Shi Xiaojun, Li Xiaosi, Kaliszewski Megan J, Zhuang Xiaodong, Smith Adam W
Department of Chemistry, The University of Akron , 190 Buchtel Common, Akron, Ohio 44325-3601, United States.
Langmuir. 2015 Feb 10;31(5):1784-91. doi: 10.1021/la504241w. Epub 2015 Jan 30.
Binding of biomacromolecules to anionic lipids in the plasma membrane is a common motif in many cell signaling pathways. Previous work has shown that macromolecules with cationic sequences can form nanodomains with sequestered anionic lipids, which alters the lateral distribution and mobility of the membrane lipids. Such sequestration is believed to result from the formation of a lipid-macromolecule complex. To date, however, the molecular structure and dynamics of the lipid-polymer interface are poorly understood. We have investigated the behavior of polycationic quaternized polyvinylpyridine (QPVP) on supported lipid bilayers doped with phosphatidylserine (PS) or phosphatidylinositol phosphate (PIP) lipids using time-resolved fluorescence microscopy, including pulsed interleaved excitation fluorescence cross-correlation spectroscopy (PIE-FCCS). PIE-FCCS is a dual-color fluorescence spectroscopy that translates fluctuations in fluorescence signal into a measurement of diffusion and colocalization. By labeling the polymer and lipids, we investigated the adsorption-induced translational mobility of lipids and systematically studied the influence of lipid charge density and solution ionic strength. Our results show that alteration of anionic lipid lateral mobility is dependent on the net charge of the lipid headgroup and is modulated by the ionic strength of the solution, indicating that electrostatic interactions drive the decrease in lateral mobility of anionic lipids by adsorbed QPVP. At physiological salt concentration we observe that the lipid lateral mobility is weakly influenced by QPVP and that there is no evidence of stable lipid-polymer complexes.
生物大分子与质膜中阴离子脂质的结合是许多细胞信号通路中的常见模式。先前的研究表明，具有阳离子序列的大分子可以与隔离的阴离子脂质形成纳米结构域，这会改变膜脂质的横向分布和流动性。这种隔离被认为是由脂质 - 大分子复合物的形成导致的。然而，迄今为止，脂质 - 聚合物界面的分子结构和动力学仍知之甚少。我们使用时间分辨荧光显微镜，包括脉冲交错激发荧光交叉相关光谱法（PIE - FCCS），研究了聚阳离子季铵化聚乙烯基吡啶（QPVP）在掺杂有磷脂酰丝氨酸（PS）或磷脂酰肌醇磷酸（PIP）脂质的支持脂质双层上的行为。PIE - FCCS是一种双色荧光光谱法，它将荧光信号的波动转化为扩散和共定位的测量。通过标记聚合物和脂质，我们研究了吸附诱导的脂质平移流动性，并系统地研究了脂质电荷密度和溶液离子强度的影响。我们的结果表明，阴离子脂质横向流动性的改变取决于脂质头部基团的净电荷，并受溶液离子强度的调节, 这表明静电相互作用驱动吸附的QPVP降低阴离子脂质的横向流动性。在生理盐浓度下，我们观察到脂质横向流动性受QPVP的影响较弱，并且没有证据表明存在稳定的脂质 - 聚合物复合物。
