le Coutre J, Narasimhan L R, Patel C K, Kaback H R
Howard Hughes Medical Institute, Department of Physiology, Molecular Biology Institute, University of California, Los Angeles, CA 90095-1662, USA.
Proc Natl Acad Sci U S A. 1997 Sep 16;94(19):10167-71. doi: 10.1073/pnas.94.19.10167.
The structure of lactose permease from Escherichia coli in its lipid environment was studied by attenuated total reflection Fourier transform infrared spectroscopy. The protein exhibits an alpha-helical content of about 65% and about 25% beta-sheet. Unusually fast hydrogen/deuterium (H/D) exchange to 90-95% completion suggests a structure that is highly accessible to the aqueous phase. An average tilt angle of 33 degrees for the helices was found with respect to the bilayer normal at a lipid-to-protein ratio of approximately 800:1 (mol/mol), and the permease exhibits optimal activity under these conditions. However, upon decreasing the lipid-to-protein ratio, activity decreases continuously in a manner that correlates with the decrease in the lipid order parameter and the increase in the average helical tilt angle. Taken together, the data indicate that the structure and function of the permease are strongly dependent on the order and integrity of the lipid bilayer.
利用衰减全反射傅里叶变换红外光谱研究了大肠杆菌乳糖通透酶在脂质环境中的结构。该蛋白质的α-螺旋含量约为65%，β-折叠约为25%。异常快速的氢/氘（H/D）交换达到90-95%的完成度，表明其结构对水相具有高度可及性。在脂质与蛋白质的比例约为800:1（摩尔/摩尔）时，发现螺旋相对于双层法线的平均倾斜角为33度，并且通透酶在这些条件下表现出最佳活性。然而，随着脂质与蛋白质比例的降低，活性以与脂质序参数的降低和平均螺旋倾斜角的增加相关的方式持续下降。综上所述，数据表明通透酶的结构和功能强烈依赖于脂质双层的有序性和完整性。
