SPR analyses of gp120 CDC451 binding to peptides. Biotinylated phages displaying peptides m1, m2 and m3 were immobilized on CM5 sensor chips coated with streptavidin and reacted with either gp120 (red), mAb CG10 (blue) or with the mixture gp120 + CG10 (black). Y-axes (Signal) were adjusted according to baseline. As can be seen, the binding to m2-phage is markedly improved as compared to m1. The m3 peptide binds marginally better than m2. A scrambled peptide which was also tested in this setting did not show any binding to gp120 or CG10 (not shown). The two right-hand panels depict binding kinetics of two fold serial dilutions of gp120 (3.9-250nM) to the immobilized m2 displaying phage. The experimental data (colored curves) were fitted (black curves) using TraceDrawer 1.5 software (Ridgeview Instruments AB Uppsala, Sweden). As can be seen in A the OneToOne model does not fit the data very well (Chi2 4.25). Using the OneToOne TwoState model the fit is markedly improved (Chi2 0.32) supporting the conclusion that binding of m2-phage to gp120 is associated with conformational rearrangements.