title: Crystal structure of the amino-terminal fragment of vaccinia virus DNA topoisomerase I at 1.6 A resolution.
abstract: BACKGROUND
  Vaccinia virus, a cytoplasmically-replicating poxvirus, encodes a type I DNA topoisomerase that is biochemically similar to eukaryotic-like DNA topoisomerases I, and which has been widely studied as a model topoisomerase. It is the smallest topoisomerase known and is unusual in that it is resistant to the potent chemotherapeutic agent camptothecin.
  
  
  RESULTS
  The crystal structure of a 9 kDa amino-terminal fragment of vaccinia virus DNA topoisomerase I has been determined at 1.6 A resolution. The fragment forms a five-stranded, antiparallel beta-sheet with two short alpha-helices and connecting loops. Residues that are conserved between all eukaryotic-like type I topoisomerases are not clustered in particular regions of the structure.
  
  
  CONCLUSIONS
  This is the first atomic structure of any region of a eukaryotic-like DNA topoisomerase I. It has provided insights into the structural bases of the phenotypes of some single-site mutants of the intact topoisomerase. The structure has enabled us to study the interactions within a well-folded protein fragment and the camptothecin resistance of the viral topoisomerase.
authors.affiliation: Department of Biochemistry, Molecular Biology and Cell Biology, Northwestern University, Evanston, IL 60208-3500.
authors.forename: A
authors.initials: A
authors.lastname: Sharma
authors.forename: R
authors.initials: R
authors.lastname: Hanai
authors.forename: A
authors.initials: A
authors.lastname: Mondragón
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002166:Camptothecin / Q000378:metabolism; D017124:Conserved Sequence; D018360:Crystallography, X-Ray; D004252:DNA Mutational Analysis; D004264:DNA Topoisomerases, Type I / Q000737:chemistry* / Q000378:metabolism; D005057:Eukaryotic Cells / Q000201:enzymology; D006801:Humans; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000737:chemistry*; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000737:chemistry; D017386:Sequence Homology, Amino Acid; D014616:Vaccinia virus / Q000201:enzymology*
chemical_list: D010446:Peptide Fragments; D011994:Recombinant Proteins; D004264:DNA Topoisomerases, Type I; D002166:Camptothecin