Improved method for the immobilization of heparin

Preparation of affinity adsorbents and purification of lectins from natural sources

Lectins are purified by affinity chromatography to take advantage of their carbohydrate-specific interactions. Highly efficient affinity adsorbents are powerful tools to obtain homogeneous lectins with distinct specificities. Here, we describe three methods to prepare affinity adsorbents by immobilizing carbohydrates or glycoconjugates on agarose gel beads. Because the ligands are immobilized via a stable and nonionic linkage under mild conditions, the adsorbents possess high binding capacity for lectins with low nonspecific adsorption and can withstand repeated use. The procedures require neither specialized techniques and apparatus nor highly toxic compounds. Using these adsorbents, many plant and animal lectins can be purified in a few steps.

Heparin-immobilized microspheres for the capture of cytokines

The preparation and characterization of heparin-immobilized microspheres which were used to bind acidic fibroblast growth factor (aFGF), vascular endothelial growth factor (VEGF), monocyte chemoattractant protein 1 (MCP-1/CCL2), and regulation upon activation normal T cell express sequence (RANTES/CCL5) is described. These beads were used as trapping agents in microdialysis sampling experiments in a separate study. Both free heparin and a synthesized heparin-albumin conjugate were immobilized onto microspheres and compared for their effectiveness. The heparin-albumin conjugate microspheres exhibited significant nonspecific adsorption which appeared to be due to the albumin content. The prepared heparin-immobilized microspheres were stable for 3 months at 4 °C. A bead-based flow cytometric assay was developed to study the binding capacity and specificity of the heparin-immobilized microspheres to cytokines. These heparin-immobilized microspheres exhibited broad dynamic ranges for binding to the four cytokines (aFGF, 1.0-1,000 ng/mL; VEGF, 0.5-1,000 ng/mL; CCL2, 1.95-1,000 ng/mL; CCL5, 1.95-500 ng/mL). Fast binding kinetics of the cytokines to the heparin-immobilized beads suggests that these beads may be useful as affinity agents in microfluidic flow systems.

Pseudoproteoglycan (pseudoPG) probes that simulate PG macromolecular structure for screening and isolation of PG-binding proteins

A proteoglycan (PG) monomer is a macromolecule consisting of one or more glycosaminoglycan (GAG) chains attached to a core protein. PGs have signaling roles and modulatory functions in the extracellular matrix and at the cell surface. To elucidate the functions of higher-order PG structures, pseudoPGs that imitate the PG structure were prepared to develop probes and affinity adsorbents. Poly-L: -lysine (PLL) or polyacrylamide (PAA) was coupled with various GAGs, then biotinylated, and the remaining amino groups were blocked to obtain the pseudoPG probes, biotinyl PLL (BPL)- or PAA (BPA)-GAGs. Lactoferrin exhibited 30-times higher affinity toward BPL-heparin than the conventional single-strand probe, biotin-hydrazide-heparin. Heparin-PLL was immobilized on a formyl-Sepharose and compared with the Hep-Sepharose in which heparin was directly immobilized to amino-Sepharose. Screening for ligands in normal rat brain revealed several proteins that specifically bound to either of the two adsorbents, indicating that the heparin-binding proteins exhibit specific recognition depending on the higher-order structure of the PG.

Molecular interactions in the insulin-like growth factor (IGF) axis: a surface plasmon resonance (SPR) based biosensor study

This review describes a comprehensive analysis of a surface plasmon resonance (SPR)-based biosensor study of molecular interactions in the insulin-like growth factor (IGF) molecular axis. In this study, we focus on the interaction between the polypeptide growth factors IGF-I and IGF-II with six soluble IGF binding proteins (IGFBP 1-6), which occur naturally in various biological fluids. We have describe the conditions required for the accurate determination of kinetic rate constants for these interactions and highlight the experimental and theoretical pitfalls, which may be encountered in the early stages of such a study. We focus on IGFBP-5 and describe a site-directed mutagenesis study, which examines the contribution of various residues in the protein to high affinity interaction with IGF-I and -II. We analyse the interaction of IGFBP-5 (and IGFBP-3) with heparin and other biomolecules and describe experiments, which were designed to monitor multi-protein complex formation in this molecular axis.

