Shi Zheng, Baumgart Tobias
Department of Chemistry, University of Pennsylvania, 231 S. 34th St., Philadelphia, PA 19104, USA.
Department of Chemistry, University of Pennsylvania, 231 S. 34th St., Philadelphia, PA 19104, USA.
Adv Colloid Interface Sci. 2014 Jun;208:76-88. doi: 10.1016/j.cis.2014.01.004. Epub 2014 Jan 25.
Biological membranes undergo constant shape remodeling involving the formation of highly curved structures. The lipid bilayer represents the fundamental architecture of the cellular membrane with its shapes determined by the Helfrich curvature bending energy. However, the dynamics of bilayer shape transitions, especially their modulation by membrane proteins, and the resulting shape instabilities, are still not well understood. Here, we review in a unifying manner several theories that describe the fluctuations (i.e. undulations) of bilayer shapes as well as their local coupling with lipid or protein density variation. The coupling between local membrane curvature and lipid density gives rise to a 'slipping mode' in addition to the conventional 'bending mode' for damping the membrane fluctuation. This leads to a number of interesting experimental phenomena regarding bilayer shape dynamics. More importantly, curvature-inducing proteins can couple with membrane shape and eventually render the membrane unstable. A criterion for membrane shape instability is derived from a linear stability analysis. The instability criterion reemphasizes the importance of membrane tension in regulating the stability and dynamics of membrane geometry. Recent progresses in understanding the role of membrane tension in regulating dynamical cellular processes are also reviewed. Protein density is emphasized as a key factor in regulating membrane shape transitions: a threshold density of curvature coupling proteins is required for inducing membrane morphology transitions.
生物膜经历着持续的形状重塑，其中涉及高度弯曲结构的形成。脂质双层代表细胞膜的基本结构，其形状由赫尔弗里希曲率弯曲能决定。然而，双层形状转变的动力学，尤其是它们受膜蛋白的调节以及由此产生的形状不稳定性，仍然没有得到很好的理解。在这里，我们以统一的方式回顾几种理论，这些理论描述了双层形状的波动（即起伏）以及它们与脂质或蛋白质密度变化的局部耦合。局部膜曲率与脂质密度之间的耦合除了产生用于抑制膜波动的传统“弯曲模式”外，还产生了一种“滑动模式”。这导致了一些关于双层形状动力学的有趣实验现象。更重要的是，曲率诱导蛋白可以与膜形状耦合，最终使膜不稳定。通过线性稳定性分析得出了膜形状不稳定性的判据。该不稳定性判据再次强调了膜张力在调节膜几何形状的稳定性和动力学方面的重要性。本文还回顾了在理解膜张力在调节动态细胞过程中的作用方面的最新进展。蛋白质密度被强调为调节膜形状转变的关键因素：诱导膜形态转变需要曲率耦合蛋白的阈值密度。
