Molecular architecture of human polycomb repressive complex 2.
Molecular architecture of human polycomb repressive complex 2.
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DOI：
10.7554/elife.00005
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发表时间：
2012-10-30
期刊：
影响因子：
7.7
通讯作者：
Nogales E
中科院分区：
文献类型：
--
作者：
Ciferri C;Lander GC;Maiolica A;Herzog F;Aebersold R;Nogales E
多梳抑制复合物2（PRC2）是基因沉默所必需的，通过三甲基化组蛋白H3的赖氨酸27来建立特定基因的转录抑制，这是一个由辅因子如AEBP 2介导的过程。尽管它的生物学重要性，很少有人知道PRC2的结构和亚基组织。在这里，我们提出了第一个三维电子显微镜结构的人PRC2复合物结合其辅因子AEBP 2。使用一种新的内部蛋白质标记方法，结合同位素化学交联和质谱，我们已经定位了所有PRC2亚基及其功能域，并生成了详细的相互作用图。AEBP 2的位置和稳定作用表明该辅因子在调节基因沉默中的变构作用。PRC2中与修饰的组蛋白尾部相互作用的区域位于甲基转移酶位点附近，表明PRC2活性的基于染色质的调节的分子机制。DOI：www.example.com蛋白质复合物（包含两种或多种蛋白质的稳定结构）在与基因表达相关的生化过程中发挥着重要作用。有些有助于沉默基因，而另一些则参与基因的激活。这种复合物的重要性是由以下事实强调的：如果小鼠不具有被称为Polycomb Repressive Complex 2（简称PRC2）的蛋白质复合物，则小鼠在胚胎时死亡，或者出生时具有严重缺陷。众所周知，这种复合物的核心是由四种不同的蛋白质组成的，从果蝇到人类，其中两种蛋白质的结构已经用原子精度确定。还已知PRC2需要特定的蛋白质辅因子（称为AEBP 2）来执行该功能。此外，已经确定PRC2通过将两个或三个甲基（CH3）基团添加到DNA链在细胞核中缠绕的蛋白质（组蛋白H3）中的一个特定氨基酸（赖氨酸27）来沉默基因。然而，尽管它在生物学上很重要，但对PRC2的详细结构知之甚少。Ciferri等人通过使用电子显微镜产生与其辅因子结合的人类PRC2复合物的第一个三维图像，揭示了这种复合物的结构。通过将各种蛋白质标签整合到辅因子和PRC2的四个亚基中，并采用质谱和其他技术，Ciferri等人能够在PRC2-辅因子系统中鉴定出大约60个相互作用位点，并确定它们在整个结构中的位置。结果表明，辅因子通过在中心铰链点与复合物结合来稳定复合物的结构。特别是，PRC2内与组蛋白标记物相互作用的蛋白质结构域靠近转移甲基的位点，这有助于解释PRC2复合物的基因沉默活性是如何调节的。这些结果应该为更全面地了解PRC2及其辅因子如何能够沉默基因铺平道路。DOI：www.example.com网站
Polycomb Repressive Complex 2 (PRC2) is essential for gene silencing, establishing transcriptional repression of specific genes by tri-methylating Lysine 27 of histone H3, a process mediated by cofactors such as AEBP2. In spite of its biological importance, little is known about PRC2 architecture and subunit organization. Here, we present the first three-dimensional electron microscopy structure of the human PRC2 complex bound to its cofactor AEBP2. Using a novel internal protein tagging-method, in combination with isotopic chemical cross-linking and mass spectrometry, we have localized all the PRC2 subunits and their functional domains and generated a detailed map of interactions. The position and stabilization effect of AEBP2 suggests an allosteric role of this cofactor in regulating gene silencing. Regions in PRC2 that interact with modified histone tails are localized near the methyltransferase site, suggesting a molecular mechanism for the chromatin-based regulation of PRC2 activity. DOI: http://dx.doi.org/10.7554/eLife.00005.001 Protein complexes—stable structures that contain two or more proteins—have an important role in the biochemical processes that are associated with the expression of genes. Some help to silence genes, whereas others are involved in the activation of genes. The importance of such complexes is emphasized by the fact that mice die as embryos, or are born with serious defects, if they do not possess the protein complex known as Polycomb Repressive Complex 2, or PRC2 for short. It is known that the core of this complex, which is found in species that range from Drosophila to humans, is composed of four different proteins, and that the structures of two of these have been determined with atomic precision. It is also known that PRC2 requires a particular protein co-factor (called AEBP2) to perform this function. Moreover, it has been established that PRC2 silences genes by adding two or three methyl (CH3) groups to a particular amino acid (Lysine 27) in one of the proteins (histone H3) that DNA strands wrap around in the nucleus of cells. However, despite its biological importance, little is known about the detailed architecture of PRC2. Ciferri et al. shed new light on the structure of this complex by using electron microscopy to produce the first three-dimensional image of the human PRC2 complex bound to its cofactor. By incorporating various protein tags into the co-factor and the four subunits of the PRC2, and by employing mass spectrometry and other techniques, Ciferri et al. were able to identify 60 or so interaction sites within the PRC2-cofactor system, and to determine their locations within the overall structure. The results show that the cofactor stabilizes the architecture of the complex by binding to it at a central hinge point. In particular, the protein domains within the PRC2 that interact with the histone markers are close to the site that transfer the methyl groups, which helps to explain how the gene silencing activity of the PRC2 complex is regulated. The results should pave the way to a more complete understanding of how PRC2 and its cofactor are able to silence genes. DOI: http://dx.doi.org/10.7554/eLife.00005.002