LAUSR

An electrophilic 5‐methylene‐2‐pyrrolone modification (KMP) is produced at lysine residues of histone proteins in nucleosome core particles upon reaction with a commonly formed DNA lesion (C4‐AP). The nonenzymatic KMP modification is also generated in the histones of HeLa cells treated with the antitumor agent, bleomycin that oxidizes DNA and forms C4‐AP. This nonenzymatic covalent histone modification has the same charge as the N‐acetyllysine (KAc) modification but is more electrophilic. In this study we show that KMP‐containing histone peptides are recognized by, and covalently modify bromodomain proteins that are KAc readers. Distinct selectivity preferences for covalent bromodomain modification are observed following incubation with KMP‐containing peptides of different sequence. MS/MS analysis of 3 covalently modified bromodomain proteins confirmed that Cys adduction was selective. The modified Cys was not always proximal to the KAc binding site, indicating that KMP‐containing peptide interaction with bromodomain protein is distinct from the former. Analysis of protein adduction yields as a function of bromodomain pH at which the protein charge is zero (pI) or cysteine solvent accessible surface area are also consistent with non‐promiscuous interaction between the proteins and electrophilic peptides. These data suggest that intracellular formation of KMP could affect cellular function and viability by modifying proteins that regulate genetic expression.