Biochemical Analysis of DNA Glycosylase in Dragonfish (Scleropages Formosus, Sfo) TDG

TDG, which is a member of the uracil DNA glycosylase superfamily, plays a critical role in the active demethylation process in mammals by removing oxidized derivatives of 5-methylcytosine (mC). While human TDG has been extensively studied and found to possess 5-formylcytosine and 5-carboxylcytosine DNA glycosylase activity, little is known regarding this demethylation process in vertebrates other than the human species. Previous research proposed a catalytic sequence in motif 1 of zebrafish TDG1 and TDG2 that modulates DNA glycosylase activity based on mutational, kinetic, and modeling analyses of these enzymes. Building on this work, researchers discovered that the Sfo TDG is an exclusive 5-carboxylcytosine-glycosylase and that a strong correlation exists between the -IGHHYPN- of motif 1 and this activity. By converting I190-H192 within -IGHHYPN- to K190-R192, researchers were able to oppose the decrease in 5-carboxylcytosine activity from the single mutagenesis of I190K and H192R, reaffirming the heavy correlation existing between these residues. Since I190K-H192R maintain such a strong correlation, the Sfo structure was predicted and displayed the role of this double positive mutation in positioning the adjacent H193 to stabilize the leaving group in the transition state of catalysis.The study expanded our knowledge of TDG catalyzation in other species besides human and has important implications in studying protein structural determinants and their functions