1
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Kephart SM, Hom N, Lee KK. Visualizing intermediate stages of viral membrane fusion by cryo-electron tomography. Trends Biochem Sci 2024; 49:916-931. [PMID: 39054240 PMCID: PMC11455608 DOI: 10.1016/j.tibs.2024.06.012] [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: 03/06/2024] [Revised: 06/07/2024] [Accepted: 06/18/2024] [Indexed: 07/27/2024]
Abstract
Protein-mediated membrane fusion is the dynamic process where specialized protein machinery undergoes dramatic conformational changes that drive two membrane bilayers together, leading to lipid mixing and opening of a fusion pore between previously separate membrane-bound compartments. Membrane fusion is an essential stage of enveloped virus entry that results in viral genome delivery into host cells. Recent studies applying cryo-electron microscopy techniques in a time-resolved fashion provide unprecedented glimpses into the interaction of viral fusion proteins and membranes, revealing fusion intermediate states from the initiation of fusion to release of the viral genome. In combination with complementary structural, biophysical, and computation modeling approaches, these advances are shedding new light on the mechanics and dynamics of protein-mediated membrane fusion.
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Affiliation(s)
- Sally M Kephart
- Department of Medicinal Chemistry, University of Washington, Seattle, WA, USA
| | - Nancy Hom
- Department of Medicinal Chemistry, University of Washington, Seattle, WA, USA
| | - Kelly K Lee
- Department of Medicinal Chemistry, University of Washington, Seattle, WA, USA; Biological Structure Physics and Design Graduate Program, University of Washington, Seattle, WA, USA.
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2
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Tavakoli A, Hu S, Ebrahim S, Kachar B. Hemifusomes and Interacting Proteolipid Nanodroplets: Formation of a Novel Cellular Organelle Complex. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.08.28.610112. [PMID: 39253452 PMCID: PMC11383319 DOI: 10.1101/2024.08.28.610112] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 09/11/2024]
Abstract
Within cells, vesicle fusion, scission, and the formation of intraluminal vesicles are critical processes that facilitate traffic, degradation, and recycling of cellular components, and maintenance of cellular homeostasis. Despite significant advancements in elucidating the molecular mechanisms that drive these dynamic processes, the direct in situ visualization of membrane remodeling intermediates remains challenging. Here, through the application of cryo-electron tomography in mammalian cells, we have identified a previously undescribed vesicular organelle complex with unique membrane topology: heterotypic hemifused vesicles that share extended hemifusion diaphragms (HDs) with a 42 nm proteolipid nanodroplet (PND) at their rim. We have termed these organelle complexes "hemifusomes". The HDs of hemifusomes exhibit a range of sizes and curvatures, including the formation of lens-shaped compartments encapsulated within the membrane bilayer. The morphological diversity of the lens-shaped vesicle aligns with a step-wise process of their intraluminal budding, ultimately leading to their scission and the generation of intraluminal vesicles. We propose that hemifusomes function as versatile platforms for protein and lipid sorting and as central hubs for the biogenesis of intraluminal vesicles and the formation of multivesicular bodies.
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3
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Spencer RKW, Smirnova YG, Soleimani A, Müller M. Transient pores in hemifusion diaphragms. Biophys J 2024; 123:2455-2475. [PMID: 38867448 PMCID: PMC11365115 DOI: 10.1016/j.bpj.2024.06.009] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2024] [Revised: 05/07/2024] [Accepted: 06/07/2024] [Indexed: 06/14/2024] Open
Abstract
Exchange of material across two membranes, as in the case of synaptic neurotransmitter release from a vesicle, involves the formation and poration of a hemifusion diaphragm (HD). The nontrivial geometry of the HD leads to environment-dependent control, regarding the stability and dynamics of the pores required for this kind of exocytosis. This work combines particle simulations, field-based calculations, and phenomenological modeling to explore the factors influencing the stability, dynamics, and possible control mechanisms of pores in HDs. We find that pores preferentially form at the HD rim, and that their stability is sensitive to a number of factors, including the three line tensions, membrane tension, HD size, and the ability of lipids to "flip-flop" across leaflets. Along with a detailed analysis of these factors, we discuss ways that vesicles or cells may use them to open and close pores and thereby quickly and efficiently transport material.
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Affiliation(s)
- Russell K W Spencer
- Institute for Theoretical Physics, Georg-August University, Göttingen, Germany.
| | - Yuliya G Smirnova
- Institute for Theoretical Physics, Georg-August University, Göttingen, Germany; Technische Universität Dortmund, Dortmund, Germany
| | - Alireza Soleimani
- Institute for Theoretical Physics, Georg-August University, Göttingen, Germany
| | - Marcus Müller
- Institute for Theoretical Physics, Georg-August University, Göttingen, Germany.
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4
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Bottacchiari M, Gallo M, Bussoletti M, Casciola CM. The diffuse interface description of fluid lipid membranes captures key features of the hemifusion pathway and lateral stress profile. PNAS NEXUS 2024; 3:pgae300. [PMID: 39114574 PMCID: PMC11304589 DOI: 10.1093/pnasnexus/pgae300] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 02/15/2024] [Accepted: 07/09/2024] [Indexed: 08/10/2024]
Abstract
Topological transitions of lipid membranes are ubiquitous in key biological processes for cell life, like neurotransmission, fertilization, morphogenesis, and viral infections. Despite this, they are not well understood due to their multiscale nature, which limits the use of molecular models and calls for a mesoscopic approach such as the celebrated Canham-Helfrich one. Unfortunately, such a model cannot handle topological transitions, hiding the crucial involved forces and the appearance of the experimentally observed hemifused intermediates. In this work, we describe the membrane as a diffuse interface preserving the Canham-Helfrich elasticity. We show that pivotal features of the hemifusion pathway are captured by this mesoscopic approach, e.g. a (meta)stable hemifusion state and the fusogenic behavior of negative monolayer spontaneous curvatures. The membrane lateral stress profile is calculated as a function of the elastic rigidities, yielding a coarse-grained version of molecular models findings. Insights into the fusogenic mechanism are reported and discussed.
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Affiliation(s)
- Matteo Bottacchiari
- Department of Basic and Applied Sciences for Engineering, Sapienza University of Rome, via Antonio Scarpa 16, Rome 00161, Italy
- Department of Mechanical and Aerospace Engineering, Sapienza University of Rome, via Eudossiana 18, Rome 00184, Italy
| | - Mirko Gallo
- Department of Mechanical and Aerospace Engineering, Sapienza University of Rome, via Eudossiana 18, Rome 00184, Italy
| | - Marco Bussoletti
- Department of Mechanical and Aerospace Engineering, Sapienza University of Rome, via Eudossiana 18, Rome 00184, Italy
| | - Carlo M Casciola
- Department of Mechanical and Aerospace Engineering, Sapienza University of Rome, via Eudossiana 18, Rome 00184, Italy
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5
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Gallo A, Mansueto S, Emendato A, Fusco G, De Simone A. α-Synuclein and Mitochondria: Probing the Dynamics of Disordered Membrane-protein Regions Using Solid-State Nuclear Magnetic Resonance. JACS AU 2024; 4:2372-2380. [PMID: 38938811 PMCID: PMC11200226 DOI: 10.1021/jacsau.4c00323] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/11/2024] [Revised: 05/13/2024] [Accepted: 05/14/2024] [Indexed: 06/29/2024]
Abstract
The characterization of intrinsically disordered regions (IDRs) in membrane-associated proteins is of crucial importance to elucidate key biochemical processes, including cellular signaling, drug targeting, or the role of post-translational modifications. These protein regions pose significant challenges to powerful analytical techniques of molecular structural investigations. We here applied magic angle spinning solid-state nuclear magnetic resonance to quantitatively probe the structural dynamics of IDRs of membrane-bound α-synuclein (αS), a disordered protein whose aggregation is associated with Parkinson's disease (PD). We focused on the mitochondrial binding of αS, an interaction that has functional and pathological relevance in neuronal cells and that is considered crucial for the underlying mechanisms of PD. Transverse and longitudinal 15N relaxation revealed that the dynamical properties of IDRs of αS bound to the outer mitochondrial membrane (OMM) are different from those of the cytosolic state, thus indicating that regions generally considered not to interact with the membrane are in fact affected by the spatial proximity with the lipid bilayer. Moreover, changes in the composition of OMM that are associated with lipid dyshomeostasis in PD were found to significantly perturb the topology and dynamics of IDRs in the membrane-bound state of αS. Taken together, our data underline the importance of characterizing IDRs in membrane proteins to achieve an accurate understanding of the role that these elusive protein regions play in numerous biochemical processes occurring on cellular surfaces.
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Affiliation(s)
- Angelo Gallo
- Department
of Chemistry, University of Turin, Via Giuria 7, Turin 10124, Italy
| | - Silvia Mansueto
- Department
of Pharmacy, University of Naples, Via Montesano 49, Naples 80131, Italy
| | - Alessandro Emendato
- Department
of Pharmacy, University of Naples, Via Montesano 49, Naples 80131, Italy
| | - Giuliana Fusco
- Department
of Pharmacy, University of Naples, Via Montesano 49, Naples 80131, Italy
- Centre
for Misfolding Diseases, Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, U.K.
| | - Alfonso De Simone
- Department
of Pharmacy, University of Naples, Via Montesano 49, Naples 80131, Italy
- Department
of Life Sciences, Imperial College London, London SW7 2AZ, U.K.
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6
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Jaczynska K, Esser V, Xu J, Sari L, Lin MM, Rosenmund C, Rizo J. A lever hypothesis for Synaptotagmin-1 action in neurotransmitter release. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.06.17.599417. [PMID: 38948826 PMCID: PMC11212951 DOI: 10.1101/2024.06.17.599417] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 07/02/2024]
Abstract
Neurotransmitter release is triggered in microseconds by Ca2+-binding to the Synaptotagmin-1 C2 domains and by SNARE complexes that form four-helix bundles between synaptic vesicles and plasma membranes, but the coupling mechanism between Ca2+-sensing and membrane fusion is unknown. Release requires extension of SNARE helices into juxtamembrane linkers that precede transmembrane regions (linker zippering) and binding of the Synaptotagmin-1 C2B domain to SNARE complexes through a 'primary interface' comprising two regions (I and II). The Synaptotagmin-1 Ca2+-binding loops were believed to accelerate membrane fusion by inducing membrane curvature, perturbing lipid bilayers or helping bridge the membranes, but SNARE complex binding orients the Ca2+-binding loops away from the fusion site, hindering these putative activities. Molecular dynamics simulations now suggest that Synaptotagmin-1 C2 domains near the site of fusion hinder SNARE action, providing an explanation for this paradox and arguing against previous models of Sytnaptotagmin-1 action. NMR experiments reveal that binding of C2B domain arginines to SNARE acidic residues at region II remains after disruption of region I. These results and fluorescence resonance energy transfer assays, together with previous data, suggest that Ca2+ causes reorientation of the C2B domain on the membrane and dissociation from the SNAREs at region I but not region II. Based on these results and molecular modeling, we propose that Synaptotagmin-1 acts as a lever that pulls the SNARE complex when Ca2+ causes reorientation of the C2B domain, facilitating linker zippering and fast membrane fusion. This hypothesis is supported by the electrophysiological data described in the accompanying paper.
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Affiliation(s)
- Klaudia Jaczynska
- Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, Texas 75390, USA
- Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, Texas 75390, USA
- Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, Texas 75390, USA
| | - Victoria Esser
- Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, Texas 75390, USA
- Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, Texas 75390, USA
- Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, Texas 75390, USA
| | - Junjie Xu
- Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, Texas 75390, USA
- Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, Texas 75390, USA
- Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, Texas 75390, USA
| | - Levent Sari
- Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, Texas 75390, USA
- Green Center for Systems Biology, University of Texas Southwestern Medical Center, Dallas, Texas 75390, USA
| | - Milo M. Lin
- Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, Texas 75390, USA
- Green Center for Systems Biology, University of Texas Southwestern Medical Center, Dallas, Texas 75390, USA
| | - Christian Rosenmund
- Charité – Universitätsmedizin Berlin, corporate member of Freie Universität Berlin and Humboldt-Universität zu Berlin, Institute of Neurophysiology, Berlin, Germany
- NeuroCure Cluster of Excellence, Berlin, Germany
| | - Josep Rizo
- Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, Texas 75390, USA
- Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, Texas 75390, USA
- Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, Texas 75390, USA
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7
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Bhaskar BR, Yadav L, Sriram M, Sanghrajka K, Gupta M, V BK, Nellikka RK, Das D. Differential SNARE chaperoning by Munc13-1 and Munc18-1 dictates fusion pore fate at the release site. Nat Commun 2024; 15:4132. [PMID: 38755165 PMCID: PMC11099066 DOI: 10.1038/s41467-024-46965-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2023] [Accepted: 03/14/2024] [Indexed: 05/18/2024] Open
Abstract
The regulated release of chemical messengers is crucial for cell-to-cell communication; abnormalities in which impact coordinated human body function. During vesicular secretion, multiple SNARE complexes assemble at the release site, leading to fusion pore opening. How membrane fusion regulators act on heterogeneous SNARE populations to assemble fusion pores in a timely and synchronized manner, is unknown. Here, we demonstrate the role of SNARE chaperones Munc13-1 and Munc18-1 in rescuing individual nascent fusion pores from their diacylglycerol lipid-mediated inhibitory states. At the onset of membrane fusion, Munc13-1 clusters multiple SNARE complexes at the release site and synchronizes release events, while Munc18-1 stoichiometrically interacts with trans-SNARE complexes to enhance N- to C-terminal zippering. When both Munc proteins are present simultaneously, they differentially access dynamic trans-SNARE complexes to regulate pore properties. Overall, Munc proteins' direct action on fusion pore assembly indicates their role in controlling quantal size during vesicular secretion.
