Fig. 1: A particle-based model for bivalent binding quantifies the impact of molecular reach and accurately analyses bivalent SPR traces.
From: The molecular reach of antibodies crucially underpins their viral neutralisation capacity
a Schematic of the chemical reactions in models describing monovalent and bivalent SPR. The ODE-based and particle-based bivalent models assume that any free antigen on the surface or only free antigen within reach, respectively, can be bound by an antibody already bound to the surface with one arm (grey shaded regions). b Representative monovalent (left) or bivalent (middle, right) SPR traces using the antibody FD-11A interacting with RBD of SARs-CoV-2. The family of SPR traces are generated by 2-fold dilution of RBD starting at 2000 nM (left) or by a 2-fold dilution of FD-11A starting at 300 nM (middle, right—same data but different model fit). c The fitted binding parameters for monovalent (N = 4) and bivalent (N = 6) SPR experiments. Data are presented as geometric mean values ± SD. A two-way t-test with Dunnett’s multiple comparison correction on log-transformed values was used to determine p-values. d Simulated SPR traces (bottom) for antibodies injected over a surface with a random distribution of antigen (top) but with different values of reach. Antigens (circles) are coloured red if they are within reach of another antigen and blue otherwise. Parameter values: kon = 0.05 μM−1s−1, koff = 0.05s−1, kon,b = 1.0s−1, and [RBD] = 0.0025 nm−2. e The fitted bivalent binding parameters from the N = 6 bivalent SPR experiments. Data are presented as geometric mean values (for kon,b) or mean values (for reach) ± SD. f, g Comparison of five antibodies analysed using monovalent and bivalent SPR from N ≥ 2 independent experiments (EY6A: N = 6, FD-5D: N = 6, FD11A: N = 8, CR3022: N = 5, FI-3A: N = 2). f Comparison of the indicated parameter using both methods with the dashed line displaying perfect agreement (y = x). An F-test was used to determine a p-value for the null hypothesis that the dashed line and the fitted line to log-transformed binding parameters were equal. g The bivalent binding parameters. Source data for this figure are provided as a Source Data file.
