Figure 5.

Comparison of measured and calculated electrostatic potentials for a range of biomolecular systems. ϕ_ENS potentials measured using Gd-DOTA (−1e) and Gd-DOTAM-BA (+1e) are shown in red for (A) ubiquitin, (B) G48A Fyn SH3, (C) 15-bp DNA, and (D) RtoK CAPRIN1. ϕ_ENS values were determined from the solvent PRE data shown in Figure 4 using eq 2. In (A–C), the measured ϕ_ENS potentials are compared with potentials obtained via Poisson–Boltzmann calculations (ϕ^PB_ENS), which are shown in blue, and the middle panels show correlations between the experimental (ϕ^Gd_ENS) and predicted (ϕ^PB_ENS) potentials. The right panels show correlations between the experimental potentials measured with the Gd chelates and those measured with PROXYL derivatives. In (A, B, D), ϕ^Proxyl_ENS values were measured using amino-methyl-PROXYL (+1e) and carboxy-PROXYL (−1e) cosolutes, while in (C), ϕ^Proxyl+/n_ENS values were measured using aminomethyl-PROXYL (+1e) and carbamoyl-PROXYL (neutral) cosolutes. In (D), ϕ_ENS potentials measured using carboxy-PROXYL (−1e) and aminomethyl-PROXYL (+1e) are shown in green, and a correlation plot for the two experimental datasets (Gd- and PROXYL-based) is shown. In each correlation plot, the dotted line is the diagonal (i.e., y = x), whereas the solid line, y = x + a, is based on linear regression. Outlier ϕ_ENS values (residues D52, N60, L73) are circled in (A) and discussed in the text. D52 and N60 were excluded in the calculation of RMSD between ϕ^Gd_ENS and ϕ^Proxyl_ENS. See text and SI for discussion. Error bars were obtained using eq 4. In (C), errors in ϕ_ENS potentials for CH₃ groups are far smaller than those for other DNA ¹H nuclei.