Membrane Binding and Self-Association of the Epsin N-Terminal Homology Domain

Chun-Liang Lai,Christine C. Jao,Edward Lyman,Brian J. Peter,Harvey T. McMahon,Ralf Langen,Jennifer L. Gallop,Gregory A. Voth

doi:10.1016/j.jmb.2012.08.010

Abstract

Epsin possesses a conserved epsin N-terminal homology (ENTH) domain that acts as a phosphatidylinositol 4,5-bisphosphate‐lipid‐targeting and membrane‐curvature‐generating element. Upon binding phosphatidylinositol 4,5‐bisphosphate, the N-terminal helix (H0) of the ENTH domain becomes structured and aids in the aggregation of ENTH domains, which results in extensive membrane remodeling. In this article, atomistic and coarse-grained (CG) molecular dynamics (MD) simulations are used to investigate the structure and the stability of ENTH domain aggregates on lipid bilayers. EPR experiments are also reported for systems composed of different ENTH-bound membrane morphologies, including membrane vesicles as well as preformed membrane tubules. The EPR data are used to help develop a molecular model of ENTH domain aggregates on preformed lipid tubules that are then studied by CG MD simulation. The combined computational and experimental approach suggests that ENTH domains exist predominantly as monomers on vesiculated structures, while ENTH domains self-associate into dimeric structures and even higher‐order oligomers on the membrane tubes. The results emphasize that the arrangement of ENTH domain aggregates depends strongly on whether the local membrane curvature is isotropic or anisotropic. The molecular mechanism of ENTH‐domain-induced membrane vesiculation and tubulation and the implications of the epsin's role in clathrin-mediated endocytosis resulting from the interplay between ENTH domain membrane binding and ENTH domain self-association are also discussed.

Highlights

The cytoplasmic membrane surface serves as a platform for many critical cellular signaling and trafficking pathways
We present EPR data showing that the N-terminal helix of epsin N-terminal homology (ENTH) (H0) becomes structured when ENTH domain binds to PIP2containing membrane
Depth is measured parallel to the membrane normal with respect to the lipid bilayer phosphate groups. (c) Distribution of the center of mass of H0 with respect to the lipid bilayer phosphate groups as was calculated from the last 50‐ns trajectory of molecular dynamics (MD) simulation. (d) Close-up view of the ENTH domain membraneinteracting motifs and the binding site of the PIP2 headgroup to the ENTH domain

Summary

Introduction

The cytoplasmic membrane surface serves as a platform for many critical cellular signaling and trafficking pathways. The invagination of the clathrin-coated pit is an energetically costly step in this process involving several proteins, including epsin,[8,9,10] that come into direct contact with and bind to the membrane surface. Accumulating evidence suggests a dual role for epsin of inducing membrane curvature and recruiting accessory proteins in the early stage of CME11,12; it contains multiple conserved binding motifs that can interact with several accessory proteins associated with CME, for example, AP2, Eps[15], clathrin, and ubiquitinated proteins.[13,14] In addition, it has been recently shown that epsin is required for clathrincoated vesicle scission.[15] Specific membrane targeting by proteins and dramatic changes in the shape and topology of the membrane are often involved in these complex cellular processes, which require coordinated efforts between proteins and lipids in a spatially and temporally precise manner.[1,2,3,4,5] Clathrin-mediated endocytosis (CME) is one of the essential cellular processes that requires the coordinated action of multiple membrane proteins functioning together.[6,7]

Methods

Results

Conclusion