Abstact

Uracil-DNA glycosylase (UDG), a key highly conserved DNA repair enzyme involved in uracil excision repair, was discovered in Escherichia coli . The Bacillus subtilis bacteriophage, PBS-1 and PBS-2, which contain dUMP residues in their DNA, express a UDG inhibitor protein, Ugi which binds to UDG very tightly to form a physiologically irreversible complex. The X-ray analysis of the E. coli UDG (Ec UDG)-Ugi complex at 3.2 A resolution, leads to the first structure elucidation of a bacterial UDG molecule. This structure is similar to the enzymes from human and viral sources. A comparison of the available structures involving UDG permits the delineation of the constant and the variable regions of the molecule. Structural comparison and mutational analysis also indicate that the mode of action of the enzyme from these sources are the same. The crystal structure shows a remarkable spatial conservation of the active site residues involved in DNA binding in spite of significant differences in the structure of the enzyme-inhibitor complex, in comparison with those from the mammalian and viral sources. Ec UDG could serve as a prototype for UDGs from pathogenic prokaryotes, and provide a framework for possible drug development against such pathogens with emphasis on features of the molecule that differ from those in the human enzyme.