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

H+/K(+)-ATPase is the proton pump in the gastric parietal cell that is responsible for gastric acid secretion. Stimulation of acid secretion is associated with a reorganization of the parietal cells resulting in the incorporation of H+/K(+)-ATPase from a cytoplasmic membrane pool, the tubulovesicle compartment, into the apical canalicular membrane. To better characterize the role of membrane trafficking events in the morphological and physiological changes associated with acid secretion from parietal cells, we have characterized the expression and localization of soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs) in these cells. Each of the six different SNARE proteins examined [syntaxins 1 through 4 of 25-kDa synaptosome-associated protein, and vesicle-associated membrane protein] were found to be expressed in parietal cells. Furthermore, two of these SNAREs, vesicle-associated membrane protein and syntaxin 3, were associated with H+/K(+)-ATPase-containing tubulovesicles while the remainder were excluded from this compartment. The expression of syntaxin 1 and synaptosome-associated protein of 25 kDa in parietal cells, two SNAREs previously thought to be restricted to neuroendocrine tissues, suggests that parietal cells may utilize membrane trafficking machinery that is similar to that utilized for regulated exocytosis in neurons. Furthermore, the localization of syntaxin 3, a putative target membrane SNARE, to the tubulovesicle compartment indicates that syntaxin 3 may have an alternative function. These observations support a role for intracellular membrane trafficking events in the regulated recruitment of H+/K(+)-ATPase to the plasma membrane after parietal cell stimulation.
Mol Biol Cell 1997 Mar
PMID:Association of syntaxin 3 and vesicle-associated membrane protein (VAMP) with H+/K(+)-ATPase-containing tubulovesicles in gastric parietal cells. 918 93

The early Golgi t-SNARE (target-membrane-associated soluble-N-ethylmaleimide-sensitive factor attachment protein receptor) syntaxin 5 is thought to specify the docking site for both COPI and COPII coated vesicles originating from the endoplasmic reticulum (ER) and COPI vesicles on the retrograde pathway. We now show that there are two forms of syntaxin 5 that appear to be generated from the same mRNA by alternative initiation of translation. The short form (35 kDa) corresponds to the published sequence. The long form (42 kDa) has an N-terminal cytoplasmic extension containing a predicted type II ER retrieval signal. When grafted onto a reporter molecule, this signal localized the construct to the ER. Biochemical fractionation and immunofluorescence microscopy showed that there was less of the long form in the Golgi apparatus and more in peripheral punctate structures, some of which colocalized with markers of the intermediate compartment. The predicted absence of the long form in budding yeast points to a function unique to higher organisms.
Mol Biol Cell 1997 Sep
PMID:An isoform of the Golgi t-SNARE, syntaxin 5, with an endoplasmic reticulum retrieval signal. 930 73

The occurrence of clathrin-coated buds on immature granules (IGs) of the regulated secretory pathway suggests that specific transmembrane proteins are sorted into these buds through interaction with cytosolic adaptor proteins. By quantitative immunoelectron microscopy of rat endocrine pancreatic beta cells and exocrine parotid and pancreatic cells, we show for the first time that the mannose 6-phosphate receptors (MPRs) for lysosomal enzyme sorting colocalize with the AP-1 adaptor in clathrin-coated buds on IGs. Furthermore, the concentrations of both MPR and AP-1 decline by approximately 90% as the granules mature. Concomitantly, in exocrine secretory cells lysosomal proenzymes enter and then are sorted out of IGs, just as was previously observed in beta cells (Kuliawat, R., J. Klumperman, T. Ludwig, and P. Arvan. 1997. J. Cell Biol. 137:595-608). The exit of MPRs in AP-1/clathrin-coated buds is selective, indicated by the fact that the membrane protein phogrin is not removed from maturing granules. We have also made the first observation of a soluble N-ethylmaleimide-sensitive factor attachment protein receptor, syntaxin 6, which has been implicated in clathrin-coated vesicle trafficking from the TGN to endosomes (Bock, J.B., J. Klumperman, S. Davanger, and R.H. Scheller. 1997. Mol. Biol. Cell. 8:1261-1271) that enters and then exits the regulated secretory pathway during granule maturation. Thus, we hypothesize that during secretory granule maturation, MPR-ligand complexes and syntaxin 6 are removed from IGs by AP-1/clathrin-coated vesicles, and then delivered to endosomes.
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PMID:Mannose 6-phosphate receptors are sorted from immature secretory granules via adaptor protein AP-1, clathrin, and syntaxin 6-positive vesicles. 954 15

