Quantitation of non-ideal behavior in protein size-exclusion chromatography

Choice of mobile phase: Implications for size exclusion chromatography-inductively coupled plasma-mass spectrometry analyses of copper, zinc and iron metalloproteins

The correct identification of the metalloproteins present in human tissues and fluids is essential to our understanding of the cellular mechanisms underpinning a host of health disorders. Separation and analysis of biological samples are typically done via size exclusion chromatography hyphenated with inductively coupled plasma-mass spectrometry (SEC-ICP-MS). Although this technique can be extremely effective in identification of potential metalloproteins, the choice of mobile phase may have a marked effect on results, results by adversely affecting metal-protein bonds of the metalloproteins of interest. To assess the choice of mobile phase on SEC-ICP-MS resolution and the resulting metalloproteome pattern, we analysed several different sample types (brain homogenate; Cu/Zn-superoxide dismutase (SOD1); a molecular weight standard mix containing ferritin (Ft), ceruloplasmin (Cp), cytochrome c (CytC), vitamin B12 (B12) and thyroglobulin (Tg) using six different mobile phase conditions (200 mM, pH 7.5 solutions of ammonium salts nitrate, acetate, and sulfate; HEPES, MOPS and Tris-HCl). Our findings suggest that ammonium nitrate, ammonium acetate and Tris-HCl are optimal choices for the mobile phase, with the specific choice being dependent on both the number of samples and method of detection that is hyphenated with separation. Furthermore, we found that MOPS, HEPES and ammonium sulfate mobile phases all caused significant changes to peak resolution, retention time and overall profile shape. MOPS and HEPES, in particular, produced additional Fe peaks that were not detected with any of the other mobile phases that were investigated. As well as this, MOPS and HEPES both caused significant concentration dependent matrix suppression of the internal standard.

Evaluation of size exclusion chromatography columns packed with sub-3μm particles for the analysis of biopharmaceutical proteins

The aim of this study was to evaluate the practical possibilities and limitations of several recently introduced size exclusion chromatographic (SEC) columns of 150×4.6mm, sub-3μm (Agilent AdvanceBioSEC 2.7μm, Tosoh TSKgel UP-SW3000 2.0μm, Phenomenex Yarra SEC X-150 1.8μm and Waters Acquity BEH200 1.7μm) for the separation of biopharmaceutical proteins. For this purpose, some model proteins were tested, as well as several commercial therapeutic monoclonal antibodies (mAbs) and antibody-drug-conjugates (ADCs). Calibration curves were drawn to highlight the applicability of these new SEC columns for the separation of mAbs, ADCs and their aggregates, despite some differences in their nominal pore diameter (vary from 150 to 300Å). The kinetic performance (van Deemter curves and kinetic pots) was evaluated. Columns packed with 1.7-2.0μm particles improved the plate count by a factor of 1.5-2 compared to 2.7μm particles, which is in agreement with theoretical expectations. Finally, possible secondary hydrophobic and/or electrostatic interactions between the SEC stationary phases and biopharmaceutical proteins were systematically studied. Significant differences in nonspecific interactions were observed, with hydrophobic interactions generally exerting more influence than electrostatic interactions. The use of a novel bond chemistry with the AdvanceBioSEC column was found highly effective to limit non-specific interactions and pave the way to further improvements for column provider. At the end, the average resolutions achieved on the four sub-3μm SEC columns between monomer and dimer structures were comparable for ten approved mAbs products.

Structural aspects of a protein-surfactant assembly: native and reduced States of human serum albumin

The inherently present seventeen disulfide bonds of the circulatory protein, human serum albumin (HSA) provide the necessary structural stability. Various spectroscopic approaches were used to investigate the effect of reduction of these disulfide bonds and its binding with the anionic surfactant, sodium dodecyl sulfate (SDS). Based on several spectroscopic analyses, our investigations highlight the following interesting aspects: (1) HSA on reduction loses not only its tertiary structure but also a significant amount of secondary structure as well. However, the reduced state of the protein is not like the molten-globule, (2) this structural loss of the protein due to reduction is more prominent than that caused by higher SDS concentrations alone and can certainly be attributed to the role of disulfide bonds, (3) lower surfactant concentrations provide marginal structural rigidity to the native state of the protein, whereas, higher concentrations of SDS induces secondary structure to the reduced state of HSA, (4) the binding of SDS with both the native and reduced states of HSA, occurred in three distinct stages which was followed by a saturation stage. However, the nature of such binding is different for both the states as investigated by using the Stern-Volmer equations and estimating the thermodynamic parameters. Besides, in contrast to the native state, the reduced state of HSA shows that the lone tryptophan residue gets more buried. However, there occurs a sudden decrement in the lifetime of the tryptophan and the hydrodynamic diameter increases by twofold.

