Ion-exchange displacement chromatography of proteins

Dynamic behavior of binary component ion-exchange displacement chromatography of proteins visualized by confocal laser scanning microscopy

Confocal laser scanning microscopy (CLSM) was introduced to visualize particle-scale binary component protein displacement behavior in Q Sepharose HP column. To this end, displacement chromatography of two intrinsic fluorescent proteins, enhanced green fluorescent protein (eGFP) and red fluorescent protein (RFP), were developed using sodium saccharin (NaSac) as a displacer. The results indicated that RFP as well as eGFP could be effectively displaced in the single-component experiments by 50 mmol/L NaSac at 120 and 140 mmol/L NaCl whereas a fully developed displacement train with eGFP and RFP was only observed at 120 mmol/L NaCl in binary component displacement. At 140 mmol/L NaCl, there was a serious overlapping of the zones of the two proteins, indicating the importance of induced-salt effect on the formation of an isotachic displacement train. CLSM provided particle-scale evidence that induced-salt effect occurred likewise in the interior of an adsorbent and was synchronous to the introduction of the displacer. CLSM results at 140 mmol/L NaCl also demonstrated that both the proteins had the same fading rate at 50 mmol/L NaSac in the initial stage, suggesting the same displacement ability of NaSac to both the proteins. In the final stage, the fading rate of RFP in the adsorbent became slow, particularly at lower displacer concentrations. In the binary component displacement, the two proteins exhibited distinct fading rates as compared to the single component displacement and the remarkable lagging of the fading rate was observed in protein displacements. It suggested that the co-adsorbed proteins had significant influence on the formation of an isotachic train and the displacement chromatography of the proteins. Therefore, this research provided particle-scale insight into the dynamic behavior and complexity in the displacement of proteins.

Detection of trace proteins in multicomponent mixtures using displacement chromatography

Model protein feed mixtures containing three abundant and seven trace proteins at various concentrations were identified and employed in a series of displacement experiments. Reversed-phase liquid chromatography (RPLC) and matrix assisted laser desorption ionization-time-of-flight (MALDI-TOF) mass spectrometry were used to evaluate the compositions of both the feed mixtures and effluent fractions from the displacement experiments. The results demonstrated that trace proteins were focused at the boundaries between the abundant solutes where they were enriched and concentrated. For many of the multicomponent feed mixtures, mass spectrometry analyses of the displacement column effluent fractions resulted in the identification of trace proteins that were not detectable in the feed. In addition, the use of minimal or no salt in the carrier solutions enabled the analysis of displacement fractions by direct infusion mass spectrometry. These results are significant in that they indicate that while the presence of abundant proteins can often be problematic for the detection of trace components, displacement chromatography may be able to employ these abundant proteins to focus trace proteins in the displacement train, thus facilitating detection.

Application of displacement chromatography for the proteome analysis of a human plasma protein fraction

It was the aim of this study to compare the performance of displacement chromatography with gradient elution chromatography both applied as the cation-exchange separation step for a proteome analysis in a bottom-up approach using multidimensional chromatography for the separation of tryptic peptides prior to their mass spectrometric analysis. The tryptic digest of the human Cohn fraction IV-4 served as a sample. For both chromatography modes commonly used operating parameters were chosen thus ensuring optimal separation results of equal sample amounts for each mode. All resulting fractions were analyzed with an HPLC-chip-LC-MS system. The eluate of the HPLC-chip column was ionized by electrospray ionization (ESI) and analyzed with an ion-trap mass spectrometer. For guaranteeing high confidence concerning the identity of the peptides, the mass spectrometric data were processed by different bioinformatic tools applying stringent criteria. By the displacement approach the total amount of identified proteins (78) was significantly higher than in the gradient mode (58). The results showed that displacement chromatography is a well suited alternative in comparison to gradient elution separation for analysis of proteomes via the bottom-up approach applying multidimensional chromatography, especially in those cases when larger quantities of proteins are available.

Synthesis and characterization of fluorescent displacers for online monitoring of displacement chromatography

One of the major impediments to the implementation of displacement chromatography for the purification of biomolecules is the need to collect fractions from the column effluent for time-consuming offline analysis. The ability to employ direct online monitoring of displacement chromatography would have significant implications for applications ranging from analytical to preparative bioseparations. To this end, a set of novel fluorescent displacers were rationally designed using known chemically selective displacers as a template. Fluorescent cores were functionalized with different charge moieties, creating a homologous library of displacers. These compounds were then tested on two protein pairs, alpha-chymotrypsinogen A/ribonuclease A and cytochrome c/lysozyme, using batch and column displacement experiments. Of the synthesized displacers, two were found to be highly selective while one was determined to be a high-affinity displacer. Column displacements using one of the selective displacers yielded complete separation of both protein pairs while facilitating direct online detection using UV and fluorescence detection. Saturation transfer difference NMR was also carried out to investigate the binding of the fluorescent displacers to proteins. The results indicated a selective binding between the selective displacers and alpha-chymotrypsinogen A, while no binding was observed for ribonuclease A, confirming that protein-displacer binding is responsible for the selectivity in these systems. This work demonstrates the utility of fluorescent displacers to enable online monitoring of displacer breakthroughs while also acting as efficient displacers for protein purification.

