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)

ClpB from Escherichia coli is a member of a protein-disaggregating multi-chaperone system that also includes DnaK, DnaJ, and GrpE. The sequence of ClpB contains two ATP-binding domains that are enclosed between the amino-terminal and carboxyl-terminal regions. The N-terminal sequence region does not contain known functional sequence motifs. Here, we performed site-directed mutagenesis of four polar residues within the N-terminal domain of ClpB (Thr7, Ser84, Asp103 and Glu109). These residues are conserved in several ClpB homologs. We found that the mutations, T7A, S84A, D103A, and E109A did not significantly affect the secondary structure and thermal stability of ClpB, nor did they inhibit the self-association of ClpB, its basal ATPase activity, or the enhanced rate of the ATP hydrolysis by ClpB in the presence of poly-L-lysine. We observed, however, that three mutations, T7A, D103A, and E109A, reduced the casein-induced activation of the ClpB ATPase. The same three mutant ClpB variants also showed low chaperone activity in the luciferase reactivation assay. We found, however, that the four ClpB mutants, as well as the wild-type, bound similar amounts of inactivated luciferase. In summary, we have identified three essential amino acid residues within the N-terminal region of ClpB that participate in the coupling between a protein-binding signal and the ATP hydrolysis, and also support the chaperone activity of ClpB.
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PMID:Conserved amino acid residues within the amino-terminal domain of ClpB are essential for the chaperone activity. 1213 37

The function of an ATP-dependent membrane protease FtsH was investigated using the enzyme from Thermus thermophilus HB8. An FtsH mutant with replacement of Glu-419 in the zinc-binding motif by Cys lost the activity to digest casein, a model unfolded protein, and the small ATPase activity of this mutant was no longer stimulated by casein. In the presence of ATP or ATPgammaS, but not ADP, a mutant FtsH-unfolded protein complex was isolated, indicating that ATP binding, but not ATP hydrolysis, is required for FtsH to form a stable complex with an unfolded protein. The FtsH without mutation at Glu-419 did not produce a stable complex with casein in the presence of any nucleotides tested and therefore it appears that blocking proteolysis also contributes to stabilization of the complex.
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PMID:Stabilization of FtsH-unfolded protein complex by binding of ATP and blocking of protease. 1214 19

ClpB is a member of a multichaperone system in Escherichia coli (with DnaK, DnaJ, and GrpE) that reactivates strongly aggregated proteins. The sequence of ClpB contains two ATP-binding domains, each containing Walker consensus motifs. The N- and C-terminal sequence regions of ClpB do not contain known functional motifs. In this study, we performed site-directed mutagenesis of selected charged residues within the Walker A motifs (Lys212 and Lys611) and the C-terminal region of ClpB (Asp797, Arg815, Arg819, and Glu826). We found that the mutations K212T, K611T, D797A, R815A, R819A, and E826A did not significantly affect the secondary structure of ClpB. The mutation of the N-terminal ATP-binding site (K212T), but not of the C-terminal ATP-binding site (K611T), and two mutations within the C-terminal domain (R815A and R819A) inhibited the self-association of ClpB in the absence of nucleotides. The defects in self-association of these mutants were also observed in the presence of ATP and ADP. The four mutants K212T, K611T, R815A, and R819A showed an inhibition of chaperone activity, which correlated with their low ATPase activity in the presence of casein. Our results indicate that positively charged amino acids that are located along the intersubunit interface (this includes Lys212 in the Walker A motif of the N-terminal ATP-binding domain as well as Arg815 and Arg819 in the C-terminal domain) participate in intersubunit salt bridges and stabilize the ClpB oligomer. Interestingly, we have identified a conserved residue within the C-terminal domain (Arg819) which does not participate directly in nucleotide binding but is essential for the chaperone activity of ClpB.
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PMID:Site-directed mutagenesis of conserved charged amino acid residues in ClpB from Escherichia coli. 1222 Jan 94

ClpB from Thermus thermophilus belongs to the Clp/Hsp100 protein family and reactivates protein aggregates in cooperation with the DnaK chaperone system. The mechanism of protein reactivation and interaction with the DnaK system remains unclear. ClpB possesses two nucleotide binding domains, which are essential for function and show a complex allosteric behavior. The role of the N-terminal domain that precedes the first nucleotide binding domain is largely unknown. We purified and characterized an N-terminal shortened ClpB variant (ClpBDeltaN; amino acids 140-854), which remained active in refolding assays with three different substrate proteins. In addition the N-terminal truncation did not significantly change the nucleotide binding affinities, the nucleotide-dependent oligomerization, and the allosteric behavior of the protein. In contrast casein binding and stimulation of the ATPase activity by kappa-casein were affected. These results suggest that the N-terminal domain is not essential for the chaperone function, does not influence the binding of nucleotides, and is not involved in the formation of intermolecular contacts. It contributes to the casein binding site of ClpB, but other substrate proteins do not necessarily interact with the N terminus. This indicates a substantial difference in the binding mode of kappa-casein that is often used as model substrate for ClpB and other possibly more suitable substrate proteins.
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PMID:The N terminus of ClpB from Thermus thermophilus is not essential for the chaperone activity. 1235 38

