Structure, dynamics, and processing of 8oxoG:A in the nucleosome.

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• Eukaryotic DNA is packaged into nucleosomes, creating a chromatin environment.
• Oxidative stress generates DNA lesions like 8-oxo-7,8-dihydroguanine (8oxoG).
• 8oxoG can form base pairs with cytosine (8oxoG:C) or adenine (8oxoG:A), potentially leading to mutations.

Purpose of the Study:

• To elucidate the structure and dynamics of 8oxoG:C and 8oxoG:A base pairs within the nucleosome.
• To investigate whether the MUTYH enzyme can excise 8oxoG:A base pairs in a nucleosomal context.

Main Methods:

• Cryo-electron microscopy (cryo-EM) for structural determination.
• Molecular dynamics (MD) simulations for analyzing base pair dynamics.
• Biochemical assays to assess MUTYH enzyme activity.

Main Results:

• Nucleosomal 8oxoG:C forms a stable base pair in the anti conformation.
• Nucleosomal 8oxoG:A forms a dynamic base pair in the syn conformation.
• MUTYH enzyme is unable to process the nucleosomal 8oxoG:A base pair.

Conclusions:

• The nucleosome's structure influences oxidative DNA damage accommodation.
• The dynamic 8oxoG:A base pair in nucleosomes evades MUTYH repair.
• This evasion contributes to higher mutagenic transversions in nucleosomal DNA compared to linker DNA.