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      The DNA cleavage reaction of topoisomerase II: wolf in sheep's clothing

      research-article
      Author(s): 1 , 1 , 2 , *
      Publication date (Electronic):
      Journal: Nucleic Acids Research
      Publisher: Oxford University Press

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          Abstract

          Topoisomerase II is an essential enzyme that is required for virtually every process that requires movement of DNA within the nucleus or the opening of the double helix. This enzyme helps to regulate DNA under- and overwinding and removes knots and tangles from the genetic material. In order to carry out its critical physiological functions, topoisomerase II generates transient double-stranded breaks in DNA. Consequently, while necessary for cell survival, the enzyme also has the capacity to fragment the genome. The DNA cleavage/ligation reaction of topoisomerase II is the target for some of the most successful anticancer drugs currently in clinical use. However, this same reaction also is believed to trigger chromosomal translocations that are associated with specific types of leukemia. This article will familiarize the reader with the DNA cleavage/ligation reaction of topoisomerase II and other aspects of its catalytic cycle. In addition, it will discuss the interaction of the enzyme with anticancer drugs and the mechanisms by which these agents increase levels of topoisomerase II-generated DNA strand breaks. Finally, it will describe dietary and environmental agents that enhance DNA cleavage mediated by the enzyme.

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          DNA topoisomerases.

          J. Wang (1996)
          The various problems of disentangling DNA strands or duplexes in a cell are all rooted in the double-helical structure of DNA. Three distinct subfamilies of enzymes, known as the DNA topoisomerases, have evolved to solve these problems. This review focuses on work in the past decade on the mechanisms and cellular functions of these enzymes. Newly discovered members and recent biochemical and structural results are reviewed, and mechanistic implications of these results are summarized. The primary cellular functions of these enzymes, including their roles in replication, transcription, chromosome condensation, and the maintenance of genome stability, are then discussed. The review ends with a summary of the regulation of the cellular levels of these enzymes and a discussion of their association with other cellular proteins.
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            Early steps in the DNA base excision/single-strand interruption repair pathway in mammalian cells.

            Sankar Mitra, Tapas K. Hazra, Muralidhar Hegde (2007)
            Base excision repair (BER) is an evolutionarily conserved process for maintaining genomic integrity by eliminating several dozen damaged (oxidized or alkylated) or inappropriate bases that are generated endogenously or induced by genotoxicants, predominantly, reactive oxygen species (ROS). BER involves 4-5 steps starting with base excision by a DNA glycosylase, followed by a common pathway usually involving an AP-endonuclease (APE) to generate 3' OH terminus at the damage site, followed by repair synthesis with a DNA polymerase and nick sealing by a DNA ligase. This pathway is also responsible for repairing DNA single-strand breaks with blocked termini directly generated by ROS. Nearly all glycosylases, far fewer than their substrate lesions particularly for oxidized bases, have broad and overlapping substrate range, and could serve as back-up enzymes in vivo. In contrast, mammalian cells encode only one APE, APE1, unlike two APEs in lower organisms. In spite of overall similarity, BER with distinct subpathways in the mammals is more complex than in E. coli. The glycosylases form complexes with downstream proteins to carry out efficient repair via distinct subpathways one of which, responsible for repair of strand breaks with 3' phosphate termini generated by the NEIL family glycosylases or by ROS, requires the phosphatase activity of polynucleotide kinase instead of APE1. Different complexes may utilize distinct DNA polymerases and ligases. Mammalian glycosylases have nonconserved extensions at one of the termini, dispensable for enzymatic activity but needed for interaction with other BER and non-BER proteins for complex formation and organelle targeting. The mammalian enzymes are sometimes covalently modified which may affect activity and complex formation. The focus of this review is on the early steps in mammalian BER for oxidized damage.
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              Structural basis for gate-DNA recognition and bending by type IIA topoisomerases.

              Ken Dong, James M Berger (2007)
              Type II topoisomerases disentangle DNA to facilitate chromosome segregation, and represent a major class of therapeutic targets. Although these enzymes have been studied extensively, a molecular understanding of DNA binding has been lacking. Here we present the structure of a complex between the DNA-binding and cleavage core of Saccharomyces cerevisiae Topo II (also known as Top2) and a gate-DNA segment. The structure reveals that the enzyme enforces a 150 degrees DNA bend through a mechanism similar to that of remodelling proteins such as integration host factor. Large protein conformational changes accompany DNA deformation, creating a bipartite catalytic site that positions the DNA backbone near a reactive tyrosine and a coordinated magnesium ion. This configuration closely resembles the catalytic site of type IA topoisomerases, reinforcing an evolutionary link between these structurally and functionally distinct enzymes. Binding of DNA facilitates opening of an enzyme dimerization interface, providing visual evidence for a key step in DNA transport.
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                Author and article information

                Journal
                Journal ID (nlm-ta): Nucleic Acids Res
                Journal ID (iso-abbrev): Nucleic Acids Res
                Journal ID (publisher-id): nar
                Journal ID (hwp): nar
                Title: Nucleic Acids Research
                Publisher: Oxford University Press
                ISSN (Print): 0305-1048
                ISSN (Electronic): 1362-4962
                Publication date (Print): February 2009
                Publication date (Electronic): 28 November 2008
                Publication date PMC-release: 28 November 2008
                Volume: 37
                Issue: 3
                Pages: 738-748
                Affiliations
                1Department of Biochemistry and 2Department of Medicine (Hematology/Oncology), Vanderbilt University School of Medicine, Nashville, TN 37232-0146 USA
                Author notes
                *To whom correspondence should be addressed. Tel: +1 615 322 4338; Fax: +1 615 343 1166; Email: neil.osheroff@ 123456vanderbilt.edu
                Article
                Publisher ID: gkn937
                DOI: 10.1093/nar/gkn937
                PMC ID: 2647315
                PubMed ID: 19042970
                SO-VID: b15b8a06-1a9a-43bc-ad94-d9bcbc9ccabe
                Copyright © © 2008 The Author(s)
                License:

                This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License ( http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

                History
                Date received : 7 October 2008
                Date revision received : 31 October 2008
                Date accepted : 5 November 2008
                Categories
                Subject: Survey and Summary

                ScienceOpen disciplines: Genetics
                Data availability:
                ScienceOpen disciplines: Genetics

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