Molecular mechanisms of regulation of NMDA receptor by protein-protein interactions

我们利用非洲爪哇卵母细胞表达系统研究了PSD-95和其他支架蛋白对NMDA受体的影响。1)PSD-95增强NR1NR2A型、NR12B型和NR1NR2D2受体的电流反应；MALS-2增强NR1NR2B型受体对L谷氨酸的电流反应，降低该受体对L谷氨酸的敏感性。MALS-2和PSD-95之间的嵌合体的构建表明，前两个PDZ结构域和两个NH2末端的半胱氨酸残基(可能的棕榈酰化位点)分别是PSD-95抑制蛋白激酶C介导的NR1-NR2A和NR1-NR2B通道增强所必需的。PSD-95的三个PDZ结构域中的第二个结构域是它抑制Src介导的NR1-NR2A通道增强所必需的。4)NMDA受体通过PSD-95的GK结构域与PSD-95结合，PSD-95通过GK结构域与GKAP相互作用。我们检测了PSD-95和GKAP对NMDA受体四种亚型的影响。GKAP与PSD-95联用可增强NR1/NR2B的通道活性，但不能增强NR1/NR2A和NR/NR2D的通道活性。只有当PSD-95和GKAP5同时存在时，NR1/NR2C的通道活性才会增强。这些结果表明MALS-2、PSD-95和GKAP以亚型特异性的方式调节NMDA受体的通道活性

We investigated the effects of PSD-95 and other scaffold proteins on the NMDA receptors using Xenopus oocyte expression system1) PSD-95 increased the current response of NR1/NR2A, NR1/NR2B and NR1/NR2D2) Other scaffold protein, MALS-2 increased the current response of the NR1-NR2B receptor to L-glutamate as well as reduced the sensitivity of this receptor to L-glutamate. In contrast, the current response of the NR1-NR2A receptor was not increased by MALS-23) Construction of chimeras between MALS-2 and PSD-95 revealed that the first two PDZ domains and two NH2terminal cysteine residues (possible palmitoylation sites) are essential for the inhibitory effects of PSD-95 on protein kinase C-mediated potentiation of NR1-NR2A and NR1-NR2B channels, respectively. The second of the three PDZ domains of PSD-95 was required for its inhibition of Src-mediated potentiation of NR1-NR2A channels4) The NMDA receptor binds PSD-95 which interacts with GKAP (Guanylate Kinase-domain Associated Protein) through the GK domain of PSD-95. We examined the effects of PSD-95 and GKAP on four subtypes of the NMDA receptor. GKAP together with PSD-95 potentiated that of NR1/NR2B but not of NR1/NR2A and NR/NR2D.The channel activity of NR1/NR2C was potentiated only in the co-presence of PSD-95 and GKAP5) These results indicate that MALS-2, PSD-95 and GKAP modulate the channel activity of the NMDA receptor in the subtype-specific manner