151
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Kienle N, Kloepper TH, Fasshauer D. Phylogeny of the SNARE vesicle fusion machinery yields insights into the conservation of the secretory pathway in fungi. BMC Evol Biol 2009; 9:19. [PMID: 19166604 PMCID: PMC2639358 DOI: 10.1186/1471-2148-9-19] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2008] [Accepted: 01/23/2009] [Indexed: 12/29/2022] Open
Abstract
Background In eukaryotic cells, directional transport between different compartments of the endomembrane system is mediated by vesicles that bud from a donor organelle and then fuse with an acceptor organelle. A family of integral membrane proteins, termed soluble N-ethylmaleimide-sensitive factor attachment receptor (SNARE) proteins, constitute the key machineries of these different membrane fusion events. Over the past 30 years, the yeast Saccharomyces cerevisiae has served as a powerful model organism for studying the organization of the secretory and endocytic pathways, and a few years ago, its entire set of SNAREs was compiled. Results Here, we make use of the increasing amount of genomic data to investigate the history of the SNARE family during fungi evolution. Moreover, since different SNARE family members are thought to demarcate different organelles and vesicles, this approach allowed us to compare the organization of the endomembrane systems of yeast and animal cells. Our data corroborate the notion that fungi generally encompass a relatively simple set of SNARE proteins, mostly comprising the SNAREs of the proto-eukaryotic cell. However, all fungi contain a novel soluble SNARE protein, Vam7, which carries an N-terminal PX-domain that acts as a phosphoinositide binding module. In addition, the points in fungal evolution, at which lineage-specific duplications and diversifications occurred, could be determined. For instance, the endosomal syntaxins Pep12 and Vam3 arose from a gene duplication that occurred within the Saccharomycotina clade. Conclusion Although the SNARE repertoire of baker's yeast is highly conserved, our analysis reveals that it is more deviated than the ones of basal fungi. This highlights that the trafficking pathways of baker's yeast are not only different to those in animal cells but also are somewhat different to those of many other fungi.
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Affiliation(s)
- Nickias Kienle
- Department of Neurobiology, Max-Planck-Institute for Biophysical Chemistry, Göttingen, Germany.
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152
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Abstract
The two universally required components of the intracellular membrane fusion machinery, SNARE and SM (Sec1/Munc18-like) proteins, play complementary roles in fusion. Vesicular and target membrane-localized SNARE proteins zipper up into an alpha-helical bundle that pulls the two membranes tightly together to exert the force required for fusion. SM proteins, shaped like clasps, bind to trans-SNARE complexes to direct their fusogenic action. Individual fusion reactions are executed by distinct combinations of SNARE and SM proteins to ensure specificity, and are controlled by regulators that embed the SM-SNARE fusion machinery into a physiological context. This regulation is spectacularly apparent in the exquisite speed and precision of synaptic exocytosis, where synaptotagmin (the calcium-ion sensor for fusion) cooperates with complexin (the clamp activator) to control the precisely timed release of neurotransmitters that initiates synaptic transmission and underlies brain function.
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Affiliation(s)
- Thomas C. Südhof
- Department of Cellular and Molecular Physiology, Stanford University, Palo Alto, CA 94304-5543 USADepartment of Cell Biology, Yale University School of Medicine, 333 Cedar Street, New Haven, CT 06520 USA
| | - James E. Rothman
- Department of Cellular and Molecular Physiology, Stanford University, Palo Alto, CA 94304-5543 USADepartment of Cell Biology, Yale University School of Medicine, 333 Cedar Street, New Haven, CT 06520 USA
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153
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Johansson JU, Ericsson J, Janson J, Beraki S, Stanić D, Mandic SA, Wikström MA, Hökfelt T, Ögren SO, Rozell B, Berggren PO, Bark C. An ancient duplication of exon 5 in the Snap25 gene is required for complex neuronal development/function. PLoS Genet 2008; 4:e1000278. [PMID: 19043548 PMCID: PMC2581893 DOI: 10.1371/journal.pgen.1000278] [Citation(s) in RCA: 64] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2008] [Accepted: 10/27/2008] [Indexed: 01/05/2023] Open
Abstract
