New packing materials for protein chromatography

Chromatographic reactors based on biological activity

In the last decade there were many papers published on the study of enzyme catalyzed reactions performed in so-called chromatographic reactors. The attractive feature of such systems is that during the course of the reaction the compounds are already separated, which can drive the reaction beyond the thermodynamic equilibrium as well as remove putative inhibitors. In this chapter, an overview of such chromatographic bioreactor systems is given. Besides, some immobilization techniques to improve enzyme activity are discussed together with modern chromatographic supports with improved hydrodynamic characteristics to be used in this context.

(Immuno)affinity chromatography: a versatile tool for fast and selective purification, concentration, isolation and analysis

Today, thanks to the availability of tailor made biomolecules with the desired biological functions, separations based upon (immuno)affinity techniques are more and more common in a large field of applications. By using the high selectivity of biomolecules (antibodies, receptors, specific proteins), this technique offers the possibility of isolating compounds from complex samples with a selectivity which cannot be achieved by other chromatographic methods. In order to succeed, however, the solid phase support for the immobilisation of the ligand of interest plays a prominent role. For this reason, numerous supports have already been introduced while research on new materials with additional advantages is continued. Here, a new solid phase support will be discussed for (immuno)affinity applications. This material demonstrates low non-specific adsorption and high ligand accessibility, which enables an enhanced selectivity and capacity. Because the material is available in large quantities and exhibits superb mechanical and physical stability, selective isolations have been performed on analytical as well as preparative scale. To demonstrate the potential of this new support, several applications will be presented. Based upon immunoaffinity, two applications for the determination of oestradiol in serum respectively vitamin B12 in fermentation broth will be presented. Regarding affinity chromatography, an enzyme reactor in which the enzyme glucose oxidase is immobilised on the new material, is made for the detection of glucose by Flow Injection Analysis and electrochemical detection. Next, to isolate, identify and test components on their xeno-oestrogenic activity, an affinity column is produced in which human oestrogen receptor is covalently coupled. Several components are screened on their biological activity and the results obtained will be presented here.

Adsorption kinetics and equilibria of bovine serum albumin on rigid ion-exchange and hydrophobic interaction chromatography matrices in a stirred cell

Rigid adsorbents have advantages over soft gel media for downstream processing of proteins. The adsorption of bovine serum albumin (BSA) has been investigated on a rigid adsorbent based on a wide-pore, hydrophilically coated, silica-gel matrix. The effects of surface chemistry (weak anion exchanger and hydrophobic interaction chromatography) and particle size have been studied on the physical properties of the adsorbent and on the adsorption equilibria and adsorption kinetics. The rates of adsorption of BSA have been measured in a stirred cell and are found to be satisfactorily described by a two-step theoretical model, in which the mass transfer involves a pore diffusion resistance and an extra-particle film resistance. On the anion exchanger, the effective pore diffusivity decreases substantially with increasing protein concentration, approximately halving as the initial concentration rises from 0.7 to 2g/l. In the hydrophobic interaction chromatography medium, the pore diffusivity is less sensitive to protein concentration and is also reduced by a factor of about 4 by aggregation of the protein. Effective pore diffusivities with the "wide-pore" silica adsorbents in anion-exchange form are 36-94 times lower than the diffusivity in free solution and are comparable with the lower of the wide range of values published for soft gels.

Preparative two-step purification of recombinant human basic fibroblast growth factor from high-cell-density cultivation of Escherichia coli

Aggregation and precipitation are major pitfalls during bioprocessing and purification of recombinant human basic fibroblast growth factor (rh-bFGF). In order to gain high yields of the soluble protein monomer with high biological activity, an efficient downstream process was developed, focussing on the combination of expanded bed adsorption (EBA) and heparin chromatography. After expression in E. coli TG1:plambdaFGFB, cells were harvested and washed; then the rh-bFGF was released via high pressure homogenization. The high viscosity of the feedstock of about 40 mPa s, showing non-newtonian behaviour, was reduced to 2 mPa s by the addition of DNase. The homogenate (5.6 l) was loaded directly on an expanded bed column (C-50) packed with the strong cation-exchanger Streamline SP. In the eluates, histone-like (HU) protein was identified as the main protein contaminant by sequence analysis. The thermodynamics and kinetics of rh-bFGF adsorption from the whole broth protein mixture were determined in view of competition and displacement effects with host-derived proteins. Optimal binding and elution conditions were developed with knowledge of the dependence of rh-bFGF adsorption isotherms on the salt concentration to allow direct application of eluates onto Heparin HyperD. This affinity support maintained selectivity and efficiency under CIP and over a wide range of flow-rates; both is advantageous for the flexibility of the purification protocol in view of a scalable process. Remaining DNA and HU protein were separated by Heparin HyperD. The endotoxin level decreased from approximately 1,000,000 EU/ml in the whole broth to 10 EU in 3 mg bFGF per ml. The final purification protocol yields >99% pure rh-bFGF as judged from SDS-PAGE and MALDI-TOF mass spectrometry with high mitogenic activity (ED50=1-1.5 ng/ml) of the lyophilized sample. In comparison to the conventional process, the overall protein recovery rose by 15% to 65% with saving time and costs.

