Affinity chromatography on immobilized dyes

DNA aptamer-based affinity chromatography system for purification of recombinant proteins tagged with lysine tag

Affinity chromatography (AC) is one of the techniques widely used for the purification of recombinant proteins. In our previous study, we presented a successful application of the Argi system [1] for the purification of recombinant proteins, based on the specific interaction between an arginine tag and a DNA aptamer. Exploring the possible application of positively charged peptide tags in the purification of recombinant proteins, in this study we developed and characterized an AC system based on the specific and reversible interaction between a DNA aptamer and a lysine tag (Lys-tag) comprising five lysine residues (5 K). We optimized the length of both the selected DNA aptamer and Lys-tag which were named B5K aptamer and 5K-tag, respectively. The results showed that the stability of the B5K aptamer and 5K-tag was dependent on the presence of potassium ions. The conditions for mild elution of 5K-tagged protein from B5K aptamer were determined. Our study proved that the developed system can be used for the purification of recombinant proteins from Escherichia coli total protein extracts.

Inspirations of Biomimetic Affinity Ligands: A Review

Affinity chromatography is a well-known method dependent on molecular recognition and is used to purify biomolecules by mimicking the specific interactions between the biomolecules and their substrates. Enzyme substrates, cofactors, antigens, and inhibitors are generally utilized as bioligands in affinity chromatography. However, their cost, instability, and leakage problems are the main drawbacks of these bioligands. Biomimetic affinity ligands can recognize their target molecules with high selectivity. Their cost-effectiveness and chemical and biological stabilities make these antibody analogs favorable candidates for affinity chromatography applications. Biomimetics applies to nature and aims to develop nanodevices, processes, and nanomaterials. Today, biomimetics provides a design approach to the biomimetic affinity ligands with the aid of computational methods, rational design, and other approaches to meet the requirements of the bioligands and improve the downstream process. This review highlighted the recent trends in designing biomimetic affinity ligands and summarized their binding interactions with the target molecules with computational approaches.

High-Throughput Screening of Dye-Ligands for Chromatography

Dye-ligand-based chromatography has become popular after Cibacron Blue, the first reactive textile dye, found application for protein purification. Many other textile dyes have since been successfully used to purify a number of proteins and enzymes. While the exact nature of their interaction with target proteins is often unclear, dye-ligands are thought to mimic the structural features of their corresponding substrates, cofactors, etc. The dye-ligand affinity matrices are therefore considered pseudo-affinity matrices. In addition, dye-ligands may simply bind with proteins due to electrostatic, hydrophobic, and hydrogen bonding interactions. Because of their low cost, ready availability, and structural stability, dye-ligand affinity matrices have gained much popularity. The choice of a large number of dye structures offers a range of matrices to be prepared and tested. When presented in the high-throughput screening mode, these dye-ligand matrices serve as a formidable tool for protein purification. One could pick from the list of dye-ligands already available or build a systematic library of such structures for use. A high-throughput screen may be set up to choose the best dye-ligand matrix as well as ideal conditions for binding and elution, for a given protein. The mode of operation could be either manual or automated. The technology is available to test the performance of dye-ligand matrices in small volumes in an automated liquid handling workstation. Screening a systematic library of dye-ligand structures can help establish a structure-activity relationship. While the origins of dye-ligand chromatography lie in exploiting pseudo-affinity, it is now possible to design very specific biomimetic dye structures. High-throughput screening will be of value in this endeavor as well.

Affinity Membranes and Monoliths for Protein Purification

Affinity capture represents an important step in downstream processing of proteins and it is conventionally performed through a chromatographic process. The performance of this step highly depends on the type of matrix employed. In particular, resin beads and convective materials, such as membranes and monoliths, are the commonly available supports. The present work deals with non-competitive binding of bovine serum albumin (BSA) on different chromatographic media functionalized with Cibacron Blue F3GA (CB). The aim is to set up the development of the purification process starting from the lab-scale characterization of a commercially available CB resin, regenerated cellulose membranes and polymeric monoliths, functionalized with CB to identify the best option. The performance of the three different chromatographic media is evaluated in terms of BSA binding capacity and productivity. The experimental investigation shows promising results for regenerated cellulose membranes and monoliths, whose performance are comparable with those of the packed column tested. It was demonstrated that the capacity of convective stationary phases does not depend on flow rate, in the range investigated, and that the productivity that can be achieved with membranes is 10 to 20 times higher depending on the initial BSA concentration value, and with monoliths it is approximately twice that of beads, at the same superficial velocity.

