Contrasting membrane interaction mechanisms of AP180 N-terminal homology (ANTH) and epsin N-terminal homology (ENTH) domains

Epsin and AP180/CALM are endocytotic accessory proteins that have been implicated in the formation of clathrin-coated pits. Both proteins have phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P-2)-binding domains in their N termini, but these domains are structurally and functionally different. To understand the basis of their distinct properties, we measured the PtdIns(4,5)P-2-dependent membrane binding of the epsin N-terminal homology (ENTH) domain and the AP180 N-terminal homology (ANTH) domain by means of surface plasmon resonance and monolayer penetration techniques and also calculated the effect of PtdIns(4,5)P-2 on the electrostatic potential of these domains. PtdIns(4,5)P-2 enhances the electrostatic membrane association of both domains; however, PtdIns(4,5)P-2 binding exerts distinct effects on their membrane dissociation. Specifically, PtdIns(4,5)P-2 induces the membrane penetration of the N-terminal alpha-helix of the ENTH domain, which slows the membrane dissociation of the domain and triggers the membrane deformation. These results provide the biophysical explanation for the membrane bending activity of epsin and its ENTH domain.