Fig. 3

Ligand-dependent reorientation of the receptor ectodomain. a Comparison of the structure of unbound BMPR-IA, the structure ensemble comprising 21 structures [PDB:2K3G] is shown as a red Cα-trace, and BMPR-IA bound to GDF-5 R57A (blue). b Structure alignment of BMPR-IA bound to GDF-5 R57A (blue) and bound to BMP-2 (green). The Cα-traces of both BMPR-IA structures overlap almost perfectly; minor conformational differences of the backbone are only observed for the β3β4-loop and the C-terminus. c Superposition of the complexes GDF-5 R57A:BMPR-IA and BMP-2:BMPR-IA reveals that the BMPR-IA ectodomains adopt slightly different orientations as illustrated by lines running through the Cα-atoms of Glu81 and Thr72 (magenta line BMPR-IA of the complex GDF-5 R57A:BMPR-IA; green line BMPR-IA of the BMP-2:BMPR-IA complex, the Cα position of either Thr72 or Glu81 is indicated by arrows). d Magnification of the two BMPR-IA molecules bound to GDF-5 R57A or bound to BMP-2 showing the different tilt angle of the BMPR-IA moieties in both ligand–receptor complexes. The Cα-atom positions of residues Thr72 and Glu81 in the BMPR-IA molecules are indicated by black circles (BMPR-IA from the complex when bound to BMP-2) and gray circles (BMPR-IA from the complex when bound to GDF-5 R57A) showing the differing orientation of both BMPR-IA molecules in the complex. Superpositioning of both BMPR-IA moieties shows that the orientational difference is not due to ligand-induced different conformations within the BMPR-IA molecules