Structural and functional analysis of bone morphogenetic proteins: Crystal structure of bone morphogenetic protein-9, binding studies with pro-domain and receptors, and mutational studies in Drosophila decapentaplegic.
Controlling cellular processes from before gastrulation and continuing throughout the life of the animal, Bone Morphogenetic Proteins (BMPs) have been the subjects of intense study for decades, but there is still much to be learned about the function of individual BMPs and the general nature of their signaling. Chapter 1 presents the crystal structure of BMP-9, an orphan ligand with significant therapeutic interest. Chapter 2 establishes some of the nature of the relationship between BMP-9 and its pro-region, and examines binding with some potential receptors. One of these receptors, Activin-Like Kinase-1 (ALK-1), was an orphan receptor with known biological function and disease pathology. ALK-1 showed strong binding and functional activity with BMP-9 in several cell-based assays, and was proposed as a candidate for a functional receptor for BMP-9. Chapter 3 shows preliminary work on the conservation of binding determinants across species, using structural and mutagenesis studies in human BMPs to direct mutagenesis in Drosophila BMPs. These experiments are intended as the first steps towards examination of the fundamental components of the signaling complex, and structural analysis of heterodimer functionality. The further directions for this project are discussed in Chapter 4. The thesis attempts to contribute to the growing understanding of how BMP ligands establish the overlap and specificity with receptors and other binding proteins necessary for highly precise control of signaling that still preserves the safeguards of redundancy.