Force generation by actin assembly shapes cellular membranes. An experimentally constrained multiscale model shows that a minimal branched actin network is sufficient to internalize endocytic pits against membrane. Around 200 activated Arp2/3 complexes are required for robust internalization. A newly developed molecule-counting method determined that ~200 Arp2/3 complexes assemble at sites of clathrin-mediated endocytosis in human cells. Simulations predict that actin self-organizes into a radial branched array with growing ends oriented toward the base of the pit. Long actin filaments bend between attachment sites in the coat and the base of the pit. Elastic energy stored in bent filaments, whose presence was confirmed by cryo-electron tomography, contributes to endocytic internalization. Elevated membrane tension directs more growing filaments toward the base of the pit, increasing actin nucleation and bending for increased force production. Thus, spatially constrained actin filament assembly utilizes an adaptive mechanism enabling endocytosis under varying physical constraints.

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网格蛋白介导的内吞作用过程中肌动蛋白细胞骨架的自组织和负荷适应原理

通过肌动蛋白组装产生的力使细胞膜成形。实验约束的多尺度模型表明，最小的分支肌动蛋白网络足以内化细胞膜内膜凹点。强大的内部化需要大约200个激活的Arp2 / 3复合物。一种新开发的分子计数方法确定〜200 Arp2 / 3复合物在网格蛋白介导的人类细胞内吞作用位点组装。模拟预测肌动蛋白自组织成一个径向分支阵列，其生长末端朝向凹坑的底部。长的肌动蛋白丝在皮层的附着部位和凹坑的底部之间弯曲。储存在弯曲细丝中的弹性能有助于细胞内吞的内在化，而弯曲电子细丝的存在被冷冻电子断层扫描所证实。较高的膜张力会将更多生长的细丝引向凹坑的底部，从而增加肌动蛋白的成核作用和弯曲度，从而增加力的产生。因此，受空间限制的肌动蛋白丝组件利用了一种适应性机制，能够在变化的物理约束条件下进行内吞。