Retention mechanism of lactate dehydrogenase in anion-exchange chromatography

Selective removal of closely related clipped protein impurities using poly(ethylenimine)- grafted anion-exchange chromatography resin

Proteolytic degradation is a serious problem that complicates downstream processing during production of recombinant therapeutic proteins. It can lead to decreased product yield, diminished biological activity, and suboptimal product quality. Proteolytic degradation or protein truncation is observed in various expression hosts and is mostly attributed to the activity of proteases released by host cells. Since these clipped proteins can impact pharmacokinetics and immunogenicity in addition to potency, they need to be appropriately controlled to ensure consistency of product quality and patient safety. A chromatography step for the selective removal of clipped proteins from an intact protein was developed in this study. Poly(ethylenimine)-grafted anion- exchange resins (PolyQUAT and PolyPEI) were evaluated and compared to traditional macroporous anion-exchange and tentacled anion-exchange resins. Isocratic retention experiments were conducted to determine the retention factors (k') and charge factors (Z) were determined through the classical stoichiometric displacement model. High selectivity in separation of closely related clipped proteins was obtained with the PolyQUAT resin. A robust design space was established for the PolyQUAT chromatography through Design-Of-Experiments (DoE) based process optimization. Results showed a product recovery of up to 63% with purity levels >99.0%. Approximately, one-log clearance of host cell protein and two-logs clearance of host cell DNA were also obtained. The newly developed PolyQUAT process was compared with an existing process and shown to be superior with respect to the number of process steps, process time, process yield, and product quality.

Toward chromatographic analysis of interacting protein networks

Protein complexes, collectively referred to as the cellular interactome, appear to play a major role in cellular regulation. At present it is thought that the interactome could be composed of hundreds of protein assemblies. The objective of the work described here was to examine the prospect that chromatographic methods widely used in the preparative isolation of native proteins could be incorporated into global proteomics methods in such a way that the primary structure of protein complexes of sufficient stability to survive chromatography could be recognized along with their participation in protein complexes. Because wide differences in sizes are a unique feature of protein complexes, size-exclusion chromatography (SEC) was incorporated into all the fractionation strategies examined. Anion-exchange chromatography (AEC) and hydrophobic-interaction chromatography (HIC) were also examined because of the broad utility that these methods have shown in the preparation of proteins with native structure. Slightly more than a third of all proteins identified in yeast lysates were found to elute from SEC, AEC, and HIC columns with an apparent molecular weight much higher than that predicted from their parent gene. These results were interpreted to mean that these proteins were migrating through columns as components of protein complexes. Based on studies with multidimensional SEC-->RPLC (reversed-phase liquid chromatography), AEC-->SEC, and HIC-->SEC systems, it was concluded that recognition of proteins in complexes could be easily incorporated into multidimensional chromatographic methods for global proteomics when at least one of the fractionation dimensions included SEC of native proteins.

Applicability of the stoichiometric displacement model to description of the retention behavior of charged-fusion proteins during fast protein liquid chromatography

The applicability of the stoichiometric displacement model (SDM) to description of the retention behavior of charged-fusion proteins in large ion exchange resin (approximately 90 microm diameter) packed column was studied. Proteins were characterized by SDM for isocratic elution. The parameters were subsequently used to evaluate their suitability in predicting protein retention and peak width under gradient elution. The proteins were beta-glucuronidase (GUS) and its fusions with polypeptides of 5, 10 and 15 aspartic acids at the C-terminal of the wild-type GUS. Predictions of retention time were within 10% of the experiment results. The plate number obtained at high salt concentration from isocratic elution was used as a first estimate for predictions of peak width. The results show that the SDM is sufficient to describe the binding equilibrium of fusion proteins in ion-exchange columns packed with large resin particles. In addition, the binding mechanism between fusion proteins and the ion exchanger is explored with the assistance of comparative molecular modeling.

Anion-exchange chromatographic behavior of recombinant rat cytochrome b5. Thermodynamic driving forces and temperature dependence of the stoichiometric displacement parameter Z

The HPLC anion-exchange isocratic retention behavior of the recombinant soluble core of wild type rat cytochrome b5 on Mono Q HR 5/5 was investigated as a function of temperature and sodium chloride concentration at fixed eluent flow-rates. Retention was measured over a range of eluent flow-rates at a specified temperature to determine if true adsorption equilibrium could be approximated by the HPLC method. Apparent Van 't Hoff enthalpies of adsorption obtained from the HPLC retention data were positive, indicating an entropically driven spontaneous adsorption process, and were found to decline with increasing ionic strength. The retention results were interpreted in terms of the stoichiometric displacement model to obtain the apparent number of binding sites in the contact region, Z, as a function of temperature and of protein concentration. Z was found to depend significantly on temperature, even under conditions of nearly complete protein recovery, but did not depend on protein concentration at the low loadings studied.

High-performance liquid chromatography of amino acids, peptides and proteins. CXXVIII. Effect of D-amino acid substitutions on the reversed-phase high-performance liquid chromatography retention behaviour of neuropeptide Y[18-36] analogues

The reversed-phase high-performance liquid chromatographic (RP-HPLC) gradient elution behaviour of a series of peptides related to Neuropeptide Y (NPY) has been investigated. The peptides studied included NPY, NPY[13-36], NPY[18-36] and a series of 16 analogues of NPY[18-36], each with a single D-amino acid substitution. Chromatographic parameters which relate to the interactive contact area and the binding affinity have been evaluated with two different stationary phase ligands and two organic modifiers. The results demonstrate that D-amino acid substitutions in the sequence region encompassing amino acid residues NPY[27-31] of these NPY[18-36] peptides significantly influence the interactive behaviour of these peptides relative to the unsubstituted NPY[18-36] molecule, while substitutions in the N- and C-terminal regions had little effect. Further, these results indicate that, in hydrophobic environments, NPY[18-36] adopts a significant degree of secondary structure which is severely disrupted by the presence of the D-amino acids in the central portion of the molecule.

