Structural insights into hedgehog ligand sequestration by the human hedgehog-interacting protein HHIP.
Hedgehog (Hh) morphogens have fundamental roles in development, whereas dysregulation of Hh signaling leads to disease. Multiple cell-surface receptors are responsible for transducing and/or regulating Hh signals. Among these, the Hedgehog-interacting protein (Hhip) is a highly conserved, vertebrate-specific inhibitor of Hh signaling. We have solved a series of crystal structures for the human HHIP ectodomain and Desert hedgehog (DHH) in isolation, as well as HHIP in complex with DHH (HHIP-DHH) and Sonic hedgehog (Shh) (HHIP-Shh), with and without Ca2+. The interaction determinants, confirmed by biophysical studies and mutagenesis, reveal previously uncharacterized and distinct functions for the Hh Zn2+ and Ca2+ binding sites--functions that may be common to all vertebrate Hh proteins. Zn2+ makes a key contribution to the Hh-HHIP interface, whereas Ca2+ is likely to prevent electrostatic repulsion between the two proteins, suggesting an important modulatory role. This interplay of several metal binding sites suggests a tuneable mechanism for regulation of Hh signaling.
Bishop
Benjamin
B
Division of Structural Biology, Wellcome Trust Centre for Human Genetics, University of Oxford, Oxford, UK.
Aricescu
A Radu
AR
Harlos
Karl
K
O'Callaghan
Chris A
CA
Jones
E Yvonne
EY
Siebold
Christian
C
D000818:Animals; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism; D002352:Carrier Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D053823:Hedgehog Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D006801:Humans; D008024:Ligands; D008562:Membrane Glycoproteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D046912:Multiprotein Complexes / Q000378:metabolism; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D015032:Zinc / Q000378:metabolism
D002352:Carrier Proteins; C117596:HHIP protein, human; D053823:Hedgehog Proteins; D008024:Ligands; D008562:Membrane Glycoproteins; D046912:Multiprotein Complexes; C509239:SHH protein, human; D015032:Zinc; D002118:Calcium