Single-stranded oligodeoxyribonucleotides are substrates of Fpg protein from Escherichia coli

The interaction of Escherichia coli Fpg protein, which catalyzes excision o f several damaged purine bases including 8-oxoguanine (oxoG) from DNA with a set of single- (ss) and double-stranded (ds) 23-mer oligodeoxyribonucleot ides (ODNs) containing d-oxoguanine(s) at various positions, has been inves tigated. The affinities of different ss ODNs (K-M = 0.55-1.3 mu M) were sho wn to be 12-170 times less than those for corresponding ds ODNs (K-M = 6-60 nM). Depending on the position of the oxoG within the ODNs, relative initi al rates of conversion of ss substrates may be less than, comparable, or gr eater than those for ds ODNs. The enzyme can remove 5'-terminal oxoG from O DNs only if the 5'-end is phosphorylated. Fpg does not release oxoG residue s from the ultimate and penultimate 3'-terminal positions. Duplexes contain ing two adjacent oxoG are poor substrates for the glycosylase.