Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.6.1.3 (ATPase)
 65,361 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The Saccharomyces cerevisiae vacuolar proton-translocating ATPase (V-ATPase) is composed of 14 subunits distributed between a peripheral V1 subcomplex and an integral membrane V0 subcomplex. Genome-wide screens have led to the identification of the newest yeast V-ATPase subunit, Vma9p. Vma9p (subunit e) is a small hydrophobic protein that is conserved from fungi to animals. We demonstrate that disruption of yeast VMA9 results in the failure of V1 and V0 V-ATPase subunits to assemble onto the vacuole and in decreased levels of the subunit a isoforms Vph1p and Stv1p. We also show that Vma9p is an integral membrane protein, synthesized and inserted into the endoplasmic reticulum (ER), which then localizes to the limiting membrane of the vacuole. All V0 subunits and V-ATPase assembly factors are required for Vma9p to efficiently exit the ER. In the ER, Vma9p and the V0 subunits interact with the V-ATPase assembly factor Vma21p. Interestingly, the association of Vma9p with the V0-Vma21p assembly complex is disrupted with the loss of any single V0 subunit. Similarly, Vma9p is required for V0 subunits Vph1p and Vma6p to associate with the V0-Vma21p complex. In contrast, the proteolipids associate with Vma21p even in the absence of Vma9p. These results demonstrate that Vma9p is an integral membrane subunit of the yeast V-ATPase V0 subcomplex and suggest a model for the arrangement of polypeptides within the V0 subcomplex.
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PMID:Vma9p (subunit e) is an integral membrane V0 subunit of the yeast V-ATPase. 1656 36

V-ATPases are multimeric proton pumps. The 100-kDa "a" subunit is encoded by four isoforms (a1-a4) in mammals and two (Vph1p and Stv1p) in yeast. a3 is enriched in osteoclasts and is essential for bone resorption, whereas a4 is expressed in the distal nephron and acidifies urine. Mutations in human a3 and a4 result in osteopetrosis and distal renal tubular acidosis, respectively. Human a3 (G405R and R444L) and a4 (P524L and G820R) mutations were recreated in the yeast ortholog Vph1p, a3 (G424R and R462L), and a4 (W520L and G812R). Mutations in a3 resulted in wild type vacuolar acidification and growth on media containing 4 mM ZnCl2, 200 mM CaCl2, or buffered to pH 7.5 with V-ATPase hydrolytic and pumping activity decreased by 30-35%. Immunoblots confirmed wild type levels for V-ATPase a, A, and B subunits on vacuolar membranes. a4 G812R resulted in defective growth on selective media with V-ATPase hydrolytic and pumping activity decreased by 83-85% yet with wild type levels of a, A, and B subunits on vacuolar membranes. The a4 W520L mutation had defective growth on selective media with no detectable V-ATPase activity and reduced expression of a, A, and B subunits. The a4 W520L mutation phenotypes were dominant negative, as overexpression of wild type yeast a isoforms, Vph1p, or Stv1p, did not restore growth. However, deletion of endoplasmic reticulum assembly factors (Vma12p, Vma21p, and Vma22p) partially restored a and B expression. That a4 W520L affects both Vo and V1 subunits is a unique phenotype for any V-ATPase subunit mutation and supports the concerted pathway for V-ATPase assembly in vivo.
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PMID:Effects of human a3 and a4 mutations that result in osteopetrosis and distal renal tubular acidosis on yeast V-ATPase expression and activity. 1684 Jul 87

The vacuolar proton-ATPase (V-ATPase) is a ubiquitous ATP-driven H(+) transporter that functions in numerous cell processes. Accumulating evidence shows important roles of V-ATPase in tumor metastasis and antigen presentation of dendritic cells (DC). A novel V-ATPase associated protein, designated as DVA9.2 (dendritic cell-derived V-ATPase associated protein of 9.2 kDa), has been identified from a human DC cDNA library by large-scale random sequencing. Full length cDNA of DVA9.2 encodes an 81-residue protein that shares 70-80% homology with human V-ATPase subunit M9.2. Distant relationship is also found with Vma21p, a yeast protein required for V-ATPase assembly. DVA9.2 contains a conserved domain, ATP synthase subunit H (pafm05493), and two membrane-spanning helices. DVA9.2 mRNA is detectable in several human tumor cell lines as well as some human normal cells and tissues. Moreover, the inducible expression of DVA9.2 mRNA in DC during maturation is observed. DVA9.2 displays integration with membrane and main localization in lysosome, endoplasmic reticulum and Golgi-associated organelles, only less at the plasma membrane. In addition, DVA9.2 is co-localized with V(0)-sector subunit a. Silencing of DVA9.2 by small interfering RNA (siRNA) does not affect the V-ATPase activity in cell membrane fractions or attenuate the migration and invasion in breast cancer MDA-MB-231 cells. These results indicate that DVA9.2, as a novel V-ATPase-associated protein, is not essential for the activity of V-ATPase complex and may be involved in functions of DC.
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PMID:Molecular cloning and characterization of a novel V-ATPase associated protein, DVA9.2, from human dendritic cells. 1690 2

