A benzoboroxole-based affinity ligand for glycoprotein purification at physiological pH.

Developing ligands capable of carbohydrate recognition has become increasingly important as the essential roles of glycoproteins and glycolipids in a diverse array of cellular signaling, pathophysiology, and immune response mechanisms are elucidated. Effective ligands for the glycan portion of glycoproteins and glycolipids are needed for pre-enrichment proteomics strategies, as well as for the purification of individual glycoproteins from complex biological milieu encountered both in biochemistry research and bio-pharmaceutical development. In this work, we developed a carbohydrate specific affinity ligand for glycoprotein purification using a one-pot, multi-component synthesis reaction (Ugi synthesis) and an amine-functionalized benzoboroxole moiety immobilized on agarose beads. Benzoboroxoles are unique boronic acid derivatives that have recently been found to bind specifically to the cis-diol groups of carbohydrates at physiological pH, with superior affinity to any other Wulff-type boronic acid. The solid-phase affinity ligand developed herein specifically binds the carbohydrate moiety of the glycoprotein glucose oxidase, as well as a fluorescein isothiocyanate-dextran, as shown through deglycosylation binding studies. Additionally, the ligand is able to purify glucose oxidase from crude Escherichia coli lysate, at physiological pH, equitably to commercially available boronic acid-functionalized agarose beads that required alkaline pH conditions. Thus, this affinity ligand is a marked improvement on current, commercially available boronic acid-based glycoprotein enrichment matrices and has the potential to exhibit high individual glycoprotein specificity because of the additional functional groups available for variation on the Ugi scaffold.

A tailor-made "tag-receptor" affinity pair for the purification of fusion proteins.

A novel affinity "tag-receptor" pair was developed as a generic platform for the purification of fusion proteins. The hexapeptide RKRKRK was selected as the affinity tag and fused to green fluorescent protein (GFP). The DNA fragments were designed, cloned in Pet-21c expression vector and expressed in E. coli host as soluble protein. A solid-phase combinatorial library based on the Ugi reaction was synthesized: 64 affinity ligands displaying complementary functionalities towards the designed tag. The library was screened by affinity chromatography in a 96-well format for binding to the RKRKRK-tagged GFP protein. Lead ligand A7C1 was selected for the purification of RKRKRK fusion proteins. The affinity pair RKRKRK-tagged GFP with A7C1 emerged as a promising solution (Ka of 2.45×10(5) M(-1) ). The specificity of the ligand towards the tag was observed experimentally and theoretically through automated docking and molecular dynamics simulations.

Inhibitory effects of in vivo oxidized high-density lipoproteins on platelet aggregation: evidence from patients with abetalipoproteinemia.

There is evidence that high-density lipoproteins (HDLs) may regulate platelet function, but disparate results exist regarding the effects of oxidized HDLs on platelets. The objective of our study was to determine the role of in vivo oxidized HDLs on platelet aggregation. Platelet aggregation and redox status were investigated in 5 patients with abetalipoproteinemia (ABLP) or homozygous hypobetalipoproteinemia, two rare metabolic diseases characterized by the absence of apolipoprotein B-containing lipoproteins, compared to 5 control subjects. Platelets isolated from plasma of patients with ABLP aggregated 4 to 10 times more than control platelets, depending on the agonist. By contrast, no differences in the extent of platelet aggregation were observed between ABLP platelet-rich plasma (PRP) and control PRP, suggesting the presence of a protective factor in ABLP plasma. ABLP HDLs inhibited agonist-induced platelet aggregation by binding to SR-BI, while control HDLs had no effect. On the other hand, lipoprotein-deficient plasma from patients with ABLP did not inhibit platelet aggregation. Severe oxidative stress was evidenced in patients with ABLP. Compared to control HDLs, ABLP HDLs showed a 40% decrease of α-tocopherol and an 11-fold increased malondialdehyde concentration. These results demonstrate that in vivo oxidized HDLs do not lose their antiaggregatory properties despite oxidation.

A biomimetic Protein G affinity adsorbent: an Ugi ligand for immunoglobulins and Fab fragments based on the third IgG-binding domain of Protein G.

This work reports the development of a synthetic affinity adsorbent for immunoglobulins based on the Fab-binding domain of Streptococcal Protein G (SpG-domain III). The ligand (A2C7I1) was synthesized by the four-component Ugi reaction to generate a substituted peptoidal scaffold mimicking key amino acid residues of SpG. Computer-aided analysis suggests a putative binding site on the CH 1 domain of the Fab molecule. In silico studies, supported by affinity chromatography in comparison with immobilized SpG, as well as analytical characterization by liquid chromatography/electrospray ionization-mass spectrometry and (1) H nuclear magnetic resonance of the ligand synthesized in solution, indicated the authenticity and suitability of the designed ligand for the purification of immunoglobulins. The immobilized ligand displayed an apparent static binding capacity of ~17 mg IgG ml(-1) and a dissociation constant of 5.34 × 10(-5) M. Preparative chromatography demonstrated the ability of the immobilized ligand to purify IgG and Fab fragments from crude mammalian and yeast cell cultures, under near physiological ionic strength and pH, to yield proteins of 99% and 93% purity, respectively.

