1
|
Duan M, Gao G, Lin A, Mackey EJ, Banfield DK, Merz AJ. SM protein Sly1 and a SNARE Habc domain promote membrane fusion through multiple mechanisms. J Cell Biol 2024; 223:e202001034. [PMID: 38478017 PMCID: PMC10943372 DOI: 10.1083/jcb.202001034] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2020] [Revised: 12/20/2023] [Accepted: 02/22/2024] [Indexed: 03/17/2024] Open
Abstract
SM proteins including Sly1 are essential cofactors of SNARE-mediated membrane fusion. Using SNARE and Sly1 mutants and chemically defined in vitro assays, we separate and assess proposed mechanisms through which Sly1 augments fusion: (i) opening the closed conformation of the Qa-SNARE Sed5; (ii) close-range tethering of vesicles to target organelles, mediated by the Sly1-specific regulatory loop; and (iii) nucleation of productive trans-SNARE complexes. We show that all three mechanisms are important and operate in parallel, and that close-range tethering promotes trans-complex assembly when cis-SNARE assembly is a competing process. Further, we demonstrate that the autoinhibitory N-terminal Habc domain of Sed5 has at least two positive activities: it is needed for correct Sed5 localization, and it directly promotes Sly1-dependent fusion. "Split Sed5," with Habc presented solely as a soluble fragment, can function both in vitro and in vivo. Habc appears to facilitate events leading to lipid mixing rather than promoting opening or stability of the fusion pore.
Collapse
Affiliation(s)
- Mengtong Duan
- Department of Biochemistry, University of Washington, Seattle, WA, USA
| | - Guanbin Gao
- The Division of Life Science, The Hong Kong University of Science and Technology, Kowloon, Hong Kong
| | - Ariel Lin
- Department of Biochemistry, University of Washington, Seattle, WA, USA
| | - Emma J. Mackey
- Department of Biochemistry, University of Washington, Seattle, WA, USA
| | - David K. Banfield
- The Division of Life Science, The Hong Kong University of Science and Technology, Kowloon, Hong Kong
| | - Alexey J. Merz
- Department of Biochemistry, University of Washington, Seattle, WA, USA
| |
Collapse
|
2
|
Zhao H, Wang W, Lin T, Gong L. Serum Metabolomics of Benign Essential Blepharospasm Using Liquid Chromatography and Orbitrap Mass Spectrometry. OXIDATIVE MEDICINE AND CELLULAR LONGEVITY 2022; 2022:6876327. [PMID: 36452462 PMCID: PMC9704060 DOI: 10.1155/2022/6876327] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 07/17/2022] [Revised: 09/04/2022] [Accepted: 09/24/2022] [Indexed: 01/19/2024]
Abstract
Background Benign essential blepharospasm (BEB) is a form of focal dystonia that causes excessive involuntary spasms of the eyelids. Currently, the pathogenesis of BEB remains unclear. This study is aimed at investigating the serum metabolites profiles in patients with BEB and healthy control and to identify the mechanism and biomarkers of this disease. Methods 30 patients with BEB and 33 healthy controls were recruited for this study. We conducted the quantitative and nontargeted metabolomics analysis of the serum samples from 63 subjects by using liquid chromatography and Orbitrap mass spectrometry (LC-Orbitrap MS). Multivariate statistical analysis was performed to detect and identify different metabolites between the two groups. The Kyoto Encyclopedia of Genes and Genomes (KEGG) and receiver operating characteristic (ROC) curve analysis of the altered metabolites were performed. Results A total of 134 metabolites were found and identified. The metabolites belonged to several metabolic pathways including phenylalanine metabolism, phenylalanine, tyrosine and tryptophan biosynthesis, arginine biosynthesis, linoleic acid metabolism, tryptophan metabolism, aminoacyl-tRNA biosynthesis, sphingolipid metabolism, glycosphingolipid biosynthesis, leucine and isoleucine biosynthesis, and vitamin B6 metabolism. Eight metabolites were identified as the potential biomarkers. Conclusions These results demonstrated that serum metabolic profiling of BEB patients was significantly different from healthy controls based on LC-Orbitrap MS. Besides, metabolomics might provide useful information for a better understanding of BEB.
Collapse
Affiliation(s)
- Han Zhao
- Department of Ophthalmology, Eye, Ear, Nose, and Throat Hospital of Fudan University, Shanghai 200000, China
- Laboratory of Myopia, NHC Key Laboratory of Myopia (Fudan University), Chinese Academy of Medical Sciences, Fudan University, Shanghai 200000, China
- Shanghai Key Laboratory of Visual Impairment and Restoration, Fudan University, Shanghai 200000, China
| | - Wushuang Wang
- Department of Ophthalmology, Eye, Ear, Nose, and Throat Hospital of Fudan University, Shanghai 200000, China
- Laboratory of Myopia, NHC Key Laboratory of Myopia (Fudan University), Chinese Academy of Medical Sciences, Fudan University, Shanghai 200000, China
- Shanghai Key Laboratory of Visual Impairment and Restoration, Fudan University, Shanghai 200000, China
| | - Tong Lin
- Department of Ophthalmology, Eye, Ear, Nose, and Throat Hospital of Fudan University, Shanghai 200000, China
- Laboratory of Myopia, NHC Key Laboratory of Myopia (Fudan University), Chinese Academy of Medical Sciences, Fudan University, Shanghai 200000, China
- Shanghai Key Laboratory of Visual Impairment and Restoration, Fudan University, Shanghai 200000, China
| | - Lan Gong
- Department of Ophthalmology, Eye, Ear, Nose, and Throat Hospital of Fudan University, Shanghai 200000, China
- Laboratory of Myopia, NHC Key Laboratory of Myopia (Fudan University), Chinese Academy of Medical Sciences, Fudan University, Shanghai 200000, China
- Shanghai Key Laboratory of Visual Impairment and Restoration, Fudan University, Shanghai 200000, China
| |
Collapse
|
3
|
Piao J, Yuan W, Dong Y. Recent Progress of DNA Nanostructures on Amphiphilic Membranes. Macromol Biosci 2021; 21:e2000440. [PMID: 33759366 DOI: 10.1002/mabi.202000440] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2020] [Revised: 02/24/2021] [Indexed: 11/11/2022]
Abstract
Employing DNA nanostructures mimicking membrane proteins on artificial amphiphilic membranes have been widely developed to understand the structures and functions of the natural membrane systems. In this review, the recent developments in artificial systems constructed by amphiphilic membranes and DNA nanostructures are summarized. First, the preparations and properties of the amphipathic bilayer models are introduced. Second, the interactions are discussed between the membrane and the DNA nanostructures, as well as their coassembly behaviors. Next, the alternative systems related to membrane protein-mediated signal transmission, selective distribution, transmembrane channels, and membrane fusion are also introduced. Moreover, the constructions of membrane skeleton protein-mimicking DNA nanostructures are also highlighted.
Collapse
Affiliation(s)
- Jiafang Piao
- CAS Key Laboratory of Colloid, Interface and Chemical Thermodynamics, Chinese Academy of Sciences, Institute of Chemistry, Beijing, 100190, China.,Beijing National Laboratory for Molecular Sciences, Chinese Academy of Sciences, Institute of Chemistry, Beijing, 100190, China
| | - Wei Yuan
- CAS Key Laboratory of Colloid, Interface and Chemical Thermodynamics, Chinese Academy of Sciences, Institute of Chemistry, Beijing, 100190, China.,Beijing National Laboratory for Molecular Sciences, Chinese Academy of Sciences, Institute of Chemistry, Beijing, 100190, China
| | - Yuanchen Dong
- CAS Key Laboratory of Colloid, Interface and Chemical Thermodynamics, Chinese Academy of Sciences, Institute of Chemistry, Beijing, 100190, China.,Beijing National Laboratory for Molecular Sciences, Chinese Academy of Sciences, Institute of Chemistry, Beijing, 100190, China
| |
Collapse
|
4
|
Scott‐Hewitt N, Perrucci F, Morini R, Erreni M, Mahoney M, Witkowska A, Carey A, Faggiani E, Schuetz LT, Mason S, Tamborini M, Bizzotto M, Passoni L, Filipello F, Jahn R, Stevens B, Matteoli M. Local externalization of phosphatidylserine mediates developmental synaptic pruning by microglia. EMBO J 2020; 39:e105380. [PMID: 32657463 PMCID: PMC7429741 DOI: 10.15252/embj.2020105380] [Citation(s) in RCA: 196] [Impact Index Per Article: 49.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2020] [Revised: 06/05/2020] [Accepted: 06/15/2020] [Indexed: 12/21/2022] Open
Abstract
Neuronal circuit assembly requires the fine balance between synapse formation and elimination. Microglia, through the elimination of supernumerary synapses, have an established role in this process. While the microglial receptor TREM2 and the soluble complement proteins C1q and C3 are recognized as key players, the neuronal molecular components that specify synapses to be eliminated are still undefined. Here, we show that exposed phosphatidylserine (PS) represents a neuronal "eat-me" signal involved in microglial-mediated pruning. In hippocampal neuron and microglia co-cultures, synapse elimination can be partially prevented by blocking accessibility of exposed PS using Annexin V or through microglial loss of TREM2. In vivo, PS exposure at both hippocampal and retinogeniculate synapses and engulfment of PS-labeled material by microglia occurs during established developmental periods of microglial-mediated synapse elimination. Mice deficient in C1q, which fail to properly refine retinogeniculate connections, have elevated presynaptic PS exposure and reduced PS engulfment by microglia. These data provide mechanistic insight into microglial-mediated synapse pruning and identify a novel role of developmentally regulated neuronal PS exposure that is common among developing brain structures.
