Characterization of the binding of sulfonylurea drugs to HSA by high-performance affinity chromatography

Sulfonylurea drugs are often prescribed as a treatment for type II diabetes to help lower blood sugar levels by stimulating insulin secretion. These drugs are believed to primarily bind in blood to human serum albumin (HSA). This study used high-performance affinity chromatography (HPAC) to examine the binding of sulfonylureas to HSA. Frontal analysis with an immobilized HSA column was used to determine the association equilibrium constants (K_a) and number of binding sites on HSA for the sulfonylurea drugs acetohexamide and tolbutamide. The results from frontal analysis indicated HSA had a group of relatively high-affinity binding regions and weaker binding sites for each drug, with average K_a values of 1.3 (±0.2) × 10⁵ and 3.5 (±3.0) × 10² M⁻¹ for acetohexamide and values of 8.7 (±0.6) × 10⁴ and 8.1 (±1.7) × 10³ M⁻¹ for tolbutamide. Zonal elution and competition studies with site-specific probes were used to further examine the relatively high-affinity interactions of these drugs by looking directly at the interactions that were occurring at Sudlow sites I and II of HSA (i.e., the major drug-binding sites on this protein). It was found that acetohexamide was able to bind at both Sudlow sites I and II, with K_a values of 1.3 (±0.1) × 10⁵ and 4.3 (±0.3) × 10⁴ M⁻¹, respectively, at 37 °C. Tolbutamide also appeared to interact with both Sudlow sites I and II, with K_a values of 5.5 (±0.2) × 10⁴ and 5.3 (±0.2) × 10⁴ M⁻¹, respectively. The results provide a more quantitative picture of how these drugs bind with HSA and illustrate how HPAC and related tools can be used to examine relatively complex drug–protein interactions.     

Biointeraction analysis of immobilized antibodies and related agents by high-performance immunoaffinity chromatography

A method is described based on high-performance immunoaffinity chromatography for examining the interactions of immobilized antibodies or related binding agents with their targets. It is shown how this method can be used to obtain information on the binding, elution and regeneration kinetics of immobilized binding agents, such as those used with immunoaffinity supports. The theory behind this approach is briefly described and it is demonstrated how both the kinetic and thermodynamic properties of a biointeraction can be determined experimentally through this method. Several applications are used to illustrate this technique, including antibody-antigen interactions and the binding of aptamers with their targets in the presence of silica-based supports. The same approach can be adapted for use with other types of targets, binding agents and support materials.     

Review: Multipoint binding and heterogeneity in immobilized metal affinity chromatography

Studies carried out using engineered proteins clearly demonstrate that adsorption to derivatized surfaces involves multiple interactions between functional groups on the protein and complementary sites distributed on the surface. The fact that adsorption involves multipoint interactions has important implications for the design of separations processes and for the interpretation of heterogeneity in biological recognition phenomena. Increasing the density of surface metal sites (immobilized copper ions) is found to be functionally equivalent to increasing the number of metal-coordinating groups on the protein (histidines and deporotonated amines), m in that both processes increase the likelihood of simultaneous interactions between the protein and the surface. A consequence of multiple-site interactions is a significant in crease in protein binding affinity that depends on the arrangement of surface sites. A protein will show the highest affinity for arrangements of surface sites which best match its own pattern of functioal groups and will show lower affinity for less optimal arrangements, resulting in binding that is inherently heterogeneous. We have found that reversible protein adsorption in immobilized metal affinity chromatography (IMAC) is described by the Temikin model, which characterizes binding heterogeneity by a uniform distribution of binding energies over the population of surface binding sites. (c) 1995 John Wiley & Sons, Inc.     

Purification of papain by immobilized metal affinity chromatography (IMAC) on chelating carboxymethyl cellulose

Chelating carboxymethyl cellulose was prepared in bead form by immobilizing iminodiacetic acid on carboxymethyl cellulose which was earlier crosslinked and activated by epichlorohydrin. The prepared matrix was used to purify papain by a factor of 2.6 from commercial papain, and by a factor of 4 from papaya latex by batch adsorption and immobilized metal affinity chromatography respectively. Purification factors obtained were equal in batch mode and double in column mode, to purifications obtained on Chelating Sepharose® Fast Flow. Flow rates up to 38 ml/cm2 h were easily possible on the prepared chelating carboxymethyl cellulose.     

