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)

A T8993G point mutation in the mtDNA results in a Leu156Arg substitution in the MTATP6 subunit of the mitochondrial F1F0-ATPase. The T8993G mutation causes impaired oxidative phosphorylation (OXPHOS) in two mitochondrial disorders, NARP (neuropathy, ataxia and retinitis pigmentosa) and MILS (maternally inherited Leigh's syndrome). It has been reported, in some studies, that the T8993G mutation results in loss of assembled F1F0-ATPase. Others reported that the mutation causes impairment of proton flow through F0. In addition, it was shown that fibroblasts from NARP subjects have a tendency to undergo apoptotic cell death, perhaps as a result of increased free radical production. Here, we show that the T8993G mutation inhibits oxidative phosphorylation and results in enhanced free radical production. We suggest that free radical-mediated inhibition of OXPHOS contributes to the loss of ATP synthesis. Importantly, we show that antioxidants restore respiration and partially rescue ATP synthesis in cells harboring the T8993G mutation. Our results indicate that free radicals might play an important role in the pathogenesis of NARP/MILS and that this can be prevented by antioxidants. The effectiveness of antioxidant agents in cultured NARP/MILS cells suggests that they might have a potential beneficial role in the treatment of patients with NARP.
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PMID:The mtDNA T8993G (NARP) mutation results in an impairment of oxidative phosphorylation that can be improved by antioxidants. 1499 33

In bacteria, yeast, and mammals, iron-sulfur (Fe-S) cluster-containing proteins are involved in numerous processes including electron transfer, metabolic reactions, sensing, signaling, and regulation of gene expression. In humans, iron-storage diseases such as X-linked sideroblastic anemia and ataxia are caused by defects in Fe-S cluster availability. The biogenesis of Fe-S clusters involves several pathways, and in bacteria, the SufABCDSE operon has been shown to play a vital role in Fe-S biogenesis and repair during oxidative stress. Although Fe-S proteins play vital roles in plants, Fe-S cluster biogenesis and maintenance and physiological consequences of dysfunctional Fe-S cluster assembly remains obscure. Here we report that Arabidopsis plants deficient for the SufC homolog AtNAP7 show lethality at the globular stage of embryogenesis. AtNAP7 is expressed in developing embryos and in apical, root, and floral meristems and encodes an ATP-binding cassette/ATPase that can partially rescue growth defects in an Escherichia coli SufC mutant during oxidative stress. AtNAP7 is plastid-localized, and mutant embryos contain abnormal developing plastids with disorganized thylakoid structures. We found that AtNAP7 can interact with AtNAP6, a plastidic Arabidopsis SufD homolog, and because Arabidopsis plastids also harbor SufA, SufB, SufS, and SufE homologs, plastids probably contain a complete SUF system. Our results imply that AtNAP7 represents a conserved SufC protein involved in the biogenesis and/or repair of oxidatively damaged Fe-S clusters and suggest an important role for plastidic Fe-S cluster maintenance and repair during Arabidopsis embryogenesis.
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PMID:AtNAP7 is a plastidic SufC-like ATP-binding cassette/ATPase essential for Arabidopsis embryogenesis. 1518 73

This mini-review summarizes our present view of the biochemical alterations associated with mitochondrial DNA (mtDNA) point mutations. Mitochondrial cytopathies caused by mutations of mtDNA are well-known genetic and clinical entities, but the biochemical pathogenic mechanisms are often obscure. Leber's hereditary optic neuropathy (LHON) is due to three main mutations in genes for complex I subunits. Even if the catalytic activity of complex I is maintained except in cells carrying the 3460/ND1 mutation, in all cases there is a change in sensitivity to complex I inhibitors and an impairment of mitochondrial respiration, eliciting the possibility of generation of reactive oxygen species (ROS) by the complex. Neurogenic muscle weakness, Ataxia and Retinitis Pigmentosa (NARP), is due to a mutation in the ATPase-6 gene. In NARP patients ATP synthesis is strongly depressed to an extent proportional to the mutation load; nevertheless, ATP hydrolysis and ATP-driven proton translocation are not affected. It is suggested that the NARP mutation affects the ability of the enzyme to couple proton transport to ATP synthesis. A point mutation in subunit III of cytochrome c oxidase is accompanied by a syndrome resembling MELAS: however, no major biochemical defect is found, if we except an enhanced production of ROS. The mechanism of such enhancement is at present unknown. In this review, we draw attention to a few examples in which the overproduction of ROS might represent a common step in the induction of clinical phenotypes and/or in the progression of several human pathologies associated with mtDNA point mutations.
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PMID:Bioenergetics of mitochondrial diseases associated with mtDNA mutations. 1528 79

