Protein encapsulation via polyelectrolyte complex coacervation: Protection against protein denaturation.

Complex coacervation can be used as a route to compartmentalize a variety of solutes such as organic small molecules, inorganic nanoparticles, and proteins within microscale coacervate droplets. To obtain insight into the accumulation of proteins within complex coacervate phases, the encapsulation of Bovine Serum Albumin (BSA) within complex coacervates containing cationic polyelectrolyte poly(allylamine hydrochloride) (PAH) and anionic polyelectrolyte poly(acrylic aid) (PAA) was investigated as a function of mixing sequence, total polyelectrolyte concentration, BSA overall concentration, and the mixing molar ratio of PAA/PAH. Mixing BSA having a negative net charge with the polycation PAH before coacervation, increasing the total polyelectrolyte concentration and PAA/PAH molar ratio, or decreasing the BSA overall concentration led to more efficient protein encapsulation. Preservation of the secondary structure of BSA during the complex coacervation process was confirmed using circular dichroism spectroscopy. Our study shows that PAA-PAH coacervates can serve as a protective system against the denaturation of BSA when exposed to extremes of pH, high temperatures, as well as in solution of urea. Additionally, it was found that by encapsulation of proteins within coacervates via complex coacervation, the complexation between proteins and heavy metal can be efficiently inhibited. Protection of BSA against severe environmental conditions via encapsulation within polyelectrolyte coacervates provides new insights and methods to issues of maintaining stability and function of proteins.