Phosphoproteomic analysis using immobilized metal ion affinity chromatography on the basis of cellulose powder

Detailed characterization of phosphoproteins as well as other post-translationally modified proteins such as glycoproteins, is required to fully understand protein function and regulatory events in cells and organisms. Therefore, an experimental strategy for the isolation of phosphoproteins using a new immobilized metal ion affinity chromatograph (IMAC) material on the basis of cellulose has been developed and characterized. Different approaches have been used to test the material. Recovery rates were determined by 32P labelling of a myelin basic protein fragment and by reversed-phase high-performance liquid chromatography-electrospray ionization mass spectrometry using a tryptic digest of the model protein bovine beta-casein. Selectivity was demonstrated by enrichment and separation of phosphopeptides from different samples, such as from a digest of horse myoglobin as well as from a digest of in vitro phosphorylated extracellular signal regulates kinase 2 (ERK2) mixed with synthetic phosphopeptides, phosphorylated on different amino acid residues. Furthermore, simplification and optimization of sample pretreatment was achieved by combining the separating (IMAC) and desalting (C18) step during preparative high performance liquid chromatography. The comparison between our material and a commercially available IMAC system (POROS 20 MC; Perspective BioSystems) emphasizes the competitiveness of the cellulose. Confirmed by the obtained data, the cellulose material performed as well as the commercially available sorbent, however with the advantage, that it can be produced rather easily and at very low cost.     

Preparation of a monolithic capillary column with immobilized alpha-mannose for affinity chromatography of lectins

A simple method for the preparation of an affinity monolithic (also called continuous bed) capillary column for alpha-mannose-specific lectins is described. 2-Hydroxyethyl methacrylate in combination with (+)-N,N -diallyltartardiamide (DATD) and piperazine diacrylamide (PDA, 1,4-bisacryloyl-piperazine) as crosslinkers, were used as monomers for the monolith. After oxidation of DATD with periodate, alpha-mannose with spacer was bound to the aldehyde groups of the polymeric skeleton via reductive amination to form an affinity column for the separation, enrichment or binding studies of mannose-specific lectins. The permeability of the column was excellent. The porosity of the monolith was investigated by scanning electron microscope (SEM) and inverse size exclusion chromatography (ISEC). The affinity of the monolith was evaluated by frontal analysis (FA) and fluorescence microscopy (FM) using fluorescently labeled concanavalin (Con A). Frontal affinity chromatography showed a specific interaction of two different lectins with the alpha-mannose-modified monolith. According to FM the affinity sites were evenly distributed over the monolithic bed.     

Purification of human liver glycoprotein sialyltransferase by affinity chromatography

A simple procedure has been developed for purifying solubilized human liver glycoprotein sialyltransferase (EC 2.4.99.1) 16 000-fold in 4–5% yield. The procedure involves two centrifugation steps, affinity chromatography of the ultrasupernatant fluid on cytidine diphosphate-hexanolamine-agarose followed by gel filtration on Sephadex G-150. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) indicated that the purified sialyltransferase preparation contains approximately equivalent amounts of three protein bands (with apparent molecular weights of 61 000, 63 000 and 70 000) and is highly purified if not homogeneous.     

An oriented adsorption strategy for efficient solid phase PEGylation of recombinant staphylokinase by immobilized metal-ion affinity chromatography

Conjugation of truncated recombinant staphylokinase (trSak) with polyethylene glycol (PEG) is an effective way to overcome its short plasma half-life and enhance its therapeutic potential. However, conventional amine directed PEGylation chemistry inevitably led to modification at its functionally important N terminus, which resulted in a significantly reduced bioactivity of trSak. In this study, a novel solid phase PEGylation process was developed to shield the N-terminal region of the protein from PEGylation. The process was achieved by oriented adsorption of an N-terminally His-tagged trSak (His-trSak) onto an immobilized metal-ion affinity chromatography (IMAC). His-trSak was efficiently separated and retained on IMAC media before reaction with succinimidyl carbonate mPEG (SC-mPEG, 5, 10 or 20 kDa). The IMAC derived mono-PEGylated His-trSak showed structural and stability properties similar to the liquid phase derived conjugate. However, isoelectric focusing electrophoresis analysis revealed that mono-PEGylated His-trSaks via solid phase PEGylation were more homogeneous than those from liquid phase PEGylation. Moreover, tryptic peptide mapping analysis suggested that a complete N-terminal blockage of IMAC bound His-trSak from PEGylation with 10 kDa- and 20 kDa-SC-mPEG. In contrast, only partial protection of the N-terminal region was obtained for 5 kDa-SC-mPEG. Bioactivities of 10 kDa- and 20 kDa-PEG-His-trSak conjugates without N-terminal PEGylation were significantly higher than those of randomly PEGylated products. This further demonstrated the advantage of our new on-column PEGylation strategy.     

