Structural analysis of BMP and BMP receptor

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Bone morphogenetic proteins (BMPs) regulate the growth, differentiation and apoptosis of various cells. To elucidate the mechanisms of signal transduction by BMP, we analyzed the structure and interactions of BMP receptor. The extracellular domain of the mouse BMP type-IA receptor was expressed as a fusion protein with thioredoxin in Escherechia coil. Using heteronuclear multidimensional NMR methods, the assignments of the BMP receptor were completed and the solution structure of BMP receptor was determined. In other words, we have obtained powerful tools and methods to investigate the BMP-BMP receptor complex at atomic resolution. Based upon the resulting structure, we have designed and synthesized several mutants of BMP receptor to identify its ligand (i.e. BMP) binding site. CD spectra of the mutant receptors indicated that all the mutants have essentially the native folding structures. Affinities of the mutants to BMP-4 were measured using several physico-chemical methods, surface plasmon resonance sensor (BIACORE), sedimentation equilibrium and NMR.Binding studies have shown that the side chains of Ile52, Glu54, Thr62 and Thr64 at the surface of the three-stranded β-sheet form a high affinity ligand-binding surface together with Phe75 in loop region. These results provide deeper insights for the structural basis of the ligand recognition by BMP receptor.