AlkB reverses etheno DNA lesions caused by lipid oxidation in vitro and in vivo

Abstract

Oxidative stress converts lipids into DNA-damaging agents. The genomic lesions formed include 1,N6-ethenoadenine (εA) and 3,N 4-ethenocytosine (εC), in which two carbons of the lipid alkyl chain form an exocyclic adduct with a DNA base. Here we show that the newly characterized enzyme AlkB repairs εA and εC. The potent toxicity and mutagenicity of εA in Escherichia coli lacking AlkB was reversed in AlkB+ cells; AlkB also mitigated the effects of εC. In vitro, AlkB cleaved the lipid-derived alkyl chain from DNA, causing εA and εC to revert to adenine and cytosine, respectively. Biochemically, εA is epoxidized at the etheno bond. The epoxide is putatively hydrolyzed to a glycol, and the glycol moiety is released as glyoxal. These reactions show a previously unrecognized chemical versatility of AlkB. In mammals, the corresponding AlkB homologs may defend against aging, cancer and oxidative stress. © 2005 Nature Publishing Group.