Surface plasmon resonance spectroscopy-based high-throughput screening of ligands for use in affinity and displacement chromatography

We describe an approach that uses surface plasmon resonance (SPR) spectroscopy and self-assembled monolayers (SAMs) for the high-throughput screening of ligands for use in displacement and affinity chromatographic processes. We identified a set of commercially available organic amines and allowed them to react with SAMs presenting interchain carboxylic anhydride groups; the resulting surfaces presented ligands of interest in a background of carboxylic acid groups. We used SPR spectroscopy to determine the extent of adsorption of two model proteinslysozyme and cytochrome conto these "multimodal" surfaces and to select promising "affinity" ligands for further characterization. The attachment of selected ligands to UltraLink Biosupport resulted in beads with a significantly greater affinity for lysozyme than for cytochrome c that would be suitable for use in affinity chromatographic processes. Furthermore, we also used the screens to design "affinity displacers"small molecules that selectively retain lysozyme on chromatographic resins, while displacing cytochrome c. The combination of SPR spectroscopy and SAMs represents a powerful technique for identifying novel ligands that enable the purification of complex protein mixtures.

An affinity-based strategy for the design of selective displacers for the chromatographic separation of proteins

We describe an affinity-based strategy for designing selective protein displacers for the chromatographic purification of proteins. To design a displacer that is selective for a target protein, we attached a component with affinity for the target protein to a resin-binding component; we then tested the ability of such displacers to selectively retain the target protein on a resin relative to another protein having a similar retention time. In particular, we synthesized displacers based on biotin, which selectively retained avidin as compared to aprotinin on SP Sepharose high performance resin. In addition, we have extended this approach to develop an affinity-peptide-based displacer that discriminates between lysozyme and cytochrome c. Here, a selective displacer was designed from a lysozyme-binding peptide that had been identified and optimized previously using phage-display technology. Our results suggest a general strategy for designing highly selective affinity-based displacers by identifying molecules (e.g., peptides) that bind to a protein of interest and using an appropriate linker to attach these molecules to a moiety that binds to the stationary phase.

Multidimensional High-Throughput Screening of Displacers

A multidimensional, batch high-throughput screening (MD-HTS) protocol was developed to investigate the effects of various parameters on the selectivity of ion-exchange protein displacement systems. A variety of molecules were screened, and the results were employed to provided insights into the influence of displacer chemistry and concentration, resin chemistry, and mobile-phase salt counterion on the efficacy and selectivity of these nonlinear chromatographic systems. These results open up the possibility of tailoring the selectivity of displacement separations by choosing appropriate combinations of operating conditions using the MD-HTS technique. The screens were also employed for the identification of displacers and conditions for the separation of a challenging protein mixture by selective displacement chromatography. Column displacements were carried out with potential lead compounds identified from the MD-HTS screens, and the results confirmed that selective displacement could indeed be achieved for this model mixture. Furthermore, the results indicated that this approach is particularly useful when the order of elution is not changed, but the inherent selectivity is increased in the presence of the displacer. The results presented in this paper demonstrate the utility of the MD-HTS technique for rapid method development in protein ion-exchange displacement chromatography.

The effect of multi-component adsorption on selectivity in ion exchange displacement systems

This paper examines chemically selective displacement chromatography using affinity ranking plots, batch displacer screening experiments, column displacements, multi-component adsorption isotherms and spectroscopy. The affinity ranking plot indicated that the displacers, sucrose octasulfate (SOS) and tatrazine, should possess sufficient affinity to displace the proteins amyloglucosidase and apoferritin over a wide range of operating conditions. In addition, the plots indicated that the separation of these proteins by displacement chromatography would be extremely difficult. Further, the two proteins were shown to have very similar retention times under shallow linear gradient conditions. When batch displacement experiments were carried out, both tartrazine and SOS exhibited significant selectivity differences with respect to their ability to displace these two proteins, in contrast to the affinity ranking plot results. Column displacement experiments carried out with sucrose octasulfate agreed with the predictions of the affinity ranking plots, with both proteins being displaced but poorly resolved under several column displacement conditions. On the other hand, column displacement with tartrazine as the displacer resulted in the selective displacement and partial purification of apoferritin. Single- and multi-component isotherms of the proteins with or without the presence of displacers were determined and were used to help explain the selectivity reversals observed in the column and batch displacement experiments. In addition, fluorescence and CD spectra suggested that the displacers did not induce any structural changes to either of the proteins. The results in this paper indicate that multi-component adsorption behavior can be exploited for creating chemically selective displacement separations.

