Topoisomerases

This chapter discusses single-molecule approaches in the study of topoisomerases. After introducing the problem posed by DNA entanglement, it describes type I and type II topoisomerases, which solve that issue. Single-molecule assays have nailed down the different mechanisms of bacterial and eukaryotic type I topoisomerases. The properties of type II topoisomerases are then described. Single-molecule experiments have shown that they relax DNA torsion by two units, passing one dsDNA segment through a break in another segment. However, while topoII relaxes positive and negative supercoils similarly, topoIV relaxes positive supercoils quickly and processively, but negative ones slowly and distributively. This chiral discrimination is compared with the activity of the enzyme on two catenated DNA molecules. After describing single-molecule assays of the activity of gyrases, in-vivo investigations of single fluorescently labelled topoIV units in single E.coli are discussed, with concluding remarks on the future of single-molecule DNA/protein studies.

The Effect of Dimethyl Sulfoxide on Supercoiled DNA Relaxation Catalyzed by Type I Topoisomerases

The effects of dimethyl sulfoxide (DMSO) on supercoiled plasmid DNA relaxation catalyzed by two typical type I topoisomerases were investigated in our studies. It is shown that DMSO in a low concentration (less than 20%, v/v) can induce a dose-related enhancement of the relaxation efficiency ofEscherichia colitopoisomerase I (type IA). Conversely, obvious inhibitory effect on the activity ofcalf thymustopoisomerase I (type IB) was observed when the same concentration of DMSO is used. In addition, our studies demonstrate that 20% DMSO has an ability to reduce the inhibitory effect on EcTopo I, which was induced by double-stranded oligodeoxyribonucleotides while the same effect cannot be found in the case of CtTopo I. Moreover, our AFM examinations suggested that DMSO can change the conformation of negatively supercoiled plasmid by creating some locally loose regions in DNA molecules. Combining all the lines of evidence, we proposed that DMSO enhanced EcTopo I relaxation activity by (1) increasing the single-stranded DNA regions for the activities of EcTopo I in the early and middle stages of the reaction and (2) preventing the formation of double-stranded DNA-enzyme complex in the later stage, which can elevate the effective concentration of the topoisomerase in the reaction solution.

Biological Activity of 1-Aryl-3-phenethylamino-1-propanone Hydrochlorides and 3-Aroyl-4-aryl-1-phenethyl-4-piperidinols on PC-3 Cells and DNA Topoisomerase I Enzyme

1aA number of studies reported Mannich bases to manifest antimicrobial, cytotoxic, anticancer, anti-inflammatory, and anticonvulsant activities. A considerable number of therapeutically important cytotoxic compounds are active on DNA topoisomerases that regulate the DNA topology. In the present study we evaluated the biological activity of mono- Mannich bases, 1-aryl-3-phenethylamino-1-propanone hydrochlorides (- 10a), and semicyclic mono- Mannich bases, 3-aroyl-4-aryl-1-phenethyl-4-piperidinols (1b - 9b), synthesized in our laboratory. We employed androgen-independent human prostate cancer cells (PC-3) to assess the cytotoxicity of the compounds and extended the biological activity evaluation to cover supercoil relaxation assays of mammalian type I topoisomerases. Our results showed that the compounds had cytotoxicity within the 8.2 - 32.1 μM range, while two compounds gave rise to a comparable average value in topo I interference of 42% and 40% for 10a (with a hydroxy substituent on the phenyl ring from mono-Mannich bases) and 5b (with a fluoro substituent on the phenyl ring from the semicyclic mono-Mannich base series, piperidinols), respectively

Molluscum Contagiosum Virus Topoisomerase: Purification, Activities, and Response to Inhibitors

ABSTRACT Molluscum contagiosum virus (MCV), the only member of theMolluscipoxvirus genus, causes benign papules in healthy people but disfiguring lesions in immunocompromised patients. The sequence of MCV has been completed, revealing that MCV encodes a probable type I topoisomerase enzyme. All poxviruses sequenced to date also encode type I topoisomerases, and in the case of vaccinia virus the topoisomerase has been shown to be essential for replication. Thus, inhibitors of the MCV topoisomerase might be useful as antiviral agents. We have cloned the gene for MCV topoisomerase, overexpressed and purified the protein, and begun to characterize its activities in vitro. Like other eukaryotic type I topoisomerases, MCV topoisomerase can relax both positive and negative supercoils. An analysis of the cleavage of plasmid and oligonucleotide substrates indicates that cleavage by MCV topoisomerase is favored just 3′ of the sequence 5′ (T/C)CCTT 3′, resulting in formation of a covalent bond to the 3′ T residue, as with other poxvirus topoisomerases. We identified solution conditions favorable for activity and measured the rate of formation and decay of the covalent intermediate. MCV topoisomerase is sensitive to inhibition by coumermycin A1 (50% inhibitory concentration, 32 μM) but insensitive to five other previously reported topoisomerase inhibitors. This work provides the point of departure for studies of the mechanism of function of MCV topoisomerase and the development of medically useful inhibitors.