1
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Patil SS, Sanghrajka K, Sriram M, Chakraborty A, Majumdar S, Bhaskar BR, Das D. Synaptobrevin2 monomers and dimers differentially engage to regulate the functional trans-SNARE assembly. Life Sci Alliance 2024; 7:e202402568. [PMID: 38238088 PMCID: PMC10796598 DOI: 10.26508/lsa.202402568] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2024] [Revised: 01/12/2024] [Accepted: 01/12/2024] [Indexed: 01/22/2024] Open
Abstract
The precise cell-to-cell communication relies on SNARE-catalyzed membrane fusion. Among ∼70 copies of synaptobrevin2 (syb2) in synaptic vesicles, only ∼3 copies are sufficient to facilitate the fusion process at the presynaptic terminal. It is unclear what dictates the number of SNARE complexes that constitute the fusion pore assembly. The structure-function relation of these dynamic pores is also unknown. Here, we demonstrate that syb2 monomers and dimers differentially engage in regulating the trans-SNARE assembly during membrane fusion. The differential recruitment of two syb2 structures at the membrane fusion site has consequences in regulating individual nascent fusion pore properties. We have identified a few syb2 transmembrane domain residues that control monomer/dimer conversion. Overall, our study indicates that syb2 monomers and dimers are differentially recruited at the release sites for regulating membrane fusion events.
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Affiliation(s)
- Swapnali S Patil
- https://ror.org/03ht1xw27 Department of Biological Sciences, Tata Institute of Fundamental Research, Mumbai, India
| | - Kinjal Sanghrajka
- https://ror.org/03ht1xw27 Department of Biological Sciences, Tata Institute of Fundamental Research, Mumbai, India
| | - Malavika Sriram
- https://ror.org/03ht1xw27 Department of Biological Sciences, Tata Institute of Fundamental Research, Mumbai, India
| | - Aritra Chakraborty
- https://ror.org/03ht1xw27 Department of Biological Sciences, Tata Institute of Fundamental Research, Mumbai, India
| | - Sougata Majumdar
- https://ror.org/03ht1xw27 Department of Biological Sciences, Tata Institute of Fundamental Research, Mumbai, India
| | - Bhavya R Bhaskar
- https://ror.org/03ht1xw27 Department of Biological Sciences, Tata Institute of Fundamental Research, Mumbai, India
| | - Debasis Das
- https://ror.org/03ht1xw27 Department of Biological Sciences, Tata Institute of Fundamental Research, Mumbai, India
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2
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Kinard TC, Wrenn SP. Triglycerides Stabilize Water/Organic Interfaces of Changing Area via Conformational Flexibility. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2024; 40:2500-2509. [PMID: 38284535 DOI: 10.1021/acs.langmuir.3c02473] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/30/2024]
Abstract
The role of triglycerides (TGs) in both natural and synthetic biological membranes has long been the subject of study, involving metabolism, disease, and colloidal synthesis. TGs have been found to be critical components for successful liposomal encapsulation via a water/oil/water double emulsion, which this work endeavors to explain. TGs can occupy multiple positions in biological membranes. The glycerol backbone can reside at the water/organic interface, adjacent to phospholipid headgroups ("m" conformation), typically with relatively low (<3%) solubility. The glycerol backbone can also occupy hydrophobic regions, where it is isolated from water ("h" or "oil" conformation). This can occur in either midmembrane positions or phospholipid-coated lipid droplets (LDs). These conformations can be distinguished using 13C-nuclear magnetic resonance spectroscopy (NMR), which determines the degree of hydration of the TG backbone. Using this method, it was revealed that TGs transition from "m" to "h" conformation as the organic solvent is removed via evaporation. A new transitional TG backbone position has been identified with a level of hydration between "m" and "h". These results suggest that TGs can temporarily coat and stabilize the large water/organic interfaces present after emulsification. As the organic solvent is removed and interfaces shrink, the TGs recede into midmembrane spaces or bud off into LDs, which are confirmed via transmission electron microscopy (TEM) and can be removed via centrifugation. Encapsulation efficiency is found to be inversely related to both the saturation and length of the TG acyl chains, indicating that membrane fluidization is a key property arising from the presence of TGs. Beyond clarification of a mechanism for high-efficiency liposomal encapsulation, these results implicate TGs as components that are able to stabilize biological membrane transitions involving a changing interfacial area and curvature. This role for TGs may be of use in the formulation of drug delivery systems as well as in the investigation of membrane transitions in life sciences.
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Affiliation(s)
- Thomas C Kinard
- Department of Chemical Engineering, Virginia Tech, 635 Prices Fork Road, Blacksburg, Virginia 24060, United States
- Department of Chemical and Biological Engineering, Drexel University, 3141 Chestnut Street, Philadelphia, Pennsylvania 19104, United States
| | - Steven P Wrenn
- Department of Chemical Engineering, Virginia Tech, 635 Prices Fork Road, Blacksburg, Virginia 24060, United States
- Department of Chemical and Biological Engineering, Drexel University, 3141 Chestnut Street, Philadelphia, Pennsylvania 19104, United States
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3
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Denker L, Dixon AM. The cell edit: Looking at and beyond non-structural proteins to understand membrane rearrangement in coronaviruses. Arch Biochem Biophys 2024; 752:109856. [PMID: 38104958 DOI: 10.1016/j.abb.2023.109856] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2023] [Revised: 11/24/2023] [Accepted: 12/08/2023] [Indexed: 12/19/2023]
Abstract
Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a positive-stranded RNA virus that sits at the centre of the recent global pandemic. As a member of the coronaviridae family of viruses, it shares features such as a very large genome (>30 kb) that is replicated in a purpose-built replication organelle. Biogenesis of the replication organelle requires significant and concerted rearrangement of the endoplasmic reticulum membrane, a job that is carried out by a group of integral membrane non-structural proteins (NSP3, 4 and 6) expressed by the virus along with a host of viral replication enzymes and other factors that support transcription and replication. The primary sites for RNA replication within the replication organelle are double membrane vesicles (DMVs). The small size of DMVs requires generation of high membrane curvature, as well as stabilization of a double-membrane arrangement, but the mechanisms that underlie DMV formation remain elusive. In this review, we discuss recent breakthroughs in our understanding of the molecular basis for membrane rearrangements by coronaviruses. We incorporate established models of NSP3-4 protein-protein interactions to drive double membrane formation, and recent data highlighting the roles of lipid composition and host factor proteins (e.g. reticulons) that influence membrane curvature, to propose a revised model for DMV formation in SARS-CoV-2.
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Affiliation(s)
- Lea Denker
- Warwick Medical School, Biomedical Sciences, University of Warwick, Coventry, CV4 7AL, UK.
| | - Ann M Dixon
- Department of Chemistry, University of Warwick, Coventry, CV4 7SH, UK.
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4
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ElNashar NT, Breitinger U, Breitinger HG, Mansour S, Tammam SN. A liposomal platform for the delivery of ion channel proteins for treatment of channelopathies - Application in therapy of cystic fibrosis. Int J Biol Macromol 2023; 253:126652. [PMID: 37673169 DOI: 10.1016/j.ijbiomac.2023.126652] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2023] [Revised: 08/21/2023] [Accepted: 08/30/2023] [Indexed: 09/08/2023]
Abstract
Channelopathies arise from ion channel dysfunction. Successful treatment entails delivery of functional ion channels to replace dysfunctional ones. Glycine receptor (GlyR)-rich cell membrane fragments (CMF) were previously delivered to target cell membranes using fusogenic liposomes. Here, cystic fibrosis transmembrane conductance regulator (CFTR)-bearing CMF were similarly delivered to target cells. We studied the effect of lipid composition on liposomes' ability to incorporate CMF and fuse with target cell membranes to deliver functional CFTR. Four formulations were prepared using thin-film hydration out of different lecithin sources, egg and soy lecithin (EL and SL), in the presence and absence of cholesterol (CHOL): EL + CHOL, EL-CHOL, SL + CHOL, and SL-CHOL. EL liposomes incorporated more CMF than SL liposomes, with CHOL only increasing CMF incorporation in SL liposomes. SL + CHOL fused better with target cell membranes than EL + CHOL. SL + CHOL and EL + CHOL equally delivered CFTR to target cell membranes, owing to the former's superior fusogenic capacity and the latter's superior CMF-incorporation capacity. SL-CHOL and EL-CHOL delivered CFTR to a lesser extent, indicating the importance of CHOL for fusion. Patch-clamp electrophysiology and confocal laser scanning microscopy (CLSM) confirmed CFTR delivery to target cell membranes by SL + CHOL. Therefore, CMF-bearing fusogenic liposomes offer a promising universal platform for the treatment of channelopathies.
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Affiliation(s)
- Noha T ElNashar
- Department of Pharmaceutical Technology, The German University in Cairo (GUC), Cairo, Egypt
| | - Ulrike Breitinger
- Department of Biochemistry, The German University in Cairo (GUC), Cairo, Egypt
| | | | - Samar Mansour
- Department of Pharmaceutical Technology, The German University in Cairo (GUC), Cairo, Egypt
| | - Salma N Tammam
- Department of Pharmaceutical Technology, The German University in Cairo (GUC), Cairo, Egypt.
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5
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Mishra S, Chakraborty H. Phosphatidylethanolamine and Cholesterol Promote Hemifusion Formation: A Tug of War between Membrane Interfacial Order and Intrinsic Negative Curvature of Lipids. J Phys Chem B 2023; 127:7721-7729. [PMID: 37644708 DOI: 10.1021/acs.jpcb.3c04489] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 08/31/2023]
Abstract
Membrane fusion is an important process for the survival of eukaryotes. The shape of lipids plays an important role in fusion by stabilizing nonlamellar fusion intermediates. Lipids with intrinsic positive curvature such as lysophosphatidylcholine and others inhibit hemifusion formation, whereas lipids having intrinsic negative curvature, e.g., phosphatidylethanolamine and cholesterol (CH), are known to promote hemifusion formation. In this work, we have measured the effect of dioleoylphosphatidylethanolamine (DOPE) and CH on the depth-dependent organization, dynamics, and fusion of dioleoylphosphatidylcholine membranes. Both DOPE and CH promote hemifusion formation despite their ability to order the interfacial and acyl chain region of the membrane and block water percolation at these regions. Generally, membrane ordering and inhibition of water percolation at the acyl chain region are detrimental to membrane fusion. This clearly emphasizes the importance of intrinsic negative curvature of lipids in membrane fusion. Interestingly, DOPE and CH show differential effects on the rate of hemifusion formation, which might be owing to their ability to induce order at the interfacial region and intrinsic negative curvature. Overall, our result is significant in understanding the role of lipidic shape in membrane fusion.
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Affiliation(s)
- Smruti Mishra
- School of Chemistry, Sambalpur University, Jyoti Vihar, Burla 768 019, Odisha, India
| | - Hirak Chakraborty
- School of Chemistry, Sambalpur University, Jyoti Vihar, Burla 768 019, Odisha, India
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6
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Li MH, Zhang X, London E, Raleigh DP. Impact of Ca 2+ on membrane catalyzed IAPP amyloid formation and IAPP induced vesicle leakage. BIOCHIMICA ET BIOPHYSICA ACTA. BIOMEMBRANES 2023; 1865:184161. [PMID: 37121365 PMCID: PMC10735052 DOI: 10.1016/j.bbamem.2023.184161] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/13/2022] [Revised: 04/10/2023] [Accepted: 04/24/2023] [Indexed: 05/02/2023]
Abstract
Human islet amyloid polypeptide (hIAPP, also known as amylin) is a 37 amino acid pancreatic polypeptide hormone that plays a role in regulating glucose levels, but forms pancreatic amyloid in type-2 diabetes. The process of amyloid formation by hIAPP contributes to β-cell death in the disease. Multiple mechanisms of hIAPP induced toxicity of β-cells have been proposed including disruption of cellular membranes. However, the nature of hIAPP membrane interactions and the effect of ions and other molecules on hIAPP membrane interactions are not fully understood. Many studies have used model membranes with a high content of anionic lipids, often POPS, however the concentration of anionic lipids in the β-cell plasma membrane is low. Here we study the concentration dependent effect of Ca2+ (0 to 50 mM) on hIAPP membrane interactions using large unilamellar vesicles (LUVs) with anionic lipid content ranging from 0 to 50 mol%. We find that Ca2+ does not effectively inhibit hIAPP amyloid formation and hIAPP induced membrane leakage from binary LUVs with a low percentage of POPS, but has a greater effect on LUVs with a high percentage of POPS. Mg2+ had very similar effects, and the effects of Ca2+ and Mg2+ can be largely rationalized by the neutralization of POPS charge. The implications for hIAPP-membrane interactions are discussed.
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Affiliation(s)
- Ming-Hao Li
- Graduate Program in Biochemistry and Structural Biology, Stony Brook University, Stony Brook, NY 11794, United States
| | - Xiaoxue Zhang
- Department of Chemistry, Stony Brook University, Stony Brook, NY 11794, United States
| | - Erwin London
- Graduate Program in Biochemistry and Structural Biology, Stony Brook University, Stony Brook, NY 11794, United States; Department of Chemistry, Stony Brook University, Stony Brook, NY 11794, United States; Department of Biochemistry and Cell Biology, Stony Brook University, Stony Brook, NY 11794, United States.
| | - Daniel P Raleigh
- Graduate Program in Biochemistry and Structural Biology, Stony Brook University, Stony Brook, NY 11794, United States; Department of Chemistry, Stony Brook University, Stony Brook, NY 11794, United States; Laufer Center for Physical and Quantitative Biology, Stony Brook University, Stony Brook, NY 11794, United States.
