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.
Publication types
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Research Support, Non-U.S. Gov't
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Research Support, U.S. Gov't, P.H.S.
MeSH terms
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Antineoplastic Agents / chemistry
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Antineoplastic Agents / pharmacology*
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Crystallography, X-Ray
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DNA / chemistry*
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DNA / metabolism
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DNA Topoisomerases, Type I / chemistry
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DNA Topoisomerases, Type I / genetics
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DNA Topoisomerases, Type I / metabolism
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Drug Resistance, Neoplasm
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Enzyme Inhibitors / chemistry
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Enzyme Inhibitors / pharmacology*
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Humans
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Hydrogen Bonding
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Intercalating Agents / chemistry
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Intercalating Agents / pharmacology*
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Macromolecular Substances
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Models, Molecular
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Molecular Structure
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Mutation
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Neoplasm Proteins / antagonists & inhibitors*
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Neoplasm Proteins / chemistry
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Neoplasm Proteins / genetics
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Neoplasm Proteins / metabolism
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Peptide Fragments / chemistry
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Peptide Fragments / metabolism
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Peptide Fragments / physiology
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Protein Binding
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Protein Conformation
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Recombinant Fusion Proteins / chemistry
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Recombinant Fusion Proteins / metabolism
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Recombinant Fusion Proteins / physiology
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Structure-Activity Relationship
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Topoisomerase I Inhibitors*
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Topotecan / chemistry
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Topotecan / pharmacology*
Substances
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Antineoplastic Agents
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Enzyme Inhibitors
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Intercalating Agents
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Macromolecular Substances
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Neoplasm Proteins
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Peptide Fragments
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Recombinant Fusion Proteins
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Topoisomerase I Inhibitors
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Topotecan
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DNA
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DNA Topoisomerases, Type I