Bending and looping of long DNA by Polycomb repressive complex 2 revealed by AFM imaging in liquid
Bending and looping of long DNA by Polycomb repressive complex 2 revealed by AFM imaging in liquid
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DOI：
10.1093/nar/gkaa073
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发表时间：
2020-04-06
影响因子：
14.9
通讯作者：
Perkins, Thomas T.
中科院分区：
文献类型：
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作者：
Heenan, Patrick R.;Wang, Xueyin;Perkins, Thomas T.
Polycomb 抑制复合物 2 (PRC2) 是一种组蛋白甲基转移酶，可在赖氨酸 27 处甲基化组蛋白 H3。PRC2 对于表观遗传基因沉默、细胞分化和兼性异染色质的形成至关重要。它还可以促进或抑制肿瘤发生。尽管具有如此重要的意义，但 PRC2 压缩染色质的分子机制仍相对未得到充分研究。在这里，我们使用原子力显微镜在单分子水平上可视化了 PRC2 与液体中裸露 DNA 的结合。对所得图像的分析显示，PRC2 由五个亚基（EZH2、EED、SUZ12、AEBP2 和 RBBP4）组成，与 2.5 kb DNA 结合，表观解离常数 (K-D(app)) 为 150 +/- 12 nM。 PRC2 没有表现出与嵌入如此长的 DNA 底物中的 CpG 岛的高 GC 含量 (76%) 区域的序列特异性结合。在较高浓度下，PRC2 通过形成通常由两个或多个 PRC2 分子锚定的 DNA 环来压缩 DNA。此外，PRC2 结合导致 DNA 螺旋骨架的局部弯曲增加 3 倍，但没有证据表明 DNA 包裹在蛋白质周围。我们认为，PRC2 使 DNA 弯曲和成环，与 PRC2 的甲基化活性无关，可能有助于异染色质形成，从而导致表观遗传基因沉默。
Polycomb repressive complex 2 (PRC2) is a histone methyltransferase that methylates histone H3 at Lysine 27. PRC2 is critical for epigenetic gene silencing, cellular differentiation and the formation of facultative heterochromatin. It can also promote or inhibit oncogenesis. Despite this importance, the molecular mechanisms by which PRC2 compacts chromatin are relatively understudied. Here, we visualized the binding of PRC2 to naked DNA in liquid at the singlemolecule level using atomic force microscopy. Analysis of the resulting images showed PRC2, consisting of five subunits (EZH2. EED, SUZ12, AEBP2 and RBBP4), bound to a 2.5-kb DNA with an apparent dissociation constant (K-D(app)) of 150 +/- 12 nM. PRC2 did not show sequence-specific binding to a region of high GC content (76%) derived from a CpG island embedded in such a long DNA substrate. At higher concentrations, PRC2 compacted DNA by forming DNA loops typically anchored by two or more PRC2 molecules. Additionally, PRC2 binding led to a 3-fold increase in the local bending of DNA's helical backbone without evidence of DNA wrapping around the protein. We suggest that the bending and looping of DNA by PRC2, independent of PRC2's methylation activity, may contribute to heterochromatin formation and therefore epigenetic gene silencing.