Alternative splicing is an evolutionary innovation to create functionally diverse proteins from a limited number of genes. SNAP-25 plays a central role in neuroexocytosis by bridging synaptic vesicles to the plasma membrane during regulated exocytosis. The SNAP-25 polypeptide is encoded by a single copy gene, but in higher vertebrates a duplication of exon 5 has resulted in two mutually exclusive splice variants, SNAP-25a and SNAP-25b. To address a potential physiological difference between the two SNAP-25 proteins, we generated gene targeted SNAP-25b deficient mouse mutants by replacing the SNAP-25b specific exon with a second SNAP-25a equivalent. Elimination of SNAP-25b expression resulted in developmental defects, spontaneous seizures, and impaired short-term synaptic plasticity. In adult mutants, morphological changes in hippocampus and drastically altered neuropeptide expression were accompanied by severe impairment of spatial learning. We conclude that the ancient exon duplication in the Snap25 gene provides additional SNAP-25-function required for complex neuronal processes in higher eukaryotes. In evolution, duplication of genes or gene segments appears to be an efficient way to add diverse functions in more complex organisms. The SNAP-25 protein plays an important role in mediating the release of neurotransmitters and hormones. SNAP-25 exists as two variants: SNAP-25a, which is present in early development, and SNAP-25b, which is most abundant from early adulthood and onwards. We have developed mouse mutants that only express SNAP-25a, but retain normal SNAP-25 levels by replacing the SNAP-25b segment in the Snap25 gene with an additional SNAP-25a copy. We show that SNAP-25b is required for early postnatal development and that a balanced expression of the two proteins is a prerequisite for maintaining an operational neuronal network during adulthood. Mice that only have SNAP-25a develop seizures, and show learning deficits and anxiety. Synaptic plasticity is impaired, and structural changes are observed in areas that are connected to such behavioral functions. In man, SNAP-25 function has been linked to behavioral and neuropsychiatric disorders, including attention deficit hyperactivity disorder, ADHD. Our present findings using genetic elimination of SNAP-25b suggest that even small alterations in the regulation of the Snap25 gene, resulting in a disturbed balance between SNAP-25a and SNAP-25b, lead to nervous system dysfunction.
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Affiliation(s)
- Jenny U. Johansson
- The Rolf Luft Research Center for Diabetes and Endocrinology, Karolinska Institutet, Stockholm, Sweden
| | - Jesper Ericsson
- Department of Neuroscience, Karolinska Institutet, Stockholm, Sweden
| | - Juliette Janson
- The Rolf Luft Research Center for Diabetes and Endocrinology, Karolinska Institutet, Stockholm, Sweden
| | - Simret Beraki
- Department of Neuroscience, Karolinska Institutet, Stockholm, Sweden
| | - Davor Stanić
- Department of Neuroscience, Karolinska Institutet, Stockholm, Sweden
| | - Slavena A. Mandic
- The Rolf Luft Research Center for Diabetes and Endocrinology, Karolinska Institutet, Stockholm, Sweden
| | | | - Tomas Hökfelt
- Department of Neuroscience, Karolinska Institutet, Stockholm, Sweden
| | - Sven Ove Ögren
- Department of Neuroscience, Karolinska Institutet, Stockholm, Sweden
| | - Björn Rozell
- Department of Laboratory Medicine, Karolinska Institutet, Stockholm, Sweden
| | - Per-Olof Berggren
- The Rolf Luft Research Center for Diabetes and Endocrinology, Karolinska Institutet, Stockholm, Sweden
| | - Christina Bark
- The Rolf Luft Research Center for Diabetes and Endocrinology, Karolinska Institutet, Stockholm, Sweden
- * E-mail:
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154
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Ebine K, Okatani Y, Uemura T, Goh T, Shoda K, Niihama M, Morita MT, Spitzer C, Otegui MS, Nakano A, Ueda T. A SNARE complex unique to seed plants is required for protein storage vacuole biogenesis and seed development of Arabidopsis thaliana. THE PLANT CELL 2008; 20:3006-21. [PMID: 18984676 PMCID: PMC2613668 DOI: 10.1105/tpc.107.057711] [Citation(s) in RCA: 170] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/20/2007] [Revised: 09/23/2008] [Accepted: 10/24/2008] [Indexed: 05/18/2023]
Abstract
The SNARE complex is a key regulator of vesicular traffic, executing membrane fusion between transport vesicles or organelles and target membranes. A functional SNARE complex consists of four coiled-coil helical bundles, three of which are supplied by Q-SNAREs and another from an R-SNARE. Arabidopsis thaliana VAMP727 is an R-SNARE, with homologs only in seed plants. We have found that VAMP727 colocalizes with SYP22/ VAM3, a Q-SNARE, on a subpopulation of prevacuolar compartments/endosomes closely associated with the vacuolar membrane. Genetic and biochemical analyses, including examination of a synergistic interaction of vamp727 and syp22 mutations, histological examination of protein localization, and coimmunoprecipitation from Arabidopsis lysates indicate that VAMP727 forms a complex with SYP22, VTI11, and SYP51 and that this complex plays a crucial role in vacuolar transport, seed maturation, and vacuole biogenesis. We suggest that the VAMP727 complex mediates the membrane fusion between the prevacuolar compartment and the vacuole and that this process has evolved as an essential step for seed development.