Collapse
Affiliation(s)
- Nicole Scott‐Hewitt
- F.M. Kirby Center for NeurobiologyBoston Children's HospitalBostonMAUSA
- Stanley Center for Psychiatric ResearchThe Broad Institute of MIT and HarvardCambridgeMAUSA
| | - Fabio Perrucci
- Laboratory of Pharmacology and Brain PathologyNeurocenterHumanitas Clinical and Research Center ‐ IRCCSRozzano (MI)Italy
- Department of Biomedical SciencesHumanitas UniversityPieve Emanuele (MI)Italy
| | - Raffaella Morini
- Laboratory of Pharmacology and Brain PathologyNeurocenterHumanitas Clinical and Research Center ‐ IRCCSRozzano (MI)Italy
| | - Marco Erreni
- Unit of Advanced Optical MicroscopyHumanitas Clinical and Research Center ‐ IRCCSRozzano (MI)Italy
| | - Matthew Mahoney
- F.M. Kirby Center for NeurobiologyBoston Children's HospitalBostonMAUSA
| | - Agata Witkowska
- Laboratory of NeurobiologyMax Planck Institute for Biophysical ChemistryGöttingenGermany
- Department of Molecular Pharmacology and Cell BiologyLeibniz‐Forschungsinstitut für Molekulare Pharmakologie (FMP)BerlinGermany
| | - Alanna Carey
- F.M. Kirby Center for NeurobiologyBoston Children's HospitalBostonMAUSA
| | - Elisa Faggiani
- Laboratory of Pharmacology and Brain PathologyNeurocenterHumanitas Clinical and Research Center ‐ IRCCSRozzano (MI)Italy
| | | | - Sydney Mason
- F.M. Kirby Center for NeurobiologyBoston Children's HospitalBostonMAUSA
| | - Matteo Tamborini
- Laboratory of Pharmacology and Brain PathologyNeurocenterHumanitas Clinical and Research Center ‐ IRCCSRozzano (MI)Italy
| | - Matteo Bizzotto
- Department of Biomedical SciencesHumanitas UniversityPieve Emanuele (MI)Italy
| | - Lorena Passoni
- Laboratory of Pharmacology and Brain PathologyNeurocenterHumanitas Clinical and Research Center ‐ IRCCSRozzano (MI)Italy
| | - Fabia Filipello
- Laboratory of Pharmacology and Brain PathologyNeurocenterHumanitas Clinical and Research Center ‐ IRCCSRozzano (MI)Italy
- Department of Biomedical SciencesHumanitas UniversityPieve Emanuele (MI)Italy
- Present address:
Department of NeurologyWashington UniversitySt. LouisMOUSA
| | - Reinhard Jahn
- Laboratory of NeurobiologyMax Planck Institute for Biophysical ChemistryGöttingenGermany
- University of GöttingenGöttingenGermany
| | - Beth Stevens
- F.M. Kirby Center for NeurobiologyBoston Children's HospitalBostonMAUSA
- Stanley Center for Psychiatric ResearchThe Broad Institute of MIT and HarvardCambridgeMAUSA
- Howard Hughes Medical InstituteBoston Children's HospitalBostonMAUSA
| | - Michela Matteoli
- Laboratory of Pharmacology and Brain PathologyNeurocenterHumanitas Clinical and Research Center ‐ IRCCSRozzano (MI)Italy
- CNR Institute of NeuroscienceMilanoItaly
| |
Collapse
|
5
|
Zhang N, Liu C, Jin L, Zhang R, Siebert HC, Wang Z, Prakash S, Yin X, Li J, Hou D, Sun B, Liu M. Influence of Long-Chain/Medium-Chain Triglycerides and Whey Protein/Tween 80 Ratio on the Stability of Phosphatidylserine Emulsions (O/W). ACS OMEGA 2020; 5:7792-7801. [PMID: 32309688 PMCID: PMC7160843 DOI: 10.1021/acsomega.9b03702] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 11/01/2019] [Accepted: 03/18/2020] [Indexed: 06/11/2023]
Abstract
Phosphatidylserine (PS) is a major anionic phospholipid constituent of membrane bilayers, which is specifically enriched in the cytoplasmic leaflet, has functions of regulating the intracellular signaling pathways of neuronal survival and differentiation, and acts as a neurotransmitter to control the activity of neurons. Oil-in-water (O/W) emulsions could improve the bio-availability of PS. Thus, there is a high level of interest in PS emulsion because of its purported health benefits. However, because of high viscosity and poor fluidity, it remains difficult to make the emulsion. A detailed analysis with suited biophysical methods would help to better understand the processes on a molecular level. Therefore, the main aim of the present study was to engineer and characterize a stable O/W phosphatidylserine emulsion. Furthermore, the effect of emulsifiers mixture, whey protein isolate (WPI), and Tween 80 (T80), as well as the oil phase was systematically evaluated. The key parameters were the chain length and the degree of nonsaturation (sunflower oil, a long-chain triglycerides [LCTs] or a medium-chain triglycerides [MCTs]). Small droplets of emulsions could be obtained by adjusting the type of emulsifier and the LCT/MCT ratio. A stable PS emulsion characterized by a smaller droplet size, higher negative zeta-potential, lower centrifugal stability constant, and longer storage time was produced by MCTs T80 (2.0%, w/w) with T80 (2.0%, w/w) as the emulsifier, and by LCTs with the WPI (0.5%, w/w)-T80 (1.5%, w/w) as the emulsifier, respectively. The PS emulsion with LCTs exhibited higher viscosity, when compared to the emulsion made by MCT at the same emulsifier concentration, while all emulsions exhibited a shear thinning behavior. The microstructure images revealed that the PS emulsions produced by MCTs and T80 (2.0%, w/w) or WPIs (0.5%, w/w)-T80 (1.5%, w/w) mixed with LCTs can form specific uniform networks, in order to prevent flocculation. After 28 days of storage, no visual phase separation was observed in the emulsions, except for the PS emulsion with the WPI (2.0%, w/w). It was concluded that the characteristics of the interfacial layer of particles in the PS emulsion system were not only dependent on the proportion of the applied emulsifiers, but also dependent on the oily phase features. These findings may provide indications for choosing the suitable process parameters when a stable PS emulsion is produced.
Collapse
Affiliation(s)
- Ning Zhang
- Institute
of Biopharmaceutical Research, Liaocheng
University, Liaocheng, Shandong 252000, China
| | - Chunhong Liu
- Institute
of Biopharmaceutical Research, Liaocheng
University, Liaocheng, Shandong 252000, China
| | - Li Jin
- Institute
of Biopharmaceutical Research, Liaocheng
University, Liaocheng, Shandong 252000, China
| | - Ruiyan Zhang
- Institute
of Biopharmaceutical Research, Liaocheng
University, Liaocheng, Shandong 252000, China
| | - Hans-Christian Siebert
- RI-B-NT—Research
Institute of Bioinformatics and Nanotechnology, Schauenburgerstr. 116, 24118 Kiel, Germany
| | - Zhengping Wang
- Institute
of Biopharmaceutical Research, Liaocheng
University, Liaocheng, Shandong 252000, China
| | - Sangeeta Prakash
- School
of Agriculture and Food Sciences, The University
of Queensland, Brisbane, Queensland 4072 Australia
| | - Xiaohan Yin
- Institute
of Biopharmaceutical Research, Liaocheng
University, Liaocheng, Shandong 252000, China
| | - Jing Li
- Shandong
Provincial Key Laboratory of Chemical Energy Storage and Novel Cell
Technology, College of Chemistry and Chemical Engineering, Liaocheng University, Liaocheng, Shandong 252059, China
| | - Danping Hou
- Institute
of Biopharmaceutical Research, Liaocheng
University, Liaocheng, Shandong 252000, China
| | - Bin Sun
- Institute
of Biopharmaceutical Research, Liaocheng
University, Liaocheng, Shandong 252000, China
| | - Min Liu
- Institute
of Biopharmaceutical Research, Liaocheng
University, Liaocheng, Shandong 252000, China
| |
Collapse
|
6
|
Taniguchi S, Toyoshima M, Takamatsu T, Mima J. Curvature-sensitive trans-assembly of human Atg8-family proteins in autophagy-related membrane tethering. Protein Sci 2020; 29:1387-1400. [PMID: 31960529 DOI: 10.1002/pro.3828] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2019] [Revised: 01/15/2020] [Accepted: 01/15/2020] [Indexed: 12/18/2022]
Abstract
In macroautophagy, de novo formation of the double membrane-bound organelles, termed autophagosomes, is essential for engulfing and sequestering the cytoplasmic contents to be degraded in the lytic compartments such as vacuoles and lysosomes. Atg8-family proteins have been known to be responsible for autophagosome formation via membrane tethering and fusion events of precursor membrane structures. Nevertheless, how Atg8 proteins act directly upon autophagosome formation still remains enigmatic. Here, to further gain molecular insights into Atg8-mediated autophagic membrane dynamics, we study the two representative human Atg8 orthologs, LC3B and GATE-16, by quantitatively evaluating their intrinsic potency to physically tether lipid membranes in a chemically defined reconstitution system using purified Atg8 proteins and synthetic liposomes. Both LC3B and GATE-16 retained the capacities to trigger efficient membrane tethering at the protein-to-lipid molar ratios ranging from 1:100 to 1:5,000. These human Atg8-mediated membrane-tethering reactions require trans-assembly between the membrane-anchored forms of LC3B and GATE-16 and can be reversibly and strictly controlled by the membrane attachment and detachment cycles. Strikingly, we further uncovered distinct membrane curvature dependences of LC3B- and GATE-16-mediated membrane tethering reactions: LC3B can drive tethering more efficiently than GATE-16 for highly curved small vesicles (e.g., 50 nm in diameter), although GATE-16 turns out to be a more potent tether than LC3B for flatter large vesicles (e.g., 200 and 400 nm in diameter). Our findings establish curvature-sensitive trans-assembly of human Atg8-family proteins in reconstituted membrane tethering, which recapitulates an essential subreaction of the biogenesis of autophagosomes in vivo.
Collapse
Affiliation(s)
- Saki Taniguchi
- Institute for Protein Research, Osaka University, Suita, Osaka, Japan
| | | | - Tomoyo Takamatsu
- Institute for Protein Research, Osaka University, Suita, Osaka, Japan
| | - Joji Mima
- Institute for Protein Research, Osaka University, Suita, Osaka, Japan
| |
Collapse
|
7
|
Sec17 (α-SNAP) and Sec18 (NSF) restrict membrane fusion to R-SNAREs, Q-SNAREs, and SM proteins from identical compartments. Proc Natl Acad Sci U S A 2019; 116:23573-23581. [PMID: 31685636 DOI: 10.1073/pnas.1913985116] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
Membrane fusion at each organelle requires conserved proteins: Rab-GTPases, effector tethering complexes, Sec1/Munc18 (SM)-family SNARE chaperones, SNAREs of the R, Qa, Qb, and Qc families, and the Sec17/α-SNAP and ATP-dependent Sec18/NSF SNARE chaperone system. The basis of organelle-specific fusion, which is essential for accurate protein compartmentation, has been elusive. Rab family GTPases, SM proteins, and R- and Q-SNAREs may contribute to this specificity. We now report that the fusion supported by SNAREs alone is both inefficient and promiscuous with respect to organelle identity and to stimulation by SM family proteins or complexes. SNARE-only fusion is abolished by the disassembly chaperones Sec17 and Sec18. Efficient fusion in the presence of Sec17 and Sec18 requires a tripartite match between the organellar identities of the R-SNARE, the Q-SNAREs, and the SM protein or complex. The functions of Sec17 and Sec18 are not simply negative regulation; they stimulate fusion with either vacuolar SNAREs and their SM protein complex HOPS or endoplasmic reticulum/cis-Golgi SNAREs and their SM protein Sly1. The fusion complex of each organelle is assembled from its own functionally matching pieces to engage Sec17/Sec18 for fusion stimulation rather than inhibition.
Collapse
|
8
|
Pariary R, Bhattacharyya D, Bhunia A. Mitochondrial-membrane association of α-synuclein: Pros and cons in consequence of Parkinson's disease pathophysiology. GENE REPORTS 2019. [DOI: 10.1016/j.genrep.2019.100423] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
|
9
|
Kim B, Sun S, Varner JA, Howell SB, Ruoslahti E, Sailor MJ. Securing the Payload, Finding the Cell, and Avoiding the Endosome: Peptide-Targeted, Fusogenic Porous Silicon Nanoparticles for Delivery of siRNA. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2019; 31:e1902952. [PMID: 31267590 PMCID: PMC6710136 DOI: 10.1002/adma.201902952] [Citation(s) in RCA: 60] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/08/2019] [Revised: 06/08/2019] [Indexed: 05/06/2023]
Abstract
Despite the promise of ribonucleic acid interference therapeutics, the delivery of oligonucleotides selectively to diseased tissues in the body, and specifically to the cellular location in the tissues needed to provide optimal therapeutic outcome, remains a significant challenge. Here, key material properties and biological mechanisms for delivery of short interfering RNAs (siRNAs) to effectively silence target-specific cells in vivo are identified. Using porous silicon nanoparticles as the siRNA host, tumor-targeting peptides for selective tissue homing, and fusogenic lipid coatings to induce fusion with the plasma membrane, it is shown that the uptake mechanism can be engineered to be independent of common receptor-mediated endocytosis pathways. Two examples of the potential broad clinical applicability of this concept in a mouse xenograft model of ovarian cancer peritoneal carcinomatosis are provided: silencing the Rev3l subunit of polymerase Pol ζ to impair DNA repair in combination with cisplatin; and reprogramming tumor-associated macrophages into a proinflammatory state.
