HEAVY METAL IONS AFFECT ACTIVITYOF DNA GLYCOSYLASES OF THE FPG FAMILY

摘要

Prokaryotic enzymes formamidopyrimidine- DNA glycosylase (Fpg) and endonuclease VIII (Nei) and their eukary-otic homologs NEIL1, NEIL2, and NEILЗ define the Fpg family of DNA glycosylases, which initiate the repair ofoxidized DNA bases. Repair of oxidative DNA lesions is known to be impaired in vivo in the presence of ions of someheavy metals. We have studied the effect of salts of several alkaline earth and transition metals on the activity of Fpgfamily DNA glycosylases in the reaction of excision of 5,б-dihydrouracil, a typical DNA oxidation product. The reac-tion catalyzed by NEIL1 was characterized by the values of K_m= 150 nM and k_(cat)= 1,2 min~(-1), which were within therange of the values for these constants for excision of other damaged bases by this enzyme. NEIL1 was inhibited byАl~(3+),Ni~CO~(2+),Сd~(Cu~(Zn~(and Fe~(2+)ions in Tris-HCl buffer, by Zn~2, Сu~(in potas-sium phosphate buffer. Fpg and Nei, the prokaryotic homologs of NEIL1, were inhibited by the same metal ions asNEIL1. The values of I_(50)for NEIL1 inhibition were 7 μM Cd~(2+),16μM Zn~(and 400 Сu~(2+).The inhi-bition of NEIL1 by Сd~(2 +), Zn~(2+),and Сu~(2+) was at least partly due to formation of metal—DNA complexes. In the caseof Сd~(2+) and Сu~(2+),which preferentially bind to DNA bases rather than phosphates, the presence of metal ions causedthe enzyme to lose the ability of preferential binding to damaged DNA. Therefore, the inhibition of NEIL1 activityin removal of oxidative lesions by heavy metal ions may be one of the reasons for their co-mutagenicity during oxida-tive stress.