title: Binding of Zn(II) to Escherichia coli DNA topoisomerase I.
abstract: Titration of Escherichia coli DNA topoisomerase I with PMPS and 65Zn(II) binding showed independent release and binding of the three Zn(II) in each enzyme molecule. Removal of Zn(II) from topoisomerase I or top85 (truncated topoisomerase I with the Zn(II) binding domain at the carboxyl terminal) affected their sensitivity to Glu-C and Asp-N endoproteases but there was no significant effect on their rate of proteolysis by trypsin or Lys-C endoprotease. This suggested that Zn(II) removal did not result in complete unfolding of topoisomerase enzyme structure but only affected folding of small local regions. Digestion with carboxypeptidase Y further demonstrated that the folding of the zinc binding region itself was altered upon Zn(II) removal.
authors.affiliation: Department of Biochemistry & Molecular Biology, New York Medical College, Valhalla 10595.
authors.forename: C X
authors.initials: CX
authors.lastname: Zhu
authors.forename: Y C
authors.initials: YC
authors.lastname: Tse-Dinh
mesh_terms: D002268:Carboxypeptidases / Q000378:metabolism; D004264:DNA Topoisomerases, Type I / Q000378:metabolism*; D004229:Dithiothreitol / Q000737:chemistry; D004591:Electrophoresis, Polyacrylamide Gel; D010450:Endopeptidases / Q000378:metabolism; D004926:Escherichia coli / Q000201:enzymology*; D010663:Phenylmercury Compounds; D011485:Protein Binding; D013056:Spectrophotometry, Ultraviolet; D017186:Titrimetry; D015032:Zinc / Q000378:metabolism*
chemical_list: D010663:Phenylmercury Compounds; C002910:4-hydroxymercuribenzenesulfonate; D002268:Carboxypeptidases; D010450:Endopeptidases; C022633:serine carboxypeptidase; D004264:DNA Topoisomerases, Type I; D015032:Zinc; D004229:Dithiothreitol