Complexation of stimuli-responsive star-like amphiphilic block polyelectrolyte micelles with lysozyme

Abstract

The complexation between the stimuli-responsive star-like polyelectrolyte micelles formed by the self-assembly of polystyrene-b-poly(sodium(sulfamate-carboxylate)isoprene) (PS-SCPI) amphiphilic diblock copolymer in water and hen egg white lysozyme (HEWL) was investigated by means of dynamic, static and electrophoretic light scattering. Due to the pH-dependent charge density of the SCPI polyelectrolyte block and surface charge distribution of HEWL, the complexation process was studied at both pH 7 and pH 3 (high and low charge density of the SCPI block, or low and high net positive charge of HEWL, respectively) and at low ionic strength conditions. The solution behavior, structure and effective charge of the formed complexes proved to be dependent on the ratio of the two components and the pH of the solution. Moreover, it was found that the degree of charge neutralization caused by complexation determines the conformation and solubility of the complexes. Increasing the ionic strength of the solution led to vast aggregation of the preformed complexes and even precipitation in some cases. The structural investigation of the complexed protein by fluorescence, circular dichroism and infrared spectroscopic measurements revealed no signs of denaturation upon complexation.