Collapse
Affiliation(s)
- Byungji Kim
- Materials Science and Engineering Program, University of California, San Diego, 9500 Gilman Dr., La Jolla, CA, 92093, USA
| | - Si Sun
- Department of Obstetrics and Gynecology, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, 430022, China
| | - Judith A Varner
- Moores Cancer Center and Department of Pathology, University of California, San Diego, La Jolla, CA, 92037, USA
| | - Stephen B Howell
- Moores Cancer Center and Department of Medicine, University of California, San Diego, La Jolla, CA, 92037, USA
| | - Erkki Ruoslahti
- Cancer Research Center, Sanford Burnham Prebys Medical Discovery Institute, La Jolla, CA, 92037, USA
| | - Michael J Sailor
- Materials Science and Engineering Program, University of California, San Diego, 9500 Gilman Dr., La Jolla, CA, 92093, USA
- Department of Chemistry and Biochemistry, University of California, San Diego, 9500 Gilman Dr., La Jolla, CA, 92093, USA
| |
Collapse
|
10
|
Segawa K, Tamura N, Mima J. Homotypic and heterotypic trans-assembly of human Rab-family small GTPases in reconstituted membrane tethering. J Biol Chem 2019; 294:7722-7739. [PMID: 30910814 DOI: 10.1074/jbc.ra119.007947] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2019] [Revised: 03/07/2019] [Indexed: 11/06/2022] Open
Abstract
Membrane tethering is a highly regulated event occurring during the initial physical contact between membrane-bounded transport carriers and their target subcellular membrane compartments, thereby ensuring the spatiotemporal specificity of intracellular membrane trafficking. Although Rab-family small GTPases and specific Rab-interacting effectors, such as coiled-coil tethering proteins and multisubunit tethering complexes, are known to be involved in membrane tethering, how these protein components directly act upon the tethering event remains enigmatic. Here, using a chemically defined reconstitution system, we investigated the molecular basis of membrane tethering by comprehensively and quantitatively evaluating the intrinsic capacities of 10 representative human Rab-family proteins (Rab1a, -3a, -4a, -5a, -6a, -7a, -9a, -11a, -27a, and -33b) to physically tether two distinct membranes via homotypic and heterotypic Rab-Rab assembly. All of the Rabs tested, except Rab27a, specifically caused homotypic membrane tethering at physiologically relevant Rab densities on membrane surfaces (e.g. Rab/lipid molar ratios of 1:100-1:3,000). Notably, endosomal Rab5a retained its intrinsic potency to drive efficient homotypic tethering even at concentrations below the Rab/lipid ratio of 1:3,000. Comprehensive reconstitution experiments further uncovered that heterotypic combinations of human Rab-family isoforms, including Rab1a/6a, Rab1a/9a, and Rab1a/33b, can directly and selectively mediate membrane tethering. Rab1a and Rab9a in particular synergistically triggered very rapid and efficient membrane tethering reactions through their heterotypic trans-assembly on two opposing membranes. In conclusion, our findings establish that, in the physiological context, homotypic and heterotypic trans-assemblies of Rab-family small GTPases can provide the essential molecular machinery necessary to drive membrane tethering in eukaryotic endomembrane systems.
Collapse
Affiliation(s)
- Kazuya Segawa
- From the Institute for Protein Research, Osaka University, Suita, Osaka 565-0871, Japan
| | - Naoki Tamura
- From the Institute for Protein Research, Osaka University, Suita, Osaka 565-0871, Japan
| | - Joji Mima
- From the Institute for Protein Research, Osaka University, Suita, Osaka 565-0871, Japan
| |
Collapse
|
11
|
Abstract
Membrane fusion mediated by SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor)-family proteins is an essential process for intracellular membrane trafficking in all eukaryotic cells, which delivers proteins and lipids to their appropriate subcellular membrane compartments such as organelles and plasma membrane. The molecular basis of SNARE-mediated membrane fusion has been revealed by studying fusion of reconstituted proteoliposomes bearing purified SNARE-family proteins and chemically defined lipid species. This chapter describes the detailed experimental protocols for (1) purification of recombinant SNARE-family and SM (Sec1/Munc18-family) proteins in the yeast Saccharomyces cerevisiae; (2) preparation of reconstituted proteoliposomes bearing purified yeast SNARE proteins; and (3) developing an assay to monitor lipid mixing between reconstituted SNARE-bearing proteoliposomes. Lipid mixing assays for reconstituted SNARE-bearing proteoliposomes are useful for evaluating the intrinsic capacity of SNARE-family proteins to directly catalyze membrane fusion and to determine the specificity of membrane fusion.
Collapse
Affiliation(s)
- Joji Mima
- Institute for Protein Research, Osaka University, Osaka, Japan.
| |
Collapse
|
12
|
Fusion assays for model membranes: a critical review. ADVANCES IN BIOMEMBRANES AND LIPID SELF-ASSEMBLY 2019. [DOI: 10.1016/bs.abl.2019.09.003] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/09/2022]
|
13
|
Kim B, Pang HB, Kang J, Park JH, Ruoslahti E, Sailor MJ. Immunogene therapy with fusogenic nanoparticles modulates macrophage response to Staphylococcus aureus. Nat Commun 2018; 9:1969. [PMID: 29773788 PMCID: PMC5958120 DOI: 10.1038/s41467-018-04390-7] [Citation(s) in RCA: 105] [Impact Index Per Article: 17.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2017] [Accepted: 04/25/2018] [Indexed: 01/06/2023] Open
Abstract
The incidence of adverse effects and pathogen resistance encountered with small molecule antibiotics is increasing. As such, there is mounting focus on immunogene therapy to augment the immune system’s response to infection and accelerate healing. A major obstacle to in vivo gene delivery is that the primary uptake pathway, cellular endocytosis, results in extracellular excretion and lysosomal degradation of genetic material. Here we show a nanosystem that bypasses endocytosis and achieves potent gene knockdown efficacy. Porous silicon nanoparticles containing an outer sheath of homing peptides and fusogenic liposome selectively target macrophages and directly introduce an oligonucleotide payload into the cytosol. Highly effective knockdown of the proinflammatory macrophage marker IRF5 enhances the clearance capability of macrophages and improves survival in a mouse model of Staphyloccocus aureus pneumonia. In the context of increasing bacterial antibiotic-resistance, gene therapy that targets the immune system to clear infection is a major goal. Here the authors show a silicon based nanosystem that modulates the macrophage response in an in vivo model of Staphylococcal pneumonia.
Collapse
Affiliation(s)
- Byungji Kim
- Materials Science and Engineering Program, University of California, San Diego, 9500 Gilman Drive, La Jolla, California, 92093, USA
| | - Hong-Bo Pang
- Cancer Research Center, Sanford Burnham Prebys Medical Discovery Institute, La Jolla, California, 92037, USA.,Department of Pharmaceutics, University of Minnesota, Minneapolis, Minnesota, 55455, USA
| | - Jinyoung Kang
- Department of Nanoengineering, University of California, San Diego, 9500 Gilman Drive, La Jolla, California, 92093, USA
| | - Ji-Ho Park
- Department of Bio and Brain Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon, 34141, Republic of Korea
| | - Erkki Ruoslahti
- Cancer Research Center, Sanford Burnham Prebys Medical Discovery Institute, La Jolla, California, 92037, USA.,Center for Nanomedicine and Department of Cell, Molecular and Developmental Biology, University of California, Santa Barbara, Santa Barbara, California, 93106-9610, USA
| | - Michael J Sailor
- Materials Science and Engineering Program, University of California, San Diego, 9500 Gilman Drive, La Jolla, California, 92093, USA. .,Department of Nanoengineering, University of California, San Diego, 9500 Gilman Drive, La Jolla, California, 92093, USA. .,Department of Chemistry and Biochemistry, University of California, San Diego, 9500 Gilman Drive, La Jolla, California, 92093, USA.
| |
Collapse
|
14
|
Jeschke A, Haas A. Sequential actions of phosphatidylinositol phosphates regulate phagosome-lysosome fusion. Mol Biol Cell 2017; 29:452-465. [PMID: 29237821 PMCID: PMC6014173 DOI: 10.1091/mbc.e17-07-0464] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2017] [Revised: 11/14/2017] [Accepted: 12/08/2017] [Indexed: 02/05/2023] Open
Abstract
Phagosome-with-lysosome fusion comprises subreactions with differential lipid requirements: PI(4)P is required during and after phagosome-to-lysosome tethering, and PI(3)P is required after tethering. Moreover, PI(4)P serves to anchor to (phago)lysosome membranes Arl8 and HOPS, whereas PI(3)P contributes to membrane binding of HOPS only. Phagosomes mature into phagolysosomes by sequential fusion with early endosomes, late endosomes, and lysosomes. Phagosome-with-lysosome fusion (PLF) results in the delivery of lysosomal hydrolases into phagosomes and in digestion of the cargo. The machinery that drives PLF has been little investigated. Using a cell-free system, we recently identified the phosphoinositide lipids (PIPs) phosphatidylinositol 3-phosphate (PI(3)P) and phosphatidylinositol 4-phosphate (PI(4)P) as regulators of PLF. We now report the identification and the PIP requirements of four distinct subreactions of PLF. Our data show that (i) PI(3)P and PI(4)P are dispensable for the disassembly and activation of (phago)lysosomal soluble N-ethylmaleimide-sensitive factor attachment protein receptors, that (ii) PI(3)P is required only after the tethering step, and that (iii) PI(4)P is required during and after tethering. Moreover, our data indicate that PI(4)P is needed to anchor Arl8 (Arf-like GTPase 8) and its effector homotypic fusion/vacuole protein sorting complex (HOPS) to (phago)lysosome membranes, whereas PI(3)P is required for membrane association of HOPS only. Our study provides a first link between PIPs and established regulators of membrane fusion in late endocytic trafficking.
Collapse
Affiliation(s)
- Andreas Jeschke
- Cell Biology Institute, University of Bonn, 53121 Bonn, Germany
| | - Albert Haas
- Cell Biology Institute, University of Bonn, 53121 Bonn, Germany
| |
Collapse
|
15
|
Harner M, Wickner W. Assembly of intermediates for rapid membrane fusion. J Biol Chem 2017; 293:1346-1352. [PMID: 29208657 DOI: 10.1074/jbc.ra117.000791] [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: 11/03/2017] [Revised: 11/27/2017] [Indexed: 11/06/2022] Open
Abstract
Membrane fusion is essential for intracellular protein sorting, cell growth, hormone secretion, and neurotransmission. Rapid membrane fusion requires tethering and Sec1-Munc18 (SM) function to catalyze R-, Qa-, Qb-, and Qc-SNARE complex assembly in trans, as well as SNARE engagement by the SNARE-binding chaperone Sec17/αSNAP. The hexameric vacuolar HOPS (homotypic fusion and vacuole protein sorting) complex in the yeast Saccharomyces cerevisiae tethers membranes through its affinities for the membrane Rab GTPase Ypt7. HOPS also has specific affinities for the vacuolar SNAREs and catalyzes SNARE complex assembly, but the order of their assembly into a 4-SNARE complex is unclear. We now report defined assembly intermediates on the path to membrane fusion. We found that a prefusion intermediate will assemble with HOPS and the R, Qa, and Qc SNAREs, and that this assembly undergoes rapid fusion upon addition of Qb and Sec17. HOPS-tethered membranes and all four vacuolar SNAREs formed a complex that underwent an even more dramatic burst of fusion upon Sec17p addition. These findings provide initial insights into an ordered fusion pathway consisting of the following intermediates and events: 1) Rab- and HOPS-tethered membranes, 2) a HOPS:R:Qa:Qc trans-complex, 3) a HOPS:4-SNARE trans-complex, 4) an engagement with Sec17, and 5) the rapid lipid rearrangements during fusion. In conclusion, our results indicate that the R:Qa:Qc complex forms in the context of membrane, Ypt7, HOPS, and trans-SNARE assembly and serves as a functional intermediate for rapid fusion after addition of the Qb-SNARE and Sec17 proteins.
Collapse
Affiliation(s)
- Max Harner
- From the Department of Biochemistry and Cell Biology, Geisel School of Medicine at Dartmouth, Hanover, New Hampshire 03755-3844
| | - William Wickner
- From the Department of Biochemistry and Cell Biology, Geisel School of Medicine at Dartmouth, Hanover, New Hampshire 03755-3844
| |
Collapse
|
16
|
Liu X, Tian F, Yue T, Zhang X, Zhong C. Pulling force and surface tension drive membrane fusion. J Chem Phys 2017; 147:194703. [PMID: 29166098 DOI: 10.1063/1.4997393] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Despite catalyzed by fusion proteins of quite different molecular architectures, intracellular, viral, and cell-to-cell fusions are found to have the essential common features and the nearly same nature of transition states. The similarity inspires us to find a more general catalysis mechanism for membrane fusion that minimally depends on the specific structures of fusion proteins. In this work, we built a minimal model for membrane fusion, and by using dissipative particle dynamics simulations, we propose a mechanism that the pulling force generated by fusion proteins initiates the fusion process and the membrane tension regulates the subsequent fusion stages. The model shows different features compared to previous computer simulation studies: the pulling force catalyzes membrane fusion through lipid head overcrowding in the contacting region, leading to an increase in the head-head repulsion and/or the unfavorable head-tail contacts from opposing membranes, both of which destabilize the contacting leaflets and thus promote membrane fusion or vesicle rupture. Our simulations produce a variety of shapes and intermediates, closely resembling cases seen experimentally. Our work strongly supports the view that the tight pulling mechanism is a conserved feature of fusion protein-mediated fusion and that the membrane tension plays an essential role in fusion.
