Stimulation of human 8-oxoguanine-DNA glycosylase by AP-endonuclease: potential coordination of the initial steps in base excision repair

8-Oxoguanine-DNA glycosylase 1 (OGG1), with intrinsic AP lyase activity, is the major enzyme for repairing 7,8-dihydro-8-oxoguanine (8-oxoG), a critic al mutagenic DNA lesion induced by reactive oxygen species. Human OGG1 exci sed the damaged base from an 8-oxoG C-containing duplex oligo with a very l ow apparent k(cat) of 0.1 min(-1) at 37 degreesC and cleaved abasic (AP) si tes at half the rate, thus leaving abasic sites as the major product. Excis ion of 8-oxoG by OGG1 alone did not follow Michaelis-Menten kinetics, Howev er, in the presence of a comparable amount of human AP endonuclease (APE1) the specific activity of OGG1 was increased similar to5-fold and Michaelis- Menten kinetics were observed. Inactive APE1, at a higher molar ratio, and a bacterial APE (Nfo) similarly enhanced OGG1 activity. The affinity of OGG 1 for its product AP.C pair (K-d similar to 2.8 nM) was substantially highe r than for its substrate 8-oxoG.C pair (K-d similar to 23.4 nM) and the aff inity for its final beta -elimination product was much lower (K-d similar t o 233 nM), These data, as well as single burst kinetics studies, indicate t hat the enzyme remains tightly bound to its AP product following base excis ion and that APE1 prevents its reassociation with its product, thus enhanci ng OGG1 turnover. These results suggest coordinated functions of OGG1 and A PE1, and possibly other enzymes, in the DNA base excision repair pathway.