Molecular Basis of Interchain Disulfide Bond Formation in BMP-9 and BMP-10

Area of Science:

• Molecular and Cellular Biology
• Biochemistry
• Structural Biology

Background:

• Bone morphogenetic proteins (BMPs) 9 and 10 are signaling ligands of the TGF-β family, essential for vascular development and maintenance.
• Mutations in the BMP-9/10 pathway, specifically in ALK1 or endoglin, are linked to hereditary hemorrhagic telangiectasia, a vascular disorder.
• BMP-9/10 heterodimers are the predominant signaling forms in circulation, but their formation mechanism remains poorly understood.

Purpose of the Study:

• To elucidate the mechanisms governing the secretion and dimerization of BMP-9 and BMP-10.
• To investigate the structural basis for the differential formation of disulfide-linked dimers between BMP-9 and BMP-10.
• To understand how monomeric and dimeric forms of BMP-9/10 influence their signaling potency and heterodimerization.

Main Methods:

• Protein crystallography was employed to determine the structure of BMP-9 homodimers and assess the conformation of the interchain disulfide bond.
• Biochemical assays were used to evaluate the self-association properties and signaling potency of BMP-9 monomers and dimers.
• Residue swapping experiments near the interchain disulfide were performed to investigate the factors influencing disulfide bond formation frequency.

Main Results:

• BMP-9 and BMP-10 monomers are secreted in a cysteinylated form, capable of forming non-covalent dimers, but exhibit reduced signaling potency.
• Protein crystallography revealed a strained syn-periplanar conformation of the interchain disulfide in BMP-9 homodimers, explaining infrequent disulfide bond formation.
• Disulfide bond formation is less frequent in BMP-9 than BMP-10, a difference that can be modulated by altering residues involved in inter-protomer interactions.

Conclusions:

• Geometric strain at the interchain disulfide bond, rather than cysteinylation, is the primary determinant of limited disulfide-linked dimer formation in BMP-9.
• The differential disulfide bond formation frequencies between BMP-9 and BMP-10 are influenced by specific residue interactions near the cysteine residues.
• These findings provide critical insights into the assembly of BMP-9/10 signaling complexes and have implications for understanding vascular development and disease.