Complimentary action of structured and unstructured domains of epsin supports clathrin-mediated endocytosis at high tension
Membrane tension plays an inhibitory role in clathrin-mediated endocytosis (CME) by impeding the transition of flat plasma membrane to hemispherical clathrin-coated structures (CCSs). Membrane tension also impedes the transition of hemispherical domes to omegashaped CCSs, a necessary step before their internalization via dynamin-mediated membrane scission. However, CME is not completely halted in cells under high tension conditions. Here we find that epsin, a membrane bending protein which inserts its N-terminus H0 helix into lipid bilayer, supports flat-to-dome transition and increases the stability of CCSs at high tension. This discovery is supported by molecular dynamic simulation of the epsin N-terminal homology (ENTH) domain that becomes more structured when embedded in a lipid bilayer. In addition, epsin has an intrinsically disordered protein (IDP) C-terminus domain which induces membrane curvature via steric repulsion. Insertion of H0 helix into lipid bilayer is not sufficient for stable epsin recruitment as deleting the IDP domain in epsin renders it cytosolic. Epsins binding to adaptor protein 2 and clathrin is critical for epsins association with CCSs under high tension conditions, supporting the importance of multivalent interactions in CCSs. Together, our results support a model where the ENTH and IDP domains of epsin have complementary roles to ensure CME initiation and CCS maturation are unimpeded under high tension environments.