RESUMO
WNT signaling is fundamental in development and homeostasis, but how the Frizzled receptors (FZDs) propagate signaling remains enigmatic. Here, we present the cryo-EM structure of FZD4 engaged with the DEP domain of Dishevelled 2 (DVL2), a key WNT transducer. We uncover a distinct binding mode where the DEP finger-loop inserts into the FZD4 cavity to form a hydrophobic interface. FZD4 intracellular loop 2 (ICL2) additionally anchors the complex through polar contacts. Mutagenesis validates the structural observations. The DEP interface is highly conserved in FZDs, indicating a universal mechanism by which FZDs engage with DVLs. We further reveal that DEP mimics G-protein/ß-arrestin/GRK to recognize an active conformation of receptor, expanding current GPCR engagement models. Finally, we identify a distinct FZD4 dimerization interface. Our findings delineate the molecular determinants governing FZD/DVL assembly and propagation of WNT signaling, providing long-sought answers underlying WNT signal transduction.
Assuntos
Proteínas Desgrenhadas , Receptores Frizzled , Via de Sinalização Wnt , Receptores Frizzled/metabolismo , Receptores Frizzled/química , Receptores Frizzled/genética , Proteínas Desgrenhadas/metabolismo , Proteínas Desgrenhadas/genética , Proteínas Desgrenhadas/química , Humanos , Células HEK293 , Ligação Proteica , Microscopia Crioeletrônica , Modelos Moleculares , Domínios ProteicosRESUMO
Adhesion G-protein-coupled receptors (aGPCRs) play key roles in a diversity of physiologies. A hallmark of aGPCR activation is the removal of the inhibitory GAIN domain and the dipping of the cleaved stalk peptide into the ligand-binding pocket of receptors; however, the detailed mechanism remains obscure. Here, we present cryoelectron microscopy (cryo-EM) structures of ADGRL3 in complex with Gq, Gs, Gi, and G12. The structures reveal unique ligand-engaging mode, distinctive activation conformation, and key mechanisms of aGPCR activation. The structures also reveal the uncharted structural information of GPCR/G12 coupling. A comparison of Gq, Gs, Gi, and G12 engagements with ADGRL3 reveals the key determinant of G-protein coupling on the far end of αH5 of Gα. A detailed analysis of the engagements allows us to design mutations that specifically enhance one pathway over others. Taken together, our study lays the groundwork for understanding aGPCR activation and G-protein-coupling selectivity.