Extraction of β-galactosidase fused protein a in aqueous two-phase systems

Aqueous two-phase systems for biomolecule separation

Over the past thirty years, aqueous polymer two-phase technology has evolved, both experimentally and theoretically, into a separation science with many useful applications in biomolecule purification and bioconversion. This paper summarizes the developments in the applications of aqueous two-phase systems to biotechnology. The main topics to be considered are the phase diagram and its characteristics, fundamentals of biomolecule partition, large-scale and multi-stage aqueous two-phase biomolecule purification, and extractive bioconversions. The first topic involves a discussion of the thermodynamics of aqueous polymer two-phase formation and how it is influenced by such factors as polymer molecular weight and concentration, temperature, and salt type and concentration. Next, the theoretical and experimental aspects of biomolecule partition in aqueous two-phase systems will be discussed in light of the factors which influence biomolecule partition: polymer concentration and molecular weight; temperature; salt type and concentration; the addition of charged, hydrophobic and affinity derivatives. Having reviewed the fundamentals of phase diagram formation and biomolecule partition, the next two topics are applications of aqueous two-phase technology. The first set of applications involve the large-scale extraction of proteins using one to three equilibrium stages and multi-stage purifications using countercurrent distribution, liquid-liquid partition chromatography and continuous countercurrent chromatography. The second application, and very promising area for future aqueous two-phase technology, is the extractive bioconversion which permits the simultaneous production and purification of a biomolecule.

Impact of genetic engineering on downstream processing of proteins produced in E. coli

Genetic engineering can be used to give a protein properties that are advantageous for downstream processing. Many heterologous proteins are degraded at high rates by proteases. Depending on which type of proteolytic degradation is encountered the strategy may be different: induction of inclusion bodies, change of the amino acid sequence in the sensitive site of the product, or protection by fusion of the product with other proteins. The number of unit operations needed to purify a protein may be reduced by addition of other polypeptides or amino acids to the product. Affinity chromatography, immobilized metal ion affinity chromatography, and extraction in aqueous two-phase systems are unit operations which can be made more versatile by the fusion technique.

Improvement of downstream processing of recombinant proteins by means of genetic engineering methods

The rapid advancement of genetic engineering has allowed to produce an impressive number of proteins on a scale which would not have been achieved by classical biotechnology. At the beginning of this development research was focussed on elucidating the mechanisms of protein overexpression. The appearance of inclusion bodies may illustrate the success. In the meantime, genetic engineering is not only expected to achieve overexpression, but to improve the whole process of protein production. For downstream processing of recombinant proteins, the synthesis of fusion proteins is of primary importance. Fusion with certain proteins or peptides may protect the target protein from proteolytic degradation and may alter its solubility. Intracellular proteins may be translocated by means of fusions with signal peptides. Affinity tags as fusion complements may render protein separation and purification highly selective. These methods as well as similar ones for improving the downstream processing of proteins will be discussed on the basis of recent literature.

Effective extraction and purification of beta-xylosidase from Trichoderma koningii fermentation culture by aqueous two-phase partitioning

Effective extraction of protein from bulk medium is an important technique in bioresearch. In the present study, we describe an extracellular beta-xylosidase from the fermentation supernatant of Trichoderma koningii G-39 that was successfully extracted and purified simultaneously in a single step by using an aqueous two-phase partitioning method. This two-phase system was prepared by dissolving suitable amount of poly(ethylene glycol) (PEG) and sodium dihydrogenphosphate (NaH(2)PO(4)) in aqueous solution. beta-Xylosidase was recovered with high yield and high concentration in the bottom salt-rich phase when 25% (w/v) PEG 1500 and 20-25% (w/v) NaH(2)PO(4) were applied. Based on a 1-liter scale extraction, the purity of the enzyme was enhanced at least 33-fold. The total activity increased 422% in comparison with that in the untreated filtrate. The effectiveness and simplicity may make this technique potentially useful in various applications. The transxylosylation activity of the enzyme purified by this technique was also investigated.

