Journal
JOURNAL OF MOLECULAR BIOLOGY
Volume 378, Issue 1, Pages 191-203Publisher
ACADEMIC PRESS LTD- ELSEVIER SCIENCE LTD
DOI: 10.1016/j.jmb.2008.02.031
Keywords
BMP; BMP receptor; ligand binding; mutagenesis; SPR
Categories
Funding
- NCI NIH HHS [CA54174] Funding Source: Medline
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ActR-IIA, ActR-IIB, and BMPR-II are low-affinity type II receptors that bind bone morphogenetic proteins (BMPs) in the same overall manner. The binding of BMPs by ActR-IIs has been analyzed structurally and functionally, but no detailed analysis of BMPR-II has been reported. The objective of this study was to determine ligand-binding epitopes and specificity determinants in two regions, the hydrophobic patch and the A-loop of the BMPR-II extracellular domain (ECD). A series of alanine-substituted variants was generated using a recently published X-ray structure of the unliganded form of the ovine BMPR-II ECD as a guide. These variants were characterized using one-dimensional NMR and functional activity assays with BMP-2, BMP-7 and GDF-5 as ligands. The results showed that alanine substitutions of conserved residues W85 and Y113 within the hydrophobic patch of the ECD differentially perturbed BMP ligand binding without disrupting receptor folding, suggesting that they are critical determinants for ligand binding and ligand specificity. Our results further revealed that the nonconserved residue L69 in the hydrophobic patch contributes to ligand-binding activity and specificity. Mutations of several residues within the A-loop resulted in minimal effects on the binding of the different BMP ligands. Overall, these observations identify several amino acid residues that play different roles in BMPR-II and ActR-II and thereby enable BMPR-II and ActR-IIs to bind different subclasses of BMP ligands.
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