We study, by means of mean field calculations and Monte Carlo simulations of a lattice-gas model, the distribution of adhesion sites of a bilayer membrane and a supporting flat surface. Our model accounts for the many-body character of the attractive interactions between adhesion points induced by the membrane thermal fluctuations. We show that while the fluctuation-mediated interactions alone are not sufficient to allow the formation of aggregation domains, they greatly reduce the strength of the direct interactions required to facilitate cluster formation. Specifically, for adhesion molecules interacting via a short range attractive potential, the strength of the direct interactions required for aggregation is reduced by about a factor of two to below the thermal energy $k_BT$.
Random pinning limits the size of membrane adhesion domains
描述膜的特定粘附力的理论模型预测（对于某些参数）键进入粘附域的宏观相分离。我们表明，这种行为是从根本上改变，如果膜是钉随机由于，例如，将细胞膜固定在细胞骨架上的蛋白质。局部限制膜高度波动的扰动诱发无规场型的淬火无序。这严格地防止了根据Imry-Ma论证[Y. Imry和S. K. Ma，Phys. Rev. Lett. 35，1399（1975）]。我们对随机场无序的预测来自分析计算，并在大规模蒙特卡罗模拟中得到了惊人的证实。这些模拟是基于一个有效的复合蒙特卡罗移动，从而膜的高度和键的自由度在一个单一的移动同时更新。这一举措的应用也应该证明对其他系统是有益的。
Cell-cell adhesion is established by specific binding of receptor and ligand proteins. The adhesion bonds attract each other and often aggregate into large clusters that are central to many biological processes. One possible origin of attractive interactions between adhesion bonds is the elastic response of the membranes to their deformation by the bonds. Here, we analyze these elasticity-mediated interactions using a novel mean-field approach. Analysis of systems at different densities of bonds, $ϕ$, reveals that the phase diagram exhibits a nearly-universal behavior when the temperature $T$ …
The detachment dynamics of a fluid membrane with an isotropic spontaneous curvature from a flat substrate are studied by using meshless membrane simulations. The membrane is detached from an open edge leading to vesicle formation. With strong adhesion, the competition between the bending and adhesion energies determines the minimum value of the spontaneous curvature for the detachment. In contrast, with weak adhesion, a detachment occurs at smaller spontaneous curvatures due to the membrane thermal undulation. When parts of the membrane are pinned on the substrate, the detachment becomes slowe…
We report on the modeling of the dynamics of confined lipid membranes. We derive a thin film model in the lubrication limit which describes an inextensible liquid membrane with bending rigidity confined between two adhesive walls. The resulting equations share similarities with the Swift-Hohenberg model. However, inextensibility is enforced by a time-dependent nonlocal tension. Depending on the excess membrane area available in the system, three different dynamical regimes, denoted as A, B and C, are found from the numerical solution of the model. In regime A, membranes with small excess area …
Biological adhesion is a critical mechanical function of complex organisms operating at multiple scales. At the cellular scale, cell-cell adhesion is remarkably tunable to enable both cohesion and malleability during development, homeostasis and disease. Such adaptable adhesion is physically supported by transient bonds between laterally mobile molecules embedded in fluid membranes. Thus, unlike specific adhesion at solid-solid or solid-fluid interfaces, peeling at fluid-fluid interfaces can proceed by breaking bonds, by moving bonds, or by a combination of both. How the additional degree of f…
The adhesion of cell membranes is mediated by the binding of membrane-anchored receptor and ligand proteins. In this article, we review recent results from simulations and theory that lead to novel insights on how the binding equilibrium and kinetics of these proteins is affected by the membranes and by the membrane anchoring and molecular properties of the proteins. Simulations and theory both indicate that the binding equilibrium constant K2D and the on- and off-rate constants of anchored receptors and ligands in their 'two-dimensional' (2D) membrane environment strongly depend on the membra…
We grafted polyacrylic acid brushes containing cysteine side chains at a defined surface density on planar lipid membranes. Specular X-ray reflectivity data indicated that the addition of Cd2+ ions induces the compaction of the polymer brush layer and modulates the adhesion of lipid vesicles. The critical threshold level inducing the switch from non-wetting to partial wetting state, [Cd2+] = 0.25 mM, was determined by microinterferometry. The interactions between vesicles and brushes were evaluated by height fluctuations of the membrane in contact with brushes and the shape of vesicles near th…
There are three regimes of cell membrane interaction with glass - Tight and loose adhesion, separated by repulsion. Explicitly including hydration, this paper evaluates the pressure between the surfaces as functions of distance for ion-correlation and ion-screened electrostatics, and electromagnetic fluctuations. The results agree with data for tight adhesion energy (0.5-3 vs 0.4-4 mJ/m2), detachment pressure (7.9 vs 9 MPa), and peak repulsion (3.4-7.5 vs 5-10 kPa), also matching the repulsion's distance dependence upon renormalization by steric pressure mainly from undulations.
