Histone acetyltransferase (HAT)- and histone deacetylase (HDAC)-mediated histone acetylation and deacetylation regulate nucleosome dynamics and gene expression. HDACs are classified into different families, with HD-tuins or HDTs being specific to plants. HDTs show some sequence similarity to nucleoplasmins, the histone chaperones that aid in binding, storing, and loading H2A/H2B dimers to assemble nucleosomes. Here, we solved the crystal structure of the N-terminal domain (NTD) of all four HDTs (HDT1, HDT2, HDT3, and HDT4) from Arabidopsis (Arabidopsis thaliana). The NTDs form a nucleoplasmin fold, exist as pentamers in solution, and are resistant to protease treatment, high temperature, salt, and urea conditions. Structurally, HDTs do not form a decamer, unlike certain classical nucleoplasmins. The HDT-NTD requires an additional A2 acidic tract C-terminal to the nucleoplasmin domain for interaction with histone H3/H4 and H2A/H2B oligomers. We also report the in-solution structures of HDT2 pentamers in complex with histone oligomers. Our study provides a detailed structural and in vitro functional characterization of HDTs, revealing them to be nucleoplasmin family histone chaperones. The experimental confirmation that HDTs are nucleoplasmins may spark new interest in this enigmatic family of proteins.

中文翻译：

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植物特异性 HDT 家族组蛋白脱乙酰酶是核蓝蛋白。

组蛋白乙酰转移酶 (HAT) 和组蛋白脱乙酰酶 (HDAC) 介导的组蛋白乙酰化和脱乙酰化调节核小体动力学和基因表达。HDAC 分为不同的家族，其中 HD-tuins 或 HDT 是植物特有的。HDT 显示出与核蓝蛋白（有助于结合、存储和加载 H2A/H2B 二聚体以组装核小体的组蛋白伴侣）的某些序列相似性。在这里，我们解析了来自拟南芥（Arabidopsis thaliana）的所有四种HDT（HDT1、HDT2、HDT3和HDT4）的N端结构域（NTD）的晶体结构。NTD 形成核蓝蛋白折叠，在溶液中以五聚体形式存在，并且对蛋白酶处理、高温、盐和尿素条件具有抵抗力。从结构上讲，HDT 不形成十聚体，这与某些经典核蓝蛋白不同。HDT-NTD 需要核纤蛋白结构域有一个额外的 A2 酸性束 C 端，以便与组蛋白 H3/H4 和 H2A/H2B 寡聚体相互作用。我们还报告了 HDT2 五聚体与组蛋白寡聚体复合物的溶液内结构。我们的研究提供了 HDT 的详细结构和体外功能表征，揭示它们是核浆蛋白家族组蛋白伴侣。HDT 是核蓝蛋白的实验证实可能会激发人们对这一神秘蛋白质家族的新兴趣。