大多数完整的膜蛋白,在原核和真核细胞中,通过Sec型转环共翻译插入膜中:原核生物中的SecYEG复合物和真核生物中的Sec61复合物。对于Sec61介导的内质网(ER)膜插入,已测量了单个氨基酸对单个跨膜α-螺旋膜插入的总自由能的贡献(Nature450:1026-1030),但尚未系统地确定SecYEG介导的细菌内膜插入。我们现在报告这样的测量,在大肠杆菌中进行。总的来说,哺乳动物内质网和大肠杆菌内膜的结果之间有很好的相关性,但是SecYEG介导的插入的疏水性阈值明显低于Sec61介导的插入。
Most integral membrane proteins, both in prokaryotic and eukaryotic cells, are co-translationally inserted into the membrane via Sec-type translocons: the SecYEG complex in prokaryotes and the Sec61 complex in eukaryotes. The contributions of individual amino acids to the overall free energy of membrane insertion of single transmembrane α-helices have been measured for Sec61-mediated insertion into the endoplasmic reticulum (ER) membrane (Nature 450:1026-1030) but have not been systematically determined for SecYEG-mediated insertion into the bacterial inner membrane. We now report such measurements, carried out in Escherichia coli. Overall, there is a good correlation between the results found for the mammalian ER and the E. coli inner membrane, but the hydrophobicity threshold for SecYEG-mediated insertion is distinctly lower than that for Sec61-mediated insertion.