We study the interaction between capillary forces and deformation in the context of a deformable capillary adhesive: a clamped, tense membrane is adhered to a rigid substrate by the surface tension of a liquid droplet. We find that the equilibrium adhesive force for this elastocapillary adhesive is significantly enhanced in comparison to the capillary adhesion between rigid plates. In particular, the equilibrium adhesion force is orders of magnitude greater when the membrane is sufficiently deformed to contact the substrate. From a dynamic perspective, however, the formation of a fluid-filled …
Eukaryotic cells adhere to extracellular matrix during the normal development of the organism, forming static adhesion as well as during cell motility. We study this process by considering a simplified coarse-grained model of a vesicle that has uniform adhesion energy with a flat substrate, mobile curved membrane proteins and active forces. We find that a high concentration of curved proteins alone increases the spreading of the vesicle, by the self-organization of the curved proteins at the high curvature vesicle-substrate contact line, thereby reducing the bending energy penalty at the vesic…
Phagocytosis is the process of engulfment and internalization of comparatively large particles by the cell, that plays a central role in the functioning of our immune system. We study the process of phagocytosis by considering a simplified coarse grained model of a three-dimensional vesicle, having uniform adhesion interaction with a rigid particle, in the presence of curved membrane proteins and active cytoskeletal forces. Complete engulfment is achieved when the bending energy cost of the vesicle is balanced by the gain in the adhesion energy. The presence of curved (convex) proteins reduces…
Direct measurement of DNA-mediated adhesion between lipid bilayers
可变形介观单元之间的多价相互作用在生物学中是普遍存在的，其中膜大分子介导相邻活细胞之间以及细胞与固体基质之间的相互作用。最近，类似的人工材料已经通过用选择性接头，特别是短DNA序列官能化顺应性布朗单元（例如乳液液滴和脂质囊泡）的外表面来合成。这一发展扩大了DNA作为选择性胶水的适用范围，最初适用于固体纳米和胶体颗粒。在非常可变形的脂质囊泡上，多价相互作用的统计效应和膜的机械变形之间的耦合引起复杂的涌现行为，正如我们最近所证明的[Parolini et al.，Nature Communications，2015，6，5948]。在这些系统中观察到的复杂现象学的几个方面仍然缺乏定量的实验表征和基本的理解。在这里，我们专注于DNA介导的多价相互作用的一个单一的脂质体粘附到一个平坦的支持双层。这种简化的几何形状使得能够估计由作用于脂质体的DNA介导的粘附力引起的膜张力。我们的实验研究完成了形态学测量和表征的DNA熔融过渡，探测原位福斯特共振能量转移光谱。实验结果进行了比较与分析理论的预测，耦合的囊泡的变形的移动连接器的统计力学的完整描述。最多只有一个拟合参数，我们的理论能够半定量地匹配实验数据，确认基本假设的质量。
Exocytosis is a common transport mechanism via which cells transport out non-essential macro-molecules (cargo) into the extra cellular space. ESCRT-III proteins are known to help in this. They polymerize into a conical spring like structure and help deform the cell membrane locally into a bud which wrapps the outgoing cargo. we model this process using a continuum energy functional. It consists of elastic energies of the membrane and the semi-rigid ESCRT-III filament, favorable adhesion energy between the cargo and the membrane, and affinity among the ESCRT-III filaments. We take the free ener…
Cellular membranes exhibit a large variety of shapes, strongly coupled to their function. Many biological processes involve dynamic reshaping of membranes, usually mediated by proteins. This interaction works both ways: while proteins influence the membrane shape, the membrane shape affects the interactions between the proteins. To study these membrane-mediated interactions on closed and anisotropically curved membranes, we use colloids adhered to ellipsoidal membrane vesicles as a model system. We find that two particles on a closed system always attract each other, and tend to align with the…
Membrane bending is an extensively studied problem from both modeling and experimental perspectives because of the wide implications of curvature generation in cell biology. Many of the curvature generating aspects in membranes can be attributed to interactions between proteins and membranes. These interactions include protein diffusion and formation of aggregates due to protein-protein interactions in the plane of the membrane. Recently, we developed a model that couples the in-plane flow of lipids and diffusion of proteins with the out-of-plane bending of the membrane. Building on this work,…
Cellular wrapping of elastic particles by a supported lipid membrane
Université Paris Cité, CNRS, Institut Jacques Monod（巴黎西岱大学，法国国家科学研究中心，雅克·莫诺研究所）；Institut Curie, Université PSL, Sorbonne Université, CNRS UMR168（居里研究所，巴黎文理研究大学，索邦大学，法国国家科学研究中心联合研究实验室）；Department of Physics, Institute for Advanced Studies in Basic Sciences (IASBS)（基础科学研究高级学院物理系）；Department of Physics and Astronomy, University of Pennsylvania（宾夕法尼亚大学物理与天文学系）
