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)

The specific functional roles of various parts of the third transmembrane segment (M3) of the sarcoplasmic reticulum Ca(2+)-ATPase were examined by functionally characterizing a series of mutants with multiple or single substitutions of M3 residues. Steady-state and transient kinetic measurements, assisted by computer simulation of the time and Ca(2+) dependences of the phosphorylation level, were used to study the partial reaction steps of the enzyme cycle, including the binding and dissociation of Ca(2+) at the high affinity cytoplasmically facing sites. The mutation Lys-Leu-Asp-Glu(255) --> Glu-Ile-Glu-His resulted in a conspicuous increase in the rate of Ca(2+) dissociation as well as a displacement of the major conformational equilibria of the phosphoenzyme and dephosphoenzyme forms. The point mutant Phe(256) --> Ala also showed an increased rate of Ca(2+) dissociation, whereas a conspicuous decrease both in the rate of Ca(2+) dissociation and in the rate of Ca(2+) binding was found for the mutant Gly-Glu-Gln-Leu(260) --> Ile-His-Leu-Ile. These findings suggest that the NH(2)-terminal half of M3 is involved in control of the gateway to the Ca(2+) sites. The main effect of two mutations to the COOH-terminal half of M3, Ser-Lys-Val-Ile-Ser(265) --> Thr-Gly-Val-Ala-Val and Leu-Ile-Cys-Val-Ala-Val-Trp-Leu-Ile(274) --> Phe-Leu-Gly-Val-Ser-Phe-Phe-Ile-Leu, was a block of the dephosphorylation.
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PMID:Importance of transmembrane segment M3 of the sarcoplasmic reticulum Ca2+-ATPase for control of the gateway to the Ca2+ sites. 1131 33

Cet1, the RNA triphosphatase component of the yeast mRNA capping apparatus, catalyzes metal-dependent gamma-phosphate hydrolysis within the hydrophilic interior of an eight-strand beta barrel (the "triphosphate tunnel"), which rests upon a globular protein core (the "pedestal"). We performed a structure-guided alanine scan of 17 residues located in the tunnel (Ser(373), Thr(375), Gln(405), His(411), Ser(429), Glu(488), Thr(490)), on the tunnel's outer surface (Ser(378), Ser(487), Thr(489), His(491)), at the tunnel-pedestal interface (Ile(304), Met(308)) and in the pedestal (Asp(315), Lys(317), Arg(321), Asp(425)). Alanine mutations at 14 positions had no significant effect on Cet1 phosphohydrolase activity in vitro and had no effect on Cet1 function in vivo. Two of the mutations (R321A and D425A) elicited a thermosensitive (ts) yeast growth phenotype. The R321A and D425A proteins had full phosphohydrolase activity in vitro, but were profoundly thermolabile. Arg(321) and Asp(425) interact to form a salt bridge within the pedestal that tethers two of the strands of the tunnel. Mutations R321Q and D411N resulted in ts defects in vivo and in vitro, as did the double-mutant R321A-D435A, whereas the R321K protein was fully stable in vivo and in vitro. These results highlight the critical role of the buried salt bridge in Cet1 stability. Replacement of Ser(429) by alanine or valine elicited a cold-sensitive (cs) yeast growth phenotype. The S429A and S429V proteins were fully active when produced in bacteria at 37 degrees C, but were inactive when produced at 17 degrees C. Replacement of Ser(429) by threonine partially suppressed the cold sensitivity of the Cet1 phosphohydrolase, but did not suppress the cs growth defect in yeast.
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PMID:Functional groups required for the stability of yeast RNA triphosphatase in vitro and in vivo. 1139 22

The Escherichia coli RuvB protein is a motor protein that forms a complex with RuvA and promotes branch migration of Holliday junctions during homologous recombination. This study describes the characteristics of two RuvB mutants, I148T and I150T, that do not promote branch migration in the presence of RuvA. These RuvB mutants hydrolyzed ATP and bound duplex DNA with the same efficiency as wild-type RuvB, but the mutants did not form a complex with RuvA and were defective in loading onto junction DNA in a RuvA-assisted manner. A recent crystallographic study revealed that Ile(148) and Ile(150) are in a unique beta-hairpin that protrudes from the AAA(+) ATPase domain of RuvB. We propose that this beta-hairpin interacts with hydrophobic residues in the mobile third domain of RuvA and that this interaction is vital for the RuvA-assisted loading of RuvB onto Holliday junction DNA.
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PMID:A unique beta-hairpin protruding from AAA+ ATPase domain of RuvB motor protein is involved in the interaction with RuvA DNA recognition protein for branch migration of Holliday junctions. 1142 34

