High impact information on VAC8

• The vacuolar DHHC-CRD protein Pfa3p is a protein acyltransferase for Vac8p [1].
• Palmitoylation of the vacuolar membrane protein Vac8p is essential for vacuole fusion in yeast (Veit, M., R. Laage, L. Dietrich, L. Wang, and C. Ungermann. 2001. EMBO J. 20:3145-3155; Wang, Y.X., E.J. Kauffman, J.E. Duex, and L.S. Weisman. 2001. J. Biol. Chem. 276:35133-35140) [1].
• Sec18 is also required for palmitoylation of the fusion factor Vac8, although the acylation machinery has not been identified [2].
• We propose that palmitoylation of Vac8p is regulated by the same machinery that controls membrane fusion [3].
• In analogy, Vac8p may link the vacuole to actin during vacuole partitioning [4].

Biological context of VAC8

• Vac8p, a vacuolar protein with armadillo repeats, functions in both vacuole inheritance and protein targeting from the cytoplasm to vacuole [4].
• Kinetic analysis of the Cvt pathway and autophagy indicates that, although Vac8p is essential for Cvt transport, it is less important for autophagy [5].
• In vivo phosphorylation experiments demonstrate that both Vac8p and Apg13p are phosphorylated proteins, and Apg13p phosphorylation is regulated by changing nutrient conditions [5].
• The VAC8 gene was identified in the C. albicans genome sequence and was resequenced [6].
• This vacuolar phenotype of acc1 mutant cells was shown biochemically to be accompanied by a reduced acylation of Vac8p which was alleviated by fatty acid supplementation [7].

Anatomical context of VAC8

• YEB3/VAC8 encodes a myristylated armadillo protein of the Saccharomyces cerevisiae vacuolar membrane that functions in vacuole fusion and inheritance [8].
• Vac8p is related to beta-catenin and plakoglobin, which connect a specific region of the plasma membrane to the actin cytoskeleton [4].
• Nvj1p is an integral membrane protein of the nuclear envelope and interacts with Vac8p in the cytosol through its C-terminal 40-60 amino acids (aa) [9].
• Fusion of docked membranes requires the armadillo repeat protein Vac8p [10].
• By analogy to the function of beta-catenin in cell-cell adhesion, alpha-karyopherin in nuclear transport, and smgGDS in the control of ras-like GTPases, Yeb3p may provide a link between vacuoles and the actin cytoskeleton during vacuolar inheritance and fusion and perhaps mediate the assembly of a GTPase regulated docking complex [8].

Associations of VAC8 with chemical compounds

• A novel cold-sensitive allele of the rate-limiting enzyme of fatty acid synthesis, acetyl coenzyme A carboxylase, affects the morphology of the yeast vacuole through acylation of Vac8p [7].
• We show that Vac8 acylation is restricted to a narrow time window, is independent of ATP hydrolysis by Sec18, and is stimulated by the ion chelator EDTA [11].
• The yeast SNARE (soluble N-ethylmaleimide-sensitive fusion protein attachment protein receptor) protein Ykt6 was shown to mediate palmitoylation of the fusion factor Vac8 in a reaction essential for the fusion of vacuoles [12].
• A mutant Vac8 protein, in which the palmitoylation sites were replaced by a stretch of basic residues, still localizes to vacuole membranes and functions in cytosol-to-vacuole transport, but can only complement the function of Vac8 in morphology and inheritance if it also contains a single cysteine within the SH4 domain [13].
• Vac8p has three putative palmitoylation sites, at Cys 4, 5 and 7 [14].

Co-localisations of VAC8

• Orphan rafts of Vac8p red-sifted GFP (YFP) colocalize at sites of NV junctions with Nvj1p blue-sifted GFP (CFP) [9].

Regulatory relationships of VAC8

• Strikingly, palmitoylation of Vac8p is blocked by the addition of antibodies to Sec18p (yeast NSF) only [3].

Other interactions of VAC8

• Apg13p and Vac8p are part of a complex of phosphoproteins that are required for cytoplasm to vacuole targeting [5].
• The Vac8 and Apg13 proteins are required for the import of aminopeptidase I (API) through the Cvt pathway [5].
• We report that mutants with conditional defects in the rate-limiting enzyme of fatty acid synthesis, acetyl coenzyme A carboxylase (ACC1), display unusually multilobed vacuoles, similar to those observed in vac8 mutant cells [7].
• Tsc13p is a polytopic endoplasmic reticulum (ER) membrane protein that accumulates at nucleus-vacuole (NV) junctions, which are formed through Velcro-like interactions between Nvj1p in the perinuclear ER and Vac8p on the vacuole membrane [15].
• Here we describe the surprising role of Vac8p-Nvj1p complexes in the formation of nucleus-vacuole (NV) junctions [9].

Analytical, diagnostic and therapeutic context of VAC8

• We have identified a protein-protein interaction between Vac8p and Apg13p by both two-hybrid and co-immunoprecipitation analysis [5].
• Confocal microscopy revealed that Yeb3p-GFP is localized over the surface of the vacuole, but is concentrated approximately 5- to 7-fold in bands located between clustered vacuoles [8].

References