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Affiliation(s)
- Bhavya R Bhaskar
- Department of Biological Sciences, Tata Institute of Fundamental Research, Mumbai, 400005, India
| | - Laxmi Yadav
- Department of Biological Sciences, Tata Institute of Fundamental Research, Mumbai, 400005, India
| | - Malavika Sriram
- Department of Biological Sciences, Tata Institute of Fundamental Research, Mumbai, 400005, India
| | - Kinjal Sanghrajka
- Department of Biological Sciences, Tata Institute of Fundamental Research, Mumbai, 400005, India
| | - Mayank Gupta
- Department of Biological Sciences, Tata Institute of Fundamental Research, Mumbai, 400005, India
| | - Boby K V
- Department of Biological Sciences, Tata Institute of Fundamental Research, Mumbai, 400005, India
| | - Rohith K Nellikka
- Department of Biological Sciences, Tata Institute of Fundamental Research, Mumbai, 400005, India
| | - Debasis Das
- Department of Biological Sciences, Tata Institute of Fundamental Research, Mumbai, 400005, India.
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8
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Rizo J, Sari L, Jaczynska K, Rosenmund C, Lin MM. Molecular mechanism underlying SNARE-mediated membrane fusion enlightened by all-atom molecular dynamics simulations. Proc Natl Acad Sci U S A 2024; 121:e2321447121. [PMID: 38593076 PMCID: PMC11032479 DOI: 10.1073/pnas.2321447121] [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: 12/05/2023] [Accepted: 03/18/2024] [Indexed: 04/11/2024] Open
Abstract
The SNAP receptor (SNARE) proteins syntaxin-1, SNAP-25, and synaptobrevin mediate neurotransmitter release by forming tight SNARE complexes that fuse synaptic vesicles with the plasma membranes in microseconds. Membrane fusion is generally explained by the action of proteins on macroscopic membrane properties such as curvature, elastic modulus, and tension, and a widespread model envisions that the SNARE motifs, juxtamembrane linkers, and C-terminal transmembrane regions of synaptobrevin and syntaxin-1 form continuous helices that act mechanically as semirigid rods, squeezing the membranes together as they assemble ("zipper") from the N to the C termini. However, the mechanism underlying fast SNARE-induced membrane fusion remains unknown. We have used all-atom molecular dynamics simulations to investigate this mechanism. Our results need to be interpreted with caution because of the limited number and length of the simulations, but they suggest a model of membrane fusion that has a natural physicochemical basis, emphasizes local molecular events over general membrane properties, and explains extensive experimental data. In this model, the central event that initiates fast (microsecond scale) membrane fusion occurs when the SNARE helices zipper into the juxtamembrane linkers which, together with the adjacent transmembrane regions, promote encounters of acyl chains from both bilayers at the polar interface. The resulting hydrophobic nucleus rapidly expands into stalk-like structures that gradually progress to form a fusion pore, aided by the SNARE transmembrane regions and without clearly discernible intermediates. The propensity of polyunsaturated lipids to participate in encounters that initiate fusion suggests that these lipids may be important for the high speed of neurotransmitter release.
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Affiliation(s)
- Josep Rizo
- Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, TX75390
- Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, TX75390
- Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, TX75390
| | - Levent Sari
- Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, TX75390
- Green Center for Systems Biology, University of Texas Southwestern Medical Center, Dallas, TX75390
| | - Klaudia Jaczynska
- Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, TX75390
- Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, TX75390
- Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, TX75390
| | - Christian Rosenmund
- Institute of Neurophysiology, Charité—Universitätsmedizin Berlin, Berlin10117, Germany
- NeuroCure Cluster of Excellence, Berlin10117, Germany
| | - Milo M. Lin
- Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, TX75390
- Green Center for Systems Biology, University of Texas Southwestern Medical Center, Dallas, TX75390
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9
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Koike S, Jahn R. Rab GTPases and phosphoinositides fine-tune SNAREs dependent targeting specificity of intracellular vesicle traffic. Nat Commun 2024; 15:2508. [PMID: 38509070 PMCID: PMC10954720 DOI: 10.1038/s41467-024-46678-x] [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: 02/06/2023] [Accepted: 03/05/2024] [Indexed: 03/22/2024] Open
Abstract
In the secretory pathway the destination of trafficking vesicles is determined by specific proteins that, with the notable exception of SNAREs, are recruited from soluble pools. Previously we have shown that microinjected proteoliposomes containing early or late endosomal SNAREs, respectively, are targeted to the corresponding endogenous compartments, with targeting specificity being dependent on the recruitment of tethering factors by some of the SNAREs. Here, we show that targeting of SNARE-containing liposomes is refined upon inclusion of polyphosphoinositides and Rab5. Intriguingly, targeting specificity is dependent on the concentration of PtdIns(3)P, and on the recruitment of PtdIns(3)P binding proteins such as rabenosyn-5 and PIKfyve, with conversion of PtdIns(3)P into PtdIns(3,5)P2 re-routing the liposomes towards late endosomes despite the presence of GTP-Rab5 and early endosomal SNAREs. Our data reveal a complex interplay between permissive and inhibitory targeting signals that sharpen a basic targeting and fusion machinery for conveying selectivity in intracellular membrane traffic.
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Affiliation(s)
- Seiichi Koike
- Laboratory of Neurobiology, Max Planck Institute for Multidisciplinary Sciences, Göttingen, Germany
- University of Toyama, Laboratory of Molecular and Cellular Biology, Department of Life Sciences and Bioengineering, 3190 Gofuku, Toyama City, 930-8555, Japan
| | - Reinhard Jahn
- Laboratory of Neurobiology, Max Planck Institute for Multidisciplinary Sciences, Göttingen, Germany.
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10
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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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11
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Abstract
Membrane fusion and budding mediate fundamental processes like intracellular trafficking, exocytosis, and endocytosis. Fusion is thought to open a nanometer-range pore that may subsequently close or dilate irreversibly, whereas budding transforms flat membranes into vesicles. Reviewing recent breakthroughs in real-time visualization of membrane transformations well exceeding this classical view, we synthesize a new model and describe its underlying mechanistic principles and functions. Fusion involves hemi-to-full fusion, pore expansion, constriction and/or closure while fusing vesicles may shrink, enlarge, or receive another vesicle fusion; endocytosis follows exocytosis primarily by closing Ω-shaped profiles pre-formed through the flat-to-Λ-to-Ω-shape transition or formed via fusion. Calcium/SNARE-dependent fusion machinery, cytoskeleton-dependent membrane tension, osmotic pressure, calcium/dynamin-dependent fission machinery, and actin/dynamin-dependent force machinery work together to generate fusion and budding modes differing in pore status, vesicle size, speed and quantity, controls release probability, synchronization and content release rates/amounts, and underlies exo-endocytosis coupling to maintain membrane homeostasis. These transformations, underlying mechanisms, and functions may be conserved for fusion and budding in general.
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Affiliation(s)
- Ling-Gang Wu
- National Institute of Neurological Disorders and Stroke, Bethesda, MD, USA.
| | - Chung Yu Chan
- National Institute of Neurological Disorders and Stroke, Bethesda, MD, USA
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12
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Bottacchiari M, Gallo M, Bussoletti M, Casciola CM. The local variation of the Gaussian modulus enables different pathways for fluid lipid vesicle fusion. Sci Rep 2024; 14:23. [PMID: 38168475 PMCID: PMC10762093 DOI: 10.1038/s41598-023-50922-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2023] [Accepted: 12/28/2023] [Indexed: 01/05/2024] Open
Abstract
Viral infections, fertilization, neurotransmission, and many other fundamental biological processes rely on membrane fusion. Straightforward calculations based on the celebrated Canham-Helfrich elastic model predict a large topological energy barrier that prevents the fusion process from being thermally activated. While such high energy is in accordance with the physical barrier function of lipid membranes, it is difficult to reconcile with the biological mechanisms involved in fusion processes. In this work, we use a Ginzburg-Landau type of free energy that recovers the Canham-Helfrich model in the limit of small width-to-vesicle-extension ratio, with the additional ability to handle topological transitions. We show that a local modification of the Gaussian modulus in the merging region both dramatically lowers the elastic energy barrier and substantially changes the minimal energy pathway for fusion, in accordance with experimental evidence. Therefore, we discuss biological examples in which such a modification might play a crucial role.
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Affiliation(s)
- Matteo Bottacchiari
- Department of Mechanical and Aerospace Engineering, Sapienza Università di Roma, Rome, Italy
| | - Mirko Gallo
- Department of Mechanical and Aerospace Engineering, Sapienza Università di Roma, Rome, Italy
| | - Marco Bussoletti
- Department of Mechanical and Aerospace Engineering, Sapienza Università di Roma, Rome, Italy
| | - Carlo Massimo Casciola
- Department of Mechanical and Aerospace Engineering, Sapienza Università di Roma, Rome, Italy.
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13
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Lira RB, Hammond JCF, Cavalcanti RRM, Rous M, Riske KA, Roos WH. The underlying mechanical properties of membranes tune their ability to fuse. J Biol Chem 2023; 299:105430. [PMID: 37926280 PMCID: PMC10716014 DOI: 10.1016/j.jbc.2023.105430] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2023] [Revised: 10/16/2023] [Accepted: 10/23/2023] [Indexed: 11/07/2023] Open
Abstract
Membrane fusion is a ubiquitous process associated with a multitude of biological events. Although it has long been appreciated that membrane mechanics plays an important role in membrane fusion, the molecular interplay between mechanics and fusion has remained elusive. For example, although different lipids modulate membrane mechanics differently, depending on their composition, molar ratio, and complex interactions, differing lipid compositions may lead to similar mechanical properties. This raises the question of whether (i) the specific lipid composition or (ii) the average mesoscale mechanics of membranes acts as the determining factor for cellular function. Furthermore, little is known about the potential consequences of fusion on membrane disruption. Here, we use a combination of confocal microscopy, time-resolved imaging, and electroporation to shed light onto the underlying mechanical properties of membranes that regulate membrane fusion. Fusion efficiency follows a nearly universal behavior that depends on membrane fluidity parameters, such as membrane viscosity and bending rigidity, rather than on specific lipid composition. This helps explaining why the charged and fluid membranes of the inner leaflet of the plasma membrane are more fusogenic than their outer counterparts. Importantly, we show that physiological levels of cholesterol, a key component of biological membranes, has a mild effect on fusion but significantly enhances membrane mechanical stability against pore formation, suggesting that its high cellular levels buffer the membrane against disruption. The ability of membranes to efficiently fuse while preserving their integrity may have given evolutionary advantages to cells by enabling their function while preserving membrane stability.
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Affiliation(s)
- Rafael B Lira
- Moleculaire Biofysica, Zernike Instituut, Rijksuniversiteit Groningen, Groningen, Netherlands.
| | - Jayna C F Hammond
- Moleculaire Biofysica, Zernike Instituut, Rijksuniversiteit Groningen, Groningen, Netherlands
| | | | - Madelief Rous
- Moleculaire Biofysica, Zernike Instituut, Rijksuniversiteit Groningen, Groningen, Netherlands
| | - Karin A Riske
- Departamento de Biofísica, Universidade Federal de São Paulo, São Paulo, Brazil
| | - Wouter H Roos
- Moleculaire Biofysica, Zernike Instituut, Rijksuniversiteit Groningen, Groningen, Netherlands.
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14
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Bogue D, Ryan G, Wassmer E, Research Consortium GE, Naik S. VAMP2 Gene-Related Neurodevelopmental Disorder: A Differential Diagnosis for Rett/Angelman-Type Spectrum of Disorders. Mol Syndromol 2023; 14:449-456. [PMID: 37901860 PMCID: PMC10601795 DOI: 10.1159/000530150] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2022] [Accepted: 03/08/2023] [Indexed: 10/31/2023] Open
Abstract
Introduction VAMP2 is an instrumental protein in neuronal synaptic transmission in the brain, facilitating neurotransmitter release. It is encoded by the VAMP2 gene, and pathogenic variants in this gene cause neurodevelopmental features including early onset axial hypotonia, intellectual disability, and features of autism spectrum disorder. To date, only three types of allelic variants (loss of function, in-frame deletions, and missense variants) in the VAMP2 gene have been previously reported in 11 patients with learning difficulties. Here, we describe a patient in whom a novel de novo pathogenic variant in the VAMP2 gene was identified. Case Presentation A 15-month-old girl presented with early onset hypotonia, global developmental delay, learning difficulties, microcephaly, nystagmus, strabismus, and stereotypies. Later, she developed a sleep disorder, challenging behaviour with self-injury, and scoliosis. Gene agnostic analysis of whole genome sequencing data identified a novel de novo heterozygous missense variant c.197G>C (p.Arg66Pro) in the VAMP2 gene SNARE motif region. Discussion This is the fourth report describing VAMP2 gene-related neurodevelopmental disorder. This report adds to the genotype-phenotype correlation and highlights this condition as an important differential diagnosis of Rett/Angelman-type spectrum of disorders. Patients presenting with features of either Rett syndrome or Angelman syndrome, in whom genetic testing is not suggestive, should be evaluated for variants in the VAMP2 gene, given the significant overlap in clinical presentation of these disorders.
