Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:3.6.1.3 (ATPase)
65,361 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Two ATP-binding domains are found in members of the family of ATP-dependent transport proteins, which includes P-glycoprotein and cystic fibrosis transmembrane conductance regulator. To investigate the involvement of the two ATP-binding domains in the ATPase activity of P-glycoprotein, full-length and the 5'-half of human MDR1 cDNA, which encodes P-glycoprotein, were fused with the Escherichia coli lacZ gene and expressed in NIH3T3 cells. Immunoprecipitated full-length P-glycoprotein beta-galactosidase showed ATPase activity with apparent specific activity of 180 nmol/mg/min, a value higher than previously reported, in the presence of phospholipids, suggesting that stabilization of the transmembrane domains is necessary for ATP hydrolysis. N-terminal half P-glycoprotein-beta-galactosidase also showed ability to hydrolyze ATP but with slightly lower specific activity. Both ATPase activities showed similar characteristics when the effect of several inhibitors was analyzed, indicating that the N-terminal ATP-binding domain contains all residues necessary to hydrolyze ATP without interacting with the C-terminal ATP-binding domain.
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PMID:P-glycoprotein. ATP hydrolysis by the N-terminal nucleotide-binding domain. 134 41

Affinity-purified polyclonal antibodies, raised against two synthetic peptides corresponding to the R domain and the C terminus of the human cystic fibrosis transmembrane conductance regulator (CFTR), were used to characterize and localize the protein in human epithelial cells. Employing an immunoblotting technique that ensures efficient detection of large hydrophobic proteins, both antibodies recognized and approximately 180-kDa protein in cell lysates and isolated membranes of airway epithelial cells from normal and cystic fibrosis (CF) patients and of T84 colon carcinoma cells. Reactivity with the anti-C terminus antibody, but not with the anti-R domain antibody, was eliminated by limited carboxypeptidase Y digestion. When normal CFTR cDNA was overexpressed via a retroviral vector in CF or normal airway epithelial cells or in mouse fibroblasts, the protein produced had an apparent molecular mass of about 180 kDa. The CFTR expressed in insect (Sf9) cells by a baculovirus vector had a molecular mass of about 140 kDa, probably representing a nonglycosylated form. The CFTR in epithelial cells appears to exist in several forms. N-glycosidase treatment of T84 cell membranes reduces the apparent molecular mass of the major CFTR band from 180 kDa to 140 kDa, but a fraction of the T84 cell CFTR could not be deglycosylated, and the CFTR in airway epithelial cell membranes could not be deglycosylated either. Moreover, wheat germ agglutinin absorbs the majority of the CFTR from detergent-solubilized T84 cell membranes but not from airway cell membranes. The CFTR in all epithelial cell types was found to be an integral membrane protein not solubilized by high salt or lithium diiodosalicylate treatment. Sucrose density gradient fractionation of crude membranes prepared from the airway epithelial cells, previously surface-labeled by enzymatic galactosidation, showed a plasma membrane localization for both the normal CFTR and the CFTR carrying the Phe508 deletion (delta F 508). The CFTR in all cases co-localized with the Na+, K(+)-ATPase and the plasma membrane calcium ATPase, while the endoplasmic reticulum calcium ATPase and mitochondrial membrane markers were enriched at higher sucrose densities. Thus, the CFTR appears to be localized in the plasma membrane both in normal and delta F 508 CF epithelial cells.
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PMID:Biochemical characterization of the cystic fibrosis transmembrane conductance regulator in normal and cystic fibrosis epithelial cells. 137 Apr 88

The epithelial cell line HT-29, which constitutively expresses the cystic fibrosis transmembrane conductance regulator (CFTR), was induced to become drug resistant by cultivation in the presence of colchicine. The gradual acquisition of drug resistance was associated with a corresponding increase in the expression of the multidrug resistance P-glycoprotein (P-gp) and a marked (> 80%) decrease in the constitutive levels of CFTR protein, as determined by immunoblotting. The reduction in CFTR content occurred at the onset of acquisition of drug resistance when P-gp expression was still relatively low. Reversal of drug resistance by removal of colchicine from the culture medium led to a 70% decrease in P-gp levels and a concomitant 40% increase in CFTR. The levels of other membrane proteins such as Na(+)-K(+)-ATPase and alkaline phosphatase remained relatively constant (< 26% variation). We propose that a selective downregulation of CFTR is elicited by acquisition of the multidrug resistance (MDR) phenotype and that induction of P-gp expression leads to a reversible repression of CFTR biosynthesis. These findings provide an experimental foundation for the complementary patterns of expression of the CFTR and MDR1 genes observed in vivo.
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PMID:Induction of multidrug resistance downregulates the expression of CFTR in colon epithelial cells. 750 92

