Adsorption and desorption of proteins in metal chelate affinity chromatography

Immobilized metal ion affinity chromatography of histidine-tagged fusion proteins

Immobilized metal ion affinity chromatography (IMAC) is a ubiquitous technique in modem recombinant production and purification. The wide range of expression vectors for the production of histidine-tagged recombinant proteins as well as the variety of stationary supports for their separation make IMAC an attractive and versatile choice for fast and reliable protein purification. It is not uncommon for IMAC purification to yield near homogenous target protein, with purities over 95%. The small size of the histidine tag means that in many cases it can remain associated with the target protein without interference with its intended function, obviating the need for any potentially complicating tag removal steps. This chapter provides protocols for the routine purification of such histidine-tagged fusion proteins. As with any purification regime, complications with IMAC can arise. Lacking the absolute specificity of a biological ligand/ligate system such as the avidin/biotin interaction or an antibody and its cognate antigen, IMAC can sometimes display non-ideal product purity. The protocols described in this chapter provide strategies for the improvement in the purity of IMAC-purified proteins. Similarly, non-specific binding may reduce product yields and purity in some circumstances. Methodologies for enhancing the yield of the target protein are therefore provided.

Immobilized metal ion affinity chromatography of native proteins

Immobilized metal affinity chromatography (IMAC) is a common place technique in modem protein purification. IMAC is distinct from most other affinity chromatography technologies in that it can operate on a native, unmodified protein without the need for a specialized affinity "tag" to facilitate binding. This can be particularly important where a protein of interest is to be separated from a complex mixture such as serum or an environmental isolate. Relying on the interaction of specific surface amino acids of the target protein and chelated metal ions, IMAC can provide powerful discrimination between small differences in protein sequence and structure. Additionally, IMAC supports have been demonstrated to function effectively as cation exchangers, allowing for two modes of purification with a single column. This chapter provides methodologies to perform IMAC in its most fundamental form, that of the interaction between histidine and immobilized metal ions, those that enable purification of proteins that lack surface histidines and the operation of IMAC supports in cation exchange mode.

Adsorption and selectivity characteristics of several human serum proteins with immobilised hard Lewis metal ion-chelate adsorbents

In this investigation, human serum has been used as an example of a crude protein mixture to define the protein binding characteristics and selectivity of several immobilised hard Lewis metal ion affinity chromatographic (IMAC) adsorbents. Specifically, the binding properties of immobilised O-phosphoserine (im-OPS) and 8-hydroxyquinoline (im-8-HQ), with immobilised iminodiacetic acid as a control system, have been investigated in combination with the hard Lewis metal ions, Al3+, Ca2+, Fe3+, Yb3+, and the borderline metal ion, Cu2+, over the pH range pH 5.5 to pH 8.0 with buffers of 0.5 M ionic strength. The same IMAC adsorbents were also investigated for their protein binding capabilities with buffers of an ionic strength of 0.06 M at pH 5.5 and pH 8.0. The binding behaviour of four "marker" proteins, namely transferrin, alpha2-macroglobulin, gammaglobulin and human serum albumin have furthermore been employed to monitor the differences in protein selectivity exhibited by these IMAC systems. The experimental findings confirm that these hard Lewis metal ion IMAC adsorbents function in a "mixed" binding mode with both coordination and electrostatic characteristics evident, depending on the ionic strength and pH of the equilibration or elution buffers. Based on a screening protocol, several members of the im-Mn+-8-HQ and im-Mn+-OPS adsorbent series have been identified with high selectivity for transferrin and alpha2-macroglobulin. These hard Lewis metal ion IMAC adsorbents thus provide attractive alternatives for selective fractionation of human serum proteins.

Isolation and purification of cat albumin from cat serum by copper ion affinity chromatography: further analysis of its primary structure

Proteins, regardless of their origin, have to be highly purified, particularly from the immunochemical point of view, if they are to be used to study their allergenicity. It is shown that cat albumin, a highly potent allergen for cat-sensitive humans, can be isolated and purified from cat serum using immobilized metal ion affinity chromatography (copper ions) instead of a salting-out process or precipitation with alcohol, techniques generally used for the preparation of serum proteins. During the process described, immunoglobulins are concomitantly isolated in a relatively pure form. Cat albumin amino acid composition and sequence were analysed after an ultimate purification by ion-exchange chromatography. The highest homology (greater than 80%) was found with the rat serum albumin.

