Structural and Functional Studies of LysRS in Mast Cell Activation

描述（由申请人提供）：拟议研究的目标是确定真核生物翻译和转录机制之间磷酸化定向串扰的结构基础。通过释放强效的促炎介质，肥大细胞是引发过敏反应的重要效应器。特定转录因子MITF的激活是产生这些介质的关键步骤。MITF靶基因的转录依赖于一种共激活因子，赖氨酸- trna合成酶（LysRS），这是细胞质蛋白质合成机制的重要组成部分。LysRS的Ser207磷酸化（得到LysRSp207）指导该酶从细胞质多trna合成酶复合物（MSC）中释放。然后，LysRSp207转运到细胞核，在那里它催化一个关键信号分子——四磷酸二腺苷（Ap4A）的合成。在细胞核中，新生的Ap4A破坏MITF与MITF功能的HINT1抑制子的相互作用。随着MITF- hint1复合体的破坏，LysRSp207结合并激活MITF，促进靶基因的转录。在肥大细胞中，一个S207D拟磷LysRS突变体（LysRSS207D）诱导Ap4A的产生，并能重现LysRSp207的活性，从而促进MITF靶基因的转录。该途径是翻译和转录机制之间磷酸化定向串扰的第一个例子。我们的中心目标是了解MSC-LysRS-MITF/HINT1通路轴的结构基础。我们的初步工作表明，S207D拟磷突变触发了一个动态的结构打开，完全关闭了LysRS的翻译功能。因此，磷酸化起着功能开关的作用。我们的目的是确定Ser207磷酸化导致LysRS从MSC支架蛋白p38分离的机制，从而从MSC分离。我们还将尝试了解LysRS如何产生Ap4A并将抑制因子HINT1从MITF中分离出来。最后，我们将研究LysRS-MITF复合物形成的结构基础。这些研究可以导致对真核生物翻译和转录机制之间的串扰的第一次结构理解。此外，从这些研究中获得的见解可以开辟新的治疗方法，通过破坏MITF功能来治疗过敏性疾病，这是一种常见的医学疾病，在美国，超过五分之一的人受到这种疾病的折磨。

DESCRIPTION (provided by applicant): The goals of the proposed research are to determine the structural basis for a phosphorylation-directed crosstalk between the eukaryotic translation and transcription machineries. By releasing potent pro-inflammatory mediators, mast cells are essential effectors in the elicitation of allergic responses. Activation of a specific transcriptio factor - MITF - is a critical step for the production of these mediators. Transcription of MITF target genes depends on a co-activator, lysyl-tRNA synthetase (LysRS), an essential component of the cytoplasmic protein synthesis machinery. Phosphorylation of Ser207 of LysRS (to give LysRSp207) directs release of this enzyme from the cytoplasmic multi-tRNA synthetase complex (MSC). LysRSp207 then translocates to the nucleus where it catalyzes the synthesis of a critical signaling molecule, diadenosine tetraphosphate (Ap4A). In the nucleus, nascent Ap4A disrupts the interaction of MITF with the HINT1 suppressor of MITF's function. With the disruption of the MITF-HINT1 complex, LysRSp207 binds to and activates MITF to promote transcription of target genes. In mast cells, a S207D phosphor-mimetic LysRS mutant (LysRSS207D) induces the production of Ap4A and can recapitulate the activity of LysRSp207, which promotes transcription of MITF target genes. This pathway is the first example of phosphorylation-directed crosstalk between the translation and transcription machineries. Our central goal is to understand the structural basis for the axis of the MSC-LysRS-MITF/HINT1 pathway. Our preliminary work showed that the S207D phosphor-mimetic mutation triggers a dynamic structural opening that completely switches off the translational function of LysRS. Thus, phosphorylation acts as a functional switch. Our aim is to determine the mechanism by which phosphorylation of Ser207 leads to dissociation of LysRS from the MSC scaffold protein p38 and therefore from the MSC. We will also attempt to understand how LysRS generates Ap4A and dissociates the suppressor HINT1 from MITF. Lastly, we will investigate the structural basis for formation of the LysRS-MITF complex. These investigations can result in the first structural understanding of the crosstalk between eukaryotic translation and transcription machineries. In addition, the insights gained by these studies could open up new therapeutic approaches to disrupting MITF function for treating allergic disorders, a common medical condition that afflicts more than one in five people in the United States.