To clarify the role of ATP in proteolysis, we studied archaeal 20S proteasomes and the PAN (proteasome-activating nucleotidase) regulatory complex, a homolog of the eukaryotic 19S ATPases. PAN's ATPase activity was stimulated similarly by globular (GFPssrA) and unfolded (casein) substrates, and by the ssrA recognition peptide. Denaturation of GFPssrA did not accelerate its degradation or eliminate the requirement for PAN and ATP. During degradation of one molecule of globular or unfolded substrates, 300-400 ATP molecules were hydrolyzed. An N-terminal deletion in the 20S alpha subunits caused opening of the substrate-entry channel and rapid degradation of unfolded proteins without PAN; however, degradation of globular GFPssrA still required PAN's ATPase activity, even after PAN-catalyzed unfolding. Thus, substrate binding activates ATP hydrolysis, which promotes three processes: substrate unfolding, gate opening in the 20S, and protein translocation.
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PMID:ATP hydrolysis by the proteasome regulatory complex PAN serves multiple functions in protein degradation. 1253 13

Like other AAA proteins, Escherichia coli FtsH, a membrane-bound AAA protease, contains highly conserved aromatic and glycine residues (Phe228 and Gly230) that are predicted to lie in the central pore region of the hexamer. The functions of Phe228 and Gly230 were probed by site-directed mutagenesis. The results of both in vivo and in vitro assays indicate that these conserved pore residues are important for FtsH function and that bulkier, uncharged/apolar residues are essential at position 228. None of the point mutants, F228A, F228E, F228K, or G230A, was able to degrade sigma32, a physiological substrate. The F228A mutant was able to degrade casein, an unfolded substrate, although the other three mutants were not. Mutation of these two pore residues also affected the ATPase activity of FtsH. The F228K and G230A mutations markedly reduced ATPase activity, whereas the F228A mutation caused a more modest decrease in this activity. The F228E mutant was actually more active ATPase. The substrates, sigma32 and casein, stimulated the ATPase activity of wild type FtsH. The ATPase activity of the mutants was no longer stimulated by casein, whereas that of the three Phe228 mutants, but not the G230A mutant, remained sigma32-stimulatable. These results suggest that Phe228 and Gly230 in the predicted pore region of the FtsH hexamer have important roles in proteolysis and its coupling to ATP hydrolysis.
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PMID:Conserved pore residues in the AAA protease FtsH are important for proteolysis and its coupling to ATP hydrolysis. 1451 80

The Hsp100 protein ClpB is a member of the AAA+ protein family that mediates the solubilization of aggregated proteins in cooperation with the DnaK chaperone system. Unstructured polypeptides such as casein or poly-L-lysine have been shown to stimulate the ATPase activity of ClpB and thus may both act as substrates. Here we compared the effects of alpha-casein and poly-L-lysine on the ATPase and chaperone activities of ClpB. alpha-Casein stimulated ATP hydrolysis by both AAA domains of ClpB and inhibited the ClpB-dependent solubilization of aggregated proteins if present in excess. In contrast, poly-L-lysine stimulated exclusively the ATPase activity of the second AAA domain and increased the disaggregation activity of ClpB. Thus poly-L-lysine does not act as substrate, but rather represents an effector molecule, which enhances the chaperone activity of ClpB.
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PMID:Poly-L-lysine enhances the protein disaggregation activity of ClpB. 1455 May 59