Familial hemiplegic migraine (FHM) is an autosomal dominant subtype of migraine with hemiparesis during the aura. In over 50% of cases the causative gene is CACNA1A (FHM1), which in some cases produces a phenotype with cerebellar signs, including ataxia and nystagmus. Recently, mutations in ATP1A2 on chromosome 1q23 encoding a Na+/K+ -ATPase subunit were identified in four families (FHM2). We now describe an FHM2 pedigree with a fifth ATP1A2 mutation coding for a G301R substitution. The phenotype was particularly severe and included hemiplegic migraine, seizure, prolonged coma, elevated temperature, sensory deficit, and transient or permanent cerebellar signs, such as ataxia, nystagmus, and dysarthria. A mild crossed cerebellar diaschisis during an attack further supported the clinical evidence of a cerebellar deficit. This is the first report suggesting cerebellar involvement in FHM2. A possible role for CACNA1A in producing the phenotype in this family was excluded by linkage studies to the FHM1 locus. The study of this family suggests that the absence of cerebellar signs may not be a reliable indicator to clinically differentiate FHM2 from FHM1.
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PMID:A G301R Na+/K+ -ATPase mutation causes familial hemiplegic migraine type 2 with cerebellar signs. 1545 25

Point and deletion mutations and a general depletion of mammalian mitochondrial DNA (mtDNA) give rise to a wide variety of medical syndromes that are refractory to treatment, possibly including aging itself. While gene therapy directed at correcting such deficits in the mitochondrial genome may offer some therapeutic benefits, there are inherent problems associated with a direct approach. These problems are primarily due to the high mitochondrial genome copy number in each cell and the mitochondrial genome being "protected" inside the double-membrane mitochondrial organelle. In an alternative approach there is evidence that genes normally present in the mitochondrial genome can be incorporated into the nuclear genome. To extend such studies, we modified the Chinese Hamster Ovary (CHO) mtDNA-located ATPase6 gene (possessing a mutation which confers oligomycin resistance- oli(r)) by altering the mtDNA code to the universal code (U-code) to permit the correct translation of its mRNA in the cytoplasm. The U-code construct was inserted into the nuclear genome (nucDNA) of a wild type CHO cell. The expressed transgene products enabled the transformed CHO cell lines to grow in up to 1000 ng mL(-1) oligomycin, while untransformed sensitive CHO cells were eliminated in 1 ng mL(-1) oligomycin. This approach, termed allotopic expression, provides a model that may make possible the transfer of all 13 mtDNA mammalian protein-encoding genes to the nucDNA, for treatments of mtDNA disorders. The CHO mtATPase6 protein is 85% identical to both the mouse and human mtATPase6 protein; these proteins are highly conserved in the region of the oligomycin resistance mutation. They are also well conserved in the regions of the oligomycin resistance mutation of the mouse, and in the region of a mutation found in Leigh's syndrome (T8993G), also called NARP (neurogenic weakness, ataxia, retinitis pigmentosum). It is likely that the CHO oli(r) mtATPase6 Ucode construct could impart oligomycin-resistance in human and mouse cells, as well as function in place of the mutant ATPase subunit in a NARP cell line. Preliminary experiments on human cybrids homoplasmic for the NARP mutation (kindly supplied by D.C. Wallace), transformed with our construct, display an increased oligomycin resistance that supports these suppositions.
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PMID:Stable transformation of CHO Cells and human NARP cybrids confers oligomycin resistance (oli(r)) following transfer of a mitochondrial DNA-encoded oli(r) ATPase6 gene to the nuclear genome: a model system for mtDNA gene therapy. 1579 71

Mutations in the ATP6 gene of mtDNA (mitochondrial DNA) have been shown to cause several different neurological disorders. The product of this gene is ATPase 6, an essential component of the F1F0-ATPase. In the present study we show that the function of the F1F0-ATPase is impaired in lymphocytes from ten individuals harbouring the mtDNA T8993G point mutation associated with NARP (neuropathy, ataxia and retinitis pigmentosa) and Leigh syndrome. We show that the impaired function of both the ATP synthase and the proton transport activity of the enzyme correlates with the amount of the mtDNA that is mutated, ranging from 13-94%. The fluorescent dye RH-123 (Rhodamine-123) was used as a probe to determine whether or not passive proton flux (i.e. from the intermembrane space to the matrix) is affected by the mutation. Under state 3 respiratory conditions, a slight difference in RH-123 fluorescence quenching kinetics was observed between mutant and control mitochondria that suggests a marginally lower F0 proton flux capacity in cells from patients. Moreover, independent of the cellular mutant load the specific inhibitor oligomycin induced a marked enhancement of the RH-123 quenching rate, which is associated with a block in proton conductivity through F0 [Linnett and Beechey (1979) Inhibitors of the ATP synthethase system. Methods Enzymol. 55, 472-518]. Overall, the results rule out the previously proposed proton block as the basis of the pathogenicity of the mtDNA T8993G mutation. Since the ATP synthesis rate was decreased by 70% in NARP patients compared with controls, we suggest that the T8993G mutation affects the coupling between proton translocation through F0 and ATP synthesis on F1. We discuss our findings in view of the current knowledge regarding the rotary mechanism of catalysis of the enzyme.
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PMID:Inefficient coupling between proton transport and ATP synthesis may be the pathogenic mechanism for NARP and Leigh syndrome resulting from the T8993G mutation in mtDNA. 1640 16

