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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complexes form bundles of four parallel alpha-helices. The central '0' layer of interacting amino acid side chains is highly conserved and contains one arginine and three glutamines, leading to the classification of SNAREs into R, Qa, Qb, and Qc-SNAREs. Replacing one of the glutamines with arginine in the yeast exocytotic SNARE complex is either lethal or causes a conditional growth defect that is compensated by replacing the R-SNARE arginine with glutamine. Using the yeast SNARE complex mediating traffic from the endoplasmic reticulum to the Golgi apparatus, we now show that functionally interacting SNAREs can be mapped by systematically exchanging glutamines and arginines in the '0' layer. The Q-->R replacement in the Qb-SNARE Bos1p has the strongest effect and can be alleviated by an Q-->R replacement in the R-SNARE Sec22p. Four Q residues in the central layer caused growth defects above 30 degrees C that were rescued by Q-->R substitutions in the Qa and Qc SNAREs Sed5p and Bet1p, respectively. The sec22(Q)/sed5(R) mutant is temperature sensitive and is rescued by a compensating R-->Q replacement in the R-SNARE Ykt6p. This rescue is attributed to the involvement of Sed5p and Ykt6p in a different SNARE complex that functions in intra-Golgi trafficking.
Mol Biol Cell 2005 May
PMID:Identification of functionally interacting SNAREs by using complementary substitutions in the conserved '0' layer. 1572 25

Ca2+-triggered exocytosis of synaptic vesicles is controlled by the Ca2+-binding protein synaptotagmin (syt) I. Fifteen additional isoforms of syt have been identified. Here, we compared the abilities of three syt isoforms (I, VII, and IX) to regulate soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE)-mediated membrane fusion in vitro in response to divalent cations. We found that different isoforms of syt couple distinct ranges of Ca2+, Ba2+, and Sr2+ to membrane fusion; syt VII was approximately 400-fold more sensitive to Ca2+ than was syt I. Omission of phosphatidylserine (PS) from both populations of liposomes completely abrogated the ability of all three isoforms of syt to stimulate fusion. Mutations that selectively inhibit syt.target-SNARE (t-SNARE) interactions reduced syt stimulation of fusion. Using Sr2+ and Ba2+, we found that binding of syt to PS and t-SNAREs can be dissociated from activation of fusion, uncovering posteffector-binding functions for syt. Our data demonstrate that different syt isoforms are specialized to sense different ranges of divalent cations and that PS is an essential effector of Ca2+.syt action.
Mol Biol Cell 2005 Oct
PMID:Synaptotagmin isoforms couple distinct ranges of Ca2+, Ba2+, and Sr2+ concentration to SNARE-mediated membrane fusion. 1609 50

GABA(A) receptors mediate most of the fast inhibitory neurotransmission in the brain, and are believed to be composed mainly of alpha, beta, and gamma subunits. It has been shown that GABA(A) receptors interact with a number of binding partners that act to regulate both receptor function and cell surface stability. Here, we reveal that GABA(A) receptors interact directly with N-ethylmaleimide-sensitive factor (NSF), a critical regulator of vesicular dependent protein trafficking, as measured by in vitro protein binding and co-immunoprecipitation assays. In addition, we established that NSF interacts with residues 395-415 of the receptor beta subunits and co-localizes with GABA(A) receptors in hippocampal neurons. We also established that NSF can regulate GABA(A) receptor cell surface expression depending upon residues 395-415 in the beta3 subunit. Together, our results suggest an important role for NSF activity in regulating the cell surface stability of GABA(A) receptors.
Mol Cell Neurosci 2005 Oct
PMID:Direct interaction of N-ethylmaleimide-sensitive factor with GABA(A) receptor beta subunits. 1609 14

The essential membrane fusion apparatus in mammalian cells, the soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complex, consists of four alpha-helices formed by three proteins: SNAP-25, syntaxin 1, and synaptobrevin 2. SNAP-25 contributes two helices to the complex and is targeted to the plasma membrane by palmitoylation of four cysteines in the linker region. It is alternatively spliced into two forms, SNAP-25a and SNAP-25b, differing by nine amino acids substitutions. When expressed in chromaffin cells from SNAP-25 null mice, the isoforms support different levels of secretion. Here, we investigated the basis of that different secretory phenotype. We found that two nonconservative substitutions in the N-terminal SNARE domain and not the different localization of one palmitoylated cysteine cause the functional difference between the isoforms. Biochemical and molecular dynamic simulation experiments revealed that the two substitutions do not regulate secretion by affecting the property of SNARE complex itself, but rather make the SNAP-25b-containing SNARE complex more available for the interaction with accessory factor(s).
Mol Biol Cell 2005 Dec
PMID:Alternative splicing of SNAP-25 regulates secretion through nonconservative substitutions in the SNARE domain. 1619 46

