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Rothman JE. A tribute to Paul A. Marks, MD, 1926–2020. J Clin Invest 2020. [DOI: 10.1172/jci140020] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
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Ramakrishnan S, Bera M, Coleman J, Rothman JE, Krishnakumar SS. Synergistic roles of Synaptotagmin-1 and complexin in calcium-regulated neuronal exocytosis. eLife 2020; 9:54506. [PMID: 32401194 PMCID: PMC7220375 DOI: 10.7554/elife.54506] [Citation(s) in RCA: 22] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2019] [Accepted: 04/22/2020] [Indexed: 01/06/2023] Open
Abstract
Calcium (Ca2+)-evoked release of neurotransmitters from synaptic vesicles requires mechanisms both to prevent un-initiated fusion of vesicles (clamping) and to trigger fusion following Ca2+-influx. The principal components involved in these processes are the vesicular fusion machinery (SNARE proteins) and the regulatory proteins, Synaptotagmin-1 and Complexin. Here, we use a reconstituted single-vesicle fusion assay under physiologically-relevant conditions to delineate a novel mechanism by which Synaptotagmin-1 and Complexin act synergistically to establish Ca2+-regulated fusion. We find that under each vesicle, Synaptotagmin-1 oligomers bind and clamp a limited number of 'central' SNARE complexes via the primary interface and introduce a kinetic delay in vesicle fusion mediated by the excess of free SNAREpins. This in turn enables Complexin to arrest the remaining free 'peripheral' SNAREpins to produce a stably clamped vesicle. Activation of the central SNAREpins associated with Synaptotagmin-1 by Ca2+ is sufficient to trigger rapid (<100 msec) and synchronous fusion of the docked vesicles.
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Ramakrishnan S, Bera M, Coleman J, Rothman JE, Krishnakumar SS. Author response: Synergistic roles of Synaptotagmin-1 and complexin in calcium-regulated neuronal exocytosis. 2020. [DOI: 10.7554/elife.54506.sa2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/16/2023]
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Rebane AA, Ziltener P, LaMonica LC, Bauer AH, Zheng H, López-Montero I, Pincet F, Rothman JE, Ernst AM. Liquid-liquid phase separation of the Golgi matrix protein GM130. FEBS Lett 2019; 594:1132-1144. [PMID: 31833055 PMCID: PMC7160038 DOI: 10.1002/1873-3468.13715] [Citation(s) in RCA: 34] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2019] [Revised: 11/26/2019] [Accepted: 12/02/2019] [Indexed: 01/22/2023]
Abstract
Golgins are an abundant class of peripheral membrane proteins of the Golgi. These very long (50–400 nm) rod‐like proteins initially capture cognate transport vesicles, thus enabling subsequent SNARE‐mediated membrane fusion. Here, we explore the hypothesis that in addition to serving as vesicle tethers, Golgins may also possess the capacity to phase separate and, thereby, contribute to the internal organization of the Golgi. GM130 is the most abundant Golgin at the cis Golgi. Remarkably, overexpressed GM130 forms liquid droplets in cells analogous to those described for numerous intrinsically disordered proteins with low complexity sequences, even though GM130 is neither low in complexity nor intrinsically disordered. Virtually pure recombinant GM130 also phase‐separates into dynamic, liquid‐like droplets in close to physiological buffers and at concentrations similar to its estimated local concentration at the cis Golgi.
