Recognition of Damaged DNA by The C-Terminal Domain of 8-Oxoguanine-DNA N-Glycosylase from <i>Escherichia Coli</i>
Formamidopyrimidine-DNA<i>-N-</i>glycosylase (Fpg) is an important enzyme involved in repair of oxidized DNA bases of Escherichia coli. Previously it was shown that the C-terminal domain of Fpg harbors DNA-binding elements. Therefore, it was proposed that C-terminal domain of Fpg plays the principal DNA-binding role. Also, it is known that actinobacteria (Mycobacterium tuberculosis, etc.) possess proteins with unknown functions homologous to the C-terminal but not N-terminal Fpg domain. We had developed a method to express and purify C-terminal Fpg domain and studied its activities. C-Fpg was rather efficient in binding damaged DNA. Despite the absence of the catalytic domain, C-Fpg possessed a low residual ability to cleave apurine/apyrimidine substrates. The DNA substrate was cleaved by β-elimination. In the presence of Mg<sup>2+</sup> ions C-Fpg showed DNase activity not observed in the original Fpg protein. Thus C-Fpg homologues from actinobacteria also can be Mg<sup>2+</sup>-dependent endonucleases involved in DNA repair or DNA metabolism.