Myoclonus epilepsy with ragged red fibers (MERRF) is one of the major mitochondrial encephalomyopathies. Its main clinical features are myoclonus epilepsy, ataxia, and myopathy with ragged red fibers. Whereas there is a close correlation between MERRF syndrome and the A8344G mutation of mitochondrial DNA, the reverse is not true. In fact, this mutation is also responsible for various other syndromes, such as Leigh syndrome, spinocerebellar degeneration, atypical Charcot-Marie-Tooth disease, and multiple truncal lipomas. We describe a child with the A8344G mutation of mitochondrial DNA and an unusual clinical, neuroradiologic, and biochemical phenotype, characterized by early-onset, nonprogressive cerebellar ataxia, and subclinical myoclonias in association with bilateral putaminal necrosis on magnetic resonance imaging and a reduction in complex V activity. Our case confirms the existence of a relationship between alteration in adenosine triphosphatase activity and basal ganglia involvement. We recommend that the possibility of a mitochondrial pathology should always be taken into consideration in the presence of bilateral symmetric lesions of the basal ganglia, even when the typical clinical picture is lacking. (J Child Neurol 2006;21:79-82).
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PMID:Bilateral putaminal necrosis associated with the mitochondrial DNA A8344G myoclonus epilepsy with ragged red fibers (MERRF) mutation: an infantile case. 1655 60

Misfolded proteins of the endoplasmic reticulum undergo retrotranslocation to enter the cytosol where they are degraded by the proteasome. Retrotranslocation of many substrates requires an ATPase complex consisting of the p97 ATPase and a dimeric cofactor, Ufd1-Npl4. We report that efficient elimination of misfolded ER proteins also involves ataxin-3 (atx3), a p97-associated deubiquitinating enzyme mutated in type-3 spinocerebellar ataxia. Overexpression of an atx3 mutant defective in deubiquitination inhibits the degradation of misfolded ER proteins and triggers ER stress. Misfolded polypeptides stabilized by mutant atx3 are accumulated in part as polyubiquitinated form, suggesting an involvement of its deubiquitinating activity in ER-associated protein degradation regulation. We demonstrate that atx3 transiently associates with the ER membrane via p97 and the recently identified Derlin-VIMP complex, and its release from the membrane appears to be governed by both the p97 ATPase cycle and its own deubiquitinating activity. We present evidence that atx3 may promote p97-associated deubiquitination to facilitate the transfer of polypeptides from p97 to the proteasome.
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PMID:Regulation of retrotranslocation by p97-associated deubiquitinating enzyme ataxin-3. 1700 Aug 76

A T-to-C missense mutation at nucleotide position 9,185 in the protein-coding ATP6 gene of the mitochondrial genome was present at high heteroplasmy in members of a Canadian family with Leigh syndrome with predominant ataxia and peripheral neuropathy. This mutation results in the substitution of a proline residue for an evolutionary-conserved leucine at position of amino acid 220 near the carboxyl terminus of the mitochondrial protein. The index patient and brother, who had an identical clinical presentation, had >90% mutant mtDNA in cultured skin fibroblasts, lymphocytes, and whole blood. Their mother and a maternal uncle, symptomatic with a peripheral neuropathy alone, had 86% and 85% heteroplasmy, respectively. Symptomatic maternal cousins with early onset revealed 90% and 91% mutant mtDNA in all tissues analyzed. Studies of lymphoblasts from the asymptomatic maternal grandmother and eldest brother of the proband were heteroplasmic for mutant mtDNA with 56% and 17%, respectively. Biochemical analysis demonstrated normal respiratory chain enzyme activity in muscle and fibroblasts, normal ATP synthesis, but reduced oligomycin-sensitive H(+)ATPase in cultured lymphoblast mitochondria. We propose that the 9,185T > C mtDNA mutation is pathogenic even though the initial phenotype is mild and the biochemical phenotype not easily detectable.
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PMID:Late onset Leigh syndrome and ataxia due to a T to C mutation at bp 9,185 of mitochondrial DNA. 1735 90

Various inherited neurodegenerative diseases result from an increase in the number of glutamine codon repeats within the open reading frame of the responsible gene. Insoluble aggregates of polyglutamine-containing proteins in neurons, which are usually conjugated with ubiquitin, are a hallmark of the polyglutamine diseases. However, the molecular mechanism underlying the ubiquitylation and aggregate formation of polyglutamine-containing proteins has been largely unclear. Here we report the identification of critical factors involved in the ubiquitylation process as well as turnover of MJD1/Ataxin-3 protein, in which the abnormal expansion of a polyglutamine tract is responsible for spinocerebellar ataxia type 3 (SCA3, also known as Machado-Joseph disease). E4 B/UFD2a (a ubiquitin chain assembly factor) and VCP (a AAA-family ATPase) were co-purified with the activity polyubiquitylating Ataxin-3. E4B mediated polyubiquitylation of MJD1/Ataxin-3, and VCP interacted with both E 4B and MJD1 Ataxin-3. In a Drosophila model of SCA3, expression of E4B suppressed the neurodegeneration induced by an Ataxin-3 mutant. These observations suggest that E4 is a rate-limiting factor in the degradation of proteins with expanded polyglutamine tracts.
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PMID:[Neurodegenerative diseases regulated by ubiquitin-proteasome system]. 1743 11


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