title: The CORVET complex promotes tethering and fusion of Rab5/Vps21-positive membranes.
abstract: Membrane fusion along the endocytic pathway occurs in a sequence of tethering, docking, and fusion. At endosomes and vacuoles, the CORVET (class C core vacuole/endosome tethering) and HOPS (homotypic fusion and vacuole protein sorting) tethering complexes require their organelle-specific Rabs for localization and function. Until now, despite the absence of experimental evidence, it has been assumed that CORVET is a membrane-tethering factor. To test this theory and understand the mechanistic analogies with the HOPS complex, we set up an in vitro system, and establish CORVET as a bona-fide tether for Vps21-positive endosome/vacuole membranes. Purified CORVET binds to SNAREs and Rab5/Vps21-GTP. We then demonstrate that purified CORVET can specifically tether Vps21-positive membranes. Tethering via CORVET is dose-dependent, stimulated by the GEF Vps9, and inhibited by Msb3, the Vps21-GAP. Moreover, CORVET supports fusion of isolated membranes containing Vps21. In agreement with its role as a tether, overexpressed CORVET drives Vps21, but not the HOPS-specific Ypt7 into contact sites between vacuoles, which likely represent vacuole-associated endosomes. We therefore conclude that CORVET is a tethering complex that promotes fusion of Rab5-positive membranes and thus facilitates receptor down-regulation and recycling at the late endosome.
authors: Department of Biology/Chemistry, University of Osnabrück, 49076 Osnabrück, Germany.
authors: Henning J kleine
authors: HJ
authors: Balderhaar
authors: Jens
authors: J
authors: Lachmann
authors: Erdal
authors: E
authors: Yavavli
authors: Cornelia
authors: C
authors: Bröcker
authors: Anna
authors: A
authors: Lürick
authors: Christian
authors: C
authors: Ungermann
mesh_terms: D004705:Endocytosis; D011992:Endosomes / Q000378:metabolism; D008247:Lysosomes / Q000378:metabolism; D008561:Membrane Fusion; D046912:Multiprotein Complexes / Q000737:chemistry / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D050600:SNARE Proteins / Q000737:chemistry / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D014617:Vacuoles / Q000378:metabolism; D020691:rab GTP-Binding Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D020696:rab5 GTP-Binding Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*
chemical_list: D046912:Multiprotein Complexes; D011994:Recombinant Proteins; D050600:SNARE Proteins; D029701:Saccharomyces cerevisiae Proteins; C086866:VPS21 protein, S cerevisiae; D020691:rab GTP-Binding Proteins; D020696:rab5 GTP-Binding Proteins