Our results did not allow for drawing any conclusions on protonation states. The reason for that may be two-fold: either the initial selection of systems is incorrect, or the mechanical force field used (99SB-ildn) is incapable of correctly modeling them. It could also be true for any mechanical force field. To streamline our experimental design, we chose to systematically revisit all possible protonation states. To avoid potentially pointless sampling of force fields, we decided to use hybrid quantum mechanical/molecular mechanical (QM/MM) calculations.