Dynamic Processing of a Common Oxidative DNA Lesion by the First Two Enzymes of the Base Excision Repair Pathway.

Base excision repair (BER) is the primary pathway by which eukaryotic cells resolve single base damage. One common example of single base damage is 8-oxo-7,8-dihydro-2'-deoxoguanine (8-oxoG). High incidence and mutagenic potential of 8-oxoG necessitate rapid and efficient DNA repair. How BER enzymes coordinate their activities to resolve 8-oxoG damage while limiting cytotoxic BER intermediates from propagating genomic instability remains unclear. Here we use single-molecule Förster resonance energy transfer (smFRET) and ensemble-level techniques to characterize the activities and interactions of consecutive BER enzymes important for repair of 8-oxoG. In addition to characterizing the damage searching and processing mechanisms of human 8-oxoguanine glycosylase 1 (hOGG1), our data support the existence of a ternary complex between hOGG1, the damaged DNA substrate, and human AP endonuclease 1 (APE1). Our results indicate that hOGG1 is actively displaced from its abasic site containing product by protein-protein interactions with APE1 to ensure timely repair of damaged DNA.