Table 2. Glycosylases in humans and Drosophila.
| Human | Drosophila | Substratesa |
|---|---|---|
| UNG | — | U |
| SMUG1 | CG5825 | U and modified U |
| TDG | Thd1b | T and U mispaired with G |
| MBD4 | MBD-R2c | T and U mispaired with G |
| OGG1 | Ogg1 | 8-oxoG, FapyG |
| RPS3 | RpS3 | |
| NTH1 | CG9272 | FapyG, hoC, hoU, Tg, urea |
| NEIL1, 2, 3 | — | Similar to NTH1 |
| MYH | — | A:8-oxoG |
| MPG | — | 3-MeA, hypoxanthine |
FapyG, 2,6-diamino-4-oxo-5-formamidopyrimidine; fU, fluorouracil; hmU, 5-(hydroxymethyl)uracil; hoU, 5-hydroxyuracil; Tg, thymine glycol; 3-meA, 3-methyl-adenine.
The largest predicted isoform of human TDG is 452 residues, but it is larger in insects—four times as large in Schizophora. It appears to have been lost from the Muscoidea superfamily as well as the Nematocera suborder (mosquitoes).
MBD4 has an N-terminal methyl-CpG binding domain (MeCP), and a C-terminal endonuclease III domain. Proteins with homology to the endo III domain, but lacking a MeCP domain are found in several arthropods in which and a MeCP domain orthologous to MBD4 cannot be found. In Holometabola (at least) the apparent ortholog of the MBD4 MeCP domain is in the middle of a large protein that has an N-terminal THAP domain, followed by a Tudor domain, the MeCP domain, and then a PhD finger domain. No endonuclease domain is found, suggesting this may not be a glycosylase.