Cells can rapidly and reversibly alter solute transport rates by changing the kinetics of transport proteins resident within the plasma membrane. Most notably, this can be brought about by reversible phosphorylation of the transporter. An additional mechanism for acute regulation of plasma membrane transport rates is by the regulated exocytic insertion of transport proteins from intracellular vesicles into the plasma membrane and their subsequent regulated endocytic retrieval. Over the past few years, the number of transporters undergoing this regulated trafficking has increased dramatically, such that what was once an interesting translocation of a few transporters has now become a widespread modality for regulating plasma membrane solute permeabilities. The aim of this article is to review the models proposed for the regulated trafficking of transport proteins and what lines of evidence should be obtained to document regulated exocytic insertion and endocytic retrieval of transport proteins. We highlight four transporters, the insulin-responsive glucose transporter, the antidiuretic hormone-responsive water channel, the urinary bladder H(+)-ATPase, and the cystic fibrosis transmembrane conductance regulator Cl- channel, and discuss the various approaches taken to document their regulated trafficking. Finally, we discuss areas of uncertainty that remain to be investigated concerning the molecular mechanisms involved in regulating the trafficking of proteins.
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PMID:Role of membrane trafficking in plasma membrane solute transport. 751 93

Cystic fibrosis is caused by mutations in the cell membrane protein called CFTR (cystic fibrosis transmembrane conductance regulator) which functions as a regulated Cl- channel. Although it is known that CFTR contains two nucleotide domains, both of which exhibit the capacity to bind ATP, it has not been demonstrated directly whether one or both domains can function as an active ATPase. To address this question, we have studied the first CFTR nucleotide binding fold (NBF1) in fusion with the maltose-binding protein (MBP), which both stabilizes NBF1 and enhances its solubility. Three different ATPase assays conducted on MBP-NBF1 clearly demonstrate its capacity to catalyze the hydrolysis of ATP. Significantly, the mutations K464H and K464L in the Walker A consensus motif of NBF1 markedly impair its catalytic capacity. MBP alone exhibits no ATPase activity and MBP-NBF1 fails to catalyze the release of phosphate from AMP or ADP. The Vmax of ATP hydrolysis (approximately 30 nmol/min/mg of protein) is significant and is markedly inhibited by azide and by the ATP analogs 2'-(3')-O-(2,4,6-trinitrophenyl)-adenosine-5'-triphosphate and adenosine 5'-(beta, gamma-imido)triphosphate. As inherited mutations within NBF1 account for most cases of cystic fibrosis, results reported here are fundamental to our understanding of the molecular basis of the disease.
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PMID:The first nucleotide binding fold of the cystic fibrosis transmembrane conductance regulator can function as an active ATPase. 754 72

The cystic fibrosis transmembrane conductance regulator (CFTR), a member of the traffic ATPase superfamily, possesses two putative nucleotide-binding folds (NBFs). The NBFs are sufficiently similar that sequence alignment of highly conserved regions can be used to identify analogous residues in the two domains. To determine whether this structural homology is paralleled in function, we compared the activation of chloride conductance by forskolin and 3-isobutyl-1-methylxanthine in Xenopus oocytes expressing CFTRs bearing mutations in NBF1 or NBF2. Mutation of a conserved glycine in the putative linker domain in either NBF produced virtually identical changes in the sensitivity of chloride conductance to activating conditions, and mutation of this site in both NBFs produced additive effects, suggesting that in the two NBFs this region plays a similar and critical role in the activation process. In contrast, amino acid substitutions in the Walker A and B motifs, thought to form an integral part of the nucleotide-binding pockets, produced strikingly different effects in NBF1 and NBF2. Substitutions for the conserved lysine (Walker A) or aspartate (Walker B) in NBF1 resulted in a marked decrease in sensitivity to activation, whereas the same changes in NBF2 produced an increase in sensitivity. These results are consistent with a model for the activation of CFTR in which both NBF1 and NBF2 are required for normal function but in which either the nature or the exact consequences of nucleotide binding differ for the two domains.
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PMID:Functional roles of the nucleotide-binding folds in the activation of the cystic fibrosis transmembrane conductance regulator. 769 98

