EPSIN IS AN EH-DOMAIN-BINDING PROTEIN IMPLICATED IN CLATHRIN-MEDIATEDENDOCYTOSIS

During endocytosis, clathrin and the clathrin adaptor protein AP-2 (re f, 1), assisted by a variety of accessory factors, help to generate an invaginated bud at the cell membrane(2,3). One of these factors is Ep s15, a clathrin-coat-associated protein that binds the alpha-adaptin s ubunit of AP-2 (refs 4-8). Here we investigate the function of Eps15 b y characterizing an important binding partner for its region containin g EH domains(9); this protein, epsin, is closely related to the Xenopu s mitotic phosphoprotein MP90 (ref. 10) and has a ubiquitous tissue di stribution. It is concentrated together with Eps15 in presynaptic nerv e terminals, which are sites specialized for the clathrin-mediated end ocytosis of synaptic vesicles. The central region of epsin binds AP-2 and its carboxyterminal region binds Eps15. Epsin is associated with c lathrin coats in situ, can be co-precipitated with AP-2 and Eps15 from brain extracts, but does not co-purify with clathrin coat components in a clathrin-coated vesicle fraction. When epsin function is disrupte d, clathrin-mediated endocytosis is blocked. We propose that epsin may participate, together with Eps15, in the molecular rearrangement of t he clathrin coats that are required for coated-pit imagination and ves icle fission.