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

---

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

Biochemical and genetic data on retroviral nucleocapsid (NC) proteins have shown that this viral protein exhibits nucleic acid annealing and strand transfer activities and is required for the formation of infectious viral particles. However, the DNA binding properties of the NC protein of the human T-cell leukemia virus type-I (HTLV-I) has not been extensively studied. In this work we characterize the DNA binding ability of the zinc-bound and zinc-free forms of the p15 NC of HTLV-I. We found that only the zinc-bound form of the p15 NC binds single-stranded and double-stranded DNA fragments, but both forms of the p15 NC protein bind and unwind supercoiled DNA. The unwinding activity of the zinc-bound form was 3-fold higher than that observed with the zinc-free form of the protein. Interestingly, eukaryotic DNA topoisomerase antagonists inhibited this unwinding activity. In addition, we showed the formation of NC protein-DNA cleavable complex, which is the result of a presumably covalent bond formed between the protein and the phosphate moiety of the DNA backbone. Moreover, the presence of the p15 NC in the reverse transcription assay significantly increased the activity of the HTLV-I reverse transcriptase. These results demonstrate new DNA binding properties of the p15 NC protein and shed light on the possibility of a novel physiological function for the HTLV-I NC protein in the viral life cycle.
...
PMID:DNA binding properties of the nucleocapsid protein from human T-cell leukemia virus type-I. 973 5

The higher order of chromatin organization is thought to be determined by the nuclear matrix, a mainly proteinaceous structure that would act as a nucleoskeleton. The matrix is obtained from isolated nuclei by a series of extraction steps involving the use of high salt and nonspecific nucleases, which remove chromatin and other loosely bound components. It is currently under debate whether these structures, isolated in vitro by unphysiological extraction buffers, correspond to a nucleoskeleton existing in vivo. In most cell types investigated, the nuclear matrix does not spontaneously resist these extractions steps; rather, it must be stabilized before the application of extracting agents. In this study nuclei, isolated from K562 human erythroleukemia cells, were stabilized by incubation with different metal ions (Ca2+, Cu2+, Zn2+, Cd2+), and the matrix was obtained by extraction with 2 M NaCl. By means of ultrastructural analysis of the resulting structures, we determined that, except for Ca2+, all the other metals induced a stabilization of the matrix, which retained the inner fibrogranular network and residual nucleoli. The biochemical composition, analyzed by two-dimensional gel electrophoresis separation, exhibited a distinct matrix polypeptide pattern, characteristic of each type of stabilizing ion employed. We also investigated to what extent metal ions could maintain in the final structures the original distribution of three inner matrix components, i.e. NuMA, topoisomerase IIalpha, and RNP. Confocal microscopy analysis showed that only NuMa, and, to a lesser extent, topoisomerase IIalpha, were unaffected by stabilization with divalent ions. On the contrary, the fluorescent RNP patterns detected in the resulting matrices were always disarranged, irrespective of the stabilization procedure. These results indicate that several metal ions are powerful stabilizing agents of the nuclear matrix prepared from K562 erythroleukemia cells and also strengthen the concept that NuMA and topoisomerase IIalpha may act as structural components of the nuclear matrix.
...
PMID:Influence of different metal ions on the ultrastructure, biochemical properties, and protein localization of the K562 cell nuclear matrix. 1032 34