Binding protein-dependent transport systems mediate the accumulation of several ions, sugars, amino acids, and peptides in Gram-negative bacteria by using the energy of ATP hydrolysis and belong to a superfamily of membrane proteins which extends to eukaryotic cells and includes the multidrug resistance P-glycoprotein and the cystic fibrosis transmembrane conductance regulator. The binding protein-dependent galactose transport system of Salmonella typhimurium comprises four proteins which have been characterized previously by molecular cloning experiments (51,000-dalton MglA protein, with a stable proteolytic product of 38,000 daltons, 33,000-dalton MglB protein, 29,000-dalton MglC protein, 21,000-dalton MglE protein). By using a MglA hyperproducing strain, we have purified a galactose-stimulated ATPase which shows a single band in polyacrylamide gels under nondenaturing conditions and shows three bands at 51,000, 38,000, and 15,000 daltons on sodium dodecyl sulfate-polyacrylamide gels (our results suggest that the bands at 38,000 and 15,000 daltons represent proteolytic products of the 51,000-dalton protein). The ATPase activity coincides with the purified protein during the two last chromatographic steps of the purification procedure, and it cannot be isolated from a strain which does not contain the mglA gene. The MglA ATPase is stimulated 3-fold by galactose and hydrolyzes ATP to ADP and Pi (Km ATP = 60 microM, Ka galactose = 0.3 mM, Vmax = 140 nmol/min/mg of protein). The gamma-phosphate of ATP is transferred neither to galactose nor to the protein itself. Vanadate, N-ethylmaleimide and 5-methoxyindole-2-carboxylic acid, a specific inhibitor of binding protein-dependent transport systems, inhibit the MglA ATPase.
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PMID:The MglA component of the binding protein-dependent galactose transport system of Salmonella typhimurium is a galactose-stimulated ATPase. 838 96

We have sought to determine the mechanisms driving fluid secretion by the cystic epithelium in autosomal dominant polycystic kidney disease (ADPKD). We have performed in vitro experiments on intact cysts dissected from discarded ADPKD kidneys, on monolayers of cells cultured from the cystic epithelium and on microcysts clonally derived from single cultured cells. These preparations absorb fluid in the control state but secrete fluid in response to native cyst fluid, to adenylate cyclase agonists and to permeant analogues of cAMP. Measurements of short-circuit current and transepithelial voltage in the monolayers indicate that anion secretion must drive the fluid secretion. Fluid secretion by the intact cysts was inhibited by basolateral application of ouabain but not by apical application. The effect of ouabain on fluid secretion and short-circuit current in the monolayers followed the same pattern. Thus the functional Na,K-ATPase enzyme complex is located only in the basolateral membrane of the cystic cells and serves to maintain the transmembrane chemical and electrical gradients that drive anion secretion by other transport mechanisms. Fluid secretion and short-circuit current in the cultured monolayers was inhibited by the basolateral application of the Na-K-2Cl cotransporter inhibitors, bumetanide and furosemide, and by apical application of the chloride channel blocker, diphenylamine-2-carboxylate (DPC). These data suggest that chloride is the anion that is actively secreted. Preliminary experiments utilizing the monolayers and the microcysts and measuring cell chloride concentration and chloride efflux across the apical membrane support this conclusion. Other preliminary data indicate that the cystic fibrosis transmembrane conductance regulator is present in the apical membrane. Thus active chloride transport generates fluid secretion by the cystic epithelium.
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PMID:Mechanisms of fluid secretion by polycystic epithelia. 874 60

Plasma membrane Cl- channels perform a variety of functions, including control of excitability in neurons and muscle, cell volume regulation and transepithelial transport. Structurally, three classes of Cl- channels have been identified: ligand-gated, postsynaptic Cl- channels (e.g. GABA and glycine receptors); the cystic fibrosis transmembrane conductance regulator (CFTR) Cl- channels (which belong to the traffic ATPase superfamily); and the CLC family of Cl- channels. Recent developments of note include further characterization of the expanding CLC Cl- channel family, advances in understanding the regulation of the CFTR Cl- channel and its emergent role as a regulator of other channels, clarification of issues related to swelling-activated Cl- channels, and the discovery that several co-transporter molecules are now known to induce Cl- currents in Xenopus oocytes.
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PMID:Chloride channels: a molecular perspective. 879 80

The kidneys of patients with autosomal dominant polycystic kidney disease become massively enlarged due to the progressive expansion of myriad fluid-filled cysts. The epithelial cells that line the cyst walls are responsible for secreting the cyst fluid, but the mechanism through which this secretion occurs is not well established. Recent studies suggest that renal cyst epithelial cells actively secrete Cl across their apical membranes, which in turn drives the transepithelial movement of Na and water. The characteristics of this secretory flux suggest that it is dependent upon the participation of an apical cystic fibrosis transmembrane conductance regulator (CFTR)-like Cl channel and basolateral Na,K-ATPase. To test this hypothesis, we have immunolocalized the CFTR and Na,K-ATPase proteins in intact cysts and in cyst epithelial cells cultured in vitro on permeable filter supports. In both settings, cyst epithelial cells were found to possess Na,K-ATPase exclusively at their basolateral surfaces; apical labeling was not detected. The CFTR protein was present at the apical surfaces of cyst epithelial cells that had been stimulated to secrete through incubation in forskolin. CFTR was detected in intracellular structures in cultured cyst epithelial cells that had not received the forskolin treatment. These results demonstrate that the renal epithelial cells that line cysts in autosomal dominant polycystic kidney disease express transport systems with the appropriate polarity to mediate active Cl and fluid secretion.
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PMID:Immunolocalization of ion transport proteins in human autosomal dominant polycystic kidney epithelial cells. 881 77


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