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Tiwari N, Graham M, Liu X, Yue X, Zhu L, Meshram D, Choi S, Qian Y, Rothman JE, Lee I. Golgin45-Syntaxin5 Interaction Contributes to Structural Integrity of the Golgi Stack. Sci Rep 2019; 9:12465. [PMID: 31462665 PMCID: PMC6713708 DOI: 10.1038/s41598-019-48875-x] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2019] [Accepted: 08/14/2019] [Indexed: 12/15/2022] Open
Abstract
The unique stacked morphology of the Golgi apparatus had been a topic of intense investigation among the cell biologists over the years. We had previously shown that the two Golgin tethers (GM130 and Golgin45) could, to a large degree, functionally substitute for GRASP-type Golgi stacking proteins to sustain normal Golgi morphology and function in GRASP65/55-double depleted HeLa cells. However, compared to well-studied GM130, the exact role of Golgin45 in Golgi structure remains poorly understood. In this study, we aimed to further characterize the functional role of Golgin45 in Golgi structure and identified Golgin45 as a novel Syntaxin5-binding protein. Based primarily on a sequence homology between Golgin45 and GM130, we found that a leucine zipper-like motif in the central coiled-coil region of Golgin45 appears to serve as a Syntaxin5 binding domain. Mutagenesis study of this conserved domain in Golgin45 showed that a point mutation (D171A) can abrogate the interaction between Golgin45 and Syntaxin5 in pull-down assays using recombinant proteins, whereas this mutant Golgin45 binding to Rab2-GTP was unaffected in vitro. Strikingly, exogenous expression of this Syntaxin5 binding deficient mutant (D171A) of Golgin45 in HeLa cells resulted in frequent intercisternal fusion among neighboring Golgi cisterna, as readily observed by EM and EM tomography. Further, double depletion of the two Syntaxin5-binding Golgin tethers also led to significant intercisternal fusion, while double depletion of GRASP65/55 didn’t lead to this phenotype. These results suggest that certain tether-SNARE interaction within Golgi stack may play a role in inhibiting intercisternal fusion among neighboring cisternae, thereby contributing to structural integrity of the Golgi stack.
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Chelban V, Wilson MP, Warman Chardon J, Vandrovcova J, Zanetti MN, Zamba‐Papanicolaou E, Efthymiou S, Pope S, Conte MR, Abis G, Liu Y, Tribollet E, Haridy NA, Botía JA, Ryten M, Nicolaou P, Minaidou A, Christodoulou K, Kernohan KD, Eaton A, Osmond M, Ito Y, Bourque P, Jepson JEC, Bello O, Bremner F, Cordivari C, Reilly MM, Foiani M, Heslegrave A, Zetterberg H, Heales SJR, Wood NW, Rothman JE, Boycott KM, Mills PB, Clayton PT, Houlden H. PDXK mutations cause polyneuropathy responsive to pyridoxal 5'-phosphate supplementation. Ann Neurol 2019; 86:225-240. [PMID: 31187503 PMCID: PMC6772106 DOI: 10.1002/ana.25524] [Citation(s) in RCA: 48] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2018] [Revised: 06/05/2019] [Accepted: 06/07/2019] [Indexed: 12/30/2022]
Abstract
OBJECTIVE To identify disease-causing variants in autosomal recessive axonal polyneuropathy with optic atrophy and provide targeted replacement therapy. METHODS We performed genome-wide sequencing, homozygosity mapping, and segregation analysis for novel disease-causing gene discovery. We used circular dichroism to show secondary structure changes and isothermal titration calorimetry to investigate the impact of variants on adenosine triphosphate (ATP) binding. Pathogenicity was further supported by enzymatic assays and mass spectroscopy on recombinant protein, patient-derived fibroblasts, plasma, and erythrocytes. Response to supplementation was measured with clinical validated rating scales, electrophysiology, and biochemical quantification. RESULTS We identified biallelic mutations in PDXK in 5 individuals from 2 unrelated families with primary axonal polyneuropathy and optic atrophy. The natural history of this disorder suggests that untreated, affected individuals become wheelchair-bound and blind. We identified conformational rearrangement in the mutant enzyme around the ATP-binding pocket. Low PDXK ATP binding resulted in decreased erythrocyte PDXK activity and low pyridoxal 5'-phosphate (PLP) concentrations. We rescued the clinical and biochemical profile with PLP supplementation in 1 family, improvement in power, pain, and fatigue contributing to patients regaining their ability to walk independently during the first year of PLP normalization. INTERPRETATION We show that mutations in PDXK cause autosomal recessive axonal peripheral polyneuropathy leading to disease via reduced PDXK enzymatic activity and low PLP. We show that the biochemical profile can be rescued with PLP supplementation associated with clinical improvement. As B6 is a cofactor in diverse essential biological pathways, our findings may have direct implications for neuropathies of unknown etiology characterized by reduced PLP levels. ANN NEUROL 2019;86:225-240.
