Structural Biology and Bioinformatics Division, CSIR-Indian Institute of Chemical Biology, Kolkata, West Bengal, India.
National Centre for Cell Science, Pune, Maharashtra, India.
Biochem J. 2021 Mar 12;478(5):1117-1136. doi: 10.1042/BCJ20200891.
Asf1 is a highly conserved histone chaperone that regulates tightly coupled nucleosome assembly/disassembly process. We observed that Plasmodium falciparum Asf1 (PfAsf1) is ubiquitously expressed in different stages of the life cycle of the parasite. To gain further insight into its biological activity, we solved the structure of N-terminal histone chaperone domain of PfAsf1 (1-159 amino acids) by X-ray crystallography to a resolution of 2.4 Å. The structure is composed of two beta-sheet to form a beta-sandwich, which resembles an immunoglobulin-like fold. The surface-charge distribution of PfAsf1 is distinct from yAsf1 and hAsf1 although the core-structure shows significant similarity. The crystal-structure indicated that PfAsf1 may exist in a dimeric-state which was further confirmed by solution cross-linking experiment. PfAsf1 was found to specifically interact with Plasmodium histone H3 and H4 and was able to deposit H3/H4 dimer onto DNA-template to form disomes, showing its characteristic histone chaperone activity. We mapped the critical residues of PfAsf1 involved in histone H3/H4 interaction and confirmed by site-directed mutagenesis. Further analysis indicates that histone interacting surface of Asf1 is highly conserved while the dimerization interface is variable. Our results identify the role of PfAsf1 as a mediator of chromatin assembly in Plasmodium falciparum, which is the causative agent of malignant malaria in humans.
Asf1 是一种高度保守的组蛋白伴侣，可调节紧密偶联的核小体组装/拆卸过程。我们观察到疟原虫 PfAsf1（PfAsf1）在寄生虫生命周期的不同阶段普遍表达。为了更深入地了解其生物学活性，我们通过 X 射线晶体学解析了 PfAsf1（1-159 个氨基酸）的 N 端组蛋白伴侣结构域的结构，分辨率为 2.4 Å。该结构由两个β-折叠组成，形成β-三明治结构，类似于免疫球蛋白样折叠。尽管核心结构具有显著的相似性，但 PfAsf1 的表面电荷分布与 yAsf1 和 hAsf1 不同。晶体结构表明 PfAsf1 可能存在二聚体状态，这进一步通过溶液交联实验得到证实。发现 PfAsf1 可特异性与疟原虫组蛋白 H3 和 H4 相互作用，并能够将 H3/H4 二聚体沉积到 DNA 模板上形成二联体，显示其特征性的组蛋白伴侣活性。我们绘制了 PfAsf1 中与组蛋白 H3/H4 相互作用相关的关键残基图谱，并通过定点突变进行了验证。进一步的分析表明，Asf1 的组蛋白相互作用表面高度保守，而二聚化界面则是可变的。我们的研究结果确定 PfAsf1 在恶性疟原虫 PfAsf1 中作为染色质组装的介质的作用，恶性疟原虫是导致人类恶性疟疾的病原体。
