells (Vmem) decreases in directionally migrating, NHE3-deficient osteoblasts and osteosarcoma cells whereas only Vmem of wild type osteoblasts is affected during directional migration. These findings suggest that pNHE3 has a mechanical function via beta-actin that is dependent on its physiological activity and Vmem. Furthermore, phosphatidylinositol 3,4,5-trisphosphate (PIP3) levels increase while PIP2 remains stable when cells have persistent directionality. Both PI3 kinase (PI3K) and Akt expression levels change proportionally to NHE3 levels. Interestingly, however, the content of pNHE3 level does not change when PI3K/Akt is inhibited. Therefore, we conclude that NHE3 can act as a direction sensor for cells and that NHE3 phosphorylation in persistent directional cell migration does not involve PI3K/Akt during electrotaxis.
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Pantano S, Montecucco C. The blockade of the neurotransmitter release apparatus by botulinum neurotoxins. Cell Mol Life Sci 2014; 71:793-811. [PMID: 23749048 PMCID: PMC11113401 DOI: 10.1007/s00018-013-1380-7] [Citation(s) in RCA: 87] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2013] [Revised: 05/15/2013] [Accepted: 05/16/2013] [Indexed: 12/22/2022]
Abstract
The high toxicity of the seven serotypes of botulinum neurotoxins (BoNT/A to G), together with their specificity and reversibility, includes them in the list A of potential bioterrorism weapons and, at the same time, among the therapeutics of choice for a variety of human syndromes. They invade nerve terminals and cleave specifically the three proteins which form the heterotrimeric SNAP REceptors (SNARE) complex that mediates neurotransmitter release. The BoNT-induced cleavage of the SNARE proteins explains by itself the paralysing activity of the BoNTs because the truncated proteins cannot form the SNARE complex. However, in the case of BoNT/A, the most widely used toxin in therapy, additional factors come into play as it only removes a few residues from the synaptosomal associate protein of 25 kDa C-terminus and this results in a long duration of action. To explain these facts and other experimental data, we present here a model for the assembly of the neuroexocytosis apparatus in which Synaptotagmin and Complexin first assist the zippering of the SNARE complex, and then stabilize and clamp an octameric radial assembly of the SNARE complexes.
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Affiliation(s)
- Sergio Pantano
- Institut Pasteur de Montevideo, Calle Mataojo 2020, CP 11400 Montevideo, Uruguay
| | - Cesare Montecucco
- Department of Biomedical Sciences, University of Padova, Padua, Italy
- Institute of Neuroscience, National Research Council, Viale G. Colombo 3, 35121 Padua, Italy
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Abstract
Exocytosis, the process in which material is transported from the cell interior to the extracellular space, proceeds through a complex mechanism. Defects in this process are linked to a number of serious illnesses including diabetes, cancer, and a range of neuropathologies. In neuroendocrine cells, exocytosis involves the fusion of secretory vesicles, carrying signaling molecules, with the plasma membrane through the coordinated interplay of proteins, lipids, and small molecules. This process is highly regulated and occurs in a complex three-dimensional environment within the cell precisely coupled to the stimulus. The study of exocytosis poses significant challenges, involving rapidly changing, nano-scale, protein-protein, and protein-lipid interactions, at specialized sites in the cell. Over the last decade our understanding of neuroendocrine exocytosis has been greatly enhanced by developments in fluorescence microscopy. Modern microscopy encompasses a toolbox of advanced techniques, pushing the limits of sensitivity and resolution, to probe different properties of exocytosis. In more recent years, the development of super-resolution microscopy techniques, side-stepping the limits of optical resolution imposed by the physical properties of light, have started to provide an unparalleled view of exocytosis. In this review we will discuss how advances in fluorescence microscopy are shedding light on the spatial and temporal organization of the exocytotic machinery.
