Department of Mechanical Engineering, University of Michigan, Ann Arbor, MI, USA.
Department of Mechanical Engineering, University of Houston, Houston, TX, USA.
Commun Biol. 2020 Dec 8;3(1):743. doi: 10.1038/s42003-020-01471-6.
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 omega-shaped CCSs. 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 H helix into lipid bilayer, supports flat-to-dome transition of a CCS and stabilizes its curvature 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 H helix into lipid bilayer is not sufficient for stable epsin recruitment. Epsin's binding to adaptor protein 2 and clathrin is critical for epsin's 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 unstructured IDP region of epsin have complementary roles to ensure CME initiation and CCS maturation are unimpeded under high tension environments.
膜张力通过阻碍扁平质膜向半球形笼形蛋白包被结构（CCS）的转变，对网格蛋白介导的内吞作用（CME）起抑制作用。膜张力也阻碍了半球形穹顶向 ω 形 CCS 的转变。然而，在高张力条件下，CME 并没有完全停止。在这里，我们发现膜弯曲蛋白 epsin 将其 N 端 H 螺旋插入脂质双层，支持 CCS 的扁平到穹顶的转变，并在高张力下稳定其曲率。这一发现得到了 epsin N 端同源（ENTH）结构域分子动力学模拟的支持，该结构域在嵌入脂质双层时变得更加结构化。此外，epsin 具有固有无序蛋白（IDP）C 端结构域，通过空间排斥诱导膜曲率。H 螺旋插入脂质双层不足以稳定 epsin 的募集。epsin 与衔接蛋白 2 和网格蛋白的结合对于 epsin 在高张力条件下与 CCS 的结合至关重要，这支持了多价相互作用在 CCS 中的重要性。总之，我们的结果支持了这样一种模型，即 epsin 的 ENTH 和无规卷曲 IDP 区域具有互补作用，以确保在高张力环境下 CME 的起始和 CCS 的成熟不受阻碍。
