title: Termination of isoform-selective Vps21/Rab5 signaling at endolysosomal organelles by Msb3/Gyp3.
abstract: Traffic through endosomes and lysosomes is controlled by small G-proteins of the Rab5 and Rab7 families. Like humans, Saccharomyces cerevisiae has three Rab5s (Vps21, Ypt52 and Ypt53) and one Rab7 (Ypt7). Here, we elucidate the functional roles and regulation of the yeast Rab5s. Using GFP-tagged cargoes, a novel quantitative multivesicular body (MVB) sorting assay, and electron microscopy, we show that MVB biogenesis and thus MVB cargo sorting is severely impaired in vps21Δ ypt52Δ double mutants. Ypt53, the third Rab5 paralog, is hardly expressed during normal growth but its transcription is strongly induced by cellular stress through the calcineurin-Crz1 pathway. The requirement for Rab5 activity in stress tolerance facilitated identification of Msb3/Gyp3 as the principal Rab5 GAP (GTPase accelerating protein). In vitro GAP assays verified that Vps21 is a preferred Gyp3 target. Moreover, we demonstrate that Gyp3 spatially restricts active Vps21 to intermediate endosomal compartments by preventing Vps21 accumulation on lysosomal vacuoles. Gyp3, therefore, operates as a compartmental insulator that helps to define the spatial domain of Vps21 signaling in the endolysosomal pathway.
authors: Department of Biochemistry University of Washington School of Medicine, Seattle WA 98195-3750.
authors: Daniel P
authors: DP
authors: Nickerson
authors: Department of Molecular, Cell and Developmental Biology University of Colorado, Boulder CO 80309-0347.
authors: Matthew R G
authors: MRG
authors: Russell
authors: Department of Biochemistry University of Washington School of Medicine, Seattle WA 98195-3750.
authors: Shing-Yeng
authors: SY
authors: Lo
authors: Department of Biochemistry University of Washington School of Medicine, Seattle WA 98195-3750.
authors: Hannah C
authors: HC
authors: Chapin
authors: Department of Biochemistry University of Washington School of Medicine, Seattle WA 98195-3750.
authors: Joshua
authors: J
authors: Milnes
authors: Department of Biochemistry University of Washington School of Medicine, Seattle WA 98195-3750.
authors: Alexey J
authors: AJ
authors: Merz
mesh_terms: D019703:Calcineurin / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D020690:GTPase-Activating Proteins / Q000235:genetics / Q000378:metabolism*; D008247:Lysosomes / Q000378:metabolism*; D057146:Multivesicular Bodies / Q000378:metabolism* / Q000648:ultrastructure; D020033:Protein Isoforms / Q000378:metabolism; D021381:Protein Transport; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D020691:rab GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: C109868:CRZ1 protein, S cerevisiae; D004268:DNA-Binding Proteins; D020690:GTPase-Activating Proteins; C540987:MSB3 protein, S cerevisiae; D020033:Protein Isoforms; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors; D019703:Calcineurin; C086866:VPS21 protein, S cerevisiae; C086868:YPT53 protein, S cerevisiae; D020691:rab GTP-Binding Proteins