AP endonuclease
![Ribbon diagram of APE1.
PDB = 1de9.[1]](/Images/godic/202412/21/ApEndonuclease11618.jpg")
![Positive residues on the surface of the APE1 protein (in blue) anchor and bend DNA though interactions with DNA's negative phosphate groups. PDB 1de9.[1]](/Images/godic/202412/21/APE1DNABend1618.jpg")
![Hydrogen bonding among key amino acid residues help stabilize active site structure. Moreover, a negatively charged residue (Glu 96) helps hold the Mg2+ also needed to stabilize the AP site in place PDB 1de9.[1]](/Images/godic/202412/21/APE1activelabeled1618.JPG")
![](/Images/godic/202412/21/MechanismAPE1colour_2.svg1618.png")
Apurinic/apyrimidinic (AP) endonuclease (BRENDA = 4.2.99.18) is an enzyme that is involved in the DNA base excision repair pathway (BER). Its main role in the repair of damaged or mismatched nucleotides in DNA is to create a nick in the phosphodiester backbone of the AP site created when DNA glycosylase removes the damaged base.