PMID: 25237188
Koag MC, Lai L, Lee S
Structural Basis for the Inefficient Nucleotide Incorporation Opposite Cisplatin-DNA Lesion by Human DNA Polymerase beta
J Biol Chem. 2014 Sep 18. pii: jbc.M114.605451.
Human DNA polymerase beta (polbeta) has been suggested to play a role in cisplatin resistance, especially in polbeta-overexpressing cancer cells. Polbeta has been shown to accurately, albeit slowly bypass the cisplatin-1,2-d(GpG) (Pt-GG) intramolecular cross-link in vitro. Currently, the structural basis for the inefficient Pt-GG bypass mechanism of polbeta is unknown. To gain structural insights into the mechanism, we determined two ternary structures of polbeta incorporating dCTP opposite the templating Pt-GG lesion in the presence of the active-site Mg2+ or Mn2+. The Mg2+-bound structure shows that the bulky Pt-GG adduct is accommodated in the polbeta active site without any steric hindrance. In addition, both guanines of the Pt-GG lesion form Watson-Crick base pairing with the primer terminus dC and the incoming dCTP, providing the structural basis for the accurate bypass of the Pt-GG adduct by polbeta. The Mn2+-bound structure shows that polbeta adopts a catalytically sub-optimal semi-closed conformation during the insertion of dCTP opposite the templating Pt-GG, explaining the inefficient replication across the Pt-GG lesion by polbeta. Overall, our studies provide the first structural insights into the mechanism of the potential polbeta-mediated cisplatin resistance.