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Affiliation(s)
- Alicja Graczyk
- Institute of Biological Chemistry, Biophysics and Bioengineering, School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh, UK
| | - Colin Rickman
- Institute of Biological Chemistry, Biophysics and Bioengineering, School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh, UK
- *Correspondence: Colin Rickman, Institute of Biological Chemistry, Biophysics and Bioengineering, School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh EH14 4AS, UK e-mail:
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Diao J, Cipriano DJ, Zhao M, Zhang Y, Shah S, Padolina MS, Pfuetzner RA, Brunger AT. Complexin-1 enhances the on-rate of vesicle docking via simultaneous SNARE and membrane interactions. J Am Chem Soc 2013; 135:15274-7. [PMID: 24083833 PMCID: PMC3854000 DOI: 10.1021/ja407392n] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
![]()
In
synaptic terminals, complexin is thought to have inhibitory
and activating roles for spontaneous “mini” release
and evoked synchronized neurotransmitter release, respectively. We
used single vesicle–vesicle microscopy imaging to study the
effect of complexin-1 on the on-rate of docking between vesicles that
mimic synaptic vesicles and the plasma membrane. We found that complexin-1
enhances the on-rate of docking of synaptic vesicle mimics containing
full-length synaptobrevin-2 and full-length synaptotagmin-1 to plasma
membrane-mimicking vesicles containing full-length syntaxin-1A and
SNAP-25A. This effect requires the C-terminal domain of complexin-1,
which binds to the membrane, the presence of PS in the membrane, and
the core region of complexin-1, which binds to the SNARE complex.
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Affiliation(s)
- Jiajie Diao
- Departments of Molecular and Cellular Physiology, Neurology and Neurological Sciences, Structural Biology, and Photon Science and Howard Hughes Medical Institute, Stanford University , Stanford, California 94305, United States
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Diao J, Zhao M, Zhang Y, Kyoung M, Brunger AT. Studying protein-reconstituted proteoliposome fusion with content indicators in vitro. Bioessays 2013; 35:658-65. [PMID: 23625805 DOI: 10.1002/bies.201300010] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
In vitro reconstitution assays are commonly used to study biological membrane fusion. However, to date, most ensemble and single-vesicle experiments involving SNARE proteins have been performed only with lipid-mixing, but not content-mixing indicators. Through simultaneous detection of lipid and small content-mixing indicators, we found that lipid mixing often occurs seconds prior to content mixing, or without any content mixing at all, during a 50-seconds observation period, for Ca(2+) -triggered fusion with SNAREs, full-length synaptotagmin-1, and complexin. Our results illustrate the caveats of commonly used bulk lipid-mixing fusion experiments. We recommend that proteoliposome fusion experiments should always employ content-mixing indicators in addition to, or in place of, lipid-mixing indicators.
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Affiliation(s)
- Jiajie Diao
- Department of Molecular and Cellular Physiology, Stanford University, Stanford, CA, USA.
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Diao J, Grob P, Cipriano DJ, Kyoung M, Zhang Y, Shah S, Nguyen A, Padolina M, Srivastava A, Vrljic M, Shah A, Nogales E, Chu S, Brunger AT. Synaptic proteins promote calcium-triggered fast transition from point contact to full fusion. eLife 2012; 1:e00109. [PMID: 23240085 PMCID: PMC3514886 DOI: 10.7554/elife.00109] [Citation(s) in RCA: 136] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2012] [Accepted: 09/18/2012] [Indexed: 12/18/2022] Open
Abstract
The molecular underpinnings of synaptic vesicle fusion for fast neurotransmitter release are still unclear. Here, we used a single vesicle-vesicle system with reconstituted SNARE and synaptotagmin-1 proteoliposomes to decipher the temporal sequence of membrane states upon Ca(2+)-injection at 250-500 μM on a 100-ms timescale. Furthermore, detailed membrane morphologies were imaged with cryo-electron microscopy before and after Ca(2+)-injection. We discovered a heterogeneous network of immediate and delayed fusion pathways. Remarkably, all instances of Ca(2+)-triggered immediate fusion started from a membrane-membrane point-contact and proceeded to complete fusion without discernible hemifusion intermediates. In contrast, pathways that involved a stable hemifusion diaphragm only resulted in fusion after many seconds, if at all. When complexin was included, the Ca(2+)-triggered fusion network shifted towards the immediate pathway, effectively synchronizing fusion, especially at lower Ca(2+)-concentration. Synaptic proteins may have evolved to select this immediate pathway out of a heterogeneous network of possible membrane fusion pathways.DOI:http://dx.doi.org/10.7554/eLife.00109.001.
