Complex coacervation of supercharged proteins with polyelectrolytes.

Area of Science:

• Biomaterials Science
• Polymer Chemistry
• Protein Chemistry

Background:

• Complexation of proteins with polyelectrolytes can form coacervate phases or coacervate core micelles.
• Many proteins do not readily coacervate under physiological conditions.

Purpose of the Study:

• To investigate the effect of protein charge on complex coacervation with polycations using protein supercharging.
• To determine the critical protein charge ratio (α) for coacervate phase formation and micelle encapsulation.

Main Methods:

• Anionic protein supercharging of four model proteins.
• Mass spectrometry for quantifying protein charge.
• Fluorescent labeling to determine coacervate composition.
• Small-angle neutron scattering and transmission electron microscopy for micelle characterization.

Main Results:

• Protein phase separation occurred when the charge ratio (α) exceeded 1.1-1.2.
• Efficient partitioning into coacervates required α values of 1.5-2.0.
• Micelle formation was observed for α > 1.3-1.4.
• Coacervate and micelle stability increased with ionic strength and protein net charge.

Conclusions:

• Protein supercharging is a viable method to induce and control complex coacervation.
• The protein charge ratio (α) is a key parameter governing coacervate and micelle formation and stability.
• Coacervates exhibit charge imbalances, and micelles demonstrate robustness to dehydration and heat.