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Affiliation(s)
- Danielle Bogue
- West Midlands Clinical Genetics Unit, Birmingham Women’s and Children’s NHS Foundation Trust, Birmingham, UK
| | - Gavin Ryan
- West Midlands Regional Genetics Laboratory, Birmingham Women’s and Children’s NHS Foundation Trust, Birmingham, UK
| | - Evangeline Wassmer
- Department of Neurology, Birmingham Women’s and Children’s NHS Foundation Trust, Birmingham, UK
- Institute of Health and Neurodevelopment, Aston University, Birmingham, UK
| | | | - Swati Naik
- West Midlands Clinical Genetics Unit, Birmingham Women’s and Children’s NHS Foundation Trust, Birmingham, UK
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15
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Stanton AE, Hughson FM. The machinery of vesicle fusion. Curr Opin Cell Biol 2023; 83:102191. [PMID: 37421936 PMCID: PMC10529041 DOI: 10.1016/j.ceb.2023.102191] [Citation(s) in RCA: 9] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2023] [Revised: 06/01/2023] [Accepted: 06/07/2023] [Indexed: 07/10/2023]
Abstract
The compartmentalization of eukaryotic cells is reliant on the fidelity of vesicle-mediated intracellular transport. Vesicles deliver their cargo via membrane fusion, a process requiring membrane tethers, Sec1/Munc18 (SM) proteins, and SNAREs. These components function in concert to ensure that membrane fusion is efficient and accurate, but the mechanisms underlying their cooperative action are still in many respects mysterious. In this brief review, we highlight recent progress toward a more integrative understanding of the vesicle fusion machinery. We focus particular attention on cryo-electron microscopy structures of intact multisubunit tethers in complex with SNAREs or SM proteins, as well as a structure of an SM protein bound to multiple SNAREs. The insights gained from this work emphasize the advantages of studying the fusion machinery intact and in context.
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Affiliation(s)
- Abigail E Stanton
- Department of Molecular Biology, Princeton University, Princeton, NJ 08544, USA
| | - Frederick M Hughson
- Department of Molecular Biology, Princeton University, Princeton, NJ 08544, USA.
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16
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Nguyen A, Lugarini F, David C, Hosnani P, Alagöz Ç, Friedrich A, Schlütermann D, Knotkova B, Patel A, Parfentev I, Urlaub H, Meinecke M, Stork B, Faesen AC. Metamorphic proteins at the basis of human autophagy initiation and lipid transfer. Mol Cell 2023:S1097-2765(23)00321-0. [PMID: 37209685 DOI: 10.1016/j.molcel.2023.04.026] [Citation(s) in RCA: 9] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2022] [Revised: 02/23/2023] [Accepted: 04/27/2023] [Indexed: 05/22/2023]
Abstract
Autophagy is a conserved intracellular degradation pathway that generates de novo double-membrane autophagosomes to target a wide range of material for lysosomal degradation. In multicellular organisms, autophagy initiation requires the timely assembly of a contact site between the ER and the nascent autophagosome. Here, we report the in vitro reconstitution of a full-length seven-subunit human autophagy initiation supercomplex built on a core complex of ATG13-101 and ATG9. Assembly of this core complex requires the rare ability of ATG13 and ATG101 to switch between distinct folds. The slow spontaneous metamorphic conversion is rate limiting for the self-assembly of the supercomplex. The interaction of the core complex with ATG2-WIPI4 enhances tethering of membrane vesicles and accelerates lipid transfer of ATG2 by both ATG9 and ATG13-101. Our work uncovers the molecular basis of the contact site and its assembly mechanisms imposed by the metamorphosis of ATG13-101 to regulate autophagosome biogenesis in space and time.
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Affiliation(s)
- Anh Nguyen
- Max-Planck Institute for Multidisciplinary Sciences, Laboratory of Biochemistry of Signal Dynamics, Göttingen, Germany
| | - Francesca Lugarini
- Max-Planck Institute for Multidisciplinary Sciences, Laboratory of Biochemistry of Signal Dynamics, Göttingen, Germany
| | - Céline David
- Institute of Molecular Medicine I, Medical Faculty and University Hospital Düsseldorf, Heinrich Heine University, Düsseldorf, Germany
| | - Pouya Hosnani
- Heidelberg University Biochemistry Center (BZH), Heidelberg, Germany; University Medical Centre Göttingen, Department of Cellular Biochemistry, Göttingen, Germany
| | - Çağla Alagöz
- Max-Planck Institute for Multidisciplinary Sciences, Laboratory of Biochemistry of Signal Dynamics, Göttingen, Germany
| | - Annabelle Friedrich
- Institute of Molecular Medicine I, Medical Faculty and University Hospital Düsseldorf, Heinrich Heine University, Düsseldorf, Germany
| | - David Schlütermann
- Institute of Molecular Medicine I, Medical Faculty and University Hospital Düsseldorf, Heinrich Heine University, Düsseldorf, Germany
| | - Barbora Knotkova
- Heidelberg University Biochemistry Center (BZH), Heidelberg, Germany; University Medical Centre Göttingen, Department of Cellular Biochemistry, Göttingen, Germany
| | - Anoshi Patel
- Max-Planck Institute for Multidisciplinary Sciences, Laboratory of Biochemistry of Signal Dynamics, Göttingen, Germany
| | - Iwan Parfentev
- Max-Planck Institute for Multidisciplinary Sciences, Bioanalytical Mass Spectrometry, Göttingen, Germany
| | - Henning Urlaub
- Max-Planck Institute for Multidisciplinary Sciences, Bioanalytical Mass Spectrometry, Göttingen, Germany; University Medical Centre Göttingen, Institute of Clinical Chemistry, Bioanalytics Group, Göttingen, Germany
| | - Michael Meinecke
- Heidelberg University Biochemistry Center (BZH), Heidelberg, Germany; University Medical Centre Göttingen, Department of Cellular Biochemistry, Göttingen, Germany
| | - Björn Stork
- Institute of Molecular Medicine I, Medical Faculty and University Hospital Düsseldorf, Heinrich Heine University, Düsseldorf, Germany
| | - Alex C Faesen
- Max-Planck Institute for Multidisciplinary Sciences, Laboratory of Biochemistry of Signal Dynamics, Göttingen, Germany.
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17
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Jabbari V, Sawczyk M, Amiri A, Král P, Shahbazian-Yassar R. Unveiling growth and dynamics of liposomes by graphene liquid cell-transmission electron microscopy. NANOSCALE 2023; 15:5011-5022. [PMID: 36790028 DOI: 10.1039/d2nr06147c] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/18/2023]
Abstract
Liposome is a model system for biotechnological and biomedical purposes spanning from targeted drug delivery to modern vaccine research. Yet, the growth mechanism of liposomes is largely unknown. In this work, the formation and evolution of phosphatidylcholine-based liposomes are studied in real-time by graphene liquid cell-transmission electron microscopy (GLC-TEM). We reveal important steps in the growth, fusion and denaturation of phosphatidylcholine (PC) liposomes. We show that initially complex lipid aggregates resembling micelles start to form. These aggregates randomly merge while capturing water and forming small proto-liposomes. The nanoscopic containers continue sucking water until their membrane becomes convex and free of redundant phospholipids, giving stabilized PC liposomes of different sizes. In the initial stage, proto-liposomes grow at a rate of 10-15 nm s-1, which is followed by their growth rate of 2-5 nm s-1, limited by the lipid availability in the solution. Molecular dynamics (MD) simulations are used to understand the structure of micellar clusters, their evolution, and merging. The liposomes are also found to fuse through lipid bilayers docking followed by the formation of a hemifusion diaphragm and fusion pore opening. The liposomes denaturation can be described by initial structural destabilization and deformation of the membrane followed by the leakage of the encapsulated liquid. This study offers new insights on the formation and growth of lipid-based molecular assemblies which is applicable to a wide range of amphiphilic molecules.
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Affiliation(s)
- Vahid Jabbari
- Mechanical and Industrial Engineering Department, University of Illinois at Chicago, Chicago, IL 60607, USA. rsyassar@uic
| | - Michal Sawczyk
- Department of Chemistry, University of Illinois at Chicago, Chicago, IL 60607, USA
| | - Azadeh Amiri
- Mechanical and Industrial Engineering Department, University of Illinois at Chicago, Chicago, IL 60607, USA. rsyassar@uic
| | - Petr Král
- Department of Chemistry, University of Illinois at Chicago, Chicago, IL 60607, USA
- Department of Physics, Pharmaceutical Sciences, and Chemical Engineering, University of Illinois at Chicago, Chicago, USA
| | - Reza Shahbazian-Yassar
- Mechanical and Industrial Engineering Department, University of Illinois at Chicago, Chicago, IL 60607, USA. rsyassar@uic
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18
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van Tilburg M, Hilbers PAJ, Markvoort AJ. On the role of membrane embedding, protein rigidity and transmembrane length in lipid membrane fusion. SOFT MATTER 2023; 19:1791-1802. [PMID: 36786821 DOI: 10.1039/d2sm01582j] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/18/2023]
Abstract
The fusion of biological membranes is ubiquitous in natural processes like exo- and endocytosis, intracellular trafficking and viral entry. Membrane fusion is also utilized in artificial biomimetic fusion systems, e.g. for drug delivery. Both the natural and the biomimetic fusion systems rely on a wide range of (artificial) proteins mediating the fusion process. Although the exact mechanisms of these proteins differ, clear analogies in their general behavior can be observed in bringing the membranes in close proximity and mediating the fusion reaction. In our study, we use molecular dynamics simulations with coarse grained models, mimicking the general behavior of fusion proteins (spikes), to systematically examine the effects of specific characteristics of these proteins on the fusion process. The protein characteristics considered are (i) the type of membrane embedding, i.e., either transmembrane or not, (ii) the rigidity, and (iii) the transmembrane domain (TMD) length. The results show essential differences in fusion pathway between monotopic and transmembrane spikes, in which transmembrane spikes seem to inhibit the formation of hemifusion diaphragms, leading to a faster fusion development. Furthermore, we observed that an increased rigidity and a decreased TMD length both proved to contribute to a faster fusion development. Finally, we show that a single spike may suffice to successfully induce a fusion reaction, provided that the spike is sufficiently rigid and attractive. Not only does this shed light on biological fusion of membranes, it also provides clear design rules for artificial membrane fusion systems.
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Affiliation(s)
- Marco van Tilburg
- Department of Biomedical Engineering, Computational Biology Group, Eindhoven University of Technology, The Netherlands.
| | - Peter A J Hilbers
- Department of Biomedical Engineering, Computational Biology Group, Eindhoven University of Technology, The Netherlands.
- Institute of Complex Molecular Systems, Eindhoven University of Technology, The Netherlands
| | - Albert J Markvoort
- Department of Biomedical Engineering, Computational Biology Group, Eindhoven University of Technology, The Netherlands.
- Institute of Complex Molecular Systems, Eindhoven University of Technology, The Netherlands
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19
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Warner JM, An D, Stratton BS, O'Shaughnessy B. A hemifused complex is the hub in a network of pathways to membrane fusion. Biophys J 2023; 122:374-385. [PMID: 36463406 PMCID: PMC9892611 DOI: 10.1016/j.bpj.2022.12.003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2022] [Revised: 06/25/2022] [Accepted: 11/30/2022] [Indexed: 12/12/2022] Open
Abstract
Membrane fusion is a critical step for many essential processes, from neurotransmission to fertilization. For over 40 years, protein-free fusion driven by calcium or other cationic species has provided a simplified model of biological fusion, but the mechanisms remain poorly understood. Cation-mediated membrane fusion and permeation are essential in their own right to drug delivery strategies based on cell-penetrating peptides or cation-bearing lipid nanoparticles. Experimental studies suggest calcium drives anionic membranes to a hemifused intermediate that constitutes a hub in a network of pathways, but the pathway selection mechanism is unknown. Here we develop a mathematical model that identifies the network hub as a highly dynamic hemifusion complex. Multivalent cations drive expansion of this high-tension hemifusion interface between interacting vesicles during a brief transient. The fate of this interface determines the outcome, either fusion, dead-end hemifusion, or vesicle lysis. The model reproduces the unexplained finding that calcium-driven fusion of vesicles with planar membranes typically stalls at hemifusion, and we show the equilibrated hemifused state is a novel lens-shaped complex. Thus, membrane fusion kinetics follow a stochastic trajectory within a network of pathways, with outcome weightings set by a hemifused complex intermediate.
