Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.6.1.25 (triphosphatase)
 1,529 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Membrane trafficking has heretofore been studied with intact organelles. Here, fusion-competent proteoliposomes were reconstituted from a yeast vacuole detergent extract. Homotypic vacuole fusion requires many membrane proteins, including the Ypt7p guanosine triphosphatase and a "SNARE complex" with Vam3p and Nyv1p. Proteoliposomes from extracts immunodepleted of either Vam3p or Ypt7p could not fuse, but vesicles reconstituted from a mixture of these depleted extracts had restored fusion activity. Purified preassembled vacuolar SNARE complex, when reconstituted with a SNARE-depleted extract, was fully functional for fusion. Thus, solubilized integral membrane components can be reconstituted for priming, docking, and fusion steps of organelle trafficking.
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PMID:Functional reconstitution of ypt7p GTPase and a purified vacuole SNARE complex. 968 64

The guanosine triphosphatase Rab1 regulates the transport of newly synthesized proteins from the endoplasmic reticulum to the Golgi apparatus through interaction with effector molecules, but the molecular mechanisms by which this occurs are unknown. Here, the tethering factor p115 was shown to be a Rab1 effector that binds directly to activated Rab1. Rab1 recruited p115 to coat protein complex II (COPII) vesicles during budding from the endoplasmic reticulum, where it interacted with a select set of COPII vesicle-associated SNAREs (soluble N-ethylmaleimide-sensitive factor attachment protein receptors) to form a cis-SNARE complex that promotes targeting to the Golgi apparatus. We propose that Rab1-regulated assembly of functional effector-SNARE complexes defines a conserved molecular mechanism to coordinate recognition between subcellular compartments.
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PMID:Rab1 recruitment of p115 into a cis-SNARE complex: programming budding COPII vesicles for fusion. 1093 51

Rab5, a small guanosine triphosphatase, is known to regulate the tethering and docking reaction leading to SNARE (soluble NSF attachment protein receptors)-mediated fusion between endosomes. However, it is uncertain how the signal of the activated Rab5 protein is transduced by its downstream effectors during endosome fusion. Here, we show that the Sec1/Munc18 gene vps-45 is essential for not only viability and development but also receptor-mediated and fluid-phase endocytosis pathways in Caenorhabditis elegans. We found that VPS-45 interacts with a Rab5 effector, Rabenosyn-5 (RABS-5), and the mutants of both vps-45 and rabs-5 show similar endocytic phenotypes. In the macrophage-like cells of vps-45 and rabs-5 mutants, aberrantly small endosomes were accumulated, and the endosome fusion stimulated by the mutant RAB-5 (Q78L) is suppressed by these mutations. Our results indicate that VPS-45 is a key molecule that functions downstream from RAB-5, cooperating with RABS-5, to regulate the dynamics of the endocytic system in multicellular organisms.
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PMID:The SM protein VPS-45 is required for RAB-5-dependent endocytic transport in Caenorhabditis elegans. 1723 59

Golgins are coiled-coil proteins involved in Golgi architecture and function. A complex of golgins (p115, GM130 and giantin), together with the rab1 guanosine triphosphatase and cis Golgi SNAREs, helps to mediate fusion processes at the entry face of the Golgi apparatus. The C-terminal acidic domain of p115 binds specifically to GM130 and giantin. However, deletion of this domain in vivo appears to have no effect on exocytic transport when using an RNA interference depletion/rescue approach (Puthenveedu MA, Linstedt AD. Gene replacement reveals that p115/SNARE interactions are essential for Golgi biogenesis. Proc Natl Acad Sci U S A 2004;101:1253-1256). In this study, we have used a different approach introducing a tobacco etch virus (tev) protease cleavage site into p115 so that the C-terminal domain can be rapidly and specifically released in vivo by microinjection of the tev protease. The results show that cleavage inhibits exocytic transport to the cell surface.
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PMID:In situ cleavage of the acidic domain from the p115 tether inhibits exocytic transport. 1856 69

Exosomes are secreted vesicles arising from the fusion of multivesicular bodies (MVBs) with the plasma membrane. Despite their importance in various processes, the molecular mechanisms controlling their formation and release remain unclear. Using nematodes and mammary tumor cells, we show that Ral GTPases are involved in exosome biogenesis. In Caenorhabditis elegans, RAL-1 localizes at the surface of secretory MVBs. A quantitative electron microscopy analysis of RAL-1-deficient animals revealed that RAL-1 is involved in both MVB formation and their fusion with the plasma membrane. These functions do not involve the exocyst complex, a common Ral guanosine triphosphatase (GTPase) effector. Furthermore, we show that the target membrane SNARE protein SYX-5 colocalizes with a constitutively active form of RAL-1 at the plasma membrane, and MVBs accumulate under the plasma membrane when SYX-5 is absent. In mammals, RalA and RalB are both required for the secretion of exosome-like vesicles in cultured cells. Therefore, Ral GTPases represent new regulators of MVB formation and exosome release.
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PMID:RAL-1 controls multivesicular body biogenesis and exosome secretion. 2645 96

Lipid incorporation from endoplasmic reticulum (ER) to lipid droplet (LD) is important in controlling LD growth and intracellular lipid homeostasis. However, the molecular link mediating ER and LD cross talk remains elusive. Here, we identified Rab18 as an important Rab guanosine triphosphatase in controlling LD growth and maturation. Rab18 deficiency resulted in a drastically reduced number of mature LDs and decreased lipid storage, and was accompanied by increased ER stress. Rab3GAP1/2, the GEF of Rab18, promoted LD growth by activating and targeting Rab18 to LDs. LD-associated Rab18 bound specifically to the ER-associated NAG-RINT1-ZW10 (NRZ) tethering complex and their associated SNAREs (Syntaxin18, Use1, BNIP1), resulting in the recruitment of ER to LD and the formation of direct ER-LD contact. Cells with defects in the NRZ/SNARE complex function showed reduced LD growth and lipid storage. Overall, our data reveal that the Rab18-NRZ-SNARE complex is critical protein machinery for tethering ER-LD and establishing ER-LD contact to promote LD growth.
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PMID:Rab18 promotes lipid droplet (LD) growth by tethering the ER to LDs through SNARE and NRZ interactions. 2936 53

Autophagy is a conserved eukaryotic process with metabolic, immune, and general homeostatic functions in mammalian cells. Mammalian autophagosomes fuse with lysosomes in a SNARE-driven process that includes syntaxin 17 (Stx17). How Stx17 translocates to autophagosomes is unknown. In this study, we show that the mechanism of Stx17 recruitment to autophagosomes in human cells entails the small guanosine triphosphatase IRGM. Stx17 directly interacts with IRGM, and efficient Stx17 recruitment to autophagosomes requires IRGM. Both IRGM and Stx17 directly interact with mammalian Atg8 proteins, thus being guided to autophagosomes. We also show that Stx17 is significant in defense against infectious agents and that Stx17-IRGM interaction is targeted by an HIV virulence factor Nef.
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PMID:Mechanism of Stx17 recruitment to autophagosomes via IRGM and mammalian Atg8 proteins. 2944 16