title: The mechanism of topoisomerase I poisoning by a camptothecin analog.
abstract: We report the x-ray crystal structure of human topoisomerase I covalently joined to double-stranded DNA and bound to the clinically approved anticancer agent Topotecan. Topotecan mimics a DNA base pair and binds at the site of DNA cleavage by intercalating between the upstream (-1) and downstream (+1) base pairs. Intercalation displaces the downstream DNA, thus preventing religation of the cleaved strand. By specifically binding to the enzyme-substrate complex, Topotecan acts as an uncompetitive inhibitor. The structure can explain several of the known structure-activity relationships of the camptothecin family of anticancer drugs and suggests that there are at least two classes of mutations that can produce a drug-resistant enzyme. The first class includes changes to residues that contribute to direct interactions with the drug, whereas a second class would alter interactions with the DNA and thereby destabilize the drug-binding site.
authors.affiliation: deCODE genetics, Incorporated, BioStructures Group, 7869 Northeast Day Road West, Bainbridge Island, WA 98110, USA.
authors.forename: Bart L
authors.initials: BL
authors.lastname: Staker
authors.forename: Kathryn
authors.initials: K
authors.lastname: Hjerrild
authors.forename: Michael D
authors.initials: MD
authors.lastname: Feese
authors.forename: Craig A
authors.initials: CA
authors.lastname: Behnke
authors.forename: Alex B
authors.initials: AB
authors.lastname: Burgin
authors.forename: Lance
authors.initials: L
authors.lastname: Stewart
mesh_terms: D000970:Antineoplastic Agents / Q000737:chemistry / Q000494:pharmacology*; D018360:Crystallography, X-Ray; D004247:DNA / Q000737:chemistry* / Q000378:metabolism; D004264:DNA Topoisomerases, Type I / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D019008:Drug Resistance, Neoplasm; D004791:Enzyme Inhibitors / Q000737:chemistry / Q000494:pharmacology*; D006801:Humans; D006860:Hydrogen Bonding; D007364:Intercalating Agents / Q000737:chemistry / Q000494:pharmacology*; D046911:Macromolecular Substances; D008958:Models, Molecular; D015394:Molecular Structure; D009154:Mutation; D009363:Neoplasm Proteins / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D010446:Peptide Fragments / Q000737:chemistry / Q000378:metabolism / Q000502:physiology; D011485:Protein Binding; D011487:Protein Conformation; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000378:metabolism / Q000502:physiology; D013329:Structure-Activity Relationship; D059004:Topoisomerase I Inhibitors; D019772:Topotecan / Q000737:chemistry / Q000494:pharmacology*
chemical_list: D000970:Antineoplastic Agents; D004791:Enzyme Inhibitors; D007364:Intercalating Agents; D046911:Macromolecular Substances; D009363:Neoplasm Proteins; D010446:Peptide Fragments; D011993:Recombinant Fusion Proteins; D059004:Topoisomerase I Inhibitors; D019772:Topotecan; D004247:DNA; D004264:DNA Topoisomerases, Type I