Affinity chromatography of GroEL chaperonin based on denatured proteins: Role of electrostatic interactions in regulation of GroEL affinity for protein substrates

The chaperonin GroEL of the heat shock protein family from Escherichia coli cells can bind various polypeptides lacking rigid tertiary structure and thus prevent their nonspecific association and provide for acquisition of native conformation. In the present work we studied the interaction of GroEL with six denatured proteins (alpha-lactalbumin, ribonuclease A, egg lysozyme in the presence of dithiothreitol, pepsin, beta-casein, and apocytochrome c) possessing negative or positive total charge at neutral pH values and different in hydrophobicity (affinity for a hydrophobic probe ANS). To prevent the influence of nonspecific association of non-native proteins on their interaction with GroEL and make easier the recording of the complexing, the proteins were covalently attached to BrCN-activated Sepharose. At low ionic strength (lower than 60 mM), tight binding of the negatively charged denatured proteins with GroEL (which is also negatively charged) needed relatively low concentrations (approximately 10 mM) of bivalent cations Mg2+ or Ca2+. At the high ionic strength (approximately 600 mM), a tight complex was produced also in the absence of bivalent cations. In contrast, positively charged denatured proteins tightly interacted with GroEL irrespectively of the presence of bivalent cations and ionic strength of the solution (from 20 to 600 mM). These features of GroEL interaction with positively and negatively charged denatured proteins were confirmed by polarized fluorescence (fluorescence anisotropy). The findings suggest that the affinity of GroEL for denatured proteins can be determined by the balance of hydrophobic and electrostatic interactions.     

Improved high-performance liquid chromatographic method in the analysis of adenovirus particles

We developed a HPLC method on a novel continuous bed matrix (UNO Q, Bio-Rad) for the direct quantification of adenoviral type 5 (Ad5) particles produced in 293S Human Embryonic Kidney cells and compared this with an existing HPLC method on a conventional ion-exchange resin (Resource Q, Pharmacia). The 293S cell extract contained large amounts of DNA. This contaminated the viral peak on the Resource Q column and only after Benzonase treatment was it possible to quantify the viral particles in the cell extract. In contrast, the virus peak on the UNO Q column was resolved from the DNA which eliminates the need for pretreatment of the sample with Benzonase. Cross-analysis of the Ad5 fraction from the UNO Q column using a size-exclusion HPLC column revealed no additional contaminating peaks. We conclude that the purity of the Ad5 virus peak on the continuous bed matrix UNO Q column was superior to the purity of the virus on the conventional Resource Q column, which is essential for reliable quantification.     

Comparative analysis of oligosaccharide specificities of fucose-specific lectins from Aspergillus oryzae and Aleuria aurantia using frontal affinity chromatography

Aleuria aurantia lectin (AAL) is widely used to estimate the extent of α1,6-fucosylated oligosaccharides and to fractionate glycoproteins for the detection of specific biomarkers for developmental antigens. Our previous studies have shown that Aspergillus oryzae lectin (AOL) reflects the extent of α1,6-fucosylation more clearly than AAL. However, the subtle specificities of these lectins to fucose linked to oligosaccharides through the 2-, 3-, 4-, or 6-position remain unclear, because large amounts of oligosaccharides are required for the systematic comparative analysis using surface plasmon resonance. Here we show a direct comparison of the dissociation constants (K_d) of AOL and AAL using 113 pyridylaminated oligosaccharides with frontal affinity chromatography. As a result, AOL showed a similar specificity as AAL in terms of the high affinity for α1,6-fucosylated oligosaccharides, for smaller fucosylated oligosaccharides, and for oligosaccharides fucosylated at the reducing terminal core GlcNAc. On the other hand, AOL showed 2.9-6.2 times higher affinity constants (K_a) for α1,6-fucosylated oligosaccharides than AAL and only AAL additionally recognized oligosaccharides which were α1,3-fucosylated at the reducing terminal GlcNAc. These results explain why AOL reflects the extent of α1,6-fucosylation on glycoproteins more clearly than AAL. This systematic comparative analysis made from a quantitative viewpoint enabled a clear physical interpretation of these fucose-specific lectins with multivalent fucose-binding sites.     

