Impact of α-hydroxy-propanodeoxyguanine adducts on DNA duplex energetics: Opposite base modulation and implications for mutagenicity and genotoxicity

Acrolein is an α,β-unsaturated aldehyde that is a major environmental pollutant, as well as a product of cellular metabolism. DNA bases react with acrolein to form two regioisomeric exocyclic guanine adducts, namely γ-hydroxy-propanodeoxyguanosine (γ-OH-PdG) and its positional isomer a-hydroxy-propanodeoxyguanosine (α-OH-PdG). The γ-OH-PdG isomer adopts a ring-opened conformation with minimal structural perturbation of the DNA host duplex. Conversely, the α-OH-PdG isomer assumes a ring-closed conformation that significantly disrupts Watson-Crick base-pair alignments within the immediate vicinity of the damaged site. We have employed a combination of calorimetric and spectroscopic techniques to characterize the thermodynamic origins of these lesion-induced structural alterations. Specifically, we have assessed the energetic impact of α-OH-PdG centered within an 11-mer duplex by hybridizing the adduct-containing oligonucleotide with its complementary strand harboring a central base N [where N = C or A], yielding a pair of duplexes containing the nascent lesion (α-OH-PdG · C) or mismatched adduct (α-OH-PdG· A), respectively. Our data reveal that the nascent lesion is highly destabilizing, whereas its mismatched counterpart partially ameliorates α-OH-PdG-induced destabilization. Collectively, our data provide energetic characterizations of the driving forces that modulate error-free versus error-prone DNA translesion synthesis. The biological implications of our findings are discussed in terms of energetically probing acrolein-mediated mutagenicity versus adduct-induced genotoxicity.