Ruiz-Cañada C, Koh Y H, Budnik V, Tejedor F J
Instituto de Neurociencias, Universidad Miguel Hernandez-CSIC, San Juan, Alicante, Spain.
J Neurochem. 2002 Sep;82(6):1490-501. doi: 10.1046/j.1471-4159.2002.01092.x.
Subcellular localization of ion channels is crucial for the transmission of electrical signals in the nervous system. Here we show that Discs-Large (DLG), a member of the MAGUK (membrane-associated guanylate kinases) family in Drosophila, co-localizes with Shaker potassium channels (Sh Kch) in most synaptic areas of the adult brain and in the outer membrane of photoreceptors. However, DLG is absent from axonal tracts in which Sh channels are concentrated. Truncation of the C-terminal of Sh (including the PDZ binding site) disturbs its pattern of distribution in both CNS and retina, while truncation of the guanylate kinase/C-terminal domain of DLG induces ectopic localization of these channels to neuronal somata in the CNS, but does not alter the distribution of channels in photoreceptors. Immunocytochemical, membrane fractionation and detergent solubilization analysis indicate that the C-terminal of Sh Kch is required for proper trafficking to its final destination. Thus, several major conclusions emerge from this study. First, DLG plays a major role in the localization of Sh channels in the CNS and retina. Second, localization of DLG in photoreceptors but not in the CNS seems to depend on its interaction with Sh. Third, the guanylate kinase/C-terminal domain of DLG is involved in the trafficking of Shaker channels but not of DLG in the CNS. Fourth, different mechanisms for the localization of Sh Kch operate in different cell types.
离子通道的亚细胞定位对于神经系统中电信号的传递至关重要。在此我们表明，盘状大蛋白（DLG）是果蝇中膜相关鸟苷酸激酶（MAGUK）家族的成员，在成年果蝇大脑的大多数突触区域以及光感受器的外膜中与震颤钾通道（Sh Kch）共定位。然而，在Sh通道集中的轴突束中不存在DLG。Sh的C末端（包括PDZ结合位点）的截短会扰乱其在中枢神经系统和视网膜中的分布模式，而DLG的鸟苷酸激酶/C末端结构域的截短会导致这些通道在中枢神经系统中异位定位于神经元胞体，但不会改变其在光感受器中的分布。免疫细胞化学、膜分级分离和去污剂增溶分析表明，Sh Kch的C末端对于其正确运输到最终目的地是必需的。因此，这项研究得出了几个主要结论。第一，DLG在中枢神经系统和视网膜中Sh通道的定位中起主要作用。第二，DLG在光感受器而非中枢神经系统中的定位似乎取决于其与Sh的相互作用。第三，DLG的鸟苷酸激酶/C末端结构域参与了中枢神经系统中震颤通道的运输，但不参与DLG的运输。第四，Sh Kch定位的不同机制在不同细胞类型中起作用。
