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: UMLS:C0029089 (ophthalmoplegia)
3,338 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) syndrome is a rare, multisystem disorder characterized clinically by ptosis, progressive external ophthalmoplegia, gastrointestinal dysmotility, leukoencephalopathy, thin body habitus, and myopathy. Laboratory studies reveal defects of oxidative-phosphorylation and multiple mtDNA deletions frequently in skeletal muscle. We studied four ethnically distinct families affected with this apparently autosomal recessive disorder. Probands from each family were shown, by Southern blot, to have multiple mtDNA deletions in skeletal muscle. We mapped the MNGIE locus to 22q13.32-qter, distal to D22S1161, with a maximum two-point LOD score of 6.80 at locus D22S526. Cosegregation of MNGIE with a single chromosomal region in families with diverse ethnic backgrounds suggests that we have mapped an important locus for this disorder. We found no evidence to implicate three candidate genes in this region, by using direct sequence analysis for DNA helicase II and by assaying enzyme activities for arylsulfatase A and carnitine palmitoyltransferase.
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PMID:Mitochondrial neurogastrointestinal encephalomyopathy syndrome maps to chromosome 22q13.32-qter. 968 10

Mutations in TWINKLE cause autosomal dominant progressive external ophthalmoplegia, a human disorder associated with multiple deletions in the mitochondrial DNA. TWINKLE displays primary sequence similarity to the phage T7 gene 4 primase-helicase, but no specific enzyme activity has been assigned to the protein. We have purified recombinant TWINKLE to near homogeneity and demonstrate here that TWINKLE is a DNA helicase with 5' to 3' directionality and distinct substrate requirements. The protein needs a stretch of 10 nucleotides of single-stranded DNA on the 5'-side of the duplex to unwind duplex DNA. In addition, helicase activity is not observed unless a short single-stranded 3'-tail is present. The helicase activity has an absolute requirement for hydrolysis of a nucleoside 5'-triphosphate, with UTP being the optimal substrate. DNA unwinding by TWINKLE is specifically stimulated by the mitochondrial single-stranded DNA-binding protein. Our enzymatic characterization strongly supports the notion that TWINKLE is the helicase at the mitochondrial DNA replication fork and provides evidence for a close relationship of the DNA replication machinery in bacteriophages and mammalian mitochondria.
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PMID:TWINKLE Has 5' -> 3' DNA helicase activity and is specifically stimulated by mitochondrial single-stranded DNA-binding protein. 1297 72

We here reconstitute a minimal mammalian mitochondrial DNA (mtDNA) replisome in vitro. The mtDNA polymerase (POLgamma) cannot use double-stranded DNA (dsDNA) as template for DNA synthesis. Similarly, the TWINKLE DNA helicase is unable to unwind longer stretches of dsDNA. In combination, POLgamma and TWINKLE form a processive replication machinery, which can use dsDNA as template to synthesize single-stranded DNA (ssDNA) molecules of about 2 kb. The addition of the mitochondrial ssDNA-binding protein stimulates the reaction further, generating DNA products of about 16 kb, the size of the mammalian mtDNA molecule. The observed DNA synthesis rate is 180 base pairs (bp)/min, corresponding closely to the previously calculated value of 270 bp/min for in vivo DNA replication. Our findings provide the first biochemical evidence that TWINKLE is the helicase at the mitochondrial DNA replication fork. Furthermore, mutations in TWINKLE and POLgamma cause autosomal dominant progressive external ophthalmoplegia (adPEO), a disorder associated with deletions in mitochondrial DNA. The functional interactions between TWINKLE and POLgamma thus explain why mutations in these two proteins cause an identical syndrome.
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PMID:Reconstitution of a minimal mtDNA replisome in vitro. 1516 97

