Department of Physical Chemistry, Faculty of Pharmacy, University of Barcelona, Barcelona, Spain.
J Phys Chem B. 2011 Nov 10;115(44):12778-84. doi: 10.1021/jp206369k. Epub 2011 Oct 18.
Phosphatidylethanolamine (PE) and phosphatidylglycerol (PG) are the two main components of the inner membrane of Escherichia coli. It is well-known that inner membrane contains phospholipids with a nearly constant polar headgroup composition. However, bacteria can regulate the degree of unsaturation of the acyl chains in order to adapt to different external stimuli. Studies on model membranes of mixtures of PE and PG, mimicking the proportions found in E. coli, can provide essential information on the phospholipid organization in biological membranes and may help in the understanding of membrane proteins activity, such as lactose permease (LacY) of E. coli. In this work we have studied how different phosphatidylethanolamines differing in acyl chain saturation influence the formation of laterally segregated domains. Three different phospholipid systems were studied: DOPE:POPG, POPE:POPG, and DPPE:POPG at molar ratios of 3:1. Lipid mixtures were analyzed at 24 and 37 °C through three different model membranes: monolayers, liposomes, and supported lipid bilayers (SLBs). Data from three different techniques, Langmuir isotherms, Laurdan generalized polarization, and atomic force microscopy (AFM), evidenced that only the DPPE:POPG system exhibited coexistence between gel (L(β)) and fluid (L(α)) phases at both 24 and 37 °C . In the POPE:POPG system the L(β)/L(α) coexistence appears at 27 °C. Therefore, in order to investigate the distribution of LacY among phospholipid phases, we have used AFM to explore the distribution of LacY in SLBs of the three phospholipid systems at 27 °C, where the DOPE:POPG is in L(α) phase and POPE:POPG and DPPE:POPG exhibit L(β)/L(α) coexistence. The results demonstrate the preferential insertion of LacY in fluid phase.
磷脂酰乙醇胺 (PE) 和磷脂酰甘油 (PG) 是大肠杆菌内膜的两种主要成分。众所周知，内膜含有极性头部基团组成几乎恒定的磷脂。然而，细菌可以调节酰链的不饱和程度，以适应不同的外部刺激。研究 PE 和 PG 混合物的模型膜，模拟大肠杆菌中发现的比例，可以提供有关生物膜中磷脂组织的重要信息，并可能有助于理解膜蛋白的活性，例如大肠杆菌的乳糖通透酶 (LacY)。在这项工作中，我们研究了不同饱和度的磷脂酰乙醇胺如何影响侧向分隔域的形成。研究了三种不同的磷脂系统：DOPE：POPG、POPE：POPG 和 DPPE：POPG，摩尔比为 3:1。通过三种不同的模型膜：单层膜、脂质体和支撑脂质双层 (SLB)，在 24 和 37°C 下分析脂质混合物。来自三种不同技术的数据，Langmuir 等温线、Laurdan 广义极化和原子力显微镜 (AFM)，证明只有 DPPE：POPG 系统在 24 和 37°C 下表现出凝胶 (L(β)) 和流体 (L(α)) 相的共存。在 POPE：POPG 系统中，L(β)/L(α) 共存出现在 27°C。因此，为了研究 LacY 在磷脂相中的分布，我们使用 AFM 来探索三种磷脂系统在 27°C 时 SLB 中 LacY 的分布，其中 DOPE：POPG 处于 L(α)相，POPE：POPG 和 DPPE：POPG 表现出 L(β)/L(α) 共存。结果表明 LacY 优先插入流体相。