Electrocatalytic artificial carbonylation assay for observation of human serum albumin inter-individual properties

Human serum albumin (HSA) is a multifunctional protein with ligand binding, transporting and buffering properties. Posttranslational modifications and ligand binding processes are closely related to albumin final functional status. In the last few decades, HSA has been characterized using a broad spectrum of methods, but quantitative data on the HSA's modifications among individuals have not been reported. The investigations presented here are based on the non-denaturing electrocatalytic screening of HSA samples isolated from the blood serum of healthy subjects. The electrocatalytic responses of the native protein (R_nat) varied depending on its modifications among individuals, which enable us to express the inter-individual variability. Consequently, the native HSA samples were subjected to ex vivo carbonylation with 50 mM methylglyoxal for 36 h. The differences between R_nat and the responses of artificially carbonylated protein (R_mod) corresponded with inter-individual binding capacity variations (ΔR = R_nat-R_mod). The coefficients of variation for the R_nat and ΔR values of purified HSA samples were estimated to be 8.5 and 23.2%, respectively. A sensitive non-denaturing electrocatalytic assay was utilized to provide new data about albumin inter-individual variations and evaluate its oxidative modifications and binding capacity, which could be used for further studies targeting not only on HSA but also other clinically important proteins.

Affinity chromatography: A versatile technique for antibody purification

Antibodies continue to be extremely utilized entities in myriad applications including basic research, imaging, targeted delivery, chromatography, diagnostics, and therapeutics. At production stage, antibodies are generally present in complex matrices and most of their intended applications necessitate purification. Antibody purification has always been a major bottleneck in downstream processing of antibodies, due to the need of high quality products and associated high costs. Over the years, extensive research has focused on finding better purification methodologies to overcome this holdup. Among a plethora of different techniques, affinity chromatography is one of the most selective, rapid and easy method for antibody purification. This review aims to provide a detailed overview on affinity chromatography and the components involved in purification. An array of support matrices along with various classes of affinity ligands detailing their underlying working principles, together with the advantages and limitations of each system in purifying different types of antibodies, accompanying recent developments and important practical methodological considerations to optimize purification procedure are discussed.

Syntheses of 2-substituted 1-amino-4-bromoanthraquinones (bromaminic acid analogues) - precursors for dyes and drugs

Anthraquinone (AQ) derivatives play a prominent role in medicine and also in textile industry. Bromaminic acid (1-amino-4-bromoanthraquinone-2-sulfonic acid) is an important precursor for obtaining dyes as well as biologically active compounds through the replacement of the C4-bromo substituent with different (ar)alkylamino residues. Here we report methods for the synthesis of bromaminic acid analogues bearing different substituents at the 2-position of the anthraquinone core. 1-Aminoanthraquinone was converted to its 2-hydroxymethyl-substituted derivative which, under different reaction conditions, yielded the corresponding carbaldehyde, carboxylic acid, and nitrile derivatives. The latter was further reacted to obtain 1-amino-2-tetrazolylanthraquinone. Subsequent bromination using bromine in DMF led to the corresponding bromaminic acid derivatives in excellent isolated yields (>90%) and high purities. Alternatively, 1-amino-4-bromo-2-hydroxymethylanthraquinone could be directly converted to the desired 2-substituted bromaminic acid analogues in high yields (85-100%). We additionally report the preparation of bromaminic acid sodium salt and 1-amino-2,4-dibromoanthraquinone directly from 1-aminoanthraquinone in excellent yields (94-100%) and high purities. The synthesized brominated AQs are valuable precursors for the preparation of AQ drugs and dyes.

High-throughput screening of dye-ligands for chromatography

Dye-ligand-based chromatography has become popular after Cibacron Blue, the first reactive textile dye, found application for protein purification. Many other textile dyes have since been successfully used to purify a number of proteins and enzymes. While the exact nature of their interaction with target proteins is often unclear, dye-ligands are thought to mimic the structural features of their corresponding substrates, cofactors, etc. The dye-ligand affinity matrices are therefore considered pseudo-affinity matrices. In addition, dye-ligands may simply bind with proteins due to electrostatic, hydrophobic, and hydrogen-bonding interactions. Because of their low cost, ready availability, and structural stability, dye-ligand affinity matrices have gained much popularity. Choice of a large number of dye structures offers a range of matrices to be prepared and tested. When presented in the high-throughput screening mode, these dye-ligand matrices provide a formidable tool for protein purification. One could pick from the list of dye-ligands already available or build a systematic library of such structures for use. A high-throughput screen may be set up to choose best dye-ligand matrix as well as ideal conditions for binding and elution, for a given protein. The mode of operation could be either manual or automated. The technology is available to test the performance of dye-ligand matrices in small volumes in an automated liquid-handling workstation. Screening a systematic library of dye-ligand structures can help establish a structure-activity relationship. While the origins of dye-ligand chromatography lay in exploiting pseudo-affinity, it is now possible to design very specific biomimetic dye structures. High-throughput screening will be of value in this endeavor as well.