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7
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Ward AE, Sokovikova D, Waxham MN, Heberle FA, Levental I, Levental KR, Kiessling V, White JM, Tamm LK. Serinc5 Restricts HIV Membrane Fusion by Altering Lipid Order and Heterogeneity in the Viral Membrane. ACS Infect Dis 2023; 9:773-784. [PMID: 36946615 PMCID: PMC10366416 DOI: 10.1021/acsinfecdis.2c00478] [Citation(s) in RCA: 8] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/23/2023]
Abstract
The host restriction factor, Serinc5, incorporates into budding HIV particles and inhibits their infection by an incompletely understood mechanism. We have previously reported that Serinc5 but not its paralogue, Serinc2, blocks HIV cell entry by membrane fusion, specifically by inhibiting fusion pore formation and dilation. A body of work suggests that Serinc5 may alter the conformation and clustering of the HIV fusion protein, Env. To contribute an additional perspective to the developing model of Serinc5 restriction, we assessed Serinc2 and Serinc5's effects on HIV pseudoviral membranes. By measuring pseudoviral membrane thickness via cryo-electron microscopy and order via the fluorescent dye, FLIPPER-TR, Serinc5 was found to increase membrane heterogeneity, skewing the distribution toward a larger fraction of the viral membrane in an ordered phase. We also directly observed for the first time the coexistence of membrane domains within individual viral membrane envelopes. Using a total internal reflection fluorescence-based single particle fusion assay, we found that treatment of HIV pseudoviral particles with phosphatidylethanolamine (PE) rescued HIV pseudovirus fusion from restriction by Serinc5, which was accompanied by decreased membrane heterogeneity and order. This effect was specific for PE and did not depend on acyl chain length or saturation. Together, these data suggest that Serinc5 alters multiple interrelated properties of the viral membrane─lipid chain order, rigidity, line tension, and lateral pressure─which decrease the accessibility of fusion intermediates and disfavor completion of fusion. These biophysical insights into Serinc5 restriction of HIV infectivity could contribute to the development of novel antivirals that exploit the same weaknesses.
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Affiliation(s)
- Amanda E. Ward
- Department of Molecular Physiology and Biological Physics, University of Virginia Health System, Charlottesville, VA 22908
- Center for Membrane and Cell Physiology, University of Virginia, Charlottesville, VA 22908
| | - Daria Sokovikova
- Department of Molecular Physiology and Biological Physics, University of Virginia Health System, Charlottesville, VA 22908
- Center for Membrane and Cell Physiology, University of Virginia, Charlottesville, VA 22908
| | - Melvin Neal Waxham
- Department of Neurobiology and Anatomy, The University of Texas Health Science Center at Houston McGovern Medical School, Houston, TX 77030
| | | | - Ilya Levental
- Department of Molecular Physiology and Biological Physics, University of Virginia Health System, Charlottesville, VA 22908
- Center for Membrane and Cell Physiology, University of Virginia, Charlottesville, VA 22908
| | - Kandice R. Levental
- Department of Molecular Physiology and Biological Physics, University of Virginia Health System, Charlottesville, VA 22908
- Center for Membrane and Cell Physiology, University of Virginia, Charlottesville, VA 22908
| | - Volker Kiessling
- Department of Molecular Physiology and Biological Physics, University of Virginia Health System, Charlottesville, VA 22908
- Center for Membrane and Cell Physiology, University of Virginia, Charlottesville, VA 22908
| | - Judith M. White
- Department of Cell Biology, University of Virginia Health System, Charlottesville, VA 22908
| | - Lukas K. Tamm
- Department of Molecular Physiology and Biological Physics, University of Virginia Health System, Charlottesville, VA 22908
- Center for Membrane and Cell Physiology, University of Virginia, Charlottesville, VA 22908
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8
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Kwarteng DO, Gangoda M, Kooijman EE. The effect of methylated phosphatidylethanolamine derivatives on the ionization properties of signaling phosphatidic acid. Biophys Chem 2023; 296:107005. [PMID: 36934676 DOI: 10.1016/j.bpc.2023.107005] [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: 02/03/2023] [Accepted: 03/07/2023] [Indexed: 03/16/2023]
Abstract
Phosphatidylethanolamine (PE) and Phosphatidylcholine (PC) are the most abundant glycerophospholipids in eukaryotic membranes. The differences in the physicochemical properties of their headgroups have contrasting modulatory effects on their interaction with intracellular macromolecules. As such, their overall impact on membrane structure and function differs significantly. Enzymatic methylation of PE's amine headgroup produces two methylated derivatives namely monomethyl PE (MMPE) and dimethyl PE (DMPE) which have physicochemical properties that generally range between that of PE and PC. Additionally, their influence on membrane properties differs from both PE and PC. Although variations in headgroup methylation have been reported to affect signaling pathways, the direct influence that these differences exert on the ionization properties of signaling phospholipids have not been investigated. Here, we briefly review membrane function and structure that are mediated by the differences in headgroup methylation between PE, MMPE, DMPE and PC. In addition, using 31P MAS NMR, we investigate the effect of these four phospholipids on the ionization properties of the ubiquitous signaling anionic lipid phosphatidic acid (PA). Our results show that PA's ionization properties are differentially affected by changes in phospholipid headgroup methylation. This could have important implications for PA-protein binding and hence physiological functions in cells where signaling events lead to changes in abundance of methylated PE derivatives in the membrane.
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Affiliation(s)
- Desmond Owusu Kwarteng
- Department of Biological Sciences, Kent State University, P.O. Box 5190, Kent, OH 44242, USA.
| | - Mahinda Gangoda
- Department of Chemistry & Biochemistry, Kent State University, P.O. Box 5190, Kent, OH 44242, USA
| | - Edgar E Kooijman
- Department of Biological Sciences, Kent State University, P.O. Box 5190, Kent, OH 44242, USA.
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9
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Gahan CG, Van Lehn RC, Blackwell HE, Lynn DM. Interactions of Bacterial Quorum Sensing Signals with Model Lipid Membranes: Influence of Membrane Composition on Membrane Remodeling. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2023; 39:295-307. [PMID: 36534123 PMCID: PMC10038191 DOI: 10.1021/acs.langmuir.2c02506] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/17/2023]
Abstract
We report the influence of membrane composition on the multiscale remodeling of multicomponent lipid bilayers initiated by contact with the amphiphilic bacterial quorum sensing signal N-(3-oxo)-dodecanoyl-l-homoserine lactone (3-oxo-C12-AHL) and its anionic headgroup hydrolysis product, 3-oxo-C12-HS. We used fluorescence microscopy and quartz crystal microbalance with dissipation (QCM-D) to characterize membrane reformation that occurs when these amphiphiles are placed in contact with supported lipid bilayers (SLBs) composed of (i) 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) containing varying amounts of cholesterol or (ii) mixtures of DOPC and either 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE, a conical zwitterionic lipid) or 1,2-dioleoyl-sn-glycero-3-phospho-l-serine (DOPS, a model anionic lipid). In general, we observe these mixed-lipid membranes to undergo remodeling events, including the formation and subsequent collapse of long tubules and the formation of hemispherical caps, upon introduction to biologically relevant concentrations of 3-oxo-C12-AHL and 3-oxo-C12-HS in ways that differ substantially from those observed in single-component DOPC membranes. These differences in bilayer reformation and their associated dynamics can be understood in terms of the influence of membrane composition on the time scales of molecular flip-flop, lipid packing defects, and lipid phase segregation in these materials. The lipid components investigated here are representative of classes of lipids that comprise both naturally occurring cell membranes and many useful synthetic soft materials. These studies thus represent a first step toward understanding the ways in which membrane composition can impact interactions with this important class of bacterial signaling molecules.
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Affiliation(s)
- Curran G. Gahan
- Department of Chemical and Biological Engineering, University of Wisconsin–Madison, 1415 Engineering Dr., Madison, WI 53706, USA
| | - Reid C. Van Lehn
- Department of Chemical and Biological Engineering, University of Wisconsin–Madison, 1415 Engineering Dr., Madison, WI 53706, USA
| | - Helen E. Blackwell
- Department of Chemistry, University of Wisconsin–Madison, 1101 University Ave., Madison, WI 53706, USA
| | - David M. Lynn
- Department of Chemical and Biological Engineering, University of Wisconsin–Madison, 1415 Engineering Dr., Madison, WI 53706, USA
- Department of Chemistry, University of Wisconsin–Madison, 1101 University Ave., Madison, WI 53706, USA
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10
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Rosenhouse-Dantsker A, Gazgalis D, Logothetis DE. PI(4,5)P 2 and Cholesterol: Synthesis, Regulation, and Functions. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2023; 1422:3-59. [PMID: 36988876 DOI: 10.1007/978-3-031-21547-6_1] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Indexed: 03/30/2023]
Abstract
Phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) is the most abundant membrane phosphoinositide and cholesterol is an essential component of the plasma membrane (PM). Both lipids play key roles in a variety of cellular functions including as signaling molecules and major regulators of protein function. This chapter provides an overview of these two important lipids. Starting from a brief description of their structure, synthesis, and regulation, the chapter continues to describe the primary functions and signaling processes in which PI(4,5)P2 and cholesterol are involved. While PI(4,5)P2 and cholesterol can act independently, they often act in concert or affect each other's impact. The chapters in this volume on "Cholesterol and PI(4,5)P2 in Vital Biological Functions: From Coexistence to Crosstalk" focus on the emerging relationship between cholesterol and PI(4,5)P2 in a variety of biological systems and processes. In this chapter, the next section provides examples from the ion channel field demonstrating that PI(4,5)P2 and cholesterol can act via common mechanisms. The chapter ends with a discussion of future directions.
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Affiliation(s)
| | - Dimitris Gazgalis
- Department of Pharmaceutical Sciences, School of Pharmacy and Pharmaceutical Sciences, Bouvé College of Health Sciences, Northeastern University, Boston, MA, USA
| | - Diomedes E Logothetis
- Department of Pharmaceutical Sciences, School of Pharmacy and Pharmaceutical Sciences, Bouvé College of Health Sciences, Northeastern University, Boston, MA, USA
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11
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Ko TH, Chen YF. Correlation between the In-Plane Critical Behavior and Out-of-Plane Interaction of Ternary Lipid Membranes. MEMBRANES 2022; 13:6. [PMID: 36676813 PMCID: PMC9860714 DOI: 10.3390/membranes13010006] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 11/25/2022] [Revised: 12/15/2022] [Accepted: 12/16/2022] [Indexed: 06/17/2023]
Abstract
Liquid-liquid phase-separating lipid membranes belong to the 2-D Ising universality class. While their in-plane critical behaviors are well studied, how the behaviors modulate out-of-plane interactions is rarely explored, despite its profound implications for biomembranes and 2-D ferromagnets. Here, we examine how the interlayer interaction, manifested as membrane fusion, is affected by the membranes' critical fluctuations. Remarkably, the critical fluctuations suppress membrane fusion, suggesting a correlation between critical behaviors and interlayer interactions for 2-D Ising systems.
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12
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Overduin M, Tran A, Eekels DM, Overduin F, Kervin TA. Transmembrane Membrane Readers form a Novel Class of Proteins That Include Peripheral Phosphoinositide Recognition Domains and Viral Spikes. MEMBRANES 2022; 12:1161. [PMID: 36422153 PMCID: PMC9692390 DOI: 10.3390/membranes12111161] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 10/12/2022] [Revised: 11/11/2022] [Accepted: 11/15/2022] [Indexed: 06/16/2023]
Abstract
Membrane proteins are broadly classified as transmembrane (TM) or peripheral, with functions that pertain to only a single bilayer at a given time. Here, we explicate a class of proteins that contain both transmembrane and peripheral domains, which we dub transmembrane membrane readers (TMMRs). Their transmembrane and peripheral elements anchor them to one bilayer and reversibly attach them to another section of bilayer, respectively, positioning them to tether and fuse membranes while recognizing signals such as phosphoinositides (PIs) and modifying lipid chemistries in proximity to their transmembrane domains. Here, we analyze full-length models from AlphaFold2 and Rosetta, as well as structures from nuclear magnetic resonance (NMR) spectroscopy and X-ray crystallography, using the Membrane Optimal Docking Area (MODA) program to map their membrane-binding surfaces. Eukaryotic TMMRs include phospholipid-binding C1, C2, CRAL-TRIO, FYVE, GRAM, GTPase, MATH, PDZ, PH, PX, SMP, StART and WD domains within proteins including protrudin, sorting nexins and synaptotagmins. The spike proteins of SARS-CoV-2 as well as other viruses are also TMMRs, seeing as they are anchored into the viral membrane while mediating fusion with host cell membranes. As such, TMMRs have key roles in cell biology and membrane trafficking, and include drug targets for diseases such as COVID-19.
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Affiliation(s)
- Michael Overduin
- Department of Biochemistry, University of Alberta, Edmonton, AB T6G 2H7, Canada
| | - Anh Tran
- Department of Biochemistry, University of Alberta, Edmonton, AB T6G 2H7, Canada
| | | | - Finn Overduin
- Institute of Nutritional Science, University of Potsdam, 14476 Potsdam, Germany
| | - Troy A. Kervin
- Department of Biochemistry, University of Alberta, Edmonton, AB T6G 2H7, Canada
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13
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Chng CP, Hsia KJ, Huang C. Modulation of lipid vesicle-membrane interactions by cholesterol. SOFT MATTER 2022; 18:7752-7761. [PMID: 36093613 DOI: 10.1039/d2sm00693f] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
Nanoscale lipid vesicles are attractive vehicles for drug delivery. Although often considered as soft nanoparticles in terms of mechanical deformability, the fluidic nature of the lipid membrane makes their interactions with another lipid membrane much more complex. Cholesterol is a key molecule that not only effectively stiffens lipid bilayer membranes but also induces membrane fusion. As such, how cholesterol modulates lipid vesicle-membrane interactions during endocytosis remains elusive. Through systematic molecular dynamics simulations, we find that membrane stiffening upon incorporating cholesterol reduces vesicle wrapping by a planar membrane, hindering endocytosis. Membrane fusion is also accelerated when either the vesicle or the planar membrane is cholesterol-rich, but fusion becomes minimal when both the vesicle and planar membrane are cholesterol-rich. This study provides insights into vesicle-membrane interactions in the presence of cholesterol and enlightens how cholesterol may be used to direct the cellular uptake pathways of nanoliposomes.
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Affiliation(s)
- Choon-Peng Chng
- School of Mechanical and Aerospace Engineering, Nanyang Technological University, Singapore 639798, Republic of Singapore.
| | - K Jimmy Hsia
- School of Mechanical and Aerospace Engineering, Nanyang Technological University, Singapore 639798, Republic of Singapore.
- School of Chemical and Biomedical Engineering, Nanyang Technological University, Singapore 637459, Republic of Singapore
| | - Changjin Huang
- School of Mechanical and Aerospace Engineering, Nanyang Technological University, Singapore 639798, Republic of Singapore.
