Development of immobilized metal affinity chromatography

Isolation of Functional Human MCT Transporters in Saccharomyces cerevisiae

Human monocarboxylate transporters (hMCTs) belong to the solute carrier 16 (SLC16) family of proteins and are responsible for the bi-directional transport of various metabolites, including monocarboxylates, hormones, and aromatic amino acids. Hence, the metabolic role of hMCTs is undisputable, as they are directly involved in providing nutrients for oxidation and gluconeogenesis as well as participate in circulation of iodothyronines. However, due to the difficulty in obtaining suitable amounts of stable hMCT samples, the structural information available for these transporters is limited, hindering the development of effective therapeutics. Here we provide a straightforward, cost-effective strategy for the overproduction of hMCTs using a whole-cell Saccharomyces cerevisiae-based system. Our results indicate that this platform is able to provide three hMCTs, i.e., hMCT1 and hMCT4 (monocarboxylate transporters), and hMCT10 (an aromatic amino acid transporter). hMCT1 and hMCT10 are recovered in the quantity and quality required for downstream structural and functional characterization. Overall, our findings demonstrate the suitability of this platform to deliver physiologically relevant membrane proteins for biophysical studies.

Virus-like particles from Escherichia Coli-derived untagged papaya ringspot virus capsid protein purified by immobilized metal affinity chromatography enhance the antibody response against a soluble antigen

There is a growing interest in using virus-like particles (VLPs) as scaffolds for the presentation of antigens of choice to the immune system. In this work, VLPs from papaya ringspot virus capsid protein expressed in Escherichia coli were evaluated as enhancers of antibody response against a soluble antigen. Interestingly, although the capsid protein lacks a histidine tag, its purification by immobilized metal affinity chromatography was achieved. The formation of VLPs was demonstrated by electron microscopy for the first time for this capsid protein. VLPs were enriched by polyethylene glycol precipitation. Additionally, these VLPs were chemically coupled to green fluorescent protein in order to evaluate them as antigen carriers; however, bioconjugate instability was observed. Nonetheless, the adjuvant effect of these VLPs on BALB/c mice was evaluated, using GFP as antigen, resulting in a significant increase in anti-GFP IgG response, particularly, IgG1 class, demonstrating that the VLPs enhance the immune response against the antigen chosen in this study.

Biochemical and EPR-spectroscopic investigation into heterologously expressed vinyl chloride reductive dehalogenase (VcrA) from Dehalococcoides mccartyi strain VS

Reductive dehalogenases play a critical role in the microbial detoxification of aquifers contaminated with chloroethenes and chlorethanes by catalyzing the reductive elimination of a halogen. We report here the first heterologous production of vinyl chloride reductase VcrA from Dehalococcoides mccartyi strain VS. Heterologously expressed VcrA was reconstituted to its active form by addition of hydroxocobalamin/adenosylcobalamin, Fe(3+), and sulfide in the presence of mercaptoethanol. The kinetic properties of reconstituted VcrA catalyzing vinyl chloride reduction with Ti(III)-citrate as reductant and methyl viologen as mediator were similar to those obtained previously for VcrA as isolated from D. mccartyi strain VS. VcrA was also found to catalyze a novel reaction, the environmentally important dihaloelimination of 1,2-dichloroethane to ethene. Electron paramagnetic resonance (EPR) spectroscopic studies with reconstituted VcrA in the presence of mercaptoethanol revealed the presence of Cob(II)alamin. Addition of Ti(III)-citrate resulted in the appearance of a new signal characteristic of a reduced [4Fe-4S] cluster and the disappearance of the Cob(II)alamin signal. UV-vis absorption spectroscopy of Ti(III)citrate-treated samples revealed the formation of two new absorption maxima characteristic of Cob(I)alamin. No evidence for the presence of a [3Fe-4S] cluster was found. We postulate that during the reaction cycle of VcrA, a reduced [4Fe-4S] cluster reduces Co(II) to Co(I) of the enzyme-bound cobalamin. Vinyl chloride reduction to ethene would be initiated when Cob(I)alamin transfers an electron to the substrate, generating a vinyl radical as a potential reaction intermediate.