Stationary phase effects on the dynamic affinity of low-molecular-mass displacers

In this paper, the selectivity of a variety of cation-exchange stationary phases was investigated using a homologous series of displacer molecules based on pentaerythritol. These displacers were derived from pentaerythritol and contained either four trimethyl ammonium groups [pentaerythrityl-(trimethylammonium chloride)4, PE(TMA)4], benzene rings [pentaerythrityl-(benzyl dimethylammonium chloride)4, PE(DMABzCl)4], heptyl groups [pentaerythrityl-(heptyl dimethylammonium iodide)4, PE(DMAHepI)4] or cyclohexyl groups [pentaerythrityl-(cyclohexyl dimethylammonium iodide)4, PE(DMACyI)4]. This series enabled us to probe the secondary interactions that can play a role in the affinity of low-molecular-mass displacers for different stationary phases. The relative affinities of these displacers were examined using a displacer ranking plot based on the steric mass action (SMA) isotherm model. While hydrophobicity and aromaticity played important roles in generating the affinity to the hydrophilized polystyrene-divinylbenzene (Source 15S) and polymethacrylate-based (Toyopearl 650M) resins, these secondary interactions had a minimal impact on the selectivity in agarose resins coated with dextran (SP Sepharose XL), "gel in a shell" (S Ceramic HyperD F), and monolithic (Bio-Rad Uno S6) cation-exchange materials. Further, the results with a tentacular stationary phase (Fractogel EMD) suggest that the alkyl chains on PE(DMAHepI)4 play an important role in increasing the affinity, possibly because of strong interactions between the alkyl moiety and the polymer matrix as well as between the charged groups and the polyelectrolyte tentacles. The results of this study provide insight into the design of high affinity, low-molecular-mass displacers for different cation-exchange stationary phase materials.

Hydrophobic displacement chromatography of proteins

Displacement chromatography of proteins was successfully carried out in both hydrophobic interaction and reversed-phase chromatographic systems using low-molecular weight displacers. The displacers employed for hydrophobic displacement chromatography were water soluble, charged molecules containing several short alkyl and/or aryl groups. Spectroscopy was employed to verify the absence of structural changes to the proteins displaced on these hydrophobic supports. Displacement chromatography on a reversed-phase material was employed to purify a growth factor protein from its closely related variants, demonstrating the high resolutions that can be achieved by hydrophobic displacement chromatography. This process combines the high-resolution/high-throughput characteristics of displacement chromatography with the unique selectivity of these hydrophobic supports and offers the chromatographic engineer a powerful tool for the preparative purification of proteins.

Protein displacement in dye-ligand chromatography using neutral and charged polymers

Displacement chromatography was demonstrated to perform separations efficiently under mass-overloaded conditions, offering advantages such as increased product recovery and purity, superior resolving power, and concentration and purification in a single processing step. The use of water-soluble polymers for protein displacement in dye-ligand chromatography was initiated in our laboratory. The polymers for displacement were selected using differences spectroscopy to monitor their interactions with a dye-ligand in solution. Non-charged polymers such as poly(N-vinyl pyrrolidone) and poly(N-vinyl caprolactam) efficiently displaced lactate dehydrogenase from porcine muscle from a Blue Sepahrose column. The latter polymer, being thermosensitive, could be easily removed from the eluate and recovered by precipitation at 45 degrees C and low-speed centrifugation. The positively charged polymer poly(ethylene imine) proved to be an even more efficient displacer. The dye-ligand column could be regenerated after application of displacer either by washing with a solution of the soluble ligand Cibacron Blue (in the case of non-charged polymers) or by washing with highly alkaline solutions containing polyanions (in the case of poly(ethylene imine)) The latter formed a soluble complex with poly(ethylene imine) and stripped the column from the polymer.

Polymer displacement/shielding in protein chromatography

An overview of different applications of polymer interactions with ion-exchange and dye-affinity chromatographic matrices is presented here. The strength of interaction between the ligand and the polymer plays a crucial role in deciding the mode of chromatographic application. Charged, non-ionic and thermosensitive polymers such as poly(ethylene imine), poly(N-vinyl pyrrolidone) and poly(vinyl caprolactam) respectively, show different degrees of interaction with the dye molecules in dye ligand chromatography. Polymers, with their ability of multipoint and hence strong attachment to the chromatographic matrices, were used as efficient displacers in displacement chromatography. The polymer displacement resulted in better recoveries and sharper elution profiles than traditional salt elutions. The globule-coil transition of the thermosensitive reversible soluble-insoluble polymer, poly(vinyl caprolactam), can be exploited in dye-affinity columns for the temperature induced displacement of the bound protein. In another situation, prior to the column chromatography of crude protein extract, polymers formed complexes with the dye matrix and "shielded" the column. The polymer shielding decreased the nonspecific interactions without affecting the specific interactions of the target protein to the dye matrix.

