Arkin I T, Russ W P, Lebendiker M, Schuldiner S
Howard Hughes Medical Institute, Yale University, New Haven, Connecticut 06520, USA.
Biochemistry. 1996 Jun 4;35(22):7233-8. doi: 10.1021/bi960094i.
EmrE is a member of a newly emerging family of MiniTEXANS, a family of multi-drug antiporters from bacteria characterized by their small size of roughly 100 amino acids. In this report we have obtained transmission FTIR spectra of EmrE in CHCl3:MeOH, DMPC vesicles, and Escherichia coli lipid vesicles. Secondary structure analysis has shown that both in DMPC vesicles and in CHCl3: MeOH the protein adopts a highly helical secondary structure that correlates remarkably well with that predicted by hydropathy analysis. The protein was shown to be resistant to amide proton H/D exchange, providing evidence that most of the protein is embedded in the lipid bilayer. Polarized ATR-FTIR spectra of the protein in DMPC vesicles have shown that the helices are oriented with an average tilt angle of 27 degrees from the bilayer normal. The protein was found to be less oriented in E. coli lipid vesicles, most likely as a result of the poor orientation of the bilayer lipids themselves. Thus, the protein is identified as a transmembrane four-helix bundle providing valuable structural data for this family of multi-drug transporters. The results set the stage for further studies aimed at deriving a detailed model for this protein.
EmrE是新出现的MiniTEXANS家族的成员，MiniTEXANS是一类来自细菌的多药反向转运蛋白家族，其特点是大小约为100个氨基酸。在本报告中，我们获得了EmrE在氯仿：甲醇、二肉豆蔻酰磷脂酰胆碱（DMPC）囊泡和大肠杆菌脂质囊泡中的傅里叶变换红外光谱（FTIR）。二级结构分析表明，在DMPC囊泡和氯仿：甲醇中，该蛋白均采用高度螺旋的二级结构，这与亲水性分析预测的结构显著相关。该蛋白对酰胺质子H/D交换具有抗性，这表明该蛋白的大部分嵌入脂质双层中。DMPC囊泡中该蛋白的偏振衰减全反射傅里叶变换红外光谱（ATR-FTIR）表明，螺旋与双层法线的平均倾斜角为27度。发现该蛋白在大肠杆菌脂质囊泡中的取向性较差，这很可能是由于双层脂质本身的取向性较差所致。因此，该蛋白被鉴定为跨膜四螺旋束，为这类多药转运蛋白家族提供了有价值的结构数据。这些结果为进一步研究该蛋白的详细模型奠定了基础。
