Dalhus Bjørn, Alseth Ingrun, Bjørås Magnar
Department of Medical Biochemistry, Institute for Clinical Medicine, University of Oslo, PO Box 4950, Nydalen, N-0424 Oslo, Norway; Department of Microbiology, Clinic for Diagnostics and Intervention, Oslo University Hospital, Rikshospitalet, PO Box 4950, Nydalen, N-0424 Oslo, Norway.
Department of Microbiology, Clinic for Diagnostics and Intervention, Oslo University Hospital, Rikshospitalet, PO Box 4950, Nydalen, N-0424 Oslo, Norway.
Prog Biophys Mol Biol. 2015 Mar;117(2-3):134-142. doi: 10.1016/j.pbiomolbio.2015.03.005. Epub 2015 Mar 28.
Deamination of the exocyclic amines in adenine, guanine and cytosine forms base lesions that may lead to mutations if not removed by DNA repair proteins. Prokaryotic endonuclease V (EndoV/Nfi) has long been known to incise DNA 3' to a variety of base lesions, including deaminated adenine, guanine and cytosine. Biochemical and genetic data implicate that EndoV is involved in repair of these deaminated bases. In contrast to DNA glycosylases that remove a series of modified/damaged bases in DNA by direct excision of the nucleobase, EndoV cleaves the DNA sugar phosphate backbone at the second phosphodiester 3' to the lesion without removing the deaminated base. Structural investigation of this unusual incision by EndoV has unravelled an enzyme with separate base lesion and active site pockets. A novel wedge motif was identified as a DNA strand-separation feature important for damage detection. Human EndoV appears inactive on DNA, but has been shown to incise various RNA substrates containing inosine. Inosine is the deamination product of adenosine and is frequently found in RNA. The structural basis for discrimination between DNA and RNA by human EndoV remains elusive.
腺嘌呤、鸟嘌呤和胞嘧啶中环外胺的脱氨基作用会形成碱基损伤，如果DNA修复蛋白不能将其清除，可能会导致突变。长期以来，人们一直知道原核内切酶V（EndoV/Nfi）能在包括脱氨基的腺嘌呤、鸟嘌呤和胞嘧啶在内的多种碱基损伤的3'端切割DNA。生化和遗传学数据表明EndoV参与了这些脱氨基碱基的修复。与通过直接切除核碱基来去除DNA中一系列修饰/损伤碱基的DNA糖基化酶不同，EndoV在损伤位点的第二个磷酸二酯键的3'端切割DNA糖磷酸主链，而不去除脱氨基碱基。对EndoV这种不寻常切割的结构研究揭示了一种具有独立碱基损伤口袋和活性位点口袋的酶。一种新的楔形基序被确定为对损伤检测很重要的DNA链分离特征。人EndoV似乎对DNA无活性，但已被证明能切割含有次黄嘌呤的各种RNA底物。次黄嘌呤是腺苷的脱氨基产物，在RNA中经常出现。人EndoV区分DNA和RNA的结构基础仍然不清楚。
