Dysregulation of phosphorylation-dependent signaling is a hallmark of tumorigenesis. Protein phosphatase 2 (PP2A) is an essential regulator of cell growth. One scaffold subunit (A) binds to a catalytic subunit (C) to form a core AC heterodimer, which together with one of many regulatory (B) subunits forms the active trimeric enzyme. The combinatorial number of distinct PP2A complexes is large, which results in diverse substrate specificity and subcellular localization. The detailed mechanism of PP2A assembly and regulation remains elusive and reports about an important role of methylation of the carboxy terminus of PP2A C are conflicting. A better understanding of the molecular underpinnings of PP2A assembly and regulation is critical to dissecting PP2A function in physiology and disease. Here, we combined biochemical reconstitution, mass spectrometry, X-ray crystallography, and functional assays to characterize the assembly of trimeric PP2A. studies demonstrated that methylation of the carboxy-terminus of PP2A C was dispensable for PP2A assembly . To corroborate these findings, we determined the X-ray crystal structure of the unmethylated PP2A Aα-B56ε-Cα trimer complex to 3.1 Å resolution. The experimental structure superimposed well with an Alphafold2Multimer prediction of the PP2A trimer. We then predicted models of all canonical PP2A complexes providing a framework for structural analysis of PP2A. In conclusion, methylation was dispensable for trimeric PP2A assembly and integrative structural biology studies of PP2A offered predictive models for all canonical PP2A complexes.

中文翻译：

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甲基化无关的 PP2A 组装的结构表征指导全家族 PP2A 复合物的 alphafold2Multimer 预测


磷酸化依赖性信号传导失调是肿瘤发生的标志。蛋白磷酸酶 2 (PP2A) 是细胞生长的重要调节剂。一个支架亚基 (A) 与催化亚基 (C) 结合，形成核心 AC 异二聚体，其与许多调节亚基 (B) 之一一起形成活性三聚酶。不同 PP2A 复合物的组合数量很大，导致底物特异性和亚细胞定位不同。 PP2A 组装和调节的详细机制仍然难以捉摸，并且关于 PP2A C 羧基末端甲基化的重要作用的报道是相互矛盾的。更好地了解 PP2A 组装和调节的分子基础对于剖析 PP2A 在生理学和疾病中的功能至关重要。在这里，我们结合生化重建、质谱、X 射线晶体学和功能测定来表征三聚 PP2A 的组装。研究表明，PP2A C 羧基末端的甲基化对于 PP2A 组装来说是可有可无的。为了证实这些发现，我们以 3.1 Å 分辨率确定了未甲基化 PP2A Aα-B56ε-Cα 三聚体复合物的 X 射线晶体结构。实验结构与 PP2A 三聚体的 Alphafold2Multimer 预测很好地叠加。然后我们预测了所有典型 PP2A 复合物的模型，为 PP2A 结构分析提供了框架。总之，甲基化对于三聚体 PP2A 组装是可有可无的，PP2A 的综合结构生物学研究为所有典型 PP2A 复合物提供了预测模型。