Aqueous two-phase systems in protein purification

Osmotic Virial Coefficients as Access to the Protein Partitioning in Aqueous Two-Phase Systems

A promising alternative to state of the art chromatographic separations of therapeutic proteins is the extraction of the target protein using an aqueous two-phase system (ATPS). The use of an additional salt working as a displacement agent can influence the protein partitioning behavior in ATPS and thus enable a selective purification of the target protein. The selection of a suitable ATPS for protein extraction requires information concerning the protein-protein interactions (second osmotic virial coefficient B22 ) as well as the interactions between protein and solute (displacement agent and phase-forming components) (cross virial coefficient B23 ). In this work, the partitioning behavior and the precipitation affinity of immunoglobulin G (IgG) is considered within a polyethylene glycol (PEG)-phosphate ATPS. The influence on IgG partitioning upon addition of NaCl and (NH4)2 SO4 was investigated. In order to access the IgG precipitation affinity and the IgG partitioning behavior, the B22 and B23 values were determined for several combinations of solute [PEG, phosphate buffer, NaCl, and (NH4)2 SO4 ] and IgG based on static light scattering measurements. A qualitative estimation of the IgG precipitation affinity and the suitability of a solute as potential displacement agent within the PEG-phosphate ATPS on the basis of the measured B22 and B23 values is presented.

Evaluation of different primary recovery methods forE. coli-derived recombinant human growth hormone and compatibility with further down-stream purification

Due to advances in fermentation technology, it is now possible to obtain fermentation broth with over 30% solids. The high solid content makes the clarification step difficult, especially at large scale. The primary protein recovery step is challenging due to the heterogeneous solution of soluble and insoluble material. In this study, we compare different primary recovery routes and the compatibility with the initial capture chromatography step. The primary recovery routes studied are standard clarification by centrifugation and extraction in aqueous two-phase systems. The compatibility of the feed streams from the different primary recovery steps with the first chromatography step is addressed. An anion-exchange column was used as the first capture column in the purification process. The aqueous two-phase system was composed of a random copolymer of ethylene oxide and propylene oxide (EOPO) in combination with a waxy starch. The target protein in this study was human growth hormone (hGH) produced in recombinant Escherichia coli. The purity of hGH in the top phase after aqueous two-phase extraction was found to be significantly higher than in clarified homogenate supernatant and increased as the EOPO polymer concentration in the aqueous two-phase system increased. Stability of the supernatant and EOPO top phases and hGH were determined by turbidity measurements and LC-MS assay. All of the feed-streams from the primary recovery steps were compatible with the anion-exchange chromatography step; however, the capacity of the resin was strongly dependent on the purity of the load. Different process aspects, e.g., resin capacity, viscosity, purification, and yield of hGH and scalability are compared.

Bioaffinity extraction of glucoamylase in aqueous two-phase systems using starch as free bioligand

Aqueous two-phase systems with bioligands bound to the polymer, usually polyethylene glycol (PEG), have high selectivity. However, such kind of systems can be costly since some specific synthetic ligands are expensive, making them non-viable for bioaffinity extraction of low-cost proteins. The use of free bioligands is an alternative for decreasing the high cost of these systems. This work describes the use of starch as a free bioligand on the partition of glucoamylase in PEG 300-phosphate system. The results were separated into two parts. In the first part, analysis of the starch distribution between the phases showed one-sided distribution to the bottom phase. In the second part, filtered broth from submerged cultivation of Aspergillus awamori, containing glucoamylase and contaminants, was submitted to the extraction in the system with starch. In the system without starch, glucoamylase and contaminants are partitioned in the upper phase. Upon starch addition, the partition coefficient of glucoamylase was decreased nine-fold without altering the partition of contaminants. These results indicate the possibility of separation of enzymes with high-molecular-mass and hydrophilic substrates, like glucoamylase, cellulase and pullulanase, from their contaminants in a one-step extraction. Since systems made of low-molecular-mass PEG partitioned almost all of the proteins to the upper phase, the separation can be achieved by extraction of the target enzyme in the bottom phase, as in the case of the presented study.

Study of cell-free protein synthesis in aqueous two-phase systems

Protein synthesis in an aqueous two-phase system is reported here as a novel type of extractive bioconversion. Translation of BMV RNA was studied using either rabbit reticulocyte lysate or wheat-germ extract in aqueous dextran-PEG systems. Both polymers inhibited protein synthesis and the translation system partitioned into both phases. In the rabbit reticulocyte two-phase system, protein synthesis reached 30% of that in free solution, while in wheat-germ extract it was 60% of that in free solution. Protein was found mainly in the dextran (lower) phase but its partitioning was related to the polymer concentration, and molecular weight, as well as the ionic strength of the system. Protein synthesis was highly influenced by PEG concentration, potassium chloride concentration, and dextran molecular weight.

Rapid purification of fructose-1,6-bisphosphate aldolase from spinach chloroplasts

A rapid procedure for the purification of fructose-1,6-bisphosphate aldolase from spinach chloroplasts is presented which involves two steps; precipitation of bulk protein with polyethylene glycol and partitioning of remaining soluble protein in aqueous two-phase systems. A 94% pure preparation is obtained within 6h with a yield of 19%. A marked difference in the partition behaviour of the aldolase activity from whole leaf tissue suggested that the procedure is less efficient when leaf extract is used as starting material.

Affinity partitioning of enzymes using dextran-bound procion yellow HE-3G. Influence of dye-ligand density

The dye Procion Yellow HE-3G was bound to dextran of molecular weight 70,000 and the partitioning of this dye-polymer within an aqueous two-phase system containing dextran and poly(ethylene glycol) was studied as function of ligand density, polymer concentration, type of salt, concentration of salt and concentration of dye-dextran. Even moderate dye:dextran molar ratios (5-8) make the partitioning strongly salt-dependent. The dye-dextran can be directed to either the upper or the lower phase with partition coefficients from 0.02 to 28 by using salts. The dye-dextran in the two-phase system affects the partitioning of dye-binding enzymes (lactate dehydrogenase, glucose-6-phosphate dehydrogenase, 3-phosphoglycerate kinase) towards the dye-containing phase. Measurements of competition with nucleotide binding show an increased affinity of the dye for the enzyme with increasing ligand:dextran ratio. Theoretical considerations indicate that 1-2 dextran molecules are attached per enzyme molecule when affinity partitioning is fully developed.