Collapse
Affiliation(s)
- Xuejuan Liu
- State Key Laboratory of Organic-Inorganic Composites, Beijing University of Chemical Technology, Beijing 100029, People's Republic of China
| | - Falin Tian
- State Key Laboratory of Organic-Inorganic Composites, Beijing University of Chemical Technology, Beijing 100029, People's Republic of China
| | - Tongtao Yue
- State Key Laboratory of Heavy Oil Processing, Center for Bioengineering and Biotechnology, China University of Petroleum (East China), Qingdao 266580, People's Republic of China
| | - Xianren Zhang
- State Key Laboratory of Organic-Inorganic Composites, Beijing University of Chemical Technology, Beijing 100029, People's Republic of China
| | - Chongli Zhong
- State Key Laboratory of Organic-Inorganic Composites, Beijing University of Chemical Technology, Beijing 100029, People's Republic of China
| |
Collapse
|
17
|
Wickner W, Rizo J. A cascade of multiple proteins and lipids catalyzes membrane fusion. Mol Biol Cell 2017; 28:707-711. [PMID: 28292915 PMCID: PMC5349777 DOI: 10.1091/mbc.e16-07-0517] [Citation(s) in RCA: 62] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2016] [Revised: 01/05/2017] [Accepted: 01/10/2017] [Indexed: 11/11/2022] Open
Abstract
Recent studies suggest revisions to the SNARE paradigm of membrane fusion. Membrane tethers and/or SNAREs recruit proteins of the Sec 1/Munc18 family to catalyze SNARE assembly into trans-complexes. SNARE-domain zippering draws the bilayers into immediate apposition and provides a platform to position fusion triggers such as Sec 17/α-SNAP and/or synaptotagmin, which insert their apolar "wedge" domains into the bilayers, initiating the lipid rearrangements of fusion.
Collapse
Affiliation(s)
- William Wickner
- Department of Biochemistry and Cell Biology, Geisel School of Medicine at Dartmouth, Hanover, NH 03755 )
| | - Josep Rizo
- Departments of Biophysics, Biochemistry, and Biophysics, University of Texas Southwestern Medical Center, Dallas, TX 75390 )
| |
Collapse
|
18
|
Heo P, Kong B, Jung YH, Park JB, Shin J, Park M, Kweon DH. Green fluorescence protein-based content-mixing assay of SNARE-driven membrane fusion. Biochem Biophys Res Commun 2017; 488:53-59. [PMID: 28476622 DOI: 10.1016/j.bbrc.2017.05.006] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2017] [Accepted: 05/01/2017] [Indexed: 11/17/2022]
Abstract
Soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) proteins mediate intracellular membrane fusion by forming a ternary SNARE complex. A minimalist approach utilizing proteoliposomes with reconstituted SNARE proteins yielded a wealth of information pinpointing the molecular mechanism of SNARE-mediated fusion and its regulation by accessory proteins. Two important attributes of a membrane fusion are lipid-mixing and the formation of an aqueous passage between apposing membranes. These two attributes are typically observed by using various fluorescent dyes. Currently available in vitro assay systems for observing fusion pore opening have several weaknesses such as cargo-bleeding, incomplete removal of unencapsulated dyes, and inadequate information regarding the size of the fusion pore, limiting measurements of the final stage of membrane fusion. In the present study, we used a biotinylated green fluorescence protein and streptavidin conjugated with Dylight 594 (DyStrp) as a Föster resonance energy transfer (FRET) donor and acceptor, respectively. This FRET pair encapsulated in each v-vesicle containing synaptobrevin and t-vesicle containing a binary acceptor complex of syntaxin 1a and synaptosomal-associated protein 25 revealed the opening of a large fusion pore of more than 5 nm, without the unwanted signals from unencapsulated dyes or leakage. This system enabled determination of the stoichiometry of the merging vesicles because the FRET efficiency of the FRET pair depended on the molar ratio between dyes. Here, we report a robust and informative assay for SNARE-mediated fusion pore opening.
Collapse
Affiliation(s)
- Paul Heo
- Department of Genetic Engineering, College of Biotechnology and Bioengineering, Sungkyunkwan University, Suwon, Gyeonggi-do 16419, South Korea
| | - Byoungjae Kong
- Department of Genetic Engineering, College of Biotechnology and Bioengineering, Sungkyunkwan University, Suwon, Gyeonggi-do 16419, South Korea
| | - Young-Hun Jung
- Department of Genetic Engineering, College of Biotechnology and Bioengineering, Sungkyunkwan University, Suwon, Gyeonggi-do 16419, South Korea
| | - Joon-Bum Park
- Department of Genetic Engineering, College of Biotechnology and Bioengineering, Sungkyunkwan University, Suwon, Gyeonggi-do 16419, South Korea
| | - Jonghyeok Shin
- Department of Genetic Engineering, College of Biotechnology and Bioengineering, Sungkyunkwan University, Suwon, Gyeonggi-do 16419, South Korea
| | - Myungseo Park
- Department of Genetic Engineering, College of Biotechnology and Bioengineering, Sungkyunkwan University, Suwon, Gyeonggi-do 16419, South Korea
| | - Dae-Hyuk Kweon
- Department of Genetic Engineering, College of Biotechnology and Bioengineering, Sungkyunkwan University, Suwon, Gyeonggi-do 16419, South Korea.
| |
Collapse
|
19
|
Hu Y, Lai Y, Wang Y, Zhao M, Zhang Y, Crowe M, Tian Z, Long J, Diao J. SNARE-Reconstituted Liposomes as Controllable Zeptoliter Nanoreactors for Macromolecules. ACTA ACUST UNITED AC 2017; 1:e1600018. [DOI: 10.1002/adbi.201600018] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2016] [Revised: 01/08/2017] [Indexed: 02/05/2023]
Affiliation(s)
- Yachong Hu
- Center for Mitochondrial Biology and Medicine; The Key Laboratory of Biomedical Information Engineering of Ministry of Education; School of Life Science and Technology; Xi'an Jiaotong University; Xi'an 710049 China
- Department of Cancer Biology; University of Cincinnati College of Medicine; Cincinnati OH 45267 USA
| | - Ying Lai
- Departments of Molecular and Cellular Physiology; Stanford University; Stanford CA 94305 USA
| | - Yongyao Wang
- Center for Mitochondrial Biology and Medicine; The Key Laboratory of Biomedical Information Engineering of Ministry of Education; School of Life Science and Technology; Xi'an Jiaotong University; Xi'an 710049 China
- Department of Cancer Biology; University of Cincinnati College of Medicine; Cincinnati OH 45267 USA
| | - Minglei Zhao
- Departments of Molecular and Cellular Physiology; Stanford University; Stanford CA 94305 USA
| | - Yunxiang Zhang
- Departments of Molecular and Cellular Physiology; Stanford University; Stanford CA 94305 USA
| | - Michael Crowe
- Department of Cancer Biology; University of Cincinnati College of Medicine; Cincinnati OH 45267 USA
| | - Zhiqi Tian
- Center for Mitochondrial Biology and Medicine; The Key Laboratory of Biomedical Information Engineering of Ministry of Education; School of Life Science and Technology; Xi'an Jiaotong University; Xi'an 710049 China
- Department of Cancer Biology; University of Cincinnati College of Medicine; Cincinnati OH 45267 USA
| | - Jiangang Long
- Center for Mitochondrial Biology and Medicine; The Key Laboratory of Biomedical Information Engineering of Ministry of Education; School of Life Science and Technology; Xi'an Jiaotong University; Xi'an 710049 China
| | - Jiajie Diao
- Department of Cancer Biology; University of Cincinnati College of Medicine; Cincinnati OH 45267 USA
| |
Collapse
|
20
|
Bu B, Tian Z, Li D, Ji B. High Transmembrane Voltage Raised by Close Contact Initiates Fusion Pore. Front Mol Neurosci 2016; 9:136. [PMID: 28018169 PMCID: PMC5145871 DOI: 10.3389/fnmol.2016.00136] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2016] [Accepted: 11/22/2016] [Indexed: 12/21/2022] Open
Abstract
Membrane fusion lies at the heart of neuronal communication but the detailed mechanism of a critical step, fusion pore initiation, remains poorly understood. Here, through atomistic molecular dynamics simulations, a transient pore formation induced by a close contact of two apposed bilayers is firstly reported. Such a close contact gives rise to a high local transmembrane voltage that induces the transient pore formation. Through simulations on two apposed bilayers fixed at a series of given distances, the process in which two bilayers approaching to each other under the pulling force from fusion proteins for membrane fusion was mimicked. Of note, this close contact induced fusion pore formation is contrasted with previous reported electroporation under ad hoc applied external electric field or ionic charge in-balance. We show that the transmembrane voltage increases with the decrease of the distance between the bilayers. Below a critical distance, depending on the lipid composition, the local transmembrane voltage can be sufficiently high to induce the transient pores. The size of these pores is approximately 1~2 nm in diameter, which is large enough to allow passing of neurotransmitters. A resealing of the membrane pores resulting from the neutralization of the transmembrane voltage by ions through the pores was then observed. We also found that the membrane tension can either prolong the lifetime of transient pores or cause them to dilate for full collapse. This result provides a possible mechanism for fusion pore formation and regulation of pathway of fusion process.
Collapse
Affiliation(s)
- Bing Bu
- Biomechanics and Biomaterials Laboratory, Department of Applied Mechanics, Beijing Institute of Technology Beijing, China
| | - Zhiqi Tian
- Key Laboratory of Biomedical Information Engineering of Ministry of Education, Center for Mitochondrial Biology and Medicine, School of Life Science and Technology, Xi'an Jiaotong University Xi'an, China
| | - Dechang Li
- Biomechanics and Biomaterials Laboratory, Department of Applied Mechanics, Beijing Institute of Technology Beijing, China
| | - Baohua Ji
- Biomechanics and Biomaterials Laboratory, Department of Applied Mechanics, Beijing Institute of Technology Beijing, China
| |
Collapse
|
21
|
Han J, Pluhackova K, Bruns D, Böckmann RA. Synaptobrevin transmembrane domain determines the structure and dynamics of the SNARE motif and the linker region. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2016; 1858:855-65. [DOI: 10.1016/j.bbamem.2016.01.030] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/05/2015] [Revised: 01/06/2016] [Accepted: 01/27/2016] [Indexed: 12/29/2022]
|
22
|
Gaul V, Lopez SG, Lentz BR, Moran N, Forster RJ, Keyes TE. The lateral diffusion and fibrinogen induced clustering of platelet integrin αIIbβ3 reconstituted into physiologically mimetic GUVs. Integr Biol (Camb) 2015; 7:402-11. [PMID: 25720532 DOI: 10.1039/c5ib00003c] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Platelet integrin αIIbβ3 is a key mediator of platelet activation and thrombosis. Upon activation αIIbβ3 undergoes significant conformational rearrangement, inducing complex bidirectional signalling and protein recruitment leading to platelet activation. Reconstituted lipid models of the integrin can enhance our understanding of the structural and mechanistic details of αIIbβ3 behaviour away from the complexity of the platelet machinery. Here, a novel method of αIIbβ3 insertion into Giant Unilamellar Vesicles (GUVs) is described that allows for effective integrin reconstitution unrestricted by lipid composition. αIIbβ3 was inserted into two GUV lipid compositions that seek to better mimic the platelet membrane. First, "nature's own", comprising 32% DOPC, 25% DOPE, 20% CH, 15% SM and 8% DOPS, intended to mimic the platelet cell membrane. Fluorescence Lifetime Correlation Spectroscopy (FLCS) reveals that exposure of the integrin to the activators Mn(2+) or DTT does not influence the diffusion coefficient of αIIbβ3. Similarly, exposure to αIIbβ3's primary ligand fibrinogen (Fg) alone does not affect αIIbβ3's diffusion coefficient. However, addition of Fg with either activator reduces the integrin diffusion coefficient from 2.52 ± 0.29 to μm(2) s(-1) to 1.56 ± 0.26 (Mn(2+)) or 1.49 ± 0.41 μm(2) s(-1) (DTT) which is consistent with aggregation of activated αIIbβ3 induced by fibrinogen binding. The Multichannel Scaler (MCS) trace shows that the integrin-Fg complex diffuses through the confocal volume in clusters. Using the Saffman-Delbrück model as a first approximation, the diffusion coefficient of the complex suggests at least a 20-fold increase in the radius of membrane bound protein, consistent with integrin clustering. Second, αIIbβ3 was also reconstituted into a "raft forming" GUV with well defined liquid disordered (Ld) and liquid ordered (Lo) phases. Using confocal microscopy and lipid partitioning dyes, αIIbβ3 showed an affinity for the DOPC rich Ld phase of the raft forming GUVs, and was effectively excluded from the cholesterol and sphingomyelin rich Lo phase. Activation and Fg binding of the integrin did not alter the distribution of αIIbβ3 between the lipid phases. This observation suggests partitioning of the activated fibrinogen bound αIIbβ3 into cholesterol rich domains is not responsible for the integrin clustering observed.
