The literature on affinity chromatography

Capture and qualitative analysis of the activated Fc receptor complex from live cells

This unit describes the isolation of activated Fc receptor complexes from RAW 264.7 macrophages using live-cell affinity receptor chromatography (LARC). The Fc receptor complex is activated and captured by IgG-coated microbeads on the surface of live macrophages. After the cells are disrupted, the receptor complexes are isolated by washing and sucrose gradient ultracentrifugation. Soluble proteins associated with the receptor complex are then eluted from the beads using a stepwise series of salt buffers and aqueous acetonitrile. The eluted proteins and the residual insoluble proteins on the beads can then be digested with trypsin and subjected to liquid chromatography, electrospray ionization, and tandem mass spectrometry (LC-ESI-MS/MS). Controls include IgG-coated beads incubated with crude cell lysates or growth medium and beads coated with oxidized LDL or bovine serum albumin. Using this method, proteins present in IgG-FcR complexes can be distinguished from those in control scavenger receptor complexes (oxLDL or BSA). Thus, LARC is capable of detecting specific members of IgG receptor supramolecular complexes.

Mass spectrometry of peptides and proteins from human blood

It is difficult to convey the accelerating rate and growing importance of mass spectrometry applications to human blood proteins and peptides. Mass spectrometry can rapidly detect and identify the ionizable peptides from the proteins in a simple mixture and reveal many of their post-translational modifications. However, blood is a complex mixture that may contain many proteins first expressed in cells and tissues. The complete analysis of blood proteins is a daunting task that will rely on a wide range of disciplines from physics, chemistry, biochemistry, genetics, electromagnetic instrumentation, mathematics and computation. Therefore the comprehensive discovery and analysis of blood proteins will rank among the great technical challenges and require the cumulative sum of many of mankind's scientific achievements together. A variety of methods have been used to fractionate, analyze and identify proteins from blood, each yielding a small piece of the whole and throwing the great size of the task into sharp relief. The approaches attempted to date clearly indicate that enumerating the proteins and peptides of blood can be accomplished. There is no doubt that the mass spectrometry of blood will be crucial to the discovery and analysis of proteins, enzyme activities, and post-translational processes that underlay the mechanisms of disease. At present both discovery and quantification of proteins from blood are commonly reaching sensitivities of ∼1 ng/mL.

A specific immunoprecipitation method for isolating isoforms of insulin-like growth factor binding protein-3 from serum

BACKGROUND

This report describes an in-house developed immunoprecipitation method to isolate insulin-like growth factor binding protein-3 (IGFBP-3) and its isoforms from serum. The method was compared to other existing immunoprecipitation methods. The study of IGFBP-3 isoforms is relevant for further studies on congenital defects in glycosylation (CDG), galactosemia, and alcoholic liver cirrhosis.

METHODS

Monoclonal and/or polyclonal anti-human IGFBP-3 antibodies were covalently immobilised on protein-A Sepharose beads using dimethyl pimelimidate as cross-linker. By incubation with these immobilised antibodies, intact IGFBP-3 and fragments of IGFBP-3 were isolated from serum. Enzyme-linked immunosorbent assay (ELISA) and one-dimensional gel electrophoresis (1-DE) experiments were performed to define the optimal immunoprecipitation method. Isolated proteins were separated by 1-DE and two-dimensional gel electrophoresis (2-DE) and visualised by Western blotting.

RESULTS

ELISA and 1-DE results illustrated that an optimal isolation was performed using PBS for the incubation with serum. Laemmli sample buffer, containing 2-amino-2-(hydroxymethyl)-1,3-propanediol hydrochloride and sodium dodecyl sulfate, or urea/CHAPS was optimal for the elution. Clinical validation was performed using CDG-Ia serum samples. The 2-DE experiments showed characteristic isoform patterns for CDG-Ia.

CONCLUSIONS

The optimized in-house developed immunoprecipitation method resulted in specific detection of IGFBP-3 isoforms and is suitable for further studies on glycosylation defects.

Metal-chelate affinity precipitation of proteins using responsive polymers

Affinity precipitation of proteins uses polymers capable of reversible soluble-insoluble transitions in response to small environmental changes (temperature, pH or solvent composition). Here we describe protocols for (i) the synthesis of responsive polymers with specific affinity to target proteins and (ii) the purification of proteins using these polymers. The purification is based on precipitation of the affinity complex between the protein and the polymer, which is induced by environmental changes. This separation strategy is simpler and more cost effective than conventional affinity column chromatography. Specifically, we describe the synthesis of thermoresponsive 1-vinylimidazole:N-isopropylacrylamide copolymers. The whole procedure takes 2-3 h when applied to purification of recombinant His-tag proteins or proteins with natural metal binding groups by means of metal chelate affinity precipitation. Optimization of the polymer composition and the type of chelating ions allows for target protein yields of 80% and higher.

