FIG. 3.

Surface plasmon resonance of gp41 6-HB binding to mF-3674. (A) Sensorgrams (red) of wild-type gp41 6-HB binding to immobilized mF-3674 Fab. The association [k_a = (1.07 ± 0.01) × 10⁶ M⁻¹ s⁻¹] and dissociation [k_d = (1.93 ± 0.01) × 10⁻² s⁻¹] phases obtained at all concentrations of the 6-HB were fit simultaneously with a heterogeneous analyte model using BIAevaluation software. All data were reference subtracted and zero-concentration corrected prior to fitting. Nonlinear least-squares best fits to the data are shown as black lines. (B) Plot of maximum response units (RU) as a function of concentration yields an equilibrium dissociation constant (K_D) of 26 ± 4 nM, in good agreement with the value of ∼18 nM derived from the association and dissociation rate constants. (The diamonds are the experimental data, and the red line represents the best fit to a simple binding isotherm.)