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Affiliation(s)
- Jiajie Diao
- Departments of Molecular and Cellular Physiology, Neurology and Neurological Sciences, Structural Biology, Photon Science and Howard Hughes Medical Institute , Stanford University , Stanford , USA
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Studying calcium-triggered vesicle fusion in a single vesicle-vesicle content and lipid-mixing system. Nat Protoc 2012; 8:1-16. [PMID: 23222454 PMCID: PMC3566647 DOI: 10.1038/nprot.2012.134] [Citation(s) in RCA: 66] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
This protocol describes a single vesicle-vesicle microscopy system to study Ca(2+)-triggered vesicle fusion. Donor vesicles contain reconstituted synaptobrevin and synaptotagmin-1. Acceptor vesicles contain reconstituted syntaxin and synaptosomal-associated protein 25 (SNAP-25), and they are tethered to a PEG-coated glass surface. Donor vesicles are mixed with the tethered acceptor vesicles and incubated for several minutes at a zero-Ca(2+) concentration, resulting in a collection of single interacting vesicle pairs. The donor vesicles also contain two spectrally distinct fluorophores that allow simultaneous monitoring of temporal changes of the content and membrane. Upon Ca(2+) injection into the sample chamber, our system therefore differentiates between hemifusion and complete fusion of interacting vesicle pairs and determines the temporal sequence of these events on a sub-100-millisecond time scale. Other factors such as complexin can be easily added. Our system is unique in that it monitors both content and lipid mixing and starts from a metastable state of interacting vesicle pairs before Ca(2+) injection.
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Matta S, Van Kolen K, da Cunha R, van den Bogaart G, Mandemakers W, Miskiewicz K, De Bock PJ, Morais VA, Vilain S, Haddad D, Delbroek L, Swerts J, Chávez-Gutiérrez L, Esposito G, Daneels G, Karran E, Holt M, Gevaert K, Moechars DW, De Strooper B, Verstreken P. LRRK2 controls an EndoA phosphorylation cycle in synaptic endocytosis. Neuron 2012; 75:1008-21. [PMID: 22998870 DOI: 10.1016/j.neuron.2012.08.022] [Citation(s) in RCA: 270] [Impact Index Per Article: 22.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/20/2012] [Indexed: 11/25/2022]
Abstract
LRRK2 is a kinase mutated in Parkinson's disease, but how the protein affects synaptic function remains enigmatic. We identified LRRK2 as a critical regulator of EndophilinA. Using genetic and biochemical studies involving Lrrk loss-of-function mutants and Parkinson-related LRRK2(G2019S) gain-of-kinase function, we show that LRRK2 affects synaptic endocytosis by phosphorylating EndoA at S75, a residue in the BAR domain. We show that LRRK2-mediated EndoA phosphorylation has profound effects on EndoA-dependent membrane tubulation and membrane association in vitro and in vivo and on synaptic vesicle endocytosis at Drosophila neuromuscular junctions in vivo. Our work uncovers a regulatory mechanism that indicates that reduced LRRK2 kinase activity facilitates EndoA membrane association, while increased kinase activity inhibits membrane association. Consequently, both too much and too little LRRK2-dependent EndoA phosphorylation impedes synaptic endocytosis, and we propose a model in which LRRK2 kinase activity is part of an EndoA phosphorylation cycle that facilitates efficient vesicle formation at synapses.
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Affiliation(s)
- Samer Matta
- VIB Center for the Biology of Disease, 3000 Leuven, Belgium
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Rizo J, Südhof TC. The Membrane Fusion Enigma: SNAREs, Sec1/Munc18 Proteins, and Their Accomplices—Guilty as Charged? Annu Rev Cell Dev Biol 2012; 28:279-308. [DOI: 10.1146/annurev-cellbio-101011-155818] [Citation(s) in RCA: 318] [Impact Index Per Article: 26.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Josep Rizo
- Departments of Biophysics, Biochemistry and Pharmacology, University of Texas Southwestern Medical Center, Dallas, Texas 75390;
| | - Thomas C. Südhof
- Department of Molecular and Cellular Physiology and Howard Hughes Medical Institute, Stanford University Medical School, Stanford, California 94305;
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Park Y, Hernandez JM, van den Bogaart G, Ahmed S, Holt M, Riedel D, Jahn R. Controlling synaptotagmin activity by electrostatic screening. Nat Struct Mol Biol 2012; 19:991-7. [PMID: 22940675 PMCID: PMC3465474 DOI: 10.1038/nsmb.2375] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2012] [Accepted: 07/27/2012] [Indexed: 01/24/2023]
Abstract
Exocytosis of neurosecretory vesicles is mediated bythe SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) proteins syntaxin-1, synaptobrevin, and SNAP-25, with synaptotagmin functioning as the major Ca2+-sensor for triggering membrane fusion. Here we show that bovine chromaffin granules readily fuse with large unilamellar liposomes in a SNARE-dependent manner. Fusion is enhanced by Ca2+ but only if the target liposomes contain PI(4,5)P2 and if polyphosphate anions such as nucleotides or pyrophosphate are present. Ca2+-dependent enhancement is mediated by endogenous synaptotagmin-1. Polyphosphates operate by an electrostatic mechanism that reverses an inactivating cis-association of synaptotagmin-1 with its own membrane whereas trans-binding is not affected. Hence, balancing trans- and cis-membrane interactions of synaptotagmin may be a crucial element in the pathway of Ca2+-dependent exocytosis.
