A small organic compound enhances the religation reaction of human topoisomerase I and identifies crucial elements for the religation mechanism.
The different steps of the human Top1 (topoisomerase I) catalytic cycle have been analysed in the presence of a pentacyclic-diquinoid synthetic compound. The experiments indicate that it efficiently inhibits the cleavage step of the enzyme reaction, fitting well into the catalytic site. Surprisingly the compound, when incubated with the binary topoisomerase-DNA cleaved complex, helps the enzyme to remove itself from the cleaved DNA and close the DNA gap, increasing the religation rate. The compound also induces the religation of the stalled enzyme-CPT (camptothecin)-DNA ternary complex. Analysis of the molecule docked over the binary complex, together with its chemical properties, suggests that the religation enhancement is due to the presence on the compound of two oxygen atoms that act as hydrogen acceptors. This property facilitates the deprotonation of the 5' DNA end, suggesting that this is the limiting step in the topoisomerase religation mechanism.
*Department of Biology, University of Rome Tor Vergata, Via Della Ricerca Scientifica, Rome 00133, Italy.
Barbara
B
Arnò
*Department of Biology, University of Rome Tor Vergata, Via Della Ricerca Scientifica, Rome 00133, Italy.
Andrea
A
Coletta
*Department of Biology, University of Rome Tor Vergata, Via Della Ricerca Scientifica, Rome 00133, Italy.
Cinzia
C
Tesauro
*Department of Biology, University of Rome Tor Vergata, Via Della Ricerca Scientifica, Rome 00133, Italy.
Laura
L
Zuccaro
†Institute of Translational Pharmacology, National Research Council, CNR, Via Del Fosso del Cavaliere 100, 00133 Rome, Italy.
Paola
P
Fiorani
‡Department of Chemical Sciences and Technology, Via Della Ricerca Scientifica, Rome 00133, Italy.
Sara
S
Lentini
‡Department of Chemical Sciences and Technology, Via Della Ricerca Scientifica, Rome 00133, Italy.
Pierluca
P
Galloni
‡Department of Chemical Sciences and Technology, Via Della Ricerca Scientifica, Rome 00133, Italy.
Valeria
V
Conte
‡Department of Chemical Sciences and Technology, Via Della Ricerca Scientifica, Rome 00133, Italy.
Barbara
B
Floris
*Department of Biology, University of Rome Tor Vergata, Via Della Ricerca Scientifica, Rome 00133, Italy.
Alessandro
A
Desideri
D002166:Camptothecin / Q000737:chemistry; D004247:DNA / Q000737:chemistry* / Q000187:drug effects; D004264:DNA Topoisomerases, Type I / Q000737:chemistry* / Q000378:metabolism; D006801:Humans; D006859:Hydrogen / Q000737:chemistry; D004103:Iodoquinol / Q000008:administration & dosage; D009690:Nucleic Acid Conformation / Q000187:drug effects*; D010100:Oxygen / Q000737:chemistry
D004103:Iodoquinol; D006859:Hydrogen; D004247:DNA; D004264:DNA Topoisomerases, Type I; C528909:TOP1 protein, human; D010100:Oxygen; D002166:Camptothecin