The heparin/heparan sulfate sequence that interacts with cyclophilin B contains a 3-O-sulfated N-unsubstituted glucosamine residue

Many of the biological functions of heparan sulfate (HS) proteoglycans can be attributed to specialized structures within HS moieties, which are thought to modulate binding and function of various effector proteins. Cyclophilin B (CyPB), which was initially identified as a cyclosporin A-binding protein, triggers migration and integrin-mediated adhesion of peripheral blood T lymphocytes by a mechanism dependent on interaction with cell surface HS. Here we determined the structural features of HS that are responsible for the specific binding of CyPB. In addition to the involvement of 2-O,6-O, and N-sulfate groups, we also demonstrated that binding of CyPB was dependent on the presence of N-unsubstituted glucosamine residues (GlcNH2), which have been reported to be precursors for sulfation by 3-O-sulfotransferases-3 (3-OST-3). Interestingly, 3-OST-3B isoform was found to be the main 3-OST isoenzyme expressed in peripheral blood T lymphocytes and Jurkat T cells. Moreover, down-regulation of the expression of 3-OST-3 by RNA interference potently reduced CyPB binding and consequent activation of p44/42 mitogen-activated protein kinases. Altogether, our results strongly support the hypothesis that 3-O-sulfation of GlcNH2 residues could be a key modification that provides specialized HS structures for CyPB binding to responsive cells. Given that 3-O-sulfation of GlcNH2-containing HS by 3-OST-3 also provides binding sites for glycoprotein gD of herpes simplex virus type I, these findings suggest an intriguing structural linkage between the HS sequences involved in CyPB binding and viral infection.

Sepharose-bound, highly sulfated glycosaminoglycans can capture HIV-1 from culture medium

In the search for new strategies against HIV-1 and on the basis of a number of previous studies reporting on the capacity of certain polyanionic compounds to influence the replication of HIV-1, we prepared a few chemically oversulfated dermatan and chondroitin sulfates. Four of these compounds and two samples of heparin were bound to activated Sepharose through either their carboxylic groups, or their aldehydic groups, or their deacetylated primary amino groups. Some of these so-derivatised resins, packed into columns, proved able to remove HIV-1 IIIB, a laboratory adapted strain, and one clinical primary isolate from an AIDS patient, from infected cell culture medium. The resins bind the virus very tightly and could be useful for capturing the virus from infected fluids.

Preparative two-step purification of recombinant human basic fibroblast growth factor from high-cell-density cultivation of Escherichia coli

Aggregation and precipitation are major pitfalls during bioprocessing and purification of recombinant human basic fibroblast growth factor (rh-bFGF). In order to gain high yields of the soluble protein monomer with high biological activity, an efficient downstream process was developed, focussing on the combination of expanded bed adsorption (EBA) and heparin chromatography. After expression in E. coli TG1:plambdaFGFB, cells were harvested and washed; then the rh-bFGF was released via high pressure homogenization. The high viscosity of the feedstock of about 40 mPa s, showing non-newtonian behaviour, was reduced to 2 mPa s by the addition of DNase. The homogenate (5.6 l) was loaded directly on an expanded bed column (C-50) packed with the strong cation-exchanger Streamline SP. In the eluates, histone-like (HU) protein was identified as the main protein contaminant by sequence analysis. The thermodynamics and kinetics of rh-bFGF adsorption from the whole broth protein mixture were determined in view of competition and displacement effects with host-derived proteins. Optimal binding and elution conditions were developed with knowledge of the dependence of rh-bFGF adsorption isotherms on the salt concentration to allow direct application of eluates onto Heparin HyperD. This affinity support maintained selectivity and efficiency under CIP and over a wide range of flow-rates; both is advantageous for the flexibility of the purification protocol in view of a scalable process. Remaining DNA and HU protein were separated by Heparin HyperD. The endotoxin level decreased from approximately 1,000,000 EU/ml in the whole broth to 10 EU in 3 mg bFGF per ml. The final purification protocol yields >99% pure rh-bFGF as judged from SDS-PAGE and MALDI-TOF mass spectrometry with high mitogenic activity (ED50=1-1.5 ng/ml) of the lyophilized sample. In comparison to the conventional process, the overall protein recovery rose by 15% to 65% with saving time and costs.

