Metal affinity partitioning

Combined hydrophobic-metal binding fusion tags for applications in aqueous two-phase partitioning

In this work, we studied the influence of fusion affinity tags containing both hydrophobic and histidines residues on the partitioning of the green fluorescent protein, GFPuv, in aqueous two-phase system. The tags were fused to the N-terminal of GFPuv and tested by immobilized metal affinity partitioning, in a PEG/salt system. The presence of both types of residues in the tag increased the partitioning greatly. Particularly, four engineered tags (H6, FH6, WH6, and YH6) containing a hexa-histidine sequence as well as different hydrophobic residues, all increased partitioning more than twice, reaching K values around 20, as compared to another construct (His6-GFP) containing an isolated hexa-histidine sequence. YH6, also proved be beneficial for protein expression.

Purification of soybean peroxidase (Glycine max) by metal affinity partitioning in aqueous two-phase systems

Combining two concepts in downstream processing, this work investigates the partitioning of a crude soybean peroxidase (Glycine max) in an aqueous two-phase system by metal affinity. A liquid-liquid extraction process using metal ligands was developed in two steps with the aim of purifying the enzyme peroxidase. PEG 4000 was activated using thionyl chloride, covalently linked to iminodiacetic acid (IDA), and the specific metal ligand Cu2+ was attached to the PEG 4000-IDA. In the first step, the system was composed of 14% (w/w) PEG 4000-IDA-Cu2+ and 8% (w/w) Na2SO4, and the peroxidase partitioned mainly to the top phase (K = 24). In the second step, a system formed by 14% PEG 4000 and 10% phosphate was used to revert the value of the partition coefficient of peroxidase to the bottom salt-rich phase (K = 0.05), thereby achieving a recovery of 64% of the purified enzyme.

Purification of microbial b-galactosidase from Kluyveromyces fragilis by bioaffinity partitioning

This work investigated the partitioning of b-galactosidase from Kluyveromyces fragilis in aqueous two-phase systems (ATPS) by bioaffinity. PEG 4000 was chemically activated with thresyl chloride, and the biospecific ligand p-aminophenyl 1-thio-b-D-galactopyranoside (APGP) was attached to the activated PEG 4000. A new two-step method for extraction and purification of the enzyme b-galactosidase from Kluyveromyces fragilis was developed. In the first step, a system composed of 6% PEG 4000-APGP and 8% dextran 505 was used, where b-galactosidase was strongly partitioned to the top phase (K = 2,330). In the second step, a system formed of 13% PEG-APGP and 9% phosphate salt was used to revert the value of the partition coefficient of b-galactosidase (K = 2 x 10-5) in order to provide the purification and recovery of 39% of the enzyme in the bottom salt-rich phase.

Protein purification with vapor-phase carbon dioxide

Gaseous CO2 was used as an antisolvent to induce the fractional precipitation of alkaline phosphatase, insulin, lysozyme, ribonuclease, trypsin, and their mixtures from dimethylsulfoxide (DMSO). Compressed CO2 was added continuously and isothermally to stationary DMSO solutions (gaseous antisolvent, GAS). Dissolution of CO2 was accompanied by a pronounced, pressure-dependent volumetric expansion of DMSO and a consequent reduction in solvent strength of DMSO towards dissolved proteins. View cell experiments were conducted to determine the pressures at which various proteins precipitate from DMSO. The solubility of each protein in CO2-expanded DMSO was different, illustrating the potential to separate and purify proteins using gaseous antisolvents. Polyacrylamide gel electrophoresis in sodium dodecyl sulfate (SDS-PAGE) was used to quantify the separation of lysozyme from ribonuclease, alkaline phosphatase from insulin, and trypsin from catalase. Lysozyme biological activity assays were also performed to determine the composition of precipitates from DMSO initially containing lysozyme and ribonuclease. SDS-PAGE characterizations suggest that the composition and purity of solid-phase precipitated from a solution containing multiple proteins may be accurately controlled through the antisolvent's pressure. Insulin, lysozyme, ribonuclease, and trypsin precipitates recovered substantial amounts of biological activity upon redissolution in aqueous media. Alkaline phosphatase, however, was irreversibly denaturated. Vapor-phase antisolvents, which are easily separated and recovered from proteins and liquid solvents upon depressurization, appear to be a reliable and effective means of selectively precipitating proteins.