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Rothman JE. Jim's view: Why basic science? FEBS Lett 2019; 593:1693-1697. [PMID: 31301070 DOI: 10.1002/1873-3468.13510] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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Rothman JE. Jim's view: Patience vs urgency. FEBS Lett 2019; 593:2081-2082. [PMID: 31301062 DOI: 10.1002/1873-3468.13518] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Rothman JE. Jim's view: What makes transformative basic science possible? FEBS Lett 2019; 593:1877-1878. [PMID: 31301063 DOI: 10.1002/1873-3468.13517] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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Salpietro V, Dixon CL, Guo H, Bello OD, Vandrovcova J, Efthymiou S, Maroofian R, Heimer G, Burglen L, Valence S, Torti E, Hacke M, Rankin J, Tariq H, Colin E, Procaccio V, Striano P, Mankad K, Lieb A, Chen S, Pisani L, Bettencourt C, Männikkö R, Manole A, Brusco A, Grosso E, Ferrero GB, Armstrong-Moron J, Gueden S, Bar-Yosef O, Tzadok M, Monaghan KG, Santiago-Sim T, Person RE, Cho MT, Willaert R, Yoo Y, Chae JH, Quan Y, Wu H, Wang T, Bernier RA, Xia K, Blesson A, Jain M, Motazacker MM, Jaeger B, Schneider AL, Boysen K, Muir AM, Myers CT, Gavrilova RH, Gunderson L, Schultz-Rogers L, Klee EW, Dyment D, Osmond M, Parellada M, Llorente C, Gonzalez-Peñas J, Carracedo A, Van Haeringen A, Ruivenkamp C, Nava C, Heron D, Nardello R, Iacomino M, Minetti C, Skabar A, Fabretto A, Raspall-Chaure M, Chez M, Tsai A, Fassi E, Shinawi M, Constantino JN, De Zorzi R, Fortuna S, Kok F, Keren B, Bonneau D, Choi M, Benzeev B, Zara F, Mefford HC, Scheffer IE, Clayton-Smith J, Macaya A, Rothman JE, Eichler EE, Kullmann DM, Houlden H. AMPA receptor GluA2 subunit defects are a cause of neurodevelopmental disorders. Nat Commun 2019; 10:3094. [PMID: 31300657 PMCID: PMC6626132 DOI: 10.1038/s41467-019-10910-w] [Citation(s) in RCA: 124] [Impact Index Per Article: 24.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2018] [Accepted: 05/22/2019] [Indexed: 01/22/2023] Open
Abstract
AMPA receptors (AMPARs) are tetrameric ligand-gated channels made up of combinations of GluA1-4 subunits encoded by GRIA1-4 genes. GluA2 has an especially important role because, following post-transcriptional editing at the Q607 site, it renders heteromultimeric AMPARs Ca2+-impermeable, with a linear relationship between current and trans-membrane voltage. Here, we report heterozygous de novo GRIA2 mutations in 28 unrelated patients with intellectual disability (ID) and neurodevelopmental abnormalities including autism spectrum disorder (ASD), Rett syndrome-like features, and seizures or developmental epileptic encephalopathy (DEE). In functional expression studies, mutations lead to a decrease in agonist-evoked current mediated by mutant subunits compared to wild-type channels. When GluA2 subunits are co-expressed with GluA1, most GRIA2 mutations cause a decreased current amplitude and some also affect voltage rectification. Our results show that de-novo variants in GRIA2 can cause neurodevelopmental disorders, complementing evidence that other genetic causes of ID, ASD and DEE also disrupt glutamatergic synaptic transmission.