The regulated release of hormones and neurotransmitters is a fundamental process throughout the animal kingdom. The short time scale for the calcium triggering of vesicle fusion in regulated secretion suggests that the calcium sensor synaptotagmin and the soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) membrane fusion machinery are well ordered before the calcium signal. To gain insight into the organization of the prefusion protein assembly in regulated exocytosis, we undertook a structural/functional study of the vesicular synaptotagmin1 and the plasma membrane SNARE proteins, which copurify from the brain in the absence of calcium. Based on an evolutionary analysis, mutagenesis screens, and a computational protein docking approach, we now provide the first testable description of the supramolecular prefusion assembly. Perturbing the determined synaptotagmin/SNARE-interacting interface in several models of regulated exocytosis altered the secretion of hormones and neurotransmitters. These mutations also disrupted the constitutive synaptotagmin/SNARE link in full agreement with our model. We conclude that the interaction of synaptotagmin with preassembled plasma membrane SNARE proteins, before the action of calcium, can provide a precisely organized "tethering" scaffold that underlies regulated secretion throughout evolution.
Mol Biol Cell 2006 Jan
PMID:Conserved prefusion protein assembly in regulated exocytosis. 1626 73

We identified a truncated form (38-117) of GEC1 that interacts with the C-tail of the human kappa opioid receptor (hKOR) by yeast two-hybrid screening. GEC1-(38-117) did not interact with the C-tail of the mu or delta opioid receptors. GEC1, a 117-amino acid protein (Pellerin, I., Vuillermoz, C., Jouvenot, M., Ordener, C., Royez, M., and Adessi, G. L. (1993) Mol. Cell Endocrinol. 90, R17-R21), is highly homologous to GABARAP, GATE-16, and Apg8/aut7, all members of the microtubule associated protein (MAP) family. In pull-down assays, GST-GEC1 interacted directly with the hKOR C-tail, full-length hKOR, and tubulin. When expressed in Chinese hamster ovary (CHO) cells, GEC1 co-immunoprecipitated with FLAG-hKOR. Expression of GEC1 greatly increased total and cell-surface KOR but not mu or delta opioid receptors. GEC1 expression slightly reduced U50,488H-promoted down-regulation, without affecting ligand binding affinity, receptor-G protein coupling, or U50,488H-induced desensitization and internalization. HA-GEC1 expressed in CHO cells was localized in the Golgi apparatus and endoplasmic reticulum (ER). When cells were pulsed with [35S]Met/Cys, GEC1 expression enhanced the level of the mature form (55-kDa band) of FLAG-hKOR at 4, 8, and 22 h after pulse without affecting the precursors (39- and 45-kDa bands), indicating that GEC1 facilitates trafficking of FLAG-hKOR from the ER/Golgi to plasma membranes. GEC1 interacted with N-ethylmaleimide-sensitive factor (NSF) in pull-down assays and co-immunoprecipitated with NSF in rat brain extracts. The interaction with NSF may contribute to GEC1 effects. This is the first report on biological functions of GEC1 and the first demonstration that a GPCR interacts with a protein of the MAP family. The interaction is important for trafficking of the receptor in the biosynthesis pathway.
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PMID:GEC1 interacts with the kappa opioid receptor and enhances expression of the receptor. 1643 22

Alveolar epithelial type II cells secrete lung surfactant via exocytosis. Soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNARE) are implicated in this process. Lipid rafts, the cholesterol- and sphingolipid-rich microdomains, may offer a platform for protein organization on the cell membrane. We tested the hypothesis that lipid rafts organize exocytotic proteins in type II cells and are essential for the fusion of lamellar bodies, the secretory granules of type II cells, with the plasma membrane. The lipid rafts, isolated from type II cells using 1% Triton X-100 and a sucrose gradient centrifugation, contained the lipid raft markers, flotillin-1 and -2, whereas they excluded the nonraft marker, Na+-K+ ATPase. SNAP-23, syntaxin 2, and VAMP-2 were enriched in lipid rafts. When type II cells were depleted of cholesterol, the association of SNAREs with the lipid rafts was disrupted and the formation of fusion pore was inhibited. Furthermore, the cholesterol-depleted plasma membrane had less ability to fuse with lamellar bodies, a process mediated by annexin A2. The secretagogue-stimulated secretion of lung surfactant from type II cells was also reduced by methyl-beta-cyclodextrin. When the raft-associated cell surface protein, CD44, was cross-linked using anti-CD44 antibodies, the CD44 clusters were observed. Syntaxin 2, SNAP-23, and annexin A2 co-localized with the CD44 clusters, which were cholesterol dependent. Our results suggested that lipid rafts may form a functional platform for surfactant secretion in alveolar type II cells, and raft integrity was essential for the fusion between lamellar bodies with the plasma membrane.
Am J Respir Cell Mol Biol 2006 Jun
PMID:Effect of cholesterol depletion on exocytosis of alveolar type II cells. 1643

Soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) proteins play key roles in membrane fusion, but their sorting to specific membranes is poorly understood. Moreover, individual SNARE proteins can function in multiple membrane fusion events dependent upon their trafficking itinerary. Synaptosome-associated protein of 25 kDa (SNAP25) is a plasma membrane Q (containing glutamate)-SNARE essential for Ca2+-dependent secretory vesicle-plasma membrane fusion in neuroendocrine cells. However, a substantial intracellular pool of SNAP25 is maintained by endocytosis. To assess the role of endosomal SNAP25, we expressed botulinum neurotoxin E (BoNT E) light chain in PC12 cells, which specifically cleaves SNAP25. BoNT E expression altered the intracellular distribution of SNAP25, shifting it from a perinuclear recycling endosome to sorting endosomes, which indicates that SNAP25 is required for its own endocytic trafficking. The trafficking of syntaxin 13 and endocytosed cargo was similarly disrupted by BoNT E expression as was an endosomal SNARE complex comprised of SNAP25/syntaxin 13/vesicle-associated membrane protein 2. The small-interfering RNA-mediated down-regulation of SNAP25 exerted effects similar to those of BoNT E expression. Our results indicate that SNAP25 has a second function as an endosomal Q-SNARE in trafficking from the sorting endosome to the recycling endosome and that BoNT E has effects linked to disruption of the endosome recycling pathway.
Mol Biol Cell 2006 May
PMID:A second SNARE role for exocytic SNAP25 in endosome fusion. 1648 93

Agarose beads carrying a cleavable, fluorescent, and photoreactive cross-linking reagent on the surface were synthesized and used to selectively pull out the proteins lining the surface of supramolecules. A quantitative comparison of the abundances of various proteins in the sample pulled out by the beads from supramolecules with their original abundances could provide information on the spatial arrangement of these proteins in the supramolecule. The usefulness of these synthetic beads was successfully verified by trials using a synthetic protein complex consisting of three layers of different proteins on glass coverslips. By using these beads, we determined the interior or superficial locations of five major and 19 minor constituent proteins in the postsynaptic density (PSD), a large protein complex and the landmark structure of asymmetric synapses in the mammalian central nervous system. The results indicate that alpha,beta-tubulins, dynein heavy chain, microtubule-associated protein 2, spectrin, neurofilament H and M subunits, an hsp70 protein, alpha-internexin, dynamin, and PSD-95 protein reside in the interior of the PSD. Dynein intermediate chain, alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate receptors, kainate receptors, N-cadherin, beta-catenin, N-ethylmaleimide-sensitive factor, an hsc70 protein, and actin reside on the surface of the PSD. The results further suggest that the N-methyl-d-aspartate receptors and the alpha-subunits of calcium/calmodulin-dependent protein kinase II are likely to reside on the surface of the PSD although with unique local protein organizations. Based on our results and the known interactions between various PSD proteins from data mining, a model for the molecular organization of the PSD is proposed.
Mol Cell Proteomics 2006 Jun
PMID:Studying the protein organization of the postsynaptic density by a novel solid phase- and chemical cross-linking-based technology. 1650 Dec 81

Recently, we reported that two siblings presenting with the clinical syndrome congenital disorders of glycosylation (CDG) have mutations in the gene encoding Cog7p, a member of the conserved oligomeric Golgi (COG) complex. In this study, we analyzed the localization and trafficking of multiple Golgi proteins in patient fibroblasts under a variety of conditions. Although the immunofluorescent staining pattern of several Golgi proteins was indistinguishable from normal, the staining of endoplasmic reticulum (ER)-Golgi intermediate compartment (ERGIC)-53 and the vesicular-soluble N-ethylmaleimide-sensitive factor attachment protein receptors GS15 and GS28 was abnormal, and the steady-state level of GS15 was greatly decreased. Retrograde transport of multiple Golgi proteins to the ER in patient fibroblasts via brefeldin A-induced tubules was significantly slower than occurs in normal fibroblasts, whereas anterograde protein trafficking was much less affected. After prolonged treatment with brefeldin A, several Golgi proteins were detected in clusters that colocalize with the microtubule-organizing center in patient cells. All of these abnormalities were normalized in COG7-corrected patient fibroblasts. These results serve to better define the role of the COG complex in facilitating protein trafficking between the Golgi and ER and provide a diagnostic framework for the identification of CDG defects involving trafficking proteins.
Mol Biol Cell 2006 May
PMID:COG-7-deficient Human Fibroblasts Exhibit Altered Recycling of Golgi Proteins. 1651 May 24


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