The titration curves of cardiotoxin V and HEWL proteins are shown in Figures and, respectively. The pK a values obtained from fitting the Henderson-Hasselbalch equation to the degree of deprotonation in the all-atom simulations of both proteins with the CHARMM36 , are in good agreement with previous constant pH MD simulations, and in reasonable agreement with experimental estimates from NMR spectroscopy. In particular, the trends in the pK a shifts are well reproduced, including the downshift of Asp-59 in cardiotoxin V, and, with the exception of Glu-35 and Asp-52 in HEWL, the deviations are below 1 pK a unit. We note that also in previous constant pH simulations with the CHARMM force field, 15,23 similar deviations were found for these two residues (see Figure ). This suggests that the origin of the discrepancy might lie beyond the implementation, and could be due to either a lack of sampling, or systematic shortcom-ings in the force field. The pK a values estimated from the Martini 2.0 force field simulations of these proteins do not agree as well to experiment as those derived from the all-atom simulations. We speculate that the larger deviation of the pK a 's in the coarse-grained constant pH simulations could be due to the lower accuracy of the electrostatic interactions.