Sodium chloride-programmed phase transition of β-conglycinin/lysozyme electrostatic complexes from amorphous precipitates to complex coacervates

The associative phase separation of biomacromolecules can produce both liquid-like coacervates or solid-like precipitates. In this study, we found that sodium chloride (NaCl) can programme the phase transition of beta-conglycinin/lysozyme (beta-CG/LYS) complexes. NaCl reduced the zeta-potential of both beta-CG and LYS. Their complex coacervate was formed at pHs 6 and 7 with 5-80 mM NaCl and at pH 8 with 40-80 mM NaCl. Unlike the high critical salt concentration and entropy gain driving force of polyelectrolyte-based complex coacervation, 100 mM NaCl almost completely inhibited beta-CG/LYS complexation, and the exothermic enthalpy change was the main driving force for beta-CG/LYS complex formation. Confocal laser scanning microscopy with fluorescein isothiocyanate-labeled proteins demonstrated dynamic protein exchange in coacervate droplets, similar to that in polyelectrolyte-based complex coacervates.