Burkovics Peter, Szukacsov Valeria, Unk Ildiko, Haracska Lajos
Institute of Genetics, Biological Research Center, Hungarian Academy of Sciences, Temesvari krt. 62, Szeged, H-6701, Hungary.
Nucleic Acids Res. 2006 May 10;34(9):2508-15. doi: 10.1093/nar/gkl259. Print 2006.
DNA damage, such as abasic sites and DNA strand breaks with 3'-phosphate and 3'-phosphoglycolate termini present cytotoxic and mutagenic threats to the cell. Class II AP endonucleases play a major role in the repair of abasic sites as well as of 3'-modified termini. Human cells contain two class II AP endonucleases, the Ape1 and Ape2 proteins. Ape1 possesses a strong AP-endonuclease activity and weak 3'-phosphodiesterase and 3'-5' exonuclease activities, and it is considered to be the major AP endonuclease in human cells. Much less is known about Ape2, but its importance is emphasized by the growth retardation and dyshematopoiesis accompanied by G2/M arrest phenotype of the APE2-null mice. Here, we describe the biochemical characteristics of human Ape2. We find that Ape2 exhibits strong 3'-5' exonuclease and 3'-phosphodiesterase activities and has only a very weak AP-endonuclease activity. Mutation of the active-site residue Asp 277 to Ala in Ape2 inactivates all these activities. We also demonstrate that Ape2 preferentially acts at mismatched deoxyribonucleotides at the recessed 3'-termini of a partial DNA duplex. Based on these results we suggest a novel role for human Ape2 as a 3'-5' exonuclease.
DNA损伤，如无碱基位点以及带有3'-磷酸和3'-磷酸乙醇酸末端的DNA链断裂，会对细胞产生细胞毒性和致突变威胁。II类AP核酸内切酶在无碱基位点以及3'-修饰末端的修复中起主要作用。人类细胞含有两种II类AP核酸内切酶，即Ape1和Ape2蛋白。Ape1具有很强的AP核酸内切酶活性以及较弱的3'-磷酸二酯酶和3'-5'核酸外切酶活性，被认为是人类细胞中的主要AP核酸内切酶。人们对Ape2了解较少，但APE2基因敲除小鼠出现的生长迟缓和造血异常并伴有G2/M期阻滞表型，凸显了其重要性。在此，我们描述了人类Ape2的生化特性。我们发现Ape2具有很强的3'-5'核酸外切酶和3'-磷酸二酯酶活性，而AP核酸内切酶活性非常弱。将Ape2中的活性位点残基天冬氨酸277突变为丙氨酸会使所有这些活性丧失。我们还证明，Ape2优先作用于部分DNA双链体凹陷3'-末端处错配的脱氧核糖核苷酸。基于这些结果，我们提出人类Ape2作为一种3'-5'核酸外切酶具有新的作用。
