Self-assembly of CIP4 drives actin-mediated asymmetric pit-closing in clathrin-mediated endocytosis

Abstract Clathrin-mediated endocytosis plays a pivotal role in signal transduction pathways between the extracellular environment and the intracellular space. Accumulating evidence from live-cell imaging and super-resolution microscopy of mammalian cells suggests an asymmetric distribution of actin fibres near the clathrin-coated pit, which induces asymmetric pit-closing, rather than radial constriction. However, detailed molecular mechanisms of this “asymmetricity” remain elusive. Herein, we used high-speed atomic force microscopy to demonstrate that CIP4, a multidomain protein with a classic F-BAR domain and intrinsically disordered regions, is necessary for asymmetric pit-closing. Strong self-assembly of CIP4 via intrinsically disordered regions, together with stereospecific interactions with the curved membrane and actin-regulating proteins, generates a small actin-rich environment near the pit, which deforms the membrane and closes the pit. Our results provide a mechanistic insight into how spatio-temporal actin polymerization near the plasma membrane is promoted by a collaboration of disordered and structured domains.