Purification of caveolae by affinity two-phase partitioning using biotinylated antibodies and NeutrAvidin-dextran

A new concept for affinity two-phase partitioning was tested. The partitioning was based on the interaction of target membranes with a primary antibody which, in turn, interacted with a biotinylated secondary antibody and NeutrAvidin-dextran in a poly(ethylene glycol)/dextran two-phase system. Caveolae selectively redistributed from the top phase to the NeutrAvidin-dextran-containing bottom phase by employing anti-caveolin as the primary antibody. This immunoaffinity approach was more selective than the established sucrose gradient centrifugation method and resulted in highly purified caveolae from Triton X-100-treated liver and lung plasma membranes. The same approach, employing other selective primary antibodies, should facilitate the purification also of other membrane fractions.     

用两相法纯化玉米精细胞质膜

纯系玉米(Zea mays L.)708的新鲜花粉经蔗糖溶液等渗温育、低渗胀破,用30％Percoll不连续密度梯度离心,制备大量的生活精细胞。精细胞用French压力室破碎后离心(90000×g,4℃),获得微粒体。随后,用16g的(6.2％Dextran T500/6.2％PEG3350)两相系统加以纯化。一级分离后,上相液(U_1)的K~ 刺激的Mg~(2 )-ATP酶活性稍低于下相液(L_1);对U_1进行二级分离后,U_2的K~ 刺激的Mg~(2 )-ATP酶活性远远高于下相液(U_2L),分离率达到61.1％。膜蛋白质的分离趋势与K~ 刺激的Mg~(2 )-ATP酶相似。选用细胞色素C氧化酶作为线粒体的标志酶,虽只经一级分离,但在U_1中已检测不到该酶活性。精细胞质膜的磷钨酸特异染色电镜观察结果显示,由二级分离所得质膜的纯度达到90％以上。     

Polymer fractionation in aqueous two-phase polymer systems.

We consider the effects of the addition of poly(ethylene glycol) (PEG) of different molecular weights to aqueous two-phase system of PEG 8000 and dextran 500. The first purpose of this study was to determine the molecular weight partitioning of the polymers themselves so that, for example, aqueous two-phase separations using affinity ligands can be improved. The second purpose was to examine whether this molecular weight partitioning could be predicted by using solution thermodynamic models so that it would be possible to optimize affinity partitioning without extensive laboratory work. Experimentally, we find that, by increasing the PEG concentration of any molecular weight in the feed, the high molecular weight PEG concentration in the dextran-rich phase is reduced. This observation can be used to reduce the loss of expensive ligated PEG used in affinity partitioning. Further, there is generally good agreement between our experimental data and the predictions of a solution thermodynamic model.     

Aqueous two-phase system formed by thermoreactive vinyl imidazole/vinyl caprolactam copolymer and dextran for partitioning of a protein with a polyhistidine tail

A new type of aqueous two-phase system (ATPS) has been developed for application combining two attractive concepts in downstream processing: the immobilised metal affinity partitioning and the use of thermoprecipitating polymers. ATPS consisting of the thermoprecipitating copolymer of N-vinyl caprolactam/1-vinyl imidazole loaded with Cu ions (Cu-poly-VI-VCL) in the top phase and dextran T70 in the bottom phase was used for purification of recombinant lactate dehydrogenase carrying an affinity tag of 6 histidine residues (His-LDH ) from a crude E. coli extract. The enzyme partitioned preferentially into the top Cu-poly-VI-VCL-rich phase. After phase separation, the latter was mixed with EDTA. Temperature increase to 45°C resulted in thermoprecipitation of VCL/VI-polymer, which could subsequently be recycled. His-LDH remained solubilized in the aqueous phase resulting in 8-fold purification and 80 % recovery in a single step.     

Protein separation using metal ion-bound particles in aqueous two-phase system

Metal ion affinity partitioning of protein in aqueous two-phase systems was studied using Sepharose as ligand carrier as an integrated adsorption partitioning. Cu(II)-bound Sepharose was mixed with protein solution and an aqueous two-phase system. The affinity sorbent was distributed quantitatively to the upper side or the interface. The binding studies of lysozyme to copper-bound gel in PEG/dextran two-phase systems demonstrate the feasibility of this bioseparation process. PEG/dextran system did not affect binding and elution of lysozyme to and from the Cu(II)-Sepharose particles.     

