3月11日《結構》（Structure）雜志封面的圖片背景是一個DNA依賴型的蛋白激酶分子（DNA-PKcs）的冷凍電鏡圖，而前景則為該圖描繪出的亞納米級的DNA依賴型的蛋白激酶分子,。DNA雙鏈斷裂被公認為由DNA依賴型的蛋白激酶決定,，DNA依賴型蛋白激酶的催化亞基是通過調節(jié)非同源末端連接通路來修復DNA的雙鏈斷鏈的。
在最新研究中,，Williams等人運用冷凍電鏡單粒子重建方法,，以7?的分辨率測定了一個DNA依賴型蛋白激酶的結構。在此分辨率下,，DNA依賴型的蛋白激酶中的α-螺旋分子結構和雙鏈DNA末端的結合位點清晰可見,。DNA-PKcs的結構由貫穿分子的密度棒組成，這些密度棒顯示出α螺旋結構,，這是在低分辨率電鏡中觀察不到的結構特征,。DNA依賴型蛋白激酶結構中對接的同源性模型表明，多達8個螺旋結構的HEAT重復圖案與密度圖完全吻合,。
令人驚訝的是,，在這樣高的分辨率下，雖然實際的空間已經精細地顯示出底部是最適合的位置,，但該激酶的結構域卻可以分別進入分子的頂或底部,。這個關于DNA與DNA依賴型蛋白激酶相互作用的模型表明，雙鏈DNA的其中一條鏈可以進入了中間的通道并與凸出α-螺旋進行相互作用,。（科學網 武彥文/編譯）
生物谷推薦原始出處：
（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.
