Interaction and Positioning of Nucleosome Core Particles on DNA Containing the Guanine-Derived Oxidative Lesion Spiroiminodihydantoin

Abstract

Oxidative DNA damage has been implicated in cellular aging, neurological disorders, and carcinogenesis. Living in an oxidizing environment makes DNA damage unavoidable, and some estimates suggest that human DNA withstands as many as 10,000 oxidative events per cell per day. One of the most widely studied DNA lesions is 7,8-dihydro-8-oxo-2’-deoxyguanosine (8-oxoG). Interestingly, the 8-oxoG lesion has a lower reduction potential than guanine and the other DNA bases, allowing it to react further to produce additional base lesions including the spiroiminodihydantoin (Sp) lesion.The Sp lesion contains two rigid five-membered rings connected via a central chiral carbon. As a result, oxidation of 8-oxoG leads to the formation of a pair of Sp diastereomers, both of which may impact the stability and functionality of genomic DNA. Both Sp diastereomers are highly mutagenic, leading to transversions. Though no structures of DNA containing the Sp lesion have yet been determined, computational studies predict that the Sp lesion disrupts hydrogen bonding and base stacking and causes groove widening, therefore disrupting the stability of the DNA double helix. Thermodynamic studies have shown that the Sp lesion destabilizes the DNA double helix by 3.6-6.7 kcal/mol, depending on the nucleotide sequence.In our current work we seek to better understand the effects of the Sp adduct as it effects packaging and positioning of a DNA sequence on nucleosomes. The locations of the histone octamer on DNA molecules are strongly influenced by nucleotide sequence and DNA structure, and this positioning is critically linked to gene expression and gene silencing. Given that the Sp lesion is likely to significantly distort helix structure, we expect the lesion to alter DNA-histone contacts generating changes to the rotational and translational setting of positioned nucleosomes.