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Affiliation(s)
- Kazuo Ebine
- Department of Biological Sciences, Graduate School of Science, University of Tokyo, Bunkyo-ku, Tokyo 113-0033, Japan
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155
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Mahoney TR, Luo S, Round EK, Brauner M, Gottschalk A, Thomas JH, Nonet ML. Intestinal signaling to GABAergic neurons regulates a rhythmic behavior in Caenorhabditis elegans. Proc Natl Acad Sci U S A 2008; 105:16350-5. [PMID: 18852466 PMCID: PMC2570992 DOI: 10.1073/pnas.0803617105] [Citation(s) in RCA: 65] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2008] [Indexed: 11/18/2022] Open
Abstract
The Caenorhabditis elegans defecation motor program (DMP) is a highly coordinated rhythmic behavior that requires two GABAergic neurons that synapse onto the enteric muscles. One class of DMP mutants, called anterior body wall muscle contraction and expulsion defective (aex) mutants, exhibits similar defects to those caused by the loss of these two neurons. Here, we demonstrate that aex-2 encodes a G-protein-coupled receptor (GPCR) and aex-4 encodes an exocytic SNAP25 homologue. We found that aex-2 functions in the nervous system and activates a G(s)alpha signaling pathway to regulate defecation. aex-4, on the other hand, functions in the intestinal epithelial cells. Furthermore, we show that aex-5, which encodes a pro-protein convertase, functions in the intestine to regulate the DMP and that its secretion from the intestine is impaired in aex-4 mutants. Activation of the G(s)alpha GPCR pathway in GABAergic neurons can suppress the defecation defect of the intestinal mutants aex-4 and aex-5. Lastly, we demonstrate that activation of GABAergic neurons using the light-gated cation channel channelrhodopsin-2 is sufficient to suppress the behavioral defects of aex-2, aex-4, and aex-5. These results genetically place intestinal genes aex-4 and aex-5 upstream of GABAergic GPCR signaling. We propose a model whereby the intestinal genes aex-4 and aex-5 control the DMP by regulating the secretion of a signal, which activates the neuronal receptor aex-2.
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Affiliation(s)
- Timothy R. Mahoney
- Department of Anatomy and Neurobiology, Washington University School of Medicine, St. Louis, MO 63110
| | - Shuo Luo
- Department of Anatomy and Neurobiology, Washington University School of Medicine, St. Louis, MO 63110
| | - Elaine K. Round
- Department of Genome Sciences, University of Washington, Seattle, WA 98195; and
| | - Martin Brauner
- Institute for Biochemistry, Department of Biochemistry, Chemistry and Pharmacy, Goethe-University Frankfurt, D-60439 Frankfurt, Germany
| | - Alexander Gottschalk
- Institute for Biochemistry, Department of Biochemistry, Chemistry and Pharmacy, Goethe-University Frankfurt, D-60439 Frankfurt, Germany
| | - James H. Thomas
- Department of Genome Sciences, University of Washington, Seattle, WA 98195; and
| | - Michael L. Nonet
- Department of Anatomy and Neurobiology, Washington University School of Medicine, St. Louis, MO 63110
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156
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Cavalier-Smith T. Predation and eukaryote cell origins: a coevolutionary perspective. Int J Biochem Cell Biol 2008; 41:307-22. [PMID: 18935970 DOI: 10.1016/j.biocel.2008.10.002] [Citation(s) in RCA: 112] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2008] [Revised: 10/06/2008] [Accepted: 10/08/2008] [Indexed: 12/23/2022]
Abstract
Cells are of only two kinds: bacteria, with DNA segregated by surface membrane motors, dating back approximately 3.5Gy; and eukaryotes, which evolved from bacteria, possibly as recently as 800-850My ago. The last common ancestor of eukaryotes was a sexual phagotrophic protozoan with mitochondria, one or two centrioles and cilia. Conversion of bacteria (=prokaryotes) into a eukaryote involved approximately 60 major innovations. Numerous contradictory ideas about eukaryogenesis fail to explain fundamental features of eukaryotic cell biology or conflict with phylogeny. Data are best explained by the intracellular coevolutionary theory, with three basic tenets: (1) the eukaryotic cytoskeleton and endomembrane system originated through cooperatively enabling the evolution of phagotrophy; (2) phagocytosis internalised DNA-membrane attachments, unavoidably disrupting bacterial division; recovery entailed the evolution of the nucleus and mitotic cycle; (3) the symbiogenetic origin of mitochondria immediately followed the perfection of phagotrophy and intracellular digestion, contributing greater energy efficiency and group II introns as precursors of spliceosomal introns. Eukaryotes plus their archaebacterial sisters form the clade neomura, which evolved from a radically modified derivative of an actinobacterial posibacterium that had replaced the ancestral eubacterial murein peptidoglycan by N-linked glycoproteins, radically modified its DNA-handling enzymes, and evolved cotranslational protein secretion, but not the isoprenoid-ether lipids of archaebacteria. I focus on this phylogenetic background and on explaining how in response to novel phagotrophic selective pressures and ensuing genome internalisation this prekaryote evolved efficient digestion of prey proteins by retrotranslocation and 26S proteasomes, then internal digestion by phagocytosis, lysosomes, and peroxisomes, and eukaryotic vesicle trafficking and intracellular compartmentation.
