Department of Chemistry and Chemical Engineering, Chalmers University of Technology , SE-412 96 Gothenburg, Sweden.
Center for Biomembrane Physics (MEMPHYS), Department of Physics, Chemistry and Pharmacy (FKF), University of Southern Denmark , Campusvej 55, 5230 Odense M, Denmark.
Langmuir. 2017 Oct 17;33(41):11010-11017. doi: 10.1021/acs.langmuir.7b01461. Epub 2017 Oct 2.
Experimental and theoretical studies on ion-lipid interactions predict that binding of calcium ions to cell membranes leads to macroscopic mechanical effects and membrane remodeling. Herein, we provide experimental evidence that a point source of Ca acting upon a negatively charged membrane generates spontaneous curvature and triggers the formation of tubular protrusions that point away from the ion source. This behavior is rationalized by strong binding of the divalent cations to the surface of the charged bilayer, which effectively neutralizes the surface charge density of outer leaflet of the bilayer. The mismatch in the surface charge density of the two leaflets leads to nonzero spontaneous curvature. We probe this mismatch through the use of molecular dynamics simulations and validate that calcium ion binding to a lipid membrane is sufficient to generate inward spontaneous curvature, bending the membrane. Additionally, we demonstrate that the formed tubular protrusions can be translated along the vesicle surface in a controlled manner by repositioning the site of localized Ca exposure. The findings demonstrate lipid membrane remodeling in response to local chemical gradients and offer potential insights into the cell membrane behavior under conditions of varying calcium ion concentrations.
离子-脂质相互作用的实验和理论研究预测，钙离子与细胞膜的结合会导致宏观机械效应和膜重塑。本文提供了实验证据表明，钙离子的点状源作用于带负电荷的膜会产生自发曲率，并触发指向远离离子源的管状突起的形成。这种行为可以通过二价阳离子与带电荷双层的表面的强结合来合理化，这有效地中和了双层外叶的表面电荷密度。两个叶层的表面电荷密度不匹配会导致非零的自发曲率。我们通过使用分子动力学模拟来探测这种不匹配，并验证了钙离子与脂质膜的结合足以产生内向自发曲率，使膜弯曲。此外，我们证明通过重新定位局部钙暴露的位置，可以以可控的方式沿囊泡表面平移形成的管状突起。这些发现表明脂质膜会响应局部化学梯度进行重塑，并为钙离子浓度变化时细胞膜行为提供潜在的见解。
