Structural Basis of the Human Endoglin-BMP9 Interaction: Insights into BMP Signaling and HHT1

Cell Rep. 2017 May 30;19(9):1917-1928. doi: 10.1016/j.celrep.2017.05.011.


Endoglin (ENG)/CD105 is an essential endothelial cell co-receptor of the transforming growth factor β (TGF-β) superfamily, mutated in hereditary hemorrhagic telangiectasia type 1 (HHT1) and involved in tumor angiogenesis and preeclampsia. Here, we present crystal structures of the ectodomain of human ENG and its complex with the ligand bone morphogenetic protein 9 (BMP9). BMP9 interacts with a hydrophobic surface of the N-terminal orphan domain of ENG, which adopts a new duplicated fold generated by circular permutation. The interface involves residues mutated in HHT1 and overlaps with the epitope of tumor-suppressing anti-ENG monoclonal TRC105. The structure of the C-terminal zona pellucida module suggests how two copies of ENG embrace homodimeric BMP9, whose binding is compatible with ligand recognition by type I but not type II receptors. These findings shed light on the molecular basis of the BMP signaling cascade, with implications for future therapeutic interventions in this fundamental pathway.

Keywords: TGF-β superfamily proteins; bone morphogenetic protein receptors; cell surface receptors; endoglin; growth differentiation factor 2; hereditary hemorrhagic telangiectasia; orphan domain; protein interaction domains and motifs; x-ray crystallography; zona pellucida domain.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Activin Receptors, Type II / metabolism
  • Crystallography, X-Ray
  • Disulfides / metabolism
  • Endoglin / chemistry*
  • Endoglin / metabolism*
  • Gene Duplication
  • Growth Differentiation Factor 2 / metabolism*
  • Humans
  • Hydrophobic and Hydrophilic Interactions
  • Kinetics
  • Ligands
  • Models, Molecular
  • Protein Binding
  • Protein Domains
  • Protein Multimerization
  • Protein Structure, Secondary
  • Signal Transduction*
  • Structure-Activity Relationship
  • Telangiectasia, Hereditary Hemorrhagic / metabolism*


  • Disulfides
  • Endoglin
  • Growth Differentiation Factor 2
  • Ligands
  • ACVRL1 protein, human
  • Activin Receptors, Type II