Thermodynamic and Mechanistic Insights into Translesion DNA Synthesis Catalyzed by Y-Family DNA Polymerase Across a Bulky Double-Base Lesion of an Antitumor Platinum Drug
To determine how the Y-family translesion DNA polymerase eta (Pol eta) processes lesions remains fundamental to understanding the molecular origins of the mutagenic translesion bypass. We utilized model systems employing a DNA double-base lesion derived from 1,2-GG intrastrand cross-links of a new antitumor PtII complex containing a bulky carrier ligand, namely [PtCl2(cis-1,4-dach)] (DACH=diaminocyclohexane). The catalytic efficiency of Pol eta for the insertion of correct dCTP, with respect to the other incorrect nucleotides, opposite the 1,2-GG cross-link was markedly reduced by the DACH carrier ligand. This reduced efficiency of Pol eta to incorporate the correct dCTP could be due to a more extensive DNA unstacking and deformation of the minor groove induced in the DNA by the cross-link of bulky [PtCl2(cis-1,4-dach)]. The major products of the bypass of this double-base lesion produced by [PtCl2(cis-1,4-dach)] by Pol eta resulted from misincorporation of dATP opposite the platinated G residues. The results of the present work support the thesis that this misincorporation could be due to sterical effects of the bulkier 1,4-DACH ligand hindering the formation of the Po eta DNAincoming nucleotide complex. Calorimetric analysis suggested that thermodynamic factors may contribute to the forces that governed enhanced incorporation of the incorrect dATP by Pol eta as well.