Dexrazoxane is a bidentate chelator of divalent cations. Pretreatment with short infusions of dexrazoxane prior to bolus doxorubicin has been shown to lessen the incidence and severity of anthracycline-associated cardiac toxicity. However, because of rapid, diffusion-mediated cellular uptake and the short plasma half-life of dexrazoxane, combined with prolonged cellular retention of doxorubicin, dexrazoxane may be more effective when administered as a continuous infusion. Thus, a Phase I pharmacokinetic trial of a 96-h infusion of dexrazoxane was performed. Dexrazoxane doses were escalated in cohorts of 3 to 6 patients per dose level. All patients received granulocyte-colony stimulating factor at a dose of 5 microg/kg/day starting 24 h after completion of the dexrazoxane infusion. Plasma samples were collected and analyzed for dexrazoxane by high-performance liquid chromatography. Urine collections were performed at baseline and during the infusion to determine the renal clearance of dexrazoxane and the excretion rate of divalent cations. Twenty-two patients were enrolled at doses ranging from 125 to 250 mg/m(2)/day. Grade 3 and 4 toxicities included grade 4 thrombocytopenia in 2 patients treated at 250 mg/m(2)/day, grade 3 thrombocytopenia and grade 4 nausea and vomiting in 1 patient treated at 221 mg/m(2)/day, grade 4 diarrhea and grade 3 nausea and vomiting in 1 patient treated at 221 mg/m(2)/day, and grade 3 hypertension in 1 patient treated at 166.25 mg/m(2)/day. Steady-state dexrazoxane levels ranged from 496 microg/l (2.2 microM) to 1639 microg/l (7.4 microM). Dexrazoxane plasma CL(ss) and elimination t(1/2) were 7.2 +/- 1.6 l/h/m(2) and 2.0 +/- 0.8 h, respectively. The mean percentage of administered dexrazoxane recovered in the urine at steady state was 30% (range, 10-66%). Urinary iron and zinc excretion during the dexrazoxane infusion increased in 12 of 18 and 19 of 19 patients by a median of 3.7- and 2.4-fold, respectively. These results suggest that dexrazoxane as a 96-h infusion can be safely administered with granulocyte-colony stimulating factor at doses that achieve plasma levels that have been demonstrated previously to inhibit topoisomerase II activity and to induce apoptosis in vitro. Additional studies will be required to determine whether the combination of continuous infusions of dexrazoxane and doxorubicin would provide enhanced cardioprotection compared with the currently recommended bolus or short infusion schedules.
...
PMID:Phase I trial of 96-hour continuous infusion of dexrazoxane in patients with advanced malignancies. 1141 Apr 92

Topoisomerases, by controlling DNA supercoiling state, are key enzymes for adaptation to high temperatures in thermophilic organisms. We focus here on the topoisomerase I from the hyperthermophilic bacterium Thermotoga maritima (optimal growth temperature, 80 degrees C). To determine the properties of the enzyme compared with those of its mesophilic homologs, we overexpressed T. maritima topoisomerase I in Escherichia coli and purified it to near homogeneity. We show that T. maritima topoisomerase I exhibits a very high DNA relaxing activity. Mapping of the cleavage sites on a variety of single-stranded oligonucleotides indicates a strong preference for a cytosine at position -4 of the cleavage, a property shared by E. coli topoisomerase I and archaeal reverse gyrases. As expected, the mutation of the putative active site Tyr 288 to Phe led to a totally inactive protein. To investigate the role of the unique zinc motif (Cys-X-Cys-X(16)-Cys-X-Cys) present in T. maritima topoisomerase I, experiments have been performed with the protein mutated on the tetracysteine motif. Strikingly, the results show that zinc binding is not required for DNA relaxation activity, contrary to the E. coli enzyme. Furthermore, neither thermostability nor cleavage specificity is altered in this mutant. This finding opens the question of the role of the zinc-binding motif in T. maritima topoisomerase I and suggests that this hyperthermophilic topoisomerase possesses a different mechanism from its mesophilic homolog.
...
PMID:Hyperthermophilic topoisomerase I from Thermotoga maritima. A very efficient enzyme that functions independently of zinc binding. 1157 8

