The C-terminal alphaO helix of human Ogg1 is essential for 8-oxoguanine DNA glycosylase activity: the mitochondrial beta-Ogg1 lacks this domain and does not have glycosylase activity.
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; alpha-Ogg1, which mainly localizes to the nucleus and beta-Ogg1, which localizes only to mitochondria. We recently showed that mitochondria from rho(0) cells, which lack mitochondrial DNA, have similar 8-oxoG DNA glycosylase activity to that of wild-type cells. Here, we show that beta-Ogg1 protein levels are approximately 80% reduced in rho(0) cells, suggesting beta-Ogg1 is not responsible for 8-oxoG incision in mitochondria. Thus, we characterized the biochemical properties of recombinant beta-Ogg1. Surprisingly, recombinant beta-Ogg1 did not show any significant 8-oxoG DNA glycosylase activity in vitro. Since beta-Ogg1 lacks the C-terminal alphaO helix present in alpha-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 alphaO helix is absolutely necessary for 8-oxoG DNA glycosylase activity, and thus its absence may explain why beta-Ogg1 does not catalyze 8-oxoG incision in vitro. Western blot analysis revealed the presence of significant amounts of alpha-Ogg1 in human mitochondria. Together with previous localization studies in vivo, this suggests that alpha-Ogg1 protein may provide the 8-oxoG DNA glycosylase activity for the repair of these lesions in human mitochondrial DNA. beta-Ogg1 may play a novel role in human mitochondria.
Hashiguchi
K
K
Laboratory of Molecular Gerontology, National Institute of Aging-IRP, National Institutes of Health, Box1, 5600 Nathan Shock Drive, Baltimore, MD 21224, USA.
Stuart
J A
JA
de Souza-Pinto
N C
NC
Bohr
V A
VA
D000595:Amino Acid Sequence; D045647:DNA Glycosylases / Q000737:chemistry* / Q000378:metabolism*; D006147:Guanine / Q000031:analogs & derivatives* / Q000378:metabolism*; D006801:Humans; D008928:Mitochondria / Q000201:enzymology*; D024101:Mitochondrial Proteins / Q000737:chemistry* / Q000378:metabolism*; D008969:Molecular Sequence Data; D010649:Phenylalanine / Q000737:chemistry; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary
D024101:Mitochondrial Proteins; D010649:Phenylalanine; C024829:8-hydroxyguanine; D006147:Guanine; D045647:DNA Glycosylases; C479058:oxoguanine glycosylase 1, human