Structural requirements of human tissue factor pathway inhibitor (TFPI) and heparin for TFPI-heparin interaction

Heparin affinity chromatography of synthetic peptide fragments mimicking tissue factor pathway inhibitor (TFPI) indicated that the minimal heparin binding sequence consists of 12 amino acid residues located at the C-terminal tail. Within this minimal sequence, Arg-257 and Arg-259 appeared to contribute most significantly to interaction with heparin. Affinity chromatography of TFPI using immobilized heparin derivatives regiospecifically desulfated at O-6 of the glucosamine residue, N-2 of the glucosamine residue, and/or O-2 of the iduronic acid residue indicated that all the sulfate groups in heparin appeared to be required for TFPI-heparin interaction. Among them, however, the 6-O-sulfate groups appeared to make the largest contribution to the interaction, while the 2-O-sulfate groups contributed the least. In vitro experiments on the inhibition of factor Xa by TFPI enhanced with native and chemically modified heparins afforded similar results.

Characterisation of silica-based heparin affinity sorbents from equilibrium binding studies on plasma fractions containing thrombin

The binding properties of rigid heparin sorbents, synthesised by end-point-attachment of heparin onto aminopropylderivatised silica through reductive amination, were characterised through batch-adsorption studies employing human plasma fractions containing thrombin. Thrombin was quantified using a chromogenic assay that had been specially modified for these studies. These investigations yielded information regarding the maximum adsorption capacities/stoichiometries and binding affinities for thrombin present in complex protein mixtures. Of the two types of heparin-silica evaluated, heparin-Fractosil 1000, with a pore size of 1000 A, displayed a capacity of 2.4 mol of thrombin/mol of heparin (mol T-mol H). This stoichiometry was significantly higher than the value of 1.8 mol T-mol H obtained for the commercial soft gel heparin-Sepharose CL-6B. Furthermore, the heparin-Fractosil 1000 sorbents were superior in capacity and binding site accessibility to heparin-LiChroprep Si60 sorbents, where the smaller pore size of 60 A largely restricts the ligand-protein interactions to the outer surface of the sorbent particles. Nevertheless, heparin-LiChroprep Si60 sorbents were useful, in that they simulated a non-porous particle system, in which intra-pore diffusion effects are eliminated. The batch adsorption results with these sorbents indicated that the adsorption involved both high and low binding affinity characteristics. This bimodal binding mechanism was also evident with the commercial heparin-Sepharose sorbent. Binding stoichiometries and affinities in the high concentration range were similar to values reported for a largely non-specific electrostatic thrombin-heparin interaction. Dissociation constants in the nanomolar range were observed in the low concentrations range. This stronger binding affinity is more similar to highly specific bio-affinity interactions. Thus, the results indicated that heparin-thrombin interactions with these systems involve both a weak electrostatic and a strong biospecific interaction component.

End point attached heparin affinity matrix

Heparin is a highly sulfated long-chain glycosaminoglycan utilized extensively for its anticoagulation properties, which has found widespread use as a general affinity ligand. The polysaccharide is composed of repeating units of uronic acid and glucosamine with great variability in sequence within the chain. The high degree of sulfation imparts strong acidity to the molecule and it may bond with many compounds simply by ionic interaction. In addition, it has been established that heparin contains certain specific monosaccharide sequences which act as unique binding sites for some proteins. For utilization as a biospecific affinity ligand it has been reported that heparin may optimally be immobilized by a single point of attachment through a terminal sugar residue. This method of immobilization allows unrestricted access to sequences within the polysaccharide chain required for biospecific interaction. Heparin immobilized to beaded agarose by single point attachment through its terminal formyl moiety was prepared. Chromatographic performance characteristics were evaluated using thrombin and antithrombin III as model compounds and elution profiles are presented. Additionally, stability of attachment was directly compared to several other commercially available supports. In conclusion, this end-point attached affinity matrix demonstrates high capacity and good stability compared with that of other methods of preparation.