The development and application of a new affinity partitioning system for enzyme isolation and purification.

A reactive water-soluble polymer was synthesized by copolymerizing N-isopropylacrylamide and glycidyl acrylate. The reactive polymer could react with the amino groups of enzymes/proteins or other ligands to form an affinity polymer. As a model, the reactive polymer was allowed to react with paraaminobenzamidine, a strong trypsin inhibitor. The affinity polymer could easily form an aqueous two-phase system with either dextran or pullulan, and the phase diagram was compared favorably to that of the well-known polyethylene glycol-dextran system. Once trypsin was attracted to the affinity polymer dominant phase, the enzyme could be dissociated from the polymer at low pH. Owing to the N-isopropylacrylamide units, the affinity polymer could be isolated from the solution by precipitation at a low level of ammonium sulfate. The enzyme recovery was always greater than 50%, and the affinity polymer could be reused in several cycles of affinity partitioning and recovery.     

Biosurfactants and aqueous two-phase fermentation

The partition of surfactants and a biosurfactant-producing microorganism was studied in polyethylene glycol and dextran aqueous two-phase systems. In the presence of sodium phosphate, surfactants distributed themselves according to charge. Cationic surfactants preferred the bottom phase, while anionic surfactants were attracted to the top phase. Incresing the phosphate molarity or the pH resulted in a more 1-sided surfactant partitioning. Biosurfactant partitioning was weaker than synthetic surfactant partitioning due to the weaker effective charge and lack to strong specific affinity for any of the phase-forming polymers. Bacillus Subtilis cells partitioned very storngly to the bottom phase. The bioscurfactant, surfactin, produced by this microorganism partitioned to the top phase. Batch fermentations were carried out in an aqueous 2-phase system. Surfactin was produced in larger quanities in the 2-phase fermentation than in the regular mineral salts medium.     

Hybridization-based affinity partitioning of nucleic acids using PEG-coupled oligonucleotides.

Polyethylene glycol (PEG)-coupled oligonucleotides are partitioned in an aqueous two-phase system PEG/dextran. The affinity of the oligonucleotide for the PEG-rich phase increases proportionally to the length of the coupled PEG polymer. After hybridization, the PEG-coupled oligonucleotide is able to force a complementary nucleic acid strand into the PEG-rich phase. This property can be used for the sequence-specific isolation of nucleic acids through hybridization-based affinity partitioning. The dependence of the partition coefficient in this system on various parameters is described. The application of this principle to multistage chromatographic separations is demonstrated.     

Interaction of the dye Remazol Yellow GGL to prealbumin and albumin studied by affinity phase partition,difference spectroscopy and equilibrium dialysis

In partition experiments in aqueous two-phase systems composed of 10% (w/w) dextran (M_r=500000) and 7.510 (w/w) poly(ethylene-glycol) (M_r=6000) prealbumin and albumin are directed into the dextran-rich phase. Addition of Remazol Yellow GGL covalently bound to poly(ethylene-glycol) causes a transfer of prealbumin and albumin into the poly(ethylene-glycol)-rich phase. This indicates an interaction of both proteins with the dye (affinity phase partitioning).The affinity partitioning effect on prealbumin is markedly increased by an excess of monomeric albumin. This points to an interaction of the two proteins in the presence of the dye.Binding of free Remazol Yellow GGL to prealbumin and albumin was investigated by means of equilibrium dialysis and difference spectroscopy. In respect to prealbumin equilibrium dialysis resulted in the binding of four molecules of the dye to two classes of binding sites with dissociation constants of K_H=3.3 IM and K_L=258 µM respectively whereas albumin was found to bind eight molecules of the dye to two classes of binding sites with K_H=5.8 µM and K_L=282 µM. Similar binding stoichiometries were found by difference spectroscopy.By application of difference spectroscopy and affinity phase partitioning thyroxine and triiodothyronine known as natural ligands of prealbumin and albumin were found to compete with Remazol Yellow GGL for the dye binding sites of the proteins.     

