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:5.99.1.2 (topoisomerase)
9,166 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The eukaryotic family of type I DNA topoisomerases includes the nuclear type I enzymes and the enzymes encoded by vaccinia and other poxviruses. The small size of the vaccinia topoisomerase (314 amino acids as compared to 765-972 amino acids for the cellular enzymes) makes it likely that this protein constitutes the minimal functional unit of a eukaryotic type I enzyme and provides an opportunity for a comprehensive structure-function analysis through mutagenesis. Two protein subregions were targeted for mutagenesis in the present study. The role of the Ser-Lys-X-X-Tyr sequence present at the active site of all family members was examined by replacing each conserved residue with alanine. Alanine substitution at the active site Tyr abrogated topoisomerase activity. In contrast, mutations at Ser-270 and Lys-271 had no effect on enzyme activity. The region of the vaccinia topoisomerase from amino acids 126-142 (MFFIRFGKMKYLKENET) is highly conserved and contains a residue, Gly-132, shown previously to be essential. Twenty-nine different mutations were generated in this region, with at least one substitution at each position. Point mutations were identified at three positions, Arg-130, Tyr-136, and Leu-137, which either abrogated or severely reduced DNA relaxation. The effects on activity could be attributed to a defect in formation of the covalent intermediate. Alterations of 13 other amino acids, including conserved residues, had little or no effect on topoisomerase activity.
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PMID:Mutational analysis of vaccinia DNA topoisomerase defines amino acid residues essential for covalent catalysis. 796 97

The frequency and functional properties of anti-topoisomerase-1 antibodies (ATA) have been studied in 58 systemic sclerosis (SSc) probands, 218 first degree relatives and 22 spouses. The dependence of ATA on the presence of certain HLA-DRB1 and HLA-DQB1 alleles was examined. ATA were detected by immunodiffusion, by absorption or inhibition of topoisomerase-1 enzymic activity, by immunoblotting of a K562 cell extract and by immunoprecipitation of 35S radiolabelled cell lines. HLA class II typing for HLA-DRB1 and HLA-DQB1 was performed by oligonucleotide typing in 49 families. Six probands and two relatives had ATA. The relatives with ATA had SSc. All eight individuals with ATA directly inhibited topoisomerase-1 function. Four of the eight had limited skin disease and four had diffuse skin involvement. The seven who were genotyped had at least one HLA-DQB1 allele encoding for tyrosine at position 30 of the first domain. Therefore, ATA are not widely dispersed within families, but rather are only present in those with SSc, and certain genetic requirements appear necessary for their generation.
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PMID:HLA-DQB1 associations with anti-topoisomerase-1 antibodies in patients with systemic sclerosis and their first degree relatives. United Kingdom Systemic Sclerosis Study Group. 798 Aug 52

A 4.6 kb Staphylococcus aureus DNA fragment containing DNA gyrase-like genes (grlA and grlB) was cloned and sequenced. The proteins GrlA and GrlB exhibit more than 30% identity with E. coli DNA topoisomerase IV subunits and with the gyrase subunits from S. aureus and Escherichia coli. The combined E. coli cell extracts of GrlA and GrlB overproducing strains catalysed ATP-dependent relaxation and decatenation specific to DNA topoisomerase IV. The temperature-sensitive phenotype of Salmonella typhimurium parC and parE mutants was complemented by the S. aureus grlA and grlB genes, when the two genes were co-expressed. These results show that GrlA and GrlB are the subunits of S. aureus DNA topoisomerase IV. The GyrA subunit of DNA gyrase has been previously defined as a primary target of quinolones based on genetic and biochemical experiments essentially carried out in E. coli. Single-point mutations occurring in the 'quinolone resistance-determining region' (QRDR) of GyrA were found in bacteria exhibiting quinolone resistance, the most common mutation being a substitution of Ser-83 on the E. coli GyrA sequence. We analysed eight S. aureus fluoroquinolone-resistant clinical isolates and observed that mutations in the QRDR of GyrA are not present in the low-quinolone-resistant isolates. In contrast, Ser-80 of GrlA, which corresponds to Ser-83 of E. coli GyrA, is substituted to Phe or Tyr in both high- and low-quinolone-resistant isolates. We propose that DNA topoisomerase IV is a primary target of fluoroquinolones in S. aureus.
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PMID:Cloning and primary structure of Staphylococcus aureus DNA topoisomerase IV: a primary target of fluoroquinolones. 799 76

