Department of Biological Sciences, Columbia University, New York, New York 10027, USA.
J Am Chem Soc. 2010 Sep 22;132(37):12874-86. doi: 10.1021/ja1002185.
Understanding the effect of mechanical stress on membranes is of primary importance in biophysics. Here we use force spectroscopy AFM to quantitatively characterize the nanomechanical stability of supported lipid bilayers as a function of their chemical composition. The onset of plastic deformation reveals itself as a repetitive jump in the approaching force curve, which represents a molecular fingerprint for the bilayer mechanical stability. By systematically probing a set of chemically distinct supported lipid bilayers (SLBs), we first show that both the headgroup and tail have a decisive effect on their mechanical properties. While the mechanical stability of the probed SLBs linearly increases by 3.3 nN upon the introduction of each additional -CH(2)- in the chain, it exhibits a significant dependence on the phospholipid headgroup, ranging from 3 nN for DPPA to 66 nN for DPPG. Furthermore, we also quantify the reduction of the membrane mechanical stability as a function of the number of unsaturations and molecular branching in the chemical structure of the apolar tails. Finally, we demonstrate that, upon introduction of cholesterol and ergosterol, contrary to previous belief the mechanical stability of membranes not only increases linearly in the liquid phase (DLPC) but also for phospholipids present in the gel phase (DPPC). Our results are discussed in the framework of the continuum nucleation model. This work highlights the compelling effect of subtle variations in the chemical structure of phospholipid molecules on the membrane response when exposed to mechanical forces, a mechanism of common occurrence in nature.
理解机械应力对膜的影响在生物物理学中至关重要。在这里，我们使用力谱原子力显微镜（AFM）定量表征支撑脂质双层的纳米力学稳定性，作为其化学组成的函数。塑性变形的开始表现为逼近力曲线的重复跳跃，这代表了双层力学稳定性的分子指纹。通过系统地探测一组化学性质不同的支撑脂质双层（SLB），我们首先表明头基和尾基都对其力学性能有决定性的影响。虽然在链中引入每个额外的-CH(2)-会使所探测的 SLB 的机械稳定性线性增加 3.3 nN，但它对头基团的依赖性很大，范围从 3 nN 的 DPPA 到 66 nN 的 DPPG。此外，我们还定量地量化了膜机械稳定性随非饱和键数量和极性尾部化学结构中分子支化的减少而降低的情况。最后，我们证明，与先前的观点相反，胆固醇和麦角固醇的引入不仅使膜的机械稳定性在液相（DLPC）中线性增加，而且在凝胶相（DPPC）中存在的磷脂中也是如此。我们的结果在连续体成核模型的框架内进行了讨论。这项工作强调了在暴露于机械力时，磷脂分子化学结构的微小变化对膜响应的强烈影响，这是自然界中常见的一种机制。
