Deconvolution of WNT-induced Frizzled conformational dynamics with fluorescent biosensors

Biosens Bioelectron. 2021 Apr 1;177:112948. doi: 10.1016/j.bios.2020.112948. Epub 2020 Dec 30.

Abstract

The G protein-coupled receptors Frizzled1-10 (FZD1-10) act as molecular checkpoints mediating intracellular signaling induced by 19 mammalian, secreted Wingless/Int-1 lipoglycoproteins (WNTs). Despite the vital roles of these signaling components in health and disease, our knowledge about WNT/FZD selectivity, and the mechanisms of receptor activation and intracellular signal propagation by individual ligand/receptor pairs is limited due to the current lack of suitable biophysical techniques. Here, we developed fluorescence-based biosensors that detect WNT-induced FZD conformational changes in living cells in order to assess WNT action via FZDs at the most proximal level, i.e. the receptor conformation. By testing a panel of recombinant ligands on conformational biosensors representing all four homology clusters of FZDs, we discover yet unappreciated selectivities of WNTs to their receptors and, surprisingly, identify distinct ligand-induced receptor conformations. Furthermore, we demonstrate that FZDs can undergo conformational changes upon WNT binding without being dependent on the WNT co-receptors LRP5/6. This sensor toolbox provides an advanced platform for a thorough investigation of the 190 possible WNT/FZD pairings and for future screening campaigns targeting synthetic FZD ligands. Furthermore, our findings shed new light on the complexity of the WNT/FZD signaling system and have substantial implications for our understanding of fundamental biological processes including embryonal development and tumorigenesis.

Keywords: Activation mechanism; Conformational biosensor; Drug screening; Frizzled; Ligand selectivity; WNT.

MeSH terms

  • Animals
  • Biosensing Techniques*
  • Frizzled Receptors
  • Ligands
  • Wnt Proteins*
  • Wnt Signaling Pathway

Substances

  • Frizzled Receptors
  • Ligands
  • Wnt Proteins