Global Repair Profile of Human Alkyladenine DNA Glycosylaseon Nucleosomes Reveals DNA Packaging Effects

Alkyladenine DNA glycosylase (AAG) is the only known human glycosylase capable of excising alkylated purines from DNA, including the highly mutagenic 1,N6-ethenoadenine (eA) lesion. Here we examine AAG’s ability to excise eA from a nucleosome core particle (NCP), which is the primary repeating unit of DNA packaging in eukaryotes. Using chemical synthesis techniques, we assembled a global population of NCPs in which A is replaced with eA. While each NCP contains no more than one eA lesion, the total population contains eA in 49 distinct geometric positions. Using this global eA-containing NCP system, we obtained kinetic parameters of AAG throughout the NCP architecture. We observed monophasic reaction kinetics across the NCP, but varying amounts of AAG excision. AAG activity is correlated with solution accessibility and local histone architecture. Notably, we identified some highly solution-accessible lesions that are not repaired well, and an increase in repair within the region of asymmetric unwrapping o...