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Affiliation(s)
- Jason M Warner
- Department of Chemical Engineering, Columbia University, New York, New York
| | - Dong An
- Department of Chemical Engineering, Columbia University, New York, New York
| | | | - Ben O'Shaughnessy
- Department of Chemical Engineering, Columbia University, New York, New York.
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20
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Kosmidis E, Shuttle CG, Preobraschenski J, Ganzella M, Johnson PJ, Veshaguri S, Holmkvist J, Møller MP, Marantos O, Marcoline F, Grabe M, Pedersen JL, Jahn R, Stamou D. Regulation of the mammalian-brain V-ATPase through ultraslow mode-switching. Nature 2022; 611:827-834. [PMID: 36418452 PMCID: PMC11212661 DOI: 10.1038/s41586-022-05472-9] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2022] [Accepted: 10/21/2022] [Indexed: 11/24/2022]
Abstract
Vacuolar-type adenosine triphosphatases (V-ATPases)1-3 are electrogenic rotary mechanoenzymes structurally related to F-type ATP synthases4,5. They hydrolyse ATP to establish electrochemical proton gradients for a plethora of cellular processes1,3. In neurons, the loading of all neurotransmitters into synaptic vesicles is energized by about one V-ATPase molecule per synaptic vesicle6,7. To shed light on this bona fide single-molecule biological process, we investigated electrogenic proton-pumping by single mammalian-brain V-ATPases in single synaptic vesicles. Here we show that V-ATPases do not pump continuously in time, as suggested by observing the rotation of bacterial homologues8 and assuming strict ATP-proton coupling. Instead, they stochastically switch between three ultralong-lived modes: proton-pumping, inactive and proton-leaky. Notably, direct observation of pumping revealed that physiologically relevant concentrations of ATP do not regulate the intrinsic pumping rate. ATP regulates V-ATPase activity through the switching probability of the proton-pumping mode. By contrast, electrochemical proton gradients regulate the pumping rate and the switching of the pumping and inactive modes. A direct consequence of mode-switching is all-or-none stochastic fluctuations in the electrochemical gradient of synaptic vesicles that would be expected to introduce stochasticity in proton-driven secondary active loading of neurotransmitters and may thus have important implications for neurotransmission. This work reveals and emphasizes the mechanistic and biological importance of ultraslow mode-switching.
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Affiliation(s)
- Eleftherios Kosmidis
- Center for Geometrically Engineered Cellular Membranes, Department of Chemistry, University of Copenhagen, Copenhagen, Denmark
| | - Christopher G Shuttle
- Center for Geometrically Engineered Cellular Membranes, Department of Chemistry, University of Copenhagen, Copenhagen, Denmark
| | - Julia Preobraschenski
- Laboratory of Neurobiology, Max Planck Institute for Multidisciplinary Sciences, Göttingen, Germany
- Institute for Auditory Neuroscience, University Medical Center, Göttingen, Germany
- Multiscale Bioimaging Cluster of Excellence (MBExC), University of Göttingen, Göttingen, Germany
| | - Marcelo Ganzella
- Laboratory of Neurobiology, Max Planck Institute for Multidisciplinary Sciences, Göttingen, Germany
| | - Peter J Johnson
- Department of Mathematical Sciences, University of Copenhagen, Copenhagen, Denmark
- Department of Mathematics, University of Manchester, Manchester, UK
| | - Salome Veshaguri
- Center for Geometrically Engineered Cellular Membranes, Department of Chemistry, University of Copenhagen, Copenhagen, Denmark
- Novozymes A/S, Kgs Lyngby, Denmark
| | - Jesper Holmkvist
- Center for Geometrically Engineered Cellular Membranes, Department of Chemistry, University of Copenhagen, Copenhagen, Denmark
| | - Mads P Møller
- Center for Geometrically Engineered Cellular Membranes, Department of Chemistry, University of Copenhagen, Copenhagen, Denmark
| | - Orestis Marantos
- Center for Geometrically Engineered Cellular Membranes, Department of Chemistry, University of Copenhagen, Copenhagen, Denmark
| | - Frank Marcoline
- Cardiovascular Research Institute, Department of Pharmaceutical Chemistry, University of California San Francisco, San Francisco, CA, USA
| | - Michael Grabe
- Cardiovascular Research Institute, Department of Pharmaceutical Chemistry, University of California San Francisco, San Francisco, CA, USA
| | - Jesper L Pedersen
- Department of Mathematical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Reinhard Jahn
- Laboratory of Neurobiology, Max Planck Institute for Multidisciplinary Sciences, Göttingen, Germany
| | - Dimitrios Stamou
- Center for Geometrically Engineered Cellular Membranes, Department of Chemistry, University of Copenhagen, Copenhagen, Denmark.
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21
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Zhang CC, Zhu LX, Shi HJ, Zhu LJ. The Role of Vesicle Release and Synaptic Transmission in Depression. Neuroscience 2022; 505:171-185. [DOI: 10.1016/j.neuroscience.2022.10.001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2022] [Revised: 09/19/2022] [Accepted: 10/03/2022] [Indexed: 11/06/2022]
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22
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Cui L, Li H, Xi Y, Hu Q, Liu H, Fan J, Xiang Y, Zhang X, Shui W, Lai Y. Vesicle trafficking and vesicle fusion: mechanisms, biological functions, and their implications for potential disease therapy. MOLECULAR BIOMEDICINE 2022; 3:29. [PMID: 36129576 PMCID: PMC9492833 DOI: 10.1186/s43556-022-00090-3] [Citation(s) in RCA: 29] [Impact Index Per Article: 14.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2022] [Accepted: 07/12/2022] [Indexed: 11/10/2022] Open
Abstract
Intracellular vesicle trafficking is the fundamental process to maintain the homeostasis of membrane-enclosed organelles in eukaryotic cells. These organelles transport cargo from the donor membrane to the target membrane through the cargo containing vesicles. Vesicle trafficking pathway includes vesicle formation from the donor membrane, vesicle transport, and vesicle fusion with the target membrane. Coat protein mediated vesicle formation is a delicate membrane budding process for cargo molecules selection and package into vesicle carriers. Vesicle transport is a dynamic and specific process for the cargo containing vesicles translocation from the donor membrane to the target membrane. This process requires a group of conserved proteins such as Rab GTPases, motor adaptors, and motor proteins to ensure vesicle transport along cytoskeletal track. Soluble N-ethyl-maleimide-sensitive factor (NSF) attachment protein receptors (SNARE)-mediated vesicle fusion is the final process for vesicle unloading the cargo molecules at the target membrane. To ensure vesicle fusion occurring at a defined position and time pattern in eukaryotic cell, multiple fusogenic proteins, such as synaptotagmin (Syt), complexin (Cpx), Munc13, Munc18 and other tethering factors, cooperate together to precisely regulate the process of vesicle fusion. Dysfunctions of the fusogenic proteins in SNARE-mediated vesicle fusion are closely related to many diseases. Recent studies have suggested that stimulated membrane fusion can be manipulated pharmacologically via disruption the interface between the SNARE complex and Ca2+ sensor protein. Here, we summarize recent insights into the molecular mechanisms of vesicle trafficking, and implications for the development of new therapeutics based on the manipulation of vesicle fusion.
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23
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Neurotransmitter uptake of synaptic vesicles studied by X-ray diffraction. EUROPEAN BIOPHYSICS JOURNAL 2022; 51:465-482. [PMID: 35904588 PMCID: PMC9463337 DOI: 10.1007/s00249-022-01609-w] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/07/2022] [Revised: 06/12/2022] [Accepted: 06/14/2022] [Indexed: 11/30/2022]
Abstract
The size, polydispersity, and electron density profile of synaptic vesicles (SVs) can be studied by small-angle X-ray scattering (SAXS), i.e. by X-ray diffraction from purified SV suspensions in solution. Here we show that size and shape transformations, as they appear in the functional context of these important synaptic organelles, can also be monitored by SAXS. In particular, we have investigated the active uptake of neurotransmitters, and find a mean vesicle radius increase of about 12% after the uptake of glutamate, which indicates an unusually large extensibility of the vesicle surface, likely to be accompanied by conformational changes of membrane proteins and rearrangements of the bilayer. Changes in the electron density profile (EDP) give first indications for such a rearrangement. Details of the protein structure are screened, however, by SVs polydispersity. To overcome the limitations of large ensemble averages and heterogeneous structures, we therefore propose serial X-ray diffraction by single free electron laser pulses. Using simulated data for realistic parameters, we show that this is in principle feasible, and that even spatial distances between vesicle proteins could be assessed by this approach.
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24
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Warner H, Mahajan S, van den Bogaart G. Rerouting trafficking circuits through posttranslational SNARE modifications. J Cell Sci 2022; 135:276344. [PMID: 35972760 DOI: 10.1242/jcs.260112] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs) are membrane-associated trafficking proteins that confer identity to lipid membranes and facilitate membrane fusion. These functions are achieved through the complexing of Q-SNAREs with a specific cognate target R-SNARE, leading to the fusion of their associated membranes. These SNARE complexes then dissociate so that the Q-SNAREs and R-SNAREs can repeat this cycle. Whilst the basic function of SNAREs has been long appreciated, it is becoming increasingly clear that the cell can control the localisation and function of SNARE proteins through posttranslational modifications (PTMs), such as phosphorylation and ubiquitylation. Whilst numerous proteomic methods have shown that SNARE proteins are subject to these modifications, little is known about how these modifications regulate SNARE function. However, it is clear that these PTMs provide cells with an incredible functional plasticity; SNARE PTMs enable cells to respond to an ever-changing extracellular environment through the rerouting of membrane traffic. In this Review, we summarise key findings regarding SNARE regulation by PTMs and discuss how these modifications reprogramme membrane trafficking pathways.
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Affiliation(s)
- Harry Warner
- Department of Molecular Immunology, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, 9747AG Groningen, The Netherlands
| | - Shweta Mahajan
- Division of Immunobiology, Center for Inflammation and Tolerance, Cincinnati Children's Hospital, Cincinnati, OH 45229, USA
| | - Geert van den Bogaart
- Department of Molecular Immunology, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, 9747AG Groningen, The Netherlands
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25
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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: 35] [Impact Index Per Article: 17.5] [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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26
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Vardar G, Salazar-Lázaro A, Zobel S, Trimbuch T, Rosenmund C. Syntaxin-1A modulates vesicle fusion in mammalian neurons via juxtamembrane domain dependent palmitoylation of its transmembrane domain. eLife 2022; 11:78182. [PMID: 35638903 PMCID: PMC9183232 DOI: 10.7554/elife.78182] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2022] [Accepted: 05/30/2022] [Indexed: 11/16/2022] Open
Abstract
SNAREs are undoubtedly one of the core elements of synaptic transmission. Contrary to the well characterized function of their SNARE domains bringing the plasma and vesicular membranes together, the level of contribution of their juxtamembrane domain (JMD) and the transmembrane domain (TMD) to the vesicle fusion is still under debate. To elucidate this issue, we analyzed three groups of STX1A mutations in cultured mouse hippocampal neurons: (1) elongation of STX1A’s JMD by three amino acid insertions in the junction of SNARE-JMD or JMD-TMD; (2) charge reversal mutations in STX1A’s JMD; and (3) palmitoylation deficiency mutations in STX1A’s TMD. We found that both JMD elongations and charge reversal mutations have position-dependent differential effects on Ca2+-evoked and spontaneous neurotransmitter release. Importantly, we show that STX1A’s JMD regulates the palmitoylation of STX1A’s TMD and loss of STX1A palmitoylation either through charge reversal mutation K260E or by loss of TMD cysteines inhibits spontaneous vesicle fusion. Interestingly, the retinal ribbon specific STX3B has a glutamate in the position corresponding to the K260E mutation in STX1A and mutating it with E259K acts as a molecular on-switch. Furthermore, palmitoylation of post-synaptic STX3A can be induced by the exchange of its JMD with STX1A’s JMD together with the incorporation of two cysteines into its TMD. Forced palmitoylation of STX3A dramatically enhances spontaneous vesicle fusion suggesting that STX1A regulates spontaneous release through two distinct mechanisms: one through the C-terminal half of its SNARE domain and the other through the palmitoylation of its TMD.
