Two glycosylase/abasic lyases from Neisseria mucosa that initiate DNA repair at sites of UV-induced photoproducts

Diverse organisms ranging from Escherichia coli to humans contain a variety of DNA repair proteins that function in the removal of damage caused by shortwave UV light. This study reports the identification, purification, and biochemical characterization of two DNA glycosylases with associated abasic lyase activity from Neisseria mucosa. These enzymes, pyrimidine dimer glycosylase I and II (Nmu-pdg I and Nmu-pdg II), were purified 30,000- and 10,000-fold, respectively. SDS-polyacrylamide gel electrophoresis analysis indicated that Nmu-pdg I is approximately 30 kDa, whereas Nmu-pdg II is approximately 19 kDa. The N-terminal amino acid sequence of Nmu-pdg II exhibits 64 and 66% identity with E. coli and Hemophilus parainfluenzae endonuclease III, respectively. Both Nmu-pdg I and Nmu-pdg II were found to have broad substrate specificities, as evidenced by their ability to incise DNA containing many types of UV and some types of oxidative damage. Consistent with other glycosylase/abasic lyases, the existence of a covalent enzyme-DNA complex could be demonstrated for both Nmu-pdg I and II when reactions were carried out in the presence of sodium borohydride. These data indicate the involvement of an amino group in the catalytic reaction mechanism of both enzymes.