Enzyme kinetics of an alternative splicing isoform of mitochondrial 8-oxoguanine DNA glycosylase, ogg1-1b, and compared with the nuclear ogg1-1a.

Eight alternatively spliced isoforms of human 8-oxoguanine DNA glycosylase (OGG1) (OGG1-1a to -1c and -2a to -2e) are registered in the National Center for Biotechnology Information. OGG1(s) in mitochondria have not yet been fully characterized biochemically. In this study, we purified mitochondrial recombinant OGG1-1b protein and compared its activity with nuclear OGG1-1a protein. The reaction rate constant (kg ) of the 7,8-dihydro-8-oxoguanine (8-oxoG) glycosylase activity of OGG1-1b was 8-oxoG:C >> 8-oxoG:T >> 8-oxoG:G > 8-oxoG:A (7.96, 0.805, 0.070, and 0.015 min(-1) , respectively) and that of the N-glycosylase/DNA lyase activity (kgl ) of OGG1-1b was 8-oxoG:C > 8-oxoG:T ≃8-oxoG:G >> 8-oxoG:A (0.286, 0.079, 0.040, and negligible min(-1) , respectively). These reaction rate constants were similar to those of OGG1-1a except for kgl against 8-oxoG:A. APEX nuclease 1 was required to promote DNA strand breakage by OGG1-1b. These results suggest that OGG1-1b is associated with 8-oxoG cleavage in human mitochondria and that the mechanism of this repair is similar to that of nuclear OGG1-1a.