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14
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Coffman RE, Kraichely KN, Kreutzberger AJB, Kiessling V, Tamm LK, Woodbury DJ. Drunken lipid membranes, not drunken SNARE proteins, promote fusion in a model of neurotransmitter release. Front Mol Neurosci 2022; 15:1022756. [PMID: 36311016 PMCID: PMC9614348 DOI: 10.3389/fnmol.2022.1022756] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2022] [Accepted: 09/20/2022] [Indexed: 11/29/2022] Open
Abstract
Alcohol affects many neuronal proteins that are upstream or down-stream of synaptic vesicle fusion and neurotransmitter release. Less well studied is alcohol’s effect on the fusion machinery including SNARE proteins and lipid membranes. Using a SNARE-driven fusion assay we show that fusion probability is significantly increased at 0.4% v/v (68 mM) ethanol; but not with methanol up to 10%. Ethanol appears to act directly on membrane lipids since experiments focused on protein properties [circular dichroism spectrometry, site-directed fluorescence interference contrast (sdFLIC) microscopy, and vesicle docking results] showed no significant changes up to 5% ethanol, but a protein-free fusion assay also showed increased lipid membrane fusion rates with 0.4% ethanol. These data show that the effects of high physiological doses of ethanol on SNARE-driven fusion are mediated through ethanol’s interaction with the lipid bilayer of membranes and not SNARE proteins, and that methanol affects lipid membranes and SNARE proteins only at high doses.
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Affiliation(s)
- Robert E. Coffman
- Neuroscience Center, Brigham Young University, Provo, UT, United States
| | - Katelyn N. Kraichely
- Department of Molecular Physiology and Biological Physics, University of Virginia Health System, Charlottesville, VA, United States
| | - Alex J. B. Kreutzberger
- Department of Molecular Physiology and Biological Physics, University of Virginia Health System, Charlottesville, VA, United States
| | - Volker Kiessling
- Department of Molecular Physiology and Biological Physics, University of Virginia Health System, Charlottesville, VA, United States
| | - Lukas K. Tamm
- Department of Molecular Physiology and Biological Physics, University of Virginia Health System, Charlottesville, VA, United States
| | - Dixon J. Woodbury
- Neuroscience Center, Brigham Young University, Provo, UT, United States
- Department of Cell Biology and Physiology, Brigham Young University, Provo, UT, United States
- *Correspondence: Dixon J. Woodbury,
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15
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Rituper B, Guček A, Lisjak M, Gorska U, Šakanović A, Bobnar ST, Lasič E, Božić M, Abbineni PS, Jorgačevski J, Kreft M, Verkhratsky A, Platt FM, Anderluh G, Stenovec M, Božič B, Coorssen JR, Zorec R. Vesicle cholesterol controls exocytotic fusion pore. Cell Calcium 2021; 101:102503. [PMID: 34844123 DOI: 10.1016/j.ceca.2021.102503] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2021] [Revised: 11/15/2021] [Accepted: 11/16/2021] [Indexed: 12/24/2022]
Abstract
In some lysosomal storage diseases (LSD) cholesterol accumulates in vesicles. Whether increased vesicle cholesterol affects vesicle fusion with the plasmalemma, where the fusion pore, a channel between the vesicle lumen and the extracellular space, is formed, is unknown. Super-resolution microscopy revealed that after stimulation of exocytosis, pituitary lactotroph vesicles discharge cholesterol which transfers to the plasmalemma. Cholesterol depletion in lactotrophs and astrocytes, both exhibiting Ca2+-dependent exocytosis regulated by distinct Ca2+sources, evokes vesicle secretion. Although this treatment enhanced cytosolic levels of Ca2+ in lactotrophs but decreased it in astrocytes, this indicates that cholesterol may well directly define the fusion pore. In an attempt to explain this mechanism, a new model of cholesterol-dependent fusion pore regulation is proposed. High-resolution membrane capacitance measurements, used to monitor fusion pore conductance, a parameter related to fusion pore diameter, confirm that at resting conditions reducing cholesterol increases, while enrichment with cholesterol decreases the conductance of the fusion pore. In resting fibroblasts, lacking the Npc1 protein, a cellular model of LSD in which cholesterol accumulates in vesicles, the fusion pore conductance is smaller than in controls, showing that vesicle cholesterol controls fusion pore and is relevant for pathophysiology of LSD.
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Affiliation(s)
- Boštjan Rituper
- Laboratory of Neuroendocrinology-Molecular Cell Physiology, Institute of Pathophysiology, University of Ljubljana, Faculty of Medicine, Ljubljana, Slovenia
| | - Alenka Guček
- Laboratory of Neuroendocrinology-Molecular Cell Physiology, Institute of Pathophysiology, University of Ljubljana, Faculty of Medicine, Ljubljana, Slovenia
| | - Marjeta Lisjak
- Laboratory of Neuroendocrinology-Molecular Cell Physiology, Institute of Pathophysiology, University of Ljubljana, Faculty of Medicine, Ljubljana, Slovenia
| | - Urszula Gorska
- Laboratory of Neuroendocrinology-Molecular Cell Physiology, Institute of Pathophysiology, University of Ljubljana, Faculty of Medicine, Ljubljana, Slovenia
| | - Aleksandra Šakanović
- Laboratory for Molecular Biology and Nanobiotechnology, National Institute of Chemistry, Ljubljana, Slovenia
| | - Saša Trkov Bobnar
- Laboratory of Neuroendocrinology-Molecular Cell Physiology, Institute of Pathophysiology, University of Ljubljana, Faculty of Medicine, Ljubljana, Slovenia; Celica Biomedical, 1000, Ljubljana, Slovenia
| | - Eva Lasič
- Laboratory of Neuroendocrinology-Molecular Cell Physiology, Institute of Pathophysiology, University of Ljubljana, Faculty of Medicine, Ljubljana, Slovenia
| | - Mićo Božić
- Laboratory of Neuroendocrinology-Molecular Cell Physiology, Institute of Pathophysiology, University of Ljubljana, Faculty of Medicine, Ljubljana, Slovenia
| | - Prabhodh S Abbineni
- Department of Pharmacology, University of Michigan, Ann Arbor, MI 48109-5632, United States of America
| | - Jernej Jorgačevski
- Laboratory of Neuroendocrinology-Molecular Cell Physiology, Institute of Pathophysiology, University of Ljubljana, Faculty of Medicine, Ljubljana, Slovenia; Celica Biomedical, 1000, Ljubljana, Slovenia
| | - Marko Kreft
- Laboratory of Neuroendocrinology-Molecular Cell Physiology, Institute of Pathophysiology, University of Ljubljana, Faculty of Medicine, Ljubljana, Slovenia; Celica Biomedical, 1000, Ljubljana, Slovenia
| | - Alexei Verkhratsky
- Celica Biomedical, 1000, Ljubljana, Slovenia; Faculty of Biology, Medicine and Health, The University of Manchester, Manchester, M13 9PT, United Kingdom; Achucarro Center for Neuroscience, IKERBASQUE, 48011 Bilbao, Spain
| | - Frances M Platt
- Department of Pharmacology, University of Oxford, Oxford, OX1 3QT, United Kingdom
| | - Gregor Anderluh
- Laboratory for Molecular Biology and Nanobiotechnology, National Institute of Chemistry, Ljubljana, Slovenia
| | - Matjaž Stenovec
- Laboratory of Neuroendocrinology-Molecular Cell Physiology, Institute of Pathophysiology, University of Ljubljana, Faculty of Medicine, Ljubljana, Slovenia; Celica Biomedical, 1000, Ljubljana, Slovenia
| | - Bojan Božič
- Institute of Biophysics, Faculty of Medicine, University of Ljubljana, Slovenia
| | - Jens R Coorssen
- Department of Health Sciences, Faculty of Applied Health Sciences and Department of Biological Sciences, Faculty of Mathematics & Science, Brock University, St Catherine's, Ontario, Canada
| | - Robert Zorec
- Laboratory of Neuroendocrinology-Molecular Cell Physiology, Institute of Pathophysiology, University of Ljubljana, Faculty of Medicine, Ljubljana, Slovenia; Celica Biomedical, 1000, Ljubljana, Slovenia.
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16
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Park S, Im W, Pastor RW. Developing initial conditions for simulations of asymmetric membranes: a practical recommendation. Biophys J 2021; 120:5041-5059. [PMID: 34653389 DOI: 10.1016/j.bpj.2021.10.009] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2021] [Revised: 05/09/2021] [Accepted: 10/08/2021] [Indexed: 01/03/2023] Open
Abstract
It has been proposed that the surface tension difference between leaflets (or differential stress) in asymmetric bilayers is generally nonvanishing. This implies that there is no unique approach to generate initial conditions for simulations of asymmetric bilayers in the absence of experimentally derived constraints. Current generation methods include individual area per lipid (APL) based, leaflet surface area (SA) matching, and zero leaflet tension based (0-DS). This work adds a bilayer-based approach that aims for achieving partial chemical equilibrium by interleaflet switching of selected lipids via P21 periodic boundary conditions. Based on a recently proposed theoretical framework, we obtained expressions for tensions in asymmetric bilayers from both the bending and area strains. We also developed a quantitative measure for the energetic penalty from the differential stress. The impacts of APL-, SA-, and 0-DS-based approaches on mechanical properties are assessed for two different asymmetric bilayers. The lateral pressure profile and its moments differ significantly for each method, whereas the area compressibility modulus is relatively insensitive. Application of P21 periodic boundary conditions (APL/P21, SA/P21, and 0-DS/P21) results in better agreement in mechanical properties between asymmetric bilayers generated by APL-, SA-, and 0-DS-based approaches, in which changes are the smallest for bilayers from the SA-based method. The estimated differential stress from the theory shows good agreement with that from the simulations. These simulation results and the good agreement between the predicted and observed differential stress further support the theoretical framework in which bilayer mechanical properties are outcomes of the interplay between intrinsic bending and asymmetric lipid packing. Based on the simulation results and theoretical predictions, the SA/P21-based, or at least the SA-based (when the differential stress is small), approach is recommended as a practical method for developing initial conditions for asymmetric bilayer simulations.
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Affiliation(s)
- Sooyhung Park
- Department of Biological Sciences, Bethlehem, Pennsylvania; Department of Chemistry, Lehigh University, Bethlehem, Pennsylvania.
| | - Wonpil Im
- Department of Biological Sciences, Bethlehem, Pennsylvania; Department of Chemistry, Lehigh University, Bethlehem, Pennsylvania
| | - Richard W Pastor
- Laboratory of Computational Biology, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, Maryland
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17
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Liu KN, Boxer SG. Single-virus content-mixing assay reveals cholesterol-enhanced influenza membrane fusion efficiency. Biophys J 2021; 120:4832-4841. [PMID: 34536389 DOI: 10.1016/j.bpj.2021.09.023] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2021] [Revised: 08/05/2021] [Accepted: 09/09/2021] [Indexed: 10/20/2022] Open
Abstract
To infect a cell, enveloped viruses must first undergo membrane fusion, which proceeds through a hemifusion intermediate, followed by the formation of a fusion pore through which the viral genome is transferred to a target cell. Single-virus fusion studies to elucidate the dynamics of content mixing typically require extensive fluorescent labeling of viral contents. The labeling process must be optimized depending on the virus identity and strain and can potentially be perturbative to viral fusion behavior. Here, we introduce a single-virus assay in which content-labeled vesicles are bound to unlabeled influenza A virus (IAV) to eliminate the problematic step of content-labeling virions. We use fluorescence microscopy to observe individual, pH-triggered content mixing and content-loss events between IAV and target vesicles of varying cholesterol compositions. We show that target membrane cholesterol increases the efficiency of IAV content mixing and decreases the fraction of content-mixing events that result in content loss. These results are consistent with previous findings that cholesterol stabilizes pore formation in IAV entry and limits leakage after pore formation. We also show that content loss due to hemagglutinin fusion peptide engagement with the target membrane is independent of composition. This approach is a promising strategy for studying the single-virus content-mixing kinetics of other enveloped viruses.
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Affiliation(s)
- Katherine N Liu
- Department of Chemistry, Stanford University, Stanford, California
| | - Steven G Boxer
- Department of Chemistry, Stanford University, Stanford, California.
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18
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Larijani B, Pytowski L, Vaux DJ. The enigma of phosphoinositides and their derivatives: Their role in regulation of subcellular compartment morphology. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2021; 1864:183780. [PMID: 34547252 DOI: 10.1016/j.bbamem.2021.183780] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/29/2021] [Revised: 08/27/2021] [Accepted: 09/14/2021] [Indexed: 11/24/2022]
Abstract
The general segregation of a molecular class, lipids, from the pathways of cellular communication, via endo-membranes, has resulted in the over-simplification and misconceptions in deciphering cell signalling mechanisms. Mechanisms in signal transduction and protein activation require targeting of proteins to membranous compartments with a specific localised morphology and dynamics that are dependent on their lipid composition. Many posttranslational events define cellular behaviours and without the active role of membranous compartments these events lead to various dysregulations of the signalling pathways. We summarise the key findings, using tools such as the rapalogue dimerisation, in the structural roles and signalling of the inter-related phosphoinositide lipids and their derivative, diacylglycerol, in the regulation of nuclear envelope biogenesis and other subcellular compartments such as the nucleoplasmic reticulum.