Size-Exclusion Chromatography for the Analysis of Protein Biotherapeutics and their Aggregates

In recent years, the use and number of biotherapeutics has increased significantly. For these largely protein-based therapies, the quantitation of aggregates is of particular concern given their potential effect on efficacy and immunogenicity. This need has renewed interest in size-exclusion chromatography (SEC). In the following review we will outline the history and background of SEC for the analysis of proteins. We will also discuss the instrumentation for these analyses, including the use of different types of detectors. Method development for protein analysis by SEC will also be outlined, including the effect of mobile phase and column parameters (column length, pore size). We will also review some of the applications of this mode of separation that are of particular importance to protein biopharmaceutical development and highlight some considerations in their implementation.

Physical alginate hydrogels based on hydrophobic or dual hydrophobic/ionic interactions: Bead formation, structure, and stability

Hydrophobically associating alginate (AA) derivatives were prepared by covalent fixation of dodecyl or octadecyl chains onto the polysaccharide backbone (AA-C12/AA-C18). In semidilute solution, intermolecular hydrophobic interactions result in the formation of physical hydrogels, the physicochemical properties of which can be controlled through polymer concentration, hydrophobic chain content, and nonchaotropic salts such as sodium chloride. The mechanical properties of these hydrogels can then be reinforced by the addition of calcium chloride. The combination of both calcium bridges and intermolecular hydrophobic interactions leads to a decrease in the swelling ratio accompanied by an increase of elastic and viscous moduli. Beads made of hydrophobically modified alginate were obtained by dropping an aqueous solution of alginate derivative into a NaCl/CaCl2 solution. As compared to unmodified alginate beads, modified alginate particles proved to be stable in the presence of nongelling cations or calcium-sequestering agents. However, evidence is presented for a more heterogeneous structure than that of plain calcium alginate hydrogels with, in particular, an increase in the effective gel mesh size, as determined by partition and diffusion coefficient measurements.

Purification and characterization of Lip2 and Lip3 isoenzymes from a Candida rugosa pilot-plant scale fed-batch fermentation

Previous purification of a crude extracellular enzyme preparation from Candida rugosa ATCC 14830 pilot-plant fed-batch fermentations showed the presence of two lipase isoenzymes, Lip2 and Lip3, differing in their molecular masses (58 and 62 kDa, respectively). These enzymes were purified but the lipases were forming active aggregates with a molecular mass higher than 200 kDa. In this work we developed a purification method following three steps: ammonium sulfate precipitation, sodium cholate treatment and ethanol/ether precipitation, and anion exchange chromatography which allowed the sequential disaggregation of the isoenzymes. Pure and monomeric Lip2 and Lip3 were characterized according to pI, glycosylation and activity for p-nitrophenol esters and triacylglycerols of varying acyl chain. Lip3 was the best catalyst for the hydrolysis of the simple esters and triacylglycerols with short and medium acyl chains.

Non-ideal behaviour of free vanadate on a Superose 12 size-exclusion column. Application to in vivo 48V-labelled rat spleen homogenate

Seven chromatographic columns were evaluated for the recovery of 48V-radiolabelled vanadate. Further, the behaviour of vanadate (H2VO4-) was studied on a size-exclusion column Superose 12 as a function of (a) buffer salt molarity, (b) different buffer salts, (c) different buffers and (d) organic solvents added to the buffer. As opposed to the unsatisfactory recovery of V-compounds on other columns, we recovered the vanadium quantitatively. We observed that in most cases vanadate eluted after the total volume of the Superose 12 column. This indicates a non-ideal behaviour of vanadate. However, through this non-ideal behaviour it was possible to separate low-molecular-mass bound (Mr<5000) and unbound vanadium which would not be possible under normal behaviour. A possible explanation for this non-ideal behaviour of vanadium is put forward. The method has been successfully applied for the fractionation of different vanadium species in rat spleen homogenate.

