PDF(Pubmed)
Abstract：
Linker histones play an essential role in chromatin packaging by facilitating compaction of the 11-nm fiber of nucleosomal \"beads on a string.\" The result is a heterogeneous condensed state with local properties that range from dynamic, irregular, and liquid-like to stable and regular structures (the 30-nm fiber), which in turn impact chromatin-dependent activities at a fundamental level. The properties of the condensed state depend on the type of linker histone, particularly on the highly disordered C-terminal tail, which is the most variable region of the protein, both between species, and within the various subtypes and cell-type specific variants of a given organism. We have developed an in vitro model system comprising linker histone tail and linker DNA, which although very minimal, displays surprisingly complex behavior, and is sufficient to model the known states of linker histone-condensed chromatin: disordered \"fuzzy\" complexes (\"open\" chromatin), dense liquid-like assemblies (dynamic condensates), and higher-order structures (organized 30-nm fibers). A crucial advantage of such a simple model is that it allows the study of the various condensed states by NMR, circular dichroism, and scattering methods. Moreover, it allows capture of the thermodynamics underpinning the transitions between states through calorimetry. We have leveraged this to rationalize the distinct condensing properties of linker histone subtypes and variants across species that are encoded by the amino acid content of their C-terminal tails. Three properties emerge as key to defining the condensed state: charge density, lysine/arginine ratio, and proline-free regions, and we evaluate each separately using a strategic mutagenesis approach.
摘要：
接头组蛋白在染色质包装中起着至关重要的作用，它可以促进字符串上11nm核小体珠的纤维压实。“结果是具有局部属性的异质凝聚状态，范围从动态，不规则,和液体状的稳定和规则的结构（30纳米的光纤），这反过来又在基础水平上影响染色质依赖性活动。凝聚态的性质取决于接头组蛋白的类型，特别是在高度无序的C端尾部，这是蛋白质中最可变的区域，物种之间，并且在给定生物体的各种亚型和细胞类型特异性变体中。我们开发了一种体外模型系统，包括接头组蛋白尾和接头DNA，虽然很小，表现出惊人的复杂行为，并且足以模拟接头组蛋白凝聚染色质的已知状态：无序的“模糊”复合物（“开放”染色质），致密的液体状组件(动态冷凝物)，和高阶结构（有组织的30纳米纤维）。这种简单模型的一个关键优点是它允许通过NMR研究各种凝聚态，圆二色性,和散射方法。此外，它允许通过量热法捕获支撑状态之间转变的热力学。我们利用这一点来合理化接头组蛋白亚型和变体在物种中的不同缩合特性，这些特性由其C末端尾部的氨基酸含量编码。三个属性成为定义凝聚态的关键：电荷密度，赖氨酸/精氨酸比，和无脯氨酸区域，我们使用战略诱变方法分别评估每个。
