title: Substrate specificity and excision kinetics of Escherichia coli endonuclease VIII (Nei) for modified bases in DNA damaged by free radicals.
abstract: Endonuclease VIII (Nei) is one of three enzymes in Escherichia coli that are involved in base-excision repair of oxidative damage to DNA. We investigated the substrate specificity and excision kinetics of this DNA glycosylase for bases in DNA that have been damaged by free radicals. Two different DNA substrates were prepared by gamma-irradiation of DNA solutions under N(2)O or air, such that they contained a multiplicity of modified bases. Although previous studies on the substrate specificity of Nei had demonstrated activity on several pyrimidine derivatives, this present study demonstrates excision of additional pyrimidine derivatives and a purine-derived lesion, 4,6-diamino-5-formamidopyrimidine, from DNA containing multiple modified bases. Excision was dependent on enzyme concentration, incubation time, and substrate concentration, and followed Michaelis-Menten kinetics. The kinetic parameters also depended on the identity of the individual modified base being removed. Substrates and excision kinetics of Nei and a naturally arising mutant form involving Leu-90-->Ser (L90S-Nei) were compared to those of Escherichia coli endonuclease III (Nth), which had previously been determined under experimental conditions similar to those in this study. This comparison showed that Nei and Nth significantly differ from each other in terms of excision rates, although they have common substrates. The present work extends the substrate specificity of Nei and shows the effect of a single mutation in the nei gene on the specificity of Nei.
authors.affiliation: Chemical Science and Technology Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland 20899-8311, USA. miral@nist.gov
authors.forename: M
authors.initials: M
authors.lastname: Dizdaroglu
authors.forename: S M
authors.initials: SM
authors.lastname: Burgess
authors.forename: P
authors.initials: P
authors.lastname: Jaruga
authors.forename: T K
authors.initials: TK
authors.lastname: Hazra
authors.forename: H
authors.initials: H
authors.lastname: Rodriguez
authors.forename: R S
authors.initials: RS
authors.lastname: Lloyd
mesh_terms: D004249:DNA Damage; D045647:DNA Glycosylases; D043224:Deoxyribonuclease (Pyrimidine Dimer); D004706:Endodeoxyribonucleases / Q000378:metabolism*; D004926:Escherichia coli / Q000201:enzymology*; D029968:Escherichia coli Proteins; D005609:Free Radicals; D007700:Kinetics; D009699:N-Glycosyl Hydrolases / Q000378:metabolism; D018384:Oxidative Stress; D013379:Substrate Specificity
chemical_list: D029968:Escherichia coli Proteins; D005609:Free Radicals; D004706:Endodeoxyribonucleases; D043224:Deoxyribonuclease (Pyrimidine Dimer); C106403:NTH protein, E coli; D045647:DNA Glycosylases; D009699:N-Glycosyl Hydrolases