MRC Laboratory of Molecular Biology, Cambridge, United Kingdom.
PLoS Biol. 2012;10(4):e1001302. doi: 10.1371/journal.pbio.1001302. Epub 2012 Apr 10.
Clathrin-mediated endocytosis proceeds by a sequential series of reactions catalyzed by discrete sets of protein machinery. The final reaction in clathrin-mediated endocytosis is membrane scission, which is mediated by the large guanosine triophosphate hydrolase (GTPase) dynamin and which may involve the actin-dependent recruitment of N-terminal containing BIN/Amphiphysin/RVS domain containing (N-BAR) proteins. Optical microscopy has revealed a detailed picture of when and where particular protein types are recruited in the ∼20-30 s preceding scission. Nevertheless, the regulatory mechanisms and functions that underpin protein recruitment are not well understood. Here we used an optical assay to investigate the coordination and interdependencies between the recruitment of dynamin, the actin cytoskeleton, and N-BAR proteins to individual clathrin-mediated endocytic scission events. These measurements revealed that a feedback loop exists between dynamin and actin at sites of membrane scission. The kinetics of dynamin, actin, and N-BAR protein recruitment were modulated by dynamin GTPase activity. Conversely, acute ablation of actin dynamics using latrunculin-B led to a ∼50% decrease in the incidence of scission, an ∼50% decrease in the amplitude of dynamin recruitment, and abolished actin and N-BAR recruitment to scission events. Collectively these data suggest that dynamin, actin, and N-BAR proteins work cooperatively to efficiently catalyze membrane scission. Dynamin controls its own recruitment to scission events by modulating the kinetics of actin and N-BAR recruitment to sites of scission. Conversely actin serves as a dynamic scaffold that concentrates dynamin and N-BAR proteins at sites of scission.
网格蛋白介导的内吞作用通过一系列由离散蛋白机器催化的连续反应进行。网格蛋白介导的内吞作用的最后一个反应是膜的断裂,这是由大的鸟嘌呤三磷酸水解酶 (GTPase) 动力蛋白介导的,可能涉及含 N 端的肌动蛋白依赖性募集BIN/Amphiphysin/RVS 结构域包含 (N-BAR) 蛋白。光学显微镜揭示了在断裂前约 20-30 秒内特定蛋白类型何时以及何地被募集的详细情况。然而,蛋白募集的调控机制和功能还不是很清楚。在这里,我们使用光学测定法研究了动力蛋白、肌动蛋白细胞骨架和 N-BAR 蛋白在单个网格蛋白介导的内吞作用断裂事件中的募集的协调性和相互依赖性。这些测量结果表明,在膜断裂部位存在动力蛋白和肌动蛋白之间的反馈环。动力学、肌动蛋白和 N-BAR 蛋白募集的动力学受动力蛋白 GTPase 活性的调节。相反,使用 latrunculin-B 急性消融肌动蛋白动力学导致断裂的发生率降低约 50%,动力蛋白募集的幅度降低约 50%,并使肌动蛋白和 N-BAR 募集到断裂事件中。总的来说,这些数据表明,动力蛋白、肌动蛋白和 N-BAR 蛋白协同工作,有效地催化膜断裂。动力蛋白通过调节肌动蛋白和 N-BAR 蛋白向断裂部位的募集动力学来控制自身向断裂事件的募集。相反,肌动蛋白作为一种动态支架,将动力蛋白和 N-BAR 蛋白集中在断裂部位。