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Coleman J, Jouannot O, Ramakrishnan SK, Zanetti MN, Wang J, Salpietro V, Houlden H, Rothman JE, Krishnakumar SS. PRRT2 Regulates Synaptic Fusion by Directly Modulating SNARE Complex Assembly. Cell Rep 2019; 22:820-831. [PMID: 29346777 PMCID: PMC5792450 DOI: 10.1016/j.celrep.2017.12.056] [Citation(s) in RCA: 60] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2017] [Revised: 11/12/2017] [Accepted: 12/17/2017] [Indexed: 11/25/2022] Open
Abstract
Mutations in proline-rich transmembrane protein 2 (PRRT2) are associated with a range of paroxysmal neurological disorders. PRRT2 predominantly localizes to the pre-synaptic terminals and is believed to regulate neurotransmitter release. However, the mechanism of action is unclear. Here, we use reconstituted single vesicle and bulk fusion assays, combined with live cell imaging of single exocytotic events in PC12 cells and biophysical analysis, to delineate the physiological role of PRRT2. We report that PRRT2 selectively blocks the trans SNARE complex assembly and thus negatively regulates synaptic vesicle priming. This inhibition is actualized via weak interactions of the N-terminal proline-rich domain with the synaptic SNARE proteins. Furthermore, we demonstrate that paroxysmal dyskinesia-associated mutations in PRRT2 disrupt this SNARE-modulatory function and with efficiencies corresponding to the severity of the disease phenotype. Our findings provide insights into the molecular mechanisms through which loss-of-function mutations in PRRT2 result in paroxysmal neurological disorders.
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Karatekin E, Rothman JE. FEBS Letters Special Issue on Exocytosis and Endocytosis. FEBS Lett 2019; 592:3477-3479. [PMID: 30417372 DOI: 10.1002/1873-3468.13274] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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Grushin K, Wang J, Coleman J, Rothman JE, Sindelar CV, Krishnakumar SS. Structural basis for the clamping and Ca 2+ activation of SNARE-mediated fusion by synaptotagmin. Nat Commun 2019; 10:2413. [PMID: 31160571 PMCID: PMC6546687 DOI: 10.1038/s41467-019-10391-x] [Citation(s) in RCA: 31] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2018] [Accepted: 05/08/2019] [Indexed: 12/22/2022] Open
Abstract
Synapotagmin-1 (Syt1) interacts with both SNARE proteins and lipid membranes to synchronize neurotransmitter release to calcium (Ca2+) influx. Here we report the cryo-electron microscopy structure of the Syt1-SNARE complex on anionic-lipid containing membranes. Under resting conditions, the Syt1 C2 domains bind the membrane with a magnesium (Mg2+)-mediated partial insertion of the aliphatic loops, alongside weak interactions with the anionic lipid headgroups. The C2B domain concurrently interacts the SNARE bundle via the 'primary' interface and is positioned between the SNAREpins and the membrane. In this configuration, Syt1 is projected to sterically delay the complete assembly of the associated SNAREpins and thus, contribute to clamping fusion. This Syt1-SNARE organization is disrupted upon Ca2+-influx as Syt1 reorients into the membrane, likely displacing the attached SNAREpins and reversing the fusion clamp. We thus conclude that the cation (Mg2+/Ca2+) dependent membrane interaction is a key determinant of the dual clamp/activator function of Synaptotagmin-1.