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Affiliation(s)
- Gülçin Vardar
- Department of Neurophysiology, Charité - Universitätsmedizin Berlin, Berlin, Germany
| | - Andrea Salazar-Lázaro
- Department of Neurophysiology, Charité - Universitätsmedizin Berlin, Berlin, Germany
| | - Sina Zobel
- Department of Neurophysiology, Charité - Universitätsmedizin Berlin, Berlin, Germany
| | - Thorsten Trimbuch
- Department of Neurophysiology, Charité - Universitätsmedizin Berlin, Berlin, Germany
| | - Christian Rosenmund
- Department of Neurophysiology, Charité - Universitätsmedizin Berlin, Berlin, Germany
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27
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Abstract
Major recent advances and previous data have led to a plausible model of how key proteins mediate neurotransmitter release. In this model, the soluble N-ethylmaleimide-sensitive factor (NSF) attachment protein (SNAP) receptor (SNARE) proteins syntaxin-1, SNAP-25, and synaptobrevin form tight complexes that bring the membranes together and are crucial for membrane fusion. NSF and SNAPs disassemble SNARE complexes and ensure that fusion occurs through an exquisitely regulated pathway that starts with Munc18-1 bound to a closed conformation of syntaxin-1. Munc18-1 also binds to synaptobrevin, forming a template to assemble the SNARE complex when Munc13-1 opens syntaxin-1 while bridging the vesicle and plasma membranes. Synaptotagmin-1 and complexin bind to partially assembled SNARE complexes, likely stabilizing them and preventing fusion until Ca2+ binding to synaptotagmin-1 causes dissociation from the SNARE complex and induces interactions with phospholipids that help trigger release. Although fundamental questions remain about the mechanism of membrane fusion, these advances provide a framework to investigate the mechanisms underlying presynaptic plasticity.
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Affiliation(s)
- Josep Rizo
- Departments of Biophysics, Biochemistry, and Pharmacology, University of Texas Southwestern Medical Center, Dallas, Texas, USA;
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28
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Joardar A, Pattnaik GP, Chakraborty H. Mechanism of Membrane Fusion: Interplay of Lipid and Peptide. J Membr Biol 2022; 255:211-224. [PMID: 35435451 PMCID: PMC9014786 DOI: 10.1007/s00232-022-00233-1] [Citation(s) in RCA: 26] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2022] [Accepted: 03/25/2022] [Indexed: 11/26/2022]
Abstract
Membrane fusion is an essential process for the survival of eukaryotes and the entry of enveloped viruses into host cells. A proper understanding of the mechanism of membrane fusion would provide us a handle to manipulate several biological pathways, and design efficient vaccines against emerging and re-emerging viral infections. Although fusion proteins take the central stage in catalyzing the process, role of lipid composition is also of paramount importance. Lipid composition modulates membrane organization and dynamics and impacts the lipid–protein (peptide) interaction. Moreover, the intrinsic curvature of lipids has strong impact on the formation of stalk and hemifusion diaphragm. Detection of transiently stable intermediates remains the bottleneck in the understanding of fusion mechanism. In order to circumvent this challenge, analytical methods can be employed to determine the kinetic parameters from ensemble average measurements of observables, such as lipid mixing, content mixing, and content leakage. The current review aims to present an analytical method that would aid our understanding of the fusion mechanism, provides a better insight into the role of lipid shape, and discusses the interplay of lipid and peptide in membrane fusion.
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Affiliation(s)
- Ankita Joardar
- School of Chemistry, Sambalpur University, Jyoti Vihar, Burla, Odisha, 768019, India
| | | | - Hirak Chakraborty
- School of Chemistry, Sambalpur University, Jyoti Vihar, Burla, Odisha, 768019, India.
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29
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Singh P, Mukherji S, Basak S, Hoffmann M, Das DK. Dynamic Ca 2+ sensitivity stimulates the evolved SARS-CoV-2 spike strain-mediated membrane fusion for enhanced entry. Cell Rep 2022; 39:110694. [PMID: 35397208 PMCID: PMC8993541 DOI: 10.1016/j.celrep.2022.110694] [Citation(s) in RCA: 15] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2021] [Revised: 12/10/2021] [Accepted: 03/25/2022] [Indexed: 12/18/2022] Open
Abstract
Mutations in the spike protein generated a highly infectious and transmissible D614G variant, which is present in newly evolved fast-spreading variants. The D614G, Alpha, Beta, and Delta spike variants of SARS-CoV-2 appear to expedite membrane fusion process for entry, but the mechanism of spike-mediated fusion is unknown. Here, we reconstituted an in vitro pseudovirus-liposome fusion reaction and report that SARS-CoV-2 wild-type spike is a dynamic Ca2+ sensor, and D614G mutation enhances dynamic calcium sensitivity of spike protein for facilitating membrane fusion. This dynamic calcium sensitivity for fusion is found to be higher in Alpha and Beta variants and highest in Delta spike variant. We find that efficient fusion is dependent on Ca2+ concentration at low pH, and the fusion activity of spike dropped as the Ca2+ level rose beyond physiological levels. Thus, evolved spike variants may control the high fusion probability for entry by increasing Ca2+ sensing ability.
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Affiliation(s)
- Puspangana Singh
- Department of Biological Sciences and Bioengineering, Indian Institute of Technology Kanpur, Kanpur, Uttar Pradesh 208016, India
| | - Shreya Mukherji
- Department of Biological Sciences and Bioengineering, Indian Institute of Technology Kanpur, Kanpur, Uttar Pradesh 208016, India
| | - Swarnendu Basak
- Department of Biological Sciences and Bioengineering, Indian Institute of Technology Kanpur, Kanpur, Uttar Pradesh 208016, India
| | - Markus Hoffmann
- Infection Biology Unit, German Primate Center, Kellnerweg 4, 37077 Göttingen, Germany; Faculty of Biology and Psychology, Georg-August-University Göttingen, Wilhelmsplatz 1, 37073 Göttingen, Germany
| | - Dibyendu Kumar Das
- Department of Biological Sciences and Bioengineering, Indian Institute of Technology Kanpur, Kanpur, Uttar Pradesh 208016, India; The Mehta Family Center for Engineering in Medicine, Indian Institute of Technology Kanpur, Kanpur, Uttar Pradesh 208016, India.
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30
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Barak-Broner N, Singer-Lahat D, Chikvashvili D, Lotan I. CK2 Phosphorylation Is Required for Regulation of Syntaxin 1A Activity in Ca 2+-Triggered Release in Neuroendocrine Cells. Int J Mol Sci 2021; 22:ijms222413556. [PMID: 34948351 PMCID: PMC8708312 DOI: 10.3390/ijms222413556] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2021] [Revised: 12/12/2021] [Accepted: 12/13/2021] [Indexed: 12/29/2022] Open
Abstract
The polybasic juxtamembrane region (5RK) of the plasma membrane neuronal SNARE, syntaxin1A (Syx), was previously shown by us to act as a fusion clamp in PC12 cells, as charge neutralization of 5RK promotes spontaneous and inhibits Ca2+-triggered release. Using a Syx-based FRET probe (CSYS), we demonstrated that 5RK is required for a depolarization-induced Ca+2-dependent opening (close-to-open transition; CDO) of Syx, which involves the vesicular SNARE synaptobrevin2 and occurs concomitantly with Ca2+-triggered release. Here, we investigated the mechanism underlying the CDO requirement for 5RK and identified phosphorylation of Syx at Ser-14 (S14) by casein kinase 2 (CK2) as a crucial molecular determinant. Thus, following biochemical verification that both endogenous Syx and CSYS are constitutively S14 phosphorylated in PC12 cells, dynamic FRET analysis of phospho-null and phospho-mimetic mutants of CSYS and the use of a CK2 inhibitor revealed that the S14 phosphorylation confers the CDO requirement for 5RK. In accord, amperometric analysis of catecholamine release revealed that the phospho-null mutant does not support Ca2+-triggered release. These results identify a functionally important CK2 phosphorylation of Syx that is required for the 5RK-regulation of CDO and for concomitant Ca2+-triggered release. Further, also spontaneous release, conferred by charge neutralization of 5RK, was abolished in the phospho-null mutant.
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Affiliation(s)
- Noa Barak-Broner
- Department of Neurobiology Biochemistry & Biophysics, The George S. Wise Faculty of Life Sciences, Tel Aviv University, Ramat Aviv, Tel Aviv-Yafo 69978, Israel;
| | - Dafna Singer-Lahat
- Department of Physiology and Pharmacology, Sackler School of Medicine, Tel Aviv University, Ramat Aviv, Tel Aviv-Yafo 69978, Israel; (D.S.-L.); (D.C.)
| | - Dodo Chikvashvili
- Department of Physiology and Pharmacology, Sackler School of Medicine, Tel Aviv University, Ramat Aviv, Tel Aviv-Yafo 69978, Israel; (D.S.-L.); (D.C.)
| | - Ilana Lotan
- Department of Physiology and Pharmacology, Sackler School of Medicine, Tel Aviv University, Ramat Aviv, Tel Aviv-Yafo 69978, Israel; (D.S.-L.); (D.C.)
- Sagol School of Neuroscience, Tel Aviv University, Ramat Aviv, Tel Aviv-Yafo 69978, Israel
- Correspondence:
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31
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Nikolaus J, Hancock K, Tsemperouli M, Baddeley D, Karatekin E. Optimal Detection of Fusion Pore Dynamics Using Polarized Total Internal Reflection Fluorescence Microscopy. Front Mol Biosci 2021; 8:740408. [PMID: 34859048 PMCID: PMC8631473 DOI: 10.3389/fmolb.2021.740408] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2021] [Accepted: 10/06/2021] [Indexed: 11/13/2022] Open
Abstract
The fusion pore is the initial narrow connection that forms between fusing membranes. During vesicular release of hormones or neurotransmitters, the nanometer-sized fusion pore may open-close repeatedly (flicker) before resealing or dilating irreversibly, leading to kiss-and-run or full-fusion events, respectively. Pore dynamics govern vesicle cargo release and the mode of vesicle recycling, but the mechanisms are poorly understood. This is partly due to a lack of reconstituted assays that combine single-pore sensitivity and high time resolution. Total internal reflection fluorescence (TIRF) microscopy offers unique advantages for characterizing single membrane fusion events, but signals depend on effects that are difficult to disentangle, including the polarization of the excitation electric field, vesicle size, photobleaching, orientation of the excitation dipoles of the fluorophores with respect to the membrane, and the evanescent field depth. Commercial TIRF microscopes do not allow control of excitation polarization, further complicating analysis. To overcome these challenges, we built a polarization-controlled total internal reflection fluorescence (pTIRF) microscope and monitored fusion of proteoliposomes with planar lipid bilayers with single molecule sensitivity and ∼15 ms temporal resolution. Using pTIRF microscopy, we detected docking and fusion of fluorescently labeled small unilamellar vesicles, reconstituted with exocytotic/neuronal v-SNARE proteins (vSUVs), with a supported bilayer containing the cognate t-SNAREs (tSBL). By varying the excitation polarization angle, we were able to identify a dye-dependent optimal polarization at which the fluorescence increase upon fusion was maximal, facilitating event detection and analysis of lipid transfer kinetics. An improved algorithm allowed us to estimate the size of the fusing vSUV and the fusion pore openness (the fraction of time the pore is open) for every event. For most events, lipid transfer was much slower than expected for diffusion through an open pore, suggesting that fusion pore flickering limits lipid release. We find a weak correlation between fusion pore openness and vesicle area. The approach can be used to study mechanisms governing fusion pore dynamics in a wide range of membrane fusion processes.
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Affiliation(s)
- Joerg Nikolaus
- Cellular and Molecular Physiology, Yale University, New Haven, CT, United States
- Nanobiology Institute, Yale University, West Haven, CT, United States
| | - Kasey Hancock
- Cellular and Molecular Physiology, Yale University, New Haven, CT, United States
- Nanobiology Institute, Yale University, West Haven, CT, United States
- Integrated Physical and Engineering Biology Program, Yale University, New Haven, CT, United States
| | - Maria Tsemperouli
- Cellular and Molecular Physiology, Yale University, New Haven, CT, United States
- Nanobiology Institute, Yale University, West Haven, CT, United States
| | - David Baddeley
- Nanobiology Institute, Yale University, West Haven, CT, United States
- Cell Biology, Yale University, New Haven, CT, United States
| | - Erdem Karatekin
- Cellular and Molecular Physiology, Yale University, New Haven, CT, United States
- Nanobiology Institute, Yale University, West Haven, CT, United States
- Molecular Biophysics and Biochemistry, Yale University, New Haven, CT, United States
- Saints-Pères Paris Institute for the Neurosciences (SPPIN), Université de Paris, Centre National de la Recherche Scientifique (CNRS), Paris, France
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32
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Sauvola CW, Littleton JT. SNARE Regulatory Proteins in Synaptic Vesicle Fusion and Recycling. Front Mol Neurosci 2021; 14:733138. [PMID: 34421538 PMCID: PMC8377282 DOI: 10.3389/fnmol.2021.733138] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2021] [Accepted: 07/20/2021] [Indexed: 01/01/2023] Open
Abstract
Membrane fusion is a universal feature of eukaryotic protein trafficking and is mediated by the soluble N-ethylmaleimide sensitive factor attachment protein receptor (SNARE) family. SNARE proteins embedded in opposing membranes spontaneously assemble to drive membrane fusion and cargo exchange in vitro. Evolution has generated a diverse complement of SNARE regulatory proteins (SRPs) that ensure membrane fusion occurs at the right time and place in vivo. While a core set of SNAREs and SRPs are common to all eukaryotic cells, a specialized set of SRPs within neurons confer additional regulation to synaptic vesicle (SV) fusion. Neuronal communication is characterized by precise spatial and temporal control of SNARE dynamics within presynaptic subdomains specialized for neurotransmitter release. Action potential-elicited Ca2+ influx at these release sites triggers zippering of SNAREs embedded in the SV and plasma membrane to drive bilayer fusion and release of neurotransmitters that activate downstream targets. Here we discuss current models for how SRPs regulate SNARE dynamics and presynaptic output, emphasizing invertebrate genetic findings that advanced our understanding of SRP regulation of SV cycling.
