前期研究中，我们首次发现CdffT是一个同时具有转运单价阳离子（Na+、Li+、K+）和二价阳离子（Zn2+、Cd2+）功能的新型CDF家族蛋白。然而，由于离子半径或者过大或者 过小，已知的CDF家族蛋白的活性中心可能无法容纳Na+、Li+、 K+。因此，揭示其具体如何同时输出单价和二价阳离子的分子机制是值得期待的。本项目拟采用原核过量表达和X衍射技术，对CdffT晶体结构予以解析；同时，通过定点突变方法对CdffT的保守氨基酸残基与其转运功能之间的结构-功能关系进行分析，以确定其中负责转运单价和二价阳离子以及与pH值调控有关的重要残基；最终，综合CdffT的晶体结构及其结构-功能关系，揭示该蛋白同时转运单价和二价阳离子的分子机制。作为新型CDF家族蛋白，本研究的开展不仅可以揭示CdffT转运多种阳离子的分子机制，而且可以增进人们对CDF家族蛋白和钠/氢逆向转运蛋白在细菌耐盐碱方面的认识。

Preliminary experiments showed for the first time that CdffT is a novel CDF family transporter with Na+(Li+, K+)/H+ antiport and Zn2+(Cd2+)/H+ antiport activity. However, due to their ionic size, all identified CDF family transporters can’t accommodate Na+, Li+, K+ in the active sites. Therefore, it’s so intriguing to discover its molecular mechanism that CdffT can extrude monovalent and divalent cations at the same time. In this project, we plan to lay more important stress on the analysis of crystal structure of CdffT through the combination of prokaryotic overexpression of CdffT and X-ray diffusion technique. Also, we plan to analyze the structure-function relationship of CdffT through site-directed mutagenesis of potential functionally important amino acid residues. Taken together, we plan to discover molecular mechanism of monovalent and divalent cation efflux by CdffT. As a novel CDF family transporter, analysis of crystal structure and structure-function relationship of CdffT will be very helpful to not only understand molecular mechanism of extruding monovalent and divalent cations at the same time, but also enhance our knowledge of the key role of CDF family transporters and Na+(Li+)/H+ antiporters in bacterial halo-alkali tolerance.