Protonation of β-lactoglobulin in the presence of strong polyelectrolyte chains: a study using Monte Carlo simulation

In this work, the molecular interaction between the protein β-lactoglobulin and strong polyelectrolyte chains was studied using Monte Carlo simulations. Different coarse-grained models were used to represent the system components. Both net charge and protonation of the isolated dimeric protein were analyzed as a function of pH. The acid-base equilibrium of each titratable group was distinctively modified by the presence of polyanion or polycation chains. The complexation on the wrong side of pI was more evident with the polycation than with the polyanion. It was mainly due to a charge regulation mechanism, where the reversion in net charge of the protein was more pronounced at the left of isoelectric point of the protein. The glutamic and aspartic groups play a key role in this charge reversion. Both polyanion and polycation were spatially adsorbed in different region on the protein surface, suggesting the importance of the surface charge distribution of the protein.