Substrate specificity of Deinococcus radiodurans Fpg protein

A DNA repair enzyme has recently been isolated from the ionizing radiation- resistant bacterium Deinococcus radiodurans [Bauche, C., and Laval, J. (199 9) J. Bacteriol. 181, 262-269]. This enzyme is a homologue of the Fpg prote in of Escherichia coli. We investigated the substrate specificity of this e nzyme for products of oxidative DNA base damage using gas chromatography/is otope-dilution mass spectrometry and DNA substrates, which were either gamm a-irradiated or treated with H2O2/Fe(III)-EDTA/ascorbic acid. Excision of p urine lesions 2,6-diamino-4-hydroxy-5-formamidopyrimidine (FapyGua), 4,6-di amino-5-formamidopyrimidine (FapyAde), and 8-hydroxyguanine (8-OH-Gua) was observed among 17 lesions detected in damaged DNA substrates. The extent of excision was determined as a function of enzyme concentration, time, and s ubstrate concentration. FapyGua and FapyAde were excised with similar speci ficities from three DNA substrates, whereas 8-OH-Gua was the least preferre d lesion. The results show that D. radiodurans Fpg protein and its homologu e E. coli Fpg protein excise the same modified DNA bases, but the excision rates of these enzymes are significantly different. Formamidopyrimidines ar e preferred substrates of D. radiodurans Fpg protein over 8-OH-Gua, whereas E. coli Fpg protein excises these three lesions with similar efficiencies from various DNA substrates. Substrate specificities of these enzymes were also compared with that of Saccharomyces cerevisiae Ogg1 protein, which exc ises FapyGua and 8-OH-Gua, but not FapyAde.