Affinity chromatography as a tool for antibody purification

The global antibody market has grown exponentially due to increasing applications in research, diagnostics and therapy. Antibodies are present in complex matrices (e.g. serum, milk, egg yolk, fermentation broth or plant-derived extracts). This has led to the need for development of novel platforms for purification of large quantities of antibody with defined clinical and performance requirements. However, the choice of method is strictly limited by the manufacturing cost and the quality of the end product required. Affinity chromatography is one of the most extensively used methods for antibody purification, due to its high selectivity and rapidity. Its effectiveness is largely based on the binding characteristics of the required antibody and the ligand used for antibody capture. The approaches used for antibody purification are critically examined with the aim of providing the reader with the principles and practical insights required to understand the intricacies of the procedures. Affinity support matrices and ligands for affinity chromatography are discussed, including their relevant underlying principles of use, their potential value and their performance in purifying different types of antibodies, along with a list of commercially available alternatives. Furthermore, the principal factors influencing purification procedures at various stages are highlighted. Practical considerations for development and/or optimizations of efficient antibody-purification protocols are suggested.

Nanoparticle technology: amplifying the effective sensitivity of biomarker detection to create a urine test for hGH

Several clinical-grade immunoassays exist for the specific measurement of hGH or its isoforms in blood but there is an urgent need to apply these same reliable assays to the measurement of hGH in urine as a preferred 'non-invasive' biofluid. Unfortunately, conventional hGH immunoassays cannot attain the sensitivity required to detect the low concentrations of hGH in urine. The lowest limit of sensitivity for existing hGH immunoassays is >50 pg/mL, while the estimated concentration of urinary hGH is about 1 pg/m-50 times lower than the sensitivity threshold. We have created novel N-isopropylacrylamide (NIPAm)-based hydrogel nanoparticles functionalized with an affinity bait. When introduced into an analyte-containing solution, the nanoparticles can perform, in one step, (1) complete harvesting of all solution phase target analytes, (2) full protection of the captured analyte from degradation and (3) sequestration of the analyte, effectively increasing the analyte concentration up to a hundredfold. N-isopropylacrylamide nanoparticles functionalized with Cibacron Blue F3GA bait have been applied to raise the concentration of urinary hGH into the linear range of clinical grade immunoassays. This technology now provides an opportunity to evaluate the concentration of hGH in urine with high precision and accuracy.

Purification, properties, and kinetic studies of cytoplasmic malate dehydrogenase from Taenia solium cysticerci

Malate dehydrogenase (L: -malate: NAD oxidoreductase, EC 1.1.1.37) from the cytoplasm of Taenia solium cysticerci (cMDHTs) was purified 48-fold through a four-step procedure involving salt fractionation, ionic exchange, and dye affinity chromatography. cMDHTs had a native M (r) of 64,000, while the corresponding value per subunit, obtained under denaturing conditions, was 32,000. The enzyme is partially positive, with an isoelectric point of 8.7, and had a specific activity of 2,615 U mg(-1) in the reduction of oxaloacetate. The second to the 21st amino acids from cMDHTs N-terminal group were P G P L R V L I T G A A G Q I A Y N L S. This sequence is 100% identical to that of Echinococcus granulosus. Basic kinetic parameters were determined for this enzyme. The optimum pH for enzyme reaction was at 7.6 for oxaloacetate reduction and at 9.6 for malate oxidation. K (m) values for oxaloacetate, malate, NAD, and NADH were 2.4, 215, 50, and 48 microM, respectively. V (max) values for the substrates and cosubstrates as described above were 1,490, 87.8, 104, and 1,714 micromol min(-1) mg(-1). Several NAD analogs, structurally altered in either the pyridine or purine moiety, were observed to function as coenzymes in the reaction catalyzed by the purified malate dehydrogenase. cMDHTs activity was uncompetitive inhibited by arsenate for both the forward (Ki = 8.2 mM) and reverse (Ki = 77 mM) reactions. The mechanism of the cMDHTs reactivity was investigated kinetically by the product inhibition approach. The results of this study are qualitatively consistent with an Ordered Bi Bi reaction mechanism, in which only the coenzymes can react with the free enzyme.

