Cryo-EM structure of oxysterol-bound human Smoothened coupled to a heterotrimeric G i

Nature. 2019 Jul;571(7764):279-283. doi: 10.1038/s41586-019-1286-0. Epub 2019 Jun 5.

Abstract

The oncoprotein Smoothened (SMO), a G-protein-coupled receptor (GPCR) of the Frizzled-class (class-F), transduces the Hedgehog signal from the tumour suppressor Patched-1 (PTCH1) to the glioma-associated-oncogene (GLI) transcription factors, which activates the Hedgehog signalling pathway1,2. It has remained unknown how PTCH1 modulates SMO, how SMO is stimulated to form a complex with heterotrimeric G proteins and whether G-protein coupling contributes to the activation of GLI proteins3. Here we show that 24,25-epoxycholesterol, which we identify as an endogenous ligand of PTCH1, can stimulate Hedgehog signalling in cells and can trigger G-protein signalling via human SMO in vitro. We present a cryo-electron microscopy structure of human SMO bound to 24(S),25-epoxycholesterol and coupled to a heterotrimeric Gi protein. The structure reveals a ligand-binding site for 24(S),25-epoxycholesterol in the 7-transmembrane region, as well as a Gi-coupled activation mechanism of human SMO. Notably, the Gi protein presents a different arrangement from that of class-A GPCR-Gi complexes. Our work provides molecular insights into Hedgehog signal transduction and the activation of a class-F GPCR.

MeSH terms

  • Cryoelectron Microscopy*
  • GTP-Binding Protein alpha Subunits, Gi-Go / chemistry*
  • GTP-Binding Protein alpha Subunits, Gi-Go / metabolism
  • GTP-Binding Protein alpha Subunits, Gi-Go / ultrastructure*
  • Hedgehog Proteins / metabolism
  • Humans
  • Immunoglobulin Fab Fragments / chemistry
  • Immunoglobulin Fab Fragments / immunology
  • Immunoglobulin Fab Fragments / ultrastructure
  • Ligands
  • Models, Molecular
  • Oxysterols / chemistry*
  • Oxysterols / metabolism
  • Patched-1 Receptor / metabolism
  • Protein Conformation
  • Signal Transduction
  • Smoothened Receptor / chemistry*
  • Smoothened Receptor / metabolism
  • Smoothened Receptor / ultrastructure*
  • Veratrum Alkaloids / chemistry

Substances

  • Hedgehog Proteins
  • Immunoglobulin Fab Fragments
  • Ligands
  • Oxysterols
  • PTCH1 protein, human
  • Patched-1 Receptor
  • SMO protein, human
  • Smoothened Receptor
  • Veratrum Alkaloids
  • GTP-Binding Protein alpha Subunits, Gi-Go
  • cyclopamine