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

  • Nature. 2019 Jul;571(7764):279-283. doi: 10.1038/s41586-019-1286-0.
Xiaofeng Qi  #  1 ,  Heng Liu  #  2 ,  Bonne Thompson  3 ,  Jeffrey McDonald  1  3 ,  Cheng Zhang  4 ,  Xiaochun Li  5  6
Affiliations
  • 1. Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, TX, USA.
  • 2. Department of Pharmacology and Chemical Biology, University of Pittsburgh, School of Medicine, Pittsburgh, PA, USA.
  • 3. Center for Human Nutrition, University of Texas Southwestern Medical Center, Dallas, TX, USA.
  • 4. Department of Pharmacology and Chemical Biology, University of Pittsburgh, School of Medicine, Pittsburgh, PA, USA. [email protected].
  • 5. Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, TX, USA. [email protected].
  • 6. Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, TX, USA. [email protected].
  • # Contributed equally.
PMID: 31168089 DOI: 10.1038/s41586-019-1286-0
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.