Integrated processing of biotechnology products

Integrated bioprocessing in which a potentially inhibitory product is continuously removed from the fermentation broth as it is produced, has important advantages in improving yield and conversion relative to conventional processes. This review discusses integrated processing for ethanol, butanol, organic acids, antibiotics, and other products. A variety of recovery operations can be used to isolate the product, as discussed. Use of some of the available options is compared.

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.

Purification and aqueous two-phase partitioning properties of recombinant Vitreoscilla hemoglobin

Soluble recombinant Vitreoscilla hemoglobin was purified from E. coli lysate by sequential two-phase extraction techniques. Extraction of lysate containing VHb in PEG/dextran gave a 3.6-fold increase in VHb purity in the PEG-rich phase via a size exclusion mechanism. Further extraction of the recovered PEG phase in PEG/sodium sulfate gave an additional 2.0-fold increase in purity in the PEG-rich phase due to an electrostatic mechanism. Final extraction of the PEG phase in PEG/magnesium sulfate gave an additional 1.3-fold increase in VHb purity in the magnesium sulfate-rich phase. The final yield from the extractive purification was 47% with purity of VHb estimated to be greater than 95%. Yields from the sulfate salt extractions are essentially quantitative due to the extreme partitioning behavior of VHb in these systems. VHb partition coefficients as large as 46 in PEG/sodium sulfate and as small as 0.06 in PEG/magnesium sulfate were observed. Similar small partition coefficients were obtained with PEG/manganese sulfate extractions. This dramatic effect of divalent cation content on the partition coefficient of VHb in PEG/sulfate salt systems was investigated by pH and magnesium ion titration experiments. Results show the effect to be largest and nearly constant for pH values greater than 6.0 and diminished at lower pH values. A model based on magnesium ion binding to negatively charged amino acids is shown to correlate with the data well. Based on model formulation and the partitioning behavior of contaminant proteins, the observed effect is expected to be applicable to other proteins.

Partitioning of β-galactosidase fusion proteins in PEG/potassium phosphate aqueous two-phase systems

Four different beta-galactosidase fusion proteins have been partitioned in poly(ethylene glycol) (PEG) 4000/potassium phosphate aqueous two-phase systems. The partition coefficients (K) of staphylococcal protein A-beta-galactosidase (SpA beta gal) (K = 3.5) and staphylococcal protein A-streptococcal protein G-beta-galactosidase (AG beta gal) (K = 2.8) were compared with the partition coefficients of their constituent molecules, beta-galactosidase, SpA, and protein AG. It was found that by fusing beta-galactosidase to the smaller proteins SpA and protein AG, their partition coefficients were increased four to five times. Experimental data were fitted into, and found to agree with, the Albertsson partition model of interacting molecules. The compatibility with PEG and potassium phosphate of beta-galactosidase, SpA, and two different versions of the SpA beta gal protein, displayed as precipitation curves, showed a relationship to the protein partition coefficients in PEG/potassium phosphate systems. High solubility in one phase component was accompanied by preferential partitioning to the phase rich in the same component in the PEG/potassium phosphate system. Also, a changed linker region in SpA beta gal resulted in a more soluble protein. This, together with the improved K values of the target proteins by fusion, shows that it is possible to use beta-galactosidase as an affinity handle.

Expression and characterization of a tripartite fusion protein consisting of chimeric IgG-binding receptors and β-galactosidase

Using protein engineering, a tripartite fusion protein was constructed consisting of five IgG-binding regions of protein A from Staphylococcus aureus, two IgG-binding regions of protein G from Streptococcus strain G148 and beta-galactosidase from Escherichia coli. The resulting protein lacks the serum albumin binding regions of native protein G. The fusion protein, which is a tetramer of approximately 660 kDa, was designed as a tool for immunological assays taking advantage of its broad spectrum of antibody affinity. The gene was placed under control of two promoters, the PR promoter and the lac UV5 promoter and the expression from the two promoters was studied in a bioreactor. Induction of the PR promoter gave an intracellular product concentration corresponding to 20% of the cell dry weight. By utilizing the properties of beta-galactosidase, the protein was purified by extraction in an aqueous two-phase system. The fusion protein was not proteolytically degraded during the cultivation and purification steps. The biological activity of all three parts of the protein was demonstrated with a competitive ELISA.