Purification and characterization of UDP-glucose : curcumin glucoside 1,6-glucosyltransferase from Catharanthus roseus cell suspension cultures

Catharanthus roseus cell suspension cultures converted exogenously added curcumin to a series of curcumin glucosides that possessed drastically enhanced water solubility. A cDNA clone encoding a glucosyltransferase responsible for glucosylation of curcumin to form curcumin 4'-O-glucoside was previously isolated, and in the present study a novel sugar-sugar glycosyltransferase, UDP-glucose:curcumin glucoside glucosyltransferase (UCGGT), was purified approximately 900-fold to apparent homogeneity from cultured cells of C. roseus. The purified enzyme (0.2% activity yield) catalyzed 1,6-glucosylation of curcumin 4'-O-glucoside to yield curcumin 4'-O-gentiobioside. The molecular weight and isoelectric point were estimated to be about 50 kDa and 5.2, respectively. The enzyme showed a pH optimum between 7.5 and 7.8. Both flavonoid 3-O- and 7-O-glucosides were also preferred acceptor substrates of the enzyme, whereas little activity was shown toward simple phenolic glucosides such as arbutin and glucovanillin, cyanogenic glucoside (prunasin) or flavonoid galactoside. These results suggest that UCGGT may also function in the biosynthesis of flavonoid glycosides in planta.

Microwave-assisted preparation of affinity medium

Microwave assistance was used for preparing polyethylene glycol (PEG)-Cibacron blue 3GA and Sepharose CL-4B-Cibacron blue 3GA affinity materials. The former was used as the affinity macroligand in a PEG-dextran aqueous two-phase system for purification of alcohol dehydrogenase and EcoRI. The Sepharose CL-4B-Cibacron blue 3GA was used for affinity chromatography of the above two enzymes. It was found that microwave assistance could reduce the time of PEG-dye preparation to 5 min (from 7h). Similarly, Sepharose CL-4B-Cibacron blue 3GA preparation time could be reduced to 21 min (from 3.5h). The performances of affinity macroligand PEG-dye and the affinity medium Sepharose-dye prepared by conventional methods and with microwave assistance were similar during purification of these enzymes.

Preparation of dye–ligand affinity chromatographic packings based on monodisperse poly(glycidylmethacrylate-co-ethylenedimethacrylate) beads and their chromatographic properties

Monodisperse porous particles, poly(glycidylmethacrylate-co-ethylenedimethacrylate), P(GMA-EDMA) beads with diameter of 7 microm were prepared by a single-step swelling and polymerization method. The polymer particles were advantaged through immobilization of Procion Bule MX-R, which was incubated by epichlorohydrin via the epoxide groups on the particles surface. The Procion Bule MX-R-immobilized P(GMA-EDMA) beads were mechanically stable and acted as the rigid matrix for column chromatography in HPLC mode. The chromatographic properties of the dye-ligand affinity chromatographic stationary phase for biopolymers separation are discussed. This affinity column has advantages of enabling biopolymer separation, high efficiency and low backpressure. Lysozyme and BSA were fast separated within 10min using this affinity column. The column was also used for the purification of lysozyme from chicken egg white.

Identification and refinement of a peptide affinity ligand with unique specificity for a monoclonal anti-tenascin-C antibody by screening of a phage display library

Using phage display technology, a 22-mer peptide was selected as a ligand with unique specificity for the murine monoclonal ST2146 antibody that recognizes the EGF repeats region of the human tumor-associated antigen tenascin-C. This peptide, synthesized in an 8-branched form to enhance its binding properties, is useful in replacing the native antigen in the affinity and immunoreactivity characterization of the ST2146 antibody and its biotinylated derivatives. Affinity resins, prepared by immobilizing the mimotope or its shorter 10-mer binding unit on a chromatographic support, were able to capture ST2146 directly from the hybridoma supernatant, with antibody recovery and host cell protein (HCP) reduction similar to or better than protein A sorbent, a purity degree exceeding 95%, and full recovery of antibody activity. The affinity constants of both peptides, as determined by frontal analysis of broad-zone elution affinity chromatography and BiaCore measurements, were very similar and included in a range suitable for affinity ligands. Column capacity, determined by applying a large excess of purified ST2146 to 1 mL of column bed volume, was close to 50 mg/mL for both resins. These matrices retain their ST2146 binding properties after various treatments, including sanitization, thus indicating very high stability in terms of ligand leakage and degradation. Moreover, the short form shows higher enzymatic stability, thus proving more suitable as ligand for ST2146 affinity purification.