A general protocol for the crystallization of membrane proteins for X-ray structural investigation

Protein crystallography is used to generate atomic resolution structures of protein molecules. These structures provide information about biological function, mechanism and interaction of a protein with substrates or effectors including DNA, RNA, cofactors or other small molecules, ions and other proteins. This technique can be applied to membrane proteins resident in the membranes of cells. To accomplish this, membrane proteins first need to be either heterologously expressed or purified from a native source. The protein has to be extracted from the lipid membrane with a mild detergent and purified to a stable, homogeneous population that may then be crystallized. Protein crystals are then used for X-ray diffraction to yield atomic resolution structures of the desired membrane protein target. Below, we present a general protocol for the growth of diffraction quality membrane protein crystals. The process of protein crystallization is highly variable, and obtaining diffraction quality crystals can require weeks to months or even years in some cases.

Affinity precipitation of proteins using metal chelates

Metal affinity precipitation has been successfully developed as a simple purification process for the proteins that have affinity for the metal ions. The copolymers of vinylimidazole with N-isopropylacrylamide are easily synthesized by radical polymerization. When loaded with Cu(II) and Ni(II) ions, these copolymers are capable of selectively precipitating proteins with natural metal-binding groups or histidine-tagged recombinant proteins.

Water-elutability of nucleic acids from metal-chelate affinity adsorbents: enhancement by control of surface charge density

Immobilized metal affinity chromatography (IMAC) is widely used for purification of proteins, especially "hexahistidine-tagged" recombinant proteins. We previously demonstrated the application of IMAC to selective capture of nucleic acids, including RNA, selectively-denatured genomic DNA, and PCR primers through interactions with purine bases exposed in single-stranded regions. We also found that the binding affinity of nucleic acids for IMAC adsorbents can be increased several-fold by addition of 20 volume% of neutral additives such as ethanol or DMSO. In the present work, it is demonstrated that bound nucleic acids can be effectively eluted with water instead of the usual imidazole-containing competitive eluants, when the surface density of negative charges is enhanced by operation at alkaline pH, or by deliberate metal-underloading of the anionic chelating ligands. With enhanced negative surface charge density, nucleic acid adsorption can be made strongly dependent on the presence of adsorption-promoting additives and/or repulsion-shielding salts, and removal of these induces elution. Complete water-elutability is demonstrated for baker's yeast RNA bound to 10% Cu(II)- underloaded IDA Chelating Sepharose in a binding buffer of 20 mM HEPES, 240 mM NaCl, pH 7. Water elutability will significantly enhance the utility of IMAC in nucleic acid separations.

Preparation of an iminodiacetic acid-modified capillary and its performance in capillary liquid chromatography and immobilized metal chelate affinity capillary electrophoresis

We prepared iminodiacetic acid (IDA)-modified and Cu(II)-IDA-modified capillaries through polymerization of N-(vinylbenzylimino) diacetic acid. The fundamental performance of these capillaries was examined in capillary liquid chromatography (LC) and immobilized metal chelate affinity capillary electrophoresis (IMACE). Copper(II), cobalt(II), and hematin were detected at different retention times by means of capillary LC with a chemiluminescence detector, during which the IDA-modified capillary was used. The difference in the retention times was attributed to the difference in the interaction between metal ions or complex and IDA moieties on the inner wall of the capillary. In addition, human serum albumin (HSA) and human serum gamma-globulin (HgammaG) were separated and detected using IMACE with an absorption detector, during which the Cu(II)-IDA-modified capillary was used. The separation of HSA and HgammaG was achieved through the interaction between proteins and Cu(II) chelate moieties on the inner wall of this capillary.

Genomic data for alternate production strategies. I. Identification of major contaminating species for Cobalt+2 immobilized metal affinity chromatography

Recent advances in technology have allowed for the identification of complex protein mixtures in a rapid fashion. This report highlights the use of 2D gel electrophoresis, mass spectrometry, and database analysis to determine contaminating species of the Escherichia coli genome that are present during immobilized metal affinity chromatography (IMAC), highlighting Co(2+) as the affinity ligand. Four proteins (triosephosphate isomerase, alpha galactosidase, Hsp90, and glucosamine 6-phosphate synthase) constitute the majority of E. coli proteins that bind and potentially may coelute during chromatography. Results are discussed within the context of changes that when implemented could lead to an increase in IMAC efficiency, not by altering column conditions, but rather by changing the nature of the nuisance proteins that principally reduce column capacity and extend processing times. Such a study illustrates the use of proteome data to aid in bioprocess design.