Collapse
Affiliation(s)
- Vinnie Gaul
- School of Chemical Sciences and National Biophotonics and Imaging Platform, Dublin City University, Dublin 9, Ireland.
| | | | | | | | | | | |
Collapse
|
23
|
Baker RW, Jeffrey PD, Zick M, Phillips BP, Wickner WT, Hughson FM. A direct role for the Sec1/Munc18-family protein Vps33 as a template for SNARE assembly. Science 2015; 349:1111-4. [PMID: 26339030 DOI: 10.1126/science.aac7906] [Citation(s) in RCA: 220] [Impact Index Per Article: 24.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Fusion of intracellular transport vesicles requires soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs) and Sec1/Munc18-family (SM) proteins. Membrane-bridging SNARE complexes are critical for fusion, but their spontaneous assembly is inefficient and may require SM proteins in vivo. We report x-ray structures of Vps33, the SM subunit of the yeast homotypic fusion and vacuole protein-sorting (HOPS) complex, bound to two individual SNAREs. The two SNAREs, one from each membrane, are held in the correct orientation and register for subsequent complex assembly. Vps33 and potentially other SM proteins could thus act as templates for generating partially zipped SNARE assembly intermediates. HOPS was essential to mediate SNARE complex assembly at physiological SNARE concentrations. Thus, Vps33 appears to catalyze SNARE complex assembly through specific SNARE motif recognition.
Collapse
Affiliation(s)
- Richard W Baker
- Department of Molecular Biology, Princeton University, Princeton, NJ 08544, USA
| | - Philip D Jeffrey
- Department of Molecular Biology, Princeton University, Princeton, NJ 08544, USA
| | - Michael Zick
- Department of Biochemistry, Geisel School of Medicine at Dartmouth, Hanover, NH 03755, USA
| | - Ben P Phillips
- Department of Molecular Biology, Princeton University, Princeton, NJ 08544, USA
| | - William T Wickner
- Department of Biochemistry, Geisel School of Medicine at Dartmouth, Hanover, NH 03755, USA
| | - Frederick M Hughson
- Department of Molecular Biology, Princeton University, Princeton, NJ 08544, USA.
| |
Collapse
|
24
|
Xu H, Arnold MG, Kumar SV. Differential Effects of Munc18s on Multiple Degranulation-Relevant Trans-SNARE Complexes. PLoS One 2015; 10:e0138683. [PMID: 26384026 PMCID: PMC4575180 DOI: 10.1371/journal.pone.0138683] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2015] [Accepted: 09/02/2015] [Indexed: 11/24/2022] Open
Abstract
Mast cell exocytosis, which includes compound degranulation and vesicle-associated piecemeal degranulation, requires multiple Q- and R- SNAREs. It is not clear how these SNAREs pair to form functional trans-SNARE complexes and how these trans-SNARE complexes are selectively regulated for fusion. Here we undertake a comprehensive examination of the capacity of two Q-SNARE subcomplexes (syntaxin3/SNAP-23 and syntaxin4/SNAP-23) to form fusogenic trans-SNARE complexes with each of the four granule-borne R-SNAREs (VAMP2, 3, 7, 8). We report the identification of at least six distinct trans-SNARE complexes under enhanced tethering conditions: i) VAMP2/syntaxin3/SNAP-23, ii) VAMP2/syntaxin4/SNAP-23, iii) VAMP3/syntaxin3/SNAP-23, iv) VAMP3/syntaxin4/SNAP-23, v) VAMP8/syntaxin3/SNAP-23, and vi) VAMP8/syntaxin4/SNAP-23. We show for the first time that Munc18a operates synergistically with SNAP-23-based non-neuronal SNARE complexes (i to iv) in lipid mixing, in contrast to Munc18b and c, which exhibit no positive effect on any SNARE combination tested. Pre-incubation with Munc18a renders the SNARE-dependent fusion reactions insensitive to the otherwise inhibitory R-SNARE cytoplasmic domains, suggesting a protective role of Munc18a for its cognate SNAREs. Our findings substantiate the recently discovered but unexpected requirement for Munc18a in mast cell exocytosis, and implicate post-translational modifications in Munc18b/c activation.
Collapse
Affiliation(s)
- Hao Xu
- Department of Biological Sciences, University of Southern Mississippi, Hattiesburg, Mississippi, United States of America
- * E-mail:
| | - Matthew Grant Arnold
- Department of Biological Sciences, University of Southern Mississippi, Hattiesburg, Mississippi, United States of America
| | - Sushmitha Vijay Kumar
- Department of Biological Sciences, University of Southern Mississippi, Hattiesburg, Mississippi, United States of America
| |
Collapse
|
25
|
Lee M, Ko YJ, Moon Y, Han M, Kim HW, Lee SH, Kang K, Jun Y. SNAREs support atlastin-mediated homotypic ER fusion in Saccharomyces cerevisiae. J Cell Biol 2015. [PMID: 26216899 PMCID: PMC4523606 DOI: 10.1083/jcb.201501043] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Dynamin-like GTPases of the atlastin family are thought to mediate homotypic endoplasmic reticulum (ER) membrane fusion; however, the underlying mechanism remains largely unclear. Here, we developed a simple and quantitative in vitro assay using isolated yeast microsomes for measuring yeast atlastin Sey1p-dependent ER fusion. Using this assay, we found that the ER SNAREs Sec22p and Sec20p were required for Sey1p-mediated ER fusion. Consistently, ER fusion was significantly reduced by inhibition of Sec18p and Sec17p, which regulate SNARE-mediated membrane fusion. The involvement of SNAREs in Sey1p-dependent ER fusion was further supported by the physical interaction of Sey1p with Sec22p and Ufe1p, another ER SNARE. Furthermore, our estimation of the concentration of Sey1p on isolated microsomes, together with the lack of fusion between Sey1p proteoliposomes even with a 25-fold excess of the physiological concentration of Sey1p, suggests that Sey1p requires additional factors to support ER fusion in vivo. Collectively, our data strongly suggest that SNARE-mediated membrane fusion is involved in atlastin-initiated homotypic ER fusion.
Collapse
Affiliation(s)
- Miriam Lee
- School of Life Sciences, Gwangju Institute of Science and Technology, Gwangju 500-712, Korea Integrative Aging Research Center, Gwangju Institute of Science and Technology, Gwangju 500-712, Korea Cell Dynamics Research Center, Gwangju Institute of Science and Technology, Gwangju 500-712, Korea
| | - Young-Joon Ko
- School of Life Sciences, Gwangju Institute of Science and Technology, Gwangju 500-712, Korea Integrative Aging Research Center, Gwangju Institute of Science and Technology, Gwangju 500-712, Korea Cell Dynamics Research Center, Gwangju Institute of Science and Technology, Gwangju 500-712, Korea
| | - Yeojin Moon
- School of Life Sciences, Gwangju Institute of Science and Technology, Gwangju 500-712, Korea Integrative Aging Research Center, Gwangju Institute of Science and Technology, Gwangju 500-712, Korea
| | - Minsoo Han
- School of Life Sciences, Gwangju Institute of Science and Technology, Gwangju 500-712, Korea Integrative Aging Research Center, Gwangju Institute of Science and Technology, Gwangju 500-712, Korea
| | - Hyung-Wook Kim
- College of Life Sciences, Sejong University, Seoul 143-747, Korea
| | - Sung Haeng Lee
- Department of Cellular and Molecular Medicine, Chosun University School of Medicine, Gwangju 501-759, Korea
| | - KyeongJin Kang
- Department of Anatomy and Cell Biology, School of Medicine, Sungkyunkwan University, Suwon 440-746, Korea
| | - Youngsoo Jun
- School of Life Sciences, Gwangju Institute of Science and Technology, Gwangju 500-712, Korea Integrative Aging Research Center, Gwangju Institute of Science and Technology, Gwangju 500-712, Korea Cell Dynamics Research Center, Gwangju Institute of Science and Technology, Gwangju 500-712, Korea
| |
Collapse
|
26
|
Gruba SM, Koseoglu S, Meyer AF, Meyer BM, Maurer-Jones MA, Haynes CL. Platelet membrane variations and their effects on δ-granule secretion kinetics and aggregation spreading among different species. BIOCHIMICA ET BIOPHYSICA ACTA 2015; 1848:1609-18. [PMID: 25906946 PMCID: PMC4431631 DOI: 10.1016/j.bbamem.2015.04.006] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/10/2015] [Revised: 04/10/2015] [Accepted: 04/14/2015] [Indexed: 01/09/2023]
Abstract
Platelet exocytosis is regulated partially by the granular/cellular membrane lipids and proteins. Some platelets contain a membrane-bound tube, called an open canalicular system (OCS), which assists in granular release events and increases the membrane surface area for greater spreading. The OCS is not found in all species, and variations in membrane composition can cause changes in platelet secretion. Since platelet studies use various animal models, it is important to understand how platelets differ in both their composition and granular release to draw conclusions among various models. The relative phospholipid composition of the platelets with (mouse, rabbit) and without (cow) an OCS was quantified using UPLC-MS/MS. Cholesterol and protein composition was measured using an Amplex Red Assay and BCA Assay. TEM and dark field platelet images were gathered and analyzed with Image J. Granular release was monitored with single cell carbon fiber microelectrode amperometry. Cow platelets contained greater amounts of cholesterol and sphingomyelin. In addition, they yield greater serotonin release and longer δ granule secretion times. Finally, they showed greater spreading area with a greater range of spread. Platelets containing an OCS had more similarities in their membrane composition and secretion kinetics compared to cow platelets. However, cow platelets showed greater fusion pore stability which could be due to extra sphingomyelin and cholesterol, the primary components of lipid rafts. In addition, their greater stability may lead to many granules assisting in spreading. This study highlights fundamental membrane differences and their effects on platelet secretion.
