Topoisomerase 235935 222513278 2008-06-29T19:11:40Z Docku 7021792 /* Topological problems */ typo [[Image:Topoisomerase I.png|thumb|Topoisomerase I solves the problem caused by tension generated by winding/unwinding of DNA. It wraps around DNA and makes a cut permitting the helix to spin. Once DNA is relaxed, topoisomerase reconnects broken strands ({{PDB|1a36}})]] '''Topoisomerases''' (type I: {{EC number|5.99.1.2}}, type II: {{EC number|5.99.1.3}}) are [[isomerase]] [[enzymes]] that acts on the [[DNA topology|topology]] of [[DNA]]. They were first discovered by Harvard Professor [[James C. Wang]].<ref>[http://www.nasonline.org/site/PageServer?pagename=AWARDS_molbio National Academy of Sciences: NAS Award in Molecular Biology<!-- Bot generated title -->]</ref> ==Function== The [[Double helix|double-helical]] configuration that DNA strands naturally reside in makes them difficult to separate, and yet they must be separated by [[helicase]] proteins if other enzymes are to [[Transcription (genetics)|transcribe]] the [[DNA sequence|sequences]] that [[genetic code|encode]] [[protein]]s, or if [[chromosomes]] are to be [[DNA replication|replicated]]. In so-called [[circular DNA]], in which double helical DNA is bent around and joined in a [[circle]], the two strands are topologically linked, or [[Knot theory|knotted]]. Otherwise identical loops of DNA having different numbers of twists are [[topoisomer]]s, and cannot be interconverted by any process that does not involve the breaking of DNA strands. Topoisomerases catalyze and guide the unknotting of DNA by creating transient breaks in the DNA using a conserved [[Tyrosine]] as the catalytic residue. The insertion of viral DNA into chromosomes and other forms of [[recombination]] can also require the action of topoisomerases. ==Clinical significance== :''See also [[topoisomerase inhibitor]]'' Many drugs operate through interference with the topoisomerases. The broad-spectrum [[Quinolone|fluoroquinolone]] [[antibiotic]]s act by disrupting the function of bacterial type II topoisomerases. Some [[chemotherapy]] drugs work by interfering with topoisomerases in [[cancer]] [[Cell (biology)|cells]]: * type 1 is inhibited by [[irinotecan]] and [[topotecan]]. * type 2 is inhibited by [[etoposide]] and [[teniposide]]. Topoisomerase I is the [[antigen]] recognized by [[Anti Scl-70]] antibodies in [[scleroderma]]. ==Topological problems== There are three main types of topology: [[DNA supercoil|supercoiling]], knotting and [[catenation]]. When outside of [[DNA replication|replication]] or [[Transcription (genetics)|transcription]], DNA needs to be kept as compact as possible and these three states help this cause. However when transcription or replication occur, DNA needs to be free and these states seriously hinder the processes. In addition, during replication, the newly replicated duplex of DNA and the original duplex of DNA become intertwined and need to be completely separated in order to ensure genomic integrity as a cell divides. ==Classes== Topoisomerases can fix these topological problems and are separated into two types separated by the number of strands cut in one round of action: * [[Type I topoisomerase]] cuts one strand of a DNA double helix and then reanneals the cut strand. Type I topoisomerases are subdivided into two subclasses: type IA topoisomerases which share many structural and mechanistic features with the type II topoisomerases, and type IB topoisomerases, which utilize a controlled rotary mechanism. Examples of type IA topoisomerases include topo I and topo III. Historically, type IB topoisomerases were referred to as eukaryotic topo I, but IB topoisomerases are present in all three kingdoms of life. Interestingly, type IA topoisomerases form a covalent intermediate with the 5' end of DNA, while the IB topoisomerases form a covalent intermediate with the 3' end of DNA. Recently, a type IC topoisomerase has been identified, called topo V. While it is structurally unique from type IA and IB topoisomerases, it shares a similar mechanism with type IB topoisomerase. * [[Type II topoisomerase]] cuts both strands of one DNA double helix, passes another unbroken DNA strand through it, and then reanneals the cut strand. It is also split into two subclasses: type IIA and type IIB topoisomerases, which share similar structure and mechanisms. Examples of type IIA topoisomerases include eukaryotic topo II, E. coli gyrase, and E. coli topo IV. Examples of type IIB topoisomerase include topo VI. Both type I and type II topoisomerases change the [[linking number]] of DNA. Type IA topoisomerases change the linking number by one, type IB and type IC topoisomerases change the linking number by any integer, while type IIA and type IIB topoisomerases change the linking number by two. ==References== <references/> * Champoux JJ (2001) DNA Topoisomerases: Structure, Function, and Mechanism ''Annual Review of Biochemistry'' '''70''': 369-413[http://www.fhcrc.org/science/labs/stoddard/MCB_542/champoux_review_2001.pdf] ==See also== * [[DNA topology]] * [[Supercoil]] * [[TOP1]] ==External links== * {{MeshName|DNA+Topoisomerases}} {{Enzymes}} {{Topoisomerases}} {{DNA replication}} {{Autoantigens}} [[Category:EC 5.99.1]] [[Category:DNA replication]] [[da:Topoisomerase]] [[de:Topoisomerase]] [[es:Topoisomerasa]] [[fr:ADN topoisomérase]] [[it:Topoisomerasi]] [[ja:DNAトポイソメラーゼ]] [[pl:Topoizomerazy]] [[pt:Topoisomerase]] [[ru:ДНК-топоизомеразы]] [[sv:Topoisomeras]] [[uk:Топоізомераза]] [[zh:拓樸異構酶]]