Natural poly-histidine affinity tag for purification of recombinant proteins on cobalt(II)-carboxymethylaspartate crosslinked agarose

A natural 19-amino-acid poly-histidine affinity tag was cloned at the N-terminus of three recombinant proteins. The vectors containing the DNA of the fusion proteins were used for transformation of Escherichia coli DH5alpha cells. Each protein was expressed, extracted and purified in one chromatographic step. The purification procedure for each protein can be accomplished in less than 1 h. A new type of immobilized metal ion affinity chromatography adsorbent--Co2+-carboxymethylaspartate agarose Superflow--was utilized at linear flow-rates as high as 5 cm/min. The final preparation of each protein is with purity greater than 95% as ascertained by sodium dodecyl sulfate-electrophoresis. Recovery for each purified protein was higher than 77% of the initial loaded amount as judged by biological activity. The operational capacity of Co2+-carboxymethylaspartate agarose for each protein was determined.

Diamine-plasma treated and Cu(II)-incorporated poly(hydroxyethylmethacrylate) microbeads for albumin adsorption

Poly(2-hydroxyethylmethacrylate) (PHEMA) microbeads prepared by suspension polymerization were treated with diamine-plasmas (i.e. ethylene-diamine (EDA) and hexamethylene diamine (HMDA)) in a glow-discharge reactor in which the exposure time and glow-discharge power were changed between 5 and 30 min and 5 and 20 W, respectively. The amount of nitrogen deposition increased both with increase in exposure time and glow-discharge power. The maximum amounts of nitrogen deposition on the microbeads were 22.3 and 23.4 micromol g(-1) with the EDA- and HMDA-plasmas. Then, Cu(II) ions were incorporated onto the PHEMA microbeads by chelating with the nitrogen-carrying functional groups. Different amounts of Cu(II) ions (2.4-6.8 mg g(-1)) were incorporated on the PHEMA microbeads by changing the initial concentration of Cu(II) ions. Bovine serum albumin (BSA) adsorption onto the unmodified PHEMA, diamine-plasma treated PHEMA, and diamine-plasma treated Cu(II)-incorporated PHEMA microbeads was investigated. The non-specific adsorption of BSA on the unmodified microbeads was very low (0.22 mg BSA g(-1)). Deposition of nitrogen increased the BSA adsorption (9.3 mg g(-1) for EDA-plasma and 12.7 mg g(-1) for HMDA-plasma). Cu(II)-incorporation significantly increased the BSA adsorption (154 mg g(-1) for EDA-plasma and 178 mg g(-1) for HMDA-plasma). Further increases in the albumin adsorption capacities of the polymer microbeads (185 mg g(-1) for EDA-plasma and 208 mg g(-1) for HMDA-plasma) were observed when human plasma was used. More than 92% of the adsorbed albumin molecules was desorbed in 1 h in the desorption medium containing 0.5 M NaSCN at pH 8.0. Repeated adsorption-desorption cycles showed the feasibility of these plasma-modified polymer microbeads.

Cadmium removal from human plasma by Cibacron Blue F3GA and thionein incorporated into polymeric microspheres

Poly(2-hydroxyethylmethacrylate-ethyleneglycoldimethacrylate) [poly(HEMA-EGDMA)] microspheres carrying Cibacron Blue F3GA and/or thionein were prepared and used for the removal of cadmium ions Cd(II) from human plasma. The poly(HEMA-EGDMA) microspheres, in the size range of 150-200 microm in diameter, were produced by a modified suspension copolymerization of HEMA and EGDMA. The reactive triazinyl dye-ligand Cibacron Blue F3GA was then covalently incorporated into the microspheres. The maximum dye incorporation was 16.5 micromol/g. Then, thionein was bound onto the Cibacron Blue F3GA-incorporated microspheres under different conditions. The maximum amount of thionein bound was 14.3 mg/g. The maximum amounts of Cd(II) ions removed from human plasma by poly(HEMA-EGDMA)-Cibacron Blue F3GA and poly(HEMA-EGDMA)-Cibacron Blue F3GA-thionein were of 17.5 mg/g and 38.0 mg/g, respectively. Cd(II) ions could be repeatedly adsorbed and desorbed with both types of microspheres without significant loss in their adsorption capacity.

