Department of Molecular and Cell Biology, University of California, Berkeley, CA 94720.
Proc Natl Acad Sci U S A. 2024 Oct 22;121(43):e2407838121. doi: 10.1073/pnas.2407838121. Epub 2024 Oct 15.
The high turgor pressure across the plasma membrane of yeasts creates a requirement for substantial force production by actin polymerization and myosin motor activity for clathrin-mediated endocytosis (CME). Endocytic internalization is severely impeded in the absence of fimbrin, an actin filament crosslinking protein called Sac6 in budding yeast. Here, we combine live-cell imaging and mathematical modeling to gain insights into the role of actin filament crosslinking proteins in force generation. Genetic manipulation showed that CME sites with more crosslinking proteins are more effective at internalization under high load. Simulations of an experimentally constrained, agent-based mathematical model recapitulate the result that endocytic networks with more double-bound fimbrin molecules internalize the plasma membrane against elevated turgor pressure more effectively. Networks with large numbers of crosslinks also have more growing actin filament barbed ends at the plasma membrane, where the addition of new actin monomers contributes to force generation and vesicle internalization. Our results provide a richer understanding of the crucial role played by actin filament crosslinking proteins during actin network force generation, highlighting the contribution of these proteins to the self-organization of the actin filament network and force generation under increased load.
酵母质膜的高渗透压使肌动蛋白聚合和肌球蛋白运动产生的力对于网格蛋白介导的内吞作用（CME）必不可少。在芽殖酵母中，网格蛋白内吞作用严重受阻，因为没有纤连蛋白，一种称为 Sac6 的肌动蛋白丝交联蛋白。在这里，我们结合活细胞成像和数学建模来深入了解肌动蛋白丝交联蛋白在力产生中的作用。遗传操作表明，交联蛋白更多的 CME 位点在高负荷下更有效地进行内吞作用。受实验限制的基于代理的数学模型的模拟再现了这样的结果，即具有更多双结合纤连蛋白分子的网格蛋白内吞网络可以更有效地抵抗升高的渗透压将质膜内吞。具有大量交联的网络在质膜上也有更多的生长肌动蛋白丝棘突，在那里添加新的肌动蛋白单体有助于产生力和囊泡内吞。我们的结果提供了对肌动蛋白丝交联蛋白在肌动蛋白网络力产生过程中所起的关键作用的更深入理解，突出了这些蛋白在增加负荷下肌动蛋白丝网络的自组织和力产生中的作用。
