Structural Analysis of the Interaction between Dishevelled2 and Clathrin AP-2 Adaptor, A Critical Step in Noncanonical Wnt Signaling

Wnt association with its receptor, Frizzled (Fz), and recruitment by the latter of an adaptor, Dishevelled (Dvl), initiates signaling through at least two distinct pathways (canonical and noncanonical). Endocytosis and compartmentalization help determine the signaling outcome. Our previous work has shown that Dvl2 links at least one Frizzled family member (Fz4) to clathrin-mediated endocytosis by interacting with the mu 2 subunit of the AP-2 clathrin adaptor, through both a classical endocytic tyrosine motif and a so-called DEP domain. We report here the crystal structure of a chimeric protein that mimics the Dvl2-mu 2 complex. The DEP domain binds at one end of the elongated, C-terminal domain of mu 2. This domain:domain interface shows that parts of the mu 2 surface distinct from the tyrosine-motif site can help recruit specific receptors or adaptors into a clathrin coated pit. Mutation of residues at the DEP-mu 2 contact or in the tyrosine motif reduce affinity of Dvl2 for mu 2 and block efficient internalization of Fz4 in response to ligation by Wnt5a. The crystal structure has thus allowed us to identify the specific interaction that leads to Frizzled uptake and to downstream, noncanonical signaling events.