Regarding DJ-1, the large pK a value of E18 implied by free energy calculations is also suggested by the constant-pH simulations on monomeric DJ-1, where values of 9.48 ± 0.42 pK and 20.99 ± 0.05 pK were calculated in the cases of protonated C106 and deprotonated C106, respectively. Here, only a single fit to Equation 10 was performed and the Hill coefficient was not fixed to n = 1. C106 was not probed as cysteine residues are not yet supported by the current CpHMD implementation. We close this section by briefly comparing our results with the popular computational pK a predictor PropKa. Overall, for PropKa, we find good agreement for the SNase dyads, but a worse accuracy for C106 in DJ-1. Specifically, estimates from PropKa were: D19: 3.21, D21: 5.44, D40: 4.30, D83: 1.21, and C106: 14.19 (Figure ).