Cao Ruili, Jones Daniel Td, Pan Li, Yang Annie, Wang Shumei, Padi Sathish K R, Rawson Shaun, Aster Jon C, Blacklow Stephen C
Department of Biological Chemistry and Molecular Pharmacology, Blavatnik Institute, Harvard Medical School, Boston, MA, USA.
Department of Pathology, Brigham and Women's Hospital, Boston, MA, USA.
bioRxiv. 2024 Aug 26:2023.08.29.555174. doi: 10.1101/2023.08.29.555174.
PP2A serine/threonine phosphatases are heterotrimeric complexes that execute many essential physiologic functions. These activities are modulated by additional regulatory proteins, such as ARPP19, FAM122A, and IER5. Here, we report the cryoelectron microscopy structure of a complex of PP2A/B55α with the N-terminal structured region of IER5 (IER5-N50), which occludes a surface on B55α used for substrate recruitment, and show that IER5-N50 inhibits PP2A/B55α catalyzed dephosphorylation of pTau in biochemical assays. Mutations of full-length IER5 that disrupt its PP2A/B55α interface interfere with co-immunoprecipitation of PP2A/B55α. These mutations and deletions that remove the nuclear localization sequence of IER5 suppress cellular events such as expression that depend on association of IER5 with PP2A/B55α. Querying the Alphafold2 predicted structure database identified SERTA domain proteins as high-confidence PP2A/B55α-binding structural homologs of IER5-N50. These studies define the molecular basis of PP2A/B55α inhibition by IER5-family proteins and suggest a roadmap for selective pharmacologic modulation of PP2A/B55α complexes.
PP2A丝氨酸/苏氨酸磷酸酶是异源三聚体复合物，执行许多重要的生理功能。这些活性受其他调节蛋白如ARPP19、FAM122A和IER5的调控。在此，我们报道了PP2A/B55α与IER5的N端结构化区域（IER5-N50）形成的复合物的冷冻电镜结构，该结构封闭了B55α上用于底物招募的一个表面，并在生化分析中表明IER5-N50抑制PP2A/B55α催化的pTau去磷酸化。破坏其PP2A/B55α界面的全长IER5突变会干扰PP2A/B55α的免疫共沉淀。这些去除IER5核定位序列的突变和缺失会抑制诸如依赖IER5与PP2A/B55α结合的细胞事件，如表达。查询Alphafold2预测结构数据库发现SERTA结构域蛋白是IER5-N50的高可信度PP2A/B55α结合结构同源物。这些研究确定了IER5家族蛋白抑制PP2A/B55α的分子基础，并为PP2A/B55α复合物的选择性药理调节提供了路线图。
