As in Donnini et al., the buffers were collectively coupled to the titratable sites in the system via a charge constraint. The charges of all buffers were thus simultaneously interpolated between -0.5 e and 0.5 e, keeping the simulation box neutral. For all peptide simulations, 10 such buffers were introduced into the system, while 20 buffers were added to the simulation boxes with the proteins (systems 4-5), in both AA and CG models. 185 buffer particles were used in GLIC simulations.