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Affiliation(s)
- Banafshé Larijani
- Centre for Therapeutic Innovation & Cell Biophysics Laboratory, Department of Pharmacy and Pharmacology & Department of Physics, University of Bath, Bath BA2 7AY, UK.
| | - Lior Pytowski
- Sir William Dunn School of Pathology, University of Oxford, Oxford OX1 3RE, UK
| | - David J Vaux
- Sir William Dunn School of Pathology, University of Oxford, Oxford OX1 3RE, UK
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19
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Allolio C, Harries D. Calcium Ions Promote Membrane Fusion by Forming Negative-Curvature Inducing Clusters on Specific Anionic Lipids. ACS NANO 2021; 15:12880-12887. [PMID: 34338519 DOI: 10.1021/acsnano.0c08614] [Citation(s) in RCA: 18] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
Vesicles enriched in certain negatively charged lipids, such as phosphatidylserine and PIP2, are known to undergo fusion in the presence of calcium ions without assistance from protein assemblies. Other lipids do not exhibit this propensity, even if they are negatively charged. Using our recently developed methodology, we extract elastic properties of a representative set of lipids. This allows us to trace the origin of lipid-calcium selectivity in membrane fusion to the formation of lipid clusters with long-range correlations that induce negative curvature on the membrane surface. Furthermore, the clusters generate lateral tension in the headgroup region at the membrane surface, concomitantly also stabilizing negative Gaussian curvature. Finally, calcium binding also reduces the orientational polarization of water around the membrane head groups, potentially reducing the hydration force acting between membranes. Binding calcium only weakly increases membrane bending rigidity and tilt moduli, in agreement with experiments. We show how the combined effects of calcium binding to membranes lower the barriers along the fusion pathway that lead to the formation of the fusion stalk as well as the fusion pore.
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Affiliation(s)
- Christoph Allolio
- Charles University, Faculty of Mathematics and Physics, Mathematical Institute, Sokolovská 83, 186 75 Prague 8, Czech Republic
- Institute of Chemistry, The Fritz Haber Center, and The Center for Nanoscience and Nanotechnology, The Hebrew University, E.J. Safra Campus, Jerusalem 9190401, Israel
| | - Daniel Harries
- Institute of Chemistry, The Fritz Haber Center, and The Center for Nanoscience and Nanotechnology, The Hebrew University, E.J. Safra Campus, Jerusalem 9190401, Israel
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20
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Wu L, Courtney KC, Chapman ER. Cholesterol stabilizes recombinant exocytic fusion pores by altering membrane bending rigidity. Biophys J 2021; 120:1367-1377. [PMID: 33582136 DOI: 10.1016/j.bpj.2021.02.005] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2020] [Revised: 01/18/2021] [Accepted: 02/03/2021] [Indexed: 12/28/2022] Open
Abstract
SNARE-mediated membrane fusion proceeds via the formation of a fusion pore. This intermediate structure is highly dynamic and can flicker between open and closed states. In cells, cholesterol has been reported to affect SNARE-mediated exocytosis and fusion pore dynamics. Here, we address the question of whether cholesterol directly affects the flickering rate of reconstituted fusion pores in vitro. These experiments were enabled by the recent development of a nanodisc⋅black lipid membrane recording system that monitors dynamic transitions between the open and closed states of nascent recombinant pores with submillisecond time resolution. The fusion pores formed between nanodiscs that bore the vesicular SNARE synaptobrevin 2 and black lipid membranes that harbored the target membrane SNAREs syntaxin 1A and SNAP-25B were markedly affected by cholesterol. These effects include strong reductions in flickering out of the open state, resulting in a significant increase in the open dwell-time. We attributed these effects to the known role of cholesterol in altering the elastic properties of lipid bilayers because manipulation of phospholipids to increase membrane stiffness mirrored the effects of cholesterol. In contrast to the observed effects on pore kinetics, cholesterol had no effect on the current that passed through individual pores and, hence, did not affect pore size. In conclusion, our results show that cholesterol dramatically stabilizes fusion pores in the open state by increasing membrane bending rigidity.
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Affiliation(s)
- Lanxi Wu
- Howard Hughes Medical Institute and the Department of Neuroscience, University of Wisconsin, Madison, Wisconsin
| | - Kevin C Courtney
- Howard Hughes Medical Institute and the Department of Neuroscience, University of Wisconsin, Madison, Wisconsin
| | - Edwin R Chapman
- Howard Hughes Medical Institute and the Department of Neuroscience, University of Wisconsin, Madison, Wisconsin.
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21
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Cholesterol Efflux Efficiency of Reconstituted HDL Is Affected by Nanoparticle Lipid Composition. Biomedicines 2020; 8:biomedicines8100373. [PMID: 32977626 PMCID: PMC7598155 DOI: 10.3390/biomedicines8100373] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2020] [Revised: 09/17/2020] [Accepted: 09/21/2020] [Indexed: 12/31/2022] Open
Abstract
Cardiovascular disease (CVD), the leading cause of mortality worldwide is primarily caused by atherosclerosis, which is promoted by the accumulation of low-density lipoproteins into the intima of large arteries. Multiple nanoparticles mimicking natural HDL (rHDL) have been designed to remove cholesterol excess in CVD therapy. The goal of this investigation was to assess the cholesterol efflux efficiency of rHDLs with different lipid compositions, mimicking different maturation stages of high-density lipoproteins (HDLs) occurring in vivo. Methods: the cholesterol efflux activity of soybean PC (Soy-PC), 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), DPPC:Chol:1-palmitoyl-2-hydroxy-sn-glycero-3-phosphocholine (LysoPC) and DPPC:18:2 cholesteryl ester (CE):LysoPC rHDLs was determined in several cell models to investigate the contribution of lipid composition to the effectiveness of cholesterol removal. Results: DPPC rHDLs are the most efficient particles, inducing cholesterol efflux in all cellular models and in all conditions the effect was potentiated when the ABCA1 transporter was upregulated. Conclusions: DPPC rHDLs, which resemble nascent HDL, are the most effective particles in inducing cholesterol efflux due to the higher physical binding affinity of cholesterol to the saturated long-chain-length phospholipids and the favored cholesterol transfer from a highly positively curved bilayer, to an accepting planar bilayer such as DPPC rHDLs. The physicochemical characteristics of rHDLs should be taken into consideration to design more efficient nanoparticles to promote cholesterol efflux.
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22
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Matsarskaia O, Roosen‐Runge F, Schreiber F. Multivalent ions and biomolecules: Attempting a comprehensive perspective. Chemphyschem 2020; 21:1742-1767. [PMID: 32406605 PMCID: PMC7496725 DOI: 10.1002/cphc.202000162] [Citation(s) in RCA: 36] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2020] [Revised: 05/13/2020] [Indexed: 12/13/2022]
Abstract
Ions are ubiquitous in nature. They play a key role for many biological processes on the molecular scale, from molecular interactions, to mechanical properties, to folding, to self-organisation and assembly, to reaction equilibria, to signalling, to energy and material transport, to recognition etc. Going beyond monovalent ions to multivalent ions, the effects of the ions are frequently not only stronger (due to the obviously higher charge), but qualitatively different. A typical example is the process of binding of multivalent ions, such as Ca2+ , to a macromolecule and the consequences of this ion binding such as compaction, collapse, potential charge inversion and precipitation of the macromolecule. Here we review these effects and phenomena induced by multivalent ions for biological (macro)molecules, from the "atomistic/molecular" local picture of (potentially specific) interactions to the more global picture of phase behaviour including, e. g., crystallisation, phase separation, oligomerisation etc. Rather than attempting an encyclopedic list of systems, we rather aim for an embracing discussion using typical case studies. We try to cover predominantly three main classes: proteins, nucleic acids, and amphiphilic molecules including interface effects. We do not cover in detail, but make some comparisons to, ion channels, colloidal systems, and synthetic polymers. While there are obvious differences in the behaviour of, and the relevance of multivalent ions for, the three main classes of systems, we also point out analogies. Our attempt of a comprehensive discussion is guided by the idea that there are not only important differences and specific phenomena with regard to the effects of multivalent ions on the main systems, but also important similarities. We hope to bridge physico-chemical mechanisms, concepts of soft matter, and biological observations and connect the different communities further.
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Affiliation(s)
| | - Felix Roosen‐Runge
- Department of Biomedical Sciences and Biofilms-Research Center for Biointerfaces (BRCB), Faculty of Health and SocietyMalmö UniversitySweden
- Division of Physical ChemistryLund UniversitySweden
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23
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Abstract
Exocytosis is a universal process of eukaryotic cells, consisting of fusion between the vesicle and the plasma membranes, leading to the formation of a fusion pore, a channel through which vesicle cargo exits into the extracellular space. In 1986, Rand and Parsegian proposed several stages to explain the nature of membrane fusion. Following stimulation, it starts with focused stress destabilization of membranes in contact, followed by the coalescence of two membrane surfaces. In the next fraction of a millisecond, restabilization of fused membranes is considered to occur to maintain the cell's integrity. This view predicted that once a fusion pore is formed, it must widen abruptly, irreversibly and fully, whereby the vesicle membrane completely integrates with and collapses into the plasma membrane (full fusion exocytosis). However, recent experimental evidence has revealed that once the fusion pore opens, it may also reversibly close (transient or kiss-and-run exocytosis). Here, we present a historical perspective on understanding the mechanisms that initiate the membrane merger and fusion pore formation. Next, post-fusion mechanisms that regulate fusion pore stability are considered, reflecting the state in which the forces of widening and constriction of fusion pores are balanced. Although the mechanisms generating these forces are unclear, they may involve lipids and proteins, including SNAREs, which play a role not only in the pre-fusion but also post-fusion stages of exocytosis. How molecules stabilize the fusion pore in the open state is key for a better understanding of fusion pore physiology in health and disease.
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Affiliation(s)
- Helena Haque Chowdhury
- Laboratory of Cell Engineering, Celica Biomedical, 1000 Ljubljana, Slovenia.,Laboratory of Neuroendocrinology - Molecular Cell Physiology, Institute of Pathophysiology, University of Ljubljana, Medical Faculty, 1000 Ljubljana, Slovenia
| | - Robert Zorec
- Laboratory of Cell Engineering, Celica Biomedical, 1000 Ljubljana, Slovenia.,Laboratory of Neuroendocrinology - Molecular Cell Physiology, Institute of Pathophysiology, University of Ljubljana, Medical Faculty, 1000 Ljubljana, Slovenia
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24
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Dhara M, Mantero Martinez M, Makke M, Schwarz Y, Mohrmann R, Bruns D. Synergistic actions of v-SNARE transmembrane domains and membrane-curvature modifying lipids in neurotransmitter release. eLife 2020; 9:e55152. [PMID: 32391794 PMCID: PMC7239655 DOI: 10.7554/elife.55152] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2020] [Accepted: 05/07/2020] [Indexed: 01/01/2023] Open
Abstract
Vesicle fusion is mediated by assembly of SNARE proteins between opposing membranes. While previous work suggested an active role of SNARE transmembrane domains (TMDs) in promoting membrane merger (Dhara et al., 2016), the underlying mechanism remained elusive. Here, we show that naturally-occurring v-SNARE TMD variants differentially regulate fusion pore dynamics in mouse chromaffin cells, indicating TMD flexibility as a mechanistic determinant that facilitates transmitter release from differentially-sized vesicles. Membrane curvature-promoting phospholipids like lysophosphatidylcholine or oleic acid profoundly alter pore expansion and fully rescue the decelerated fusion kinetics of TMD-rigidifying VAMP2 mutants. Thus, v-SNARE TMDs and phospholipids cooperate in supporting membrane curvature at the fusion pore neck. Oppositely, slowing of pore kinetics by the SNARE-regulator complexin-2 withstands the curvature-driven speeding of fusion, indicating that pore evolution is tightly coupled to progressive SNARE complex formation. Collectively, TMD-mediated support of membrane curvature and SNARE force-generated membrane bending promote fusion pore formation and expansion.
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Affiliation(s)
- Madhurima Dhara
- Institute for Physiology, Center of Integrative Physiology and Molecular Medicine, Saarland UniversityHomburgGermany
| | - Maria Mantero Martinez
- Institute for Physiology, Center of Integrative Physiology and Molecular Medicine, Saarland UniversityHomburgGermany
| | - Mazen Makke
- Institute for Physiology, Center of Integrative Physiology and Molecular Medicine, Saarland UniversityHomburgGermany
| | - Yvonne Schwarz
- Institute for Physiology, Center of Integrative Physiology and Molecular Medicine, Saarland UniversityHomburgGermany
| | - Ralf Mohrmann
- Institute for Physiology, Otto-von-Guericke UniversityMagdeburgGermany
| | - Dieter Bruns
- Institute for Physiology, Center of Integrative Physiology and Molecular Medicine, Saarland UniversityHomburgGermany
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25
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Target Membrane Cholesterol Modulates Single Influenza Virus Membrane Fusion Efficiency but Not Rate. Biophys J 2020; 118:2426-2433. [PMID: 32298636 DOI: 10.1016/j.bpj.2020.03.021] [Citation(s) in RCA: 26] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2019] [Revised: 03/09/2020] [Accepted: 03/23/2020] [Indexed: 12/11/2022] Open
Abstract
Host lipid composition influences many stages of the influenza A virus (IAV) entry process, including initial binding of IAV to sialylated glycans, fusion between the viral envelope and the host membrane, and the formation of a fusion pore through which the viral genome is transferred into a target cell. In particular, target membrane cholesterol has been shown to preferentially associate with virus receptors and alter physical properties of the membrane like fluidity and curvature. These properties affect both IAV binding and fusion, which makes it difficult to isolate the role of cholesterol in IAV fusion from receptor binding effects. Here, we develop a fusion assay that uses synthetic DNA-lipid conjugates as surrogate viral receptors to tether virions to target vesicles. To avoid the possibly perturbative effect of adding a self-quenched concentration of dye-labeled lipids to the viral membrane, we tether virions to lipid-labeled target vesicles and use fluorescence microscopy to detect individual, pH-triggered IAV membrane fusion events. Through this approach, we find that cholesterol in the target membrane enhances the efficiency of single-particle IAV lipid mixing, whereas the rate of lipid mixing is independent of cholesterol composition. We also find that the single-particle kinetics of influenza lipid mixing to target membranes with different cholesterol compositions is independent of receptor binding, suggesting that cholesterol-mediated spatial clustering of viral receptors within the target membrane does not significantly affect IAV hemifusion. These results are consistent with the hypothesis that target membrane cholesterol increases lipid mixing efficiency by altering host membrane curvature.
