Figure 5

Demonstration and deciphering at the molecular level of the physical interaction between the IL34 protein and proteins of the BMP family. (A) Surface plasmon resonance experiments (described in Materials and Methods section) and values of proteins interaction parameters between IL34 and BMPs. ka: association rate constant, kd: dissociation rate constant, KD: affinity constant. (B) Molecular modelling of the binding of two BMPR1A receptors (green) to a BMP2 dimer (brown and dark blue) by using PyMOL. (C) Molecular modelling of the binding of two IL34 proteins (cyan) to a BMP2 dimer (brown and dark blue) seen in profile (top) and from above (bottom) with a representation of the BMP2 proteins in surface (left) and in structure (right) by using PyMOL. (D) Structural representation of a BMP2 dimer seen from above with the location of the “Knuckle” and “Wrist” binding sites to the type 1 and type 2 receptors respectively as described by Sebald and collaborators 76,77. (E) Main amino acid of BMP2 and IL34 identified as being involved in binding. In addition, hydrogen bonds and salt bridges were found between BMP2 and IL34, more specifically between residues K383-D190, D312-K55 and E376-R73. (F) Localization on the representation of the BMP2 protein in structure of amino acids important for partner binding: F305 in red, W310 in bright green, W313 in yellow, Y385 in light brown and M388 in grey. These amino acids delineate the pocket in which residues F85 of BMPR1A and R48 of IL34 are positioned during their interaction with BMP2. The amino acid N341 presented in light blue, despite is localization in the most outside part of the pocket, was not identified as important for the binding to IL34. IL34 is displayed in surface representation with the entire binding region colored in yellow, and the important intercalating residue R48 is indicated in duck blue.