Soon after its identification, utilizing bioinformatics tools, FTO was predicted to be a 2-oxyglutarate (2-OG) Fe(II) dependent demethylase, closely related to the bacterial DNA demethylase AlkB and the mammalian AlkB homologues 1 & 2 (ABH1 and ABH2).140 In vitro, recombinant FTO is able to catalyze the Fe(II)- and 2OG-dependent demethylation of 3-methylthymine in single-stranded DNA,140,141 as well as 3-methyluracil (3meU)140,141 and 6-methyl adenosine (6meA)142 in single-stranded RNA, suggesting a potential role for FTO in nucleic acid repair or modification. The crystal structure of FTO is available and shows an N-terminal catalytic domain and a C-terminal domain of unknown function.143 The catalytic pocket contains five obligate amino acid residues found in all members of this enzyme superfamily; two residues, a histidine (H) and an aspartic acid (D), required for binding Fe(II); and three residues, an H and two arginines (R) separated by six amino acids, required for 2OG binding.137,143 The specificity for single stranded nucleic acids is provided by an L1 loop, not present in other members of the AlkB family, which sterically hinders double stranded nucleic acids from entering the catalytic pocket.143