A new ligand for immunoglobulin g subdomains by screening of a synthetic peptide library

By screening a synthetic peptide library of general formula (NH(2)-Cys1-X2-X3-X4)(2)-Lys-Gly-OH, a disulfide-bridged cyclic peptide, where X2-X3-X4 is the tripeptide Phe-His-His, has been selected as a ligand for immunoglobulin G (IgG). The peptide, after a preliminary chromatographic characterization, has proved useful as a new affinity ligand for the purification of polyclonal as well as monoclonal antibodies from biological fluids, with recovery yields of up to 90% (90% purity). The ligand is able to bind antibody fragments containing both Fab and Fc from different antibody isotypes, a fact suggesting the presence of at least two different antibody-binding sites. While the recognition site on Fab is unknown, comparative binding studies with Fc, in association with the striking similarities of the peptide (named Fc-receptor mimetic, FcRM) with a region of the human FcgammaRIII receptor, strongly indicate that the peptide could recognize a short amino acid stretch of the lower hinge region, which has a key role in autoimmune disease triggering. The unique properties make the ligand attractive for both the purification of antibody fragments and as a lead for the generation of Fc-receptor antagonists.

Evaluation and applications of a new dye affinity adsorbent

The basic properties of a new dye affinity adsorbent Toyopearl AF-Blue HC-650M and its applications to the purification of proteins were studied. The binding capacity for human serum albumin (HSA) was greater than 18 mg per ml gel. The dye leakage from Toyopearl AF-Blue HC-650M in 0.5 M NaOH and 0.5 M HCI was less compared with an agarose adsorbent. Caustic stability study also demonstrated this material withstood exposure to 0.1 M NaOH for 1 month with no significant loss of binding capacity for HSA. We purified human albumin from human serum and lactate dehydrogenase (LDH) from rabbit muscle extract in a single step. Sodium dodecylsulfate-polyacrylamide gel electrophoresis indicates that human albumin and LDH were highly purified.

Galactosyl-biomimetic dye-ligands for the purification of Dactylium dendroides galactose oxidase

Two anthraquinone galactosyl-biomimetic dye-ligands comprising, as terminal biomimetic moiety, galactose analogues (1-amino-1-deoxy-beta-D-galactose and D(+)-galactosamine) were designed for the enzyme galactose oxidase (GAO), using molecular modelling, synthesized and characterized. The biomimetic ligands were immobilized on agarose beads and the affinity adsorbents, together with a non-biomimetic adsorbent bearing Cibacron Blue 3GA, were studied for their ability to purify GAO from Dactylium dendroides. Both biomimetic adsorbents showed higher purifying ability for GAO compared to the non-biomimetic adsorbent, thus demonstrating their superior effectiveness as affinity chromatography materials. In particular, the affinity adsorbent comprising, as terminal biomimetic moiety, 1-amino-1-deoxy-beta-D-galactose (BM1) exhibited the highest purifying ability for GAO. This affinity adsorbent did not bind galactose dehydrogenase, glucose dehydrogenase, alcohol dehydrogenase, or glucose oxidase. The dissociation constant (K(D)) of the immobilized BM1 ligand with GAO was found to be equal to 45.8 microM, whereas the binding capacity was equal to 709 U per ml adsorbent. Therefore, the BMI adsorbent was integrated in a facile two-step purification procedure for GAO. The purified enzyme showed a specific activity equal to 2038 U/mg, the highest reported so far, approximately 74% overall recovery and a single band after sodium dodecylsulfate-polyacrylamide gel electrophoresis analysis.

Efficient elution of functional proteins in affinity chromatography

Many elution buffers are in use for the retrieval of proteins from affinity columns. While the aim of these buffers is to dissociate the various chemical bonds that make up protein-protein interactions and return the target protein to the mobile phase in active form, there is considerable difference of opinion as to which buffer is more suitable for particular applications. This review examines the chemical effect of various elution buffers on protein-protein interactions in the context of affinity chromatography and examines strategies that may be used for selection of an appropriate buffer.

An optical biosensor for monitoring recombinant proteins in process media

This paper describes the construction of a sensor for the direct monitoring of a recombinant protein, the human insulin analogue (MI3). The surface plasmon resonance (SPR) sensor incorporates an immobilised, sterilisable affinity-ligand that has been designed to bind to MI3. In practice, gold SPR devices were fabricated with; a 2D assembly of ethanethiol-modified ligand, a 2D mixed-assembly of ethanethiol-modified ligand and mercaptoethanol, a 3D coating of ligand-modified terminal-thiolated poly(vinyl)alcohol (PVA) or a 3D hydrogel of dextran coupled to a self-assembled monolayer (SAM) of mercaptohexaneundecanl-ol. Routine measurement of the concentration MI3 in the concentration range 1-100 mg/l in pilot-scale samples of crude fermentation broth have been achieved with high sensitivity levels and a high signal-to-noise ratio. Analysis can be achieved within < 10 min with the active surface being regenerable for at least 60 cycles over a 6 month period. The coupling of a robust, sterilisable and highly-selective sensor-coating with suitable transducer technologies promises to deliver sensors that are capable of direct in situ monitoring of biopharmaceuticals in industrial bioprocesses.

