Comparison of chromatographic ion-exchange resins

Heparin chromatography to deplete high-abundance proteins for serum proteomics

BACKGROUND

Serum is a very informative sample for disease diagnosis. However, a few of the high-abundance proteins existing in serum make the identification of disease-specific serum biomarkers extremely challenging using currently available technologies. A highly promising first step for most analytical approaches of serum is to deplete as many of the high-abundance proteins as possible.

METHODS

We introduced the traditional method of heparin chromatography coupled with protein G sepharose to deplete the high-abundance proteins for serum proteomics.

RESULTS

Compared with the multiple affinity removal system (MARS) column (a commercial version to deplete 6 major proteins in serum), heparin chromatography can deplete more high-abundance proteins in a single step, especially many high molecular-weight proteins. Using this simple and inexpensive method to pretreat serum for 2-DE analysis, more protein spots can be visualized. IgGs depletion by protein G sepharose can further enhance the resolution of the resulting serum proteome.

CONCLUSIONS

Heparin chromatography coupled with protein G appears to be an efficient and economical strategy to pretreat serum for serum proteomics.

Comparison of chromatographic ion-exchange resins

A comparative study on weak anion exchangers was performed to investigate the pH dependence, binding strength, particle size distribution, and static and dynamic capacity of the chromatographic resins. The resins tested included: DEAE Sepharose FF, Poros 50 D, Fractogel EMD DEAE (M), MacroPrep DEAE Support, DEAE Ceramic HyperD 20, and Toyopearl DEAE 650 M. Testing was performed with five different model proteins: Anti-FVII mAb (immunoglobulin G), aprotinin, bovine serum albumin (BSA), Lipolase (Novozymes), and myoglobin. Retention showed an expected increasing trend as a function of pH for proteins with low pI. A decrease in retention was observed for some resins at pH 9 likely due to initiation of deprotonation of the weak anion-exchange ligands. Expected particle size distribution was obtained for all resins compared to previous studies. Binding strength to weak anion-exchange resins as a function of ionic strength depends on the specific protein. Binding and elution at low salt concentration may be performed with Toyopearl DEAE 650 M, while binding and elution at high salt concentration may be performed with MacroPrep DEAE Support. Highest binding capacities were generally obtained with Poros 50 D followed by DEAE Ceramic HyperD 20. A general good agreement was obtained between this study and data obtained by the suppliers. Verification of binding strength trends with model proteins was achieved with human growth hormone (hGH) and a hGH variant on the same resins with different elution salts, sodium chloride, sodium hydrogenphosphate, sodium sulphate, and sodium acetate. Static capacity measurements obtained in the traditional experimental set-up were compared with high-throughput screening (HTS) technique experiments with reasonable agreement. Isotherm data obtained from HTS techniques and pulse experiments were successfully combined with mathematical modelling to simulate, develop and optimise the separation process of two model proteins, Lipolase and BSA. The data presented in this paper may be used for selection of resins for testing in process development.

Application of a chromatography model with linear gradient elution experimental data to the rapid scale-up in ion-exchange process chromatography of proteins

We applied the model described in our previous paper to the rapid scale-up in the ion exchange chromatography of proteins, in which linear flow velocity, column length and gradient slope were changed. We carried out linear gradient elution experiments, and obtained data for the peak salt concentration and peak width. From these data, the plate height (HETP) was calculated as a function of the mobile phase velocity and iso-resolution curve (the separation time and elution volume relationship for the same resolution) was calculated. The scale-up chromatography conditions were determined by the iso-resolution curve. The scale-up of the linear gradient elution from 5 to 100mL and 2.5L column sizes was performed both by the separation of beta-lactoglobulin A and beta-lactoglobulin B with anion-exchange chromatography and by the purification of a recombinant protein with cation-exchange chromatography. Resolution, recovery and purity were examined in order to verify the proposed method.