Immobilized metal ion affinity partitioning of cells in aqueous two-phase systems: erythrocytes as a model

Immobilized metal ion affinity partitioning of erythrocytes from different species is described. We have explored the affinity between transition metal chelates and metal-binding sites situated on the cell surface by partitioning in aqueous two-phase system composed of poly(ethylene glycol) and dextran. Soluble metal-chelate-poly(ethylene glycol) was prepared by fixing metal ions to poly(ethylene glycol) via the covalently bonded chelator, iminodiacetic acid. The partitioning behaviour of erythrocytes in systems at different concentrations of the ligand was tested. The copper-chelate-poly(ethylene glycol) was quite effective in the affinity extraction of human and rabbit erythrocytes, while the zinc-chelate-poly(ethylene glycol) displayed significant affinity only to the rabbit cells. Furthermore, the influence of various effectors such as imidazole, sialic acid on immobilized metal ion affinity partitioning of erythrocytes was examined.     

Preparation and polypeptide composition of plasma membrane and other subcellular fractions from wild oat (Avena fatua) aleurone

Plasma membranes can be isolated from a variety of plant tissues by first preparing a post-mitochondrial membrane fraction enriched in plasma membranes, by differential centrifugation, and partitioning this on a dextran-polyethylene glycol two-phase system. With wild oat aleurone, however, we observed that differential centrifugation could not be used to produce a microsomal fraction enriched in plasma membrane. Approximately 70% of the plasma membrane in aleurone homogenates was pelleted by sequential centrifugation at 100 g× 10 min and 1000 g× 10 min. The remainder sedimented at 112 000 g× 1 h. All the material that was pelletable by centrifugation was, therefore, subjected to dextran-polyethylene glycol two-phase partitioning. The plasma membrane marker enzymes glucan synthase II (GSII, EC 2. 4. 1. 34) and UDP-glucose:sterol glucosyltransferase (SGT, EC 2. 4. 1.) were enriched in the upper phase, whereas cytochrome c oxidase activity (EC 1. 9. 3. 1), a mitochondrial marker enzyme, was depleted. The presence of endoplasmic reticulum (ER) and protein body membranes in the phase system was assessed by probing western blots, of SDS-PAGE separated proteins, with polyclonal antiserum either to binding protein (BiP, an ER marker) or to tonoplast intrinsic protein (TIP, a protein body membrane marker). BiP and TIP were present in the lower phase, but were not detected in the upper phase. In addition, the polypeptide patterns of material in the upper and lower phases were very different. These observations suggested that high purity aleurone plasma membrane had been isolated. Although the procedure for isolating plasma membranes was applicable to both aleurone protoplasts and layers, the polypeptide patterns of plasma membranes prepared from these sources were very different. The major protein components of wild oat aleurone were 7 S and 12 S storage globulins. These proteins were present in the lower phase, but not in the plasma membrane enriched upper phase, after aqueous two-phase partitioning. Differential centrifugation studies showed that it was necessary to homogenise aleurone in a buffer of pH 6. 0 or less if a soluble protein fraction, essentially devoid of storage globulins, was to be obtained. The use of these fractionation techniques is discussed in relation to photoaffinity labelling of gibberellin (GA)-binding proteins in aleurone.     

Plasma membranes from oats prepared by partition in an aqueous polymer two-phase system : on the use of light-induced cytochrome B reduction as a marker for the plasma membrane

Presumptive plasma membrane fractions have been prepared from oat (Avena sativa L. cv. Brighton) roots and shoots, respectively, by partition of microsomal fractions in a dextran-polyethylene glycol two-phase system. The plasma membranes had a high affinity for the polyethylene glycol-rich upper phase, whereas membranes from mitochondria and other organelles partitioned in the dextran-rich lower phase or at the interface. Thus, relatively pure plasma membranes were obtained by only two partition steps, and within 3 hours from homogenization of the material.

The plasma membranes from both organs were enriched in K⁺-stimulated Mg²⁺-dependent ATPase and glucan synthetase II, two tentative markers for the plant plasma membrane. Silicotungstic acid, an indicative stain for the plasma membrane, stained the vesicles recovered from the upper phase, but failed to stain the membranes partitioning in the lower phase or at the interface.

The plasma membranes were also enriched in a light-reducible b-cytochrome. This b-cytochrome can be measured by its light-induced absorbance change and may serve as a marker for the plant plasma membrane.