Deletion of the yeast gene PKR1 (YMR123W) results in an inability to grow on iron-limited medium. Pkr1p is localized to the membrane of the endoplasmic reticulum. Cells lacking Pkr1p show reduced levels of the V-ATPase subunit Vph1p due to increased turnover of the protein in mutant cells. Reduced levels of the V-ATPase lead to defective copper loading of Fet3p, a component of the high affinity iron transport system. Levels of Vph1p in cells lacking Pkr1p are similar to cells unable to assemble a functional V-ATPase due to lack of a V0 subunit or an endoplasmic reticulum (ER) assembly factor. However, unlike yeast mutants lacking a V0 subunit or a V-ATPase assembly factor, low levels of Vph1p present in cells lacking Pkr1p are assembled into a V-ATPase complex, which exits the ER and is present on the vacuolar membrane. The V-ATPase assembled in the absence of Pkr1p is fully functional because the mutant cells are able to weakly acidify their vacuoles. Finally, overexpression of the V-ATPase assembly factor Vma21p suppresses the growth and acidification defects of pkr1Delta cells. Our data indicate that Pkr1p functions together with the other V-ATPase assembly factors in the ER to efficiently assemble the V-ATPase membrane sector.
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PMID:PKR1 encodes an assembly factor for the yeast V-type ATPase. 1692 53

How individual protein subunits assemble into the higher order structure of a protein complex is not well understood. Four proteins dedicated to the assembly of the V(0) subcomplex of the V-adenosine triphosphatase (V-ATPase) in the endoplasmic reticulum (ER) have been identified in yeast, but their precise mode of molecular action remains to be identified. In contrast to the highly conserved subunits of the V-ATPase, orthologs of the yeast assembly factors are not easily identified based on sequence similarity. We show in this study that two ER-localized Arabidopsis proteins that share only 25% sequence identity with Vma21p can functionally replace this yeast assembly factor. Loss of AtVMA21a function in RNA interference seedlings caused impaired cell expansion and changes in Golgi morphology characteristic for plants with reduced V-ATPase activity, and we therefore conclude that AtVMA21a is the first V-ATPase assembly factor identified in a multicellular eukaryote. Moreover, VMA21p acts as a dedicated ER escort chaperone, a class of substrate-specific accessory proteins so far not identified in higher plants.
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PMID:Arabidopsis has two functional orthologs of the yeast V-ATPase assembly factor Vma21p. 1869 37

The yeast Saccharomyces cerevisiae vacuolar ATPase (V-ATPase) is a multisubunit complex divided into two sectors: the V(1) sector catalyzes ATP hydrolysis and the V(0) sector translocates protons, resulting in acidification of its resident organelle. Four protein factors participate in V(0) assembly. We have discovered a fifth V(0) assembly factor, Voa1p (YGR106C); an endoplasmic reticulum (ER)-localized integral membrane glycoprotein. The role of Voa1p in V(0) assembly was revealed in cells expressing an ER retrieval-deficient form of the V-ATPase assembly factor Vma21p (Vma21pQQ). Loss of Voa1p in vma21QQ yeast cells resulted in loss of V-ATPase function; cells were unable to acidify their vacuoles and exhibited growth defects typical of cells lacking V-ATPase. V(0) assembly was severely compromised in voa1 vma21QQ double mutants. Isolation of V(0)-Vma21p complexes indicated that Voa1p associates most strongly with Vma21p and the core proteolipid ring of V(0) subunits c, c', and c''. On assembly of the remaining three V(0) subunits (a, d, and e) into the V(0) complex, Voa1p dissociates from the now fully assembled V(0)-Vma21p complex. Our results suggest Voa1p functions with Vma21p early in V(0) assembly in the ER, but then it dissociates before exit of the V(0)-Vma21p complex from the ER for transport to the Golgi compartment.
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PMID:Voa1p functions in V-ATPase assembly in the yeast endoplasmic reticulum. 1879 13

X-linked myopathy with excessive autophagy (XMEA) is a childhood-onset disease characterized by progressive vacuolation and atrophy of skeletal muscle. We show that XMEA is caused by hypomorphic alleles of the VMA21 gene, that VMA21 is the diverged human ortholog of the yeast Vma21p protein, and that like Vma21p it is an essential assembly chaperone of the V-ATPase, the principal mammalian proton pump complex. Decreased VMA21 raises lysosomal pH, which reduces lysosomal degradative ability and blocks autophagy. This reduces cellular free amino acids, which upregulates the mTOR pathway and mTOR-dependent macroautophagy, resulting in proliferation of large and ineffective autolysosomes that engulf sections of cytoplasm, merge together, and vacuolate the cell. Our results uncover macroautophagic overcompensation leading to cell vacuolation and tissue atrophy as a mechanism of disease.
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PMID:VMA21 deficiency causes an autophagic myopathy by compromising V-ATPase activity and lysosomal acidification. 2087 70


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