Fluorine at the C5 Position of 2′‐Deoxyuridine Enhances Repair of a O4‐Methyl Adduct by O6‐Alkylguanine DNA Alkyltransferases

Alkylation damage at the O6‐ and O4‐atoms of 2′‐deoxyguanosine (dG) and thymidine (T), respectively, can be removed by O6‐alkylguanine‐DNA alkyltransferases (AGTs). Previous studies have shown that human AGT (hAGT) repairs small adducts poorly at the O4‐atom of T, in comparison to the E. coli variants (OGT and Ada‐C). The C5 methyl group of the thymine nucleobase is suspected to contribute to hAGT repair proficiency possibly due to steric effects in the protein active site. In the present study, repair of oligonucleotides containing a 5‐fluoro‐O4‐methyl‐2′‐deoxyuridine (dFU‐Me) insert by hAGT, E. coli AGT variants (OGT and Ada‐C) and a chimeric hAGT/OGT protein was evaluated. All AGT variants, particularly hAGT and the hAGT/OGT chimera, demonstrated improved proficiency at removing the O4‐methyl group from substrates containing dFU‐Me, relative to the thymidine and 2′‐deoxyuridine counterparts. This reports demonstrates that fluorine at the C5 position of 2′‐deoxyuridine enhances the susceptibility of methyl adducts at the O4 position to be removed by human AGT.