2o54
From Proteopedia
Structure of E. coli topoisomerase III in complex with an 8-base single stranded oligonucleotide. Frozen in glycerol at pH 7.0
Structural highlights
Function[TOP3_ECOLI] Releases the supercoiling and torsional tension of DNA introduced during the DNA replication and transcription by transiently cleaving and rejoining one strand of the DNA duplex. Introduces a single-strand break via transesterification at a target site in duplex DNA. The scissile phosphodiester is attacked by the catalytic tyrosine of the enzyme, resulting in the formation of a DNA-(5'-phosphotyrosyl)-enzyme intermediate and the expulsion of a 3'-OH DNA strand. The free DNA strand than undergoes passage around the unbroken strand thus removing DNA supercoils. Finally, in the religation step, the DNA 3'-OH attacks the covalent intermediate to expel the active-site tyrosine and restore the DNA phosphodiester backbone. TOP3 is a potent decatenase.[1] [2] Evolutionary Conservation Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf. Publication Abstract from PubMedEscherichia coli DNA topoisomerase III belongs to the type IA family of DNA topoisomerases, which transiently cleave single-stranded DNA (ssDNA) via a 5' phosphotyrosine intermediate. We have solved crystal structures of wild-type E. coli topoisomerase III bound to an eight-base ssDNA molecule in three different pH environments. The structures reveal the enzyme in three distinct conformational states while bound to DNA. One conformation resembles the one observed previously with a DNA-bound, catalytically inactive mutant of topoisomerase III where DNA binding realigns catalytic residues to form a functional active site. Another conformation represents a novel intermediate in which DNA is bound along the ssDNA-binding groove but does not enter the active site, which remains in a catalytically inactive, closed state. A third conformation shows an intermediate state where the enzyme is still in a closed state, but the ssDNA is starting to invade the active site. For the first time, the active site region in the presence of both the catalytic tyrosine and ssDNA substrate is revealed for a type IA DNA topoisomerase, although there is no evidence of ssDNA cleavage. Comparative analysis of the various conformational states suggests a sequence of domain movements undertaken by the enzyme upon substrate binding. Structural studies of E. coli topoisomerase III-DNA complexes reveal a novel type IA topoisomerase-DNA conformational intermediate.,Changela A, DiGate RJ, Mondragon A J Mol Biol. 2007 Apr 20;368(1):105-18. Epub 2007 Feb 3. PMID:17331537[3] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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