Collapse
Affiliation(s)
- Sarah M Gruba
- Department of Chemistry, University of Minnesota, 207 Pleasant St. SE, Minneapolis, MN 55455, USA
| | - Secil Koseoglu
- Department of Chemistry, University of Minnesota, 207 Pleasant St. SE, Minneapolis, MN 55455, USA
| | - Audrey F Meyer
- Department of Chemistry, University of Minnesota, 207 Pleasant St. SE, Minneapolis, MN 55455, USA
| | - Ben M Meyer
- Department of Chemistry, University of Minnesota, 207 Pleasant St. SE, Minneapolis, MN 55455, USA
| | - Melissa A Maurer-Jones
- Department of Chemistry, University of Minnesota, 207 Pleasant St. SE, Minneapolis, MN 55455, USA
| | - Christy L Haynes
- Department of Chemistry, University of Minnesota, 207 Pleasant St. SE, Minneapolis, MN 55455, USA.
| |
Collapse
|
27
|
Intracellular trafficking of bio-nanocapsule-liposome complex: Identification of fusogenic activity in the pre-S1 region of hepatitis B virus surface antigen L protein. J Control Release 2015; 212:10-8. [PMID: 26074149 DOI: 10.1016/j.jconrel.2015.06.012] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2014] [Revised: 05/07/2015] [Accepted: 06/09/2015] [Indexed: 12/18/2022]
Abstract
Bio-nanocapsules (BNCs) are a hollow nanoparticle consisting of about 100-nm liposome (LP) embedding about 110 molecules of hepatitis B virus (HBV) surface antigen (HBsAg) L protein as a transmembrane protein. Owing to the human hepatocyte-recognizing domains on the N-terminal region (pre-S1 region), BNCs have recently been shown to attach and enter into human hepatic cells using the early infection mechanism of HBV. Since BNCs could form a complex with an LP containing various drugs and genes, BNC-LP complexes have been used as a human hepatic cell-specific drug and gene-delivery system in vitro and in vivo. However, the role of BNCs in cell entry and intracellular trafficking of payloads in BNC-LP complexes has not been fully elucidated. In this study, we demonstrate that low pH-dependent fusogenic activity resides in the N-terminal part of pre-S1 region (NPLGFFPDHQLDPAFG), of which the first FF residues are essential for the activity, and which facilitates membrane fusion between LPs in vitro. Moreover, BNC-LP complexes can bind human hepatic cells specifically, enter into the cells via clathrin-mediated endocytosis, and release their payloads mostly into the cytoplasm. Taken together, the BNC portion of BNC-LP complexes can induce membrane fusion between LPs and endosomal membranes under low pH conditions, and thereby facilitate the endosomal escape of payloads. Furthermore, the fusogenic domain of the pre-S1 region of HBsAg L protein may play a pivotal role in the intracellular trafficking of not only BNC-LP complexes but also of HBV.
Collapse
|
28
|
Brunger AT, Cipriano DJ, Diao J. Towards reconstitution of membrane fusion mediated by SNAREs and other synaptic proteins. Crit Rev Biochem Mol Biol 2015; 50:231-41. [PMID: 25788028 PMCID: PMC4673598 DOI: 10.3109/10409238.2015.1023252] [Citation(s) in RCA: 45] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
Proteoliposomes have been widely used for in vitro studies of membrane fusion mediated by synaptic proteins. Initially, such studies were made with large unsynchronized ensembles of vesicles. Such ensemble assays limited the insights into the SNARE-mediated fusion mechanism that could be obtained from them. Single particle microscopy experiments can alleviate many of these limitations but they pose significant technical challenges. Here we summarize various approaches that have enabled studies of fusion mediated by SNAREs and other synaptic proteins at a single-particle level. Currently available methods are described and their advantages and limitations are discussed.
Collapse
|
29
|
Fuhrmans M, Marelli G, Smirnova YG, Müller M. Mechanics of membrane fusion/pore formation. Chem Phys Lipids 2015; 185:109-28. [DOI: 10.1016/j.chemphyslip.2014.07.010] [Citation(s) in RCA: 39] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2014] [Revised: 07/07/2014] [Accepted: 07/24/2014] [Indexed: 11/27/2022]
|
30
|
Abstract
Membrane trafficking depends on transport vesicles and carriers docking and fusing with the target organelle for the delivery of cargo. Membrane tethers and small guanosine triphosphatases (GTPases) mediate the docking of transport vesicles/carriers to enhance the efficiency of the subsequent SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor)-mediated fusion event with the target membrane bilayer. Different classes of membrane tethers and their specific intracellular location throughout the endomembrane system are now well defined. Recent biochemical and structural studies have led to a deeper understanding of the mechanism by which membrane tethers mediate docking of membrane carriers as well as an appreciation of the role of tethers in coordinating the correct SNARE complex and in regulating the organization of membrane compartments. This review will summarize the properties and roles of membrane tethers of both secretory and endocytic systems.
Collapse
Affiliation(s)
- Pei Zhi Cheryl Chia
- National Institute of Dental and Craniofacial Research, National Institutes of Health30 Convent Drive, Bethesda, MD 20892-4340USA
| | - Paul A. Gleeson
- The Department of Biochemistry and Molecular Biology and Bio21 Molecular Science and Biotechnology Institute30 Flemington Road, The University of Melbourne, Victoria 3010Australia
| |
Collapse
|
31
|
Meriney SD, Umbach JA, Gundersen CB. Fast, Ca2+-dependent exocytosis at nerve terminals: shortcomings of SNARE-based models. Prog Neurobiol 2014; 121:55-90. [PMID: 25042638 DOI: 10.1016/j.pneurobio.2014.07.001] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2013] [Revised: 04/14/2014] [Accepted: 07/03/2014] [Indexed: 11/30/2022]
Abstract
Investigations over the last two decades have made major inroads in clarifying the cellular and molecular events that underlie the fast, synchronous release of neurotransmitter at nerve endings. Thus, appreciable progress has been made in establishing the structural features and biophysical properties of the calcium (Ca2+) channels that mediate the entry into nerve endings of the Ca2+ ions that trigger neurotransmitter release. It is now clear that presynaptic Ca2+ channels are regulated at many levels and the interplay of these regulatory mechanisms is just beginning to be understood. At the same time, many lines of research have converged on the conclusion that members of the synaptotagmin family serve as the primary Ca2+ sensors for the action potential-dependent release of neurotransmitter. This identification of synaptotagmins as the proteins which bind Ca2+ and initiate the exocytotic fusion of synaptic vesicles with the plasma membrane has spurred widespread efforts to reveal molecular details of synaptotagmin's action. Currently, most models propose that synaptotagmin interfaces directly or indirectly with SNARE (soluble, N-ethylmaleimide sensitive factor attachment receptors) proteins to trigger membrane fusion. However, in spite of intensive efforts, the field has not achieved consensus on the mechanism by which synaptotagmins act. Concurrently, the precise sequence of steps underlying SNARE-dependent membrane fusion remains controversial. This review considers the pros and cons of the different models of SNARE-mediated membrane fusion and concludes by discussing a novel proposal in which synaptotagmins might directly elicit membrane fusion without the intervention of SNARE proteins in this final fusion step.
Collapse
Affiliation(s)
- Stephen D Meriney
- Department of Neuroscience, Center for Neuroscience, University of Pittsburgh, Pittsburgh, PA 15260, USA
| | - Joy A Umbach
- Department of Molecular and Medical Pharmacology, UCLA David Geffen School of Medicine, Los Angeles, CA 90095, USA
| | - Cameron B Gundersen
- Department of Molecular and Medical Pharmacology, UCLA David Geffen School of Medicine, Los Angeles, CA 90095, USA.
| |
Collapse
|
32
|
Kim HY, Huang BX, Spector AA. Phosphatidylserine in the brain: metabolism and function. Prog Lipid Res 2014; 56:1-18. [PMID: 24992464 DOI: 10.1016/j.plipres.2014.06.002] [Citation(s) in RCA: 198] [Impact Index Per Article: 19.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2014] [Revised: 06/18/2014] [Accepted: 06/21/2014] [Indexed: 01/08/2023]
Abstract
Phosphatidylserine (PS) is the major anionic phospholipid class particularly enriched in the inner leaflet of the plasma membrane in neural tissues. PS is synthesized from phosphatidylcholine or phosphatidylethanolamine by exchanging the base head group with serine, and this reaction is catalyzed by phosphatidylserine synthase 1 and phosphatidylserine synthase 2 located in the endoplasmic reticulum. Activation of Akt, Raf-1 and protein kinase C signaling, which supports neuronal survival and differentiation, requires interaction of these proteins with PS localized in the cytoplasmic leaflet of the plasma membrane. Furthermore, neurotransmitter release by exocytosis and a number of synaptic receptors and proteins are modulated by PS present in the neuronal membranes. Brain is highly enriched with docosahexaenoic acid (DHA), and brain PS has a high DHA content. By promoting PS synthesis, DHA can uniquely expand the PS pool in neuronal membranes and thereby influence PS-dependent signaling and protein function. Ethanol decreases DHA-promoted PS synthesis and accumulation in neurons, which may contribute to the deleterious effects of ethanol intake. Improvement of some memory functions has been observed in cognitively impaired subjects as a result of PS supplementation, but the mechanism is unclear.
Collapse
Affiliation(s)
- Hee-Yong Kim
- Laboratory of Molecular Signaling, National Institute on Alcohol Abuse and Alcoholism, National Institutes of Health, Bethesda, MD 20892-9410, United States.
| | - Bill X Huang
- Laboratory of Molecular Signaling, National Institute on Alcohol Abuse and Alcoholism, National Institutes of Health, Bethesda, MD 20892-9410, United States
| | - Arthur A Spector
- Laboratory of Molecular Signaling, National Institute on Alcohol Abuse and Alcoholism, National Institutes of Health, Bethesda, MD 20892-9410, United States
| |
Collapse
|
33
|
In vitro assay using engineered yeast vacuoles for neuronal SNARE-mediated membrane fusion. Proc Natl Acad Sci U S A 2014; 111:7677-82. [PMID: 24821814 DOI: 10.1073/pnas.1400036111] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Intracellular membrane fusion requires not only SNARE proteins but also other regulatory proteins such as the Rab and Sec1/Munc18 (SM) family proteins. Although neuronal SNARE proteins alone can drive the fusion between synthetic liposomes, it remains unclear whether they are also sufficient to induce the fusion of biological membranes. Here, through the use of engineered yeast vacuoles bearing neuronal SNARE proteins, we show that neuronal SNAREs can induce membrane fusion between yeast vacuoles and that this fusion does not require the function of the Rab protein Ypt7p or the SM family protein Vps33p, both of which are essential for normal yeast vacuole fusion. Although excess vacuolar SNARE proteins were also shown to mediate Rab-bypass fusion, this fusion required homotypic fusion and vacuole protein sorting complex, which bears Vps33p and was accompanied by extensive membrane lysis. We also show that this neuronal SNARE-driven vacuole fusion can be stimulated by the neuronal SM protein Munc18 and blocked by botulinum neurotoxin serotype E, a well-known inhibitor of synaptic vesicle fusion. Taken together, our results suggest that neuronal SNARE proteins are sufficient to induce biological membrane fusion, and that this new assay can be used as a simple and complementary method for investigating synaptic vesicle fusion mechanisms.
Collapse
|
34
|
Multiple and distinct strategies of yeast SNAREs to confer the specificity of membrane fusion. Sci Rep 2014; 4:4277. [PMID: 24589832 PMCID: PMC3940976 DOI: 10.1038/srep04277] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2014] [Accepted: 02/17/2014] [Indexed: 01/04/2023] Open
Abstract
Trans-QabcR-SNARE pairing on opposing membranes is crucial for eukaryotic membrane fusion, but how selective pairs of Qabc- and R-SNARE proteins regulate membrane fusion specificity remains elusive. Here, we studied 14 purified full-length SNAREs that function in yeast endoplasmic reticulum (ER)-Golgi, intra-Golgi, endosomal, and vacuolar transport by comprehensively testing cis-QabcR-SNARE assembly and fusogenicity of reconstituted SNARE proteoliposomes. Strikingly, the cognate ER-Golgi and intra-Golgi SNARE-complex assemblies were highly stringent, whereas endosomal and vacuolar SNAREs assembled rather promiscuously into the non-cognate mixed complexes. However, these patterns of cis-SNARE assemblies cannot solely explain their potency to be fusogenic via trans-SNARE pairing: Only the vacuolar 3Q-SNARE combination is fusogenic in the absence of additional components; endosomal SNARE-dependent fusogenicity requires membrane-tethering factors; and ER-Golgi SNAREs can be fusogenic by synergistic actions of tethering factors and the cognate Sec1/Munc18-family protein Sly1p. Thus, our findings uncover multiple and distinct strategies of SNAREs to directly mediate fusion specificity.