Mechanisms of mitochondrial DNA (mtDNA) maintenance have recently gained wide interest owing to their role in inherited diseases as well as in aging. Twinkle is a new mitochondrial 5'-3' DNA helicase, defects of which we have previously shown to underlie a mitochondrial disease, progressive external ophthalmoplegia with multiple mtDNA deletions. Mouse Twinkle is highly similar to the human counterpart, suggesting conserved function. Here, we have characterized the mouse Twinkle gene and expression profile and report that the expression patterns are not conserved between human and mouse, but are synchronized with the adjacent gene MrpL43, suggesting a shared promoter. To elucidate the in vivo role of Twinkle in mtDNA maintenance, we generated two transgenic mouse lines overexpressing wild-type Twinkle. We could demonstrate for the first time that increased expression of Twinkle in muscle and heart increases mtDNA copy number up to 3-fold higher than controls, more than any other factor reported to date. Additionally, we utilized cultured human cells and observed that reduced expression of Twinkle by RNA interference mediated a rapid drop in mtDNA copy number, further supporting the in vivo results. These data demonstrate that Twinkle helicase is essential for mtDNA maintenance, and that it may be a key regulator of mtDNA copy number in mammals.
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PMID:Twinkle helicase is essential for mtDNA maintenance and regulates mtDNA copy number. 1550 89

We report the cloning and molecular analysis of Drosophila mitochondrial DNA helicase (d-mtDNA helicase) homologous to human TWINKLE, which encodes one of the genes responsible for autosomal dominant progressive external ophthalmoplegia. An RNA interference construct was designed that reduces expression of d-mtDNA helicase to an undetectable level in Schneider cells. RNA interference knockdown of d-mtDNA helicase decreases the copy number of mitochondrial DNA (mtDNA) approximately 5-fold. In a corollary manner, overexpression of d-mtDNA helicase increases mtDNA levels 1.4-fold. Overexpression of helicase active site mutants K388A and D483A results in a severe depletion of mtDNA and a dominant negative lethal phenotype. Overexpression of mutants analogous to human autosomal dominant progressive external ophthalmoplegia mutations shows differential effects. Overexpression of I334T and A442P mutants yields a dominant negative effect as for the active site mutants. In contrast, overexpression of A326T, R341Q, and W441C mutants results in increased mtDNA copy number, as observed with wild-type overexpression. Our dominant negative analysis of d-mtDNA helicase in cultured cells provides a tractable model for understanding human autosomal dominant progressive external ophthalmoplegia mutations.
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PMID:Differential phenotypes of active site and human autosomal dominant progressive external ophthalmoplegia mutations in Drosophila mitochondrial DNA helicase expressed in Schneider cells. 1727 69

TWINKLE is the helicase at the mitochondrial DNA (mtDNA) replication fork in mammalian cells. Mutations in the PEO1 gene, which encodes TWINKLE, cause autosomal dominant progressive external ophthalmoplegia (AdPEO), a disorder associated with deletions in mtDNA. Here, we characterized seven different AdPEO-causing mutations in the linker region of TWINKLE and we identified distinct molecular phenotypes. For some mutations, protein hexamerization and DNA helicase activity are completely abolished whereas others display more subtle effects. To better understand these distinct phenotypes, we constructed a molecular model of TWINKLE based on the three-dimensional structure of the bacteriophage T7 gene 4 protein. The structural model explains the molecular phenotypes and also predicts the functional consequences of other AdPEO-causing mutations. Our findings provide a molecular platform for further studies in cell- and animal-based model systems and demonstrate that knowledge of the bacteriophage T7 DNA replication machinery may be key to understanding the molecular and phenotypic consequences of mutations in the mtDNA replication apparatus.
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PMID:Structure-function defects of the TWINKLE linker region in progressive external ophthalmoplegia. 1827 90

The mitochondrial replicative DNA helicase is an essential cellular protein that shows high similarity with the bifunctional primase-helicase of bacteriophage T7, the gene 4 protein (T7 gp4). The N-terminal primase domain of T7 gp4 comprises seven conserved sequence motifs, I, II, III, IV, V, VI, and an RNA polymerase basic domain. The putative primase domain of metazoan mitochondrial DNA helicases has diverged from T7 gp4 and in particular, the primase domain of vertebrates lacks motif I, which comprises a zinc binding domain. Interestingly, motif I is conserved in insect mtDNA helicases. Here, we evaluate the effects of overexpression in Drosophila cell culture of variants carrying mutations in conserved amino acids in the N-terminal region, including the zinc binding domain. Overexpression of alanine substitution mutants of conserved amino acids in motifs I, IV, V and VI and the RNA polymerase basic domain results in increased mtDNA copy number as is observed with overexpression of the wild type enzyme. In contrast, overexpression of three N-terminal mutants W282L, R301Q and P302L that are analogous to human autosomal dominant progressive external ophthalmoplegia mutations results in mitochondrial DNA depletion, and in the case of R301Q, a dominant negative cellular phenotype. Thus whereas our data suggest lack of a DNA primase activity in Drosophila mitochondrial DNA helicase, they show that specific N-terminal amino acid residues that map close to the central linker region likely play a physiological role in the C-terminal helicase function of the protein.
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PMID:Functional importance of the conserved N-terminal domain of the mitochondrial replicative DNA helicase. 1906 59

