Marsh Derek, Jost Micha, Peggion Cristina, Toniolo Claudio
Max-Planck-Institut für biophysikalische Chemie, Abteilung Spektroskopie, 37070 Göttingen, Germany.
Biophys J. 2007 Jun 1;92(11):4002-11. doi: 10.1529/biophysj.107.104026. Epub 2007 Mar 9.
Alamethicin is a 19-residue hydrophobic peptide, which is extended by a C-terminal phenylalaninol but lacks residues that might anchor the ends of the peptide at the lipid-water interface. Voltage-dependent ion channels formed by alamethicin depend strongly in their characteristics on chain length of the host lipid membranes. EPR spectroscopy is used to investigate the dependence on lipid chain length of the incorporation of spin-labeled alamethicin in phosphatidylcholine bilayer membranes. The spin-label amino acid TOAC is substituted at residue positions n = 1, 8, or 16 in the sequence of alamethicin F50/5 [TOAC(n), Glu(OMe)(7,18,19)]. Polarity-dependent isotropic hyperfine couplings of the three TOAC derivatives indicate that alamethicin assumes approximately the same location, relative to the membrane midplane, in fluid diC(N)PtdCho bilayers with chain lengths ranging from N = 10-18. Residue TOAC(8) is situated closest to the bilayer midplane, whereas TOAC(16) is located farther from the midplane in the hydrophobic core of the opposing lipid leaflet, and TOAC(1) remains in the lipid polar headgroup region. Orientational order parameters indicate that the tilt of alamethicin relative to the membrane normal is relatively small, even at high temperatures in the fluid phase, and increases rather slowly with decreasing chain length (from 13 degrees to 23 degrees for N = 18 and 10, respectively, at 75 degrees C). This is insufficient for alamethicin to achieve hydrophobic matching. Alamethicin differs in its mode of incorporation from other helical peptides for which transmembrane orientation has been determined as a function of lipid chain length.
短杆菌肽A是一种由19个氨基酸残基组成的疏水肽，其C端为苯丙氨醇，但缺乏可能将肽链两端固定在脂-水界面的残基。由短杆菌肽A形成的电压依赖性离子通道的特性在很大程度上取决于宿主脂质膜的链长。电子顺磁共振光谱用于研究自旋标记的短杆菌肽A在磷脂酰胆碱双层膜中的掺入对脂质链长的依赖性。自旋标记氨基酸TOAC在短杆菌肽F50/5序列的第n = 1、8或16位残基处取代[TOAC(n)，Glu(OMe)(7,18,19)]。三种TOAC衍生物的极性依赖性各向同性超精细偶合表明，在链长范围为N = 10 - 18的流体二C(N)磷脂酰胆碱双层膜中，短杆菌肽A相对于膜中平面的位置大致相同。残基TOAC(8)最靠近双层膜中平面，而TOAC(16)位于相对脂质小叶疏水核心中离中平面较远的位置，TOAC(1)则保留在脂质极性头部区域。取向序参数表明，即使在流体相的高温下，短杆菌肽A相对于膜法线的倾斜度也相对较小，并且随着链长的减小增加相当缓慢（在75℃时，N = 18和10时分别从13度增加到23度）。这不足以使短杆菌肽A实现疏水匹配。短杆菌肽A的掺入模式与其他已确定跨膜取向与脂质链长函数关系的螺旋肽不同。
