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AP endonuclease
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.
There are four types of AP endonucleases that have been classified according to their sites of incision. Class I and class II AP endonucleases incise DNA at the phosphate groups 3´ and 5´ to the baseless site leaving 3´-OH and 5´-phosphate termini. Class III and class IV AP endonucleases also cleave DNA at the phosphate groups 3´ and 5´to the baseless site, but they generate a 3´-phosphate and a 5´-OH.
Human AP Endonuclease (APE1), like most AP endonucleases, is of class II and requires an Mg2+ in its active site in order to carry out its role in base excision repair. The yeast homolog of this enzyme is APN1.
== Structure of APE1 ==
APE1 contains several amino acid residues that enable it to react selectively with AP sites. Three APE1 residues (Arg73, Ala74, and Lys78) contact three consecutive DNA phosphates on the strand opposite the one containing the AP site while Tyr128 and Gly127 span and widen the minor groove, anchoring the DNA for the extreme kinking caused by the interaction between positive residues found in four loops and one α-helix and the negative phosphate groups found in the phosphodiester backbone of DNA.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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