Jackman Joshua A, Kim Min Chul, Zhdanov Vladimir P, Cho Nam-Joon
School of Materials Science and Engineering, Nanyang Technological University, 50 Nanyang Avenue 639798, Singapore.
Phys Chem Chem Phys. 2016 Jan 28;18(4):3065-72. doi: 10.1039/c5cp06786c.
Phospholipid assemblies on solid supports mimic the cell membrane, and provide a platform to study membrane biology. Among the different types of model membranes, the planar bilayer is a two-dimensional lipid bilayer sheet that can be formed by the adsorption and spontaneous rupture of vesicles. The formation process is influenced by the interactions between vesicles and the solid support as well as between vesicles. On silicon oxide, which is a commonly used solid support, vesicles typically adsorb until reaching a critical coverage and then spontaneous rupture begins. Although it is generally understood that spontaneous rupture leads to planar bilayer formation, oversaturation of vesicles at the critical coverage can hinder the whole process due to a steric factor. To date, the role of this factor has been scrutinized only in relation to temperature, and the influence of additional parameters remains to be elucidated. In this work, we have investigated how vesicle size and corresponding steric constraints influence the kinetics of vesicle adsorption and rupture and, more specifically, how the state of adsorbed vesicles after fusion depends on the vesicle size. Using quartz crystal microbalance-dissipation (QCM-D) and fluorescence recovery after photobleaching (FRAP), we characterized the adsorption kinetics of vesicles onto silicon oxide and the lateral mobility of solid-supported lipid assemblies. While the vesicle adsorption kinetics were diffusion-limited up to the onset of vesicle rupture, the extent of rupture depended on vesicle size and it was observed that larger vesicles are more prone to steric effects than smaller vesicles. We discuss this finding in terms of the structural transformation from adsorbed vesicles to a planar bilayer, including how the interplay of thermodynamic, kinetic and steric factors can affect vesicle rupture on solid supports.
固体支持物上的磷脂组装体模拟细胞膜，并为研究膜生物学提供了一个平台。在不同类型的模型膜中，平面双层是一种二维脂质双层片，可以通过囊泡的吸附和自发破裂形成。形成过程受囊泡与固体支持物之间以及囊泡之间相互作用的影响。在常用的固体支持物氧化硅上，囊泡通常会吸附直至达到临界覆盖率，然后开始自发破裂。虽然一般认为自发破裂会导致平面双层的形成，但在临界覆盖率下囊泡的过饱和由于空间位阻因素会阻碍整个过程。迄今为止，仅在与温度相关的方面研究了该因素的作用，其他参数的影响仍有待阐明。在这项工作中，我们研究了囊泡大小和相应的空间位阻如何影响囊泡吸附和破裂的动力学，更具体地说，融合后吸附囊泡的状态如何取决于囊泡大小。使用石英晶体微天平耗散（QCM-D）和光漂白后荧光恢复（FRAP），我们表征了囊泡在氧化硅上的吸附动力学以及固体支持脂质组装体横向迁移率。虽然在囊泡破裂开始之前囊泡吸附动力学受扩散限制，但破裂程度取决于囊泡大小，并且观察到较大的囊泡比较小的囊泡更容易受到空间位阻效应的影响。我们从吸附囊泡到平面双层的结构转变方面讨论了这一发现，包括热力学、动力学和空间位阻因素的相互作用如何影响固体支持物上囊泡的破裂。
