Our results reveal that the Amber14SB 73 / Amber99SB*-ILDN 141 partial charges for lysine are likely erroneous, yielding pK a and thermostability estimates that deviate significantly from experiment. Importantly, we demonstrate that this error can be resolved using charges assigned in Amber99SB*-ILDN-Q . Whether such a change resolves previously documented ion-overbinding problems and conformational discrepancies in polyelectrolytes 144 remains to be seen.