Fig. 2: RBD mutant avidity for its ACE2 host receptor quantified by AFM.
From: Molecular insights into receptor binding energetics and neutralization of SARS-CoV-2 variants
a Box plot of specific binding frequencies (BF) measured by AFM between the functionalized tip (RBD mutants) and the grafted ACE2 model surface or the NHS-EDC surface, lacking ACE2 receptor (dashed boxes). One data point belongs to the BF from one map acquired at 1 µm s−1 retraction speed and 250 ms contact time. The square in the box indicates the mean, the min/ max of the box the 25th and 75th percentiles respectively, and the whiskers the s.d. of the mean value. The line in the box indicates the median. N = 10 maps examined over 3 independent experiments for the ACE2 surface. N = 3 maps examined over 1–2 independent experiments for the NHS-EDC surface. P-values were determined by the two-sample t test in Origin. b–f Dynamic force spectroscopy (DFS) plot showing the individual force extracted from individual FD curves (gray data points) as well as the average rupture forces, determined at seven distinct loading rate (LR) ranges measured either between ACE2 receptor and WT-RBD (b, N = 1434 data points), Alpha-RBD (c, N = 1541 data points), Beta-RBD (d, N = 1094 data points), Gamma-RBD (e, N = 1952 data points) or Kappa-RBD (f, N = 2719 data points). Data corresponding to single interactions were fitted with the Bell−Evans (BE) model (straight line), providing average koff and xu values. Dashed lines represent predicted binding forces for multiple simultaneous uncorrelated interactions ruptured in parallel (Williams−Evans [WE] prediction). Plots on the right: The binding frequency (BF) is plotted as a function of the contact time. Least-squares fits of the data to a mono-exponential decay curve (line) provide average kinetic on-rates (kon) of the probed interaction. Further calculation (koff/kon) leads to KD. One data point belongs to the BF from one map acquired at 1 µm s−1 retraction speed for the different contact times. All experiments were reproduced at least three times with independent tips and samples. The error bars indicate s.d. of the mean value. WT-RBD is colored in gray/black, and the VoCs Alpha-RBD in blue, Beta-RBD in green, Gamma-RBD in orange, and Kappa-RBD in purple.
