High impact information on VPS21

• Membrane fusion also required the rab protein Vps21p [1].
• Using a PCR approach to identify rab5 homologs in Saccharomyces cerevisiae, two genes encoding proteins with 54 and 52% identity to rab5, YPT51 and YPT53 have been identified [2].
• Endocytic delivery to the vacuole of two markers, lucifer yellow CH (LY) and alpha-factor, was inhibited in delta ypt51 mutants and aggravated in the double ypt51ypt52 and triple ypt51ypt52ypt53 mutants, suggesting a requirement for these small GTPases in endocytic membrane traffic [2].
• VPS21 encodes a 22 kDa protein that binds GTP and fractionates with subcellular membranes [3].
• VPS21 encodes a rab5-like GTP binding protein that is required for the sorting of yeast vacuolar proteins [3].

Biological context of VPS21

• We have constructed an activated allele of VPS21, a yeast Rab protein involved in vacuolar protein sorting, and demonstrated an allele-specific interaction between Vps21p and Vac1p [4].
• The class D VPS genes include VPS21, PEP12, and VPS45, which appear to encode components of a membrane fusion complex involved in Golgi-to-endosome transport [5].
• Vps21p is a member of the Rab family of small Ras-like GTPases and shows strong homology to the mammalian Rab5 protein, which is involved in endocytosis and the homotypic fusion of early endosomes [5].
• Point mutations constructed within these conserved regions inactivate Vps21p function; the mutant cells missort and secrete the soluble vacuolar hydrolase carboxypeptidase Y (CPY) [3].
• Mutant analysis indicates that the association with a membrane(s) is dependent on geranylgeranylation of the C-terminal cysteine residue(s) of Vps21p [3].

Anatomical context of VPS21

• Loading of Vps21p by loading-defective Gdi1p was restored when acceptor membranes prepared from a deletion strain lacking Vps21p were used [6].
• In vps21 null mutant cells, Vps8p is found in the cytosol [7].

Associations of VPS21 with chemical compounds

• The yeast Rab5 ortholog Vps21p is activated by its guanine nucleotide exchange factor Vps9p [8].
• We present the 1.5 A high-resolution crystal structure of Ypt51 in its active, GppNHp-bound conformation [9].
• The transport blockade can be achieved by deleting a GTPase of the endocytic pathway, Ypt51p, or ethanol [10].
• Chloroquine affects the compartments of the late endocytic pathway, and no effect is seen on transfection in a strain that is defective for YPT51 and accumulates the DNA in the early endocytic intermediates [10].

Physical interactions of VPS21

• However, Vps9p did not stimulate guanine nucleotide exchange of GTP-bound Vps21p or GTP hydrolysis [11].

Co-localisations of VPS21

• Cdc50p colocalized with Vps21p in endosomal compartments and was also localized to the class E compartment in the vps27 mutant [12].

Regulatory relationships of VPS21

• Vac1 proteins with mutant FYVE fingers still associated with membranes but showed vacuolar protein sorting defects and reduced interactions with Vps45p and activated Vps21p [4].

Other interactions of VPS21

• Using an in vitro assay which reconstitutes Gdi1p-mediated membrane loading of Rab, this mutant Gdi1p was found to be defective in loading of Vps21p but not Ypt1p [6].
• This association was found to depend on the function of Vps21p, a member of the Rab/Ypt/Sec4 family of small GTPases [7].
• One of them, Gyp1p, acts on Sec4p, Ypt1p, Ypt7p, and Ypt51p in vitro [13].
• These results implicate Vac1p as an effector of Vps21p and as a novel Sec1p-family-binding protein [14].
• By contrast, a vps21 mutant produces a synthetic defect with lte1 in proprotein processing, as well as a synthetic growth defect [15].

Analytical, diagnostic and therapeutic context of VPS21

• By sequence analysis, Tem1p has highest similarity to Vps21p (yeast homolog of mammalian Rab5) [15].
• Using both yeast two-hybrid assays and chemical cross-linking, we have identified another VPS gene product, Vps9p, that preferentially interacts with a mutant form of Vps21p-S21N that binds GDP but not GTP [11].
• In immuno-electron microscopy experiments these compartments labeled with antibodies directed against the rab5 homologue Ypt51p (Vps21p), the resident vacuolar protease carboxypeptidase Y, and the vacuolar H+-ATPase Vph1p [16].
• Cell fractionation analysis revealed cofractionation of Ypt51p with endocytic intermediates, while no association with the late Golgi compartment could be detected [17].
• Indirect immunofluorescence microscopy allowed us to morphologically identify the Ypt51p-containing compartment [17].

References