RESUMEN
Human DNA polymerase ß (polß) has been suggested to play a role in cisplatin resistance, especially in polß-overexpressing cancer cells. Polß 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 polß is unknown. To gain structural insights into the mechanism, we determined two ternary structures of polß 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 polß 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 polß. The Mn(2+)-bound structure shows that polß 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 polß. Overall, our studies provide the first structural insights into the mechanism of the potential polß-mediated cisplatin resistance.