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Affiliation(s)
- T Cavalier-Smith
- Department of Zoology, University of Oxford, South Parks Road, Oxford, OX1 3PS, UK.
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157
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Elias EV, Quiroga R, Gottig N, Nakanishi H, Nash TE, Neiman A, Lujan HD. Characterization of SNAREs determines the absence of a typical Golgi apparatus in the ancient eukaryote Giardia lamblia. J Biol Chem 2008; 283:35996-6010. [PMID: 18930915 DOI: 10.1074/jbc.m806545200] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Giardia is a eukaryotic protozoal parasite with unusual characteristics, such as the absence of a morphologically evident Golgi apparatus. Although both constitutive and regulated pathways for protein secretion are evident in Giardia, little is known about the mechanisms involved in vesicular docking and fusion. In higher eukaryotes, soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs) of the vesicle-associated membrane protein and syntaxin families play essential roles in these processes. In this work we identified and characterized genes for 17 SNAREs in Giardia to define the minimal set of subcellular organelles present during growth and encystation, in particular the presence or not of a Golgi apparatus. Expression and localization of all Giardia SNAREs demonstrate their presence in distinct subcellular compartments, which may represent the extent of the endomembrane system in eukaryotes. Remarkably, Giardia SNAREs, homologous to Golgi SNAREs from other organisms, do not allow the detection of a typical Golgi apparatus in either proliferating or differentiating trophozoites. However, some features of the Golgi, such as the packaging and sorting function, seem to be performed by the endoplasmic reticulum and/or the nuclear envelope. Moreover, depletion of individual genes demonstrated that several SNAREs are essential for viability, whereas others are dispensable. Thus, Giardia requires a smaller number of SNAREs compared with other eukaryotes to accomplish all of the vesicle trafficking events that are critical for the growth and differentiation of this important human pathogen.
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Affiliation(s)
- Eliana V Elias
- Laboratory of Biochemistry and Molecular Biology, School of Medicine, Catholic University of Cordoba/National Council for Science and Technology, Cordoba CP X5004ASK, Argentina
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158
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Pajonk S, Kwon C, Clemens N, Panstruga R, Schulze-Lefert P. Activity determinants and functional specialization of Arabidopsis PEN1 syntaxin in innate immunity. J Biol Chem 2008; 283:26974-84. [PMID: 18678865 DOI: 10.1074/jbc.m805236200] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
In eukaryotes, proteins of the soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) family are believed to have a general role for the fusion of intracellular transport vesicles with acceptor membranes. Arabidopsis thaliana PEN1 syntaxin resides in the plasma membrane and was previously shown to act together with its partner SNAREs, the adaptor protein SNAP33, and endomembrane-anchored VAMP721/722 in the execution of secretory immune responses against powdery mildew fungi. We conducted a structure-function analysis of PEN1 and show that N-terminal phospho-mimicking and non-phosphorylatable variants neither affected binary nor ternary SNARE complex formation with cognate partners in vitro. However, expression of these syntaxin variants at native protein levels in a pen1 mutant background suggests that phosphorylation is required for full resistance activity in planta. All tested site-directed substitutions of SNARE domain or "linker region" residues reduced PEN1 defense activity. Two of the variants failed to form ternary complexes with the partner SNAREs in vitro, possibly explaining their diminished in planta activity. However, impaired pathogen defense in plants expressing a linker region variant is likely because of PEN1 destabilization. Although Arabidopsis PEN1 and SYP122 syntaxins share overlapping functions in plant growth and development, PEN1 activity in disease resistance is apparently the result of a complete functional specialization. Our findings are consistent with the hypothesis that PEN1 acts in plant defense through the formation of ternary SNARE complexes and point to the existence of unknown regulatory factors. Our data indirectly support structural inferences that the four-helical coiled coil bundle in ternary SNARE complexes is formed in a sequential order from the N- to C-terminal direction.
