RESUMO
8-Oxoguanine-DNA glycosylases play a key role in the repair of oxidatively damaged DNA. The Escherichia coli formamidopyrimidine-DNA glycosylase (Fpg) and human 8-oxoguanine-DNA glycosylase (hOGG1) are DNA base excision repair enzymes that catalyze the removal of 7,8-dihydro-8-oxoguanine (oxoG) residue, and cleave DNA strand. Specific contacts between DNA phosphate groups and amino acids from active centers of these enzymes play a significant role in DNA-protein interactions. In order to design new non-hydrolyzable substrate analogs of Fpg and hOGG1 for structural studies modified DNA duplexes containing pyrophosphate or OEt-substituted pyrophosphate internucleotide (SPI) groups near the damage were tested. We showed that enzymes recognize and specifically bind to DNA duplexes obtained. The mechanism of incision of oxoG by the Fpg and hOGG1 was determined. We revealed that both enzymes were not able to excise the oxoG residue from DNA containing modified phosphates immediately 3' to the oxoG. In contrast, Fpg and hOGG1 effectively incise DNA duplex carrying analogous phosphate modifications 5' to the oxoG. Non-cleavable oxoG-containing DNA duplexes bearing pyrophosphate or substituted pyrophosphate groups immediately 3' to the oxoG are specific inhibitors for both 8-oxoguanine-DNA glycosylases and can be used for structural studies of complexes comprising a oxoG-containing DNA bound to catalytically active wild-type enzymes as well as their pro- and eucaryotic homologs.