Design, synthesis, and assessment of a de novo affinity adsorbent for the purification of recombinant human erythropoietin.

This work describes the assessment of a de novo synthetic affinity ligand for recombinant human erythropoietin (rHuEPO), based on the multicomponent Ugi reaction. Four Ugi ligands were designed based on the X-ray crystallographic structure of the complex between human erythropoietin and site 1 of its cell-surface receptor (EPObp)2 ; screening of the ligands with pure rHuEPO samples identified a lead ligand (A9C10I8) immobilized on aldehyde-functionalized agarose beads, which was able to bind and elute erythropoietin, as determined by SDS-PAGE and Western blot analyses. Furthermore, small-scale affinity chromatography performed on the immobilized adsorbent showed its ability to isolate rHuEPO from a spiked mammalian cell supernatant with a purity of ∼80%, as estimated with gel densitometry. This approach could lead to the development of a cost-effective downstream process for rHuEPO, as an alternative to the current multi-step purification protocols.

Development of miniaturized immunoassay: influence of surface chemistry and comparison with enzyme-linked immunosorbent assay and Western blot.

Protein microarray technology provides a useful approach for the simultaneous serodetection of various antibodies in low sample volumes. To implement functional protein microarrays, appropriate surface chemistry must be designed so that both the protein structure and the biological activity can be retained. In the current study, two surface chemistries for protein microarrays and immunofluorescent assays were developed. Glass slides were functionalized with N-hydroxysuccinimide (NHS) ester via a monofunctional silane or maleic anhydride-alt-methyl vinyl ether (MAMVE) copolymer to allow covalent grafting of histone proteins. Analytical performance of these microarrays was then evaluated for the detection of anti-histone autoantibodies present in the sera of patients suffering from a systemic autoimmune disease, namely systemic lupus erythematosus (SLE), and the results were compared with those of the classical enzyme-linked immunosorbent assay (ELISA) and Western blot. The detection limit of our MAMVE copolymer microarrays was 50-fold lower than that of the classical ELISA. Furthermore, 100-fold less volume of biological samples was required with these miniaturized immunoassays.

A carbohydrate-binding affinity ligand for the specific enrichment of glycoproteins.

One challenge facing the production of glycoprotein therapeutics is the lack of stable and selective affinity ligands for their enrichment. Synthetic affinity ligands based on the solid phase multi-component Ugi reaction represent a desirable option, particularly those incorporating benzoboroxole and its derivatives, which have been shown to enrich glycoproteins under physiological conditions. Thus, an Ugi ligand, A21C11I8, comprising 5-amino-2-hydroxymethylphenylboronic acid was synthesised on aldehyde-functionalised Sepharose™. Immobilised A21C11I8 displayed affinity for the glycosylated protein, glucose oxidase (GOx), which bound primarily through its glycan moiety. The ligand had a preference for sugar alcohols and the furanose form of the monosaccharides tested. Compared with immobilised 3-aminophenylboronic acid and Concanavalin A, the Ugi ligand was able to purify GOx from spiked Escherichia coli supernatants with retention of its maximum enzymatic activity and protein recovery. Glycan profiles of human immunoglobulin G tested on A21C11I8 columns suggested that the adsorbent possesses the potential to resolve sialylated and neutral glycoforms. The benzoboroxole-functionalised Ugi ligand may find application in selective glycoform separation.

Mild and cost-effective green fluorescent protein purification employing small synthetic ligands.

The green fluorescent protein (GFP) is a useful indicator in a broad range of applications including cell biology, gene expression and biosensing. However, its full potential is hampered by the lack of a selective, mild and low-cost purification scheme. In order to address this demand, a novel adsorbent was developed as a generic platform for the purification of GFP or GFP fusion proteins, giving GFP a dual function as reporter and purification tag. After screening a solid-phase combinatorial library of small synthetic ligands based on the Ugi-reaction, the lead ligand (A4C7) selectively recovered GFP with 94% yield and 94% purity under mild conditions and directly from Escherichia coli extracts. Adsorbents containing the ligand A4C7 maintained the selectivity to recover other proteins fused to GFP. The performance of A4C7 adsorbents was compared with two commercially available methods (immunoprecipitation and hydrophobic interaction chromatography), confirming the new adsorbent as a low-cost viable alternative for GFP purification.

Biomimetic affinity ligands for immunoglobulins based on the multicomponent Ugi reaction.

Affinity chromatography is the method of choice for biomolecule separation and isolation with highly specific target recognition; it is ideally suited to the purification of immunotherapeutic proteins (i.e., mAbs). Conventional affinity purification protocols are based on natural immunoglobulin (Ig)-binding proteins, which are expensive to produce, labile, unstable, and exhibit lot-to-lot variability. Biological ligands are now being replaced by cost-effective, synthetic ligands, derived from the concepts of rational design and combinatorial chemistry, aided by in silico approaches. In this chapter, we describe a new synthetic procedure for the development of affinity ligands for immunoglobulins based on the multicomponent Ugi reaction. The lead ligand developed herein is specific for the IgG-Fab fragment and mimics Protein L (PpL), an IgG-binding protein isolated from Peptostreptococcus magnus strains and usually used for the purification of antibodies and their fragments.

