Pip2 Lipids As Regulators Of Membrane Curvature Sensing By Enth Domains

The ENTH (Epsin N-Terminal Homology) domain is an amino-acid sequence found in multiple proteins within the body. This repeated motif is understood to play a crucial role in connecting proteins to cellular membranes. Indeed, the ENTH domain binds phosphatidylinositol-4,5-bisphosphate (PIP2) lipids in the membrane allowing it to act as an ‘anchor’ for protein attachment. The localization and binding of this domain to the cell membrane, as part of the larger Epsin-1 protein, is an essential step during clathrin-mediated endocytosis. The cascade of events, however, involved in ENTH binding to PIP lipids in the cell membrane is still far from understood. Furthermore, ENTH domains localize to regions of membrane curvature and the role of such curvature in endocytosis is not clear. Here, using coarse-grained molecular dynamics simulations, we investigate the relationship between the structure of the ENTH domain and its spontaneous membrane-curvature sensing. Interestingly, we observe switchable protein behaviour depending on the presence of PIP2 lipids in the membrane and the presence of the terminal H0 amphiphilic helix within the domain. Our model shows that PIP2 lipids play a key role in the spontaneous localization of ENTH domains to membrane curvature. Furthermore, our model upholds that the H0 helix of the domain forms post-PIP2 binding. This suggests a potential mechanism for initiating endocytosis whereby membrane curvature coupled with PIP2-enrichment at curved membrane regions can localize Epsin-1 and subsequently kick-off the endocytotic process.