Shindell O, Mica N, Ritzer M, Gordon V D
The University of Texas at Austin, Department of Physics and Center for Nonlinear Dynamics, 2515 Speedway, Stop C1610, Austin, Texas 78712-1199, USA.
Phys Chem Chem Phys. 2015 Jun 28;17(24):15598-607. doi: 10.1039/c4cp05877a. Epub 2015 Apr 14.
Membrane adhesion is a vital component of many biological processes. Heterogeneities in lipid and protein composition are often associated with the adhesion site. These heterogeneities are thought to play functional roles in facilitating signalling. Here we experimentally examine this phenomenon using model membranes made of a mixture of lipids that is near a phase boundary at room temperature. Non-adherent model membranes are in a well-mixed, disordered-fluid lipid phase indicated by homogeneous distribution of a fluorescent dye that is a marker for the fluid-disordered (Ld) phase. We specifically adhere membranes to a flat substrate bilayer using biotin-avidin binding. Adhesion produces two types of coexisting heterogeneities: an ordered lipid phase that excludes binding proteins and the fluorescent membrane dye, and a disordered lipid phase that is enriched in both binding proteins and membrane dye compared with the non-adhered portion of the same membrane. Thus, a single type of adhesion interaction (biotin-avidin binding), in an initially-homogeneous system, simultaneously stabilizes both ordered-phase and disordered-phase heterogeneities that are compositionally distinct from the non-adhered portion of the vesicle. These heterogeneities are long-lived and unchanged upon increased temperature.
膜黏附是许多生物过程的重要组成部分。脂质和蛋白质组成的异质性通常与黏附位点相关。这些异质性被认为在促进信号传导中发挥功能作用。在这里，我们使用由在室温下接近相界的脂质混合物制成的模型膜，通过实验研究这一现象。非黏附性模型膜处于一种充分混合的、无序流体脂质相，这由作为流体无序（Ld）相标记的荧光染料的均匀分布表明。我们使用生物素 - 抗生物素蛋白结合将膜特异性地黏附到平坦的底物双层上。黏附产生两种共存的异质性：一种有序脂质相，它排斥结合蛋白和荧光膜染料；另一种无序脂质相比同一膜的未黏附部分富含结合蛋白和膜染料。因此，在一个初始均匀的系统中，单一类型的黏附相互作用（生物素 - 抗生物素蛋白结合）同时稳定了与囊泡未黏附部分在组成上不同的有序相和无序相异质性。这些异质性寿命长，并且在温度升高时不变。
