Functional Analysis of Molecular Mechanisms of Presynaptic Metabotropic Glutamate Receptors

已经报道了许多含有PDZ结构域的蛋白质通过识别位于其C-末端区域的PDZ结合基序与靶蛋白相互作用。在受体相关蛋白的情况下，它们可能在受体信号传导中发挥不同的作用。为了了解代谢型谷氨酸受体（metabotropic glutamate receptor，mGluRs）的功能，我们寻找受体相关蛋白，并鉴定了一种与第1组mGluRs相互作用的含PDZ结构域的蛋白Tamalin，Tamalin是一种包含多个蛋白质相互作用结构域的支架蛋白。它具有一个PDZ结构域，一个亮氨酸拉链区，一个富含脯氨酸的区域，和一个羧基末端PDZ结合基序。Tamalin的PDZ结构域与第1组和第2组mGluRs和GABAB 2受体的羧基末端相互作用，而亮氨酸拉链区与鸟嘌呤核苷酸交换因子细胞粘连蛋白的卷曲螺旋区结合。Tamalin通过与细胞粘连素相互作用促进COS-7细胞和培养的海马神经元中第1组mGluRs的细胞内运输和细胞表面表达Tamalin与典型的突触后支架蛋白PSD-95、S-SCAM和SAPAP 1/3相互作用，并且Tamalin介导的突触后支架蛋白的不同组装可能在组织突触后信号中具有独特而重要的作用-专门用于第1组mGluRs的加工机械。Tamalin还与参与蛋白质转运的Mint 2和CASK相关。总之，我们的研究表明，Tamalin与许多参与神经元突触后组织和蛋白质运输的重要支架蛋白相互作用。这表明Tamalin可能参与受体聚集、运输和细胞内信号传导。

A number of PDZ domain-containing proteins have been reported to interact with target proteins via the recognition of a PDZ-binding motif located at their C-terminal regions. In the cases of receptor-associated proteins, they may play distinct roles in receptor signalling. In order to understand the function of metabotropic glutamate receptors (mGluRs), we searched for receptor-associated proteins and identified a PDZ domain-containing protein, tamalin, that interacts with group 1 mGluRs.Tamalin is a scaffold protein that comprises multiple protein-interacting domains. It possesses a PDZ domain, a leucine-zipper region, a proline-rich region, and a carboxyl-terminal PDZ binding motif. The PDZ domain of tamalin interacts with the carboxyl termini of group 1 and group 2 mGluRs and GABAB2 receptor, whereas the leucine-zipper region binds to the coiled coil region of guanine nucleotide exchange factor cytohesins. Tamalin promotes intracellular trafficking and cell surface expression of group 1 mGluRs in COS-7 cells and cultured hippocampal neurons through the interaction with cytohesins.Tamalin interacts with typical postsynaptic scaffold proteins, PSD-95, S-SCAM, and SAPAP1/3, and the tamalin-mediated different assembly of postsynaptic scaffold proteins may have a distinct and important role in organizing a postsynaptic signal-processing machinery specific for group 1 mGluRs. Tamalin also associates with Mint2 and CASK, which are involved in protein transport.In summary, our study shows that tamalin interacts with many important scaffold proteins involved in postsynaptic organization and protein trafficking in neurons. This indicates that tamalin may participate in receptor clustering, trafficking, and intracellular signalling.