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Affiliation(s)
- Simone Pajonk
- Max Planck Institute for Plant Breeding Research, Department of Plant Microbe Interactions, D-50829 Köln, Germany
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159
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Schilde C, Lutter K, Kissmehl R, Plattner H. Molecular identification of a SNAP-25-like SNARE protein in Paramecium. EUKARYOTIC CELL 2008; 7:1387-402. [PMID: 18552286 PMCID: PMC2519768 DOI: 10.1128/ec.00012-08] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/08/2008] [Accepted: 05/25/2008] [Indexed: 01/16/2023]
Abstract
Using database searches of the completed Paramecium tetraurelia macronuclear genome with the metazoan SNAP-25 homologues, we identified a single 21-kDa Qb/c-SNARE in this ciliated protozoan, named P. tetraurelia SNAP (PtSNAP), containing the characteristic dual heptad repeat SNARE motifs of SNAP-25. The presence of only a single Qb/c class SNARE in P. tetraurelia is surprising in view of the multiple genome duplications and the high number of SNAREs found in other classes of this organism. As inferred from the subcellular localization of a green fluorescent protein (GFP) fusion construct, the protein is localized on a variety of intracellular membranes, and there is a large soluble pool of PtSNAP. Similarly, the PtSNAP that is detected with a specific antibody in fixed cells is associated with a number of intracellular membrane structures, including food vacuoles, the contractile vacuole system, and the sites of constitutive endo- and exocytosis. Surprisingly, using gene silencing, we could not assign a role to PtSNAP in the stimulated exocytosis of dense core vesicles (trichocysts), but we found an increased number of food vacuoles in PtSNAP-silenced cells. In conclusion, we identify PtSNAP as a Paramecium homologue of metazoan SNAP-25 that shows several divergent features, like resistance to cleavage by botulinum neurotoxins.
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Affiliation(s)
- Christina Schilde
- Department of Biology, University of Konstanz, P.O. Box 5560, 78457 Konstanz, Germany.
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160
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Kloepper TH, Kienle CN, Fasshauer D. SNAREing the basis of multicellularity: consequences of protein family expansion during evolution. Mol Biol Evol 2008; 25:2055-68. [PMID: 18621745 DOI: 10.1093/molbev/msn151] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Abstract
Vesicle trafficking between intracellular compartments of eukaryotic cells is mediated by conserved protein machineries. In each trafficking step, fusion of the vesicle with the acceptor membrane is driven by a set of distinctive soluble N-ethylmaleimide sensitive factor attachment protein receptor (SNARE) proteins that assemble into tight 4-helix bundle complexes between the fusing membranes. During evolution, about 20 primordial SNARE types were modified independently in different eukaryotic lineages by episodes of duplication and diversification. Here we show that 2 major changes in the SNARE repertoire occurred in the evolution of animals, each reflecting a main overhaul of the endomembrane system. In addition, we found several lineage-specific losses of distinct SNAREs, particularly in nematodes and platyhelminthes. The first major transformation took place during the transition to multicellularity. The primary event that occurred during this transformation was an increase in the numbers of endosomal SNAREs, but the SNARE-related factor lethal giant larvae also emerged. Apparently, enhanced endosomal sorting capabilities were an advantage for early multicellular animals. The second major transformation during the rise of vertebrates resulted in a robust expansion of the secretory set of SNAREs, which may have helped develop a more versatile secretory apparatus.