Collapse
|
35
|
Hayakawa EH, Mochizuki E, Tsuda T, Akiyoshi K, Matsuoka H, Kuwabata S. The effect of hydrophilic ionic liquids 1-ethyl-3-methylimidazolium lactate and choline lactate on lipid vesicle fusion. PLoS One 2013; 8:e85467. [PMID: 24392011 PMCID: PMC3877375 DOI: 10.1371/journal.pone.0085467] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2013] [Accepted: 11/28/2013] [Indexed: 11/18/2022] Open
Abstract
Ionic liquids (ILs) are room-temperature molten salts that have applications in both physical sciences and more recently in the purification of proteins and lipids, gene transfection and sample preparation for electron microscopy (EM) studies. Transfection of genes into cells requires membrane fusion between the cell membrane and the transfection reagent, thus, ILs may be induce a membrane fusion event. To clarify the behavior of ILs with cell membranes the effect of ILs on model membranes, i.e., liposomes, were investigated. We used two standard ILs, 1-ethyl-3-methylimidazolium lactate ([EMI][Lac]) and choline lactate ([Ch][Lac]), and focused on whether these ILs can induce lipid vesicle fusion. Fluorescence resonance energy transfer and dynamic light scattering were employed to determine whether the ILs induced vesicle fusion. Vesicle solutions at low IL concentrations showed negligible fusion when compared with the controls in the absence of ILs. At concentrations of 30% (v/v), both types of ILs induced vesicle fusion up to 1.3 and 1.6 times the fluorescence intensity of the control in the presence of [Ch][Lac] and [EMI][Lac], respectively. This is the first demonstration that [EMI][Lac] and [Ch][Lac] induce vesicle fusion at high IL concentrations and this observation should have a significant influence on basic biophysical studies. Conversely, the ability to avoid vesicle fusion at low IL concentrations is clearly advantageous for EM studies of lipid samples and cells. This new information describing IL-lipid membrane interactions should impact EM observations examining cell morphology.
Collapse
Affiliation(s)
- Eri H. Hayakawa
- Laboratory of Medical Zoology and Parasitology, Department of Infection and Immunity, Jichi Medical University, Shimotsuke, Tochigi, Japan
- *E-mail: (EHH); (SK)
| | - Eiko Mochizuki
- Department of Applied Chemistry, Graduate School of Engineering, Osaka University, Suita, Osaka, Japan
| | - Tetsuya Tsuda
- Department of Applied Chemistry, Graduate School of Engineering, Osaka University, Suita, Osaka, Japan
| | - Kazunari Akiyoshi
- Department of Polymer Chemistry, Graduate School of Engineering, Kyoto University, Kyoto, Kyoto, Japan
- Japan Science and Technology Agency, ERATO, Kawaguchi, Saitama, Japan
| | - Hiroyuki Matsuoka
- Laboratory of Medical Zoology and Parasitology, Department of Infection and Immunity, Jichi Medical University, Shimotsuke, Tochigi, Japan
| | - Susumu Kuwabata
- Department of Applied Chemistry, Graduate School of Engineering, Osaka University, Suita, Osaka, Japan
- Japan Science and Technology Agency, CREST, Kawaguchi, Saitama, Japan
- *E-mail: (EHH); (SK)
| |
Collapse
|
36
|
Kiessling V, Ahmed S, Domanska MK, Holt MG, Jahn R, Tamm LK. Rapid fusion of synaptic vesicles with reconstituted target SNARE membranes. Biophys J 2013; 104:1950-8. [PMID: 23663838 DOI: 10.1016/j.bpj.2013.03.038] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2013] [Revised: 03/19/2013] [Accepted: 03/22/2013] [Indexed: 12/29/2022] Open
Abstract
Neurotransmitter release at neuronal synapses occurs on a timescale of 1 ms or less. Reconstitution of vesicle fusion from purified synaptic proteins and lipids has played a major role in elucidating the synaptic exocytotic fusion machinery with ever increasing detail. However, one limitation of most reconstitution approaches has been the relatively slow rate of fusion that can be produced in these systems. In a related study, a notable exception is an approach measuring fusion of single reconstituted vesicles bearing the vesicle fusion protein synaptobrevin with supported planar membranes harboring the presynaptic plasma membrane proteins syntaxin and SNAP-25. Fusion times of ∼20 ms were achieved in this system. Despite this advance, an important question with reconstituted systems is how well they mimic physiological systems they are supposed to reproduce. In this work, we demonstrate that purified synaptic vesicles from rat brain fuse with acceptor-SNARE containing planar bilayers equally fast as equivalent reconstituted vesicles and that their fusion efficiency is increased by divalent cations. Calcium boosts fusion through a combined general electrostatic and synaptotagmin-specific mechanism.
Collapse
Affiliation(s)
- Volker Kiessling
- Center for Membrane Biology and Department of Molecular Physiology and Biological Physics, University of Virginia, Charlottesville, Virginia, USA
| | | | | | | | | | | |
Collapse
|
37
|
Abbineni PS, Hibbert JE, Coorssen JR. Critical role of cortical vesicles in dissecting regulated exocytosis: overview of insights into fundamental molecular mechanisms. THE BIOLOGICAL BULLETIN 2013; 224:200-217. [PMID: 23995744 DOI: 10.1086/bblv224n3p200] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
Regulated exocytosis is one of the defining features of eukaryotic cells, underlying many conserved and essential functions. Definitively assigning specific roles to proteins and lipids in this fundamental mechanism is most effectively accomplished using a model system in which distinct stages of exocytosis can be effectively separated. Here we discuss the establishment of sea urchin cortical vesicle fusion as a model to study regulated exocytosis-a system in which the docked, release-ready, and late Ca(2+)-triggered steps of exocytosis are isolated and can be quantitatively assessed using the rigorous coupling of functional and molecular assays. We provide an overview of the insights this has provided into conserved molecular mechanisms and how these have led to and integrate with findings from other regulated exocytotic cells.
Collapse
Affiliation(s)
- Prabhodh S Abbineni
- Department of Molecular Physiology, School of Medicine, University of Western Sydney, NSW, Australia
| | | | | |
Collapse
|
38
|
Tarafdar PK, Chakraborty H, Dennison SM, Lentz BR. Phosphatidylserine inhibits and calcium promotes model membrane fusion. Biophys J 2013. [PMID: 23199916 DOI: 10.1016/j.bpj.2012.09.030] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022] Open
Abstract
PEG-mediated fusion of SUVs composed of dioleoylphosphatidylcholine, dioleoylphosphatidylethanolamine, sphingomyelin, cholesterol, and dioleoylphosphatidylserine was examined to investigate the effects of PS on the fusion mechanism. Lipid mixing, content mixing, and content leakage measurements were carried out with vesicles containing from 0 to 8 mol % PS and similar amounts of phosphatidylglycerol. Fitting these time courses globally to a 3-state (aggregate, intermediate, pore) sequential model established rate constants for each step and probabilities of lipid mixing, content mixing, and leakage in each state. Charged lipids inhibited both the rates of intermediate and pore formation as well as the extents of lipid and contents mixing, although electrostatics were not solely responsible for inhibition. Ca(2+) counteracted this inhibition and increased the extent of fusion in the presence of PS to well beyond that seen in the absence of charged lipids. The effects of both PS and Ca(2+) could be interpreted in terms of a previous proposal for the nature of lipid fluctuations that account for transition states for the two steps of the fusion process examined. The results suggest a more significant role for Ca(2+)-lipid interactions than is acknowledged in current thinking about cell membrane fusion.
Collapse
Affiliation(s)
- Pradip K Tarafdar
- Department of Biochemistry and Biophysics and Program in Molecular and Cellular Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA
| | | | | | | |
Collapse
|
39
|
Ma C, Su L, Seven AB, Xu Y, Rizo J. Reconstitution of the vital functions of Munc18 and Munc13 in neurotransmitter release. Science 2012; 339:421-5. [PMID: 23258414 DOI: 10.1126/science.1230473] [Citation(s) in RCA: 289] [Impact Index Per Article: 24.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
Neurotransmitter release depends critically on Munc18-1, Munc13, the Ca(2+) sensor synaptotagmin-1, and the soluble N-ethylmaleimide-sensitive factor (NSF) attachment protein (SNAP) receptors (SNAREs) syntaxin-1, synaptobrevin, and SNAP-25. In vitro reconstitutions have shown that syntaxin-1-SNAP-25 liposomes fuse efficiently with synaptobrevin liposomes in the presence of synaptotagmin-1-Ca(2+), but neurotransmitter release also requires Munc18-1 and Munc13 in vivo. We found that Munc18-1 could displace SNAP-25 from syntaxin-1 and that fusion of syntaxin-1-Munc18-1 liposomes with synaptobrevin liposomes required Munc13, in addition to SNAP-25 and synaptotagmin-1-Ca(2+). Moreover, when starting with syntaxin-1-SNAP-25 liposomes, NSF-α-SNAP disassembled the syntaxin-1-SNAP-25 heterodimers and abrogated fusion, which then required Munc18-1 and Munc13. We propose that fusion does not proceed through syntaxin-1-SNAP-25 heterodimers but starts with the syntaxin-1-Munc18-1 complex; Munc18-1 and Munc13 then orchestrate membrane fusion together with the SNAREs and synaptotagmin-1-Ca(2+) in an NSF- and SNAP-resistant manner.
Collapse
Affiliation(s)
- Cong Ma
- Key Laboratory of Molecular Biophysics, Ministry of Education, and Institute of Biophysics and Biochemistry, Huazhong University of Science and Technology, Wuhan 430074, China.
| | | | | | | | | |
Collapse
|
40
|
Rizo J, Südhof TC. The Membrane Fusion Enigma: SNAREs, Sec1/Munc18 Proteins, and Their Accomplices—Guilty as Charged? Annu Rev Cell Dev Biol 2012; 28:279-308. [DOI: 10.1146/annurev-cellbio-101011-155818] [Citation(s) in RCA: 318] [Impact Index Per Article: 26.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Josep Rizo
- Departments of Biophysics, Biochemistry and Pharmacology, University of Texas Southwestern Medical Center, Dallas, Texas 75390;
| | - Thomas C. Südhof
- Department of Molecular and Cellular Physiology and Howard Hughes Medical Institute, Stanford University Medical School, Stanford, California 94305;
| |
Collapse
|
41
|
Risselada HJ, Grubmüller H. How SNARE molecules mediate membrane fusion: recent insights from molecular simulations. Curr Opin Struct Biol 2012; 22:187-96. [PMID: 22365575 DOI: 10.1016/j.sbi.2012.01.007] [Citation(s) in RCA: 94] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2012] [Revised: 01/11/2012] [Accepted: 01/13/2012] [Indexed: 10/28/2022]
Abstract
SNARE molecules are the core constituents of the protein machinery that facilitate fusion of synaptic vesicles with the presynaptic plasma membrane, resulting in the release of neurotransmitter. On a molecular level, SNARE complexes seem to play a quite versatile and involved role during all stages of fusion. In addition to merely triggering fusion by forcing the opposing membranes into close proximity, SNARE complexes are now seen to also overcome subsequent fusion barriers and to actively guide the fusion reaction up to the expansion of the fusion pore. Here, we review recent advances in the understanding of SNARE-mediated membrane fusion by molecular simulations.
Collapse
Affiliation(s)
- Herre Jelger Risselada
- Theoretical Molecular Biophysics Group, Max-Planck-Institute for Biophysical Chemistry, Göttingen, Germany
| | | |
Collapse
|
42
|
Izawa R, Onoue T, Furukawa N, Mima J. Distinct contributions of vacuolar Qabc- and R-SNARE proteins to membrane fusion specificity. J Biol Chem 2011; 287:3445-53. [PMID: 22174414 DOI: 10.1074/jbc.m111.307439] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
In eukaryotic endomembrane systems, Qabc-SNAREs (soluble N-ethylmaleimide-sensitive factor attachment protein receptors) on one membrane and R-SNARE on the opposing membrane assemble into a trans-QabcR-SNARE complex to drive membrane fusion. However, it remains ambiguous whether pairing of Qabc- and R-SNAREs mediates membrane fusion specificity. Here, we explored the fusion specificity of reconstituted proteoliposomes bearing purified SNAREs in yeast vacuoles and other organelles. We found that not only vacuolar R-SNARE Nyv1p but also the non-cognate R-SNAREs, endosomal Snc2p, and endoplasmic reticulum-Golgi Sec22p caused efficient fusion with vacuolar Qabc-SNAREs. In contrast, their fusion is blocked completely by replacing vacuolar Qc-SNARE Vam7p with the non-cognate endosomal Tlg1p and Syn8p, although these endosomal Qc-SNAREs fully retained the ability to form cis-SNARE complexes with vacuolar SNAREs in solution and on membranes. Thus, our current study establishes that an appropriate assembly of Qabc-SNAREs is crucial for regulating fusion specificity, whereas R-SNARE itself has little contribution to specificity.
