Structural Basis of Frizzled 7 Activation and Allosteric Regulation

Frizzleds (ten paralogs: FZD1 − 10) belong to the class F of G protein-coupled receptors (GPCRs), which remains poorly understood despite its crucial role in multiple key biological functions including embryonic development, stem cell regulation, and homeostasis in the adult. FZD7, one of the most studied members of the family, is more specifically involved in the migration of mesendoderm cells during the development and renewal of intestinal stem cells in adults. Moreover, FZD7 has been highlighted for its involvement in tumor development predominantly in the gastrointestinal tract. This study reports the structure of inactive FZD7, without any stabilizing mutations, determined by cryo-electron microscopy (cryo-EM) at 1.9Å resolution. We characterized a fluctuating water pocket in the core of the receptor important for FZD7 dynamics. Molecular dynamics simulations were then used to investigate the temporal distribution of those water molecules and their importance for potential conformational changes in FZD7. Moreover, we identified lipids interacting with the receptor core and a conserved cholesterol-binding site, which displays a key role in FZD7 association with a transducer protein, Dishevelled (DVL), and initiation of downstream signaling and signalosome formation.