Department of Chemistry and Biochemistry, University of Arizona, Tucson, United States.
The Novo Nordisk Foundation Center for Protein Research, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark.
Elife. 2020 Mar 20;9:e55966. doi: 10.7554/eLife.55966.
The recruitment of substrates by the ser/thr protein phosphatase 2A (PP2A) is poorly understood, limiting our understanding of PP2A-regulated signaling. Recently, the first PP2A:B56 consensus binding motif, LxxIxE, was identified. However, most validated LxxIxE motifs bind PP2A:B56 with micromolar affinities, suggesting that additional motifs exist to enhance PP2A:B56 binding. Here, we report the requirement of a positively charged motif in a subset of PP2A:B56 interactors, including KIF4A, to facilitate B56 binding via dynamic, electrostatic interactions. Using molecular and cellular experiments, we show that a conserved, negatively charged groove on B56 mediates dynamic binding. We also discovered that this positively charged motif, in addition to facilitating KIF4A dephosphorylation, is essential for condensin I binding, a function distinct and exclusive from PP2A-B56 binding. Together, these results reveal how dynamic, charge-charge interactions fine-tune the interactions mediated by specific motifs, providing a new framework for understanding how PP2A regulation drives cellular signaling.
丝氨酸/苏氨酸蛋白磷酸酶 2A（PP2A）对底物的招募机制了解甚少，这限制了我们对 PP2A 调控信号的理解。最近，首次鉴定出第一个 PP2A：B56 共识结合基序 LxxIxE。然而，大多数经过验证的 LxxIxE 基序与 PP2A：B56 的结合亲和力为微摩尔级，这表明存在其他基序来增强 PP2A：B56 的结合。在这里，我们报告了一组包括 KIF4A 在内的 PP2A：B56 相互作用蛋白子集需要一个带正电荷的基序，通过动态静电相互作用来促进 B56 的结合。使用分子和细胞实验，我们表明 B56 上保守的带负电荷的凹槽介导动态结合。我们还发现，除了促进 KIF4A 去磷酸化外，这个带正电荷的基序对于着丝粒蛋白 I 的结合也是必不可少的，这是一个与 PP2A-B56 结合截然不同且独特的功能。总之，这些结果揭示了动态的、电荷相互作用如何微调特定基序介导的相互作用，为理解 PP2A 调控如何驱动细胞信号提供了新的框架。