The hypothesis that increased dietary protein augments distal nephron acidification and does so through an endothelin (ET-1)-dependent mechanism was tested. Munich-Wistar rats that ate minimum electrolyte diets of 50% (HiPro) and 20% (CON) casein-provided protein, the latter comparable to standard diet, were compared. HiPro versus CON had higher distal nephron net HCO(3) reabsorption by in vivo microperfusion (37.8 +/- 3.2 versus 16.6 +/- 1.5 pmol/mm per min; P < 0.001) as a result of higher H(+) secretion (41.3 +/- 4.0 versus 23.0 +/- 2.1 pmol/mm per min; P < 0.002) and lower HCO(3) secretion (-3.5 +/- 0.4 versus -6.4 +/- 0.8 pmol/mm per min; P < 0.001). Perfusion with H(+) inhibitors support that increased H(+) secretion was mediated by augmented Na(+)/H(+) exchange and H(+)-ATPase activity without augmented H(+),K(+)-ATPase activity. HiPro versus CON had higher levels of urine ET-1 excretion, renal cortical ET-1 addition to microdialysate in vivo, and renal cortical ET-1 mRNA, consistent with increased renal ET-1 production. Oral bosentan, an ET A/B receptor antagonist, decreased distal nephron net HCO(3) reabsorption (22.4 +/- 1.9 versus 37.8 +/- 3.2 pmol/mm per min; P < 0.001) as a result of lower H(+) secretion (28.4 +/- 2.4 versus 41.3 +/- 4.0 pmol/mm per min; P < 0.016) and higher HCO(3) secretion (-6.0 +/- 0.7 versus -3.5 +/- 0.4 pmol/mm per min; P < 0.006). The H(+) inhibitors had no additional effect in HiPro ingesting bosentan, supporting that ET mediated the increased distal nephron Na(+)/H(+) exchange and H(+)-ATPase activity in HiPro. Increased dietary protein augments distal nephron acidification that is mediated through an ET-sensitive increase in Na(+)/H(+) exchange and H(+)-ATPase activity.
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PMID:Increased endothelin activity mediates augmented distal nephron acidification induced by dietary protein. 1533 76

HslVU is an ATP-dependent protease consisting of HslU ATPase and HslV peptidase. In an HslVU complex, the central pores of HslU hexamer and HslV dodecamer are aligned and the proteolytic active sites are sequestered in the inner chamber of HslV. Thus, the degradation of natively folded proteins requires unfolding and translocation processes for their access into the proteolytic chamber of HslV. A highly conserved GYVG(93) sequence constitutes the central pore of HslU ATPase. To determine the role of the pore motif on protein unfolding and translocation, we generated various mutations in the motif and examined their effects on the ability of HslU in supporting the proteolytic activity of HslV against three different substrates: SulA as a natively folded protein, casein as an unfolded polypeptide, and a small peptide. Flexibility provided by Gly residues and aromatic ring structures of the 91st amino acid were essential for degradation of SulA. The same structural features of the GYVG motif were highly preferred, although not essential, for degradation of casein. In contrast, none of the features were required for peptide hydrolysis. Mutations in the GYVG motif of HslU also showed marked influence on its ATPase activity, affinity to ADP, and interaction with HslV. These results suggest that the GYVG motif of HslU plays important roles in unfolding of natively folded proteins as well as in translocation of unfolded proteins for degradation by HslV. These results also implicate a role of the pore motif in ATP cleavage and in the assembly of HslVU complex.
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PMID:Role of the GYVG pore motif of HslU ATPase in protein unfolding and translocation for degradation by HslV peptidase. 1584

The hypothesis that increased dietary protein augments distal nephron acidification through endothelin-mediated increased aldosterone activity was tested. Munich-Wistar rats were studied after 3 wk of diets with 50% high protein (HiPro) and 20% control (CON) casein-provided protein, the latter comparable to standard diet. HiPro versus CON rats had higher distal nephron H+ secretion by in vivo microperfusion as shown previously. Perfusion with inhibitors of Na+/H+ exchange (EIPA, 10(-5) M), H+-ATPase (bafilomycin, 10(-7) M), and H+-K+-ATPase (Sch 28080 [10(-5) M] and ouabain [10(-3) M]) support that higher Na+/H+ exchange and higher H+-ATPase but not higher H+-K+-ATPase activity mediated increased H+ secretion in HiPro rats. Oral bosentan, an endothelin A/B receptor antagonist, decreased distal nephron H+ secretion in HiPro rats as a result of reduced Na+/H+ exchange and H+-ATPase activity as shown previously by the authors' laboratory. HiPro versus CON rats had higher plasma aldosterone (60.9 +/- 5.9 versus 42.2 +/- 4.4 pg/ml; P < 0.024) and higher urine aldosterone excretion (21.9 +/- 3.9 versus 10.5 +/- 2.8 ng/d; P < 0.04) in the absence but not presence of bosentan, consistent with endothelin-mediated increased aldosterone secretion. HiPro rats that did versus did not ingest the aldosterone antagonist spironolactone had lower distal nephron H+ secretion (29.2 +/- 3.3 versus 42.1 +/- 3.8 pmol/mm per min; P < 0.05) as a result of lower H+-ATPase activity without differences in Na+/H+ exchange or H+-K+-ATPase activity. The data support that dietary protein provided as casein increases distal nephron acidification through endothelin-stimulated Na+/H+ exchange and endothelin-stimulated aldosterone secretion that increases H+-ATPase activity.
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PMID:Endothelin-induced increased aldosterone activity mediates augmented distal nephron acidification as a result of dietary protein. 1587 74


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