title: Solution structure of the C-terminal single-stranded DNA-binding domain of Escherichia coli topoisomerase I.
abstract: Escherichia coli DNA topoisomerase I catalyzes the interconversion of different topological forms of DNA. In this paper we describe NMR studies of a 14K C-terminal fragment of this enzyme that binds preferentially to single-stranded DNA and enhances the enzyme's ability to relax negatively supercoiled DNA under high salt conditions. The 1H, 13C, and 15N resonances of the protein were assigned from a number of heteronuclear multidimensional NMR experiments, and the three-dimensional structure of the protein was determined from a total of 2188 NMR-derived restraints. The root-mean-square deviation about the mean coordinate positions for residues 13-120 is 0.68 +/- 0.11 A for the backbone atoms and 1.09 +/- 0.09 A for all heavy atoms. The overall fold, which consists of two four-stranded beta-sheets separated by two helices, differs from other DNA- and RNA-binding proteins such as gene 5, cold shock protein, and hnRNP C. From an analysis of the changes in chemical shift upon the addition of single-stranded DNA, the location of the oligonucleotide binding site was determined. The binding site consists of a beta-sheet containing positively charged and aromatic amino acids and, in spite of its different structure, is similar to that found in other proteins that bind single-stranded oligonucleotides.
authors.affiliation: NMR Research, D-47G, AP10, Abbott Laboratories, Illinois 60064, USA.
authors.forename: L
authors.initials: L
authors.lastname: Yu
authors.forename: C X
authors.initials: CX
authors.lastname: Zhu
authors.forename: Y C
authors.initials: YC
authors.lastname: Tse-Dinh
authors.forename: S W
authors.initials: SW
authors.lastname: Fesik
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry; D001483:Base Sequence; D001665:Binding Sites; D004264:DNA Topoisomerases, Type I / Q000737:chemistry*; D004277:DNA, Single-Stranded / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000737:chemistry*; D004926:Escherichia coli / Q000201:enzymology*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009838:Oligodeoxyribonucleotides / Q000378:metabolism; D010446:Peptide Fragments / Q000737:chemistry; D017434:Protein Structure, Tertiary; D012996:Solutions
chemical_list: D001426:Bacterial Proteins; D004277:DNA, Single-Stranded; D004268:DNA-Binding Proteins; D009838:Oligodeoxyribonucleotides; D010446:Peptide Fragments; D012996:Solutions; D004264:DNA Topoisomerases, Type I