A.N. Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, 31/4 Leninskiy Prospekt, 119071 Moscow, Russia.
Biomolecules. 2024 Nov 19;14(11):1471. doi: 10.3390/biom14111471.
Lipid membranes, which are fundamental to cellular function, undergo various mechanical deformations. Accurate modeling of these processes necessitates a thorough understanding of membrane elasticity. The lateral shear modulus, a critical parameter describing membrane resistance to lateral stresses, remains elusive due to the membrane's fluid nature. Two contrasting hypotheses, local fluidity and global fluidity, have been proposed. While the former suggests a zero local lateral shear modulus anywhere within lipid monolayers, the latter posits that only the integral of this modulus over the monolayer thickness vanishes. These differing models lead to distinct estimations of other elastic moduli and affect the modeling of biological processes, such as membrane fusion/fission and membrane-mediated interactions. Notably, they predict distinct local stress distributions in cylindrically curved membranes. The local fluidity model proposes isotropic local lateral stress, whereas the global fluidity model predicts anisotropy due to anisotropic local lateral stretching of lipid monolayers. Using molecular dynamics simulations, this study directly investigates these models by analyzing local stress in a cylindrically curved membrane. The results conclusively demonstrate the existence of static local lateral shear stress and anisotropy in local lateral stress within the monolayers of the cylindrical membrane, strongly supporting the global fluidity model. These findings have significant implications for the calculation of surface elastic moduli and offer novel insights into the fundamental principles governing lipid membrane elasticity.
脂质膜对于细胞功能至关重要，会发生各种力学变形。准确模拟这些过程需要深入了解膜的弹性。由于膜的流体性质，侧向剪切模量（描述膜抵抗侧向应力的关键参数）仍然难以捉摸。有两种相互矛盾的假说，局部流动性和整体流动性。前者表明在脂质单层的任何位置局部侧向剪切模量均为零，而后者则认为只有该模量在单层厚度上的积分才为零。这些不同的模型导致对其他弹性模量的不同估计，并影响膜融合/裂变和膜介导相互作用等生物过程的建模。值得注意的是，它们预测了在圆柱状弯曲膜中的不同局部应力分布。局部流动性模型提出了各向同性的局部侧向应力，而整体流动性模型则由于脂质单层的各向异性局部侧向拉伸而预测了各向异性。本研究通过分析圆柱状弯曲膜中的局部应力，直接利用分子动力学模拟对这些模型进行了研究。结果明确证明了静态局部侧向剪切应力以及圆柱状膜的单层中局部侧向应力的各向异性的存在，这强烈支持了整体流动性模型。这些发现对于表面弹性模量的计算具有重要意义，并为脂质膜弹性的基本原理提供了新的见解。