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26
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Joensuu M, Wallis TP, Saber SH, Meunier FA. Phospholipases in neuronal function: A role in learning and memory? J Neurochem 2020; 153:300-333. [PMID: 31745996 DOI: 10.1111/jnc.14918] [Citation(s) in RCA: 22] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2019] [Revised: 10/29/2019] [Accepted: 11/15/2019] [Indexed: 12/20/2022]
Abstract
Despite the human brain being made of nearly 60% fat, the vast majority of studies on the mechanisms of neuronal communication which underpin cognition, memory and learning, primarily focus on proteins and/or (epi)genetic mechanisms. Phospholipids are the main component of all cellular membranes and function as substrates for numerous phospholipid-modifying enzymes, including phospholipases, which release free fatty acids (FFAs) and other lipid metabolites that can alter the intrinsic properties of the membranes, recruit and activate critical proteins, and act as lipid signalling molecules. Here, we will review brain specific phospholipases, their roles in membrane remodelling, neuronal function, learning and memory, as well as their disease implications. In particular, we will highlight key roles of unsaturated FFAs, particularly arachidonic acid, in neurotransmitter release, neuroinflammation and memory. In light of recent findings, we will also discuss the emerging role of phospholipase A1 and the creation of saturated FFAs in the brain.
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Affiliation(s)
- Merja Joensuu
- Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, The University of Queensland, Brisbane, Qld, Australia.,Minerva Foundation Institute for Medical Research, Helsinki, Finland
| | - Tristan P Wallis
- Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, The University of Queensland, Brisbane, Qld, Australia
| | - Saber H Saber
- Laboratory of Molecular Cell Biology, Department of Zoology, Faculty of Science, Assiut University, Assiut, Egypt
| | - Frédéric A Meunier
- Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, The University of Queensland, Brisbane, Qld, Australia
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27
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Synaptotagmin-1 and Doc2b Exhibit Distinct Membrane-Remodeling Mechanisms. Biophys J 2019; 118:643-656. [PMID: 31952804 DOI: 10.1016/j.bpj.2019.12.021] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2019] [Revised: 12/13/2019] [Accepted: 12/16/2019] [Indexed: 11/24/2022] Open
Abstract
Synaptotagmin-1 (Syt1) is a calcium sensor protein that is critical for neurotransmission and is therefore extensively studied. Here, we use pairs of optically trapped beads coated with SNARE-free synthetic membranes to investigate Syt1-induced membrane remodeling. This activity is compared with that of Doc2b, which contains a conserved C2AB domain and induces membrane tethering and hemifusion in this cell-free model. We find that the soluble C2AB domain of Syt1 strongly affects the probability and strength of membrane-membrane interactions in a strictly Ca2+- and protein-dependent manner. Single-membrane loading of Syt1 yielded the highest probability and force of membrane interactions, whereas in contrast, Doc2b was more effective after loading both membranes. A lipid-mixing assay with confocal imaging reveals that both Syt1 and Doc2b are able to induce hemifusion; however, significantly higher Syt1 concentrations are required. Consistently, both C2AB fragments cause a reduction in the membrane-bending modulus, as measured by a method based on atomic force microscopy. This lowering of the energy required for membrane deformation may contribute to Ca2+-induced fusion.
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28
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Furber KL, Backlund PS, Yergey AL, Coorssen JR. Unbiased Thiol-Labeling and Top-Down Proteomic Analyses Implicate Multiple Proteins in the Late Steps of Regulated Secretion. Proteomes 2019; 7:proteomes7040034. [PMID: 31569819 PMCID: PMC6958363 DOI: 10.3390/proteomes7040034] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2019] [Revised: 09/20/2019] [Accepted: 09/23/2019] [Indexed: 12/12/2022] Open
Abstract
Regulated exocytosis enables temporal and spatial control over the secretion of biologically active compounds; however, the mechanism by which Ca2+ modulates different stages of exocytosis is still poorly understood. For an unbiased, top-down proteomic approach, select thiol- reactive reagents were used to investigate this process in release-ready native secretory vesicles. We previously characterized a biphasic effect of these reagents on Ca2+-triggered exocytosis: low doses potentiated Ca2+ sensitivity, whereas high doses inhibited Ca2+ sensitivity and extent of vesicle fusion. Capitalizing on this novel potentiating effect, we have now identified fluorescent thiol- reactive reagents producing the same effects: Lucifer yellow iodoacetamide, monobromobimane, and dibromobimane. Top-down proteomic analyses of fluorescently labeled proteins from total and cholesterol-enriched vesicle membrane fractions using two-dimensional gel electrophoresis coupled with mass spectrometry identified several candidate targets, some of which have been previously linked to the late steps of regulated exocytosis and some of which are novel. Initial validation studies indicate that Rab proteins are involved in the modulation of Ca2+ sensitivity, and thus the efficiency of membrane fusion, which may, in part, be linked to their previously identified upstream roles in vesicle docking.
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Affiliation(s)
- Kendra L Furber
- Northern Medical Program, University of Northern British Columbia, Prince George, BC V2N 4Z9, Canada.
| | - Peter S Backlund
- Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA.
| | - Alfred L Yergey
- Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA.
| | - Jens R Coorssen
- Department of Health Sciences, Faculty of Applied Health Sciences and Department of Biological Sciences, Faculty of Mathematics & Science, Brock University, St. Catharines, ON L2S 3A1, Canada.
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29
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Ulloa G, Hamati F, Dick A, Fitzgerald J, Mantell J, Verkade P, Collinson L, Arkill K, Larijani B, Poccia D. Lipid species affect morphology of endoplasmic reticulum: a sea urchin oocyte model of reversible manipulation. J Lipid Res 2019; 60:1880-1891. [PMID: 31548365 PMCID: PMC6824487 DOI: 10.1194/jlr.ra119000210] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2019] [Revised: 09/11/2019] [Indexed: 12/22/2022] Open
Abstract
The ER is a large multifunctional organelle of eukaryotic cells. Malfunction of the ER in various disease states, such as atherosclerosis, diabetes, cancer, Alzheimer’s and Parkinson’s and amyotrophic lateral sclerosis, often correlates with alterations in its morphology. The ER exhibits regionally variable membrane morphology that includes, at the extremes, large relatively flat surfaces and interconnected tubular structures highly curved in cross-section. ER morphology is controlled by shaping proteins that associate with membrane lipids. To investigate the role of these lipids, we developed a sea urchin oocyte model, a relatively quiescent cell in which the ER consists mostly of tubules. We altered levels of endogenous diacylglycerol (DAG), phosphatidylethanolamine (PtdEth), and phosphatidylcholine by microinjection of enzymes or lipid delivery by liposomes and evaluated shape changes with 2D and 3D confocal imaging and 3D electron microscopy. Decreases and increases in the levels of lipids such as DAG or PtdEth characterized by negative spontaneous curvature correlated with conversion to sheet structures or tubules, respectively. The effects of endogenous alterations of DAG were reversible upon exogenous delivery of lipids of negative spontaneous curvature. These data suggest that proteins require threshold amounts of such lipids and that localized deficiencies of the lipids could contribute to alterations of ER morphology. The oocyte modeling system should be beneficial to studies directed at understanding requirements of lipid species in interactions leading to alterations of organelle shaping.
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Affiliation(s)
| | - Fadi Hamati
- Department of Biology, Amherst College, Amherst, MA
| | | | | | - Judith Mantell
- School of Biochemistry, University of Bristol, Bristol, United Kingdom
| | - Paul Verkade
- School of Biochemistry, University of Bristol, Bristol, United Kingdom
| | | | - Kenton Arkill
- School of Medicine, Faculty of Medicine and Health Sciences, University of Nottingham Medical School, Nottingham, United Kingdom
| | - Banafshe Larijani
- Centre for Therapeutic Innovation, Cell Biophysics Laboratory, Department of Pharmacy and Pharmacology and Department of Physics, University of Bath, Claverton Down, Bath, United Kingdom, and Cell Biophysics Laboratory, Ikerbasque, Basque Foundation for Science, Research Centre for Experimental Marine Biology and Biotechnology (PiE) and Biophysics Institute (UPV/EHU, CSIC), University of the Basque Country, Leioa, Spain
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30
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Zhukovsky MA, Filograna A, Luini A, Corda D, Valente C. Phosphatidic acid in membrane rearrangements. FEBS Lett 2019; 593:2428-2451. [PMID: 31365767 DOI: 10.1002/1873-3468.13563] [Citation(s) in RCA: 99] [Impact Index Per Article: 19.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2019] [Revised: 07/25/2019] [Accepted: 07/26/2019] [Indexed: 12/16/2022]
Abstract
Phosphatidic acid (PA) is the simplest cellular glycerophospholipid characterized by unique biophysical properties: a small headgroup; negative charge; and a phosphomonoester group. Upon interaction with lysine or arginine, PA charge increases from -1 to -2 and this change stabilizes protein-lipid interactions. The biochemical properties of PA also allow interactions with lipids in several subcellular compartments. Based on this feature, PA is involved in the regulation and amplification of many cellular signalling pathways and functions, as well as in membrane rearrangements. Thereby, PA can influence membrane fusion and fission through four main mechanisms: it is a substrate for enzymes producing lipids (lysophosphatidic acid and diacylglycerol) that are involved in fission or fusion; it contributes to membrane rearrangements by generating negative membrane curvature; it interacts with proteins required for membrane fusion and fission; and it activates enzymes whose products are involved in membrane rearrangements. Here, we discuss the biophysical properties of PA in the context of the above four roles of PA in membrane fusion and fission.
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Affiliation(s)
- Mikhail A Zhukovsky
- Institute of Protein Biochemistry and Institute of Biochemistry and Cell Biology, National Research Council, Naples, Italy
| | - Angela Filograna
- Institute of Protein Biochemistry and Institute of Biochemistry and Cell Biology, National Research Council, Naples, Italy
| | - Alberto Luini
- Institute of Protein Biochemistry and Institute of Biochemistry and Cell Biology, National Research Council, Naples, Italy
| | - Daniela Corda
- Institute of Protein Biochemistry and Institute of Biochemistry and Cell Biology, National Research Council, Naples, Italy
| | - Carmen Valente
- Institute of Protein Biochemistry and Institute of Biochemistry and Cell Biology, National Research Council, Naples, Italy
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31
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In vitro fusion of single synaptic and dense core vesicles reproduces key physiological properties. Nat Commun 2019; 10:3904. [PMID: 31467284 PMCID: PMC6715626 DOI: 10.1038/s41467-019-11873-8] [Citation(s) in RCA: 28] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2019] [Accepted: 08/02/2019] [Indexed: 12/29/2022] Open
Abstract
Regulated exocytosis of synaptic vesicles is substantially faster than of endocrine dense core vesicles despite similar molecular machineries. The reasons for this difference are unknown and could be due to different regulatory proteins, different spatial arrangements, different vesicle sizes, or other factors. To address these questions, we take a reconstitution approach and compare regulated SNARE-mediated fusion of purified synaptic and dense core chromaffin and insulin vesicles using a single vesicle-supported membrane fusion assay. In all cases, Munc18 and complexin are required to restrict fusion in the absence of calcium. Calcium triggers fusion of all docked vesicles. Munc13 (C1C2MUN domain) is required for synaptic and enhanced insulin vesicle fusion, but not for chromaffin vesicles, correlating inversely with the presence of CAPS protein on purified vesicles. Striking disparities in calcium-triggered fusion rates are observed, increasing with curvature with time constants 0.23 s (synaptic vesicles), 3.3 s (chromaffin vesicles), and 9.1 s (insulin vesicles) and correlating with rate differences in cells.
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32
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Arachidonic acid and lysophosphatidylcholine inhibit multiple late steps of regulated exocytosis. Biochem Biophys Res Commun 2019; 515:261-267. [PMID: 31126681 DOI: 10.1016/j.bbrc.2019.05.106] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2019] [Accepted: 05/15/2019] [Indexed: 02/05/2023]
Abstract
The canonical Phospholipase A2 (PLA2) metabolites lysophosphatidylcholine (LPC) and arachidonic acid (ARA) affect regulated exocytosis in a wide variety of cells and are proposed to directly influence membrane merger owing to their respective spontaneous curvatures. According to the Stalk-pore hypothesis, negative curvature ARA inhibits and promotes bilayer merger upon introduction into the distal or proximal monolayers, respectively; in contrast, with positive curvature, LPC has the opposite effects. Using fully primed, release-ready native cortical secretory vesicles (CV), well-established fusion assays and standardized lipid analyses, we show that exogenous ARA and LPC, as well as their non-metabolizable analogous, ETYA and ET-18-OCH3, inhibit the docking/priming and membrane merger steps, respectively, of regulated exocytosis.
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33
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Andrushchenko V, Pohle W. Influence of the hydrophobic domain on the self-assembly and hydrogen bonding of hydroxy-amphiphiles. Phys Chem Chem Phys 2019; 21:11242-11258. [PMID: 31099371 DOI: 10.1039/c9cp01475f] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The amphiphiles 1-octadecanol (octadecyl (stearyl) alcohol, ODA) and 1,2-dioleoylglycerol (DOG) were studied by IR spectroscopy and X-ray diffraction combined with multiscale theoretical modeling. The computations allowed us to rationalize the experimental findings and deduce the supramolecular structure of the formed assemblies while providing a fairly detailed insight into their hydrogen-bonding patterns. IR spectra revealed that the amphiphilic assemblies dramatically differ in structural order and hydrogen-bond strength, both being high in ODA and low in DOG. On the other hand, both compounds demonstrated common features, namely a splitting of the IR bands arising from O-H stretching vibrations (νOH) as well as complete hydrophobicity. However, the observed phenomena have different origins in the two amphiphiles. While the νOH split in ODA occurs due to a vibrational coupling along the string of inter-layer O-HO hydrogen bonds, in DOG it arises from different types of hydrogen bonds (intra- and intermolecular). The hydrophobicity of ODA stems from the very tight O-HO hydrogen bonding network connecting the opposite monolayers in a densely packed tilted crystalline phase (Lc'), whereas in DOG it occurs because the polar sites are locked inside reverted micellar-like assemblies. ODA and DOG illustrate that, in the assemblies of amphiphilic hydroxyl compounds, hydrogen bonds can be formed in a wide structural latitude, which is primarily governed by the chemical nature of apolar chains. Such a wide structural variability of OH-involving hydrogen bonds can be essential for the biological functioning of relevant molecules, such as glycolipids, acylglycerols, and, potentially, glycoproteins and carbohydrates.
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Affiliation(s)
- Valery Andrushchenko
- Institute of Organic Chemistry and Biochemistry, Academy of Sciences, Flemingovo nám. 2, 16610, Prague, Czech Republic.
| | - Walter Pohle
- Center for Molecular Biomedicine, Department of Biophysics, Friedrich Schiller University Jena, Hans-Knöll-Str. 2, 07745 Jena, Germany.
