STRUCTURAL ANALYSIS OF THE NFATC CYTOPLASMIC TO NUCLEAR TRANSLOCATION MECHANISM

这个子项目是利用资源的许多研究子项目之一。 由NIH/NCRR资助的中心拨款提供。对子项目的主要支持 子项目的首席调查员可能是由其他来源提供的， 包括美国国立卫生研究院的其他来源。为子项目列出的总成本可能 表示该子项目使用的中心基础设施的估计数量， 不是由NCRR赠款提供给次级项目或次级项目工作人员的直接资金。 许多生物过程对NFATc蛋白的核占有率非常敏感。快速的核进出口过程受蛋白质N端一个未知的变构开关调控，该开关调节NFATc蛋白与核进出口机制之间的交互作用。NFAT信号是由持续的低幅度钙信号启动的，它激活了异二聚体磷酸酶钙调神经磷酸酶。钙调神经磷酸酶通过一个保守的基序直接与NFATc蛋白结合，并使NFATc家族成员N端的SP重复序列中的丝氨酸和富含丝氨酸的基序(SRR和SP-重复)去磷酸化。这种去磷酸化揭示了核定位序列，允许与Importin复合体相互作用和快速细胞质到核的易位。在细胞核中，NFAT蛋白与其他转录因子(NFATn)结合形成特定的转录复合体。Dyrk1a和GSK3随后依次起作用，介导蛋白质从细胞核输出。核内的重新磷酸化会引起另一种构象变化，从而暴露核输出序列(NES)，并允许与核输出受体CRM1相互作用。N-末端这种变构开关的机制还没有从结构上定义。N-末端区域被预测为展开，而核磁共振光谱和SAXS数据显示部分无序的蛋白质。据报道，真核转录因子中的一些内在无序区域在与其伴侣结合时采用结构。我们正在研究NFAT在磷酸化(细胞质)和去磷酸化(核)形式的各种结合伙伴的复合体中，以通过小角X射线散射来表征蛋白质N-末端发生的构象变化。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Many biological processes are exquisitely sensitive to the level of nuclear occupancy of NFATc proteins. The process of rapid nuclear import and export is regulated by an uncharacterized allosteric switch in the N-terminus of the protein, which regulates the alternate interaction between NFATc proteins and the nuclear import and export machinery. NFAT signaling is initiated by sustained low amplitude Ca2+ signals that activate the heterodimeric phosphatase calcineurin. Calcineurin binds directly to NFATc proteins through a conserved motif and dephosphorylates serines within the SP repeats and serine rich motifs (SRR and SP-repeats) in the N-terminus of NFATc family members. This dephosphorylation unmasks the nuclear localization sequence, allowing interaction with the importin complex and rapid cytoplasmic-to-nuclear translocation. In the nucleus NFAT proteins combine with other transcription factors (NFATn) to form specific transcription complexes. Dyrk1a and GSK3 then act sequentially to mediate export of the proteins from the nucleus. Rephosphorylation in the nucleus induces another conformational change, which exposes the nuclear export sequence (NES) and allows interaction with the nuclear export receptor Crm1. The mechanism of this allosteric switch in the N-terminus has not been defined structurally. The N-terminal region is predicted to be unfolded, while NMR spectra and SAXS data reveal a partially disordered protein. A number of intrinsically disordered regions in eukaryotic transcription factors have been reported to adopt structure upon binding to their partners. We are investigating NFAT in complex with a variety of binding partners in both the phosphorylated (cytoplasmic) and dephosphorylated (nuclear) forms to characterize the conformational change that occurs in the N-terminus of the protein by Small Angle X-ray Scattering.