Purification of muscle enzymes by pseudoaffinity chromatography

A method based on pseudoaffinity chromatography has been developed for the separation of lactate dehydrogenase (LDH), pyruvate kinase (PK) and aldolase from rabbit muscle extract using cross-linked guar (CLG) and cross-linked pectin (CLP) as the matrices, and dyes as the ligands. Screening of several dyes revealed that dyes No. 1014 and No. 1015, immobilized on CLG and CLP displayed a higher affinity for LDH and PK. Aldolase was not retained on any of the dye columns. It was observed that 1014-CLP and 1014-CLG columns retained 90% and 55% LDH activities, respectively, whereas 1015-CLP and 1015-CLG retained 83% LDH and 72% PK. A coupled-column system comprising 1014-CLP and 1015-CLP or 1014-CLG and 1015-CLG could separate LDH, PK, and aldolase from a mixture of these enzymes, as well as from rabbit muscle extract. Enzymes were found to be homogeneous on polyacrylamide gel electrophoresis. The method has been found to be simple and economical.

Affinity purification of recombinant interferon-alpha on a mimetic ligand adsorbent

A method for improved refolding and purification of recombinant human interferon-alpha (rh-IFN-alpha) from inclusion bodies is described. The optimal conditions of refolding were obtained by the addition of 0.5 M l-arginine to the refolding buffer. The rh-IFN-alpha was purified to near homogeneity utilizing a single-step chromatography on a mimetic dye-ligand matrix. Improved refolding, coupled to a single-column affinity purification strategy, resulted in a 10-fold increase in the yield of rh-IFN-alpha. This single-step purification protocol yielded approximately 50 mg of purified rh-IFN-alpha from 1 liter of shake flask culture. The rh-IFN-alpha prepared by this protocol was found to be essentially monomeric based on HPLC gel filtration and nonreducing SDS-PAGE. It had a specific activity of approximately 2.8 x 10(8) IU/mg, measured as inhibition of cytopathic effect of encephalomyocarditis virus on A549 human lung carcinoma cells.

Purification, characterization, and cloning of an S-adenosylmethionine-dependent 3-amino-3-carboxypropyltransferase in nocardicin biosynthesis

S-Adenosylmethionine:nocardicin 3-amino-3-carboxypropyltransferase catalyzes the biosynthetically rare transfer of the 3-amino-3-carboxypropyl moiety from S-adenosylmethionine to a phenolic site in the beta-lactam substrates nocardicin E, F, and G, a late step of the biosynthesis of the monocyclic beta-lactam antibiotic nocardicin A. Whereas a number of conventional methods were ineffective in purifying the transferase, it was successfully obtained by two complementary affinity chromatography steps that took advantage of the two substrate-two product reaction scheme. S-Adenosylhomocysteine-agarose selected enzymes that utilize S-adenosylmethionine, and a second column, nocardicin A-agarose, specifically bound the desired transferase to yield the enzyme as a single band of 38 kDa on a silver-stained SDS-polyacrylamide gel. The transferase is active as a monomer and exhibits sequential kinetics. Further kinetic characterization of this protein is described and its role in the biosynthesis of nocardicin A discussed. The gene encoding this transferase was cloned from a sublibrary of Nocardia uniformis DNA. Translation gave a protein of deduced mass 32,386 Da which showed weak homology to small molecule methyltransferases. However, three correctly disposed signature motifs characteristic of these enzymes were observed.

Affinity chromatography of serine proteases on the triazine dye ligand Cibacron Blue F3G-A

The interaction between complement component factor B and the triazine dye ligand Cibacron Blue F3G-A coupled to a cross-linked agarose matrix (Blue Sepharose) was found to involve the Bb part of the molecule, and to be inhibited by benzamidine. Human, chicken and rainbow trout factor B which had bound to Blue Sepharose could, subsequently be eluted with benzamidine. Other serine proteases (C2, factor II, factor IX, trypsin, chymotrypsin, proteinase 3) also bound to Blue Sepharose but only those belonging to the trypsin family could be eluted with benzamidine. Trypsin treated with the active-site inhibitor phenylmethylsulfonyl fluoride did not bind to Blue Sepharose and pretreatment of Blue Sepharose with benzamidine did not influence binding of proteases. We conclude that trypsin-like serine proteases can be purified on Blue Sepharose and that the interaction of these serine proteases with Blue Sepharose involves the active site of the enzyme.