In this report we examine biochemical and genetic alterations in DNA topoisomerase II (topoisomerase II) in K562 cells selected for resistance in the presence of etoposide (VP-16). Previously, we have demonstrated that the 30-fold VP-16-resistant K/VP.5 cell line exhibits decreased stability of drug-induced topoisomerase II/DNA covalent complexes, requires greater ATP concentrations to stimulate VP-16-induced topoisomerase II/DNA complex formation, and contains reduced mRNA and protein levels of the M(r) 170,000 isoform of topoisomerase II, compared with parental K562 cells. K/VP.5 cells grown in the absence of VP-16 for 2 years maintained resistance to VP-16, decreased levels of topoisomerase II, and attenuated ATP stimulation of VP-16-induced topoisomerase II/DNA binding, compared with K562 cells. Sequencing of cDNA coding for two consensus ATP binding sites and the active site tyrosine in the K/VP.5 topoisomerase II gene indicated that no mutations were present in these domains. In addition, single-strand conformational polymorphism analysis of restriction fragments encompassing the entire topoisomerase II cDNA revealed no evidence of mutations in the gene for this enzyme in K/VP.5 cells. Nuclear extracts from K562 (but not K/VP.5) cells contained a heat-labile factor that potentiated VP-16-induced topoisomerase II/DNA covalent complex formation in isolated nuclei from K/VP.5 cells. Immunoprecipitated topoisomerase II from K/VP.5 cells was 2.5-fold less phosphorylated, compared with enzyme from K562 cells. Collectively, our data suggest that acquired VP-16 resistance is mediated, at least in part, by altered levels or activity of a kinase that regulates topoisomerase II phosphorylation and hence drug-induced topoisomerase II/DNA covalent complex formation and stability.
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PMID:Reduced phosphorylation of topoisomerase II in etoposide-resistant human leukemia K562 cells. 805 57

Inhibitors of protein tyrosine kinases (PTK) and DNA topoisomerases are potential antitumour agents. Drugs which bind to the ATP site of PTK, such as genistein, are common inhibitors to both types of enzymes. Eleven erbstatin and tyrphostin derivatives, which inhibit epidermal growth factor receptor PTK activity by competing with both the peptide substrate and ATP were tested for their capacity to inhibit DNA topoisomerases I and II. Erbstatin, two synthetic derivatives with a modified side chain and the tyrphostin AG 786 inhibited both topoisomerases in the same range of concentrations (20-50 microM). The tyrphostin AG 213 inhibited only topoisomerase II. In this series, absence of PTK inhibitory effect was correlated with the absence of DNA topoisomerase inhibition, while the detection of PTK inhibition may or may not be associated with DNA topoisomerase inhibition. In contrast to genistein, none of these molecules induced the stabilization of the topoisomerase-DNA cleavable complex, either in vitro or in vivo. Alcaline elution analysis revealed that erbstatin did not induce the formation of protein associated DNA strand breaks. However, an extensive degradation of the cellular DNA was observed which was shown to result from an internucleosomal fragmentation. Furthermore, typical morphological modifications associated with apoptosis were observed in the erbstatin treated cells by electron microscopy. These data indicate that erbstatin induces an apoptotic cell death.
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PMID:Inhibition of DNA topoisomerases I and II and induction of apoptosis by erbstatin and tyrphostin derivatives. 806 42

Mucosal healing requires enterocyte migration (restitution) supplemented by proliferation. Proliferation and migration may be studied independently by thymidine uptake and proliferation-blocked cell migration using human Caco-2 enterocyte monolayers in culture. Since epidermal growth factor (EGF) promotes mucosal healing and the EGF receptor is a tyrosine kinase, we hypothesized that tyrosine kinases might therefore modulate enterocyte migration and proliferation. The tyrosine kinase inhibitors genistein and 2,5-dihydroxymethylcinnamate, which block kinase ATP-binding and substrate-binding sites, respectively, were studied alone and with EGF. Proliferation was blocked with mitomycin. Although each inhibitor decreased basal and EGF-stimulated monolayer expansion when cell proliferation occurred, neither genistein nor 2,5-dihydroxymethylcinnamate decreased migration when proliferation was blocked. However, each inhibitor prevented EGF stimulation of proliferation-blocked migration and thymidine uptake. More substantial inhibition of basal proliferation by genistein correlated with increased protein-linked DNA breaks, which may reflect nonspecific inhibition of DNA topoisomerase activity by genistein. The more specific 2,5-dihydroxymethylcinnamate blocked changes in the alpha 2 integrin subunit organization which may modulate EGF-stimulated migration. Antiproliferative effects of tyrosine kinase inhibitors decrease basal monolayer expansion but true basal enterocyte migration appears independent of tyrosine kinase regulation. However, a specific tyrosine kinase-dependent modulation of cell-matrix interaction inhibits EGF-stimulated migration.
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PMID:Effect of tyrosine kinase inhibition on basal and epidermal growth factor-stimulated human Caco-2 enterocyte sheet migration and proliferation. 807 87

A 69-kDa protein with topoisomerase I activity has been homogeneously purified from the chloroplasts of pea leaves. The topoisomerase properties are detected in crude lysate of pea chloroplasts using the technique of transferring 32P radioactivity from the 32P-labeled DNA to the protein. The purified enzyme relaxes both positive and negative supercoils in topological steps of unity without requiring magnesium ions. The enzyme is sensitive to topoisomerase I-specific inhibitors like camptothecin and berenil, and unaffected by reagents like novobiocin and doxorubicin at the topoisomerase II-inhibitory dosage. In the presence of the enzyme, supercoiled DNA is nicked, and the 3'-phosphoryl end of the nick becomes covalently linked with the enzyme. A tyrosine residue of the enzyme is responsible for the covalent linkage. Rabbit antiserum raised against the 16-mer peptide spanning the active residues of human topoisomerase I recognizes the 69-kDa protein within the crude lysate of pea chloroplasts as does the antiserum to the purified 69-kDa protein. From the enzymatic characteristics, the protein has been classified as a eukaryotic type I topoisomerase.
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PMID:Purification and characterization of a eukaryotic type 1 topoisomerase from pea chloroplast. 810 24