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Heo P, Ramakrishnan S, Coleman J, Rothman JE, Fleury JB, Pincet F. Highly Reproducible Physiological Asymmetric Membrane with Freely Diffusing Embedded Proteins in a 3D-Printed Microfluidic Setup. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2019; 15:e1900725. [PMID: 30977975 DOI: 10.1002/smll.201900725] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/08/2019] [Revised: 03/28/2019] [Indexed: 06/09/2023]
Abstract
Experimental setups to produce and to monitor model membranes have been successfully used for decades and brought invaluable insights into many areas of biology. However, they all have limitations that prevent the full in vitro mimicking and monitoring of most biological processes. Here, a suspended physiological bilayer-forming chip is designed from 3D-printing techniques. This chip can be simultaneously integrated to a confocal microscope and a path-clamp amplifier. It is composed of poly(dimethylsiloxane) and consists of a ≈100 µm hole, where the horizontal planar bilayer is formed, connecting two open crossed-channels, which allows for altering of each lipid monolayer separately. The bilayer, formed by the zipping of two lipid leaflets, is free-standing, horizontal, stable, fluid, solvent-free, and flat with the 14 types of physiologically relevant lipids, and the bilayer formation process is highly reproducible. Because of the two channels, asymmetric bilayers can be formed by making the two lipid leaflets of different composition. Furthermore, proteins, such as transmembrane, peripheral, and pore-forming proteins, can be added to the bilayer in controlled orientation and keep their native mobility and activity. These features allow in vitro recapitulation of membrane process close to physiological conditions.
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Erdmann RS, Baguley SW, Richens JH, Wissner RF, Xi Z, Allgeyer ES, Zhong S, Thompson AD, Lowe N, Butler R, Bewersdorf J, Rothman JE, St Johnston D, Schepartz A, Toomre D. Labeling Strategies Matter for Super-Resolution Microscopy: A Comparison between HaloTags and SNAP-tags. Cell Chem Biol 2019; 26:584-592.e6. [PMID: 30745239 PMCID: PMC6474801 DOI: 10.1016/j.chembiol.2019.01.003] [Citation(s) in RCA: 81] [Impact Index Per Article: 16.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2017] [Revised: 07/13/2018] [Accepted: 01/07/2019] [Indexed: 12/22/2022]
Abstract
Super-resolution microscopy requires that subcellular structures are labeled with bright and photostable fluorophores, especially for live-cell imaging. Organic fluorophores may help here as they can yield more photons-by orders of magnitude-than fluorescent proteins. To achieve molecular specificity with organic fluorophores in live cells, self-labeling proteins are often used, with HaloTags and SNAP-tags being the most common. However, how these two different tagging systems compare with each other is unclear, especially for stimulated emission depletion (STED) microscopy, which is limited to a small repertoire of fluorophores in living cells. Herein, we compare the two labeling approaches in confocal and STED imaging using various proteins and two model systems. Strikingly, we find that the fluorescent signal can be up to 9-fold higher with HaloTags than with SNAP-tags when using far-red rhodamine derivatives. This result demonstrates that the labeling strategy matters and can greatly influence the duration of super-resolution imaging.
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Manca F, Pincet F, Truskinovsky L, Rothman JE, Foret L, Caruel M. SNARE machinery is optimized for ultrafast fusion. Proc Natl Acad Sci U S A 2019; 116:2435-2442. [PMID: 30700546 PMCID: PMC6377469 DOI: 10.1073/pnas.1820394116] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
Abstract
SNARE proteins zipper to form complexes (SNAREpins) that power vesicle fusion with target membranes in a variety of biological processes. A single SNAREpin takes about 1 s to fuse two bilayers, yet a handful can ensure release of neurotransmitters from synaptic vesicles much faster: in a 10th of a millisecond. We propose that, similar to the case of muscle myosins, the ultrafast fusion results from cooperative action of many SNAREpins. The coupling originates from mechanical interactions induced by confining scaffolds. Each SNAREpin is known to have enough energy to overcome the fusion barrier of 25-[Formula: see text]; however, the fusion barrier only becomes relevant when the SNAREpins are nearly completely zippered, and from this state, each SNAREpin can deliver only a small fraction of this energy as mechanical work. Therefore, they have to act cooperatively, and we show that at least three of them are needed to ensure fusion in less than a millisecond. However, to reach the prefusion state collectively, starting from the experimentally observed half-zippered metastable state, the SNAREpins have to mechanically synchronize, which takes more time as the number of SNAREpins increases. Incorporating this somewhat counterintuitive idea in a simple coarse-grained model results in the prediction that there should be an optimum number of SNAREpins for submillisecond fusion: three to six over a wide range of parameters. Interestingly, in situ cryoelectron microscope tomography has very recently shown that exactly six SNAREpins participate in the fusion of each synaptic vesicle. This number is in the range predicted by our theory.