Triazine dyes inhibit HIV-1 entry by binding to envelope glycoproteins

We have attempted to purify envelope (Env) glycoproteins of human immunodeficiency virus (HIV) from the culture supernatants of CHO-Sec cells that secreted truncated 140-kDa precursor and mature 120-kDa Env glycoproteins. The concentrated culture supernatants were applied to a column coupled with cibacron blue 3GA (CB3GA) to separate albumin from the Env proteins because CB3GA, a triazine dye, has been known to have a high affinity to albumin. Unexpectedly, Env proteins as well as albumin bound to the column, and the bound Env proteins were eluted by increasing the ionic strength using KCl. Gp120 was eluted at 0.5-0.9 M of KCl, while a higher concentration (0.9-1.5 M) was necessary for the elution of gp140. The agarose gel coupled with reactive red 120 (RR120), another triazine dye with similar characteristics, also retained both Env proteins, and the bound Env proteins could be eluted in a similar manner. In addition, these agents inhibited syncytium formation caused by HTLV-IIIB and HTLV-IIIMN. Inhibition was also seen when a virus-free fusion assay between Env protein expressed in CHO cells and fluorescent labeled SupT1 cells were used. These findings indicate that triazine dyes bind to the functional regions of Env proteins of HIV-1 that play important role(s) for HIV infection.

The product of the molybdenum cofactor gene mobB of Escherichia coli is a GTP-binding protein

The mob mutants of Escherichia coli are pleiotropically defective in molybdoenzyme activities because they are unable to catalyse the conversion of molybdopterin guanine dinucleotide, the active form of the molybdenum cofactor. The mob locus comprises two genes. The product of mobA, protein FA, has previously been purified to homogeneity and is able to restore molybdoenzyme activities following incubation with cell extracts of mob strains. The mobB gene, although not essential for the biosynthesis of active molybdoenzymes, encodes a protein which, sequence analysis strongly suggests, contains a nucleotide-binding site. We have overproduced the products of both the mobA and mobB genes in engineered E. coli strains and purified each to homogeneity. The preparation of protein FA (MobA) is simpler than that previously published and produces a much greater yield of active protein. The isolated MobB protein, which is dimeric in solution, acts in the presence of protein FA, to enhance the level of nitrate reductase activation achieved on incubation with mob cell extracts. Equilibrium dialysis experiments show that purified MobB binds 0.83 mol GTP/mol protein with a Kd of 2.0 microM. Isolated MobB also catalyses a low GTPase activity (turnover number of 3 x 10(-3) min-1) with a K(m) for GTP to GDP of 7.5 microM. Under the conditions tested, protein FA did not affect the GTP-binding or GTPase activity of MobB. Intrinsic (tryptophan) protein fluorescence measurements show that MobB also binds the nucleotides ATP, TTP and GDP, but with lower affinity than GTP. These results are consistent with a model whereby MobB binds the guanine nucleotide which is attached to molybdopterin during the biosynthesis of the molybdenum cofactor.

Affinity chromatography of yeast alcohol dehydrogenase using immobilized monochlorotriazine colourless compounds

Four new symmetrical colourless biomimetics bearing two monochlorotriazine rings have been rationally designed and synthesized. These immobilized colourless ligands and one analogue of Cibacron Blue F3GA on Sepharose CL-4B were used to purify alcohol dehydrogenase from baker's yeast extract. Twenty-two-fold purification with 78% enzyme recovery was achieved in a single step with specific elution of NAD+ (5 mM) from the colourless absorbent comprised of two ortho-aminobenzene sulphonates as terminal rings, which is comparable to the result obtained from the analogue of Cibacron Blue F3GA. Differential spectra between ligand-enzyme complexes and free ligands were studied.

Screening of a large number of dyes for the separation of human immunoglobulin G2 from the other immunoglobulin G subclasses immunoglobulin G2 enrichment on immobilized Procion Yellow HE-4R

Human immunoglobulins (IgG) are produced on a multi-ton scale for therapeutic applications. There is presently no available method to manufacture IgG preparations enriched with immunoglobulins from the IgG2 subclass although they might be useful for therapeutic purposes. By frontal chromatography, we have screened 69 immobilized dyes, among which, six display a different affinity for IgG2 and other subclasses. One (Procion Yellow HE-4R) was studied further. The screening of various mobile phase conditions allowed us to devise a procedure to prepare IgG2 enriched IgG solutions: The cumulative yield for IgG2 was 43% and IgG2/total IgG ratio in the final product was 67%.

Purification and characterisation of isocitrate dehydrogenase and malate dehydrogenase from Mycobacterium tuberculosis and evaluation of their potential as suitable antigens for the serodiagnosis of tuberculosis

SETTING

Enzymes from Mycobacterium tuberculosis are potent antigens and might thus be of interest in the serodiagnosis of tuberculosis.

