1. Howard Hughes Medical Institute and Department of Cell Biology, Yale University School of Medicine, 295 Congress Avenue, New Haven, Connecticut 06510, USA
2. Department of Experimental Oncology, European Institute of Oncology, Milan 20141, Italy
3. Istituto di Microbiologia, Universita' di Bari, Bari 70124, Italy

Correspondence to: Pietro De Camilli¹ Correspondence and requests for materials should be addressed to P.D.C. (e-mail: Email: pietro.decamilli@yale.edu).The accession number for the rat epsin nucleotide and amino-acid sequences is AF018261 in GenBank.

Abstract

During endocytosis, clathrin and the clathrin adaptor protein AP-2 (ref. 1), assisted by a variety of accessory factors, help to generate an invaginated bud at the cell membrane²,³. One of these factors is Eps15, a clathrin-coat-associated protein that binds the -adaptin subunit of AP-2 (refs 4–8). Here we investigate the function of Eps15 by characterizing an important binding partner for its region containing EH domains⁹; this protein, epsin, is closely related to the Xenopus mitotic phosphoprotein MP90 (ref. 10) and has a ubiquitous tissue distribution. It is concentrated together with Eps15 in presynaptic nerve terminals, which are sites specialized for the clathrin-mediated endocytosis of synaptic vesicles. The central region of epsin binds AP-2 and its carboxy-terminal region binds Eps15. Epsin is associated with clathrin 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 disrupted, clathrin-mediated endocytosis is blocked. We propose that epsin may participate, together with Eps15, in the molecular rearrangement of the clathrin coats that are required for coated-pit invagination and vesicle fission.