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NONCOVALENT COMPLEX OF E.COLI DNA TOPOISOMERASE III WITH AN 8-BASE SINGLE-STRANDED DNA OLIGONUCLEOTIDENONCOVALENT COMPLEX OF E.COLI DNA TOPOISOMERASE III WITH AN 8-BASE SINGLE-STRANDED DNA OLIGONUCLEOTIDE
Structural highlights
FunctionTOP3_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 PubMedA variety of cellular processes, including DNA replication, transcription, and chromosome condensation, require enzymes that can regulate the ensuing topological changes occurring in DNA. Such enzymes-DNA topoisomerases-alter DNA topology by catalysing the cleavage of single-stranded DNA (ssDNA) or double-stranded DNA (dsDNA), the passage of DNA through the resulting break, and the rejoining of the broken phosphodiester backbone. DNA topoisomerase III from Escherichia coli belongs to the type IA family of DNA topoisomerases, which transiently cleave ssDNA via formation of a covalent 5' phosphotyrosine intermediate. Here we report the crystal structure, at 2.05 A resolution, of an inactive mutant of E. coli DNA topoisomerase III in a non-covalent complex with an 8-base ssDNA molecule. The enzyme undergoes a conformational change that allows the oligonucleotide to bind within a groove leading to the active site. We note that the ssDNA molecule adopts a conformation like that of B-DNA while bound to the enzyme. The position of the DNA within the realigned active site provides insight into the role of several highly conserved residues during catalysis. These findings confirm various aspects of the type IA topoisomerase mechanism while suggesting functional implications for other topoisomerases and proteins that perform DNA rearrangements. Crystal structure of a complex of a type IA DNA topoisomerase with a single-stranded DNA molecule.,Changela A, DiGate RJ, Mondragon A Nature. 2001 Jun 28;411(6841):1077-81. PMID:11429611[3] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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