Quantitative analysis of protein-protein interactions using Biacore assay (surface plasmon resonance biosensor assay). Strep-tagged AID peptides and Strep-tag control peptide were immobilized on sensor chips CM5 (Biacore). Binding curves for GST-Grb2, Numb p71, and X11β proteins were expressed in resonance units (RU) as a function of time. (A) AIDpY and GST-Grb2 interaction, (B) AIDpTpY and GST-Grb2 interaction, (C) AID and GSTNUMB-p71 interaction, (D) AIDpY and GST-NUMB-p71 interaction, (E) AIDpTpY and GST-NUMB-p71 interaction, (F) AID and X11β interaction, (G) AIDpT and X11β interaction, and (H) AIDpTpY and X11β interaction. The kinetic parameters and concentrations of the analytes are indicated in A-H.