In the previous study, we have found that G65C and I125T double mutant of alpha chaperonin homo-oligomer from a hyperthermophilic archaeum, Thermococcus sp. strain KS-1, lacks ATP-dependent protein refolding activity despite showing ATPase activity and the ability to bind the denatured proteins. In this study, we have characterized several mutant Thermococcus chaperonin homo-oligomers with the amino acid substitutions of Gly-65 or Ile-125. The results showed that amino acid residue at 65th position should be a small amino acid such as glycine or alanine for the ATP-dependent refolding activity. The alpha chaperonin homo-oligomers with amino acid substitution of Gly-65 by amino acids whose side chains are larger than the methyl group did not have ATP-dependent protein refolding activity, but exhibited an increase of the binding affinity for unfolded proteins in the presence of ATP or AMP-PNP. (c)2001 Elsevier Science.
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PMID:Glycine at the 65th position plays an essential role in ATP-dependent protein folding by Archael group II chaperonin. 1174 8

The effects of some residues in maize chloroplast epsilon subunit on its activity have been studied by site-directed mutagenesis. After replacing Thr-42 of epsilon subunit with Cys, Arg, Ile or Pro, and forming the mutant epsilonT42C, mutant epsilonT42R, mutant epsilonT42I and mutant epsilonT42P respectively, it was found that the mutant epsilonT42P protein could no longer be expressed, but expression of other epsilon subunit mutants was similar to that of wild type. Comparing the inhibitory potency of different mutants of epsilon subunit with that of the wild type, it was found that the inhibitory effects of epsilon subunit mutants epsilonT42C and epsilonT42R on ATPase activity were slightly higher than that of wild type, but the epsilonT42I protein strongly inhibited the Ca(2+)-ATPase activity.
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PMID:Site-directed Mutagenesis of epsilon Subunit of ATP Synthase of Maize Chloroplast. 1216 18

The yeast Saccharomyces cerevisiae reproduces by asymmetric cell division, or budding. In each cell division, the daughter cell is usually smaller and younger than the mother cell, as defined by the number of divisions it can potentially complete before it dies. Although individual yeast cells have a limited life span, this age asymmetry between mother and daughter ensures that the yeast strain remains immortal. To understand the mechanisms underlying age asymmetry, we have isolated temperature-sensitive mutants that have limited growth capacity. One of these clonal-senescence mutants was in ATP2, the gene encoding the beta-subunit of mitochondrial F(1), F(0)-ATPase. A point mutation in this gene caused a valine-to-isoleucine substitution at the ninetieth amino acid of the mature polypeptide. This mutation did not affect the growth rate on a nonfermentable carbon source. Life-span determinations following temperature shift-down showed that the clonal-senescence phenotype results from a loss of age asymmetry at 36 degrees, such that daughters are born old. It was characterized by a loss of mitochondrial membrane potential followed by the lack of proper segregation of active mitochondria to daughter cells. This was associated with a change in mitochondrial morphology and distribution in the mother cell and ultimately resulted in the generation of cells totally lacking mitochondria. The results indicate that segregation of active mitochondria to daughter cells is important for maintenance of age asymmetry and raise the possibility that mitochondrial dysfunction may be a normal cause of aging. The finding that dysfunctional mitochondria accumulated in yeasts as they aged and the propensity for old mother cells to produce daughters depleted of active mitochondria lend support to this notion. We propose, more generally, that age asymmetry depends on partition of active and undamaged cellular components to the progeny and that this "filter" breaks down with age.
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PMID:A mutation in the ATP2 gene abrogates the age asymmetry between mother and daughter cells of the yeast Saccharomyces cerevisiae. 1224 24

The NS3 ATPase/helicase was isolated and characterized from three different infectious clones of hepatitis C virus (HCV). One helicase was from a genotype that normally responds to therapy (Hel-2a), and the other two were from more resistant genotypes, 1a (Hel-1a) and 1b (Hel-1b). Although the differences among these helicases are generally minor, all three enzymes have distinct properties. Hel-1a is less selective for nucleoside triphosphates, Hel-1b hydrolyzes nucleoside triphosphates less rapidly, and Hel-2a unwinds DNA more rapidly and binds DNA more tightly than the other two enzymes. Unlike related proteins, different nucleic acid sequences stimulate ATP hydrolysis by HCV helicase at different maximum rates and with different apparent efficiencies. This nucleic acid stimulation profile is conserved among the enzymes, but it does not result entirely from differential DNA-binding affinities. Although the amino acid sequences of the three proteins differ by up to 15%, one variant amino acid that is critical for helicase action was identified. NS3 residue 450 is a threonine in Hel-1a and Hel-1b and is an isoleucine in Hel-2a. A mutant Hel-1a with an isoleucine substituted for threonine 450 unwinds DNA more rapidly and binds DNA more tightly than the parent protein.
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PMID:Hepatitis C virus NS3 ATPases/helicases from different genotypes exhibit variations in enzymatic properties. 1263 55

