Binding properties of BMP2. In vitro binding between BMP2, ALK3, and BMP-type II, receptors quantified using biolayer interferometry. (A) Example of kinetic experiment of BMP2 binding to immobilized ALK3 receptor. BMP2 was added at increasing concentrations, let interact and then removed from the solution. (B) Kinetic experiment of BMP2 binding to immobilized BMPR-II receptor. (C) The association constant (ka) was deduced from the fit of the kinetic data for the four studied receptors. (D) The dissociation constant (kd) was deduced from the fit of the kinetic data. (E) Summary table of the equilibrium constant Kd of BMP2 interaction with all four BMP receptors. Note the better affinity of ALK3 for BMP2. The results are representative of three independent experiments. (F) BMP2 interacts with vitronectin. Interaction between recombinant BMP2 and the proteins vitronectin and bovine serum albumin was measured by ELISA. Increasing concentrations of vitronectin or BSA were incubated for 1 h in PBS at 37°C in contact with BMP2 coated 96-well plate. The absorbance at 450 nm is plotted in function of the initial BMP2 concentration used to coat the multi-well plate. The figure illustrates one representative experiment of two performed, giving similar results.