Collapse
Affiliation(s)
- Ryota Izawa
- Institute for Protein Research, Osaka University, Suita, Osaka 565-0871, Japan
| | | | | | | |
Collapse
|
43
|
Abstract
Membrane fusion is one of the most important cellular processes by which two initially distinct lipid bilayers merge their hydrophobic cores, resulting in one interconnected structure. Proteins, called SNARE (soluble N-ethylmaleimide-sensitive factor-attachment protein receptor), play a central role in the fusion process that is also regulated by several accessory proteins. In order to study the SNARE-mediated membrane fusion, the in vitro protein reconstitution assay involving ensemble FRET (fluorescence resonance energy transfer) has been used over a decade. In this mini-review, we describe several single-molecule-based FRET approaches that have been applied to this field to overcome the shortage of the bulk assay in terms of protein and fusion dynamics.
Collapse
Affiliation(s)
- Jiajie Diao
- Department of Physics and Center for the Physics of Living Cells, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
| | - Yuji Ishitsuka
- Department of Physics and Center for the Physics of Living Cells, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
- Howard Hughes Medical Institute, University of Illinois at Urbana–Champaign, Urbana, IL 61801, USA
| | - Woo-Ri Bae
- Department of Physics, KAIST, Daejeon 305-701, Republic of Korea
| |
Collapse
|
44
|
Abstract
Intracellular membrane fusion requires R-SNAREs and Q-SNAREs to assemble into a four-helical parallel coiled-coil, with their hydrophobic anchors spanning the two apposed membranes. Based on the fusion properties of chemically defined SNARE- proteoliposomes, it has been proposed that the assembly of this helical bundle transduces force through the entire bilayer via the transmembrane SNARE anchor domains to drive fusion. However, an R-SNARE, Nyv1p, with a genetically engineered lipid anchor that spans half of the bilayer suffices for the fusion of isolated vacuoles, although this organelle has other R-SNAREs. To demonstrate unequivocally the fusion activity of lipid-anchored Nyv1p, we reconstituted proteoliposomes with purified lipid-anchored Nyv1p as the only protein. When these proteoliposomes were incubated with those bearing cognate Q-SNAREs, there was trans-SNARE complex assembly but, in accord with prior studies of the neuronal SNAREs, little lipid mixing. However, the addition of physiological fusion accessory proteins (HOPS, Sec17p, and Sec18p) allows lipid-anchored Nyv1p to support fusion, suggesting that trans-SNARE complex function is not limited to force transduction across the bilayers through the transmembrane domains.
Collapse
|
45
|
Zucchi PC, Zick M. Membrane fusion catalyzed by a Rab, SNAREs, and SNARE chaperones is accompanied by enhanced permeability to small molecules and by lysis. Mol Biol Cell 2011; 22:4635-46. [PMID: 21976702 PMCID: PMC3226480 DOI: 10.1091/mbc.e11-08-0680] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
The fusion of biological membranes entails a drastic rearrangement of the lipid bilayer. New assays that distinguish fusion from lysis were developed to study an in vitro reconstitution of the yeast vacuolar fusion machinery. These assays revealed that true fusion is accompanied by strongly enhanced membrane permeability to small molecules and by lysis. The fusion of sealed biological membranes joins their enclosed aqueous compartments while mixing their membrane bilayers. Reconstituted fusion reactions are commonly assayed by lipid mixing, which can result from either true fusion or from lysis and its attendant reannealing of membranes. Fusion is also frequently assayed by the mixing of lumenal aqueous compartments, using probes of low molecular weight. With several probes (biotin, methylumbelliferyl-N-acetyl-α-d-neuraminic acid, and dithionite), we find that yeast vacuolar SNAREs (SNAP [Soluble NSF attachment protein] Receptors) increase the permeability of membranes to small molecules and that this permeabilization is enhanced by homotypic fusion and vacuole protein sorting complex (HOPS) and Sec17p/Sec18p, the vacuolar tethering and SNARE chaperone proteins. We now report the development of a novel assay that allows the parallel assessment of lipid mixing, the mixing of intact lumenal compartments, any lysis that occurs, and the membrane permeation of small molecules. Applying this assay to an all-purified reconstituted system consisting of vacuolar lipids, the four vacuolar SNAREs, the SNARE disassembly chaperones Sec17p and Sec18p, the Rab Ypt7p, and the Rab effector/SM protein complex HOPS, we show that true fusion is accompanied by strongly enhanced membrane permeability to small molecules and a measurable rate of lysis.
Collapse
Affiliation(s)
- Paola C Zucchi
- Department of Biochemistry, Dartmouth Medical School, Hanover, NH 03755-3844, USA
| | | |
Collapse
|
46
|
Read JA, Duncan R. Biophysical and functional assays for viral membrane fusion peptides. Methods 2011; 55:122-6. [PMID: 21958986 DOI: 10.1016/j.ymeth.2011.09.010] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2011] [Revised: 09/12/2011] [Accepted: 09/13/2011] [Indexed: 11/26/2022] Open
Abstract
Membrane fusion is a protein catalyzed biophysical reaction that involves the simultaneous intermixing of two phospholipid bilayers and of the aqueous compartments bound by their respective bilayers. In the case of enveloped virus fusogens, short hydrophobic or amphipathic fusion peptides that are components of the larger fusion complex are essential for the membrane merger event. The process of cell-cell membrane fusion and syncytium formation induced by the nonenveloped fusogenic orthoreoviruses is driven by the Fusion-Associated Small Transmembrane (FAST) proteins, which are similarly dependent on the action of fusion peptides. In this article, we describe some simple methods for the biophysical characterization of viral membrane fusion peptides. Liposomes serve as an ideal model system for characterizing peptide-membrane interactions because their size, shape and composition can be readily manipulated. We present details of fluorescence assays used to elucidate the kinetics of membrane fusion as well as complimentary assays used to characterize peptide-induced liposome binding and aggregation.
Collapse
Affiliation(s)
- Jolene A Read
- Department of Microbiology and Immunology, Dalhousie University, Halifax, Nova Scotia, Canada B3H4R2
| | | |
Collapse
|
47
|
Smith EA, Weisshaar JC. Docking, not fusion, as the rate-limiting step in a SNARE-driven vesicle fusion assay. Biophys J 2011; 100:2141-50. [PMID: 21539781 DOI: 10.1016/j.bpj.2011.03.015] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2010] [Revised: 03/09/2011] [Accepted: 03/14/2011] [Indexed: 10/18/2022] Open
Abstract
In vitro vesicle fusion assays that monitor lipid mixing between t-SNARE and v-SNARE vesicles in bulk solution exhibit remarkably slow fusion on the nonphysiological timescale of tens of minutes to several hours. Here, single-vesicle, fluorescence resonance energy transfer-based assays cleanly separate docking and fusion steps for individual vesicle pairs containing full-length SNAREs. Docking is extremely inefficient and is the rate-limiting step. Of importance, the docking and fusion kinetics are comparable in the two assays (one with v-SNARE vesicles tethered to a surface and the other with v-SNARE vesicles free in solution). Addition of the V(C) peptide synaptobrevin-2 (syb(57-92)) increases the docking efficiency by a factor of ∼30, but docking remains rate-limiting. In the presence of V(C) peptide, the fusion step occurs on a timescale of ∼10 s. In previous experiments involving bulk fusion assays in which the addition of synaptotagmin/Ca(2+), Munc-18, or complexin accelerated the observed lipid-mixing rate, the enhancement may have arisen from the docking step rather than the fusion step.
Collapse
Affiliation(s)
- Elizabeth A Smith
- Graduate Program in Molecular Biophysics, University of Wisconsin, Madison, Wisconsin, USA
| | | |
Collapse
|
48
|
Xu Y, Seven AB, Su L, Jiang QX, Rizo J. Membrane bridging and hemifusion by denaturated Munc18. PLoS One 2011; 6:e22012. [PMID: 21765933 PMCID: PMC3130787 DOI: 10.1371/journal.pone.0022012] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2011] [Accepted: 06/10/2011] [Indexed: 11/19/2022] Open
Abstract
Neuronal Munc18-1 and members of the Sec1/Munc18 (SM) protein family play a critical function(s) in intracellular membrane fusion together with SNARE proteins, but the mechanism of action of SM proteins remains highly enigmatic. During experiments designed to address this question employing a 7-nitrobenz-2-oxa-1,3-diazole (NBD) fluorescence de-quenching assay that is widely used to study lipid mixing between reconstituted proteoliposomes, we observed that Munc18-1 from squid (sMunc18-1) was able to increase the apparent NBD fluorescence emission intensity even in the absence of SNARE proteins. Fluorescence emission scans and dynamic light scattering experiments show that this phenomenon arises at least in part from increased light scattering due to sMunc18-1-induced liposome clustering. Nuclear magnetic resonance and circular dichroism data suggest that, although native sMunc18-1 does not bind significantly to lipids, sMunc18-1 denaturation at 37°C leads to insertion into membranes. The liposome clustering activity of sMunc18-1 can thus be attributed to its ability to bridge two membranes upon (perhaps partial) denaturation; correspondingly, this activity is hindered by addition of glycerol. Cryo-electron microscopy shows that liposome clusters induced by sMunc18-1 include extended interfaces where the bilayers of two liposomes come into very close proximity, and clear hemifusion diaphragms. Although the physiological relevance of our results is uncertain, they emphasize the necessity of complementing fluorescence de-quenching assays with alternative experiments in studies of membrane fusion, as well as the importance of considering the potential effects of protein denaturation. In addition, our data suggest a novel mechanism of membrane hemifusion induced by amphipathic macromolecules that does not involve formation of a stalk intermediate.
Collapse
Affiliation(s)
- Yi Xu
- Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, Texas, United States of America
- Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, Texas, United States of America
| | - Alpay B. Seven
- Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, Texas, United States of America
- Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, Texas, United States of America
| | - Lijing Su
- Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, Texas, United States of America
- Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, Texas, United States of America
| | - Qiu-Xing Jiang
- Department of Cell Biology, University of Texas Southwestern Medical Center, Dallas, Texas, United States of America
| | - Josep Rizo
- Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, Texas, United States of America
- Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, Texas, United States of America
- * E-mail:
| |
Collapse
|
49
|
In vitro system capable of differentiating fast Ca2+-triggered content mixing from lipid exchange for mechanistic studies of neurotransmitter release. Proc Natl Acad Sci U S A 2011; 108:E304-13. [PMID: 21705659 DOI: 10.1073/pnas.1107900108] [Citation(s) in RCA: 133] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Understanding the molecular principles of synaptic vesicle fusion is a long-sought goal. It requires the development of a synthetic system that allows manipulations and observations not possible in vivo. Here, we report an in vitro system with reconstituted synaptic proteins that meets the long-sought goal to produce fast content release in the millisecond time regime upon Ca(2+) triggering. Our system simultaneously monitors both content and lipid exchange, and it starts from stable interacting pairs of donor and acceptor vesicles, mimicking the readily releasable pool of synaptic vesicles prior to an action potential. It differentiates between single-vesicle interaction, hemifusion, and complete fusion, the latter mimicking quantized neurotransmitter release upon exocytosis of synaptic vesicles. Prior to Ca(2+) injection, the system is in a state in which spontaneous fusion events between donor and acceptor vesicles are rare. Upon Ca(2+) injection, a rapid burst of complete fusion events emerges, followed by a biphasic decay. The present study focuses on neuronal SNAREs, the Ca(2+) sensor synaptotagmin 1, and the modulator complexin. However, other synaptic proteins could be added and their function examined. Ca(2+) triggering is cooperative, requiring the presence of synaptotagmin, whereas SNAREs alone do not produce a fast fusion burst. Manipulations of the system mimic effects observed in vivo. These results also show that neuronal SNAREs alone do not efficiently produce complete fusion, that the combination of SNAREs with synaptotagmin lowers the activation barriers to full fusion, and that complexin enhances this kinetic control.
Collapse
|
50
|
Neumann S, Langosch D. Conserved conformational dynamics of membrane fusion protein transmembrane domains and flanking regions indicated by sequence statistics. Proteins 2011; 79:2418-27. [DOI: 10.1002/prot.23063] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2011] [Revised: 03/26/2011] [Accepted: 04/19/2011] [Indexed: 11/07/2022]
|