蔡时青研究组最新文章揭示离子通道功能调控机制

　　

　2月4日，中国科学院上海生命科学研究院神经科学研究所蔡时青组在《神经科学杂志》发表了题为《线虫Kv4钾离子通道KChIP辅助亚基调控肌肉兴奋性和控制雄虫交配行为》的研究论文。文章报道了线虫KChIP辅助亚基通过促进Kv4钾离子通道的生成，调控神经元和肌肉细胞的兴奋性，进而影响动物的一些重要行为。

　　电压门控钾离子通道（Kv）是一类可选择性通透钾离子的跨膜蛋白，它参与了动作电位的形成，直接影响神经元和肌肉细胞的兴奋性。Kv4是其中一类通导快速瞬时电流（fast transient current）的钾离子通道，而钾离子通道相互作用蛋白（K+ Channel Interacting Protein, KChIP）则是Kv4的辅助亚基，它不参与离子通道跨膜孔道的形成，但影响Kv4的电生理特征，并且也可以促进Kv4的表达与运输。

    目前，有关KChIP对Kv4的调控机制尚不明确。蔡时青组博士生陈欣等克隆了编码线虫KChIP蛋白的ncs-4,ncs-5和ncs-7基因，发现这些线虫KChIP蛋白对于SHL-1（线虫Kv4同源蛋白）的生成和运输都是必要的。同时敲除ncs-4,ncs-5和ncs-7基因导致SHL-1蛋白不能在线虫体壁肌肉细胞中表达，这些细胞中的快速瞬时外向钾电流也因此消失。KChIP是一类钙离子结合蛋白，在体实验结果发现钙离子信号不影响线虫KChIP蛋白NCS-4促进SHL-1蛋白生成，但是钙离子和NCS-4结合对于SHL-1蛋白从高尔基体运输到细胞膜的过程是必要的。

    这些结果解析了钙离子信号在辅助亚基KChIP调控Kv4家族钾离子通道功能中所扮演的角色，阐明了KChIP和Kv4相互作用机制。

　　该研究还发现，KChIP蛋白NCS-4和SHL-1共同表达在雄性线虫尾部的斜方肌中，敲除ncs-4或shl-1基因的雄虫有严重的交配能力缺陷。钙成像结果显示这些雄性线虫在交配时斜方肌兴奋性过强，尾部不能正常弯曲，无法完成交配过程。该结果揭示了钾离子通道辅助亚基KChIP在调控细胞兴奋性和动物行为中的重要作用。

　　该课题由博士生陈欣、助理研究员阮美煜在研究员蔡时青指导下完成。课题受中国科学院“****”、国家自然科学基金委面上项目和神经科学国家重点实验室资助，在上海生科院神经所独立完成。

 
 
图A 线虫KChIP蛋白调控内源SHL-1 介导的快速瞬时钾电流

 
 
图B 敲除ncs-4或shl-1基因影响雄性线虫斜方肌细胞兴奋性

原文摘要：

KChIP-Like Auxiliary Subunits of Kv4 Channels Regulate Excitability of Muscle Cells and Control Male Turning Behavior during Mating in Caenorhabditis elegans.

Voltage-gated Kv4 channels control the excitability of neurons and cardiac myocytes by conducting rapidly activating-inactivating currents. The function of Kv4 channels is profoundly modulated by K(+) channel interacting protein (KChIP) soluble auxiliary subunits. However, the in vivo mechanism of the modulation is not fully understood. Here, we identified three C. elegans KChIP-like (ceKChIP) proteins, NCS-4, NCS-5, and NCS-7. All three ceKChIPs alter electrical characteristics of SHL-1, a C. elegans Kv4 channel ortholog, currents by slowing down inactivation kinetics and shifting voltage dependence of activation to more hyperpolarizing potentials. Native SHL-1 current is completely abolished in cultured myocytes of Triple KO worms in which all three ceKChIP genes are deleted. Reexpression of NCS-4 partially restored expression of functional SHL-1 channels, whereas NCS-4(efm), a NCS-4 mutant with impaired Ca(2+)-binding ability, only enhanced expression of SHL-1 proteins, but failed to transport them from the Golgi apparatus to the cell membrane in body wall muscles of Triple KO worms. Moreover, translational reporter revealed that NCS-4 assembles with SHL-1 K(+) channels in male diagonal muscles. Deletion of either ncs-4 or shl-1 significantly impairs male turning, a behavior controlled by diagonal muscles during mating. The phenotype of the ncs-4 null mutant could be rescued by reexpression of NCS-4, but not NCS-4(efm), further emphasizing the importance of Ca(2+) binding to ceKChIPs in regulating native SHL-1 channel function. Together, these data reveal an evolutionarily conserved mechanism underlying the regulation of Kv4 channels by KChIPs and unravel critical roles of ceKChIPs in regulating muscle cell excitability and animal behavior in C. elegans.