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34
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Dabral D, Coorssen JR. Combined targeted Omic and Functional Assays Identify Phospholipases A₂ that Regulate Docking/Priming in Calcium-Triggered Exocytosis. Cells 2019; 8:cells8040303. [PMID: 30986994 PMCID: PMC6523306 DOI: 10.3390/cells8040303] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2019] [Revised: 03/24/2019] [Accepted: 03/28/2019] [Indexed: 12/12/2022] Open
Abstract
The fundamental molecular mechanism underlying the membrane merger steps of regulated exocytosis is highly conserved across cell types. Although involvement of Phospholipase A₂ (PLA₂) in regulated exocytosis has long been suggested, its function or that of its metabolites-a lyso-phospholipid and a free fatty acid-remain somewhat speculative. Here, using a combined bioinformatics and top-down discovery proteomics approach, coupled with lipidomic analyses, PLA₂ were found to be associated with release-ready cortical secretory vesicles (CV) that possess the minimal molecular machinery for docking, Ca2+ sensing and membrane fusion. Tightly coupling the molecular analyses with well-established quantitative fusion assays, we show for the first time that inhibition of a CV surface calcium independent intracellular PLA₂ and a luminal secretory PLA₂ significantly reduce docking/priming in the late steps of regulated exocytosis, indicating key regulatory roles in the critical step(s) preceding membrane merger.
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Affiliation(s)
- Deepti Dabral
- Molecular Physiology and Molecular Medicine Research Group, School of Medicine, Western Sydney University, Campbelltown Campus, NSW 2560, Australia.
| | - Jens R Coorssen
- Department of Health Sciences, Faculty of Applied Health Sciences and Department of Biological Sciences, Faculty of Mathematics & Science, Brock University, St. Catharines, ON L2S 3A1, Canada.
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35
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Istvan ES, Das S, Bhatnagar S, Beck JR, Owen E, Llinas M, Ganesan SM, Niles JC, Winzeler E, Vaidya AB, Goldberg DE. Plasmodium Niemann-Pick type C1-related protein is a druggable target required for parasite membrane homeostasis. eLife 2019; 8:40529. [PMID: 30888318 PMCID: PMC6424564 DOI: 10.7554/elife.40529] [Citation(s) in RCA: 44] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2018] [Accepted: 02/05/2019] [Indexed: 01/05/2023] Open
Abstract
Plasmodium parasites possess a protein with homology to Niemann-Pick Type C1 proteins (Niemann-Pick Type C1-Related protein, NCR1). We isolated parasites with resistance-conferring mutations in Plasmodium falciparum NCR1 (PfNCR1) during selections with three diverse small-molecule antimalarial compounds and show that the mutations are causative for compound resistance. PfNCR1 protein knockdown results in severely attenuated growth and confers hypersensitivity to the compounds. Compound treatment or protein knockdown leads to increased sensitivity of the parasite plasma membrane (PPM) to the amphipathic glycoside saponin and engenders digestive vacuoles (DVs) that are small and malformed. Immuno-electron microscopy and split-GFP experiments localize PfNCR1 to the PPM. Our experiments show that PfNCR1 activity is critically important for the composition of the PPM and is required for DV biogenesis, suggesting PfNCR1 as a novel antimalarial drug target. Editorial note: This article has been through an editorial process in which the authors decide how to respond to the issues raised during peer review. The Reviewing Editor's assessment is that all the issues have been addressed (see decision letter).
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Affiliation(s)
- Eva S Istvan
- Department of Medicine, Division of Infectious Diseases, Washington University School of Medicine, Saint Louis, United States.,Department of Molecular Microbiology, Washington University School of Medicine, Saint Louis, United States
| | - Sudipta Das
- Department of Microbiology and Immunology, Center for Molecular Parasitology, Drexel University College of Medicine, Philadelphia, United States
| | - Suyash Bhatnagar
- Department of Microbiology and Immunology, Center for Molecular Parasitology, Drexel University College of Medicine, Philadelphia, United States
| | - Josh R Beck
- Department of Medicine, Division of Infectious Diseases, Washington University School of Medicine, Saint Louis, United States.,Department of Molecular Microbiology, Washington University School of Medicine, Saint Louis, United States
| | - Edward Owen
- Department of Biochemistry and Molecular Biology, Pennsylvania State University, University Park, United States.,Huck Center for Malaria Research, Pennsylvania State University, University Park, United States.,Department of Chemistry, Pennsylvania State University, University Park, United States
| | - Manuel Llinas
- Department of Biochemistry and Molecular Biology, Pennsylvania State University, University Park, United States.,Huck Center for Malaria Research, Pennsylvania State University, University Park, United States.,Department of Chemistry, Pennsylvania State University, University Park, United States
| | - Suresh M Ganesan
- Department of Biological Engineering, Massachusetts Institute of Technology, Cambridge, United States
| | - Jacquin C Niles
- Department of Biological Engineering, Massachusetts Institute of Technology, Cambridge, United States
| | - Elizabeth Winzeler
- Department of Pediatrics, University of California San Diego School of Medicine, La Jolla, United States
| | - Akhil B Vaidya
- Department of Microbiology and Immunology, Center for Molecular Parasitology, Drexel University College of Medicine, Philadelphia, United States
| | - Daniel E Goldberg
- Department of Medicine, Division of Infectious Diseases, Washington University School of Medicine, Saint Louis, United States.,Department of Molecular Microbiology, Washington University School of Medicine, Saint Louis, United States
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36
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Shaaban A, Dhara M, Frisch W, Harb A, Shaib AH, Becherer U, Bruns D, Mohrmann R. The SNAP-25 linker supports fusion intermediates by local lipid interactions. eLife 2019; 8:41720. [PMID: 30883328 PMCID: PMC6422494 DOI: 10.7554/elife.41720] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2018] [Accepted: 03/05/2019] [Indexed: 12/22/2022] Open
Abstract
SNAP-25 is an essential component of SNARE complexes driving fast Ca2+-dependent exocytosis. Yet, the functional implications of the tandem-like structure of SNAP-25 are unclear. Here, we have investigated the mechanistic role of the acylated “linker” domain that concatenates the two SNARE motifs within SNAP-25. Refuting older concepts of an inert connector, our detailed structure-function analysis in murine chromaffin cells demonstrates that linker motifs play a crucial role in vesicle priming, triggering, and fusion pore expansion. Mechanistically, we identify two synergistic functions of the SNAP-25 linker: First, linker motifs support t-SNARE interactions and accelerate ternary complex assembly. Second, the acylated N-terminal linker segment engages in local lipid interactions that facilitate fusion triggering and pore evolution, putatively establishing a favorable membrane configuration by shielding phospholipid headgroups and affecting curvature. Hence, the linker is a functional part of the fusion complex that promotes secretion by SNARE interactions as well as concerted lipid interplay.
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Affiliation(s)
- Ahmed Shaaban
- ZHMB, Saarland University, Homburg, Germany.,Department of Molecular Neurobiology, Max Planck Institute for Experimental Medicine, Göttingen, Germany
| | - Madhurima Dhara
- Institute for Physiology, Center of Integrative Physiology and Molecular Medicine, Saarland University, Homburg, Germany
| | - Walentina Frisch
- Institute for Physiology, Center of Integrative Physiology and Molecular Medicine, Saarland University, Homburg, Germany
| | - Ali Harb
- ZHMB, Saarland University, Homburg, Germany
| | - Ali H Shaib
- Department of Molecular Neurobiology, Max Planck Institute for Experimental Medicine, Göttingen, Germany
| | - Ute Becherer
- Institute for Physiology, Center of Integrative Physiology and Molecular Medicine, Saarland University, Homburg, Germany
| | - Dieter Bruns
- Institute for Physiology, Center of Integrative Physiology and Molecular Medicine, Saarland University, Homburg, Germany
| | - Ralf Mohrmann
- ZHMB, Saarland University, Homburg, Germany.,Institute for Physiology, Otto-von-Guericke University, Magdeburg, Germany.,Center for Behavioral Brain Science, Otto-von-Guericke University, Magdeburg, Germany
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37
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Starr ML, Sparks RP, Arango AS, Hurst LR, Zhao Z, Lihan M, Jenkins JL, Tajkhorshid E, Fratti RA. Phosphatidic acid induces conformational changes in Sec18 protomers that prevent SNARE priming. J Biol Chem 2019; 294:3100-3116. [PMID: 30617180 PMCID: PMC6398130 DOI: 10.1074/jbc.ra118.006552] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2018] [Revised: 12/31/2018] [Indexed: 11/06/2022] Open
Abstract
Eukaryotic cell homeostasis requires transfer of cellular components among organelles and relies on membrane fusion catalyzed by SNARE proteins. Inactive SNARE bundles are reactivated by hexameric N-ethylmaleimide-sensitive factor, vesicle-fusing ATPase (Sec18/NSF)-driven disassembly that enables a new round of membrane fusion. We previously found that phosphatidic acid (PA) binds Sec18 and thereby sequesters it from SNAREs and that PA dephosphorylation dissociates Sec18 from the membrane, allowing it to engage SNARE complexes. We now report that PA also induces conformational changes in Sec18 protomers and that hexameric Sec18 cannot bind PA membranes. Molecular dynamics (MD) analyses revealed that the D1 and D2 domains of Sec18 contain PA-binding sites and that the residues needed for PA binding are masked in hexameric Sec18. Importantly, these simulations also disclosed that a major conformational change occurs in the linker region between the D1 and D2 domains, which is distinct from the conformational changes that occur in hexameric Sec18 during SNARE priming. Together, these findings indicate that PA regulates Sec18 function by altering its architecture and stabilizing membrane-bound Sec18 protomers.
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Affiliation(s)
- Matthew L Starr
- From the Department of Biochemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801
| | - Robert P Sparks
- From the Department of Biochemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801
| | - Andres S Arango
- the Center for Biophysics and Quantitative Biology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801
| | - Logan R Hurst
- From the Department of Biochemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801
| | - Zhiyu Zhao
- the Center for Biophysics and Quantitative Biology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801
| | - Muyun Lihan
- the Center for Biophysics and Quantitative Biology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801
| | - Jermaine L Jenkins
- the Department of Pathology and Laboratory Medicine, University of Rochester Medical Center, Rochester, New York 14642
| | - Emad Tajkhorshid
- From the Department of Biochemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801
- the Center for Biophysics and Quantitative Biology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801
- the Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, and
| | - Rutilio A Fratti
- From the Department of Biochemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801,
- the Center for Biophysics and Quantitative Biology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801
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38
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Fantini J, Epand RM, Barrantes FJ. Cholesterol-Recognition Motifs in Membrane Proteins. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2019; 1135:3-25. [PMID: 31098808 DOI: 10.1007/978-3-030-14265-0_1] [Citation(s) in RCA: 50] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
The impact of cholesterol on the structure and function of membrane proteins was recognized several decades ago, but the molecular mechanisms underlying these effects have remained elusive. There appear to be multiple mechanisms by which cholesterol interacts with proteins. A complete understanding of cholesterol-sensing motifs is still undergoing refinement. Initially, cholesterol was thought to exert only non-specific effects on membrane fluidity. It was later shown that this lipid could specifically interact with membrane proteins and affect both their structure and function. In this article, we have summarized and critically analyzed our evolving understanding of the affinity, specificity and stereoselectivity of the interactions of cholesterol with membrane proteins. We review the different computational approaches that are currently used to identify cholesterol binding sites in membrane proteins and the biochemical logic that governs each type of site, including CRAC, CARC, SSD and amphipathic helix motifs. There are physiological implications of these cholesterol-recognition motifs for G-protein coupled receptors (GPCR) and ion channels, in membrane trafficking and membrane fusion (SNARE) proteins. There are also pathological implications of cholesterol binding to proteins involved in neurological disorders (Alzheimer, Parkinson, Creutzfeldt-Jakob) and HIV fusion. In each case, our discussion is focused on the key molecular aspects of the cholesterol and amino acid motifs in membrane-embedded regions of membrane proteins that define the physiologically relevant crosstalk between the two. Our understanding of the factors that determine if these motifs are functional in cholesterol binding will allow us enhanced predictive capabilities.
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Affiliation(s)
- Jacques Fantini
- INSERM UMR_S 1072, Marseille, France. .,Aix-Marseille Université, Marseille, France.
| | - Richard M Epand
- Department of Biochemistry and Biomedical Sciences, McMaster University, Health Sciences Centre, Hamilton, ON, Canada
| | - Francisco J Barrantes
- Laboratory of Molecular Neurobiology, Biomedical Research Institute (BIOMED), UCA-CONICET, Buenos Aires, Argentina
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39
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Krishna A, Sengupta D. Interplay between Membrane Curvature and Cholesterol: Role of Palmitoylated Caveolin-1. Biophys J 2018; 116:69-78. [PMID: 30579563 DOI: 10.1016/j.bpj.2018.11.3127] [Citation(s) in RCA: 50] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2018] [Revised: 10/14/2018] [Accepted: 11/01/2018] [Indexed: 01/07/2023] Open
Abstract
Caveolin-1 (cav-1) is an important player in cell signaling and endocytosis that has been shown to colocalize with cholesterol-rich membrane domains. Experimental studies with varying cav-1 constructs have suggested that it can induce both cholesterol clustering and membrane curvature. Here, we probe the molecular origin of membrane curvature and cholesterol clustering by cav-1 by using coarse-grain molecular dynamics simulations. We have performed a series of simulations of a functionally important cav-1 construct, comprising the membrane-interacting domains and a C-terminal palmitoyl tail. Our results suggest that cav-1 is able to induce cholesterol clustering in the membrane leaflet to which it is bound as well as the opposing leaflet. A positive membrane curvature is observed upon cav-1 binding in cholesterol-containing bilayers. Interestingly, we observe an interplay between cholesterol clustering and membrane curvature such that cav-1 is able to induce higher membrane curvature in cholesterol-rich membranes. The role of the cav-1 palmitoyl tail is less clear and appears to increase the membrane contacts. Further, we address the importance of the secondary structure of cav-1 domains and show that it could play an important role in membrane curvature and cholesterol clustering. Our work is an important step toward a molecular picture of caveolae and vesicular endocytosis.
