Chiu C Y, Cary R B, Chen D J, Peterson S R, Stewart P L
Department of Molecular and Medical Pharmacology, Crump Institute for Biological Imaging, UCLA School of Medicine, Los Angeles, CA 90095, USA.
J Mol Biol. 1998 Dec 11;284(4):1075-81. doi: 10.1006/jmbi.1998.2212.
The DNA-dependent protein kinase (DNA-PK) plays an important role in mammalian DNA double-strand break repair and immunoglobulin gene rearrangement. The DNA-PK holoenzyme is activated by assembly at DNA ends and is comprised of DNA-PKcs, a 460 kDa protein kinase catalytic subunit, and Ku, a 70 kDa/80 kDa heterodimeric DNA-targeting component. We have solved the three-dimensional structure of DNA-PKcs to approximately 21 A resolution by analytically combining images of nearly 9500 individual particles extracted from cryo-electron micrographs. The DNA-PKcs protein has an open, pseudo 2-fold symmetric structure with a gap separating a crown-shaped top from a rounded base. Columns of density are observed to protrude into the gap from both the crown and the base. Measurements of the enclosed volume indicate that the interior of the protein is largely hollow. The structure of DNA-PKcs suggests that its association with DNA may involve the internalization of double-stranded ends.
DNA依赖性蛋白激酶（DNA-PK）在哺乳动物DNA双链断裂修复和免疫球蛋白基因重排中起重要作用。DNA-PK全酶通过在DNA末端组装而被激活，它由DNA-PKcs（一种460 kDa的蛋白激酶催化亚基）和Ku（一种70 kDa/80 kDa异二聚体DNA靶向成分）组成。我们通过分析组合从冷冻电子显微照片中提取的近95,000个单独颗粒的图像，将DNA-PKcs的三维结构解析到约21埃的分辨率。DNA-PKcs蛋白具有开放的、近似2倍对称的结构，在一个冠状顶部和一个圆形底部之间有一个间隙。观察到密度柱从冠状和底部都突出到间隙中。对封闭体积的测量表明，该蛋白的内部大部分是中空的。DNA-PKcs的结构表明，它与DNA的结合可能涉及双链末端的内化。