     

Isolation of a caveolae-enriched fraction from rat lung by affinity partitioning and sucrose gradient centrifugation

Caveolae were isolated from rat lungs by a combination of affinity partitioning and sucrose gradient centrifugation. After homogenization of the lungs directly in a polyethylene glycol-dextran two-phase system and conventional phase partitioning, the polyethylene glycol-rich top phase was affinity partitioned with fresh bottom phase containing dextran-linked wheat-germ agglutinin. The lectin selectively attracted plasma membranes to the bottom phase. The isolated plasma membrane fraction was treated with Triton X-100 or, alternatively, sonicated before centrifugation in a stepwise sucrose gradient. Caveolin-enriched material collected at the 5/24% sucrose boundary. This material also contained 5'-nucleotidase activity and actin. Electron microscopy showed the material to consist of a homogeneous population of 50- to 100-nm vesicles. This purification protocol should allow the facile purification of caveolae also from other tissues, facilitating structural and functional studies.     

Enhanced metal-affinity partitioning of genetically engineered hirudin variants in polyethylene glycol/dextran two-phase systems

Hirudin variants were constructed to exhibit an increased metal-binding affinity in an attempt to apply a metal-affinity partitioning process in a primary separation step for purification of hirudin. The hirudin variants were genetically engineered to contain additional surface-accessible histidines and produced by recombinant Saccharomyces cerevisiae. The partitioning behavior of these variants was compared with that of the wild type with a single surface-accessible histidine at position 51. Upon the addition of a small amount of Cu(II)IDA-PEG (Cu(II)iminodiacetic acid-polyethylene glycol) ligand to PEG/dextran two-phase systems, the hirudin variants with two or three surface-accessible histidines were more selectively partitioned into the PEG-rich phase than the wild type. Integrating protein engineering to metal-affinity partitioning offers the potential for general application of this technique to facilitate protein isolation, but the genetically engineered protein variants should be carefully constructed in a manner to minimize reduction of native protein activity.     

Liquid-liquid partitioning of some enzymes, especially phosphofuctokinase, from Saccharomyces cerevisiae at subzero temperature

The effects of low temperature (−18°C) on the stability and partitioning of some glycolytic enzymes within an aqueous two-phase system were studied. The enzymes were phosphofructokinase, glyceraldehyde-3-phosphate dehydrogenase and alcohol dehydrogenase present in a crude extract of bakers' yeast. The partitioning of pure phosphofructokinase, isolated from bakers' yeast, was also examined. The two-phase systems were composed of water, poly(ethylene glycol), dextran, and ethylene glycol and buffer. The influence on the partitioning of the presence of ethylene glycol, phenylmethylsulfonyl fluoride and poly(ethylene glycol)-bound Cibacron Blue F3G-A was investigated at −18, 0 and (in some cases) 20°C. The presence of ethylene glycol, phase polymers and low temperature stabilized all three enzyme activities. Cibacron Blue, an affinity ligand for phosphofructokinase, increased its partitioning into the upper phase with decreasing temperature. Depending on the conditions, various amounts of the enzymes were recovered at the interface, also in systems not containing ethylene glycol. The implications of the observed effects on the use of aqueous two-phase systems for the extraction and fractionation of proteins are discussed.     

Genetically engineered charge modifications to enhance protein separation in aqueous two-phase systems: Charge directed partitioning

This report continues or examination of the effect of genetically engineered charge modifications on the partitioning behavior of proteins in aqueous two-phase extration. The genetic modifications consisted of the fusion of charged peptide tails to beta-galactosidase and charge-change point mutations to T4 lysozyme. Our previous article examined the influence of these charge modifications on partitioning as a function of interfacial potential difference. In this study, we examined charge directed partitioning behavior in PEG/dextran systems containing small amounts of the charged polymers diethylaminoethyl-dextran (DEAE-dextran) or dextran sulfate. The best results were obtained when attractive forces between the protein and polymer were present. Nearly 100% of the beta-galactosidase, which carries a net negative charge, partitioned to the DEAE-dextran-rich phase regardless of whether the phase was dextran or PEG. In these cases, cloudiness of the protein-rich phases suggest that strong charge interactions resulted in protein/polymer aggregation, which may have contributed to the extreme partitioning. Unlike the potentialdriven partitioning reported previously, consistent partitioning trends were observed as a result of the fusion tails, with observed shifts in partition coefficient (K(p)) of up to 37-fold. However, these changes could not be solely attributed to charge-based interactions. Similarly, T4 lysozyme, carrying a net positive charge, partitioned to the dextran sulfate-containing phase, and displayed four- to sevenfold shifts in K(p) as a result of the point mutations. These shifts were two to four times stronger than those observed for potential driven partitioning. Little effect on partitioning was observed when the protein and polymer had the same charge, with the exception of beta-galactosidase with polyarginine tails. The high positive charge density of these tails provided for a localized interaction with the dextran sulfate, and resulted in 2- to 15-fold shifts in K(p). (c) 1995 John Wiley & Sons, Inc.     

