BMP-3 and BMP-6 Structures Illuminate the Nature of Binding Specificity with Receptors^,

Abstract

Bone morphogenetic proteins (BMPs) are extracellular messenger ligands involved in controlling a wide array of developmental and intercellular signaling processes. To initiate their specific intracellular signaling pathways, the ligands recognize and bind two structurally related serine/threonine kinase receptors, termed type I and type II, on the cell surface. Here, we present the crystal structures of BMP-3 and BMP-6, of which BMP-3 has remained poorly understood with respect to its receptor identity, affinity, and specificity. Using surface plasmon resonance (BIAcore) we show that BMP-3 binds Activin Receptor type II (ActRII) with Kd approximately 1.8 microM but ActRIIb with 30-fold higher affinity at Kd approximately 53 nM. This low affinity for ActRII may involve Ser-28 and Asp-33 of BMP-3, which are found only in BMP-3's type II receptor-binding interfaces. Point mutations of either residue to alanine results in up to 20-fold higher affinity to either receptor. We further demonstrate by Smad-based whole cell luciferase assays that the increased affinity of BMP-3S28A to ActRII enables the ligand's signaling ability to a level comparable to that of BMP-6. Focusing on BMP-3's preference for ActRIIb, we find that Lys-76 of ActRII and the structurally equivalent Glu-76 of ActRIIb are distinct between the two receptors. We demonstrate that ActRIIbE76K and ActRII bind BMP-3 with similar affinity, indicating BMP-3 receptor specificity is controlled by the interaction of Lys-30 of BMP-3 with Glu-76 of ActRIIb. These studies illustrate how a single amino acid can regulate the specificity of ligand-receptor binding and potentially alter biological signaling and function in vivo.

Selected Bone Morphogenetic Proteins—The Possibility of Their Use in the Diagnostics and Therapy of Severe Asthma

“…Although BMP-3 remains not fully understood, the BMP-3 gene is known to be present in chromosome 4q21.21 [26]. The BMP-3 molecule demonstrates high affinity to the activin receptor ActRII, but lower to ActRIIb.…”

Beyond CDR-grafting: Structure-guided humanization of framework and CDR regions of an anti-myostatin antibody

“…It is important to note that the structure of the myostatin dimer is noticeably different than those previously reported, and does not show the typical butterfly structure of other myostatin structures 44 or closely related TGF-b family members. [45][46][47] There are 2 crystal structures in the PDB with 100% sequence identity in the myostatin region. These are 3hh2, which contains a myostatin dimer in complex with follistatin 288, 44 and 3sek which contains a myostatin monomer in complex with follistatin-like 3 complex.…”

Association of BMP6 Methylation and Expression with Clinicopathological Features in Colorectal Cancer

“…Although highly homologous, BMP6 and BMP7 emerge to have distinct type I receptor specificities with BMP6 displaying a 20-fold higher affinity to BMPRIA than BMP7, but 20-fold lower than BMP2. This is absolutely an unexpected finding having in mind which BMP6 shares numerous receptor binding and signaling characteristics with BMP7 [47][48][49]. N-glycosylation recognition motif of BMP6 at Asn 73 in the wrist epitope is crucial for the recognition by the ACVRI [50].…”

“…In the BMP6 crystal structure, the H3 pre-helix loop region (residues 65-73) presents the largest difference between the BMP6 and BMP7 structures [47], (Figure 4). Although highly homologous, BMP6 and BMP7 emerge to have distinct type I receptor specificities with BMP6 displaying a 20-fold higher affinity to BMPRIA than BMP7, but 20-fold lower than BMP2.…”