We and others have previously shown that insulin-secreting cells of the pancreas express high levels of SNAP-25 (synaptosomal-associated protein of 25 kDa), a 206-amino acid t-SNARE (target soluble N-ethylmaleimide-sensitive factor attachment protein receptors) implicated in synaptic vesicle exocytosis. In the present study, we show that SNAP-25 is required for insulin secretion by transient transfection of Botulinum Neurotoxin A (BoNT/A) into insulin-secreting HIT-T15 cells. Transient expression of BoNT/A cleaved the endogenous as well as overexpressed SNAP-25 proteins and caused significant reductions in K+ and glucose-evoked secretion of insulin. To determine whether the inhibition of release was due to the depletion of functional SNAP-25 or the accumulation of proteolytic by-products, we transfected cells with SNAP-25 proteins from which the C-terminal nine amino acids had been deleted to mimic the effects of the toxin. This modified SNAP-25 (amino acids 1-197) remained bound to the plasma membrane but was as effective as the toxin at inhibiting insulin secretion. Microfluorimetry revealed that the inhibition of secretion was due neither to changes in basal cytosolic Ca2+ levels nor in Ca2+ influx evoked by K(+)-mediated plasma membrane depolarization. Electron microscopy revealed that cells transfected with either BoNT/A or truncated SNAP-25 contained significantly higher numbers of insulin granules, many of which clustered close to the plasma membrane. Together, these results demonstrate that functional SNAP-25 proteins are required for insulin secretion and suggest that the inhibitory action of BoNT/A toxin on insulin secretion is in part caused by the production of the plasma membrane-bound cleavage product, which itself interferes with insulin granule docking and fusion.
Mol Endocrinol 1998 Jul
PMID:Truncated SNAP-25 (1-197), like botulinum neurotoxin A, can inhibit insulin secretion from HIT-T15 insulinoma cells. 965 9

Yeast Sec22p participates in both anterograde and retrograde vesicular transport between the endoplasmic reticulum (ER) and the Golgi apparatus by functioning as a v-SNARE (soluble N-ethylmaleimide-sensitive factor [NSF] attachment protein receptor) of transport vesicles. Three mammalian proteins homologous to Sec22p have been identified and are referred to as Sec22a, Sec22b/ERS-24, and Sec22c, respectively. The existence of three homologous proteins in mammalian cells calls for detailed cell biological and functional examinations of each individual protein. The epitope-tagged forms of all three proteins have been shown to be primarily associated with the ER, although functional examination has not been carefully performed for any one of them. In this study, using antibodies specific for Sec22b/ERS-24, it is revealed that endogenous Sec22b/ERS-24 is associated with vesicular structures in both the perinuclear Golgi and peripheral regions. Colabeling experiments for Sec22b/ERS-24 with Golgi mannosidase II, the KDEL receptor, and the envelope glycoprotein G (VSVG) of vesicular stomatitis virus (VSV) en route from the ER to the Golgi under normal, brefeldin A, or nocodazole-treated cells suggest that Sec22b/ERS-24 is enriched in the pre-Golgi intermediate compartment (IC). In a well-established semi-intact cell system that reconstitutes transport from the ER to the Golgi, transport of VSVG is inhibited by antibodies against Sec22b/ERS-24. EGTA is known to inhibit ER-Golgi transport at a stage after vesicle/transport intermediate docking but before the actual fusion event. Antibodies against Sec22b/ERS-24 inhibit ER-Golgi transport only when they are added before the EGTA-sensitive stage. Transport of VSVG accumulated in pre-Golgi IC by incubation at 15 degreesC is also inhibited by Sec22b/ERS-24 antibodies. Morphologically, VSVG is transported from the ER to the Golgi apparatus via vesicular intermediates that scatter in the peripheral as well as the Golgi regions. In the presence of antibodies against Sec22b/ERS-24, VSVG is seen to accumulate in these intermediates, suggesting that Sec22b/ERS-24 functions at the level of the IC in ER-Golgi transport.
Mol Biol Cell 1999 Feb
PMID:Morphological and functional association of Sec22b/ERS-24 with the pre-Golgi intermediate compartment. 995 Jun 87

