Protein
DNA topoisomerase I, plasmid
Organism
Xylella fastidiosa (strain 9a5c)
Function
Releases the supercoiling and torsional tension of DNA, which is 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 then 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.
Similarity
Belongs to the type IA topoisomerase family.
Sequence
MKLMIIESPGKIEKLSTILGDGWKIAASVGHVRDLPQKEMGVAAPDFKPSYELTERGEGVVAKLKNLLKQADSVYLATDPDREGEAISWHLQQCLKLSNPLRVTFNEITANAVKASLVAPRTIDVKRVAAQEARRVLDRLVGYMVSPELSRLTGKRLSAGRVQSPAVRLVVEREREIKAFKVTNHFGAMLFFADAKTSGEWSAEWLTKPKFVAEDNPYFMDRDFAAAVAQVKAVVVKSFDESEAKRSPPPPFTTSTMQQAASVTLGVDPKAAMDAAQKLYEQGHITYHRTDNPNVSDESLGDIYAVSVKLGLDIAEKPRKFKAPAGAQVGHPAVTPTHWEVEEAGETSDQKALYKLIRLRAIACQLADARYAVRTVRLEAAQPVGGKNVEFEARGRTLIYQGWLKLIAGDQTEEEDGNEKESSNPIPVCAPGECLDVARGKLLEKKTKPPSHYTQATLVKKLESEGIGRPATYAAIMDNIVSRGYVKTEKKYLFPTETGELIVDSLVGKFEFLDLGFTREIEESLDRIAQGESGYKAVIAKVHDQLNMELSTLQVSATPKHPCQECGKPLRRIPGKNGHFWGCSGYPDCSVTFPDEGGKPGQKKPVEVSNFACVKCGNPLKHLVKKGKGGYDFWGCSGFKEGCKATYEDKKGKPNFEKAK