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Affiliation(s)
- Anjali Krishna
- CSIR-National Chemical Laboratory, Pune, Maharashtra, India
| | - Durba Sengupta
- CSIR-National Chemical Laboratory, Pune, Maharashtra, India.
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40
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Allolio C, Magarkar A, Jurkiewicz P, Baxová K, Javanainen M, Mason PE, Šachl R, Cebecauer M, Hof M, Horinek D, Heinz V, Rachel R, Ziegler CM, Schröfel A, Jungwirth P. Arginine-rich cell-penetrating peptides induce membrane multilamellarity and subsequently enter via formation of a fusion pore. Proc Natl Acad Sci U S A 2018. [PMID: 30397112 DOI: 10.1073/pnas.1811520115/suppl_file/pnas.1811520115.sm01.mp4] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/19/2023] Open
Abstract
Arginine-rich cell-penetrating peptides do not enter cells by directly passing through a lipid membrane; they instead passively enter vesicles and live cells by inducing membrane multilamellarity and fusion. The molecular picture of this penetration mode, which differs qualitatively from the previously proposed direct mechanism, is provided by molecular dynamics simulations. The kinetics of vesicle agglomeration and fusion by an iconic cell-penetrating peptide-nonaarginine-are documented via real-time fluorescence techniques, while the induction of multilamellar phases in vesicles and live cells is demonstrated by a combination of electron and fluorescence microscopies. This concert of experiments and simulations reveals that the identified passive cell penetration mechanism bears analogy to vesicle fusion induced by calcium ions, indicating that the two processes may share a common mechanistic origin.
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Affiliation(s)
- Christoph Allolio
- Institute of Organic Chemistry and Biochemistry, Czech Academy of Sciences, CZ-166 10 Prague 6, Czech Republic
- Institute of Physical and Theoretical Chemistry, University of Regensburg, D-93040 Regensburg, Germany
- Fritz Haber Research Center, The Hebrew University of Jerusalem, Jerusalem 9190401, Israel
- Department of Chemistry, The Hebrew University of Jerusalem, Jerusalem 9190401, Israel
| | - Aniket Magarkar
- Institute of Organic Chemistry and Biochemistry, Czech Academy of Sciences, CZ-166 10 Prague 6, Czech Republic
- Faculty of Pharmacy, University of Helsinki, Helsinki 00014, Finland
| | - Piotr Jurkiewicz
- J. Heyrovský Institute of Physical Chemistry, Czech Academy of Sciences, 182 23 Prague 8, Czech Republic
| | - Katarína Baxová
- Institute of Organic Chemistry and Biochemistry, Czech Academy of Sciences, CZ-166 10 Prague 6, Czech Republic
| | - Matti Javanainen
- Institute of Organic Chemistry and Biochemistry, Czech Academy of Sciences, CZ-166 10 Prague 6, Czech Republic
| | - Philip E Mason
- Institute of Organic Chemistry and Biochemistry, Czech Academy of Sciences, CZ-166 10 Prague 6, Czech Republic
| | - Radek Šachl
- J. Heyrovský Institute of Physical Chemistry, Czech Academy of Sciences, 182 23 Prague 8, Czech Republic
| | - Marek Cebecauer
- J. Heyrovský Institute of Physical Chemistry, Czech Academy of Sciences, 182 23 Prague 8, Czech Republic
| | - Martin Hof
- J. Heyrovský Institute of Physical Chemistry, Czech Academy of Sciences, 182 23 Prague 8, Czech Republic
| | - Dominik Horinek
- Institute of Physical and Theoretical Chemistry, University of Regensburg, D-93040 Regensburg, Germany
| | - Veronika Heinz
- Institute of Biophysics and Biophysical Chemistry, University of Regensburg, D-93040 Regensburg, Germany
| | - Reinhard Rachel
- Microbiology and Archaea Centre, University of Regensburg, D-93040 Regensburg, Germany
| | - Christine M Ziegler
- Institute of Biophysics and Biophysical Chemistry, University of Regensburg, D-93040 Regensburg, Germany
- Institute of Biophysics and Biophysical Chemistry, University of Regensburg, D-93040 Regensburg, Germany
| | - Adam Schröfel
- Imaging Methods Core Facility at Biocev, Faculty of Sciences, Charles University, 242 50 Vestec, Czech Republic
| | - Pavel Jungwirth
- Institute of Organic Chemistry and Biochemistry, Czech Academy of Sciences, CZ-166 10 Prague 6, Czech Republic;
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41
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Allolio C, Magarkar A, Jurkiewicz P, Baxová K, Javanainen M, Mason PE, Šachl R, Cebecauer M, Hof M, Horinek D, Heinz V, Rachel R, Ziegler CM, Schröfel A, Jungwirth P. Arginine-rich cell-penetrating peptides induce membrane multilamellarity and subsequently enter via formation of a fusion pore. Proc Natl Acad Sci U S A 2018; 115:11923-11928. [PMID: 30397112 PMCID: PMC6255155 DOI: 10.1073/pnas.1811520115] [Citation(s) in RCA: 141] [Impact Index Per Article: 23.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
Abstract
Arginine-rich cell-penetrating peptides do not enter cells by directly passing through a lipid membrane; they instead passively enter vesicles and live cells by inducing membrane multilamellarity and fusion. The molecular picture of this penetration mode, which differs qualitatively from the previously proposed direct mechanism, is provided by molecular dynamics simulations. The kinetics of vesicle agglomeration and fusion by an iconic cell-penetrating peptide-nonaarginine-are documented via real-time fluorescence techniques, while the induction of multilamellar phases in vesicles and live cells is demonstrated by a combination of electron and fluorescence microscopies. This concert of experiments and simulations reveals that the identified passive cell penetration mechanism bears analogy to vesicle fusion induced by calcium ions, indicating that the two processes may share a common mechanistic origin.
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Affiliation(s)
- Christoph Allolio
- Institute of Organic Chemistry and Biochemistry, Czech Academy of Sciences, CZ-166 10 Prague 6, Czech Republic
- Institute of Physical and Theoretical Chemistry, University of Regensburg, D-93040 Regensburg, Germany
- Fritz Haber Research Center, The Hebrew University of Jerusalem, Jerusalem 9190401, Israel
- Department of Chemistry, The Hebrew University of Jerusalem, Jerusalem 9190401, Israel
| | - Aniket Magarkar
- Institute of Organic Chemistry and Biochemistry, Czech Academy of Sciences, CZ-166 10 Prague 6, Czech Republic
- Faculty of Pharmacy, University of Helsinki, Helsinki 00014, Finland
| | - Piotr Jurkiewicz
- J. Heyrovský Institute of Physical Chemistry, Czech Academy of Sciences, 182 23 Prague 8, Czech Republic
| | - Katarína Baxová
- Institute of Organic Chemistry and Biochemistry, Czech Academy of Sciences, CZ-166 10 Prague 6, Czech Republic
| | - Matti Javanainen
- Institute of Organic Chemistry and Biochemistry, Czech Academy of Sciences, CZ-166 10 Prague 6, Czech Republic
| | - Philip E Mason
- Institute of Organic Chemistry and Biochemistry, Czech Academy of Sciences, CZ-166 10 Prague 6, Czech Republic
| | - Radek Šachl
- J. Heyrovský Institute of Physical Chemistry, Czech Academy of Sciences, 182 23 Prague 8, Czech Republic
| | - Marek Cebecauer
- J. Heyrovský Institute of Physical Chemistry, Czech Academy of Sciences, 182 23 Prague 8, Czech Republic
| | - Martin Hof
- J. Heyrovský Institute of Physical Chemistry, Czech Academy of Sciences, 182 23 Prague 8, Czech Republic
| | - Dominik Horinek
- Institute of Physical and Theoretical Chemistry, University of Regensburg, D-93040 Regensburg, Germany
| | - Veronika Heinz
- Institute of Biophysics and Biophysical Chemistry, University of Regensburg, D-93040 Regensburg, Germany
| | - Reinhard Rachel
- Microbiology and Archaea Centre, University of Regensburg, D-93040 Regensburg, Germany
| | - Christine M Ziegler
- Institute of Biophysics and Biophysical Chemistry, University of Regensburg, D-93040 Regensburg, Germany
- Institute of Biophysics and Biophysical Chemistry, University of Regensburg, D-93040 Regensburg, Germany
| | - Adam Schröfel
- Imaging Methods Core Facility at Biocev, Faculty of Sciences, Charles University, 242 50 Vestec, Czech Republic
| | - Pavel Jungwirth
- Institute of Organic Chemistry and Biochemistry, Czech Academy of Sciences, CZ-166 10 Prague 6, Czech Republic;
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42
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Abbineni PS, Coorssen JR. Sphingolipids modulate docking, Ca 2+ sensitivity and membrane fusion of native cortical vesicles. Int J Biochem Cell Biol 2018; 104:43-54. [PMID: 30195064 DOI: 10.1016/j.biocel.2018.09.001] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2018] [Revised: 08/31/2018] [Accepted: 09/01/2018] [Indexed: 12/16/2022]
Abstract
Docking, priming, and membrane fusion of secretory vesicles (i.e. regulated exocytosis) requires lipids and proteins. Sphingolipids, in particular, sphingosine and sphingosine-1-phosphate, have been implicated in the modulation of exocytosis. However, the specific exocytotic steps that sphingolipids modulate and the enzymes that regulate sphingolipid concentrations on native secretory vesicle membranes remain unknown. Here we use tightly coupled functional and molecular analyses of fusion-ready cell surface complexes and cortical vesicles isolated from oocytes to assess the role of sphingolipids in the late, Ca2+-triggered steps of exocytosis. The molecular changes resulting from treatments with sphingolipid modifying compounds coupled with immunoblotting analysis revealed the presence of sphingosine kinase on native vesicles; the presence of a sphingosine-1-phosphate phosphatase is also indicated. Changes in sphingolipid concentrations on vesicles altered their docking/priming, Ca2+-sensitivity, and ability to fuse, indicating that sphingolipid concentrations are tightly regulated and maintained at optimal levels and ratios to ensure efficient exocytosis.
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Affiliation(s)
- Prabhodh S Abbineni
- Department of Molecular Physiology, and the WSU Molecular Medicine Research Group, School of Medicine, Western Sydney University, Campbelltown, NSW, 2560, Australia
| | - Jens R Coorssen
- Department of Health Sciences, Faculty of Applied Health Sciences, Department of Biology, Faculty of Mathematics and Science, Brock University, St. Catharines, Ontario, Canada.
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43
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Yu Q, Othman S, Dasgupta S, Auth T, Gompper G. Nanoparticle wrapping at small non-spherical vesicles: curvatures at play. NANOSCALE 2018; 10:6445-6458. [PMID: 29565057 DOI: 10.1039/c7nr08856f] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Nanoparticles in biological systems encounter lipid-bilayer membranes as barriers. They interact with plasma membranes, membranous organelles, such as the endoplasmic reticulum and the Golgi apparatus, the nucleus, and intracellular and extracellular vesicles, such as autophagosomes, lysosomes, and exosomes. Extracellular vesicles have recently attracted particular attention, as they are involved in the transmission of biological signals and as regulators for biological processes. For example, exosomes, small vesicles containing proteins, mRNA, and miRNA, that are released by cells into the extracellular environment, have been suggested to participate in tumor metastasis. Furthermore, vesicles can be applied as targeted-drug-delivery systems. We systematically characterize wrapping of spherical nanoparticles that enter and exit vesicles, depending on particle size, vesicle size, vesicle reduced volume, and membrane spontaneous curvature. We predict the complex wrapping behavior, in particular for large particle-to-vesicle size ratios, where the shape changes of the free membrane contribute significantly to the deformation energy and where nanoparticle wrapping transitions and vesicle shape transitions are coupled. Partial-wrapped membrane-bound particles impose boundary conditions on the membrane that stabilise oblates and stomatocytes for particle entry, and prolates and stomatocytes for particle exit. Our results suggest that nanoparticles may stimulate autophagocytic engulfment, which would facilitate transport of the nanoparticles into lysosomes and would lead to subsequent degradation of nanoparticle-attached proteins.
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Affiliation(s)
- Qingfen Yu
- Theoretical Soft Matter and Biophysics, Institute of Complex Systems and Institute for Advanced Simulation, Forschungszentrum Jülich, D-52425 Jülich, Germany.
| | - Sameh Othman
- Theoretical Soft Matter and Biophysics, Institute of Complex Systems and Institute for Advanced Simulation, Forschungszentrum Jülich, D-52425 Jülich, Germany.
| | - Sabyasachi Dasgupta
- Theoretical Soft Matter and Biophysics, Institute of Complex Systems and Institute for Advanced Simulation, Forschungszentrum Jülich, D-52425 Jülich, Germany. and Mechanobiology Institute, National University of Singapore, 11899 Singapore
| | - Thorsten Auth
- Theoretical Soft Matter and Biophysics, Institute of Complex Systems and Institute for Advanced Simulation, Forschungszentrum Jülich, D-52425 Jülich, Germany.
| | - Gerhard Gompper
- Theoretical Soft Matter and Biophysics, Institute of Complex Systems and Institute for Advanced Simulation, Forschungszentrum Jülich, D-52425 Jülich, Germany.
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44
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Kreft M, Jorgačevski J, Stenovec M, Zorec R. Ångstrom-size exocytotic fusion pore: Implications for pituitary hormone secretion. Mol Cell Endocrinol 2018; 463:65-71. [PMID: 28457949 DOI: 10.1016/j.mce.2017.04.023] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/09/2017] [Revised: 04/26/2017] [Accepted: 04/26/2017] [Indexed: 02/08/2023]
Abstract
In the past, vesicle content release was thought to occur immediately and completely after triggering of exocytosis. However, vesicles may merge with the plasma membrane to form an Ångstrom diameter fusion pore that prevents the exit of secretions from the vesicle lumen. The advantage of such a narrow pore is to minimize the delay between the trigger and the release. Instead of stimulating a sequence of processes, leading to vesicle merger with the plasma membrane and a formation of a fusion pore, the stimulus only widens the pre-established fusion pore. The fusion pore may be stable and may exhibit repetitive opening of the vesicle lumen to the cell exterior accompanied by a content discharge. Such release of vesicle content is partial (subquantal), and depends on fusion pore open time, diameter and the diffusibility of the cargo. Such transient mode of fusion pore opening was not confirmed until the development of the membrane capacitance patch-clamp technique, which enables high-resolution measurement of changes in membrane surface area. It allows millisecond dwell-time measurements of fusion pores with subnanometer diameters. Currently, the soluble N-ethylmaleimide-sensitive factor-attachment protein receptor (SNARE) proteins are considered to be key entities in end-stage exocytosis, and the SNARE complex assembly/disassembly may regulate the fusion pore. Moreover, lipids or other membrane constituents with anisotropic (non-axisymmetric) geometry may also favour the establishment of stable narrow fusion pores, if positioned in the neck of the fusion pore.