N-ethylmaleimide-sensitive factor (NSF) is a hexameric ATPase essential for eukaryotic vesicle fusion. Along with SNAP proteins, it disassembles cis-SNARE complexes upon ATP hydrolysis, preparing SNAREs for trans complex formation. We have determined the crystal structure of the N-terminal domain of NSF (N) to 1.9 A resolution. N contains two subdomains which form a groove that is a likely SNAP interaction site. Unexpectedly, both N subdomains are structurally similar to domains in EF-Tu. Based on this similarity, we propose a model for a large conformational change in NSF that drives SNARE complex disassembly.
Mol Cell 1999 Jul
PMID:NSF N-terminal domain crystal structure: models of NSF function. 1044 31

Recycling of vesicles of the regulated secretory pathway presumably involves passage through an early endosomal compartment as an intermediate step. To learn more about the involvement of endosomes in the recycling of synaptic and secretory vesicles we studied in vitro fusion of early endosomes derived from pheochromocytoma (PC12) cells. Fusion was not affected by cleavage of the SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) proteins synaptobrevin and syntaxin 1 that operate at the exocytotic limb of the pathway. Furthermore, fusion was inhibited by the fast Ca(2+) chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetra-acetic acid but not by the slow Ca(2+) chelator EGTA. Endosome fusion was restored by the addition of Ca(2+) with an optimum at a free Ca(2+) concentration of 0.3 x 10(-6) M. Other divalent cations did not substitute for Ca(2+). A membrane-permeant EGTA derivative caused inhibition of fusion, which was reversed by addition of Ca(2+). We conclude that the fusion of early endosomes participating in the recycling of synaptic and neurosecretory vesicles is mediated by a set of SNAREs distinct from those involved in exocytosis and requires the local release of Ca(2+) from the endosomal interior.
Mol Biol Cell 1999 Sep
PMID:Fusion of endosomes involved in synaptic vesicle recycling. 1047 44

To understand molecular mechanisms that regulate the intricate and dynamic organization of the endosomal compartment, it is important to establish the morphology, molecular composition, and functions of the different organelles involved in endosomal trafficking. Syntaxins and vesicle-associated membrane protein (VAMP) families, also known as soluble N-ethylmaleimide-sensitive factor (NSF) attachment protein receptors (SNAREs), have been implicated in mediating membrane fusion and may play a role in determining the specificity of vesicular trafficking. Although several SNAREs, including VAMP3/cellubrevin, VAMP8/endobrevin, syntaxin 13, and syntaxin 7, have been localized to the endosomal membranes, their precise localization, biochemical interactions, and function remain unclear. Furthermore, little is known about SNAREs involved in lysosomal trafficking. So far, only one SNARE, VAMP7, has been localized to late endosomes (LEs), where it is proposed to mediate trafficking of epidermal growth factor receptor to LEs and lysosomes. Here we characterize the localization and function of two additional endosomal syntaxins, syntaxins 7 and 8, and propose that they mediate distinct steps of endosomal protein trafficking. Both syntaxins are found in SNARE complexes that are dissociated by alpha-soluble NSF attachment protein and NSF. Syntaxin 7 is mainly localized to vacuolar early endosomes (EEs) and may be involved in protein trafficking from the plasma membrane to the EE as well as in homotypic fusion of endocytic organelles. In contrast, syntaxin 8 is likely to function in clathrin-independent vesicular transport and membrane fusion events necessary for protein transport from EEs to LEs.
Mol Biol Cell 1999 Nov
PMID:Differential roles of syntaxin 7 and syntaxin 8 in endosomal trafficking. 1056 79