Preparation of magnetic immobilized metal affinity separation media and its use in the isolation of proteins

A new method of pseudobiospecific protein isolation is developed and tested, which employs both metal affinity and magnetism as the basis for isolation. The chelating group iminodiacetic acid (IDA) has been coupled to the surface of magnetic agarose, and when charged with metal ions (Cu2+ or Zn2+) is capable of binding model proteins which display metal affinity, and of separating protein mixtures. Magnetic properties of the medium facilitated the batch recovery of the adsorbent, as losses are minimized by concentrating and retaining the separation medium with the aid of a magnet. Model proteins were used to characterize protein adsorption, capacity, and stability of IDA magnetic agarose. Recovery from a cell lysate was demonstrated by protein isolation from extracts of E. coli containing a target protein. Overall, this study effectively illustrates the engineering of separation media which combine several desired properties for the development of a new branch of metal affinity-based bioseparation.

Protein selectivity with immobilized metal ion-tacn sorbents: chromatographic studies with human serum proteins and several other globular proteins

The chromatographic selectivity of the immobilized chelate system, 1,4,7-triazocyclononane (tacn), complexed with the borderline metal ions Cu2+, Cr3+, Mn2+, Co2+, Zn2+, and Ni2+ has been investigated with hen egg white lysozyme, horse heart cytochrome c, and horse skeletal muscle myoglobin, as well as proteins present in partially fractionated preparations of human plasma. The effects of ionic strength and pH of the loading and elution buffers on protein selectivities of these new immobilized metal ion affinity chromatographic (IMAC) systems have been examined. The results confirm that immobilized Mn;pl-tacn sorbents exhibit a novel type of IMAC behavior with proteins. In particular, the chromatographic properties of these immobilized M(n+)-tacn ligand systems were significantly different compared to the IMAC behavior observed with other types of immobilized tri- and tetradentate chelating ligands, such as iminodiacetic acid, O-phosphoserine, or nitrilotriacetic acid, when complexed with borderline metal ions. The experimental results have consequently been evaluated in terms of the additional contributions to the interactive processes mediated by effects other than solely the conventional lone pair Lewis soft acid-Lewis soft base coordination interactions, typically found for the IMAC of proteins with borderline and soft metal ions, such as Cu2+ or Ni2+.

Microcalorimetric Studies of the Interactions of Lysozyme with Immobilized Cu(II): Effects of pH Value and Salt Concentration

In this investigation, employing a highly sensitive microcalorimeter, we measure the influence of pH value and salt concentration on the heat of interaction between lysozyme and CS-IDA-Cu(II) gel. The direct enthalpy measurement of the interaction provides thermodynamic information regarding the binding behavior of lysozyme toward the immobilized metal ion. The binding enthalpy altered by adsorbed lysozyme at various pH values and salt concentrations are measured. The findings, along with the reported binding isotherm, are discussed herein.

Chromatographic separation and behavior of microsomal cytochrome P450 and cytochrome b5

The methods used for separation of the multiple mammalian cytochrome P450 enzymes by liquid chromatography are reviewed. In addition to the chromatographic techniques, preparation and handling of samples and prefractionation procedures are considered. Conditions that affect stability and chromatographic resolution of cytochromes P450 are also discussed. Special emphasis is put on useful methods which are not routinely used for P450 separation, such as immobilized metal affinity or hydrophobic-interaction chromatography. Applications of low- and high-pressure methods with regard to preparative and analytical separations are compared. It is shown that high- and medium-pressure ion-exchange chromatography are suitable tools for separation of closely related P450 enzymes, especially when specific detection methods are available. In addition to fractionation of cytochromes P450, the isolation and chromatographic behavior of cytochrome b5 is discussed.

