Structural and functional characterization of soluble endoglin receptor

Endoglin, an accessory membrane receptor of transforming growth factor-β (TGF-β)1, modulates the cellular response to TGF-β via its interaction with type I and II TGF-β receptors. It has been considered a promising target for the development of therapeutics and cancer markers. We have established stable CHO cell lines that efficiently secrete soluble endoglin (s-endoglin) fused with human growth hormone. Two oligomeric forms were observed in a homogeneous preparation of s-endoglin, as a dimer and a tetramer. The dimeric s-endoglin enhanced TGF-β responsiveness in U937 cells, thus proving its potential for therapeutic applications. Small angle X-ray scattering (SAXS) experiments revealed elongated conformations of both dimeric and tetrameric s-endoglins in solution, suggesting that s-endoglin might undergo conformational adaptations upon TGF-β binding. The current results provide important references and material for high-resolution structural studies and for medical applications of s-endoglin.