Structure of a heparin-dependent complex of Hedgehog and Ihog
- Jason S. McLellan*,
- Shenqin Yao†,‡,
- Xiaoyan Zheng†,‡,
- Brian V. Geisbrecht*,§,
- Rodolfo Ghirlando¶,
- Philip A. Beachy†,‡, and
- Daniel J. Leahy*,‖
- Departments of *Biophysics and Biophysical Chemistry and
- †Molecular Biology and Genetics and
- the ‡Howard Hughes Medical Institute, Johns Hopkins University School of Medicine, Baltimore, MD 21205; and
- ¶Laboratory of Molecular Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892
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Edited by Jeremy Nathans, Johns Hopkins University School of Medicine, Baltimore, MD, and approved September 15, 2006 (received for review August 4, 2006)
Abstract
Hedgehog (Hh) signaling molecules mediate key tissue-patterning events during animal development, and inappropriate activation of Hh signaling in adults has been associated with human cancers. Recently, a conserved family of type I integral membrane proteins required for normal response to the Hh signal was discovered. One member of this family, Ihog (interference hedgehog), functions upstream or at the level of Patched (Ptc), but how Ihog participates in Hh signaling remains unclear. Here, we show that heparin binding induces Ihog dimerization and is required to mediate high-affinity interactions between Ihog and Hh. We also present crystal structures of a Hh-binding fragment of Ihog, both alone and complexed with Hh. Heparin is not well ordered in these structures, but a basic cleft in the first FNIII domain of Ihog (IhogFn1) is shown by mutagenesis to mediate heparin binding. These results establish that Hh directly binds Ihog and provide the first demonstration of a specific role for heparin in Hh responsiveness.
Footnotes
- ‖To whom correspondence should be addressed at: Department of Biophysics and Biophysical Chemistry, Johns Hopkins University School of Medicine, 725 North Wolfe Street, Baltimore, MD 21205. E-mail: dleahy{at}jhmi.edu
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Author contributions: J.S.M., S.Y., X.Z., B.V.G., R.G., P.A.B., and D.J.L. designed research; J.S.M., S.Y., X.Z., B.V.G., and R.G. performed research; J.S.M., S.Y., X.Z., B.V.G., R.G., P.A.B., and D.J.L. analyzed data; and J.S.M., S.Y., X.Z., B.V.G., R.G., P.A.B., and D.J.L. wrote the paper.
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↵ §Present address: School of Biological Sciences, University of Missouri, Kansas City, MO 64110.
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The authors declare no conflict of interest.
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This article is a PNAS direct submission.
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Data deposition: The atomic coordinates and structure factors have been deposited in the Protein Data Bank, www.pdb.org (PDB ID codes 2IBB, 2IBG, and 2IC2).
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See Commentary on page 17069.
- Abbreviations:
- AUC,
- analytical ultracentrifugation;
- Hh,
- hedgehog;
- HSPGs,
- heparan sulfate proteoglycans.
- © 2006 by The National Academy of Sciences of the USA
