title: VPS21 encodes a rab5-like GTP binding protein that is required for the sorting of yeast vacuolar proteins.
abstract: Many of the vacuolar protein sorting (vps) mutants of Saccharomyces cerevisiae exhibit severe defects in the sorting of vacuolar proteins but still retain near-normal vacuole morphology. The gene affected in one such mutant, vps21, has been cloned and found to encode a member of the ras-like GTP binding protein family. Sequence comparisons with other known GTP binding proteins indicate that Vps21p is unique but shares striking similarity with mammalian rab5 proteins (> 50% identity and > 70% similarity). Regions with highest similarity are clustered within the putative GTP binding motifs and the proposed effector domains of the Vps21/rab5 proteins. Point mutations constructed within these conserved regions inactivate Vps21p function; the mutant cells missort and secrete the soluble vacuolar hydrolase carboxypeptidase Y (CPY). Cells carrying a complete deletion of the VPS21 coding sequence (i) are viable but exhibit a growth defect at 38 degrees C, (ii) missort multiple vacuolar proteins, (iii) accumulate 40-50 nm vesicles and (iv) contain a large vacuole. VPS21 encodes a 22 kDa protein that binds GTP and fractionates with subcellular membranes. Mutant analysis indicates that the association with a membrane(s) is dependent on geranylgeranylation of the C-terminal cysteine residue(s) of Vps21p. We propose that Vps21p functions in the targeting and/or fusion of transport vesicles that mediate the delivery of proteins to the vacuole.
authors.affiliation: Division of Cellular and Molecular Medicine, University of California, San Diego, School of Medicine, La Jolla 92093-0668.
authors.forename: B F
authors.initials: BF
authors.lastname: Horazdovsky
authors.forename: G R
authors.initials: GR
authors.lastname: Busch
authors.forename: S D
authors.initials: SD
authors.lastname: Emr
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001692:Biological Transport; D005656:Fungal Proteins / Q000378:metabolism*; D019204:GTP-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D000072235:Mating Factor; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D010455:Peptides / Q000378:metabolism; D017354:Point Mutation; D015183:Restriction Mapping; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D014617:Vacuoles / Q000378:metabolism; D020691:rab GTP-Binding Proteins; D020696:rab5 GTP-Binding Proteins
chemical_list: D005656:Fungal Proteins; D008565:Membrane Proteins; D010455:Peptides; D000072235:Mating Factor; D019204:GTP-Binding Proteins; D020691:rab GTP-Binding Proteins; D020696:rab5 GTP-Binding Proteins