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Affiliation(s)
- Yongsoo Park
- Department of Neurobiology, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
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Hernandez JM, Stein A, Behrmann E, Riedel D, Cypionka A, Farsi Z, Walla PJ, Raunser S, Jahn R. Membrane fusion intermediates via directional and full assembly of the SNARE complex. Science 2012; 336:1581-4. [PMID: 22653732 PMCID: PMC3677693 DOI: 10.1126/science.1221976] [Citation(s) in RCA: 172] [Impact Index Per Article: 14.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Cellular membrane fusion is thought to proceed through intermediates including docking of apposed lipid bilayers, merging of proximal leaflets to form a hemifusion diaphragm, and fusion pore opening. A membrane-bridging four-helix complex of soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs) mediates fusion. However, how assembly of the SNARE complex generates docking and other fusion intermediates is unknown. Using a cell-free reaction, we identified intermediates visually and then arrested the SNARE fusion machinery when fusion was about to begin. Partial and directional assembly of SNAREs tightly docked bilayers, but efficient fusion and an extended form of hemifusion required assembly beyond the core complex to the membrane-connecting linkers. We propose that straining of lipids at the edges of an extended docking zone initiates fusion.
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Affiliation(s)
- Javier M. Hernandez
- Department of Neurobiology, Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, 37077 Göttingen, Germany
| | - Alexander Stein
- Department of Neurobiology, Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, 37077 Göttingen, Germany
| | - Elmar Behrmann
- Department of Physical Biochemistry, Max Planck Institute of Molecular Physiology, Otto-Hahn-Str. 11, 44227 Dortmund, Germany
| | - Dietmar Riedel
- Department of Neurobiology, Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, 37077 Göttingen, Germany
| | - Anna Cypionka
- Department of Neurobiology, Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, 37077 Göttingen, Germany
- AG Biomolecular Spectroscopy and Single-Molecule Detection, Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, 37077 Göttingen, Germany
| | - Zohreh Farsi
- Department of Neurobiology, Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, 37077 Göttingen, Germany
| | - Peter J. Walla
- AG Biomolecular Spectroscopy and Single-Molecule Detection, Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, 37077 Göttingen, Germany
- Department of Biophysical Chemistry, Institute for Physical and Theoretical Chemistry, Technical University of Braunschweig, Hans-Sommer-Str. 10, 38106 Braunschweig, Germany
| | - Stefan Raunser
- Department of Physical Biochemistry, Max Planck Institute of Molecular Physiology, Otto-Hahn-Str. 11, 44227 Dortmund, Germany
| | - Reinhard Jahn
- Department of Neurobiology, Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, 37077 Göttingen, Germany
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Abstract
In neurotransmission synaptotagmin-1 tethers synaptic vesicles to the presynaptic plasma membrane by binding to acidic membrane lipids and SNAREs and promotes rapid SNARE-mediated fusion upon Ca(2+) triggering. However, recent studies suggested that upon membrane contact synaptotagmin may not only bind in trans to the target membrane but also in cis to its own membrane. Using a sensitive membrane tethering assay we have now dissected the structural requirements and concentration ranges for Ca(2+)-dependent and -independent cis-binding and trans-tethering in the presence and absence of acidic phospholipids and SNAREs. Using variants of membrane-anchored synaptotagmin in which the Ca(2+)-binding sites in the C2 domains and a basic cluster involved in membrane binding were disrupted we show that Ca(2+)-dependent cis-binding prevents trans-interactions if the cis-membrane contains 12-20% anionic phospholipids. Similarly, no trans-interactions were observable using soluble C2AB-domain fragments at comparable concentrations. At saturating concentrations, however, tethering was observed with soluble C2AB domains, probably due to crowding on the vesicle surface and competition for binding sites. We conclude that trans-interactions of synaptotagmin considered to be essential for its function are controlled by a delicate balance between cis- and trans-binding, which may play an important modulatory role in synaptic transmission.
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