Structural and Functional Analysis of Sulfolobus solfataricus Y-Family DNA Polymerase Dpo4-Catalyzed Bypass of the Malondialdehyde−Deoxyguanosine Adduct(,)

[Image: see text] Oxidative stress can induce the formation of reactive electrophiles, such as DNA peroxidation products, e.g., base propenals, and lipid peroxidation products, e.g., malondialdehyde. Base propenals and malondialdehyde react with DNA to form adducts, including 3-(2′-deoxy-β-d-erythro-pentofuranosyl)pyrimido[1,2-α]purin-10(3H)-one (M(1)dG). When paired opposite cytosine in duplex DNA at physiological pH, M(1)dG undergoes ring opening to form N(2)-(3-oxo-1-propenyl)-dG (N(2)-OPdG). Previous work has shown that M(1)dG is mutagenic in bacteria and mammalian cells and that its mutagenicity in Escherichia coli is dependent on induction of the SOS response, indicating a role for translesion DNA polymerases in the bypass of M(1)dG. To probe the mechanism by which translesion polymerases bypass M(1)dG, kinetic and structural studies were conducted with a model Y-family DNA polymerase, Dpo4 from Sulfolobus solfataricus. The level of steady-state incorporation of dNTPs opposite M(1)dG was reduced 260−2900-fold and exhibited a preference for dATP incorporation. Liquid chromatography−tandem mass spectrometry analysis of the full-length extension products revealed a spectrum of products arising principally by incorporation of dC or dA opposite M(1)dG followed by partial or full-length extension. A greater proportion of −1 deletions were observed when dT was positioned 5′ of M(1)dG. Two crystal structures were determined, including a “type II” frameshift deletion complex and another complex with Dpo4 bound to a dC·M(1)dG pair located in the postinsertion context. Importantly, M(1)dG was in the ring-closed state in both structures, and in the structure with dC opposite M(1)dG, the dC residue moved out of the Dpo4 active site, into the minor groove. The results are consistent with the reported mutagenicity of M(1)dG and illustrate how the lesion may affect replication events.