Purification of rat C6 glioma plasma membranes by affinity partitioning

We have studied the feasibility of purifying rat C6 glioma plasma membranes by a phase partitioning approach. The purification procedure involves cell homogenization and fractionation with an aqueous two-phase polymer system followed by selective affinity purification of plasma membranes by a wheat germ agglutinin-coupled polymer system. We demonstrate that the two-phase affinity partitioning technique is a simple and efficient method of isolating cell plasma membranes with high purity and yield. Furthermore, the isolated plasma membranes retain their functional integrity, as shown by the high-affinity insulin-like growth factor-I (IGF-I) binding capacity of IGF-I receptors.     

Affinity partitioning of phosphofructokinase from baker's yeast using polymer-bound Cibacron blue F3G-A

1. Phosphofructokinase from baker's yeast is partitioned between the phases of an aqueous two-phase system, containing dextran (Mr = 500000) and poly(ethyleneglycol) (Mr = 6000), in favour of the dextran-rich phase. By covalent binding of the dye Cibacron blue F3G-A to poly(ethyleneglycol) the enzyme can be extracted to the phase rich in this polymer, i.e. affinity partitioning. 2. The affinity partitioning effect, measured as the logarithmic increase of the partition coefficient by introducing polymer-bound Cibacron blue, depends on several factors. The influence of dye-polymer concentration, polymer concentration, polymer molecular weight, kind of salt and salt concentration, pH and temperature has been studied. 3. The effect of ATP, ADP, AMP, ITP, fructose 1,6-bis-phosphate and fructose 6-phosphate show large differences in the binding strength of these substances to the Cibacron blue binding sites. AMP cannot compete with Cibacron blue while ATP is strongly competing. 4. The use of affinity partitioning for enzyme isolation and determination of ligand binding is discussed, as well as possible mechanisms concerning this type of liquid/liquid extraction.     

Aqueous two-phase metal affinity extraction of heme proteins

An iminodiacetic acid derivative of poly(ethylene glycol) (PEG-IDA) that chelates metal cations has been synthesized and used to extract proteins in metal affinity aqueous two-phase PEG/dextran systems. With less than 1% of the PEG substituted with chelated copper, partition coefficients are shown to increase by factors of up to 37 over extraction with unsubstituted PEG. The proteins studied are preferentially extracted into the Cu(II)PEGIDA phase in proportion to the number of accessible histidine residues on their surface. The affinity contribution to partitioning is proportional to the number of exposed histidine over a very wide range. The partition coefficients of heme-containing proteins measured in the Cu(II)PEG-IDA/dextran systems increase with the pH of the extraction mixture from pH 5.5 to pH 8.0, while partition coefficients in the unsubstituted PEG/dextran systems are very nearly independent of pH. The strong pH dependence of the metalaffinity extraction can be utilized in the recovery of the extracted protein.     

A mathematical model for metal affinity protein partitioning

A mathematical model of metal affinity partitioning has been derived and used to describe protein partitioning in Cu (II)PEG/dextran systems. A working model has been extended to account for inhibition, which for metal affinity extraction is the inhibition of protein-metal binding by hydrogen ion. PEG/dextran partitioning experiments were performed on four proteins, tuna heart cytochrome c, Candida krusei cytochrome c, horse myoglobin, and sperm whale myoglobin. The partition coefficients for these proteins are increased by the addition of Cu (II)PEG-IDA, due to the affinity between the chelated copper atom and metal-coordinating histidine residues on the protein surface. The results of experiments to determine the effects of the number of binding sites on the protein, the copper concentration, and pH on partitioning are all well-described by the mathematical model. The pK(a) value of the metal binding site was determined to be 6.5, which is in the range of pK(a) values commonly observed for surface histidines. The average association constant for the binding of Cu (II)PEG-IDA to accessible histidines was found to be 4.5 x 10(3). This value is comparable to stability constants measured by conventional potentiometry techniques for analogous small complexes.