A 26 kDa yeast DNA topoisomerase I fragment: crystallographic structure and mechanistic implications.

TitleA 26 kDa yeast DNA topoisomerase I fragment: crystallographic structure and mechanistic implications.
Publication TypeJournal Article
Year of Publication1995
AuthorsLue N, Sharma A, Mondragón A, Wang JC
Date Published1995 Dec 15
KeywordsCamptothecin, Cross-Linking Reagents, Crystallography, X-Ray, DNA Topoisomerases, Type I, DNA, Fungal, Drug Resistance, Microbial, Fungal Proteins, Macromolecular Substances, Models, Molecular, Photochemistry, Protein Binding, Protein Conformation, Recombinant Fusion Proteins, Saccharomyces cerevisiae, Topoisomerase I Inhibitors

BACKGROUND: Type I DNA topoisomerases, divided mechanistically into two subfamilies, are ubiquitous enzymes that participate in replication and transcription. In addition to its role in these fundamental processes, the biological importance of eukaryotic DNA topoisomerase I is underscored by its identification as the target of the antitumor alkaloid camptothecin. An understanding of the mechanism of catalysis and interactions with camptothecin and other drugs has been hampered by a lack of detailed structural information.

RESULTS: The three-dimensional structure of a 26 kDA fragment (residues 135 to about 363) of Saccharomyces cerevisiae DNA topoisomerase I has been determined at 1.9 A resolution. The fragment has a novel architecture comprising a concave platform and a pair of outlying V-shaped helices. Photocrosslinking and protein footprinting experiments show that the positively charged concave surface and the junction region of the V-shaped pair of helices contact DNA in the enzyme-DNA complex.

CONCLUSIONS: Crystallographic, biochemical and genetic data indicate that this 26 kDa fragment of yeast DNA topoisomerase I is involved in complex formation between the enzyme and DNA, and probably also in camptothecin-enzyme-DNA ternary complex formation. A molecular model for protein-DNA interaction based on these data is proposed. The bipartite DNA-binding regions of the 26 kDa fragment may enable eukaryotic DNA topoisomerase I to adapt to sequence-dependent structural variations in its DNA substrates.

Alternate JournalStructure
PubMed ID8747458
Grant ListR01 GM051350 / GM / NIGMS NIH HHS / United States

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