真核生物CSC/OSCA家族阳离子通道的结构与功能

CSC1/OSCA1是新近鉴定出的植物的渗透压感应器，是作物抗旱改造的一个潜在分子靶标，其分子本质是一个渗透压门控的、可通透钙离子的非选择性阳离子通道。干旱胁迫或高渗透压下通道被激活，引发胞浆钙离子浓度升高，以响应胁迫。CSC/OSCA家族成员众多，广泛存在于植物、衣藻、真菌、动物等各种真核生物中。预测CSC/OSCA家族蛋白与TRP、DEG/ENaC、K2P、MscS 及Piezo等家族机械力敏感通道的折叠模式及结构完全不同，但目前尚无该家族的三维结构信息。解析其结构，有助于阐明高渗透压所致细胞膜机械张力是如何激活该通道、引发钙离子内流的分子机理，并揭示该离子通道对阳离子底物的非选择性通透的结构基础。我们拟将晶体衍射与冷冻电镜技术相结合，解析该家族离子通道的结构，揭示其独特的结构特征及工作机理。目前，课题前期进展良好，已获得可衍射的晶体，冷冻电镜样品制备条件已初步成熟，课题突破大有希望。

The CSC1/OSCA1, a newly identified osmosensor in plant，may become a potential molecular target for engineering drought-resistant crops. Its molecular nature is a hyperosmolality-gated nonselective cation channel that permeates calcium ions. Drought or osmotic-stress evokes the channel，which triggers calcium influx and calcium concentration increases in the cytosol as response. The CSC/OSCA family is comprised of numerous homologues，which are found in all plant species and throughout eukaryotes. Prediction shows that the structure-folding mode adopted by the CSC/OSCA family proteins is totally different from any of known mechanical-sensitive channel of TRP, DEG/ENaC, K2P, MscS and Piezo families. Currently, no any 3-D structure information is reported on the CSC/OSCA family proteins. Structure determination of the family proteins helps to elucidate how hyperosmolality-evoked plasma membrane stretching activates the channel to promote calcium influx, and also sheds light on the structure basis for the non-selective cation permeation. We plan to solve the structure of the ion channel family by using crystal diffraction in combination with cyro-EM method. So far, our preliminary study on the project has already made some solid progress. We have harvested X-ray diffractable crystals and optimized the cryoEM-sample preparation protocol. It is expectable to make breakthrough on the project.