Polyelectrolyte complex coacervates (PECCs) result from liquid-liquid phase separation (LLPS) in solutions containing oppositely charged polymers 1. Multiphase polyelectrolyte complex coacervates (MPECCs) result from the combination of multiple, specific PECCs 2. The encapsulation of proteins in PECCs can serve as promising vehicles for the effective delivery of protein-based therapeutics, which are notoriously difficult to deliver. The encapsulation of model proteins, such as Bovine Serum Albumin (BSA) 3 or Human Hemoglobin (Hb) 4 have illustrated the protein-encapsulating capabilities of these PECC systems. The encapsulation of proteins in MPECCs is a topic that has yet to be explored; however, it can serve to mimic the structure and function of multiphase membraneless organelles, which are abundantly available in cells. This project sought to understand and quantify the encapsulation of enzymes in both PECC and MPECC models; as well as evaluate their efficiency upon encapsulation, as enzymes are simply proteins with catalytic functions 5. A synthesized library of charged, heterochiral polypeptides were used to form both PECC and MPECC systems. Glucose oxidase (GOx) and horseradish peroxidase (HRP) were the enzymes chosen to be assessed in both PECC and MPECC systems. Turbidity measurements, in terms of percent mole of polycation, were used to determine the optimal stoichiometric ratio between the polyanion and polyanion, in the presence of a given concentration of both or either enzyme, in which maximum complex formation occurred. Here we report that a 1:1 stoichiometric ratio of polycation to polyanion in either a solution with 25ug/mL HRP and 25ug/mL GOx, a solution with 50ug/mL GOx, or a solution with 50ug/mL HRP leads to the highest level of complexation. Enzyme encapsulation efficiency of individual PECCs for both enzymes was assessed using the Bradford assay, in which the supernatant was used to determine the concentration of enzyme left in the PECC post-centrifugation. Here we report that all PECC systems were able to encapsulate both GOx and HRP. Higher encapsulation efficiencies were seen with GOx samples compared to HRP samples. Enzymatic activity and efficiency were assessed using the 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid (ABTS) assay in the presence of ß-D-glucose. The chromogenic change in intensity over time of each sample was assessed using optical microscopy. Michaelis-Menten graphs were made from the data collected. The resulting data was used to evaluate the Km and Vmax of the enzyme cascade in PECC and MPECC systems compared to a control. Here we report that enzyme cascade efficiency varied among PECC and MPECC samples, with some being more efficient than others. We find that both PECC and MPECC systems generally have lower enzyme-substrate affinity (higher Km) compared to performing the reactions in water. However, this may be related to the need for the substrate to diffuse into a different phase or phases. Interestingly, many of the PECC and MPECC systems have lower Vmax values compared to the water control, indicating a faster enzyme saturation. The enzyme kinetics and efficiency could also be controlled by varying the location of the enzymes in each phase within the MPECC systems. Overall, we show that using MPECC systems allows one to select advantageous properties of individual PECCs and combine them together.
Bachelor of Science (B.S.)
College of Medicine
Burnett School of Biomedical Sciences
Rajaram, Akash R., "The Encapsulation of Enzymes in Multiphase Complex Coacervates" (2023). Honors Undergraduate Theses. 1408.