High-performance liquid chromatography of amino acids, peptides and proteins. LXXXIX. The influence of different displacer salts on the retention properties of proteins separated by gradient anion-exchange chromatography

The influence of eight different displacer salts on the retention properties of four globular proteins, ranging in molecular weight from 14,000 to 43,000, was investigated by using the Mono-Q strong-anion-exchange resin as the stationary phase. Proteins were eluted under gradient conditions with a range of alkali metal halides to vary systematically the anion and cation species in the series F-, Cl-, and Br- and Li+, Na+ and K+. Protein Zc values (i.e. slopes of the ion-exchange retention plots, derived from the dependency of the logarithmic capacity factor log k' on the concentration of the ionic displacer) generally increased when both the anion and cation were either chaotropic, e.g. KBr, or kosmotropic, e.g. NaF, in nature. Conversely, Zc values decreased when the displacer salt contained an anion-cation combination of a chaotropic and a kosmotropic ion, e.g. KF. These results indicate that the lyotropic properties of salts are additive in their effect on the interactive properties of proteins in anion-exchange chromatography. The Zc values were also found to depend on the manner in which the ionic strength was manipulated to affect elution, i.e. isocratic or gradient change in concentration of the displacing salt. Thus, isocratic experiments and gradient experiments with varied gradient time or varied flow-rate were observed to result in log k' versus log l/c dependencies with non-coincident Zc values. The relationship between protein Zc values, the electrostatic contact area or ionotope, Ac, and the electrostatic potential of the protein surface psis, is discussed.

Immunological-chromatographic analysis

Tandem immunoaffinity and conventional high-performance liquid chromatography columns, coupled with a switching valve, were used for the analysis of single and multicomponent antigen samples. Immunoaffinity columns were prepared by hydrophobic adsorption or covalent immobilization of poly- or monoclonal antibodies on macroporous poly(styrene-divinylbenzene) packing materials. Capacities of these columns were constant through at least 77 cycles. Macromolecular antigens were analyzed at submicrogram levels. Antigens bound to the immunoaffinity column were desorbed and concentrated on a conventional analytical column. Gradient elution on the analytical column separated the desorbed antigen(s) from interfering species and permitted the analysis of all species which bound to the immunoaffinity column. Immunological-chromatographic analysis was useful for purification and discrimination of polypeptides of similar three dimensional structures, such as several lysozyme variants.

Surface-mediated retention effects of subtilisin site-specific variants in cation-exchange chromatography

Wild-type subtilisin and several site-specific variants were resolved on a strong cation-exchange column by isocratic elution and a series of sodium chloride concentrations. Changes in primary sequence at the protein surface have an observable effect on the chromatographic behavior of subtilisin. This supports the concept that three-dimensional structure determines which biopolymer surface residues are in position to interact with the stationary phase surface. The retention data fit the stoichiometric displacement model (SDM) of retention. Plots of ln k' vs. ln 1/[NaCl] yield values for the average number of ionic groups (Z) on the protein that interact with the support matrix. Application of the SDM to the chromatographic retention of the variants has uncovered an unusual phenomenon at the protein surface at low ionic strength. A SDM plot normally provides a linear relationship between ln k' and ln 1/[NaCl] with the slope corresponding to the Z number. This study revealed two lines differing in slope and intercept, indicating that the Z number of subtilisin changes at some intermediate ionic strength of the eluent. These results are attributed to some salt-induced protein surface event that triggers a change in structure. Chromatographic detection of this occurrence reflects the connection between the surface-mediated event and mobile phase ionic strength.

Effects of large sample loads on column lifetime in preparative-scale liquid chromatography

In preparative-scale liquid chromatography of proteins, the use of high sample concentration and large sample mass may result in irreversible adsorption to the support surface. This can change the stationary phase characteristics, reduce the capacity, shorten the column lifetime and diminish the economic viability of a particular separation method. Column recycling and regeneration can influence the throughput (mass purified per time unit) and selectivity, and affect the reproducibility. The effects of large sample loads on column lifetime and performance were evaluated for three strong anion-exchange columns: (1) a silica support with a quaternized polyethyleneimine (PEI) coating, (2) a polymeric support with an adsorbed PEI coating which also was quaternized, and (3) a polymeric support with a proprietary quaternary amine stationary phase. The column capacity for proteins was measured by frontal chromatography and monitored as a function of cycle number. The column lifetime was determined by examining chromatographic properties subsequent to the frontal chromatography. The change in protein binding capacity was then compared to the change in nitrate binding capacity. The column performance was evaluated under analytical conditions by measuring the change in resolution of standard protein mixtures.

The role of protein structure in chromatographic behavior

Chromatographic retention is determined by a relatively small number of amino acids located in a chromatographic contact region on the surface of a polypeptide. This region is determined by the mode of separation and the amino acid distribution within the polypeptide. The contact area may be as small as a few hundred square angstroms in bioaffinity chromatography. In contrast, the contact region in ion exchange, reversed phase, hydrophobic interaction and the other nonbioaffinity separation modes is much broader, ranging from one side to the whole external surface of a polypeptide. Furthermore, structural changes that alter the chromatographic contact region will alter chromatographic properties. Thus, although immunosorbents can be very useful in purifying proteins of similar primary structure, they will be ineffective in discriminating between small, random variations within a structure. Nonbioaffinity columns complement affinity columns in probing a much larger portion of solute surface and being able to discriminate between protein variants.