Structural and functional insights into endoglin ligand recognition and binding

12 pages, 4 figures, 2 tables. PMID:22347366[PubMed] PMCID:PMC3275592Endoglin, a type I membrane glycoprotein expressed as a disulfide-linked homodimer on human vascular endothelial cells, is a component of the transforming growth factor (TGF)-β receptor complex and is implicated in a dominant vascular dysplasia known as hereditary hemorrhagic telangiectasia as well as in preeclampsia. It interacts with the type I TGF-β signaling receptor activin receptor-like kinase (ALK)1 and modulates cellular responses to Bone Morphogenetic Protein (BMP)-9 and BMP-10. Structurally, besides carrying a zona pellucida (ZP) domain, endoglin contains at its N-terminal extracellular region a domain of unknown function and without homology to any other known protein, therefore called the orphan domain (OD). In this study, we have determined the recognition and binding ability of full length ALK1, endoglin and constructs encompassing the OD to BMP-9 using combined methods, consisting of surface plasmon resonance and cellular assays. ALK1 and endoglin ectodomains bind, independently of their glycosylation state and without cooperativity, to different sites of BMP-9. The OD comprising residues 22 to 337 was identified among the present constructs as the minimal active endoglin domain needed for partner recognition. These studies also pinpointed to Cys350 as being responsible for the dimerization of endoglin. In contrast to the complete endoglin ectodomain, the OD is a monomer and its small angle X-ray scattering characterization revealed a compact conformation in solution into which a de novo model was fitted.This study was supported by grants from the Ministerio de Ciencia e Innovación of Spain (grants BIO2009-10872 and BIO2010-15424 to AM, SAF2010-19222 to CB), Conselleria de Sanitat of Valencian Government (grant AP-072/11 to AM), Centro de Investigación Biomédica en Red de Enfermedades Raras (CIBERER) (intramural grant to AM, VR and CB), Prometeo (grant 2009/051 to VR), and Genoma España (MEICA). CIBERER is an initiative of the Instituto de Salud Carlos III of Spain.Peer reviewe