Retention behaviour of proteins on poly(vinylimidazole)-copper(II) complexes supported on silica: application to the fractionation of desialylated human alpha 1-acid glycoprotein variants

The retention behaviour of various amino acids, peptides and proteins on poly(vinylimidazole)-Cu(II) complexes supported on silica was investigated. Free amino acids and peptides containing one histidine and in some instances one additional tryptophan residue in their primary structure were found to elute from the supports only after addition of a competing complexing agent to the mobile phase. However, the results obtained the proteins containing metal binding groups suggested that, in addition to the presence of donor-acceptor interactions between the macromolecules and the immobilized metal, other additional (essentially ionic and/or hydrophobic) interactions took place between the proteins and the surrounding of the metal. When donor-acceptor interactions were predominant, proteins were strongly adsorbed on the stationary phase and their elution required the addition of a competing complexing agent in the mobile phase. However, when the binding between the proteins and the supports via donor-acceptor interactions was less favourable, proteins were eluted from the columns without the addition of a competing agent in the mobile phase. With respect to the binding of these proteins, ionic and/or hydrophobic interactions were no longer negligible during the chromatographic process and the retention of the macromolecules by the stationary phase depended on the elution conditions (ionic strength, pH, etc.). These supports were used in the fractionation of the three main genetic variants of desialylated alpha 1-acid glycoprotein.

Chromatography in the downstream processing of biotechnological products

Chromatography techniques are essential for the isolation and purification of most of the high value products of modern biotechnology. The economically sensible and technically satisfactory downstream processing of a therapeutic protein, usually involves a number of chromatographic steps. Its development and optimization require considerable knowledge of the various physico-chemical and engineering aspects of biochemical chromatography. This review addresses the various modes of chromatography and the design of chromatographic separation processes from a biotechnologist's point of view. Strategies for optimizing the structure of the downstream process are outlined and scaling up consideration are discussed. The importance of the different chromatographic methods in research and development is estimated in an analysis of protein purification schemes recently published in the literature. Finally, examples of the application of chromatographic procedures for process scale product purification in the biotechnological industry are given.

Purification of tryptophan containing synthetic peptides by selective binding of the alpha-amino group to immobilised metal ions

Immobilised metal ion affinity chromatography (IMAC) based on selective binding via the alpha-amino group to Cu2+ and Ni2+ ions has been used to purify tryptophan containing synthetic peptides. A free alpha-amino group, serving as an affinity handle, is present only in the target peptide when the peptides are synthesised by the solid-phase method and remaining amino groups after each coupling step are blocked by acetylation. A free alpha-amino group is necessary to retain the peptide on the column. The tryptophan residue may contribute to the binding only if the peptide is simultaneously anchored via the alpha-amino group.

Immobilized metal ion affinity chromatography

The introduction of immobilized metal ion affinity chromatography, directed toward specific protein side chains, has opened a new dimension in protein purification. This review covers the principles and practice of IMAC that can be performed under very mild, nondenaturing conditions. IMAC is particularly suitable for preparative group fractionation of complex extracts and biofluids, but can also be used in high-performance mode: "HP-IMAC." Single-step purifications of 1000-fold or more may allow isolation of a particular protein from crude extracts on a milligram or gram scale. With respect to separation efficiency, IMAC compares well with biospecific affinity chromatography, and the immobilized metal ion ligand complexes are more likely to withstand wear and tear than are antibodies or enzymes. The enormous potential of IMAC and related metal affinity techniques is only in the initial stages of being explored and exploited. Synthesis of IMA adsorbents, and various modes of performing IMAC are discussed and exemplified with selected applications. Advantages and disadvantages are listed. Effective means of counteracting the few undesirable effects that can occur are suggested.

Evaluation of the interaction of protein alpha-amino groups with M(II) by immobilized metal ion affinity chromatography

The adsorption properties of various peptides and proteins, lacking histidyl groups, on immobilized Cu(II), Ni(II), Zn(II) and Co(II) ions are described; at pH 6 and below they were little retarded. At higher pH the retention became pronounced for iminodiacetate (IDA)-Cu(II) gel. This effect seems to be related to the presence of a terminal alpha-amino group; in the absence of this group the retention of the protein was largely eliminated. At pH 8.5 a terminal alpha-amino group is adsorbed as strongly as a histidyl group. IDA-Ni(II), IDA-Zn(II) and IDA-Co(II) gels display little or no attraction for the terminal alpha-amino group of a protein.