3月11日《结构》（Structure）杂志封面的图片背景是一个DNA依赖型的蛋白激酶分子（DNA-PKcs）的冷冻电镜图，而前景则为该图描绘出的亚纳米级的DNA依赖型的蛋白激酶分子。DNA双链断裂被公认为由DNA依赖型的蛋白激酶决定，DNA依赖型蛋白激酶的催化亚基是通过调节非同源末端连接通路来修复DNA的双链断链的。
在最新研究中，Williams等人运用冷冻电镜单粒子重建方法，以7?的分辨率测定了一个DNA依赖型蛋白激酶的结构。在此分辨率下，DNA依赖型的蛋白激酶中的α-螺旋分子结构和双链DNA末端的结合位点清晰可见。DNA-PKcs的结构由贯穿分子的密度棒组成，这些密度棒显示出α螺旋结构，这是在低分辨率电镜中观察不到的结构特征。DNA依赖型蛋白激酶结构中对接的同源性模型表明，多达8个螺旋结构的HEAT重复图案与密度图完全吻合。
令人惊讶的是，在这样高的分辨率下，虽然实际的空间已经精细地显示出底部是最适合的位置，但该激酶的结构域却可以分别进入分子的顶或底部。这个关于DNA与DNA依赖型蛋白激酶相互作用的模型表明，双链DNA的其中一条链可以进入了中间的通道并与凸出α-螺旋进行相互作用。（科学网 武彦文/编译）
生物谷推荐原始出处：
（Structure），Vol 16, 468-477, 11 March 2008，Dewight R. Williams, Phoebe L. Stewart
Cryo-EM Structure of the DNA-Dependent Protein Kinase Catalytic Subunit at Subnanometer Resolution Reveals α Helices and Insight into DNA Binding
Dewight R. Williams,1 Kyung-Jong Lee,2 Jian Shi,1 David J. Chen,2 and Phoebe L. Stewart1,
1 Department of Molecular Physiology and Biophysics, Vanderbilt University Medical Center, Nashville, TN 37232, USA
2 Molecular Radiation Biology Division, Department of Radiation Oncology, UT Southwestern Medical Center at Dallas, Dallas, Texas 75390, USA
Summary
The DNA-dependent protein kinase catalytic subunit (DNA-PKcs) regulates the nonhomologous end joining pathway for repair of double-stranded DNA (dsDNA) breaks. Here, we present a 7Å resolution structure of DNA-PKcs determined by cryo-electron microscopy single-particle reconstruction. This structure is composed of density rods throughout the molecule that are indicative of α helices and reveals structural features not observed in lower resolution EM structures. Docking of homology models into the DNA-PKcs structure demonstrates that up to eight helical HEAT repeat motifs fit well within the density. Surprisingly, models for the kinase domain can be docked into either the crown or base of the molecule at this resolution, although real space refinement suggests that the base location is the best fit. We propose a model for the interaction of DNA with DNA-PKcs in which one turn of dsDNA enters the central channel and interacts with a resolved α-helical protrusion.