Metal chelate affinity chromatography of Zn2+-inhibited protein Tyr(P) phosphatases

Metal chelate affinity chromatography using Zn2+-iminodiacetate agarose is shown to provide quantitative recoveries of Zn2+-inhibited protein Tyr(P) phosphatases. To elute adsorbed enzymes from immobilized Zn2+ three methods were compared: (1) removal of Zn2+ with chelators such as EDTA, (2) introduction of ligands to compete with enzyme for Zn2+ and (3) lowering pH to protonate sidechains in the enzyme that serve as ligands to Zn2+. Results show highest yields but poor purification for method 1, high purification but poor yields of active enzyme for method 3. It is concluded that gradients of competing Zn2+ ligands, such as imidazole, provide the best strategy for the purification of enzymes with retention of activity using metal chelate affinity chromatography.

Metal chelate-interaction chromatography of proteins with iminodiacetic acid-bonded stationary phases on silica support

An iminodiacetic acid (IDA)-bonded stationary phase on a wide-pore microparticulate silica support was used for the chromatography of amino acids and proteins at pH 5.0 and 6.0. Without chelated metal the retention behavior of the stationary phase parallelled that of other silica-bound cation exchangers used in high-performance liquid chromatography of proteins. In metal chelate-interaction chromatography (MCIC) with IDA, chelated by Cu(II), Zn(II), Ni(II), Fe(II), or Fe(III), amino acids were most strongly retained on Cu(II)-IDA, whereas all metal chelates separated the proteins under investigation but with different selectivity. The effect of salt concentration in the eluent on protein retention was investigated and the pertinent electrostatic and hydrophobic interaction parameters were evaluated. The proteins were separated by MCIC with increasing salt gradient and, using the same column, by hydrophobic-interaction chromatography with decreasing salt gradient. In MCIC the addition of methanol to the mobile phase had disparate effect on protein retention, whereas addition of histidine or glycine, which acted as competing ligands, reduced the retention.

Fractionation of human serum proteins by immobilized metal affinity chromatography

Human serum was fractionated on zinc and cadmium iminodiacetate and tris(carboxymethyl)ethylenediamine chelates. Zinc iminodiacetate was found to be useful in the isolation of hemopexin and alpha 2-macroglobulin. The chromatographic behaviour of serum proteins on zinc iminodiacetate could be modulated by the nature of the eluent; a sulphate-containing solvent increased the binding of serum proteins to immobilized metal ions.

Immobilized metal ion affinity adsorption and immobilized metal ion affinity chromatography of biomaterials. Serum protein affinities for gel-immobilized iron and nickel ions

Immobilized metal ion affinity adsorption (IMA adsorption) is a collective term that is proposed to include all kinds of adsorptions whereby metal atoms or ions immobilized on a polymer cause or dominate the interaction at the sorption sites. IMA chromatography is one of the most powerful methods available to date for protein fractionation although this is not as yet widely recognized. This study deals with the theoretical aspects of IMA adsorption and its practical applications as exemplified by the various results reported here. The synthesis of iminodiacetate-substituted agarose (IDA-agarose) and tris(carboxymethyl)ethylenediamine-agarose (TED-agarose) is described. Many types of metal ions can easily be immobilized on these gel derivatives to form IMA adsorbents. We have not observed any damage to the proteins during the adsorption-desorption process. After performance of an experiment, the gels can easily be regenerated and can be loaded with the same or a different metal ion for an ensuing experiment. Specific adsorption is demonstrated for serum proteins on immobilized Ni(II) and Fe(III). Ligand-specific desorption (affinity elution) is also demonstrated by including in the buffer system certain solutes which are similar to or identical with some particular amino acids found in proteins. High concentrations of certain salts that affect the structure of water, such as Na2SO4, promote coordinate covalent bonding of proteins by a mechanism that is apparently similar to that found in hydrophobic interactions. Neutral detergents and aquoorganic solvents may be used. This opens up the possibility for the fractionation of membrane components. The IMA-adsorption method could also be expanded to other areas besides protein fractionation.