Structural Basis of Smoothened Activation in Hedgehog Signaling
Open accessAbstract
The seven-transmembrane-spanning protein Smoothened is the central transducer in Hedgehog signaling, a pathway fundamental in development and in cancer. Smoothened is activated by cholesterol binding to its extracellular cysteine-rich domain (CRD). How this interaction leads to changes in the transmembrane domain and Smoothened activation is unknown. Here, we report crystal structures of sterol-activated Smoothened. The CRD undergoes a dramatic reorientation, allosterically causing the transmembrane domain to adopt a conformation similar to active G-protein-coupled receptors. We show that Smoothened contains a unique inhibitory π-cation lock, which is broken on activation and is disrupted in constitutively active oncogenic mutants. Smoothened activation opens a hydrophobic tunnel, suggesting a pathway for cholesterol movement from the inner membrane leaflet to the CRD. All Smoothened antagonists bind the transmembrane domain and block tunnel opening, but cyclopamine also binds the CRD, inducing the active transmembrane conformation. Together, these results define the mechanisms of Smoothened activation and inhibition.
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Oxysterols can bind to the cysteine-rich domain and activate SMO downstream and independent of PTCH1 removal from cilia, but the physiological role of oxysterols in HH pathway activation is not clear.
“Oxysterols can also bind to the cysteine rich domain and activate SMO downstream and independent of PTCH1 removal from cilia 102, 114; however, the physiological role of oxysterols in HH pathway activation is not clear.”
From Cellular signalling by primary cilia in development, organ function and disease (2019) · cites this paper as [114]
The Results section, “Allosteric activation of the 7TM domain by sterol-bound CRD” (page unavailable), reports that 20(S)-hydroxycholesterol activates SMO and that oxysterol-bound CRD allosterically activates its 7TM domain. The paper does not establish that this occurs independently of PTCH1 removal from cilia, nor does it specifically state that oxysterols’ physiological role in HH activation is unclear. (LLM, conf=0.85)
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Cellular signalling by primary cilia in development, organ function and disease
Anvarian, Z., Mykytyn, K., Mukhopadhyay, S., Pedersen, L. B., & Christensen, S. T. (2019) · Nature Reviews Nephrology · doi:10.1038/s41581-019-0116-9 · Cited by 845 · see citing works
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- Authors
- Huang, P., Zheng, S., Wierbowski, B. M., Kim, Y., Nedelcu, D., Aravena, L., Liu, J., Kruse, A. C., & Salic, A.
- Affiliations
- Harvard University (US)
- Argonne National Laboratory (US)
- Corresponding author
- Salic, Adrian
- ORCID
- Venue
- Cell
- Publisher
- Elsevier BV
- Published
- 2018-07
- Volume
- 174
- Issue
- 2
- Pages
- 312-324.e16
- ISSN
- 0092-8674 (ISSN-L)
- PMC
- PMC6046275
- OpenAlex
- W2803585099
- Cited by
- 176
- References
- 54
- Citations by year
- 2026: 6 · 2025: 13 · 2024: 15 · 2023: 15 · 2022: 29 · 2021: 20 · 2020: 25 · 2019: 39 · 2018: 14
- FWCI
- 9.07
- Type
- journal article
- Language
- en
- Update notices
- erratum (2018-09-20)
- Open access
- bronze
- doi.org
- Licence
- Locations
- Cell (publishedVersion)
- PubMed (publishedVersion)
- PubMed Central (acceptedVersion)
- Funders
- National Institutes of Health (F31 GM120833, R01 GM110041)
- Topics
- Life Sciences › Biochemistry, Genetics and Molecular Biology › Molecular Biology › Hedgehog Signaling Pathway Studies
- Life Sciences › Biochemistry, Genetics and Molecular Biology › Molecular Biology › Receptor Mechanisms and Signaling
- Life Sciences › Biochemistry, Genetics and Molecular Biology › Molecular Biology › Wnt/β-catenin signaling in development and cancer
- Keywords
- Smoothened, Hedgehog signaling, cholesterol binding, cysteine-rich domain, allosteric activation, cholesterol transport, Smoothened antagonists, cyclopamine, crystal structure
- MeSH terms
- Smoothened Receptor, Protein Domains, Allosteric Regulation, Animals, Binding Sites, Cell Line, Cholesterol, Flow Cytometry, Humans, Protein Binding, Veratrum Alkaloids, Xenopus laevis, Signal Transduction, Protein Structure, Tertiary, Crystallography, X-Ray, Xenopus Proteins, Mice, Hedgehog Proteins, Small Molecule Libraries, Molecular Dynamics Simulation
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