title: Functional separation of endosomal fusion factors and the class C core vacuole/endosome tethering (CORVET) complex in endosome biogenesis.
abstract: Transport along the endolysosomal system requires multiple fusion events at early and late endosomes. Deletion of several endosomal fusion factors, including the Vac1 tether and the Class C core vacuole/endosome tethering (CORVET) complex-specific subunits Vps3 and Vps8, results in a class D vps phenotype. As these mutants have an apparently similar defect in endosomal transport, we asked whether CORVET and Vac1 could still act in distinct tethering reactions. Our data reveal that CORVET mutants can be rescued by Vac1 overexpression in the endocytic pathway but not in CPY or Cps1 sorting to the vacuole. Moreover, when we compared the ultrastructure, CORVET mutants were most similar to deletions of the Rab Vps21 and its guanine nucleotide exchange factor Vps9 and different from vac1 deletion, indicating separate functions. Likewise, CORVET still localized to endosomes even in the absence of Vac1, whereas Vac1 localization became diffuse in CORVET mutants. Importantly, CORVET localization requires the Rab5 homologs Vps21 and Ypt52, whereas Vac1 localization is strictly Vps21-dependent. In this context, we also uncover that Muk1 can compensate for loss of Vps9 in CORVET localization, indicating that two Rab5 guanine nucleotide exchange factors operate in the endocytic pathway. Overall, our study reveals a unique role of CORVET in the sorting of biosynthetic cargo to the vacuole/lysosome.
authors.affiliation: Department of Biology/Chemistry, Biochemistry Section, University of Osnabrück, Barbarastr 13, 49076 Osnabrück, Germany. Margarita.Cabrera@biologie.uni-osnabrueck.de
authors.forename: Margarita
authors.initials: M
authors.lastname: Cabrera
authors.forename: Henning
authors.initials: H
authors.lastname: Arlt
authors.forename: Nadine
authors.initials: N
authors.lastname: Epp
authors.forename: Jens
authors.initials: J
authors.lastname: Lachmann
authors.forename: Janice
authors.initials: J
authors.lastname: Griffith
authors.forename: Angela
authors.initials: A
authors.lastname: Perz
authors.forename: Fulvio
authors.initials: F
authors.lastname: Reggiori
authors.forename: Christian
authors.initials: C
authors.lastname: Ungermann
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism*; D001692:Biological Transport; D002172:Canavanine / Q000378:metabolism; D004705:Endocytosis; D011992:Endosomes / Q000378:metabolism*; D017353:Gene Deletion; D008247:Lysosomes / Q000378:metabolism; D020930:MAP Kinase Kinase Kinases / Q000378:metabolism; D008856:Microscopy, Fluorescence / Q000379:methods; D008954:Models, Biological; D009154:Mutation; D010641:Phenotype; D012441:Saccharomyces cerevisiae / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism*; D014617:Vacuoles / Q000378:metabolism*; D020696:rab5 GTP-Binding Proteins / Q000378:metabolism
chemical_list: D048868:Adaptor Proteins, Signal Transducing; C106978:PEP7 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D002172:Canavanine; D020930:MAP Kinase Kinase Kinases; C090757:mitogen-activated protein kinase kinase kinase 12; D020696:rab5 GTP-Binding Proteins