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Affiliation(s)
- Chad W Sauvola
- The Picower Institute for Learning and Memory, Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, MA, United States
| | - J Troy Littleton
- The Picower Institute for Learning and Memory, Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, MA, United States.,Department of Biology, Massachusetts Institute of Technology, Cambridge, MA, United States
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33
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Otrin L, Witkowska A, Marušič N, Zhao Z, Lira RB, Kyrilis FL, Hamdi F, Ivanov I, Lipowsky R, Kastritis PL, Dimova R, Sundmacher K, Jahn R, Vidaković-Koch T. En route to dynamic life processes by SNARE-mediated fusion of polymer and hybrid membranes. Nat Commun 2021; 12:4972. [PMID: 34404795 PMCID: PMC8371082 DOI: 10.1038/s41467-021-25294-z] [Citation(s) in RCA: 18] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2021] [Accepted: 07/30/2021] [Indexed: 12/11/2022] Open
Abstract
A variety of artificial cells springs from the functionalization of liposomes with proteins. However, these models suffer from low durability without repair and replenishment mechanisms, which can be partly addressed by replacing the lipids with polymers. Yet natural membranes are also dynamically remodeled in multiple cellular processes. Here, we show that synthetic amphiphile membranes also undergo fusion, mediated by the protein machinery for synaptic secretion. We integrated fusogenic SNAREs in polymer and hybrid vesicles and observed efficient membrane and content mixing. We determined bending rigidity and pore edge tension as key parameters for fusion and described its plausible progression through cryo-EM snapshots. These findings demonstrate that dynamic membrane phenomena can be reconstituted in synthetic materials, thereby providing new tools for the assembly of synthetic protocells.
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Affiliation(s)
- Lado Otrin
- Electrochemical Energy Conversion, Max Planck Institute for Dynamics of Complex Technical Systems, Magdeburg, Germany.
| | - Agata Witkowska
- Laboratory of Neurobiology, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
- Department of Molecular Pharmacology and Cell Biology, Leibniz-Forschungsinstitut für Molekulare Pharmakologie (FMP), Berlin, Germany
| | - Nika Marušič
- Process Systems Engineering, Max Planck Institute for Dynamics of Complex Technical Systems, Magdeburg, Germany
| | - Ziliang Zhao
- Department of Theory and Bio-Systems, Max Planck Institute of Colloids and Interfaces, Potsdam, Germany
| | - Rafael B Lira
- Department of Theory and Bio-Systems, Max Planck Institute of Colloids and Interfaces, Potsdam, Germany
- Moleculaire Biofysica, Zernike Instituut, Rijksuniversiteit Groningen, Groningen, Netherlands
| | - Fotis L Kyrilis
- Interdisciplinary Research Center HALOmem & Institute of Biochemistry and Biotechnology, Martin Luther University Halle-Wittenberg, Biozentrum, Halle/Saale, Germany
| | - Farzad Hamdi
- Interdisciplinary Research Center HALOmem & Institute of Biochemistry and Biotechnology, Martin Luther University Halle-Wittenberg, Biozentrum, Halle/Saale, Germany
| | - Ivan Ivanov
- Process Systems Engineering, Max Planck Institute for Dynamics of Complex Technical Systems, Magdeburg, Germany
| | - Reinhard Lipowsky
- Department of Theory and Bio-Systems, Max Planck Institute of Colloids and Interfaces, Potsdam, Germany
| | - Panagiotis L Kastritis
- Interdisciplinary Research Center HALOmem & Institute of Biochemistry and Biotechnology, Martin Luther University Halle-Wittenberg, Biozentrum, Halle/Saale, Germany
| | - Rumiana Dimova
- Department of Theory and Bio-Systems, Max Planck Institute of Colloids and Interfaces, Potsdam, Germany
| | - Kai Sundmacher
- Process Systems Engineering, Max Planck Institute for Dynamics of Complex Technical Systems, Magdeburg, Germany
| | - Reinhard Jahn
- Laboratory of Neurobiology, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
| | - Tanja Vidaković-Koch
- Electrochemical Energy Conversion, Max Planck Institute for Dynamics of Complex Technical Systems, Magdeburg, Germany
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34
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Tight docking of membranes before fusion represents a metastable state with unique properties. Nat Commun 2021; 12:3606. [PMID: 34127664 PMCID: PMC8203622 DOI: 10.1038/s41467-021-23722-8] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2021] [Accepted: 05/11/2021] [Indexed: 12/26/2022] Open
Abstract
Membrane fusion is fundamental to biological processes as diverse as membrane trafficking or viral infection. Proteins catalyzing membrane fusion need to overcome energy barriers to induce intermediate steps in which the integrity of bilayers is lost. Here, we investigate the structural features of tightly docked intermediates preceding hemifusion. Using lipid vesicles in which progression to hemifusion is arrested, we show that the metastable intermediate does not require but is enhanced by divalent cations and is characterized by the absence of proteins and local membrane thickening. Molecular dynamics simulations reveal that thickening is due to profound lipid rearrangements induced by dehydration of the membrane surface. Proteins need to overcome energy barriers to induce intermediate steps in membrane fusion. Using lipid vesicles in which progression to hemifusion is arrested, the authors show that the metastable intermediate is enhanced by divalent cations and is characterized by the absence of proteins and local membrane thickening. Simulations reveal that thickening is induced by dehydration of the membrane surface.
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35
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Wang S, Liu Y, Crisman L, Wan C, Miller J, Yu H, Shen J. Genetic evidence for an inhibitory role of tomosyn in insulin-stimulated GLUT4 exocytosis. Traffic 2021; 21:636-646. [PMID: 32851733 DOI: 10.1111/tra.12760] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2020] [Revised: 08/21/2020] [Accepted: 08/22/2020] [Indexed: 12/11/2022]
Abstract
Exocytosis is a vesicle fusion process driven by soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs). A classic exocytic pathway is insulin-stimulated translocation of the glucose transporter type 4 (GLUT4) from intracellular vesicles to the plasma membrane in adipocytes and skeletal muscles. The GLUT4 exocytic pathway plays a central role in maintaining blood glucose homeostasis and is compromised in insulin resistance and type 2 diabetes. A candidate regulator of GLUT4 exocytosis is tomosyn, a soluble protein expressed in adipocytes. Tomosyn directly binds to GLUT4 exocytic SNAREs in vitro but its role in GLUT4 exocytosis was unknown. In this work, we used CRISPR-Cas9 genome editing to delete the two tomosyn-encoding genes in adipocytes. We observed that both basal and insulin-stimulated GLUT4 exocytosis was markedly elevated in the double knockout (DKO) cells. By contrast, adipocyte differentiation and insulin signaling remained intact in the DKO adipocytes. In a reconstituted liposome fusion assay, tomosyn inhibited all the SNARE complexes underlying GLUT4 exocytosis. The inhibitory activity of tomosyn was relieved by NSF and α-SNAP, which act in concert to remove tomosyn from GLUT4 exocytic SNAREs. Together, these studies revealed an inhibitory role for tomosyn in insulin-stimulated GLUT4 exocytosis in adipocytes. We suggest that tomosyn-arrested SNAREs represent a reservoir of fusion capacity that could be harnessed to treat patients with insulin resistance and type 2 diabetes.
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Affiliation(s)
- Shifeng Wang
- Department of Molecular, Cellular and Developmental Biology, University of Colorado, Boulder, Colorado, USA.,Department of Chinese Medicine Information Science, Beijing University of Chinese Medicine, Beijing, China
| | - Yinghui Liu
- Department of Molecular, Cellular and Developmental Biology, University of Colorado, Boulder, Colorado, USA
| | - Lauren Crisman
- Department of Molecular, Cellular and Developmental Biology, University of Colorado, Boulder, Colorado, USA
| | - Chun Wan
- Department of Molecular, Cellular and Developmental Biology, University of Colorado, Boulder, Colorado, USA
| | - Jessica Miller
- Department of Molecular, Cellular and Developmental Biology, University of Colorado, Boulder, Colorado, USA
| | - Haijia Yu
- Department of Molecular, Cellular and Developmental Biology, University of Colorado, Boulder, Colorado, USA
| | - Jingshi Shen
- Department of Molecular, Cellular and Developmental Biology, University of Colorado, Boulder, Colorado, USA
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36
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Hubrich BE, Wehland JD, Groth MC, Schirmacher A, Hubrich R, Steinem C, Diederichsen U. Membrane fusion mediated by peptidic SNARE protein analogues: Evaluation of FRET-based bulk leaflet mixing assays. J Pept Sci 2021; 27:e3327. [PMID: 33825251 DOI: 10.1002/psc.3327] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2021] [Revised: 03/22/2021] [Accepted: 03/22/2021] [Indexed: 11/06/2022]
Abstract
Peptide-mediated membrane fusion is frequently studied with in vitro bulk leaflet mixing assays based on Förster resonance energy transfer (FRET). In these, customized liposomes with fusogenic peptides are equipped with lipids which are labeled with fluorophores that form a FRET pair. Since FRET is dependent on distance and membrane fusion comes along with lipid mixing, the assays allow for conclusions on the membrane fusion process. The experimental outcome of these assays, however, greatly depends on the applied parameters. In the present study, the influence of the peptides, the size of liposomes, their lipid composition and the liposome stoichiometry on the fusogenicity of liposomes are evaluated. As fusogenic peptides, soluble N-ethylmaleimide-sensitive-factor attachment receptor (SNARE) protein analogues featuring artificial recognition units attached to the native SNARE transmembrane domains are used. The work shows that it is important to control these parameters in order to be able to properly investigate the fusion process and to prevent undesired effects of aggregation.
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Affiliation(s)
- Barbara E Hubrich
- Institute of Organic and Biomolecular Chemistry, Georg-August-University of Göttingen, Göttingen, Germany
| | - Jan-Dirk Wehland
- Institute of Organic and Biomolecular Chemistry, Georg-August-University of Göttingen, Göttingen, Germany
| | - Mike C Groth
- Institute of Organic and Biomolecular Chemistry, Georg-August-University of Göttingen, Göttingen, Germany
| | - Anastasiya Schirmacher
- Institute of Organic and Biomolecular Chemistry, Georg-August-University of Göttingen, Göttingen, Germany
| | - Raphael Hubrich
- Institute of Organic and Biomolecular Chemistry, Georg-August-University of Göttingen, Göttingen, Germany
| | - Claudia Steinem
- Institute of Organic and Biomolecular Chemistry, Georg-August-University of Göttingen, Göttingen, Germany
| | - Ulf Diederichsen
- Institute of Organic and Biomolecular Chemistry, Georg-August-University of Göttingen, Göttingen, Germany
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37
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Sorting sub-150-nm liposomes of distinct sizes by DNA-brick-assisted centrifugation. Nat Chem 2021; 13:335-342. [PMID: 33785892 PMCID: PMC8049973 DOI: 10.1038/s41557-021-00667-5] [Citation(s) in RCA: 27] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2020] [Accepted: 02/23/2021] [Indexed: 02/01/2023]
Abstract
In cells, myriad membrane-interacting proteins generate and maintain curved membrane domains with radii of curvature around or below 50 nm. To understand how such highly curved membranes modulate specific protein functions, and vice versa, it is imperative to use small liposomes with precisely defined attributes as model membranes. Here, we report a versatile and scalable sorting technique that uses cholesterol-modified DNA 'nanobricks' to differentiate hetero-sized liposomes by their buoyant densities. This method separates milligrams of liposomes, regardless of their origins and chemical compositions, into six to eight homogeneous populations with mean diameters of 30-130 nm. We show that these uniform, leak-resistant liposomes serve as ideal substrates to study, with an unprecedented resolution, how membrane curvature influences peripheral (ATG3) and integral (SNARE) membrane protein activities. Compared with conventional methods, our sorting technique represents a streamlined process to achieve superior liposome size uniformity, which benefits research in membrane biology and the development of liposomal drug-delivery systems.