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Affiliation(s)
- Marko Kreft
- Laboratory of Neuroendocrinology-Molecular Cell Physiology, Faculty of Medicine, University of Ljubljana, Zaloška 4, 1000 Ljubljana, Slovenia; Celica Biomedical, Tehnološki Park 24, 1000 Ljubljana, Slovenia; Department of Biology, Biotechnical Faculty, University of Ljubljana, Večna Pot 111, 1000 Ljubljana, Slovenia
| | - Jernej Jorgačevski
- Laboratory of Neuroendocrinology-Molecular Cell Physiology, Faculty of Medicine, University of Ljubljana, Zaloška 4, 1000 Ljubljana, Slovenia; Celica Biomedical, Tehnološki Park 24, 1000 Ljubljana, Slovenia
| | - Matjaž Stenovec
- Laboratory of Neuroendocrinology-Molecular Cell Physiology, Faculty of Medicine, University of Ljubljana, Zaloška 4, 1000 Ljubljana, Slovenia; Celica Biomedical, Tehnološki Park 24, 1000 Ljubljana, Slovenia
| | - Robert Zorec
- Laboratory of Neuroendocrinology-Molecular Cell Physiology, Faculty of Medicine, University of Ljubljana, Zaloška 4, 1000 Ljubljana, Slovenia; Celica Biomedical, Tehnološki Park 24, 1000 Ljubljana, Slovenia.
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45
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Abbineni PS, Coorssen JR. Application of High-Throughput Assays to Examine Phospho-Modulation of the Late Steps of Regulated Exocytosis. High Throughput 2017; 6:ht6040017. [PMID: 29479054 PMCID: PMC5748596 DOI: 10.3390/ht6040017] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2017] [Revised: 11/01/2017] [Accepted: 11/06/2017] [Indexed: 01/19/2023] Open
Abstract
Abstract: Regulated exocytosis enables a range of physiological functions including neurotransmission, and the late steps (i.e., docking, priming and Ca2+-triggered membrane fusion) are modulated by a highly conserved set of proteins and lipids. Many of the molecular components and biochemical interactions required have been identified; the precise mechanistic steps they modulate and the biochemical interactions that need to occur across steps are still the subject of intense investigation. Particularly, although the involvement of phosphorylation in modulating exocytosis has been intensively investigated over the past three decades, it is unclear which phosphorylation events are a conserved part of the fundamental fusion mechanism and/or serve as part of the physiological fusion machine (e.g., to modulate Ca2+ sensitivity). Here, the homotypic fusion of cortical vesicles was monitored by utilizing new high-throughput, cost-effective assays to assess the influence of 17 small molecule phospho-modulators on docking/priming, Ca2+ sensitivity and membrane fusion. Specific phosphatases and casein kinase 2 are implicated in modulating the Ca2+ sensitivity of fusion, whereas sphingosine kinase is implicated in modulating the ability of vesicles to fuse. These results indicate the presence of multiple kinases and phosphatases on the vesicles and critical phosphorylation sites on vesicle membrane proteins and lipids that directly influence late steps of regulated exocytosis.
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Affiliation(s)
- Prabhodh S Abbineni
- Department of Molecular Physiology, and the WSU Molecular Medicine Research Group, School of Medicine, Western Sydney University, Campbelltown, NSW 2560, Australia.
| | - Jens R Coorssen
- Faculty of Applied Health Sciences and Faculty of Mathematics and Science, Brock University, St. Catharines, ON L2S 3A1, Canada.
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46
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Kreutzberger AJB, Kiessling V, Liang B, Yang ST, Castle JD, Tamm LK. Asymmetric Phosphatidylethanolamine Distribution Controls Fusion Pore Lifetime and Probability. Biophys J 2017; 113:1912-1915. [PMID: 29037600 DOI: 10.1016/j.bpj.2017.09.014] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2017] [Revised: 09/11/2017] [Accepted: 09/13/2017] [Indexed: 01/18/2023] Open
Abstract
Little attention has been given to how the asymmetric lipid distribution of the plasma membrane might facilitate fusion pore formation during exocytosis. Phosphatidylethanolamine (PE), a cone-shaped phospholipid, is predominantly located in the inner leaflet of the plasma membrane and has been proposed to promote membrane deformation and stabilize fusion pores during exocytotic events. To explore this possibility, we modeled exocytosis using plasma membrane SNARE-containing planar-supported bilayers and purified neuroendocrine dense core vesicles (DCVs) as fusion partners, and we examined how different PE distributions between the two leaflets of the supported bilayers affected SNARE-mediated fusion. Using total internal reflection fluorescence microscopy, the fusion of single DCVs with the planar-supported bilayer was monitored by observing DCV-associated neuropeptide Y tagged with a fluorescent protein. The time-dependent line shape of the fluorescent signal enables detection of DCV docking, fusion-pore opening, and vesicle collapse into the planar membrane. Four different distributions of PE in the planar bilayer mimicking the plasma membrane were examined: exclusively in the leaflet facing the DCVs; exclusively in the opposite leaflet; equally distributed in both leaflets; and absent from both leaflets. With PE in the leaflet facing the DCVs, overall fusion was most efficient and the extended fusion pore lifetime (0.7 s) enabled notable detection of content release preceding vesicle collapse. All other PE distributions decreased fusion efficiency, altered pore lifetime, and reduced content release. With PE exclusively in the opposite leaflet, resolution of pore opening and content release was lost.
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Affiliation(s)
- Alex J B Kreutzberger
- Department of Molecular Physiology and Biological Physics, Center for Cell and Membrane Physiology at the University of Virginia, Charlottesville, Virginia
| | - Volker Kiessling
- Department of Molecular Physiology and Biological Physics, Center for Cell and Membrane Physiology at the University of Virginia, Charlottesville, Virginia
| | - Binyong Liang
- Department of Molecular Physiology and Biological Physics, Center for Cell and Membrane Physiology at the University of Virginia, Charlottesville, Virginia
| | - Sung-Tae Yang
- Department of Molecular Physiology and Biological Physics, Center for Cell and Membrane Physiology at the University of Virginia, Charlottesville, Virginia
| | - J David Castle
- Department of Cell Biology, Center for Cell and Membrane Physiology at the University of Virginia, Charlottesville, Virginia
| | - Lukas K Tamm
- Department of Molecular Physiology and Biological Physics, Center for Cell and Membrane Physiology at the University of Virginia, Charlottesville, Virginia.
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47
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Abstract
Regulated exocytosis can be split into a sequence of steps ending with the formation and the dilation of a fusion pore, a neck-like connection between the vesicle and the plasma membrane. Each of these steps is precisely controlled to achieve the optimal spatial and temporal profile of the release of signalling molecules. At the level of the fusion pore, tuning of the exocytosis can be achieved by preventing its formation, by stabilizing the unproductive narrow fusion pore, by altering the speed of fusion pore expansion and by completely closing the fusion pore. The molecular structure and dynamics of fusion pores have become a major focus of cell research, especially as a promising target for therapeutic strategies. Electrophysiological, optical and electrochemical methods have been used extensively to illuminate how cells regulate secretion at the level of a single fusion pore. Here, we describe recent advances in the structure and mechanisms of the initial fusion pore formation and the progress in therapeutic strategies with the focus on exocytosis.
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48
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Miner GE, Starr ML, Hurst LR, Fratti RA. Deleting the DAG kinase Dgk1 augments yeast vacuole fusion through increased Ypt7 activity and altered membrane fluidity. Traffic 2017; 18:315-329. [PMID: 28276191 DOI: 10.1111/tra.12479] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2016] [Revised: 03/06/2017] [Accepted: 03/06/2017] [Indexed: 12/20/2022]
Abstract
Diacylglycerol (DAG) is a fusogenic lipid that can be produced through phospholipase C activity on phosphatidylinositol 4,5-bisphosphate [PI(4,5)P2 ], or through phosphatidic acid (PA) phosphatase activity. The fusion of Saccharomyces cerevisiae vacuoles requires DAG, PA and PI(4,5)P2 , and the production of these lipids is thought to provide temporally specific stoichiometries that are critical for each stage of fusion. Furthermore, DAG and PA can be interconverted by the DAG kinase Dgk1 and the PA phosphatase Pah1. Previously we found that pah1 Δ vacuoles were fragmented, blocked in SNARE priming and showed arrested endosomal maturation. In other pathways the effects of deleting PAH1 can be compensated for by additionally deleting DGK1 ; however, deleting both genes did not rescue the pah1 Δ vacuolar defects. Deleting DGK1 alone caused a marked increase in vacuole fusion that was attributed to elevated DAG levels. This was accompanied by a gain in resistance to the inhibitory effects of PA as well as inhibitors of Ypt7 activity. Together these data show that Dgk1 function can act as a negative regulator of vacuole fusion through the production of PA at the cost of depleting DAG and reducing Ypt7 activity.
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Affiliation(s)
- Gregory E Miner
- Department of Biochemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois
| | - Matthew L Starr
- Department of Biochemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois
| | - Logan R Hurst
- Department of Biochemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois
| | - Rutilio A Fratti
- Department of Biochemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois.,Center for Biophysics and Quantitative Biology, University of Illinois at Urbana-Champaign, Urbana, Illinois
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49
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Ormerod KG, LePine OK, Abbineni PS, Bridgeman JM, Coorssen JR, Mercier AJ, Tattersall GJ. Drosophila development, physiology, behavior, and lifespan are influenced by altered dietary composition. Fly (Austin) 2017; 11:153-170. [PMID: 28277941 DOI: 10.1080/19336934.2017.1304331] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022] Open
Abstract
Diet profoundly influences the behavior of animals across many phyla. Despite this, most laboratories using model organisms, such as Drosophila, use multiple, different, commercial or custom-made media for rearing their animals. In addition to measuring growth, fecundity and longevity, we used several behavioral and physiological assays to determine if and how altering food media influence wild-type (Canton S) Drosophila melanogaster, at larval, pupal, and adult stages. Comparing 2 commonly used commercial food media we observed several key developmental and morphological differences. Third-instar larvae and pupae developmental timing, body weight and size, and even lifespan significantly differed between the 2 diets, and some of these differences persisted into adulthood. Diet was also found to produce significantly different thermal preference, locomotory capacity for geotaxis, feeding rates, and lower muscle response to hormonal stimulation. There were no differences, however, in adult thermal preferences, in the number or viability of eggs laid, or in olfactory learning and memory between the diets. We characterized the composition of the 2 diets and found particularly significant differences in cholesterol and (phospho)lipids between them. Notably, diacylglycerol (DAG) concentrations vary substantially between the 2 diets, and may contribute to key phenotypic differences, including lifespan. Overall, the data confirm that 2 different diets can profoundly influence the behavior, physiology, morphology and development of wild-type Drosophila, with greater behavioral and physiologic differences occurring during the larval stages.
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Affiliation(s)
- Kiel G Ormerod
- a Department of Biological Sciences , Brock University , St. Catharines , ON , Canada
| | - Olivia K LePine
- a Department of Biological Sciences , Brock University , St. Catharines , ON , Canada
| | - Prabhodh S Abbineni
- b Department of Molecular Physiology, and the WSU Molecular Medicine Research Group, School of Medicine , Western Sydney University , Penrith , New South Wales , Australia
| | - Justin M Bridgeman
- a Department of Biological Sciences , Brock University , St. Catharines , ON , Canada
| | - Jens R Coorssen
- a Department of Biological Sciences , Brock University , St. Catharines , ON , Canada.,b Department of Molecular Physiology, and the WSU Molecular Medicine Research Group, School of Medicine , Western Sydney University , Penrith , New South Wales , Australia.,c Faculty of Graduate Studies, Department of Health Sciences , Brock University , St. Catharines , ON , Canada
| | - A Joffre Mercier
- a Department of Biological Sciences , Brock University , St. Catharines , ON , Canada
| | - Glenn J Tattersall
- a Department of Biological Sciences , Brock University , St. Catharines , ON , Canada
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50
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Dabral D, Coorssen JR. Phospholipase A 2: Potential roles in native membrane fusion. Int J Biochem Cell Biol 2017; 85:1-5. [PMID: 28131878 DOI: 10.1016/j.biocel.2017.01.011] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2016] [Revised: 12/29/2016] [Accepted: 01/22/2017] [Indexed: 12/22/2022]
Abstract
Membrane fusion is a fundamental molecular mechanism by which two apposed membrane bilayers coalesce in rapid, transient steps that enable the successive merging of the outer and inner leaflets allowing lipid intermixing and subsequent mixing of the two previously separate compartments. The actual membrane merger mechanism - fusion, by definition - is conceptualized to be protein- or lipid-centric. According to the widely vetted stalk-pore hypothesis, membrane fusion proceeds via high curvature lipid intermediates. By cleaving membrane phospholipids at the sn-2 position, Phospholipase A2 generates metabolites that exert spontaneous curvature stress (both negative and positive) on the membrane, thus influencing local membrane bending by altering the packing and conformation of lipids and proteins, respectively. Such changes could potentially modulate priming and attachment/docking steps that precede fusion, as well as the membrane merger steps per se.
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Affiliation(s)
- Deepti Dabral
- Molecular Physiology, and Molecular Medicine Research Group, School of Medicine, Western Sydney University, Campbelltown Campus, Penrith, NSW 2751, Australia
| | - Jens R Coorssen
- Faculty of Graduate Studies and the Departments of Health Sciences and Biological Sciences, Brock University,St. Catharines, ON L2S 3A1, Canada.
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