Comparative Pore Structure Analysis of Dextran-Coated Polystyrene Particles

Porous poly(styrene-divinylbenzene) (PS-DVB) particles were modified by adsorption of hydrophobically-modified dextrans, to provide chromatographic matrices for biomolecule chromatography. The dextran distribution and the pore characteristics of various coated PS-DVB beads were examined using nitrogen adsorption-desorption, mercury intrusion, and size exclusion chromatography. It was found that the adsorption of dextran does not result in homogeneous layers but rather in inhomogeneous ones. At high dextran loading and high content of hydrophobic groups in the adsorbed polymer, most of the pores of the macroporous rigid material are filled with a soft and porous dextran network being stabilized by hydrophobic interactions. According to chromatographic experiments, most of the surface was nevertheless expected to be covered at least by a thin and dense protecting layer since proteins-even those that are small enough to penetrate the dextran network-cannot interact nonspecifically with the internal pore surface. At low content of hydrophobic groups, dextran deposits preferentially as a thicker and more diffuse layer. However, the thickness of the coating is expected to be irregular and probably contributes to an increase in the roughness of the polystyrene surface. Copyright 1999 Academic Press.

Continuous-bed chromatography for the analysis and purification of recombinant human basic fibroblast growth factor

The chromatographic properties of the commercial cation exchanger UNO-S1 (35x7 mm) was investigated using lysozyme from hen egg white as model protein and recombinant human basic fibroblast growth factor (rh-bFGF) from a high cell density cultivation of E. coli. The dynamic capacity for lysozyme (c(o) = 1 mg/ml) in 100 mM acetate buffer, pH 5 was 27 mg per ml sorbent. It was found independent of the flow-rate from 78 to 935 cm/h owing to the absence of mass transfer restrictions with this column concept. Regarding the selectivity for rh-bFGF and the capacity for lysozyme, no changes were apparent after cleaning-in-place (CIP) procedures with 0.5 M NaOH. Clogging of the column by a clarified crude cell homogenate of E. coli was not critical as precipitates were removed by reversal of the flow during CIP. Rh-bFGF elutes in three consequent peaks from the UNO-S1 column, which could be attributed to soluble rh-bFGF aggregates of different size. The dynamics of rh-bFGF aggregation and reaggregation in the crude feedstock was monitored by fast gradient elution chromatography.

Cibacron blue F3G-A-attached uniform and macroporous poly(styrene-co-divinylbenzene) particles for specific albumin adsorption

Cibacron blue F3G-A-carrying uniform macroporous particles were proposed as an alternative sorbent for specific albumin adsorption. These particles were produced by a multistep polymerization procedure. In the first step of production, the uniform polystyrene seed particles were prepared by a dispersion polymerization method. Next. the polystyrene seed particles were first swollen by dibutylphthalate and then by styrene-divinylbenzene mixture in an aqueous emulsion medium. In the last step (i.e. repolymerization), styrene-divinylbenzene mixture was copolymerized within the swollen seed particles in the absence or presence of a stabilizer (e.g. poly(vinyl alcohol)). Although a considerable amount of non-specific BSA adsorption was observed on the surface of the particles produced in the absence of PVA, zero non-specific albumin adsorption could be achieved with the uniform macroporous particles produced in the presence of PVA. The stabilizer on the particle surface was also used as a ligand in the further derivatization of macroporous particles for specific albumin adsorption. Cibacron blue F3G-A was then covalently attached onto the surface of uniform macroporous particles. Specific albumin adsorption capacities up to 93 mg g(-1) could be achieved with the cibacron blue F3G-A-carrying macroporous particles of 6.25 microm in size.

Protein variant separations by cation-exchange chromatography on tentacle-type polymeric stationary phases

We developed a set of prototype cation-exchange column packings that are based on a hydrophilic coated, pellicular polymeric support with a grafted tentacular surface chemistry that is highly suited to resolving closely related protein variants. These column packings (1) afford minimal band spreading in conjunction with extremely high selectivity, (2) exhibit a very hydrophilic character and (3) have moderate loading capacity. Cytochrome c variants (bovine, horse, rabbit) were baseline-separated, as was native ribonuclease A and its two deamidation products, the Asp67 and isoAsp67 forms. Humanized monoclonal antibody variants differing in the presence of lysine at the C terminus of the heavy chains were baseline-resolved. Finally, the separation of hemoglobin variants found in a sample containing elevated levels of glycated hemoglobin was also demonstrated.

Bioseparation and bioanalytical techniques in environmental monitoring

The growing use of antibody-based separation methods has paralleled the expansion of immunochemical detection methods in moving beyond the clinical diagnostic field to applications in environmental monitoring. In recent years high-performance immunoaffinity chromatography, which began as a separation technique in biochemical and clinical research, has been adapted for separating and quantifying environmental pollutants. Bioaffinity offers a selective biological basis for separation that can be incorporated into a modular analytical process for more efficient environmental analysis. The use of immunoaffinity chromatography for separation complements the use of immunoassay for detection. A widely used immunochemical detection method for environmental analyses is enzyme immunoassay. The objective of this paper is to review the status of bioaffinity-based analytical procedures for environmental applications and human exposure assessment studies. Environmental methods based on bioaffinity range from mature immunoassays to emerging techniques such as immunosensors and immunoaffinity chromatography procedures for small molecules.