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Affiliation(s)
- Tobias H Kloepper
- Research Group Structural Biochemistry, Department of Neurobiology, Max-Planck-Institute for Biophysical Chemistry, Göttingen, Germany
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161
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Nagy G, Milosevic I, Mohrmann R, Wiederhold K, Walter AM, Sørensen JB. The SNAP-25 linker as an adaptation toward fast exocytosis. Mol Biol Cell 2008; 19:3769-81. [PMID: 18579690 DOI: 10.1091/mbc.e07-12-1218] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
The assembly of four soluble N-ethylmaleimide-sensitive factor attachment protein receptor domains into a complex is essential for membrane fusion. In most cases, the four SNARE-domains are encoded by separate membrane-targeted proteins. However, in the exocytotic pathway, two SNARE-domains are present in one protein, connected by a flexible linker. The significance of this arrangement is unknown. We characterized the role of the linker in SNAP-25, a neuronal SNARE, by using overexpression techniques in synaptosomal-associated protein of 25 kDa (SNAP-25) null mouse chromaffin cells and fast electrophysiological techniques. We confirm that the palmitoylated linker-cysteines are important for membrane association. A SNAP-25 mutant without cysteines supported exocytosis, but the fusion rate was slowed down and the fusion pore duration prolonged. Using chimeric proteins between SNAP-25 and its ubiquitous homologue SNAP-23, we show that the cysteine-containing part of the linkers is interchangeable. However, a stretch of 10 hydrophobic and charged amino acids in the C-terminal half of the SNAP-25 linker is required for fast exocytosis and in its absence the calcium dependence of exocytosis is shifted toward higher concentrations. The SNAP-25 linker therefore might have evolved as an adaptation toward calcium triggering and a high rate of execution of the fusion process, those features that distinguish exocytosis from other membrane fusion pathways.
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Affiliation(s)
- Gábor Nagy
- Molecular Mechanism of Exocytosis, Max Planck Institute for Biophysical Chemistry, 37077 Göttingen, Germany
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162
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Meiringer CTA, Auffarth K, Hou H, Ungermann C. Depalmitoylation of Ykt6 prevents its entry into the multivesicular body pathway. Traffic 2008; 9:1510-21. [PMID: 18541004 DOI: 10.1111/j.1600-0854.2008.00778.x] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
The dually lipidated SNARE Ykt6 is found on intracellular membranes and in the cytosol. In this study, we show that Ykt6 localizes to the Golgi as well as endosomal and vacuolar membranes in vivo. The ability of Ykt6 to cycle between the cytosol and the membranes depends on the intramolecular interaction of the N-terminal longin and C-terminal SNARE domains and not on either domain alone. A mutant deficient in this interaction accumulates on membranes and--in contrast to the wild-type protein--does not get released from vacuoles. Our data also indicate that Ykt6 is a substrate of the DHHC (Asp-His-His-Cys) acyltransferase network. Overexpression of the vacuolar acyltransferase Pfa3 drives the F42S mutant not only to the vacuole but also into the vacuolar lumen. Thus, depalmitoylation and release of Ykt6 are needed for its recycling and to circumvent its entry into the endosomal multivesicular body pathway.
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163
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Affiliation(s)
- James A McNew
- Department of Biochemistry and Cell Biology, Rice University, 6100 Main Street MS-140, Houston, Texas 77251-1892, USA.
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164
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Abstract
Soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs) play a key role in membrane fusion in the secretory pathway. In vitro, SNAREs spontaneously assemble into helical SNARE complexes with the transmembrane domains at the C-terminal end. During fusion, SNAREs are thought to bridge the two membranes and assemble in a zipper-like fashion, pulling the membranes together and initiating fusion. However, it is not clear to what extent SNARE assembly contributes to membrane attachment and membrane fusion. Using the neuronal SNAREs synaptobrevin (VAMP), SNAP-25, and syntaxin as examples, we show here that liposomes containing synaptobrevin firmly attach to planar surfaces containing immobilized syntaxin. Attachment requires the formation of SNARE complexes because it is dependent on the presence of SNAP-25. Binding is competed for by soluble SNARE fragments, with noncognate SNAREs such as endobrevin (VAMP8), VAMP4, and VAMP7 (Ti-VAMP) being effective but less potent in some cases. Furthermore, although SNAP-23 is unable to substitute for SNAP-25 in the attachment assay, it forms complexes of comparable stability and is capable of substituting in liposome fusion assays. Vesicle attachment is initiated by SNARE assembly at the N-terminal end of the helix bundle. We conclude that SNAREs can indeed form stable trans-complexes that result in vesicle attachment if progression to fusion is prevented, further supporting the zipper model of SNARE function.
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