Proteomic survey of copper-binding proteins in Arabidopsis roots by immobilized metal affinity chromatography and mass spectrometry

To plants, copper is vitally essential at low concentrations but extremely toxic at elevated concentrations. Plants have evolved a suite of mechanisms that modulate the uptake, distribution, and utilization of copper ions. These mechanisms require copper-interacting proteins for transporting, chelating, and sequestrating copper ions. In this study, we have systematically screened for copper-interacting proteins in Arabidopsis roots via copper-immobilized metal affinity chromatography (Cu-IMAC). We also compared Arabidopsis root metalloproteomes with affinity to Cu-IMAC and Zn-IMAC. From the identities of 38 protein spots with affinity to Cu-IMAC, 35 unique proteins were identified. Functional classification of these proteins includes redox/hydrolytic reactions, amino acid metabolism, glutathione metabolism, phosphorylation, translation machinery, membrane-associated proteins, and vegetative storage proteins. Potential copper-interacting motifs were predicted and scored. Six candidate motifs, H-(X)5 -H, H-(X)7 -H, H-(X)12 -H, H-(X)6 -M, M-(X)7 -H, and H-(X)3 -C, are present in Cu-IMAC-isolated proteins with higher frequency than in the whole Arabidopsis proteome.     

Immunoaffinity co-purification of cytokinins and analysis by high-performance liquid chromatography with ultraviolet-spectrum detection

A rapid methodology for the simultaneous analysis of a large number of cytokinins is presented. The cross-reactivity of a mixture of polyclonal antibodies against zeatin riboside and isopentenyladenosine was exploited in a protocol that can be used for immunoaffinity purification of 23 additional cytokinins. Ligands include the cytokinin bases zeatin, dihydrozeatin, isopentenyladenine, benzyl-adenine and kinetin, and their corresponding nucleoside, nucleoside-5′-monophosphate, and 9-glucoside derivatives, as well as cis-zeatin, cis-zeatin riboside, the 2-methylthiol derivatives of isopentenyladenosine and zeatin riboside, and benzyl-adenine-3-glucoside. Mixtures of cytokinins could be retained with high recoveries of all the components. Immunoaffinity purification of extracts of Arabidopsis thaliana (L.) Heynh. and Solarium tuberosum L. gave fractions clean enough, as verified by gas chromatographymass spectrometry (GC-MS), to allow analysis of endogenous cytokinins using a single high-performance liquid chromatography (HPLC) step with on-line UV-spectrum detection. The detection limit was 4–6 pmol. The procedure described forms a routine assaying technique that is faster and simpler, yet yields better qualitative and quantitative information than the commonly used procedure of immunoassaying of HPLC fractions.     

Detection of rutin by high-performance liquid chromatography and its application to taxonomic studies ofCalamagrostis (Poaceae)

A rapid and reproducible microanalysis technique for detecting rutin was established using reversed phase high-performance liquid chromatography. The usefulness of its application to studies in complicated internal structures of some species or species complexes ofCalamagrostis was discussed.     

Nanoengineered analytical immobilized metal affinity chromatography stationary phase by atom transfer radical polymerization: separation of synthetic prion peptides

Atom transfer radical polymerization (ATRP) was employed to create isolated, metal-containing nanoparticles on the surface of nonporous polymeric beads with the goal of developing a new immobilized metal affinity chromatography (IMAC) stationary phase for separating prion peptides and proteins. Transmission electron microscopy was used to visualize nanoparticles on the substrate surface. Individual ferritin molecules were also visualized as ferritin-nanoparticle complexes. The column's resolving power was tested by synthesizing peptide analogs to the copper binding region of prion protein and injecting mixtures of these analogs onto the column. As expected, the column was capable of separating prion-related peptides differing in number of octapeptide repeat units (PHGGGWGQ), (PHGGGWGQ)(2), and (PHGGGWGQ)(4). Unexpectedly, the column could also resolve peptides containing the same number of repeats but differing only in the presence of a hydrophilic tail, Q-->A substitution, or amide nitrogen methylation.     