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Ernst AM, Syed SA, Zaki O, Bottanelli F, Zheng H, Hacke M, Xi Z, Rivera-Molina F, Graham M, Rebane AA, Björkholm P, Baddeley D, Toomre D, Pincet F, Rothman JE. S-Palmitoylation Sorts Membrane Cargo for Anterograde Transport in the Golgi. Dev Cell 2019; 47:479-493.e7. [PMID: 30458139 DOI: 10.1016/j.devcel.2018.10.024] [Citation(s) in RCA: 88] [Impact Index Per Article: 17.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2018] [Revised: 09/07/2018] [Accepted: 10/20/2018] [Indexed: 12/11/2022]
Abstract
While retrograde cargo selection in the Golgi is known to depend on specific signals, it is unknown whether anterograde cargo is sorted, and anterograde signals have not been identified. We suggest here that S-palmitoylation of anterograde cargo at the Golgi membrane interface is an anterograde signal and that it results in concentration in curved regions at the Golgi rims by simple physical chemistry. The rate of transport across the Golgi of two S-palmitoylated membrane proteins is controlled by S-palmitoylation. The bulk of S-palmitoylated proteins in the Golgi behave analogously, as revealed by click chemistry-based fluorescence and electron microscopy. These palmitoylated cargos concentrate in the most highly curved regions of the Golgi membranes, including the fenestrated perimeters of cisternae and associated vesicles. A palmitoylated transmembrane domain behaves similarly in model systems.
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Li X, Radhakrishnan A, Grushin K, Kasula R, Chaudhuri A, Gomathinayagam S, Krishnakumar SS, Liu J, Rothman JE. Symmetrical organization of proteins under docked synaptic vesicles. FEBS Lett 2019; 593:144-153. [PMID: 30561792 PMCID: PMC6353562 DOI: 10.1002/1873-3468.13316] [Citation(s) in RCA: 28] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2018] [Revised: 12/13/2018] [Accepted: 12/17/2018] [Indexed: 11/11/2022]
Abstract
During calcium‐regulated exocytosis, the constitutive fusion machinery is ‘clamped’ in a partially assembled state until synchronously released by calcium. The protein machinery involved in this process is known, but the supra‐molecular architecture and underlying mechanisms are unclear. Here, we use cryo‐electron tomography analysis in nerve growth factor‐differentiated neuro‐endocrine (PC12) cells to delineate the organization of the release machinery under the docked vesicles. We find that exactly six exocytosis modules, each likely consisting of a single SNAREpin with its bound Synaptotagmins, Complexin, and Munc18 proteins, are symmetrically arranged at the vesicle–PM interface. Mutational analysis suggests that the symmetrical organization is templated by circular oligomers of Synaptotagmin. The observed arrangement, including its precise radial positioning, is in‐line with the recently proposed ‘buttressed ring hypothesis’.
