Formamidopyrimidine-DNA glycosylase (Fpg; MutM) is a DNA repair enzyme widely distributed in bacteria. Fpg recognizes and excises oxidatively modified purines, 4,6-diamino-5-formamidopyrimidine, 2,6-diamino-4-hydroxy-5-formamidopyrimidine and 8-oxoguanine (8-oxoG), with similar excision kinetics. It also exhibits some lesser activity toward 8-oxoadenine. Fpg enzymes are also present in some plant and fungal species. The eukaryotic Fpg homologs are not active against 8-oxoG, but they recognize and process its oxidation products guanidinohydantoin (Gh) and spiroiminohydantoin (Sp). To date, several structures of bacterial Fpg enzymes unliganded or in complex with DNA containing a damaged base have been published but there is no structure of a eukaryotic Fpg. Here we describe the first crystal structure of a plant Fpg, Arabidopsis thaliana (AthFpg), unliganded and bound to DNA containing an abasic site analog, tetrahydrofuran (THF). Although AthFpg shares a common architecture with other members of the Fpg enzymes, it harbors a zincless finger, previously described in some Nei enzymes, such as human NEIL1 and Mimivirus Nei1. Importantly the F-10 loop capping the modified DNA base in the active site of bacterial Fpg is very short in AthFpg. Deletion of a segment encompassing residues 213 to 229 in Escherichia coli Fpg (EcoFpg) and corresponding to the F-10 loop does not affect the recognition and removal of oxidatively damaged DNA base lesions, with the exception of 8-oxoG. Although the exact role of the loop remains to be further explored, it is now clear that this protein segment is specific to the processing of 8-oxoG.
Citation: Dna Repair
Pub Type: Journals
Base excision repair, DNA glycosylase, abasic site, 8-oxoguanine, Fpg, MutM