interaction of 7-amino-2-(6'-carboxy-2'-pyridyl)-6-methoxy-5,8-quinolinedione, an ABC ring analogue of the antitumour antibiotic streptonigrin, with zinc(II), oligonucleotides and DNA in the presence of zinc(II), and on the relaxation of DNA by topoisomerase II, has been studied. This ligand contains the key functional groups present in streptonigrin required for biological activity, but lacks the phenolic ring D which confers optical activity on streptonigrin. Variable temperature NMR experiments showed that in the presence of zinc(II) triflate, the methyl ester of the ligand forms a mixture of 1:1 and 1:2 metal:ligand bipyridyl complexes, whose relative stabilities are temperature dependent. Titrations of the water-soluble ligand with zinc(II) nitrate at room temperature showed that the predominant species present in aqueous solution at physiological pH is the 1:1 bipyridyl complex. The interaction of the ligand with the hexanucleotides d(GCATGC)2 and d(ATGCAT)2 was studied by 1H- and 31P-NMR spectroscopy. In the presence of 1 equiv of zinc(II) nitrate and 1 equiv of the ligand, small changes in chemical shifts of the proton resonances associated with the purine resonances were detected consistent with a weak interaction of the zinc(II) complex of the ligand with the oligonucleotides, possibly via a groove binding mechanism. UV-VIS titrations showed a weak interaction of the ligand with calf thymus DNA and poly(dG-dC)2 in the presence of zinc(II) but negligible interaction with poly(dA-dT)2. Gel electrophoresis experiments showed that, in contrast to streptonigrin, the ligand did not inhibit the relaxation of plasmid DNA by human topoisomerase II. These results show that the interaction of the ABC ligand with zinc(II), oligonucleotides, DNA and topoisomerase II is different to streptonigrin and hence the design of biologically active ABC ring analogues of streptongrin that operate via different mechanisms should be possible.
...
PMID:The role of ring D in the antitumour antibiotic streptonigrin: metal complexation, DNA binding and topoisomerase inhibition by ABC ring analogues of streptonigrin. 1196 12

Escherichia coli DNA topoisomerase I (encoded by the topA gene) is important for maintaining steady-state DNA supercoiling and has been shown to influence vital cellular processes including transcription. Topoisomerase I activity is also needed to remove hypernegative supercoiling generated on the DNA template by the progressing RNA polymerase complex during transcription elongation. The accumulation of hypernegative supercoiling in the absence of topoisomerase I can lead to R-loop formation by the nascent transcript and template strand, leading to suppression of transcription elongation. Here we show by affinity chromatography and overlay blotting that E. coli DNA topoisomerase I interacts directly with the RNA polymerase complex. The protein-protein interaction involves the beta' subunit of RNA polymerase and the C-terminal domains of E. coli DNA topoisomerase I, which are homologous to the zinc ribbon domains in a number of transcription factors. This direct interaction can bring the topoisomerase I relaxing activity to the site of transcription where its activity is needed. The zinc ribbon C-terminal domains of other type IA topoisomerases, including mammalian topoisomerase III, may also help link the enzyme activities to their physiological functions, potentially including replication, transcription, recombination, and repair.
...
PMID:Direct interaction between Escherichia coli RNA polymerase and the zinc ribbon domains of DNA topoisomerase I. 1278 50

Poly(ADP-ribose) polymerase 1 (PARP-1) is a zinc-finger DNA-binding enzyme that is activated by binding to DNA breaks. Poly(ADP-ribosyl)ation of nuclear proteins by PARP-1 converts DNA damage into intracellular signals that activate either DNA repair by the base-excision pathway or cell death. A family of 18 PARPs has been identified, but only the most abundant, PARP-1 and PARP-2, which are both nuclear enzymes, are activated by DNA damage. PARP inhibitors of ever-increasing potency have been developed in the 40 years since the discovery of PARP-1, both as tools for the investigation of PARP-1 function and as potential modulators of DNA-repair-mediated resistance to cytotoxic therapy. Owing to the high level of homology between the catalytic domains of PARP-1 and PARP-2, the inhibitors probably affect both enzymes. Convincing biochemical evidence, which has been corroborated by genetic manipulation of PARP-1 activity, shows that PARP inhibition is associated with increased sensitivity to DNA-alkylating agents, topoisomerase I poisons and ionising radiation. Novel PARP inhibitors of sufficient potency and suitable pharmacokinetic properties to allow evaluation in animal models have been shown to enhance the antitumour activity of temozolomide (a DNA-methylating agent), topoisomerase poisons and ionising radiation; indeed, the combination with temozolomide resulted in complete tumour regression in two independent studies. The combination of a PARP inhibitor and temozolomide is currently undergoing clinical evaluation for the first time.
...
PMID:PARP inhibitors for cancer therapy. 1583 99

