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Nature:清华大学陈柱成研究组揭示嗜热酵母ISWI蛋白的原子分辨率结构并揭示其分子机理

摘要 : 2016年12月6日,国际学术权威刊物自然出版集团《Nature》杂志在线发表了清华大学生命学院、结构生物学高精尖创新中心陈柱成研究组题为“Structure and regulation of the chromatin remodeller ISWI”的研究论文。

 2016年12月6日,国际学术权威刊物自然出版集团《Nature》杂志在线发表了清华大学生命学院、结构生物学高精尖创新中心陈柱成研究组题为“Structure and regulation of the chromatin remodeller ISWI”的研究论文。论文报道了研究人员通过X-ray晶体衍射的研究手段,解析了嗜热酵母的ISWI蛋白以及ISWI蛋白与组蛋白H4复合物的原子分辨率结构;结合相应的生化实验,揭示了ISWI蛋白的自抑制、被底物识别与激活以及感知接头DNA的长度,发挥染色质组装功能的分子机理。清华大学生命学院直博生严丽娟和硕士生王丽为论文的共同第一作者,陈柱成老师为通讯作者。

染色质是真核生物的生命蓝图。染色质重塑蛋白利用ATP水解的能量,改变染色质结构,参与生命蓝图的绘制和重绘。ISWI是多个染色质重塑复合物的催化亚基。ISWI驱动核小体在基因组DNA上滑动,调控基因转录、异染色质形成、X-染色体失活以及其它重要的染色质活动。ISWI蛋白的催化核心(图a,Core)是一个自主的染色质重塑分子机器,其运作受严格的调控。ISWI活性受到AutoN结构域和NegC结构域的抑制作用,确保ISWI分子机器在没有结合底物时不会消耗ATP的能量。这些抑制作用分别被底物核小体的组蛋白H4尾巴和接头DNA拮抗。然而,组蛋白H4的乙酰化修饰削弱其对ISWI激活。这些多层次的调控作用确保细胞形成正确的高级染色质结构, 保证正常的生命活动。

该论文揭示了ISWI的AutoN包含两个抑制元件(图b, L3 和 4),均与core2结合,使得ISWI处于抑制状态。组蛋白H4尾巴与core2的一个负电荷表面结合, 与其中一个AutoN抑制元件有竞争关系 (图c),从而解析了H4激活ISWI以及乙酰化作用细调ISWI活性的分子机理。另外,结合生化功能分析,该论文研究表明ISWI蛋白的NegC 与core2存在相互作用,这种相互作用是ISWI蛋白通过HSS结构域感知接头DNA长度、发挥染色质组装功能的分子基础 (图d-f)。本论文是陈柱成研究组关于染色质重塑蛋白系列工作的一个重要组成部分。

a) Domain architecture of ISWI. (b) Overall structure of ISWI. (c) Superimposition of the structures of the core2 domain in the peptide-bound (cyan) and the auto-inhibited (grey) states. H4 peptide, yellow; L3 loop, magenta. (d) Cartoon image of ISWI in the auto-inhibited state. The tethering HSS domain is omitted. (e) Proposed model of ISWI bound to the nucleosome with long linker DNA. The dotted line illustrates NegC under stressed condition. (f) Proposed model of ISWI bound to the nucleosome with short linker DNA, in which the Brace helix is partly disrupted and NegC binds to core2 intramolecularly. The HSS domain is omitted.

原文链接:

Structure and regulation of the chromatin remodeller ISWI

原文摘要:

ISWI is a member of the SWI2/SNF2 family of chromatin remodellers1, 2, which also includes Snf2, Chd1, and Ino80. ISWI is the catalytic subunit of several chromatin remodelling complexes, which mobilize nucleosomes along genomic DNA, promoting replication progression, transcription repression, heterochromatin formation, and many other nuclear processes3, 4, 5. The ATPase motor of ISWI is an autonomous remodelling machine6, wheras its carboxy (C)-terminal HAND–SAND–SLIDE (HSS) domain functions in binding extranucleosomal linker DNA7, 8, 9, 10. The activity of the catalytic core of ISWI is inhibited by the regulatory AutoN and NegC domains, which are in turn antagonized by the H4 tail and extranucleosomal DNA, respectively, to ensure the appropriate chromatin landscape in cells11. How AutoN and NegC inhibit ISWI and regulate its nucleosome-centring activity remains elusive. Here we report the crystal structures of ISWI from the thermophilic yeast Myceliophthora thermophila and its complex with a histone H4 peptide. Our data show the amino (N)-terminal AutoN domain contains two inhibitory elements, which collectively bind the second RecA-like domain (core2), holding the enzyme in an inactive conformation. The H4 peptide binds to the core2 domain coincident with one of the AutoN-binding sites, explaining the ISWI activation by H4. The H4-binding surface is conserved in Snf2 and functions beyond AutoN regulation. The C-terminal NegC domain is involved in binding to the core2 domain and functions as an allosteric element for ISWI to respond to the extranucleosomal DNA length.

来源: Nature 浏览次数:0

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