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 vacuolar membrane H(+)-ATPase of the yeast Saccharomyces cerevisiae is a multisubunit enzyme complex composed of an integral membrane V0 sector, and a peripherally associated V1 sector. Deletion of one of several structural genes for vacuolar H(+)-ATPase subunits was previously demonstrated to prevent proper assembly of the remaining V1 subunits onto the vacuolar membrane (Kane, P.M., Kuehn, M.C., Howald-Stevenson, I., and Stevens, T.H. (1992) J. Biol. Chem. 267, 447-454). A genetic screen was designed to identify new genes whose products were essential for the synthesis, assembly, and/or function of the yeast vacuolar H(+)-ATPase. Mutants were identified based on phenotypes associated with vacuolar membrane H(+)-ATPase loss of function (vma), including an inability to grow on media buffered at neutral pH. Representatives in five complementation groups were identified, including four novel mutant vma5, vma21, vma22, and vma23, all of which were defective in vacuolar ATPase enzyme activity. We report here the characterization of two genes, VMA4 and VMA5, that encode peripheral subunits of the vacuolar H(+)-ATPase. We determined that VMA5 encodes the 42-kDa subunit of the vacuolar H(+)-ATPase. The VMA4 gene, originally described by Foury (Foury, F. (1990) J. Biol. Chem. 265, 18554-18560), was determined to encode the 27-kDa subunit of the purified yeast vacuolar H(+)-ATPase. Characterization of the vma5 and vma4 mutants revealed that the 42- and 27-kDa subunits are essential for the assembly of the peripheral membrane portion of the H(+)-ATPase onto the vacuolar membrane.
 ...
PMID:Isolation of vacuolar membrane H(+)-ATPase-deficient yeast mutants; the VMA5 and VMA4 genes are essential for assembly and activity of the vacuolar H(+)-ATPase. 841 31

Cdc24p is the guanine-nucleotide exchange factor for the Cdc42p GTPase, which controls cell polarity in Saccharomyces cerevisiae. To identify new genes that may affect cell polarity, we characterized six UV-induced csl (CDC24 synthetic-lethal) mutants that exhibited synthetic-lethality with cdc24-4ls at 23 degrees. Five mutants were not complemented by plasmid-borne CDC42, RSR1, BUD5, BEM1, BEM2, BEM3 or CLA4 genes, which are known to play a role in cell polarity. The csl3 mutant displayed phenotypes similar to those observed with calcium-sensitive, Pet- vna mutants defective in vacuole function. CSL5 was allelic to VMA5, the vacuolar H(+)-ATPase subunit C, and one third of csl5 cdc24-4ls cells were elongated or had misshapen buds. A cdc24-4ls delta vma5::LEU2 double mutant did not exhibit synthetic lethality, suggesting that the csl5/vma5 cdc24-4ls synthetic-lethality was not simply due to altered vacuole function. The cdc24-4ls mutant, like delta vma5::LEU2 and csl3 mutants, was sensitive to high levels of Ca2+ as well as Na+ in the growth media, which did not appear to be a result of a fragile cell wall because the phenotypes were not remedied by 1 M sorbitol. Our results indicated that Cdc24p was required in one V-ATPase mutant and another mutant affecting vacuole morphology, and also implicated Cdc24p in Na+ tolerance.
 ...
PMID:Characterization of synthetic-lethal mutants reveals a role for the Saccharomyces cerevisiae guanine-nucleotide exchange factor Cdc24p in vacuole function and Na+ tolerance. 928 67

In the vacuolar-type H+-ATPase (V-ATPase), highly hydrophobic subunits known as the proteolipids are components of the integral membrane V0 sector. Previously, we described the identification of three different proteolipid genes in Caenorhabditis elegans (Oka, T., Yamamoto, R., and Futai, M. (1997) J. Biol. Chem. 272, 24387-24392): vha-1 and vha-2 encoded 16-kDa subunits, and vha-4, a 23-kDa isoform. We report here that a third 16-kDa gene, vha-3, has been identified on chromosome IV. This is the first example in which four proteolipid genes have been found in a single organism. vha-2 and vha-3 exhibited 85% nucleotide identity within the open reading frames which encoded the identical amino acid sequence. Northern blot analysis indicated that all four genes were expressed in a similar pattern during the worm life cycle; however, studies with transgenic worms indicated that the vha-3 gene was expressed differently from other proteolipid genes in a cell-specific manner. These results implied that the isoforms of the proteolipids may be related to functional differences of V-ATPases in various cell types. Another new gene, vha-11, contained seven exons and was found to be located immediately downstream of vha-3. The two genes constitute a single transcriptional unit. The VHA-11 protein had 384 amino acids and shared strong sequence similarities with the C subunit, a component of the peripheral V1 sector of the V-ATPase, from yeast, bovine, and human. Expression of the vha-11 cDNA complemented a null mutation of VMA5, the yeast C subunit gene, thus demonstrating that vha-11 was the functional C subunit of C. elegans.
 ...
PMID:Multiple genes for vacuolar-type ATPase proteolipids in Caenorhabditis elegans. A new gene, vha-3, has a distinct cell-specific distribution. 971 84

Subunit C is a V(1) sector subunit found in all vacuolar H(+)-ATPases (V-ATPases) that may be part of the peripheral stalk connecting the peripheral V(1) sector with the membrane-bound V(0) sector of the enzyme (Wilkens, S., Vasilyeva, E., and Forgac, M. (1999) J. Biol. Chem. 274, 31804--31810). To elucidate subunit C function, we performed random and site-directed mutagenesis of the yeast VMA5 gene. Site-directed mutations in the most highly conserved region of Vma5p, residues 305--325, decreased catalytic activity of the V-ATPase by up to 48% without affecting assembly. A truncation mutant (K360stop) identified by random mutagenesis suggested a small region near the C terminus of the protein (amino acids 382--388) might be important for subunit stability. Site-directed mutagenesis revealed that three aromatic amino acids in this region (Tyr-382, Phe-385, and Tyr-388) in addition to four other conserved aromatic amino acids (Phe-260, Tyr-262, Phe-296, Phe-300) are essential for stable assembly of V(1) with V(0), although alanine substitutions at these positions support some activity in vivo. Surprisingly, three mutations (F260A, Y262A, and F385A) greatly decrease the stability of the V-ATPase in vitro but increase its k(cat) for ATP hydrolysis and proton transport by at least 3-fold. The peripheral stalk of V-ATPases must balance the stability essential for productive catalysis with the dynamic instability involved in regulation; these three mutations may perturb that balance.
 ...
PMID:Mutational analysis of the subunit C (Vma5p) of the yeast vacuolar H+-ATPase. 1177 35