TWINKLE is a DNA helicase needed for mitochondrial DNA replication. In lower eukaryotes the protein also harbors a primase activity, which is lost from TWINKLE encoded by mammalian cells. Mutations in TWINKLE underlie autosomal dominant progressive external ophthalmoplegia (adPEO), a disorder associated with multiple deletions in the mtDNA. Four different adPEO-causing mutations (W315L, K319T, R334Q, and P335L) are located in the N-terminal domain of TWINKLE. The mutations cause a dramatic decrease in ATPase activity, which is partially overcome in the presence of single-stranded DNA. The mutated proteins have defects in DNA helicase activity and cannot support normal levels of DNA replication. To explain the phenotypes, we use a molecular model of TWINKLE based on sequence similarities with the phage T7 gene 4 protein. The four adPEO-causing mutations are located in a region required to bind single-stranded DNA. These mutations may therefore impair an essential element of the catalytic cycle in hexameric helicases, i.e. the interplay between single-stranded DNA binding and ATP hydrolysis.
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PMID:Structure-function defects of the twinkle amino-terminal region in progressive external ophthalmoplegia. 1908 93

The C10orf2 gene encodes the mitochondrial DNA helicase Twinkle, which is one of the proteins important for mitochondrial DNA maintenance. Dominant mutations cause multiple mitochondrial DNA deletions and progressive external ophthalmoplegia, but recent findings associate recessive mutations with mitochondrial DNA depletion and encephalopathy or hepatoencephalopathy. The latter clinical phenotypes resemble those associated with recessive POLG1 mutations. We have previously described patients with infantile onset spinocerebellar ataxia (MIM271245) caused either by homozygous (Y508C) or compound heterozygous (Y508C and A318T) Twinkle mutations. Our earlier reports focused on the spinocerebellar degeneration, but the 20-year follow-up of 23 patients has shown that refractory status epilepticus, migraine-like headaches and severe psychiatric symptoms are also pathognomonic for the disease. All adolescent patients have experienced phases of severe migraine, and seven patients had antipsychotic medication. Epilepsia partialis continua occurred in 15 patients leading to generalized epileptic statuses in 13 of them. Eight of these patients have died. Valproate treatment was initiated on two patients, but had to be discontinued because of a severe elevation of liver enzymes. The patients recovered, and we have not used valproate in infantile onset spinocerebellar ataxia since. The first status epilepticus manifested between 15 and 34 years of age in the homozygotes, and at 2 and 4 years in the compound heterozygotes. The epileptic statuses lasted from several days to weeks. Focal, stroke-like lesions were seen in magnetic resonance imaging, but in infantile onset spinocerebellar ataxia these lesions showed no predilection. They varied from resolving small cortical to large hemispheric oedematous lesions, which reached from cerebral cortex to basal ganglia and thalamus and caused permanent necrotic damage and brain atrophy. Brain atrophy with focal laminar cortical necrosis and hippocampal damage was confirmed on neuropathological examination. The objective of our study was to describe the development and progression of encephalopathy in infantile onset spinocerebellar ataxia syndrome, and compare the pathognomonic features with those in other mitochondrial encephalopathies.
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PMID:Recessive twinkle mutations cause severe epileptic encephalopathy. 1930 94

Nuclear genes affecting mitochondrial genome stability were screened in an Italian family presenting with autosomal dominant progressive external ophthalmoplegia (adPEO) associated with multiple mitochondrial DNA (mtDNA) deletions. We report on a heterozygous c.907C>T (p.R303W) mutation found in the N-terminal domain of the human mitochondrial DNA helicase, Twinkle protein, in six members of a family, in which two individuals manifested late-onset PEO and morphological and molecular signs of mitochondrial dysfunction along with two carriers who are presently free of disease manifestation. We also investigated if the p.R303W mutation in PEO1 gene affected the relative copy number of mitochondrial DNA genomes.
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PMID:Molecular analysis in a family presenting with a mild form of late-onset autosomal dominant chronic progressive external ophthalmoplegia. 1942 52


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