Study on switching mechanisms of protein-protein interactions underlying the establishment of cell polarity

多细胞生物中存在着上皮细胞连接、神经突触和质膜脂筏等功能结构域，这些结构域对细胞间有效的信号转导起着重要作用。这些结构域由不同的蛋白质组分组成，它们以多种方式相互作用。支架蛋白已经成为细胞连接的基础分子结构的关键分子。支架蛋白具有结合多种蛋白质并促进这些配体之间的相互作用的多个模块。由于一个以上的配体结合到同一个模块，一些组件可以同时与支架蛋白相互作用，而其他组件则不能。因此，由支架蛋白组装的蛋白质的组合应根据细胞环境而改变。我们目前正在研究在细胞连接成熟的不同阶段，哪些蛋白质被支架蛋白组装。1）我们已经报道了突触支架分子（S-SCAM）参与了突触细胞粘附分子神经配素的积累。S-SCAM似乎提供了一个支架来激活一个小的GTP结合蛋白，该蛋白参与神经树突棘中细胞骨架的调节。2）膜相关鸟苷酸激酶与倒置组织（MAGI）-1是S-SCAM的上皮同种型。我们最近在免疫电子显微镜中揭示了MAGI-1在肾裂膈的定位。MAGI-1与nephrin相互作用，nephrin是一种细胞粘附分子，是狭缝粘附的基本组分。3）连接粘附分子（JAM）4被鉴定为MAGI-1的配体。我们已经鉴定了编号X配体（LNX）1作为一种新的JAM 4结合伴侣，并分析了LNX 1对JAM 4内吞作用的影响。

Multicellular organisms develop functional domains such as epithelial cell junctions, neural synapses and lipid rafts on plasma membranes, which are important for the efficient intercellular signal transductions. These domains are composed of distinct protein components that interact with each other in manifold ways. Scaffold proteins have emerged as key molecules underlying basal molecular architectures of cell junctions. Scaffold proteins have multiple modules that bind a wide variety of proteins and facilitate the interactions among these ligands. As more than one ligands bind to the same module, some components can interact with a scaffold protein simultaneously, whereas others can not. Thereby, the combination of proteins assembled by a scaffold protein should alter depending on the cellular context. We currently examine which proteins are assembled by scaffold proteins at various stages of the maturation of cell junctions.1) We have reported that synaptic scaffold molecule (S-SCAM) is involved in the accumulation of synaptic cell adhesion molecule named neuroligin. S-SCAM appears to provide a scaffold to activate a small GTP-binding protein implicated in the regulation of the cytoskeleton in neural dendritic spines.2) Membrane-associated guanylate kinase with inverted organization (MAGI)-1 is an epithelial isoform of S-SCAM. We have recently revealed in the immunoelectron microscope the localization of MAGI-1 at slit diaphragm in kidney. MAGI-1 interacts with nephrin, a cell adhesion molecule that is an essential component of slit diaphragm.3) Junctional adhesion molecule (JAM) 4 was identified as a ligand for MAGI-1. We have identified Ligand-of-Numb X (LNX) 1 as a novel JAM4-binding partner and analyzed the effect of LNX1 on endocytosis of JAM4.