The virulence plasmid pXO1 is responsible for toxin production in Bacillus anthracis. A DNA fragment from pXO1 was isolated and was shown, by sequence analysis, to contain part of a type 1 DNA topoisomerase gene. Attempts to clone the entire wild-type gene, designated topX, in Escherichia coli, were unsuccessful. In order to obtain the complete gene, it was first insertionally inactivated and then cloned in the mutated form. The deduced amino acid sequence of Topo X1 shows similarities to that of the two E. coli type 1 DNA topoisomerases. The N-terminal two-thirds of the putative B. anthracis protein exhibits strongest sequence similarity to topoisomerase III, whereas the C-terminal portion contains cysteine residues that could form three zinc-binding domains, as they do in topoisomerase I. The suggested active-site tyrosine is conserved in all three proteins. The regulation of expression from the topX promoter is modified by addition of a gyrase inhibiting antibiotic. The Topo X1 protein is likely to be involved in the stability of pXO1.
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PMID:Bacillus anthracis pXO1 virulence plasmid encodes a type 1 DNA topoisomerase. 815 71

Experimental evidence suggests that hematopoietic growth factors promote cell survival by suppressing apoptosis or programmed cell death. Since interleukin 3 (IL-3) and granulocyte-macrophage colony stimulating factor (GM-CSF) induce tyrosine phosphorylation of a common set of proteins in the factor-dependent cell line M07e, we have investigated whether growth-factor-induced tyrosine phosphorylation is involved in the promotion of cell survival and suppression of apoptosis. Experiments were carried out with the leukemic cell lines HL-60 and M07e and the tyrosine kinase inhibitors genistein and tyrphostin AG82. Both the tyrosine kinase inhibitors induced apoptosis of HL-60 and M07e cells. This was indicated by the appearance of DNA degradation and morphologic evidence of nuclear condensation and fragmentation. It was also confirmed by flow cytometry of DNA, which showed apoptotic cells as a fraction of cells characterized by a diminished DNA stainability, represented on the DNA frequency histograms as a distinct peak below the G0/G1 population. Kinase inhibitors also reduced the fraction of cells in the S phase of the cell cycle. That tyrphostin specifically inhibited tyrosine kinases was further suggested by the prevention of its effects by the tyrosine phosphatase inhibitor sodium orthovanadate (vanadate), at least during the first 18-24 h of treatment. The incomplete prevention of genistein effects by vanadate suggests that genistein is a less specific inhibitor of tyrosine kinases than tyrphostin, and may also act as an inhibitor of topoisomerase II. Vanadate also prevented apoptosis and reduction of the S phase in M07e cells cultured for 24 h in the absence of growth factors. These results suggest that tyrosine phosphorylation is an essential step in IL-3 and GM-CSF signal transduction. Since in our experimental model the effects of tyrosine kinase inhibition and growth factor deprivation could be reversed by concomitant inhibition of tyrosine phosphatases, it is suggested that a balance between tyrosine kinases and tyrosine phosphatases establishes whether a cell will survive or undergo apoptosis.
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PMID:Inhibitors of tyrosine phosphorylation induce apoptosis in human leukemic cell lines. 825 1

The TraI protein of plasmid RP4 (IncP alpha) catalyzes a site- and strand-specific cleaving-joining reaction on form I or single-stranded DNA. Thus, TraI is one of the key components involved in the initiation and termination of horizontal DNA transfer by bacterial conjugation. Amino acid sequence comparison revealed three motifs in the TraI sequence conserved in relaxases from different origins. Site-directed mutagenesis of the traI structural gene and application of purified mutant TraI proteins for in vitro assays served to evaluate the functional importance of conserved amino acid residues. Two regions of TraI designated as motifs I and III are involved in catalyzing the cleaving-joining reaction. Motif I carries the tyrosine residue (Tyr-22), which covalently attaches TraI in a transesterification reaction to the 5' terminus of the cleaved DNA. Motif III contains one histidine residue (His-116) essential for relaxase activity and therefore proposed to activate the aromatic hydroxyl group of tyrosine 22 by proton abstraction. Exchange of a serine residue (Ser-74), located in motif II, against alanine prevents formation of stable relaxosomes but strongly enhances topoisomerase activity of the combination TraI/TraJ on form I oriT DNA. Motif II therefore might represent the DNA recognition domain of TraI. Our studies allowed us to establish a model of the interplay of three motifs located in the N-terminal region (amino acid positions 19-124) of TraI.
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PMID:Concerted action of three distinct domains in the DNA cleaving-joining reaction catalyzed by relaxase (TraI) of conjugative plasmid RP4. 830 Jun 11


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