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Nature. 2016 Jul 28;535(7613):517-522. doi: 10.1038/nature18934. Epub 2016 Jul 20.

Structural basis of Smoothened regulation by its extracellular domains.

Author information

1
Division of Structural Biology, Wellcome Trust Centre for Human Genetics, University of Oxford, Oxford, UK.
2
Departments of Biochemistry and Medicine, Stanford University School of Medicine, Stanford, California, United States of America.
3
Department of Biochemistry, University of Oxford, Oxford, UK.
4
Diamond Light Source Ltd, Harwell Science &Innovation Campus, Didcot, UK.
5
Department of Developmental Biology, Washington University School of Medicine, St. Louis, Missouri, United States of America.
#
Contributed equally

Abstract

Developmental signals of the Hedgehog (Hh) and Wnt families are transduced across the membrane by Frizzledclass G-protein-coupled receptors (GPCRs) composed of both a heptahelical transmembrane domain (TMD) and an extracellular cysteine-rich domain (CRD). How the large extracellular domains of GPCRs regulate signalling by the TMD is unknown. We present crystal structures of the Hh signal transducer and oncoprotein Smoothened, a GPCR that contains two distinct ligand-binding sites: one in its TMD and one in the CRD. The CRD is stacked a top the TMD, separated by an intervening wedge-like linker domain. Structure-guided mutations show that the interface between the CRD, linker domain and TMD stabilizes the inactive state of Smoothened. Unexpectedly, we find a cholesterol molecule bound to Smoothened in the CRD binding site. Mutations predicted to prevent cholesterol binding impair the ability of Smoothened to transmit native Hh signals. Binding of a clinically used antagonist, vismodegib, to the TMD induces a conformational change that is propagated to the CRD, resulting in loss of cholesterol from the CRD-linker domain-TMD interface. Our results clarify the structural mechanism by which the activity of a GPCR is controlled by ligand-regulated interactions between its extracellular and transmembrane domains.

PMID:
27437577
PMCID:
PMC4970916
DOI:
10.1038/nature18934
[Indexed for MEDLINE]
Free PMC Article

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