OBJECTIVE

The purpose of the study was to purify and characterize the two enzymes isocitrate dehydrogenase (IDH) and malate dehydrogenase (MDH) from, M. tuberculosis and to evaluate their potential in the serodiagnosis of tuberculosis.

DESIGN

The two enzymes were analysed for specificity by electrophoresis and then purified by means of affinity chromatography using reactive dyes and ion exchange chromatography. The two isolated enzyme fractions were analysed by ELISA, using antisera against related organisms. They were then tested as antigens in ELISA together with sera from tuberculous patients and controls.

RESULTS

The electrophoretical analyses showed that the two enzymes each differed markedly from the corresponding enzymes of other mycobacteria. The serological analyses, however, could not distinguish between either IDH or MDH from other mycobacteria, but organisms of other genera, such as Nocardia, gave much weaker responses. When IDH and MDH were tested with sera from tuberculous patients and controls the former gave clearly higher optical density values than the latter.

CONCLUSION

The enzymes/antigens IDH and MDH may be of value in developing a serological test for tuberculosis. The latter fraction seemed particularly capable of discriminating patients from controls.

Kinamycin acetyltransferase I from Streptomyces murayamaensis, an apparently large, membrane-associated enzyme

Identification and initial characterization of an apparently large, membrane-associated multifunctional enzyme, kinamycin acetyltransferase I (KAT I), is described. KAT I activity was enriched 29-fold over the level in cell-free extracts of Streptomyces murayamaensis. Two acetyltransferase activities catalyzing acetyl coenzyme A dependent conversion of kinamycin F and E to kinamycin E and D, respectively, were inseparable in the course of the partial purification. Partial purification involved separation of KAT I from cytosolic proteins by differential ultracentrifugation, solubilization with 0.5% CHAPS zwitterionic detergent followed by ultracentrifugation, and Sephacryl S400 gel filtration chromatography of the resulting supernatant.

Dye-affinity techniques for bioprocessing: recent developments

Textile or triazine dyes play an important role as affinity ligands in protein purification. Each step of the protein purification protocol can be divided into three stages, partitioning between two phases, separation of these phases and recovery of the target protein from the enriched phase. Now developments in dye-affinity techniques are discussed emphasizing the innovations in all three stages of the protein purification process. Dye-affinity chromatography has become a routine step in protein purification. New dyes have been developed and used successfully in both traditional chromatographic mode and new modes like affinity precipitation, polymer aqueous two-phase partitioning or expanded bed chromatography. The specificity of dye techniques has been increased by both purposeful designing of new dyes and decreasing non-specific protein-dye interactions with polymer shielding. One can envisage further development and ramification of dye-affinity techniques in protein purification.

The proteins encoded by the rbs operon of Escherichia coli: II. Use of chimeric protein constructs to isolate and characterize RbsC

Chimeric genes encoding full-length copies of rbsA and rbsC connected by segments coding for short bridge peptides were constructed and expressed in Escherichia coli. Surprisingly, the chimeric genes complemented the strain in which rbsA and rbsC were deleted. The chimeric proteins were overproduced, and the products were purified by affinity chromatography. In order to obtain highly purified protein, a poly-His leader peptide was incorporated so that Ni-chelate affinity chromatography could be employed. The leader peptide and the bridge peptide were designed with factor Xa-cleavable sites to permit recovery of the individual RbsA and RbsC protein. A rbsC gene encoding a poly-His leader was also constructed and expressed. Both the chimeric RbsA-C species and the poly-HisRbsC were produced at levels that permitted isolation of the equivalent of milligram quantities of RbsC per liter of culture. This is a substantial increase in amounts from any previous RbsC production vectors. All proteins from the rbs operon have now been overproduced and substantially purified.

Inhibition of camel lens zeta-crystallin/NADPH:quinone oxidoreductase activity by Cibacron blue

Camel lens zeta-crystallin/NADH:quinone oxidoreductase activity was inhibited by Cibacron blue 3GA (CB) with 9.10-phenanthrenequinone (PQ) as an electron acceptor and NADPH as an electron donor in a time-independent and concentration dependent manner. The IC50 value of CB was 50 nM. The Lineweaver-Burk plots and the secondary plots indicated that the inhibition was linear mixed type (partial competitive and pure noncompetitive) with respect to NADPH and noncompetitive with respect to PQ. The estimated inhibition constant (Ki) values were 26.0 nM for NADPH and 55.0 nM for PQ respectively, suggesting that CB has high affinity towards the NADPH binding site. The secondary plots of inhibition with respect to NADPH, also indicate a dissociation constant (Ki) value of 68.0 nM for the zeta-crystallin-NADPH-CB complex. This Ki being greater than the Ki value suggests that noncompetitive inhibition is predominant over competitive inhibition at the NADPH binding site.