Jayasinghe S, Barranger-Mathys M, Ellena J F, Franklin C, Cafiso D S
Department of Chemistry and Biophysics Program at the University of Virginia, Charlottesville 22901, USA.
Biophys J. 1998 Jun;74(6):3023-30. doi: 10.1016/S0006-3495(98)78010-5.
Two approaches employing nuclear magnetic resonance (NMR) were used to investigate the transmembrane migration rate of the C-terminal end of native alamethicin and a more hydrophobic analog called L1. Native alamethicin exhibits a very slow transmembrane migration rate when bound to phosphatidylcholine vesicles, which is no greater than 1 x 10(-4) min(-1). This rate is much slower than expected, based on the hydrophobic partition energies of the amino acid side chains and the backbone of the exposed C-terminal end of alamethicin. The alamethicin analog L1 exhibits crossing rates that are at least 1000 times faster than that of native alamethicin. A comparison of the equilibrium positions of these two peptides shows that L1 sits approximately 3-4 A deeper in the membrane than does native alamethicin (Barranger-Mathys and Cafiso. 1996. Biochemistry. 35:489). The slow rate of alamethicin crossing can be explained if the peptide helix is irregular at its C-terminus and hydrogen bonded to solvent or lipid. We postulate that L1 does not experience as large a barrier to transport because its C-terminus is already buried within the membrane interface. This difference is most easily explained by conformational differences between L1 and alamethicin rather than differences in hydrophobicity. The results obtained here demonstrate that side-chain hydrophobicity alone cannot account for the energy barriers to peptide and protein transport across membranes.
采用两种利用核磁共振（NMR）的方法来研究天然短杆菌肽的C末端以及一种名为L1的疏水性更强的类似物的跨膜迁移速率。当与磷脂酰胆碱囊泡结合时，天然短杆菌肽的跨膜迁移速率非常缓慢，不超过1×10⁻⁴ min⁻¹。基于短杆菌肽暴露的C末端氨基酸侧链和主链的疏水分配能，这个速率比预期的要慢得多。短杆菌肽类似物L1的穿越速率比天然短杆菌肽至少快1000倍。对这两种肽平衡位置的比较表明，L1在膜中的位置比天然短杆菌肽大约深3 - 4埃（Barranger - Mathys和Cafiso，1996年，《生物化学》，35:489）。如果肽螺旋在其C末端不规则且与溶剂或脂质形成氢键，那么短杆菌肽缓慢的穿越速率就可以得到解释。我们推测L1没有经历同样大的运输障碍，因为它的C末端已经埋在膜界面内。这种差异最容易通过L1和短杆菌肽之间的构象差异而不是疏水性差异来解释。此处获得的结果表明，仅侧链疏水性不能解释肽和蛋白质跨膜运输的能量障碍。
