Structure and function of the Smoothened extracellular domain in vertebrate Hedgehog signaling
Sigrid Nachtergaele,
Daniel M Whalen,
Laurel K Mydock,
Zhonghua Zhao,
Tomas Malinauskas,
Kathiresan Krishnan,
Philip W Ingham,
Douglas F Covey,
Christian Siebold,
Rajat Rohatgi
Affiliations
Sigrid Nachtergaele
Department of Biochemistry, Stanford University School of Medicine, Stanford, United States
Daniel M Whalen
Division of Structural Biology, Wellcome Trust Centre for Human Genetics, University of Oxford, Oxford, United Kingdom
Laurel K Mydock
Department of Developmental Biology, Washington University School of Medicine, St. Louis, United States
Zhonghua Zhao
A*STAR Institute of Molecular and Cell Biology, Singapore, Singapore
Tomas Malinauskas
Division of Structural Biology, Wellcome Trust Centre for Human Genetics, University of Oxford, Oxford, United Kingdom
Kathiresan Krishnan
Department of Developmental Biology, Washington University School of Medicine, St. Louis, United States
Philip W Ingham
A*STAR Institute of Molecular and Cell Biology, Singapore, Singapore; Lee Kong Chian School of Medicine, Imperial College London/Nanyang Technological University, Singapore, Singapore
Douglas F Covey
Department of Developmental Biology, Washington University School of Medicine, St. Louis, United States
Christian Siebold
Division of Structural Biology, Wellcome Trust Centre for Human Genetics, University of Oxford, Oxford, United Kingdom
Rajat Rohatgi
Department of Biochemistry, Stanford University School of Medicine, Stanford, United States; Department of Medicine, Stanford University School of Medicine, Stanford, United States
The Hedgehog (Hh) signal is transduced across the membrane by the heptahelical protein Smoothened (Smo), a developmental regulator, oncoprotein and drug target in oncology. We present the 2.3 Å crystal structure of the extracellular cysteine rich domain (CRD) of vertebrate Smo and show that it binds to oxysterols, endogenous lipids that activate Hh signaling. The oxysterol-binding groove in the Smo CRD is analogous to that used by Frizzled 8 to bind to the palmitoleyl group of Wnt ligands and to similar pockets used by other Frizzled-like CRDs to bind hydrophobic ligands. The CRD is required for signaling in response to native Hh ligands, showing that it is an important regulatory module for Smo activation. Indeed, targeting of the Smo CRD by oxysterol-inspired small molecules can block signaling by all known classes of Hh activators and by clinically relevant Smo mutants.
