Stonin 2: An adaptor-like protein that interacts with components of the endocytic machinery

Endocytosis of cell surface proteins is mediated by a complex molecular mac hinery that assembles on the inner surface of the plasma membrane. Here, we report the identification of two ubiquitously expressed human proteins, st onin 1 and stonin 2, related to components of the endocytic machinery. The human stonins are homologous to the Drosophila melanogaster stoned B protei n and exhibit a modular structure consisting of an NH2-terminal proline-ric h domain, a central region of homology specific to the stonins, and a COOH- terminal region homologous to the mu subunits of adaptor protein (AP) compl exes. Stonin 2, but not stonin 1, interacts with the endocytic machinery pr oteins Eps15, Eps15R, and intersectin 1. These interactions occur via two N PF motifs in the proline-rich domain of stonin 2 and Eps15 homology domains of Eps15, Eps15R, and intersectin 1. Stonin 2 also interacts indirectly wi th the adaptor protein complex. AP-2, In addition, stonin 2 binds to the C2 B domains of synaptotagmins I and II. Overexpression of GFP-stonin 2 interf eres with recruitment of AP-2 to the plasma membrane and impairs internaliz ation of the transferrin, epidermal growth factor, and low density lipoprot ein receptors. These observations suggest that stonin 2 is a novel componen t of the general endocytic machinery.