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38
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Xu YF, Chen X, Yang Z, Xiao P, Liu CH, Li KS, Yang XZ, Wang YJ, Zhu ZL, Xu ZG, Zhang S, Wang C, Song YC, Zhao WD, Wang CH, Ji ZL, Zhang ZY, Cui M, Sun JP, Yu X. PTP-MEG2 regulates quantal size and fusion pore opening through two distinct structural bases and substrates. EMBO Rep 2021; 22:e52141. [PMID: 33764618 DOI: 10.15252/embr.202052141] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2020] [Revised: 01/26/2021] [Accepted: 02/18/2021] [Indexed: 02/02/2023] Open
Abstract
Tyrosine phosphorylation of secretion machinery proteins is a crucial regulatory mechanism for exocytosis. However, the participation of protein tyrosine phosphatases (PTPs) in different exocytosis stages has not been defined. Here we demonstrate that PTP-MEG2 controls multiple steps of catecholamine secretion. Biochemical and crystallographic analyses reveal key residues that govern the interaction between PTP-MEG2 and its substrate, a peptide containing the phosphorylated NSF-pY83 site, specify PTP-MEG2 substrate selectivity, and modulate the fusion of catecholamine-containing vesicles. Unexpectedly, delineation of PTP-MEG2 mutants along with the NSF binding interface reveals that PTP-MEG2 controls the fusion pore opening through NSF independent mechanisms. Utilizing bioinformatics search and biochemical and electrochemical screening approaches, we uncover that PTP-MEG2 regulates the opening and extension of the fusion pore by dephosphorylating the DYNAMIN2-pY125 and MUNC18-1-pY145 sites. Further structural and biochemical analyses confirmed the interaction of PTP-MEG2 with MUNC18-1-pY145 or DYNAMIN2-pY125 through a distinct structural basis compared with that of the NSF-pY83 site. Our studies thus provide mechanistic insights in complex exocytosis processes.
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Affiliation(s)
- Yun-Fei Xu
- Key Laboratory Experimental Teratology of the Ministry of Education and Department of Biochemistry and Molecular Biology, Shandong University School of Medicine, Jinan, China.,Department of General Surgery, Qilu Hospital of Shandong University, Jinan, China
| | - Xu Chen
- Key Laboratory Experimental Teratology of the Ministry of Education and Department of Physiology, Shandong University School of Medicine, Jinan, China
| | - Zhao Yang
- Key Laboratory Experimental Teratology of the Ministry of Education and Department of Biochemistry and Molecular Biology, Shandong University School of Medicine, Jinan, China
| | - Peng Xiao
- Key Laboratory Experimental Teratology of the Ministry of Education and Department of Biochemistry and Molecular Biology, Shandong University School of Medicine, Jinan, China
| | - Chun-Hua Liu
- Department of Physiology, Shandong First Medical University, Taian, China
| | - Kang-Shuai Li
- Key Laboratory Experimental Teratology of the Ministry of Education and Department of Biochemistry and Molecular Biology, Shandong University School of Medicine, Jinan, China.,Department of General Surgery, Qilu Hospital of Shandong University, Jinan, China
| | - Xiao-Zhen Yang
- State Key Laboratory of Cellular Stress Biology, School of Life Sciences, Xiamen University, Xiamen, China
| | - Yi-Jing Wang
- Key Laboratory Experimental Teratology of the Ministry of Education and Department of Biochemistry and Molecular Biology, Shandong University School of Medicine, Jinan, China
| | - Zhong-Liang Zhu
- School of Life Sciences, University of Science and Technology of China, Hefei, China
| | - Zhi-Gang Xu
- Shandong Provincial Key Laboratory of Animal Cells and Developmental Biology, School of Life Sciences, Shandong University, Jinan, China
| | - Sheng Zhang
- Departments of Medicinal Chemistry and Molecular Pharmacology and of Chemistry, Center for Cancer Research, and Institute for Drug Discovery, Purdue University, West Lafayette, IN, USA
| | - Chuan Wang
- Department of Pharmacology, Hebei Medical University, Shijiazhuang, China
| | - You-Chen Song
- Department of Medical Biophysics, University of Toronto, Toronto, ON, Canada
| | - Wei-Dong Zhao
- Department of Developmental Cell Biology, China Medical University, Shenyang, China
| | - Chang-He Wang
- Center for Mitochondrial Biology and Medicine, The Key Laboratory of Biomedical Information Engineering of Ministry of Education, School of Life Science and Technology, Xi'an Jiaotong University, Xi'an, China
| | - Zhi-Liang Ji
- State Key Laboratory of Cellular Stress Biology, School of Life Sciences, Xiamen University, Xiamen, China
| | - Zhong-Yin Zhang
- Departments of Medicinal Chemistry and Molecular Pharmacology and of Chemistry, Center for Cancer Research, and Institute for Drug Discovery, Purdue University, West Lafayette, IN, USA
| | - Min Cui
- Key Laboratory Experimental Teratology of the Ministry of Education and Department of Physiology, Shandong University School of Medicine, Jinan, China
| | - Jin-Peng Sun
- Key Laboratory Experimental Teratology of the Ministry of Education and Department of Biochemistry and Molecular Biology, Shandong University School of Medicine, Jinan, China
| | - Xiao Yu
- Key Laboratory Experimental Teratology of the Ministry of Education and Department of Physiology, Shandong University School of Medicine, Jinan, China
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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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40
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Wittig S, Ganzella M, Barth M, Kostmann S, Riedel D, Pérez-Lara Á, Jahn R, Schmidt C. Cross-linking mass spectrometry uncovers protein interactions and functional assemblies in synaptic vesicle membranes. Nat Commun 2021; 12:858. [PMID: 33558502 PMCID: PMC7870876 DOI: 10.1038/s41467-021-21102-w] [Citation(s) in RCA: 31] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2020] [Accepted: 12/18/2020] [Indexed: 02/08/2023] Open
Abstract
Synaptic vesicles are storage organelles for neurotransmitters. They pass through a trafficking cycle and fuse with the pre-synaptic membrane when an action potential arrives at the nerve terminal. While molecular components and biophysical parameters of synaptic vesicles have been determined, our knowledge on the protein interactions in their membranes is limited. Here, we apply cross-linking mass spectrometry to study interactions of synaptic vesicle proteins in an unbiased approach without the need for specific antibodies or detergent-solubilisation. Our large-scale analysis delivers a protein network of vesicle sub-populations and functional assemblies including an active and an inactive conformation of the vesicular ATPase complex as well as non-conventional arrangements of the luminal loops of SV2A, Synaptophysin and structurally related proteins. Based on this network, we specifically target Synaptobrevin-2, which connects with many proteins, in different approaches. Our results allow distinction of interactions caused by 'crowding' in the vesicle membrane from stable interaction modules.
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Affiliation(s)
- Sabine Wittig
- Interdisciplinary Research Centre HALOmem, Charles Tanford Protein Centre, Institute for Biochemistry and Biotechnology, Martin Luther University Halle-Wittenberg, Halle, Germany
| | - Marcelo Ganzella
- Department for Neurobiology, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
| | - Marie Barth
- Interdisciplinary Research Centre HALOmem, Charles Tanford Protein Centre, Institute for Biochemistry and Biotechnology, Martin Luther University Halle-Wittenberg, Halle, Germany
| | - Susann Kostmann
- Interdisciplinary Research Centre HALOmem, Charles Tanford Protein Centre, Institute for Biochemistry and Biotechnology, Martin Luther University Halle-Wittenberg, Halle, Germany
| | - Dietmar Riedel
- Department for Neurobiology, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
| | - Ángel Pérez-Lara
- Department for Neurobiology, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
- Department of Physical Chemistry, Faculty of Pharmacy, University of Granada, Granada, Spain
| | - Reinhard Jahn
- Department for Neurobiology, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
| | - Carla Schmidt
- Interdisciplinary Research Centre HALOmem, Charles Tanford Protein Centre, Institute for Biochemistry and Biotechnology, Martin Luther University Halle-Wittenberg, Halle, Germany.
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41
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Narahari AK, Kreutzberger AJB, Gaete PS, Chiu YH, Leonhardt SA, Medina CB, Jin X, Oleniacz PW, Kiessling V, Barrett PQ, Ravichandran KS, Yeager M, Contreras JE, Tamm LK, Bayliss DA. ATP and large signaling metabolites flux through caspase-activated Pannexin 1 channels. eLife 2021; 10:e64787. [PMID: 33410749 PMCID: PMC7806264 DOI: 10.7554/elife.64787] [Citation(s) in RCA: 53] [Impact Index Per Article: 17.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2020] [Accepted: 01/05/2021] [Indexed: 12/16/2022] Open
Abstract
Pannexin 1 (Panx1) is a membrane channel implicated in numerous physiological and pathophysiological processes via its ability to support release of ATP and other cellular metabolites for local intercellular signaling. However, to date, there has been no direct demonstration of large molecule permeation via the Panx1 channel itself, and thus the permselectivity of Panx1 for different molecules remains unknown. To address this, we expressed, purified, and reconstituted Panx1 into proteoliposomes and demonstrated that channel activation by caspase cleavage yields a dye-permeable pore that favors flux of anionic, large-molecule permeants (up to ~1 kDa). Large cationic molecules can also permeate the channel, albeit at a much lower rate. We further show that Panx1 channels provide a molecular pathway for flux of ATP and other anionic (glutamate) and cationic signaling metabolites (spermidine). These results verify large molecule permeation directly through caspase-activated Panx1 channels that can support their many physiological roles.
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Affiliation(s)
- Adishesh K Narahari
- Department of Pharmacology, University of VirginiaCharlottesvilleUnited States
| | - Alex JB Kreutzberger
- Department of Molecular Physiology and Biological Physics, University of VirginiaCharlottesvilleUnited States
| | - Pablo S Gaete
- Department of Pharmacology, Physiology, and Neuroscience, Rutgers New Jersey Medical SchoolNewarkUnited States
| | - Yu-Hsin Chiu
- Department of Pharmacology, University of VirginiaCharlottesvilleUnited States
| | - Susan A Leonhardt
- Department of Molecular Physiology and Biological Physics, University of VirginiaCharlottesvilleUnited States
| | - Christopher B Medina
- Department of Microbiology, Immunology, and Cancer Biology, University of VirginiaCharlottesvilleUnited States
| | - Xueyao Jin
- Department of Molecular Physiology and Biological Physics, University of VirginiaCharlottesvilleUnited States
| | - Patrycja W Oleniacz
- Department of Pharmacology, University of VirginiaCharlottesvilleUnited States
| | - Volker Kiessling
- Department of Molecular Physiology and Biological Physics, University of VirginiaCharlottesvilleUnited States
| | - Paula Q Barrett
- Department of Pharmacology, University of VirginiaCharlottesvilleUnited States
| | - Kodi S Ravichandran
- Department of Microbiology, Immunology, and Cancer Biology, University of VirginiaCharlottesvilleUnited States
| | - Mark Yeager
- Department of Molecular Physiology and Biological Physics, University of VirginiaCharlottesvilleUnited States
| | - Jorge E Contreras
- Department of Pharmacology, Physiology, and Neuroscience, Rutgers New Jersey Medical SchoolNewarkUnited States
| | - Lukas K Tamm
- Department of Molecular Physiology and Biological Physics, University of VirginiaCharlottesvilleUnited States
| | - Douglas A Bayliss
- Department of Pharmacology, University of VirginiaCharlottesvilleUnited States
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Witkowska A, Spindler S, Mahmoodabadi RG, Sandoghdar V, Jahn R. Differential Diffusional Properties in Loose and Tight Docking Prior to Membrane Fusion. Biophys J 2020; 119:2431-2439. [PMID: 33189687 PMCID: PMC7822739 DOI: 10.1016/j.bpj.2020.10.033] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2020] [Revised: 10/20/2020] [Accepted: 10/27/2020] [Indexed: 12/21/2022] Open
Abstract
Fusion of biological membranes, although mediated by divergent proteins, is believed to follow a common pathway. It proceeds through distinct steps, including docking, merger of proximal leaflets (stalk formation), and formation of a fusion pore. However, the structure of these intermediates is difficult to study because of their short lifetime. Previously, we observed a loosely and tightly docked state preceding leaflet merger using arresting point mutations in SNARE proteins, but the nature of these states remained elusive. Here, we used interferometric scattering (iSCAT) microscopy to monitor diffusion of single vesicles across the surface of giant unilamellar vesicles (GUVs). We observed that the diffusion coefficients of arrested vesicles decreased during progression through the intermediate states. Modeling allowed for predicting the number of tethering SNARE complexes upon loose docking and the size of the interacting membrane patches upon tight docking. These results shed new light on the nature of membrane-membrane interactions immediately before fusion.
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Affiliation(s)
- Agata Witkowska
- Laboratory of Neurobiology, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany.
| | - Susann Spindler
- Max Planck Institute for the Science of Light, Erlangen, Germany; Department of Physics, Friedrich-Alexander University Erlangen-Nuremberg, Erlangen, Germany
| | - Reza Gholami Mahmoodabadi
- Max Planck Institute for the Science of Light, Erlangen, Germany; Max-Planck-Zentrum für Physik und Medizin, Erlangen, Germany
| | - Vahid Sandoghdar
- Max Planck Institute for the Science of Light, Erlangen, Germany; Department of Physics, Friedrich-Alexander University Erlangen-Nuremberg, Erlangen, Germany; Max-Planck-Zentrum für Physik und Medizin, Erlangen, Germany.
| | - Reinhard Jahn
- Laboratory of Neurobiology, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany; University of Göttingen, Göttingen, Germany.