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Ramakrishnan S, Bera M, Coleman J, Krishnakumar SS, Pincet F, Rothman JE. Synaptotagmin oligomers are necessary and can be sufficient to form a Ca 2+ -sensitive fusion clamp. FEBS Lett 2019; 593:154-162. [PMID: 30570144 PMCID: PMC6349546 DOI: 10.1002/1873-3468.13317] [Citation(s) in RCA: 35] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2018] [Revised: 12/16/2018] [Accepted: 12/17/2018] [Indexed: 12/11/2022]
Abstract
The buttressed‐ring hypothesis, supported by recent cryo‐electron tomography analysis of docked synaptic‐like vesicles in neuroendocrine cells, postulates that prefusion SNAREpins are stabilized and organized by Synaptotagmin (Syt) ring‐like oligomers. Here, we use a reconstituted single‐vesicle fusion analysis to test the prediction that destabilizing the Syt1 oligomers destabilizes the clamp and results in spontaneous fusion in the absence of Ca2+. Vesicles in which Syt oligomerization is compromised by a ring‐destabilizing mutation dock and diffuse freely on the bilayer until they fuse spontaneously, similar to vesicles containing only v‐SNAREs. In contrast, vesicles containing wild‐type Syt are immobile as soon as they attach to the bilayer and remain frozen in place, up to at least 1 h until fusion is triggered by Ca2+.
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Rothman JE. Jim's view: analog to digital conversion in biology. FEBS Lett 2018; 592:4009-4010. [PMID: 30552677 DOI: 10.1002/1873-3468.13308] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Rothman JE. Jim's View: "Playing Billiards with Science". FEBS Lett 2018; 592:2381-2382. [PMID: 29920662 DOI: 10.1002/1873-3468.13125] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Ramakrishnan S, Gohlke A, Li F, Coleman J, Xu W, Rothman JE, Pincet F. High-Throughput Monitoring of Single Vesicle Fusion Using Freestanding Membranes and Automated Analysis. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2018; 34:5849-5859. [PMID: 29694054 DOI: 10.1021/acs.langmuir.8b00116] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
In vivo membrane fusion primarily occurs between highly curved vesicles and planar membranes. A better understanding of fusion entails an accurate in vitro reproduction of the process. To date, supported bilayers have been commonly used to mimic the planar membranes. Soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) proteins that induce membrane fusion usually have limited fluidity when embedded in supported bilayers. This alters the kinetics and prevents correct reconstitution of the overall fusion process. Also, observing content release across the membrane is hindered by the lack of a second aqueous compartment. Recently, a step toward resolving these issues was achieved by using membranes spread on holey substrates. The mobility of proteins was preserved but vesicles were prone to bind to the substrate when reaching the edge of the hole, preventing the observation of many fusion events over the suspended membrane. Building on this recent advance, we designed a method for the formation of pore-spanning lipid bilayers containing t-SNARE proteins on Si/SiO2 holey chips, allowing the observation of many individual vesicle fusion events by both lipid mixing and content release. With this setup, proteins embedded in the suspended membrane bounced back when they reached the edge of the hole which ensured vesicles did not bind to the substrate. We observed SNARE-dependent membrane fusion with the freestanding bilayer of about 500 vesicles. The time between vesicle docking and fusion is ∼1 s. We also present a new multimodal open-source software, Fusion Analyzer Software, which is required for fast data analysis.
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Gruget C, Coleman J, Bello O, Krishnakumar SS, Perez E, Rothman JE, Pincet F, Donaldson SH. Rearrangements under confinement lead to increased binding energy of Synaptotagmin‐1 with anionic membranes in Mg
2+
and Ca
2+. FEBS Lett 2018; 592:1497-1506. [DOI: 10.1002/1873-3468.13040] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2018] [Revised: 03/05/2018] [Accepted: 03/16/2018] [Indexed: 11/09/2022]
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50
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Grushin K, Wang J, Coleman J, Rothman JE, Sindelar CV, Krishnakumar SS. Structural Insight into the Interaction of Synaptotagmin-1 and Snare Complex on Lipid Bilayer by Cryo-Electron Microscopy. Biophys J 2018. [DOI: 10.1016/j.bpj.2017.11.1622] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
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