Kleinschmidt Jörg H, Tamm Lukas K
Department of Molecular Physiology and Biological Physics, University of Virginia Health System, Charlottesville, Virginia 22908-0736, USA.
Biophys J. 2002 Aug;83(2):994-1003. doi: 10.1016/S0006-3495(02)75225-9.
The self-assembled supramolecular structures of diacylphosphatidylcholine (diC(n)PC), diacylphosphatidylethanolamine (diC(n)PE), diacylphosphatidyglycerol (diC(n)PG), and diacylphosphatidylserine (diC(n)PS) were investigated by (31)P nuclear magnetic resonance (NMR) spectroscopy as a function of the hydrophobic acyl chain length. Short-chain homologs of these lipids formed micelles, and longer-chain homologs formed bilayers. The shortest acyl chain lengths that supported bilayer structures depended on the headgroup of the lipids. They increased in the order PE (C(6)) < PC (C(9)) < or = PS (C(9) or C(10)) < PG (C(11) or C(12)). This order correlated with the effective headgroup area, which is a function of the physical size, charge, hydration, and hydrogen-bonding capacity of the four headgroups. Electrostatic screening of the headgroup charge with NaCl reduced the effective headgroup area of PS and PG and thereby decreased the micelle-to-bilayer transition of these lipid classes to shorter chain lengths. The experimentally determined supramolecular structures were compared to the assembly states predicted by packing constraints that were calculated from the hydrocarbon-chain volume and effective headgroup area of each lipid. The model accurately predicted the chain-length threshold for bilayer formation if the relative displacement of the acyl chains of the phospholipid were taken into account. The model also predicted cylindrical rather than spherical micelles for all four diacylphospholipid classes and the (31)P-NMR spectra provided evidence for a tubular network that appeared as an intermediate phase at the micelle-to-bilayer transition. The free energy of micellization per methylene group was independent of the structure of the supramolecular assembly, but was -0.95 kJ/mol (-0.23 kcal/mol) for the PGs compared to -2.5 kJ/mol (-0.60 kcal/mol) for the PCs. The integral membrane protein OmpA did not change the bilayer structure of thin (diC(10)PC) bilayers.
通过³¹P核磁共振（NMR）光谱研究了二酰基磷脂酰胆碱（diC(n)PC）、二酰基磷脂酰乙醇胺（diC(n)PE）、二酰基磷脂酰甘油（diC(n)PG）和二酰基磷脂酰丝氨酸（diC(n)PS）的自组装超分子结构与疏水酰基链长度的关系。这些脂质的短链同系物形成胶束，而长链同系物形成双层。支持双层结构的最短酰基链长度取决于脂质的头基。它们按以下顺序增加：PE（C(6)）＜PC（C(9)）≤PS（C(9)或C(10)）＜PG（C(11)或C(12)）。该顺序与有效头基面积相关，有效头基面积是这四种头基的物理尺寸、电荷、水合作用和氢键结合能力的函数。用NaCl对头基电荷进行静电屏蔽会减小PS和PG的有效头基面积，从而降低这些脂质类别从胶束到双层的转变至更短的链长度。将实验确定的超分子结构与根据每种脂质的烃链体积和有效头基面积计算出的堆积限制所预测的组装状态进行了比较。如果考虑磷脂酰基链的相对位移，该模型能准确预测双层形成的链长阈值。该模型还预测所有四种二酰基磷脂类形成的是圆柱形而非球形胶束，并且³¹P-NMR光谱为在胶束到双层转变时作为中间相出现的管状网络提供了证据。每个亚甲基的胶束化自由能与超分子组装结构无关，但PGs为-0.95 kJ/mol（-0.23 kcal/mol），而PCs为-2.5 kJ/mol（-0.60 kcal/mol）。整合膜蛋白OmpA不会改变薄（diC(10)PC）双层的双层结构。
