Morinière Jeanne, Rousseaux Sophie, Steuerwald Ulrich, Soler-López Montserrat, Curtet Sandrine, Vitte Anne-Laure, Govin Jérôme, Gaucher Jonathan, Sadoul Karin, Hart Darren J, Krijgsveld Jeroen, Khochbin Saadi, Müller Christoph W, Petosa Carlo
European Molecular Biology Laboratory, Grenoble Outstation, 6 rue Jules Horowitz, BP 181, 38042 Grenoble Cedex 9, France.
Nature. 2009 Oct 1;461(7264):664-8. doi: 10.1038/nature08397.
A key step in many chromatin-related processes is the recognition of histone post-translational modifications by effector modules such as bromodomains and chromo-like domains of the Royal family. Whereas effector-mediated recognition of single post-translational modifications is well characterized, how the cell achieves combinatorial readout of histones bearing multiple modifications is poorly understood. One mechanism involves multivalent binding by linked effector modules. For example, the tandem bromodomains of human TATA-binding protein-associated factor-1 (TAF1) bind better to a diacetylated histone H4 tail than to monoacetylated tails, a cooperative effect attributed to each bromodomain engaging one acetyl-lysine mark. Here we report a distinct mechanism of combinatorial readout for the mouse TAF1 homologue Brdt, a testis-specific member of the BET protein family. Brdt associates with hyperacetylated histone H4 (ref. 7) and is implicated in the marked chromatin remodelling that follows histone hyperacetylation during spermiogenesis, the stage of spermatogenesis in which post-meiotic germ cells mature into fully differentiated sperm. Notably, we find that a single bromodomain (BD1) of Brdt is responsible for selectively recognizing histone H4 tails bearing two or more acetylation marks. The crystal structure of BD1 bound to a diacetylated H4 tail shows how two acetyl-lysine residues cooperate to interact with one binding pocket. Structure-based mutagenesis that reduces the selectivity of BD1 towards diacetylated tails destabilizes the association of Brdt with acetylated chromatin in vivo. Structural analysis suggests that other chromatin-associated proteins may be capable of a similar mode of ligand recognition, including yeast Bdf1, human TAF1 and human CBP/p300 (also known as CREBBP and EP300, respectively). Our findings describe a new mechanism for the combinatorial readout of histone modifications in which a single effector module engages two marks on a histone tail as a composite binding epitope.
许多与染色质相关的过程中的一个关键步骤是效应器模块对组蛋白翻译后修饰的识别，比如皇家家族的溴结构域和类染色质结构域。虽然效应器介导的对单个翻译后修饰的识别已得到充分表征，但细胞如何实现对带有多种修饰的组蛋白进行组合式读出却知之甚少。一种机制涉及相连的效应器模块的多价结合。例如，人TATA结合蛋白相关因子1（TAF1）的串联溴结构域与双乙酰化的组蛋白H4尾巴的结合比与单乙酰化尾巴的结合更好，这种协同效应归因于每个溴结构域与一个乙酰化赖氨酸标记结合。在此，我们报道了小鼠TAF1同源物Brdt（BET蛋白家族的睾丸特异性成员）的一种不同的组合式读出机制。Brdt与高度乙酰化的组蛋白H4相关（参考文献7），并参与精子发生过程中组蛋白高度乙酰化后显著的染色质重塑，精子发生是减数分裂后生殖细胞成熟为完全分化精子的阶段。值得注意的是，我们发现Brdt的单个溴结构域（BD1）负责选择性识别带有两个或更多乙酰化标记的组蛋白H4尾巴。与双乙酰化H4尾巴结合的BD1的晶体结构展示了两个乙酰化赖氨酸残基如何协同与一个结合口袋相互作用。基于结构的诱变降低了BD1对双乙酰化尾巴的选择性，这在体内破坏了Brdt与乙酰化染色质的结合。结构分析表明，其他与染色质相关的蛋白质可能也能够进行类似的配体识别模式，包括酵母Bdf1、人TAF1和人CBP/p300（分别也称为CREBBP和EP300）。我们的研究结果描述了一种组蛋白修饰组合式读出的新机制，其中单个效应器模块将组蛋白尾巴上的两个标记作为复合结合表位进行结合。