Characterisation of silica-based heparin-affinity adsorbents through column chromatography of plasma fractions containing thrombin

Different heparin-silicas, synthesised in this laboratory via directional end-point attachment of heparin (H) onto various amino-derivatised silicas, have been evaluated in packed-bed and expanded-bed column chromatographic experiments using crude preparations of the therapeutic protein, thrombin (T). Adsorbent capacities, determined through batch adsorption experiments, were verified by employing frontal analysis in packed-bed systems. The performance of these adsorbents was also investigated in terms of thrombin purification factors and recoveries. The potential of the heparin-silicas was further examined in the expanded-bed column chromatographic mode using a scaled-up procedure. With heparin-Fractosil 1000 adsorbents, capacities of around 100,000 U thrombin/ml adsorbent could be achieved. Heparin-Fractosil 1000 adsorbents of intermediate heparin content (around 4 mg heparin/ml sorbent) displayed binding stoichiometries similar to that of the commercial heparin-Sepharose (2.6-2.7 mol T/mol H). Furthermore, binding stoichiometries were largely unaffected by increasing the heparin content on the heparin-Fractosil 1000 adsorbents from 0.8 to 4.6 mg of heparin/ml of sorbent. This result suggests that optimal binding site accessibilities for the thrombin-heparin interaction occurs at lower ligand density values. The binding capacity values determined from frontal analysis were confirmed by the recovery data, thus indicating minimal irreversible adsorption. Specific activities of ca. 2100 U/mg were obtained for thrombin when affinity-purified on these heparin-LiChroprep Si60 or heparin-Fractosil 1000 adsorbents. These values were higher than the maximum achievable purity obtained through alternative, multi-step chromatographic purification procedures reported by other investigators. These results indicated that the packed-bed performances with these silica-based adsorbents were superior to currently available commercial soft gel adsorbents, with the more dense heparin-silicas exhibiting very good potential for use in expanded-bed applications.

Purification of lipases, phospholipases and kinases by heparin-Sepharose chromatography

Heparin interacts with lipases, phospholipases and kinases. Immobilized heparin can be used for the purification of diacylglycerol and triacylglycerol lipases, phospholipases A2 and C and protein and lipid kinases. The use of heparin-Sepharose is an important development in analytical and preparative techniques for the separation and isolation of lipases, phospholipases and kinases.

Membrane chromatography for rapid purification of recombinant antithrombin III and monoclonal antibodies from cell culture supernatant

The task of purifying monoclonal antibodies (MAbs) and human recombinant antithrombin III (rATIII) from cell culture supernatant was carried out using two different approaches, both based on the use of membraneous matrices. The first approach employed a strongly acidic and a strongly basic membrane ion exchanger, which were evaluated for their ability to purify monoclonal antibodies and the human active recombinant antithrombin III from cell culture supernatant. Within minutes gram amounts of product could be purified in a high-flux system, specially developed for this purpose, achieving purities of 80% for MAbs and 75% for rATIII, respectively. The capacity of the acidic membrane ion exchanger for MAbs was found to be 1 mg/cm2 with recoveries up to 96% and that of the basic membrane ion exchanger for rATIII was 0.15 mg/cm2 with recoveries up to 91%. The second approach consisted of using heparin, a mucopolysaccharide with a strong affinity towards ATIII, coupled to amine-modified or epoxy-activated membranes by reductive amination, for the purification of rATIII. The ATIII binding capacities of the membranes were found to be 91 micrograms/cm2 for the amine-modified and 39 micrograms/cm2 for the epoxy-activated membrane, achieving purities of 75%. The coupling proved to be fairly stable over a period of 5 months and the membranes remained operable even after steam sterilization and treatment with sodium dodecyl sulphate. Final purification in both instances was carried out by gel filtration.

Hydrazido-derivatized supports in affinity chromatography

Many chemistries have been developed for the immobilization of ligands onto insoluble matrices for subsequent use in affinity systems. One such chemistry which has received little attention involves the use of hydrazido-derivatized solid supports. Hydrazine derivatives are strong nucleophiles which will react with a number of functional groups including aldehydes which may be generated on the oligosaccharide moieties of glycoconjugates by specific oxidation reactions. This paper presents a brief overview of the chemistries involved and the uses of hydrazido-derivatized solid supports for the site-directed immobilization of glycoconjugates. Specific examples from the literature on the uses of affinity matrices prepared by this method are cited.