Optimization of ion-exchange displacement separations. II. Comparison of displacement separations on various ion-exchange resins

A variety of stationary-phase materials are currently available for the chromatographic purification of biomolecules. However, the effect of various resin characteristics on the performance of displacement chromatography has not been studied in depth. In Part I, a novel iterative scheme was presented for the rapid optimization of displacement separations in ion-exchange systems. In this article, the optimization scheme is employed to identify the optimum operating conditions for displacement separations on various ion-exchange resin materials. In addition, the effect of different classes of separation problems (e.g., diverging, converging or parallel affinity lines) on the performance of displacement separations is also presented. The solid film linear driving force model is employed in concert with the Steric Mass Action isotherm to describe the chromatographic behavior in these systems. The results presented in this article provide insight into the effects of resin capacity and efficiency as well as the type of separation problem on the performance of various ion-exchange displacement systems.

Structural characteristics of low-molecular-mass displacers for cation-exchange chromatography. II. Role of the stationary phase

The relative efficacy of a variety of low-molecular-mass displacers was examined on three different stationary phase materials. Several homologous series of displacer molecules were evaluated on these ion-exchange resins using a displacer ranking plot based on the steric mass action model. The results demonstrate that while aromaticity and hydrophobicity can play a significant role in the affinity of displacer molecules on polymethacrylate based and hydrophilized polystyrene-divinylbenzene based materials, this effect is much less pronounced on an agarose based resin. The work presented in this paper demonstrates that different structural features of low-molecular-mass displacers can dominate their affinity on various stationary phase materials employed and provides rules of thumb for the design of high affinity, low-molecular-mass displacers for a variety of commercial cation-exchange materials.

Cation-exchange displacement chromatography for the purification of recombinant protein therapeutics from variants

Removal of low level impurities that are closely related to the bioproduct is a commonly encountered challenge in the purification of biopharmaceuticals. These separations are typically carried out by using shallow linear salt gradients at relatively low column loadings, significantly limiting the throughput of the purification process. In this manuscript we examine the utility of displacement chromatography for the purification of recombinant human brain-derived neurotrophic factor, rHuBDNF. The utility of displacement chromatography is compared to gradient elution for the removal of variants of the rHuBDNF. The results demonstrate that displacement chromatography is capable of achieving high yields and purity at high column loadings. Displacements developed on 20 microns and 50 microns cation-exchange resins are shown to provide 8-fold and 4.5-fold increases in production rates, respectively, when compared to an existing linear gradient elution operation. These results demonstrate the efficacy of displacement chromatography for the purification of therapeutic proteins from complex feed streams.

Structural characteristics of low-molecular-mass displacers for cation-exchange chromatography

The relative efficacy of a variety of low-molecular-mass displacers was examined using a displacer ranking plot. This method enables an evaluation of the dynamic affinity of a variety of displacers over a range of operating conditions. Several homologous series of molecules were evaluated to provide insight into the effects of various structural features on displacer efficacy. The results indicate that linear flexible geometries may have advantages over branched or cyclic structures. Data also indicate that the spreading out of charges may increase affinity. The incorporation of aromatic moieties in these displacers, particularly near the surface of the molecules, appears to result in a dramatic increase in displacer affinity. The ability of several high-affinity low-molecular-mass displacers a very strongly bound cationic protein is also examined. The results confirm the predictions of the theory and indicate that it is indeed possible to displace highly bound macromolecules with low-molecular-mass dispatchers. The work presented in this paper indicates that non-specific interactions can be exploited for producing high-affinity low-molecular-mass displacers.

Alginate as a displacer for protein displacement chromatography

Alginate use in displacement chromatography as a displacer has been studied. The experiments showed that untreated alginate is the basis of potential displacer for displacement chromatography, but needs to be cleaved into smaller chains. Alginate treated with ultrasound, which cleaves alginate into shorter polysaccharide chains, gave better displacement than untreated alginate, while alginate subjected to limited acid hydrolysis gave the best results in displacement chromatography. It was found that the mixture of ovalbumin and beta-lactoglobulin separated well, and several components of ovalbumin were also separated and purified when alginate hydrolysate was used as a displacer. beta-Lactoglobulins A and B, which have the same molecular weight and differ in isoelectric point by only 0.1 pH units, were displaced from Q-Sepharose by alginate hydrolysate.