The use of selective adsorbents in capillary electrophoresis-mass spectrometry for analyte preconcentration and microreactions: a powerful three-dimensional tool for multiple chemical and biological applications

Much attention has recently been directed to the development and application of online sample preconcentration and microreactions in capillary electrophoresis using selective adsorbents based on chemical or biological specificity. The basic principle involves two interacting chemical or biological systems with high selectivity and affinity for each other. These molecular interactions in nature usually involve noncovalent and reversible chemical processes. Properly bound to a solid support, an "affinity ligand" can selectively adsorb a "target analyte" found in a simple or complex mixture at a wide range of concentrations. As a result, the isolated analyte is enriched and highly purified. When this affinity technique, allowing noncovalent chemical interactions and biochemical reactions to occur, is coupled on-line to high-resolution capillary electrophoresis and mass spectrometry, a powerful tool of chemical and biological information is created. This paper describes the concept of biological recognition and affinity interaction on-line with high-resolution separation, the fabrication of an "analyte concentrator-microreactor", optimization conditions of adsorption and desorption, the coupling to mass spectrometry, and various applications of clinical and pharmaceutical interest.

Rapid optimization of immunoadsorbent characteristics

Immunoaffinity chromatography is employed in many research areas. We have developed an assay system that overcomes some of the tediousness and uncertainty in dealing with immunoadsorbents (IA). The preparation of IA and the effect of various procedures on the dissociation of antigen-antibody complex and the regeneration of IA are rapidly screened by polyacrylamide-gel electrophoresis in the presence of sodium dodecyl sulphate. Non-covalently bound proteins are dissociated and separated during the electrophoresis from IA beads. A wide variety of associative and dissociative conditions can be tested on small amounts of IA. Information about biospecifially and non-biospecifically adsorbed proteins can also be obtained. By using relatively small volumes of media containing either an antigen or another biospecific molecule, the optimal parameters for affinity chromatography (specificity, binding capacity, efficiency of solvents in dissociation of the complex and their effect on the adsorbent), or even for ion-exchange chromatography, can be determined without first performing several time- and material-consuming chromatographic experiments.

Use of affinity elution chromatography for the microassay of adenosine 3':5'-monophosphate

Using the principle of affinity elution chromatography, a microassay has been developed for the determination of picomolar and even smaller quantities of adenosine 3'.5' -monophosphate (cyclic AMP) in biological samples. In principle, cyclic AMP along with the other anions is adsorbed onto an anion exchange cellulose and subsequently, the cyclic nucleotide is specifically eluted with cyclic-AMP -dependent protein kinase. In the actual assay cyclic AMP is determined by competitive displacement of radiolabelled cyclic AMP by non-labelled cyclic nucleotide. The described procedure results in a linear dependence for the displacement of the radioactive nucleotide on cyclic AMP concentration and obviates the usual procedure of sample enrichment by lyophilization. The degree of interference of different nucleotides including cyclic GMP was found to be minimal and in this respect the use affinity elution chromatography was comparable to radioimmunoassay.

Membrane-bound F1 ATPase from Micrococcus Sp. ATCC 398E. Purificationa and characterization ny affinity chromatography

A chemically reactive ATP analogue, 6-[(3-carboxy-4-nitrophenyl)thio]-9-beta-D-ribofuranosylpurine 5'-triphosphate (Nbs6ITP) has been synthesized. It has the ability to form stable thioether bonds between the 6-position of the purine ring and aliphatic mercapto groups. The nucleotide moiety of the reagent has been covalently bound to agarose, via iminobispropylamine and N-acetyl-homocysteine as space with the purpose of producing an affinity chromatography material. The affinity matrix binds solubilized F1 ATPase from a crude extract of Micrococcus sp. membranes. Afterwards the enzyme can be selectively eluted from the column at a defined ATP concentration. This method is superior to the conventional purification with respect to speed and convenince of the preparation. The affinity chromatography leads in a one-step process to the same purity to enzyme, substituting several steps of the conventional method. In addition, the affinity matrix was used for binding studies. Although the presence of Mg2+ ions is a prerequisite for the hydrolysis of nucleoside 5'-triphosphates, evidence is presented indicating that the binding of the nucleoside triphosphates to highly purified F1 ATPase from Micrococcus sp. appears not to be influenced by Mg2+ ion concentrations so far examined.