PARALLEL DIMERS AND ANTI-PARALLEL TETRAMERS FORMED BY EPIDERMAL GROWTH-FACTOR RECEPTOR PATHWAY SUBSTRATE CLONE-15 (EPS15)

The recently discovered localization of epidermal growth factor recept or pathway substrate clone 15 (Eps15) to plasma membrane clathrin-coat ed pits and its constitutive association with the endocytic clathrin a daptor protein complex, AP-2, strongly suggest that Eps15 has an impor tant role in the pathway of clathrin-dependent endocytic traffic. We r eport here that Eps15 forms dimers and tetramers of distinct shape, Th e Eps15 dimer is an elongated molecule, 32 nm in length. There is a gl obular ''head'' at one end of the molecule and an extended ''stalk'' o f 25 nm which is kinked at about 17 nm away from the head. In the Eps1 5 dimer, two sub-units are arranged parallel to each other, so that th e head corresponds to two side by side copies of the N-terminal region I, which contains the three Eps15 homology domains, The proximal part of the stalk is the coiled-coil central region II containing 20 hepta d repeats. The kink is at the boundary between region II and the C-ter minal region III, which contains the AP-2 binding site, 15 aspartic-pr oline-phenylalanine repeats, and proline-rich Src homology domain liga nd sites. The Eps15 tetramer has a ''dumbbell'' shape, similar to 31 n m in length; it is formed by the anti-parallel association of two Eps1 5 dimers, Formation of these Eps15 tetramers appears to require contac ts between regions I of one dimer and regions III of a second apposing dimer. The extended shapes of the Eps15 dimers and tetramers suggest how Eps15 oligomers are located in the clathrin coat. We discuss the i mplications for accessibility to partners and for proposed functions o f Eps15.