Department of Pharmacology, Yale School of Medicine, New Haven, CT, USA.
Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT, USA.
Nat Commun. 2022 Feb 8;13(1):749. doi: 10.1038/s41467-022-28427-0.
Tousled-like kinases (TLKs) are nuclear serine-threonine kinases essential for genome maintenance and proper cell division in animals and plants. A major function of TLKs is to phosphorylate the histone chaperone proteins ASF1a and ASF1b to facilitate DNA replication-coupled nucleosome assembly, but how TLKs selectively target these critical substrates is unknown. Here, we show that TLK2 selectivity towards ASF1 substrates is achieved in two ways. First, the TLK2 catalytic domain recognizes consensus phosphorylation site motifs in the ASF1 C-terminal tail. Second, a short sequence at the TLK2 N-terminus docks onto the ASF1a globular N-terminal domain in a manner that mimics its histone H3 client. Disrupting either catalytic or non-catalytic interactions through mutagenesis hampers ASF1 phosphorylation by TLK2 and cell growth. Our results suggest that the stringent selectivity of TLKs for ASF1 is enforced by an unusual interaction mode involving mutual recognition of a short sequence motifs by both kinase and substrate.
缠结样激酶（TLKs）是动物和植物中维持基因组稳定性和细胞正常分裂所必需的核丝氨酸-苏氨酸激酶。TLKs 的主要功能是磷酸化组蛋白伴侣蛋白 ASF1a 和 ASF1b，以促进与 DNA 复制偶联的核小体组装，但 TLKs 如何选择性地靶向这些关键底物尚不清楚。在这里，我们表明 TLK2 对 ASF1 底物的选择性是通过两种方式实现的。首先，TLK2 催化结构域识别 ASF1 C 端尾部的保守磷酸化位点模体。其次，TLK2 N 端的一小段序列以模拟其组蛋白 H3 底物的方式对接至 ASF1a 球状 N 端结构域。通过突变破坏催化或非催化相互作用会阻碍 TLK2 对 ASF1 的磷酸化和细胞生长。我们的结果表明，TLKs 对 ASF1 的严格选择性是通过一种不寻常的相互作用模式来实现的，该模式涉及激酶和底物对短序列模体的相互识别。
