DNA Topology on an Increase in Positive Writhing Number of DNA: Conformation Changes in the Time Course of cis-Diamminedichloroplatinum (2) DNA Adducts

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  • KOBAYASHI Shigeki
    Department of Analytical Chemistry of Medicines, Showa Pharmaceutical University
  • NAKAMURA Yoshihide
    Department of Analytical Chemistry of Medicines, Showa Pharmaceutical University
  • MAEHARA Tamae
    Department of Analytical Chemistry of Medicines, Showa Pharmaceutical University
  • HAMASHIMA Hajime
    Departments of Microbiology, Showa Pharmaceutical University
  • SASATSU Masanori
    Department of Microbiology, School of Pharmacy, Tokyo University of Pharmacy and Life Science
  • ASANO Koji
    Department of Urology, Jikei University School of Medicine
  • OHISHI Yukihiko
    Department of Urology, Jikei University School of Medicine
  • TANAKA Akira
    Department of Analytical Chemistry of Medicines, Showa Pharmaceutical University

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  • DNA Topology on an Increase in Positive Writhing Number of DNA: Conformation Changes in the Time Course of cis-Diamminedichloroplatinum(II)-DNA Adducts.

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We show that the topological significance of the gel mobility of cis-diamminedichloroplatinum(II) (DDP)-closed circular DNA (ccDNA) adducts decreases with reaction time, until a point at which it joins relaxed DNA, and that the mobility of the adducts increases again. There is no relationship between the relative length of the adducts and the gel mobility. Although the significance of the decrease of gel mobility is due to the unwinding of cis-DDP-DNA (or trans-DDP-DNA) adducts, the conformational significance of the subsequent increase in mobility is unclear. To elucidate the conformational significance for unwinding of the adducts, we measured the writhing number (Wκ) of the adducts using electron microscopy and analyzed the topological states of cis-DDP (or trans-DDP) adducts based on the White rule, Lκ=Wκ+Tκ. Where, Lκ and Tκ represent the linking and twisting number in the ring, respectively. From the data, we found that the Wκ of cis-DDP-ccDNA adducts in comparison with trans-DDP-ccDNA adducts increases from a negative to a positive number with time. This suggests that cis-DDP plays a role in the chaneg of the topological state of ccDNA. In the abstraction of platinum from the adducts with CN- ion, the differences in both topological states may explain why Pt in trans-DDP is abstracted more easily than in cis-DDP. To explain the abstraction of Pt ion, we also discuss the findings based on the thermodynamic cycle in a intermolecular crosslink model Pt(NH3)2(guanine)22+→Pt(CN)42- using the Pt parametrized PM3 method.

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