Purification of catechol siderophores by boronate affinity chromatography: Identification of chrysobactin from Erwinia carotovora subsp. carotovora

Catechols are co-planar cis-diols known to form stable, isolable complexes with borate under weakly basic conditions. We exploited this chemistry and developed a boronate affinity chromatography for isolating catechol siderophores. The method was applied to the isolation of chrysobactin, enterobactin, and an unknown catechol siderophore produce by Erwinia carotovora subsp. carotovora W3C105. Yields of chrysobactin and enterobactin purified by boronate affinity chromatography were at least two-fold greater than those achieved through alternate methods. The unknown catechol produced by E. carotovora subsp. carotovora W3C105 was isolated by boronate affinity chromatography and shown to be identical to chrysobactin. Boronate affinity chromatography enabled separation of catechol from its rust-colored decomposition products, and simultaneous isolation of catechol and hydroxamate siderophores. Boronate affinity chromatography is a rapid and efficient method for purifying catechol siderophores from bacterial culture supernatants     

One-step purification and refolding of recombinant photoprotein aequorin by immobilized metal-ion affinity chromatography

A hexahistidine tag was fused to the N-terminus of apoaequorin. A suitable vector encoding the fusion protein was constructed and used for transformation of Escherichia coli JM109 cells. Apoaequorin was overexpressed under the control of tac promoter. It was found, however, that most of the protein existed in the form of inclusion bodies. Inclusion bodies were solubilized with urea, followed by purification and refolding of (His)(6)-apoaequorin in a single chromatographic step by immobilized metal-ion affinity chromatography using Ni(2+)-nitrilotriacetic acid agarose. The purity, as determined by SDS-PAGE analysis, was greater than 80%. The yield was 0.7-1 mg apoaequorin from a 50 ml bacterial culture. The kinetics of light emission of purified aequorin upon addition of Ca(2+) was typical of the commercial aequorin. The luminescence of the purified aequorin was a linear function of its concentration extending over six orders of magnitude. As low as 0.5 attomoles purified aequorin gave a signal-to-noise ratio of 1.8.     

Improved purification of recombinant adenoviral vector by metal affinity membrane chromatography

The increasing importance of adenoviral vectors for gene therapy clinical trials necessitates the development of processes suitable for large-scale and commercial production of adenovirus. Here, we evaluated a novel purification process combining an anion-exchange chromatography and an immobilized metal affinity membrane chromatography for the purification of recombinant adenovirus. Adenovirus was initially purified from clarified infectious lysate by anion-exchange chromatography using Q Sepharose XL resin and further polished using a Sartobind IDA membrane unit charged with Zn²⁺ ions as affinity ligands. The metal affinity membrane chromatography efficiently removed residual host cell impurities that co-eluted with adenovirus during the previous anion-exchange chromatography step. The metal affinity membrane chromatography also separated defective adenovirus particles from the infectious adenovirus fraction. Furthermore, the metal affinity membrane chromatography showed an improved yield, when compared with a conventional bead-based metal affinity chromatography. The purity and specific activity of the adenovirus prepared using this two-step chromatography was comparable to those of adenovirus produced by the conventional CsCl density centrifugation. Therefore, our data provide an improved method for the purification of adenoviral vectors for clinical applications.     

Purification of hepatocyte growth factor using polyvinyldiene fluoride-based immobilized metal affinity membranes: equilibrium adsorption study

Polyvinyldiene fluoride (PVDF)-based affinity membranes with immobilized copper ions were developed in this study. The resulting membranes were tested for their adsorption properties using a model protein, lysozyme, in batch mode. First, different lengths of diamine were utilized as spacer arms to immobilize the metal ions onto the membranes. It was found that the application of 1,8-diaminooctane as the spacer arm led to the highest adsorption capacity. Moreover, the effects of pH and salt concentration were investigated to distinguish the proportion of specific and nonspecific interactions. A big fraction of lysozyme adsorption capacity for the immobilized metal affinity membranes was considered to come from nonspecific electrostatic interactions, which could be reduced by increasing salt concentration. Lastly, the purification of hepatocyte growth factor (HGF) from insect cell supernatant was performed using the immobilized metal affinity membranes in batch mode. HGF was found in the elution condition using EDTA, indicating the successful purification of HGF.