Lasch P, Schultz C P, Naumann D
Robert Koch-Institut, 13353 Berlin, Germany.
Biophys J. 1998 Aug;75(2):840-52. doi: 10.1016/S0006-3495(98)77573-3.
Fourier transform infrared (FTIR) spectroscopy has been used to study the thermotropic phase behavior of binary lipid mixtures composed of deuterated phospholipids (PLs) and lipopolysaccharides (LPSs). Furthermore, the influence of an extrinsic high-molecular, polycationic polypeptide (poly-(L-lysine), PLL(500)) and an intrinsic membrane protein (outer membrane protein F, OmpF) on these binary mixtures was investigated by FTIR spectroscopy. "Deep rough" mutant LPS (ReLPS), isolated from Salmonella minnesota R595, and perdeuterated 1,2-dimyristoylphosphatidylethanolamine (DMPEd54) were used as model lipids. Deuteration of one of the lipids permitted the detection of lipid protein interaction with each lipid component separately. For this purpose, the symmetric >CH2 and >CD2 stretching bands were utilized as specific monitors to scrutinize the state of order of the membranes. From the individual phase transition temperatures Tm and the shape of the phase transition profiles, it is established that ReLPS and DMPEd54 are molecularly immiscible. In addition to the two domains of the pure lipid components, a third, domain-like structure is detected that may coexist with these pure domains. This domain-like structure undergoes a gel to liquid-crystalline L1 (beta <--> alpha) phase transition at temperatures distinctly different from that of the respective pure lipid domains. The nature of this type of domain is discussed in terms of a "border region" model that adequately explains the experimentally observed complex phase transition profiles. It is further demonstrated that the extrinsic polycationic polypeptide PLL(500) and the intrinsic, pore-forming protein OmpF isolated from Escherichia coli interact preferentially and highly specifically with the negatively charged ReLPS. Both the synthetic polypeptide and the pore-forming protein increased the tendency of ReLPS and DMPEd54 to segregate into distinct, well-separated domains. Whereas the transition profiles of the ternary system ReLPS/DMPEd54/PLL(500) showed the features of a phase segregation phenomenon not affecting the transition temperatures of the pure lipid components, the ternary system composed of ReLPS/DMPEd54 and OmpF exhibited phase transition curves that were characterized by an unspecific (DMPEd54/OmpF) and a strong and unique (ReLPS/OmpF) type of lipid-protein interaction. Furthermore, semiquantitative estimations supported the supposition that OmpF might be able to induce bilayer asymmetry in preformed symmetrical ReLPS/DMPEd54 vesicles.
傅里叶变换红外（FTIR）光谱已被用于研究由氘代磷脂（PLs）和脂多糖（LPSs）组成的二元脂质混合物的热致相行为。此外，通过FTIR光谱研究了外在的高分子聚阳离子多肽（聚-L-赖氨酸，PLL(500)）和内在膜蛋白（外膜蛋白F，OmpF）对这些二元混合物的影响。从明尼苏达沙门氏菌R595分离得到的“深度粗糙”突变型LPS（ReLPS）和全氘代1,2-二肉豆蔻酰磷脂酰乙醇胺（DMPEd54）被用作模型脂质。其中一种脂质的氘代使得能够分别检测脂质与每种脂质成分的相互作用。为此，利用对称的>CH2和>CD2伸缩带作为特定监测器来仔细研究膜的有序状态。从各个相变温度Tm和相变曲线的形状可以确定，ReLPS和DMPEd54在分子水平上是不混溶的。除了纯脂质成分的两个区域外，还检测到第三个类似区域的结构，它可能与这些纯区域共存。这种类似区域的结构在与各自纯脂质区域明显不同的温度下经历凝胶到液晶L1（β<-->α）的相变。根据“边界区域”模型讨论了这种区域类型的性质，该模型充分解释了实验观察到的复杂相变曲线。进一步证明，外在的聚阳离子多肽PLL(500)和从大肠杆菌分离得到的内在成孔蛋白OmpF优先且高度特异性地与带负电荷的ReLPS相互作用。合成多肽和成孔蛋白都增加了ReLPS和DMPEd54分离成不同的、分隔良好的区域的趋势。三元体系ReLPS/DMPEd54/PLL(500)的相变曲线显示出相分离现象的特征，且不影响纯脂质成分的转变温度，而由ReLPS/DMPEd54和OmpF组成的三元体系的相变曲线的特征是存在非特异性的（DMPEd54/OmpF）以及强烈且独特的（ReLPS/OmpF）脂质-蛋白质相互作用类型。此外，半定量估计支持了OmpF可能能够在预先形成的对称ReLPS/DMPEd54囊泡中诱导双层不对称性的假设。
