Reactive Oxygen Species Induced by DNA-heme-based G-Quadruplex Structures with Hydrogen Peroxide: Insights into Oxidative DNA Damage

Abstract

G-quadruplexes are four-stranded structures built from stacked G-tetrads, which are planar cyclical assemblies of four guanine bases interacting through Hoogsteen hydrogen bonds. This structure forms naturally in our genome where there is a prevalence of Guanine (G). G has the lowest redox potential among all native nucleotides, making the structure prone to oxidative damage, generating several guanine base lesions, including the most common one called 8-oxoguanine. However, the function and the role of this system are not clear. To have more insight into the activity and consequences of oxidative DNA damage in vivo, understanding the oxidative mechanism of hemin-G-quadruplexes in vitro is vital. Experiments with G4s and varying [H2O2] with chromogenic substrates such as 3,3',5,5'-tetramethylbenzidine (TMB), 2,2′-Azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS) TMB and ABTS oxidation show that the catalytic activity of G4s is significant. To test which reactive oxygen species (ROS) is the main species generated in the system, different experiments with selective probes and trapping agents were done. The result supports the hypothesis of singlet oxygen is the main intermediate species. This discovery is critical as it enhances our knowledge of the impact of oxidative damage on local and regional DNA structures and neighboring biomolecules, potentially discovering treatments for subsequent mutations or carcinogenesis due to the selectivity of this ROS to 8-oxoguanine.