Size-exclusion chromatography--multiangle laser light scattering analysis of beta-lactoglobulin and bovine serum albumin in aqueous solution with added salt

The solution characteristics of beta-LGB (beta-lactoglobulin) and BSA (bovine serum albumin) are reported as determined by size-exclusion chromatography with on-line multiangle laser light scattering, differential refractive index and UV detection. The order of the three in series placed detectors as well as the interdetector volumes have been carefully pointed out. At concentrations below 2.5 mg/ml and at different values of pH the weight-average molecular mass of both proteins have been obtained. They indicate the appearance of monomers, dimers and higher order multimers. For beta-LGB the growth of self-associates could be observed at the isoelectric point over a period of days. The range of applicability of the method is discussed.

Control and measurement of permeability for design of microcapsule cell delivery system

Transplantation of immunoisolated islets of Langerhans has been proposed as a promising approach to treating insulin-dependent diabetes mellitus. Recently, a cell delivery system based on a multicomponent microcapsule has been designed for the immunoisolation of insulin-secreting pancreatic islets. The capsule, formed by polyelectrolyte complexation of sodium alginate and cellulose sulfate with poly(methylene-co-guanidine), markedly has improved mechanical strength compared with the widely used alginate/poly(L-lysine) capsules. It also provides a flexibility for readily adjusting membrane thickness and capsule size, and, more important, the membrane permeability can be altered over a wide range of molecular sizes. To rigorously test the capsule diffusion properties, we have improved capsule permeability measurement by using two complementary methods: (1) size exclusion chromatography with dextran standards; and (2) newly developed methodology for assessing permeability to a series of biologically relevant proteins. Viability and function of rat pancreatic islets enclosed in the capsules with different permeability were tested in vitro. The insulin secretion of encapsulated islets was well preserved even though slightly delayed in comparison with a control group of free islets. We believe that the unique features of this encapsulation system together with the precise characterization of its physical parameters will enable us to find the optimal range of capsule permeability for in vitro and in vivo survival and function of encapsulated pancreatic islets.

Characterization of antigen-antibody complexes by size-exclusion chromatography coupled with low-angle light-scattering photometry and viscometry

In this paper, the molecular masses (M(r)s) of the complexes of monoclonal anti-BSA (antibody to bovine serum albumin) (clone: 33) and monomer BSA were determined on-line by using size-exclusion chromatography (SEC) coupled with a low-angle laser light-scattering (LALLS) detector and two concentration detectors, ultraviolet (UV) and refractive index (RI) (SEC-LALLS/UV/RI system). Also, the size and M(r)s of the complexes were evaluated by the SEC-LALLS/UV/viscometer (VISC) system. This study demonstrated that, for small size macromolecules, the combination of light scattering and viscosity detection was a suitable choice for determining their M(r)s and sizes.

Chromatographic separation of low-molecular-mass recombinant proteins and peptides on Superdex 30 prep grade

The chromatographic properties of Superdex 30 prep grade medium have been investigated in non-denaturing and denaturing mobile phases using commercially available proteins and peptides as well as low-molecular-mass (M(r)) recombinant polypeptides. The medium is a macroreticular gel composed of crosslinked agarose beads to which dextran has been covalently bound. The mean particle size is approximately 34 microns. Experimental results show a linear relation between the distribution coefficient (KD) and the log10 M(r) in the fractionation range 24,000-3000. The relationships between resolution and flow-rate or load volume were investigated and shown to be comparable with those of Superdex 75 and 200 prep grade media. Minimal loss of resolution occurred in the flow-range from 30-60 cm/h. Load volumes of up to 5% total column volume could be applied while maintaining baseline resolution of polypeptide mixtures. Non-specific interactions between the matrix and certain samples were characterized. The predominant interactions with the resin appear to be hydrophobic in nature rather than ionic. Hydrogen bonding may also play a role in the retardation of certain small molecules. The applicability of the resin for separating dimeric and oligomeric forms of low-molecular-mass recombinant proteins was shown.