Oxoguanine Glycosylase - Function

Function

OGG1 is the primary enzyme responsible for the excision of 7,8-dihydro-8-oxoguanine (8-oxoG), a mutagenic base byproduct that occurs as a result of exposure to reactive oxygen species (ROS). OGG1 is a bifunctional glycosylase, as it is able to both cleave the glycosidic bond of the mutagenic lesion and cause a strand break in the DNA backbone. Alternative splicing of the C-terminal region of this gene classifies splice variants into two major groups, type 1 and type 2, depending on the last exon of the sequence. Type 1 alternative splice variants end with exon 7 and type 2 end with exon 8. All variants have the N-terminal region in common. Many alternative splice variants for this gene have been described, but the full-length nature for every variant has not been determined. In eukaryotes, the N-terminus of this gene contains a mitochondrial targeting signal, essential for mitochondrial localization. A conserved N-terminal domain contributes residues to the 8-oxoguanine binding pocket. This domain is organised into a single copy of a TBP-like fold.

Despite the presumed importance of this enzyme, mice lacking Ogg1 have been generated and found to have a normal lifespan, and despite some early reports, do not show increased mutagenesis or cancer incidence. Interestingly, mice lacking Ogg1 have been shown to be prone to increased body weight and obesity, as well as high-fat diet induced insulin resistance. There is some controversy as to whether deletion of Ogg1 actually leads to increased 8-oxo-dG levels: the HPLC-EC assay suggests up to 6 fold higher levels of 8-oxo-dG in nuclear DNA and 20-fold higher in mitochondrial DNA whereas the fappy-glycosylase assay indicates no change.