Structural biololgy of tumor suppressor PP2A and its regulatory proteins

可逆的蛋白质磷酸化，即蛋白质的磷酸化和去磷酸化，是一种基本的 生物学各个方面的调控机制。蛋白磷酸酶2A(PP2A)是一种主要的丝氨酸/苏氨酸 哺乳动物细胞中的蛋白磷酸酶和主要的肿瘤抑制蛋白 转型。PP2A的核心成分由支架亚基(A亚基)和催化亚基组成 子单位(C亚单位)。C亚基的甲基化，由PP2A甲基转移酶(PMT)和 PP2A甲基酯酶(PME)是PP2A发挥功能所必需的。PP2A-A-C杂二聚体和 调节亚基(B亚基)组装成一个功能完整的酶。DMAVirus SV40小肿瘤 抗原(ST)至少部分通过与B亚基竞争结合来拮抗PP2A的功能 PP2A A-C杂二聚体。Dlpha4蛋白通过形成一种 与PP2A的C亚基形成复合体。尽管有大量的研究，但PP2A的结构和机制 在很大程度上仍然不为人知。PP2A核心的系统X射线结晶学和生化分析 它的组成成分、调节蛋白和修饰酶已经启动。取得了重大进展 已经实现；这里提议的工作将建立在初步成果的基础上，具体目标如下： (1)PME、PMT及其同系物的晶体结构测定 底物/抑制剂。(2)PP2A核心成分A-C杂二聚体的结构测定。(3) 含A-C异源二聚体和B亚基的PP2A全酶的结构测定。(4) 小肿瘤抗原(ST)结合的PP2A-C异源二聚体结构的测定(5) Dlpha4单独及与PP2A C亚单位的复合体结构测定。建议数 这项赠款申请的具体目标代表了一项重要的和系统的努力，以揭开结构 PP2A的调控机制。蛋白质及其同系物的一般优异的溶液性质 综合体使这项任务变得可行。

Reversible protein phosphorylation, namely protein phosphorylation and dephosphorylation, is a fundamental regulatory mechanism in all aspects of biology. Protein phosphatase 2A (PP2A) is a dominant Ser/Thr protein phosphatase in mammalian cells and a principal tumor suppressor protein against oncogenic transformation. The core component of PP2A consists of the scaffolding subunit (A subunit) and the catalytic ubunit (C subunit). The methylation of the C subunit, controlled by the PP2A methyl transferase (PMT) and the PP2A methyl esterase (PME), is essential to the function of PP2A. The PP2A A-C hetero-dimer and the regulatory subunit (B subunit) assemble into a functional holoenzyme. The DMAvirus SV40 Small Tumor Antigen (ST) antagonizes the function of PP2A at least in part by competing with the B subunit for binding to the PP2A A-C hetero-dimer. The Dlpha4 protein antagonizes the normal function of PP2A by forming a complex with the C subunit of PP2A. Despite intense investigation, the structure and mechanisms of PP2A remain largely unknown. Systematic X-ray crystallographic and biochemical analyses of the PP2A core component, its regulatory proteins, and its modifying enzymes have been initiated. Significant progress has been achieved; the work proposed here will build on the preliminary results with the following specific aims: (1) Determination of the crystal structures of PME, PMT, and their cognate complexes with substrate/inhibitor. (2) Determination of the structure of the core component A-C hetero-dimer of PP2A. (3) Determination of the structure of a PP2A holoenzyme involving A-C hetero-dimer and a B subunit. (4) Determination of the structure of a PP2A A-C hetero-dimer bound to Small Tumor Antigen (ST). (5) Determination of the structure of Dlpha4 alone and in complex with the C subunit of PP2A. The proposed specific aims in this grant application represent an important and systematic effort to unravel the structural mechanisms of PP2A regulation. The generally excellent solution properties of the proteins and their cognate complexes make this undertaking feasible.