Figure 2.

Binary complex of agrin LG3 (agrin) and LRP4^V396–A737 (LRP4). (A) The association of agrin (green) and LRP4 (orange) is mostly mediated by the neuron-specific z8 alternative splicing sequence in agrin. This loop is unambiguously defined by excellent electron densities (2F_o − F_c map contoured at 1σ) (in cyan). (B) The structure of rat agrin (green) in the context of an agrin–LRP4 complex is superimposed on the structure of an apo form of chicken agrin that also has an eight-amino-acid insert at the B/z site (magenta; PDB code 1PZ8). The arrows indicate the boundaries of the disordered z8 loop of the apo chicken agrin. (C) Stereoview of the detailed interactions between agrin (green/cyan) and LRP4 (yellow). Key residues that are directly involved in complex interactions are shown as the ball-and-stick model. Hydrogen bonds are indicated by dotted lines. (D) Open-book view of the electrostatic potential of the z8-interacting surfaces (highlighted with squares). The negatively charged z8 loop is complementary to the positively charged surface in LRP4.