The human multidrug resistance P-glycoprotein (ABCB1) transports a broad range of structurally diverse compounds out of the cell. The transport cycle involves coupling of drug binding in the transmembrane domains with ATP hydrolysis. Compounds such as verapamil stimulate ATPase activity. We used cysteine-scanning mutagenesis of the transmembrane segments and reaction with the thiol-reactive substrate analog of verapamil, methanethiosulfonate (MTS)-verapamil, to test whether it caused permanent activation of ATP hydrolysis. Here we report that one mutant, I306C(TM5) showed increased ATPase activity (8-fold higher than untreated) when treated with MTS-verapamil and isolated by nickel-chelate chromatography. Drug substrates that either enhance (calcein acetoxymethyl ester, demecolcine, and vinblastine) or inhibit (cyclosporin A and trans-(E)-flupentixol) ATPase activity of Cys-less or untreated mutant I306C P-glycoprotein did not affect the activity of MTS-verapamil-treated mutant I306C. Addition of dithiothreitol released the covalently attached verapamil, and ATPase activity returned to basal levels. Pretreatment with substrates such as cyclosporin A, demecolcine, verapamil, vinblastine, or colchicine prevented activation of mutant I306C by MTS-verapamil. The results suggest that MTS-verapamil reacts with I306C in a common drug-binding site. Covalent modification of I306C affects the long range linkage between the drug-binding site and the distal ATP-binding sites. This results in the permanent activation of ATP hydrolysis in the absence of transport. Trapping mutant I306C in a permanently activated state indicates that Ile-306 may be part of the signal to switch on ATP hydrolysis when the drug-binding site is occupied.
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PMID:Permanent activation of the human P-glycoprotein by covalent modification of a residue in the drug-binding site. 1271 2

A series of mutations were introduced into the sequence Glu(282)-Ile-Glu-His-Phe-Ile-His(288) of the NH(2)-terminal part of M3 of the rat kidney Na(+),K(+)-ATPase, and the resulting mutant pumps were analyzed functionally. Several of the mutations affected the conformational transitions between E(1) and E(2) forms of dephospho- and phosphoenzyme. Mutations to Glu(282) and Phe(286) affected the E(1)-E(2) and E(1)P-E(2)P equilibria in parallel, indicating a role for these two residues in both conformational changes. Mutation to His(285) preferentially affected the E(1)P-E(2)P equilibrium, and mutation to Ile(283) affected only the E(1)-E(2) equilibrium of the dephosphoenzyme, demonstrating that the conformational changes of M3 in the phospho- and dephospho-forms are not identical. Several of the mutants showed a reduced apparent affinity for Na(+), pointing to an important role of the region in optimizing the Na(+) binding properties of the enzyme. It is possible that this part of M3 is closely associated with an entry pathway through which the Na(+) ions pass from the cytoplasmic surface to reach the cation-binding pocket. Some of the mutants also displayed an increased Na(+)-ATPase activity, and a good correlation was observed between the turnover rate for Na(+)-ATPase activity and the rate of dephosphorylation in the absence of K(+), indicating an increased ability of Na(+) to activate dephosphorylation of E(2)P by binding in place of K(+) at the extracellularly facing sites. Thus, M3 also seems to be a part of the signaling pathway between the external cation sites and the catalytic site.
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PMID:Importance of transmembrane segment M3 of Na+,K+-ATPase for control of conformational changes and the cytoplasmic entry pathway for Na. 1276 74

Purified ATPsynthase of bovine heart mitochondria has been analyzed for its mobility and reactivity of oligomycin-sensitive sulfhydryl regions in presence of the substrate ADP and oligomycin. Labeling of thiol groups at the hydrophobic F_0 region of the ATPsynthase was increased in the enzyme initially treated with SDS, N-ethylmaleimide and dithiothreitol (modified enzyme). After dialysis or gel permeation the ATPsynthase was treated with [14C] alpha lipoic acid at a molar ratio of 35-85/1 (lipoic acid/ATPsynthase) corresponding to 4-8.6 nmol/mg protein. Under these conditions, ATPase activity of the native enzyme was significantly decreased. After preincubation with ADP, PAGE of the native, [14C] labeled enzyme revealed an increase of radioactivity at a region of 25 kDa deduced to Cys 197 of subunit b. In the modified enzyme the increase in radioactivity was found at 10 kDa. In this context, the sequence Lys-Cys-Ile around Cys 197 of subunit b suggests excessive reactivity of this thiol, as well as ready reversibility by -SH-S-S- interchange. Therefore, previously observed reaction by thiol reagents and antioxidants from outside the mitochondrion can be interpreted with Cys 197 of F0 b. It accounts for sulfhydryl unmasked by binding of ADP at F1.
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PMID:ADP- and oligomycin-sensitive redox behavior of F0 b thiol in ATPsynthase depends on neighbored primary structure: investigations using 14-C-labeled alpha lipoic acid. 1475 74


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