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Ginger L, Malsam J, Sonnen AFP, Morado D, Scheutzow A, Söllner TH, Briggs JAG. Arrangements of proteins at reconstituted synaptic vesicle fusion sites depend on membrane separation. FEBS Lett 2020; 594:3450-3463. [PMID: 32860428 PMCID: PMC7711843 DOI: 10.1002/1873-3468.13916] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2020] [Revised: 07/16/2020] [Accepted: 08/09/2020] [Indexed: 11/18/2022]
Abstract
Synaptic vesicle proteins, including N‐ethylmaleimide‐sensitive factor attachment protein receptors (SNAREs), Synaptotagmin‐1 and Complexin, are responsible for controlling the synchronised fusion of synaptic vesicles with the presynaptic plasma membrane in response to elevated cytosolic calcium levels. A range of structures of SNAREs and their regulatory proteins have been elucidated, but the exact organisation of these proteins at synaptic junction membranes remains elusive. Here, we have used cryoelectron tomography to investigate the arrangement of synaptic proteins in an in vitro reconstituted fusion system. We found that the separation between vesicle and target membranes strongly correlates with the organisation of protein complexes at junctions. At larger membrane separations, protein complexes assume a ‘clustered’ distribution at the docking site, inducing a protrusion in the target membrane. As the membrane separation decreases, protein complexes become displaced radially outwards and assume a ‘ring‐like’ arrangement. Our findings indicate that docked vesicles can possess a wide range of protein complex numbers and be heterogeneous in their protein arrangements.
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Affiliation(s)
- Lucy Ginger
- MRC Laboratory of Molecular Biology, Cambridge, UK
| | - Joerg Malsam
- Heidelberg University Biochemistry Center, Heidelberg, Germany
| | - Andreas F-P Sonnen
- Structural and Computational Biology Unit, European Molecular Biology Laboratory, Heidelberg, Germany
| | | | | | | | - John A G Briggs
- MRC Laboratory of Molecular Biology, Cambridge, UK.,Structural and Computational Biology Unit, European Molecular Biology Laboratory, Heidelberg, Germany
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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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45
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Huang F, Duan R, Zhou Z, Vázquez-González M, Xia F, Willner I. Near-infrared light-activated membrane fusion for cancer cell therapeutic applications. Chem Sci 2020; 11:5592-5600. [PMID: 32874503 PMCID: PMC7441577 DOI: 10.1039/d0sc00863j] [Citation(s) in RCA: 24] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2020] [Accepted: 05/07/2020] [Indexed: 12/15/2022] Open
Abstract
The spatiotemporal stimulation of liposome-liposome or liposome-membrane fusion processes attracts growing interest as a means to mimic cell-cell interactions in nature and for using these processes for biomedical applications. We report the use of o-nitrobenzyl phosphate functionalized-cholesterol tethered nucleic acid-modified liposomes as functional photoresponsive units for inducing, by NIR-irradiation, spatiotemporal liposome-liposome or liposome-membrane fusion processes. The liposomes are loaded with upconversion nanoparticles (UCNPs) and their NIR irradiation (λ = 980 nm) yields luminescence at λ = 365 nm, providing a localized light-source to deprotect the o-nitrobenzyl phosphate groups and resulting in the fragmentation of the nucleic acid structures. In one system, the NIR-triggered fusion of two liposomes, L1 and L2, is exemplified. Liposome L1 is loaded with UCNPs and Tb3+ ions, and the liposome boundary is functionalized with a cholesterol-tethered, o-nitrobenzyl phosphate caged hairpin nucleic acid structure. Liposome L2 is loaded with 2,6-pyridinedicarboxylic acid, DPA, and its boundary is modified with a cholesterol-tethered nucleic acid, complementary to a part of the caged hairpin, associated with L1. NIR-irradiation of the L1/L2 mixture resulted in the photocleavage of the hairpin structure, associated with L1, and the resulting fragmented nucleic acid associated with L1 hybridized with the nucleic acid linked to L2, leading to the fusion of the two liposomes. The fusion process was followed by dynamic light scattering, and by monitoring the fluorescence of the Tb3+-DPA complex generated upon the fusion of the liposomes and their exchange of contents (fusion efficiency 30%). In a second system, the fusion of the liposomes L1, loaded with UCNPs and doxorubicin (DOX), with HeLa cancer cells functionalized with nucleic acid tethers, complementary to the hairpin units associated with the boundary of L1, and linked to the MUC-1 receptor sites associated with the HeLa cells, through a MUC-1 aptamer unit is exemplified. The effect of DOX-loaded L1/HeLa cell fusion on the cytotoxicity towards HeLa cells is addressed. The NIR UCNP-stimulated cleavage of the o-nitrobenzyl phosphate caged hairpin units associated with L1 leads to the fragmentation of the hairpin units and the resulting nucleic acid tethers hybridize with the nucleic acid-modified HeLa cells, resulting in the liposome-HeLa cell fusion and the release of DOX into the HeLa cells. Selective spatiotemporal cytotoxicity towards HeLa cells is demonstrated (ca. 40% cell killing within two days). The study presents a comprehensive stepwise set of experiments directed towards the development of NIR-driven liposome-liposome or liposome-membrane fusion processes.
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Affiliation(s)
- Fujian Huang
- Engineering Research Center of Nano-Geomaterials of Ministry of Education , Faculty of Materials Science and Chemistry , China University of Geosciences , Wuhan 430074 , China . ;
| | - Ruilin Duan
- Engineering Research Center of Nano-Geomaterials of Ministry of Education , Faculty of Materials Science and Chemistry , China University of Geosciences , Wuhan 430074 , China . ;
| | - Zhixin Zhou
- Institute of Chemistry , Center for Nanoscience and Nanotechnology , The Hebrew University of Jerusalem , Jerusalem 91904 , Israel .
| | - Margarita Vázquez-González
- Institute of Chemistry , Center for Nanoscience and Nanotechnology , The Hebrew University of Jerusalem , Jerusalem 91904 , Israel .
| | - Fan Xia
- Engineering Research Center of Nano-Geomaterials of Ministry of Education , Faculty of Materials Science and Chemistry , China University of Geosciences , Wuhan 430074 , China . ;
| | - Itamar Willner
- Institute of Chemistry , Center for Nanoscience and Nanotechnology , The Hebrew University of Jerusalem , Jerusalem 91904 , Israel .
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Fusion Pore Formation Observed during SNARE-Mediated Vesicle Fusion with Pore-Spanning Membranes. Biophys J 2020; 119:151-161. [PMID: 32533941 DOI: 10.1016/j.bpj.2020.05.023] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2020] [Revised: 05/22/2020] [Accepted: 05/26/2020] [Indexed: 12/27/2022] Open
Abstract
Planar pore-spanning membranes (PSMs) have been shown to be a versatile tool to resolve elementary steps of the neuronal fusion process. However, in previous studies, we monitored only lipid mixing between fusing large unilamellar vesicles and PSMs and did not gather information about the formation of fusion pores. To address this important step of the fusion process, we entrapped sulforhodamine B at self-quenching concentrations into large unilamellar vesicles containing the v-SNARE synaptobrevin 2, which were docked and fused with lipid-labeled PSMs containing the t-SNARE acceptor complex ΔN49 prepared on gold-coated porous silicon substrates. By dual-color spinning disk fluorescence microscopy with a time resolution of ∼20 ms, we could unambiguously distinguish between bursting vesicles, which was only rarely observed (<0.01%), and fusion pore formation. From the time-resolved dual-color fluorescence time traces, we were able to identify different fusion pathways, including remaining three-dimensional postfusion structures with released content and transient openings and closings of the fusion pores. Our results on fusion pore formation and lipid diffusion from the PSM into the fusing vesicle let us conclude that the content release, i.e., fusion pore formation after the merger of the two lipid membranes occurs almost simultaneously.
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Komorowski K, Schaeper J, Sztucki M, Sharpnack L, Brehm G, Köster S, Salditt T. Vesicle adhesion in the electrostatic strong-coupling regime studied by time-resolved small-angle X-ray scattering. SOFT MATTER 2020; 16:4142-4154. [PMID: 32319505 DOI: 10.1039/d0sm00259c] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
We have used time-resolved small-angle X-ray scattering (SAXS) to study the adhesion of lipid vesicles in the electrostatic strong-coupling regime induced by divalent ions. The bilayer structure and the interbilayer distance dw between adhered vesicles was studied for different DOPC:DOPS mixtures varying the surface charge density of the membrane, as well as for different divalent ions, such as Ca2+, Sr2+, and Zn2+. The results are in good agreement with the strong coupling theory predicting the adhesion state and the corresponding like-charge attraction based on ion-correlations. Using SAXS combined with the stopped-flow rapid mixing technique, we find that in highly charged bilayers the adhesion state is only of transient nature, and that the adhering vesicles subsequently transform to a phase of multilamellar vesicles, again with an inter-bilayer distance according to the theory of strong binding. Aside from the stopped-flow SAXS instrumentations used primarily for these results, we also evaluate microfluidic sample environments for vesicle SAXS in view of future extension of this work.
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Affiliation(s)
- Karlo Komorowski
- Institute for X-Ray Physics, University of Göttingen, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany.
| | - Jannis Schaeper
- Institute for X-Ray Physics, University of Göttingen, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany.
| | - Michael Sztucki
- European Synchrotron Radiation Facility, CS 40220, 38043 Grenoble Cedex 9, France
| | - Lewis Sharpnack
- European Synchrotron Radiation Facility, CS 40220, 38043 Grenoble Cedex 9, France
| | - Gerrit Brehm
- Institute for X-Ray Physics, University of Göttingen, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany.
| | - Sarah Köster
- Institute for X-Ray Physics, University of Göttingen, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany.
| | - Tim Salditt
- Institute for X-Ray Physics, University of Göttingen, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany.
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48
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Benhaim MA, Lee KK. New Biophysical Approaches Reveal the Dynamics and Mechanics of Type I Viral Fusion Machinery and Their Interplay with Membranes. Viruses 2020; 12:E413. [PMID: 32276357 PMCID: PMC7232462 DOI: 10.3390/v12040413] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2020] [Revised: 04/04/2020] [Accepted: 04/04/2020] [Indexed: 12/27/2022] Open
Abstract
Protein-mediated membrane fusion is a highly regulated biological process essential for cellular and organismal functions and infection by enveloped viruses. During viral entry the membrane fusion reaction is catalyzed by specialized protein machinery on the viral surface. These viral fusion proteins undergo a series of dramatic structural changes during membrane fusion where they engage, remodel, and ultimately fuse with the host membrane. The structural and dynamic nature of these conformational changes and their impact on the membranes have long-eluded characterization. Recent advances in structural and biophysical methodologies have enabled researchers to directly observe viral fusion proteins as they carry out their functions during membrane fusion. Here we review the structure and function of type I viral fusion proteins and mechanisms of protein-mediated membrane fusion. We highlight how recent technological advances and new biophysical approaches are providing unprecedented new insight into the membrane fusion reaction.
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Affiliation(s)
- Mark A. Benhaim
- Department of Medicinal Chemistry, University of Washington, Seattle, WA 98195-7610, USA;
| | - Kelly K. Lee
- Department of Medicinal Chemistry, University of Washington, Seattle, WA 98195-7610, USA;
- Biological Physics Structure and Design Program, University of Washington, Seattle, WA 98195-7610, USA
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49
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Hrd1 forms the retrotranslocation pore regulated by auto-ubiquitination and binding of misfolded proteins. Nat Cell Biol 2020; 22:274-281. [DOI: 10.1038/s41556-020-0473-4] [Citation(s) in RCA: 34] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2019] [Accepted: 01/20/2020] [Indexed: 01/01/2023]
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50
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Abstract
Biological transmission of vesicular content occurs by opening of a fusion pore. Recent experimental observations have illustrated that fusion pores between vesicles that are docked by an extended flat contact zone are located at the edge (vertex) of this zone. We modeled this experimentally observed scenario by coarse-grained molecular simulations and elastic theory. This revealed that fusion pores experience a direct attraction toward the vertex. The size adopted by the resulting vertex pore strongly depends on the apparent contact angle between the adhered vesicles even in the absence of membrane surface tension. Larger contact angles substantially increase the equilibrium size of the vertex pore. Because the cellular membrane fusion machinery actively docks membranes, it facilitates a collective expansion of the contact zone and increases the contact angle. In this way, the fusion machinery can drive expansion of the fusion pore by free energy equivalents of multiple tens of kBT from a distance and not only through the fusion proteins that reside within the fusion pore.
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Affiliation(s)
- Edgar M Blokhuis
- Leiden Institute of Chemistry (LIC) , Leiden University , 2333 CD Leiden , The Netherlands
| | - Massimo D'Agostino
- Department of Molecular Medicine and Medical Biotechnology , University of Naples Federico II , 80138 Naples , Italy
| | - Andreas Mayer
- Département de Biochimie , Université de Lausanne , CH-1015 Epalinges , Switzerland
| | - H Jelger Risselada
- Leiden Institute of Chemistry (LIC) , Leiden University , 2333 CD Leiden , The Netherlands
- Department of Theoretical Physics , Georg-August University of Goettingen , 37077 Goettingen , Germany
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