Paramagnetic resonance enhancement NMR experiments (PRE) can measure the electrostatic component of the potential of mean force in solution with spin-probe cosolutes. We compare the results with theory and simulations to determine the contribution of different chemical components to the near-surface electrostatic potentials in different salt solutions. Salt-dependence of the electrostatic potentials for the protein ubiquitin was studied in ionic strengths from 0 mM to 730 mM.  The results of Poisson-Boltzmann continuum solvent theory are in good agreement for many of the residues. We found discrepancies are caused by correlations of the probe molecule with the protein in the calculations. Mutual validations of the experiment and the computations emphasize the importance of orientational correlations of probes in the determination of surface potentials by PRE.

Biopolymer electrostatic potentials in solution: Comparing experiment and theory

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