A synthetic Protein G adsorbent based on the multi-component Ugi reaction for the purification of mammalian immunoglobulins.

Numerous efforts have been devoted to develop synthetic affinity ligands mimicking natural immunoglobulin-binding proteins, such as Proteins A and L, in order to overcome intrinsic drawbacks involving their high cost and acidic pH elution. However, few reports have focused on a Protein G mimic. This work describes the use of the solid phase multi-component Ugi reaction to generate a low cost, rationally designed, affinity ligand to mimic Protein G for the purification of mammalian immunoglobulins, including the heavy-chain only camelid IgGs, with effective elution at neutral pH. An aldehyde-functionalised Sepharose™ resin constituted one component (aldehyde) of the four-component Ugi reaction, whilst the other three components (a primary or secondary amine, a carboxylic acid and an isonitrile) were varied to generate a tri-substituted Ugi scaffold, with a wide range of functionality, suitable for mimicking peptides for immunoglobulin purification. Ligand A2C11I1 was designed to mimic Asn35 and Trp43 of Protein G (PDB: 1FCC) and in silico docking into the Fc domain showed a key binding interface closely resembling native Protein G. This candidate ligand demonstrated affinity towards IgGs derived from human, cow, goat, mouse, sheep, pig, rabbit and rat serum, chicken IgY and recombinant camelid Fc domain, out of which cow and sheep IgG demonstrated 100% binding under the conditions selected. Preparative chromatography of IgG from human serum under a standardised buffer regime eluted IgG of ∼65% purity, compared to ∼62% with Protein G. This adsorbent achieved highest elution of IgG at neutral pH (0.1M sodium phosphate pH 7.0, 30%, v/v, ethylene glycol), an advantage for purifying antibodies sensitive to extremes of pH. The ligand demonstrated a static binding capacity of 24.6 mg Ig G ml⁻¹ resin and a dissociation constant (K(d)) of 4.78 × 10⁻6 M. The solid phase Ugi scaffold provides a strategy to develop pseudo-biospecific ligands to purify immunoglobulins and other potentially high-value biotherapeutic proteins.

A generic surface chemistry for peptide microarrays implementation: application to the detection of anti-H3 antibody.

Peptide microarray can be implemented by immobilization of peptides on a solid support or by direct on-chip peptide synthesis (OCPS). In the first case, peptide primary sequences can be ensured prior to their immobilization but structural diversity is achieved at high cost in terms of reagents. In the second case, high diversity is achieved with low amount of reagents but the primary and secondary structures cannot be ascertained. In both cases, the immobilization step will influence the overall biological activity. We proposed a strategy where direct peptide on-chip synthesis and peptide immobilization are viewed as complementary approaches. In a first step, OCPS is envisioned for the screening and selection of biologically relevant peptides. In a second step, selected peptides would be synthesized on resin, qualified and immobilized for implementing microarrays (i.e. for diagnosis). A versatile surface chemistry for both OCPS and peptide immobilization was developed allowing for an identical physico-chemical environment for both implementation strategies. In the present report, a 16 mer peptide corresponding to the human histone H3 epitope was synthesized on an amino-functionalized support. Surface stability (including upon deprotection steps) and peptide primary and secondary structures were assessed with Cy3-streptavidine conjugates and with immunoassays. Peptides, either on-chip synthesized or immobilized, exhibited a similar biological activity.

Acid deprotection of covalently immobilized peptide probes on glass slides for peptide microarrays.

Protein microarray technology has shown great advancements in the field of biomedical research and diagnosis, it allows to study and understand protein activities and protein - ligand interactions (e.g. detection of antigen-autoantibody interaction in autoimmune diseases. Autoantibodies are frequently targeted against antigens of the cell nucleus (double and single stranded DNA, histones, and nuclear antigens). The biological activities of proteins (e.g. enzymes, antibodies...) are controlled by peptides sequences of the active site. Consequently, we were interested in the investigation of peptide microarrays in order to further implement in situ peptide synthesis, in particular, deprotection reaction on glass supported peptides. In this work, a protected and biotinylated synthetic peptide was covalently immobilized onto amino functionalized glass surface by activation of its the C-terminus; this allows to orientate the peptide onto the surface. The peptide contains a fragment of the C-terminal end of the human histone H3 protein. The immobilized peptide was then deprotected by using concentrated trifluoroacetic acid solution. After the deprotection, surface stability and peptide grafting density were evaluated by indirect labelling of the immobilized peptide using Cy3 streptavidin conjugates. We also studied biological interaction of IgG polyclonal anti-histone H3 antibody with the immobilized peptide epitope to insure the efficiency of the acid deprotection. The specificity of the antibody interaction with the protected versus non protected peptides. This approach may be applied to in situ synthetic and prototected peptides, in order to elaborate a micro-immunoassay prototype for measurement of peptide-protein interactions on high density microarrays, and detection of antibodies in biological fluids such as serum.