前期研究暗示SdmlT是一个可能具有钠（锂）/氢逆向转运蛋白功能的新型HCT家族蛋白，但其确切功能仍然未定。因此，本项目拟采用基于RSO膜微囊或反转膜微囊的同位素14C标记的检测技术，鉴定SdmlT具体作为何种HCT家族蛋白行使功能；采用基于反转膜微囊的吖啶橙荧光猝灭恢复法或同位素22Na的检测技术，鉴定SdmlT是否具有钠（锂）/氢逆向转运蛋白功能，以及该功能是否与HCT家族蛋白功能偶联；在此基础上，通过定点突变方法着重对SdmlT的保守氨基酸残基进行功能分析，以确定其中负责转运2-羟基羧酸和钠、锂离子以及与pH值调控有关的重要残基。作为新型HCT家族蛋白，SdmlT的功能及其重要残基的鉴定，不仅可以揭示该蛋白转运2-羟基羧酸以及耐盐碱的分子机制，而且可以增进人们对HCT家族蛋白和钠（锂）/氢逆向转运蛋白在细菌耐盐碱方面的认识，同时指导我们对SdmlT的分子改造以进一步提高其耐盐碱能力。

Preliminary experiments suggest that SdmlT may be a novel HCT family transporter with Na+(Li+)/H+ antiport activity, but its function hasn't been identified experimentally as yet. In this project, we plan to identify the exact function of SdmlT as a novel HCT family transporter by analyzing the uptake of 14C labeled 2-hydroxycarboxylate by RSO membrane vesicles or inverted membrane vesicles containing pUC-sdmlT. Also, we plan to identify whether SdmlT functions as a Na+(Li+)/H+ antiporter through the acridine orange fluorescence dequenching method based on inverted membrane vesicles or by analyzing the uptake of 22Na by inverted membrane vesicles containing pUC-sdmlT, and whether Na+(Li+)/H+ antiport by SdmlT needs to be coupled to the transportation of 2-hydroxycarboxylate. More importantly, we plan to analyze the structure-function relationship of SdmlT through site-directed mutagenesis of potential functionally important amino acid residues. As a novel HCT family transporter, identification of SdmlT and its functionally important amino acid residues will be very helpful to not only understand molecular mechanism of 2-hydroxycarboxylate transportation by SdmlT and halo-alkali tolerant molecular machnism of SdmlT, but also enhance our knowledge of the key role of HCT family transporter and Na+(Li+)/H+ antiporter in bacterial halo-alkali tolerance. Moreover, identification of functionally important amino acid residues may provide a theoretical basis for us to carry out gene-level modification of SdmlT based on site-directed mutagenesis to further enhance the capacity of halo-alkali tolerance.