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

我们利用爪蟾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增加NR 1/NR 2A、NR 1/NR 2B和NR 1/NR 2D的电流响应2）其他支架蛋白MALS-2增加NR 1-NR 2B受体对L-谷氨酸的电流响应，并降低该受体对L-谷氨酸的敏感性。MALS-2和PSD-95之间嵌合体的构建揭示了前两个PDZ结构域和两个NH 2末端半胱氨酸残基（可能的棕榈酰化位点）对于PSD-95分别对蛋白激酶C介导的NR 1-NR 2A和NR 1-NR 2B通道的增强的抑制作用是必需的。PSD-95的三个PDZ结构域中的第二个是其抑制Src介导的NR 1-NR 2A通道增强所必需的。4）NMDA受体结合PSD-95，PSD-95通过PSD-95的GK结构域与GKAP（鸟苷酸激酶结构域相关蛋白）相互作用。我们研究了PSD-95和GKAP对NMDA受体四种亚型的影响。GKAP和PSD-95共同作用可增强NR 1/NR 2B的通道活性，但对NR 1/NR 2A和NR/NR 2D的通道活性无明显影响。只有PSD-95和GKAP共同作用才能增强NR 1/NR 2C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