National Center for
4TUQ: Human Dna Polymerase Beta Inserting Dcmpnpp Opposite Gg Template (gg0b)
Structural basis for the inefficient nucleotide incorporation opposite cisplatin-DNA lesion by human DNA polymerase beta
J. Biol. Chem. (2014) 289 p.31341-31348
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 Mg(2+) or Mn(2+). The Mg(2+)-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 Mn(2+)-bound structure shows that polbeta adopts a catalytically suboptimal semiclosed 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.