Human 8-oxoguanine-DNA-glycosylase (OGG1) efficiently removes mutagenic 8-oxoguanine (8-oxoGua) and 2,6-diamino-4-hydroxy-5-formamidopyrimidine (FapyGua) when paired with cytosine in damaged DNA. Excision of 8-oxoGua mispaired with adenine may lead to GT transversions. Posttranslational modifications such as phosphorylation could affect cellular distribution and enzymatic activity of OGG1. Mutations and polymorphisms of OGG1 may affect enzymatic activity and have been associated with increased risk of several cancers. In this study, using double-stranded oligodeoxynucleotides containing 8-oxoGua:Cyt or 8-oxoGua:Ade pairs, as well as -irradiated calf thymus DNA, we have investigated the kinetics and substrate specificity of several known OGG1 polymorphic variants and phosphomimetic SerGlu mutants. Among the polymorphic variants, A288V and S326C displayed opposite-base specificity similar to that of wild type OGG1, and OGG1-D322N was 2.5-fold more specific for the correct opposite base than the wild type enzyme. S231E, S232E, S231/232E, and S280E phosphomimetic mutants had slightly lower activity and specificity similar to the wild type enzyme in both assays. OGG1-S326C efficiently excised 8-oxoGua from oligodeoxynucleotides and FapyGua from -irradiated DNA but excised 8-oxoG rather inefficiently from the latter. Otherwise kcat values for 8-oxoGua excision obtained from both types of experiments were broadly similar for all OGG1 variants studied. It is known that human AP endonuclease APEX1 can stimulate OGG1 activity by increasing its turnover rate. However, when wild type OGG1 was replaced with one of the phosphomimetic mutants, very little stimulation of 8-oxoGua removal was observed in the presence of APEX1.
Citation: Febs Journal
Pub Type: Journals
DNA glycosylases, DNA repair, GC/MS, Hydroxyl radical, Oxidative DNA damage