Pro-alpha-factor (pro-alphaf) is posttranslationally modified in the yeast Golgi complex by the addition of alpha1,6-, alpha1,2-, and alpha1,3-linked mannose to N-linked oligosaccharides and by a Kex2p-initiated proteolytic processing event. Previous work has indicated that the alpha1,6- and alpha1,3-mannosylation and Kex2p-dependent processing of pro-alphaf are initiated in three distinct compartments of the Golgi complex. Here, we present evidence that alpha1,2-mannosylation of pro-alphaf is also initiated in a distinct Golgi compartment. Linkage-specific antisera and an endo-alpha1,6-D-mannanase (endoM) were used to quantitate the amount of each pro-alphaf intermediate during transport through the Golgi complex. We found that alpha1,6-, alpha1,2-, and alpha1,3-mannose were sequentially added to pro-alphaf in a temporally ordered manner, and that the intercompartmental transport factor Sec18p/N-ethylmaleimide-sensitive factor was required for each step. The Sec18p dependence implies that a transport event was required between each modification event. In addition, most of the Golgi-modified pro-alphaf that accumulated in brefeldin A-treated cells received only alpha1,6-mannosylation as did approximately 50% of pro-alphaf transported to the Golgi in vitro. This further supports the presence of an early Golgi compartment that houses an alpha1,6-mannosyltransferase but lacks alpha1,2-mannosyltransferase activity in vivo. We propose that the alpha1,6-, alpha1,2-, and alpha1,3-mannosylation and Kex2p-dependent processing events mark the cis, medial, trans, and trans-Golgi network of the yeast Golgi complex, respectively.
Mol Biol Cell 2000 Jan
PMID:Organization of the yeast Golgi complex into at least four functionally distinct compartments. 1063

The Sec1p family of proteins are thought to be involved in the regulation of vesicle fusion reactions through interaction with t-SNAREs (target soluble N-ethylmaleimide-sensitive factor attachment protein receptors) at the target membrane. AtVPS45 is a member of this family from Arabidopsis thaliana that we now demonstrate to be present on the trans-Golgi network (TGN), where it colocalizes with the vacuolar cargo receptor AtELP. Unlike yeast Vps45p, AtVPS45 does not interact with, or colocalize with, the prevacuolar t-SNARE AtPEP12. Instead, AtVPS45 interacts with two t-SNAREs, AtTLG2a and AtTLG2b, that show similarity to the yeast t-SNARE Tlg2p. AtTLG2a and -b each colocalize with AtVPS45 at the TGN; however, AtTLG2a is in a different region of the TGN than AtTLG2b by immunogold electron microscopy. Therefore, we propose that complexes containing AtVPS45 and either AtTLG2a or -b define functional subdomains of the TGN and may be required for different trafficking events. Among other Arabidopsis SNAREs, AtVPS45 antibodies preferentially coprecipitate AtVTI1b over the closely related isoform AtVTI1a, implying that AtVTI1a and AtVTI1b also have distinct functions within the cell. These data point to a functional complexity within the plant secretory pathway, where proteins encoded by gene families have specialized functions, rather than functional redundancy.
Mol Biol Cell 2000 Jul
PMID:AtVPS45 complex formation at the trans-Golgi network. 1088 66


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