Published online 19 October 2004
Nucleic Acids Research, Vol. 32 No. 18 © Oxford University Press 2004; all rights reserved
The C-terminal 
O helix of human Ogg1 is essential for 8-oxoguanine DNA glycosylase activity: the mitochondrial ß-Ogg1 lacks this domain and does not have glycosylase activity
Laboratory of Molecular Gerontology, National Institute of Aging-IRP, National Institutes of Health, Box1, 5600 Nathan Shock Drive, Baltimore, MD 21224, USA
* To whom correspondence should be addressed. Tel: +1 410 558 8162; Fax: +1 410 558 8157; Email: vbohr{at}nih.gov
Present address: J. A. Stuart, Department of Biology, Brock University, St Catharines, Ontario, Canada L2S 3A1
Received July 28, 2004; Revised and Accepted September 14, 2004
The human Ogg1 glycosylase is responsible for repairing 8-oxo-7,8-dihydroguanine (8-oxoG) in both nuclear and mitochondrial DNA. Two distinct Ogg1 isoforms are present; 
-Ogg1, which mainly localizes to the nucleus and ß-Ogg1, which localizes only to mitochondria. We recently showed that mitochondria from 
0 cells, which lack mitochondrial DNA, have similar 8-oxoG DNA glycosylase activity to that of wild-type cells. Here, we show that ß-Ogg1 protein levels are 
80% reduced in 0 cells, suggesting ß-Ogg1 is not responsible for 8-oxoG incision in mitochondria. Thus, we characterized the biochemical properties of recombinant ß-Ogg1. Surprisingly, recombinant ß-Ogg1 did not show any significant 8-oxoG DNA glycosylase activity in vitro. Since ß-Ogg1 lacks the C-terminal O helix present in -Ogg1, we generated mutant proteins with various amino acid substitutions in this domain. Of the seven amino acid positions substituted (317–323), we identified Val-317 as a novel critical residue for 8-oxoG binding and incision. Our results suggest that the O helix is absolutely necessary for 8-oxoG DNA glycosylase activity, and thus its absence may explain why ß-Ogg1 does not catalyze 8-oxoG incision in vitro. Western blot analysis revealed the presence of significant amounts of -Ogg1 in human mitochondria. Together with previous localization studies in vivo, this suggests that -Ogg1 protein may provide the 8-oxoG DNA glycosylase activity for the repair of these lesions in human mitochondrial DNA. ß-Ogg1 may play a novel role in human mitochondria.
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