Yoshina-Ishii Chiaki, Chan Yee-Hung M, Johnson Joseph M, Kung Li A, Lenz Peter, Boxer Steven G
Department of Chemistry, Stanford University, Stanford, California 94305, USA.
Langmuir. 2006 Jun 20;22(13):5682-9. doi: 10.1021/la0534219.
We recently introduced a method to tether intact phospholipid vesicles onto a fluid supported lipid bilayer using DNA hybridization (Yoshina-Ishii, C.; Miller, G. P.; Kraft, M. L; Kool, E. T.; Boxer, S. G. J. Am. Chem. Soc. 2005, 127, 1356-1357). Once tethered, the vesicles can diffuse in two dimensions parallel to the supported membrane surface. The average diffusion coefficient, D, is typically 0.2 microm(2)/s; this is 3-5 times smaller than for individual lipid or DNA-lipid conjugate diffusion in supported bilayers. In this article, we investigate the origin of this difference in the diffusive dynamics of tethered vesicles by single-particle tracking under collision-free conditions. D is insensitive to tethered vesicle size from 30 to 200 nm, as well as a 3-fold change in the viscosity of the bulk medium. The addition of macromolecules such as poly(ethylene glycol) reversibly stops the motion of tethered vesicles without causing the exchange of lipids between the tethered vesicle and supported bilayer. This is explained as a depletion effect at the interface between tethered vesicles and the supported bilayer. Ca ions lead to transient vesicle-vesicle interactions when tethered vesicles contain negatively charged lipids, and vesicle diffusion is greatly reduced upon Ca ion addition when negatively charged lipids are present both in the supported bilayer and tethered vesicles. Both effects are interesting in their own right, and they also suggest that tethered vesicle-supported bilayer interactions are possible; this may be the origin of the reduction in D for tethered vesicles. In addition, the effects of surface defects that reversibly trap diffusing vesicles are modeled by Monte Carlo simulations. This shows that a significant reduction in D can be observed while maintaining normal diffusion behavior on the time scale of our experiments.
我们最近介绍了一种利用DNA杂交将完整的磷脂囊泡拴系到流体支撑脂质双层上的方法（吉名井智惠子、C.；米勒、G.P.；克拉夫特、M.L；库尔、E.T.；博克瑟、S.G.《美国化学会志》2005年，127卷，1356 - 1357页）。一旦拴系，囊泡就能在与支撑膜表面平行的二维空间中扩散。平均扩散系数D通常为0.2微米²/秒；这比支撑双层中单个脂质或DNA - 脂质共轭物的扩散系数小3 - 5倍。在本文中，我们通过在无碰撞条件下的单粒子追踪来研究拴系囊泡扩散动力学中这种差异的起源。D对30至200纳米的拴系囊泡大小以及本体介质粘度3倍的变化不敏感。添加诸如聚乙二醇等大分子会可逆地使拴系囊泡的运动停止，而不会导致拴系囊泡与支撑双层之间的脂质交换。这被解释为拴系囊泡与支撑双层之间界面处的耗尽效应。当拴系囊泡含有带负电荷的脂质时，钙离子会导致囊泡 - 囊泡之间的瞬时相互作用，并且当支撑双层和拴系囊泡中都存在带负电荷的脂质时，添加钙离子后囊泡扩散会大大降低。这两种效应本身都很有趣，它们还表明拴系囊泡 - 支撑双层之间的相互作用是可能的；这可能是拴系囊泡扩散系数降低的原因。此外，通过蒙特卡罗模拟对可逆捕获扩散囊泡的表面缺陷的影响进行了建模。这表明在我们实验的时间尺度上保持正常扩散行为的同时，可以观察到扩散系数的显著降低。
