Department of Molecular Medicine, Cornell University, Ithaca, NY, USA.
Department of Biochemistry and Biophysics, University of North Carolina (UNC) Chapel Hill School of Medicine, Chapel Hill, NC, USA.
Nat Struct Mol Biol. 2022 Apr;29(4):339-347. doi: 10.1038/s41594-022-00749-z. Epub 2022 Mar 28.
Clathrin-mediated endocytosis (CME) is the main route of internalization from the plasma membrane. It is known that the heterotetrameric AP2 clathrin adaptor must open to simultaneously engage membrane and endocytic cargo, yet it is unclear how transmembrane cargos are captured to catalyze CME. Using cryogenic-electron microscopy, we discover a new way in which mouse AP2 can reorganize to expose membrane- and cargo-binding pockets, which is not observed in clathrin-coated structures. Instead, it is stimulated by endocytic pioneer proteins called muniscins, which do not enter vesicles. Muniscin-engaged AP2 is primed to rearrange into the vesicle-competent conformation on binding the tyrosine cargo internalization motif (YxxΦ). We propose adaptor priming as a checkpoint to ensure cargo internalization.
网格蛋白介导的内吞作用（CME）是从质膜内化的主要途径。已知异源四聚体 AP2 网格蛋白衔接蛋白必须打开才能同时结合膜和内吞货物，但尚不清楚如何捕获跨膜货物以催化 CME。使用低温电子显微镜，我们发现了一种新的方式，即小鼠 AP2 可以重新组织以暴露膜和货物结合袋，在网格蛋白包被结构中观察不到这种方式。相反，它受到称为 muniscins 的内吞先驱蛋白的刺激，这些蛋白不会进入囊泡。与 muniscin 结合的 AP2 在结合酪氨酸货物内化基序（YxxΦ）时被预先配置为重新排列成具有囊泡能力的构象。我们提出衔接蛋白的启动作为确保货物内化的检查点。
