Monte Carlo simulations of polyelectrolyte-protein complexation

The complexation between one polyelectrolyte and one protein has been exami ned by employing a simple model system solved by Monte Carlo simulations. T he polyelectrolyte was composed of a sequence of negatively charged hard sp heres, and the protein was represented by a hard sphere with embedded pH-de pendent discrete charges, the positions of which were taken from lysozyme. A short-range attractive interaction between the polyelectrolyte and the pr otein accounting for hydrophobic interactions completed the model. The comp lexation was found to depend decisively on the charge status of the protein model as well as on the presence of the short-range attractive interaction . In particular, the complexation weakens at decreasing ionic strength exce pt for the highest positive protein net charge considered. and in the absen ce of the short-range attraction, a positively charged protein was required to obtain a complex. The distribution of the polyelectrolyte beads was inh omogeneous at the protein surface, and the polyelectrolyte contracted upon complexation. Finally, the protein model with discrete charges gave a stron ger complex than the corresponding protein model with a homogeneous surface charge density.