Mycobacterium smegmatis topoisomerase I differs from the typical type IA topoisomerase in many properties. The enzyme recognizes both single and double-stranded DNA with high affinity and makes sequence-specific contacts during DNA relaxation reaction. The enzyme has a conserved N-terminal domain and a highly varied C-terminal domain, which lacks the characteristic zinc binding motifs found in most of the type I eubacterial enzymes. The roles of the individual domains of the enzyme in the topoisomerase I catalyzed reactions were examined by comparing the properties of full-length topoisomerase I with those of truncated polypeptides lacking the conserved N-terminal or the divergent C-terminal region. The N-terminal larger fragment retained the site-specific binding, DNA cleavage and religation properties, hallmark characteristics of the full-length M.smegmatis topoisomerase I. In contrast, the non-conserved C-terminal fragment lacking the typical DNA binding motif, exhibited non-specific DNA binding behaviour. The two polypeptide fragments, on their own do not catalyze DNA relaxation reaction. The relaxation activity is restored when both the fragments are mixed in vitro reconstituting the enzyme function. These results along with the DNA interaction pattern of the proteins implicate an essential role for the C-terminal region in single-strand DNA passage between the two transesterification reactions catalyzed by the N-terminal domain.
...
PMID:Indispensable, functionally complementing N and C-terminal domains constitute site-specific topoisomerase I. 1649 Feb 13

DNA topoisomerases are a family of enzymes altering the topology of DNA by concerted breakage and rejoining of the phosphodiester backbone of DNA. Bacterial and archeal type IA topoisomerases, including topoisomerase I, topoisomerase III, and reverse gyrase, are crucial in regulation of DNA supercoiling and maintenance of genetic stability. The crystal structure of full length topoisomerase I from Thermotoga maritima was determined at 1.7A resolution and represents an intact and fully active bacterial topoisomerase I. It reveals the torus-like structure of the conserved transesterification core domain comprising domains I-IV and a tightly associated C-terminal zinc ribbon domain (domain V) packing against domain IV of the core domain. The previously established zinc-independence of the functional activity of T.maritima topoisomerase I is further supported by its crystal structure as no zinc ion is bound to domain V. However, the structural integrity is preserved by the formation of two disulfide bridges between the four Zn-binding cysteine residues. A functional role of domain V in DNA binding and recognition is suggested and discussed in the light of the structure and previous biochemical findings. In addition, implications for bacterial topoisomerases I are provided.
...
PMID:Crystal structure of full length topoisomerase I from Thermotoga maritima. 1660 Feb 96

Nuclear respiratory factor 1 (NRF-1) is one of the key transcriptional activators for nuclear-coded genes involved in mitochondrial biogenesis and function as well as for many housekeeping genes. A transcriptional co-activator PGC-1 and its related family member PRC have previously been shown to interact with NRF-1 and co-activate NRF-1. We show here that NRF-1 can also directly interact with poly(ADP-ribose) polymerase 1 (PARP-1) and co-purify the PARP-1.DNA-PK.Ku80.Ku70.topoisomerase IIbeta-containing protein complex. Our in vitro binding experiments show that DNA-binding/dimerization domain of NRF-1 and the N-terminal half of PARP-1, which contains two Zinc fingers and the auto-modification domain, are responsible for the interaction, and that this interaction occurs with or without PARP-1 poly(ADP-ribosyl)ation (PARylation). DNA-bound NRF-1 can form a complex with PARP-1, suggesting that NRF-1 can recruit the PARP-1.DNA-PK.Ku80.Ku70.topoisomerase IIbeta-containing protein complex to the promoter. PARP-1 can also PARylate the DNA-binding domain of NRF-1 and negatively regulate NRF-1.PARP-1 interaction. Transient transfection and chromatin immunoprecipitation experiments suggest that PARP-1 plays a role during transcriptional activation by NRF-1. Our finding identifies a new aspect of transcriptional regulation used by NRF-1.
...
PMID:Poly(ADP-ribose) Polymerase 1 Interacts with Nuclear Respiratory Factor 1 (NRF-1) and Plays a Role in NRF-1 Transcriptional Regulation. 1918 65


<< Previous 1 2 3 4 5 6 Next >>

---