Role of the ENTH Domain in Phosphatidylinositol-4,5-Bisphosphate Binding and Endocytosis

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Abstract
Endocytic proteins such as epsin, AP180, and Hip1R (Sla2p) share a conserved modular region termed the epsin NH 2 -terminal homology (ENTH) domain, which plays a crucial role in clathrin-mediated endocytosis through an unknown target. Here, we demonstrate a strong affinity of the ENTH domain for phosphatidylinositol-4,5-bisphosphate [PtdIns(4,5)P 2 ]. With nuclear magnetic resonance analysis of the epsin ENTH domain, we determined that a cleft formed with positively charged residues contributed to phosphoinositide binding. Overexpression of a mutant, epsin Lys 76 → Ala 76 , with an ENTH domain defective in phosphoinositide binding, blocked epidermal growth factor internalization in COS-7 cells. Thus, interaction between the ENTH domain and PtdIns(4,5)P 2 is essential for endocytosis mediated by clathrin-coated pits.