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Abstract：
The protein phosphatase 2A (PP2A) and kinases such as germinal center kinase III (GCKIII) can interact with striatins to form a supramolecular complex called striatin-interacting phosphatase and kinase (STRIPAK) complex. Despite the fact that the STRIPAK complex regulates multiple cellular events, it remains only partially understood how this complex itself is assembled and regulated for differential biological functions. Our recent work revealed the activation mechanism of GCKIIIs by MO25, as well as how GCKIIIs heterodimerize with CCM3, a molecular bridge between GCKIII and striatins. Here we dissect the structural features of the coiled coil domain of striatin 3, a novel type of PP2A regulatory subunit that functions as a scaffold for the assembly of the STRIPAK complex. We have determined the crystal structure of a selenomethionine-labeled striatin 3 coiled coil domain, which shows it to assume a parallel dimeric but asymmetric conformation containing a large bend. This result combined with a number of biophysical analyses provide evidence that the coiled coil domain of striatin 3 and the PP2A A subunit form a stable core complex with a 2:2 stoichiometry. Structure-based mutational studies reveal that homodimerization of striatin 3 is essential for its interaction with PP2A and therefore assembly of the STRIPAK complex. Wild-type striatin 3 but not the mutants defective in PP2A binding strongly suppresses apoptosis of Jurkat cells induced by the GCKIII kinase MST3, most likely through a mechanism in which striatin recruits PP2A to negatively regulate the activation of MST3. Collectively, our work provides structural insights into the organization of the STRIPAK complex and will facilitate further functional studies.
摘要：
蛋白磷酸酶2A（PP2A）和诸如生发中心激酶III（GCKIII）的激酶可以与纹状体蛋白相互作用，形成称为纹状体蛋白相互作用磷酸酶和激酶（STRIPAK）复合物的超分子复合物。尽管STRIPAK复合物调节多种细胞事件，它仍然只是部分理解这种复合物本身是如何组装和调节不同的生物学功能。我们最近的工作揭示了MO25对GCKIIIs的激活机制，以及GCKIIs如何与CCM3异源二聚化，CCM3是GCKIII和纹状体蛋白之间的分子桥梁。在这里，我们剖析了纹状体蛋白3的卷曲螺旋结构域的结构特征，纹状体蛋白3是一种新型的PP2A调节亚基，可作为STRIPAK复合物组装的支架。我们已经确定了硒代蛋氨酸标记的纹状体蛋白3卷曲螺旋结构域的晶体结构，这表明它具有平行的二聚体但不对称的构象，其中包含大的弯曲。该结果与许多生物物理分析相结合提供了证据，表明striatin3的卷曲螺旋结构域和PP2AA亚基形成具有2：2化学计量的稳定核心复合物。基于结构的突变研究表明，纹状体蛋白3的同源二聚化对于其与PP2A的相互作用以及因此的STRIPAK复合物的组装至关重要。野生型纹状体蛋白3而不是PP2A结合缺陷的突变体强烈抑制GCKIII激酶MST3诱导的Jurkat细胞的凋亡，这很可能是通过纹状体蛋白募集PP2A来负调节MST3激活的机制。总的来说，我们的工作为STRIPAK复合体的组织提供了结构性见解,并将促进进一步的功能研究.
