Fig. 4. BIAcore analysis of megalin and adaptor interaction. Immobilized rabbit megalin (A,C) or human megalin tail protein (B,D) were incubated with the indicated concentrations of purified GST-MegBP (A,B) or GST-Dab1 (C,D). Binding to the receptor polypeptide was detected by surface plasmon resonance signal (BIAcore) and indicated in response units. As a control, binding of 1 µM GST to the megalin tail was tested (B,D). From the kinetic data, the K_d values for the interactions were calculated as 1.1 µM (MegBP to megalin), 0.8 µM (MegBP to the megalin tail), 0.25 µM (Dab1 to megalin) and 0.15 µM (Dab1 to the megalin tail).