High capacity, charge-selective protein uptake by polyelectrolyte brushes

Surface plasmon resonance was used to measure binding of proteins from solution to poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) brushes end-grafted from gold surfaces by atom transfer radical polymerization (ATRP). PDMAEMA brushes were prepared with a variety of grafting densities and degrees of polymerization. These brushes displayed charge selective protein uptake. The extent of uptake for net negatively charged bovine serum albumin (BSA) scaled linearly with the surface mass concentration of grafted PDMAEMA, regardless of grafting density. BSA was bound at a constant ratio of 120 DMAEMA monomer units per protein molecule for all brushes examined. The equivalent three-dimensional concentration of BSA bound in the brush (i.e., the bound BSA surface excess concentration divided by the brush thickness) decreased monotonically with decreasing grafting density. The concentration of BSA bound within brushes prepared at higher grafting densities was comparable with the aqueous protein solubility limit. BSA desorption from the brush required changes in solution pH and/or ionic strength to eliminate its net electrostatic attraction to PDMAEMA. Net positively charged lysozyme was completely rejected by the PDMAEMA brushes.

Cation exchange chromatography in antibody purification: pH screening for optimised binding and HCP removal

The production of pharmaceutical antibodies requires reliable and rapid processes with high purity and yield. Although protein A gels selectively and efficiently bind antibodies in the capture step, intense research is going on to find alternatives that can abolish the drawbacks of protein A chromatography. Ion exchangers e.g. are more robust, considerably cheaper and can eliminate ligand leaching. For the strong cation exchangers Fractogel EMD SO3- (M) and Fractogel EMD SE Hicap (M) we have evaluated the influence of pH for optimised binding and removal of host cell protein (HCP). In a fast initial screening we measured batch binding capacities. Subsequent scale-down to 96-well plate format proved that assay miniaturisation still provided reliable data. We demonstrated with the principle of residence time that scout columns are suitable for dynamic studies. The optimum pH range from batch binding was transferred to scout columns which were then used to screen for maximum dynamic capacities. In addition IEF titration curve analysis was employed to define a final operational pH. With this pH we ran labscale columns to purify monoclonal antibody. The cation exchangers showed high step yields and host cell proteins in the pools from gradient elution were reduced very effectively.

Effects of pore structure and molecular size on diffusion in chromatographic adsorbents

Two computational approaches, namely Brownian dynamics and network modeling, are presented for predicting effective diffusion coefficients of probes of different sizes in three chromatographic adsorbents, the structural properties of which were determined previously using electron tomography. Three-dimensional reconstructions of the adsorbents provide detailed, explicit characteristics of the pore network, so that no assumptions have to be made regarding pore properties such as connectivity, pore radius and pore length. The diffusivity predictions obtained from the two modeling approaches were compared to experimental diffusivities measured for dextran and protein probes. Both computational methods captured the same qualitative results, while their predictive capabilities varied among adsorbents.

Comparison of chromatographic ion-exchange resins

Strong and weak cation-exchangers were compared for a number of chromatographic parameters, i.e. pH dependence, efficiency, binding strength, particle size distribution, static and dynamic capacity, and scanning electron microscopy (SEM) pictures. Chromatographic resins investigated were Fractogel EMD SO3- (M), Fractogel EMD SE Hicap (M), Fractogel EMD COO- (M), MacroPrep 25S, MacroPrep High S, MacroPrep CM, CM HyperZ, and Matrex Cellufine C-500. Testing was done with three proteins: Anti-FVII Mab (IgG), aprotinin, and lysozyme. For lysozyme and aprotinin with pI above experimental pH, dependence of pH on retention was generally low, though some pronounced decrease of retention with increasing pH was observed for CM HyperZ. For Anti-FVII Mab with pI<7.5, binding was observed on several resins at pH 7.5. Efficiency results present the expected trend of increasing dependence of plate height as a function of increasing flow rate, and the highest flow dependence was observed for Fractogel EMD COO-. Particle size distribution was determined by two independent methods, coulter counting and SEM pictures, with fair agreement. Binding strength data of cation-exchange resins as a function of ionic strength depends on the protein, but binding and elution at high salt concentration may in general be performed with MacroPrep resins. Comparison of dynamic capacity data at 10% break-through and static capacity measurements shows that a very diverse utilization of approximately 25-90% of the total available capacity is employed during chromatographic operation. The effect of competitive binding from yeast fermentation components on dynamic binding capacity of aprotinin was studied showing a significant decrease in binding capacity. Sepharose FF, Toyopearl 650 M, and Ceramic HyperD F strong and weak cation-exchange resins were included in this study. Resins with good pure aprotinin capacity also performed well for aprotinin in fermentation broth, but the highest relative capacity was obtained with MacroPrep High S having a fairly low pure component dynamic capacity. Results of this paper may be used in the selection of resins for further testing in biopharmaceutical protein purification process development.