Development of immobilized metal affinity chromatography

Protein interactions with surface-immobilized metal ions: structure-dependent variations in affinity and binding capacity with temperature and urea concentration

We have used equilibrium binding analyses to evaluate the influence of temperature and urea on the affinity of hen egg white lysozyme and bovine pancreatic ribonuclease A for surface-immobilized Cu(II) ions. Linear Scatchard plots suggested that these model proteins were interacting with immobilized metal ions via a single class of intermediate-affinity (Kd = 10-40 microM) binding sites. Alterations in temperature had little or no effect on the immobilized Cu(II) binding capacity of either protein. Temperature effects on the interaction affinity, however, were protein-dependent and varied considerably. The affinity of lysozyme for immobilized Cu(II) ions was significantly decreased with increased temperature (0 degree C-37 degrees C), yet the affinity of ribonuclease did not vary measurably over the same temperature range. The van 't Hoff plot (1n K vs 1/T) for lysozyme suggests a straight line relationship (single mechanism) with a delta H of approximately -5.5 kcal/mol. Urea effects also varied in a protein-dependent manner. A 10-fold reduction in the affinity of lysozyme for the immobilized Cu(II) was observed with the urea concentrations up to 3 M; yet urea had no effect on the affinity of ribonuclease for the immobilized metal ions. Although the interaction capacity of lysozyme with the immobilized Cu(II) ions was decreased by 50% in 3 M urea, ribonuclease interaction capacity was not diminished in urea. Thus, temperature- and urea-dependent alterations in protein-metal ion interactions were observed for lysozyme but not ribonuclease A. The complete, yet reversible, inhibition of lysozyme- and ribonuclease-metal ion interactions by carboxyethylation with low concentrations of diethylpyrocarbonate provided direct evidence of histidyl involvement. The differential response of these proteins to the effects of temperature and urea was, therefore, interpreted based on calculated solvent-accessibilities and surface distributions of His residues, individual His residue pKa values, and specific features of the protein surface structure in the immediate environment of the surface-exposed histidyl residues. Possible interaction mechanisms involved in protein recognition of macromolecular surface-immobilized metal ions are presented.

Immobilized metal ion affinity chromatography. Effect of solute structure, ligand density and salt concentration on the retention of peptides

The adsorption characteristics of a variety of synthetic peptide hormones and di-, tri- and tetrapeptides on Cu(II) immobilized on two commercially available high-performance chelating gels run under various experimental conditions are described. Methods for determining the concentration of immobilized Cu(II) in situ are also described. The Cu(II)-charged columns exhibit a net negative charge as judged from the significantly higher retention of some basic peptides in the absence of NaCl in the equilibration and elution buffers. At higher NaCl concentrations (2-4 M), aromatic interactions seem to be superimposed on the metal ion affinity characteristics of the peptides. The relationship between resolution of peptides and the concentration of immobilized Cu(II) ions has also been established for the Chelating Superose gel where 40 mumol Cu(II) ml-1 gel apparently gives the optimum resolution. The nature of the gel matrix also plays a role in the resolution of some peptides, the extent of which is difficult to predict. The results obtained also suggest that peptides containing aromatic and hydroxy amino acids are retarded more than those which lack them. Moreover, these same amino acids apparently strengthen the existing strong binding of peptides containing His, Trp or Cys to a Chelating Superose-Cu(II) column. Dipeptides with C-terminal His (i.e., X-His) are neither bound nor retarded on a column of Chelating Superose-Cu(II) whereas those having the structure His-X are strongly bound. Some tri- and tetrapeptides containing His were also found not to bind to the column. The underlying cause of this anomalous adsorption behaviour is discussed and is ascribed to "metal ion transfer" arising from the relatively higher affinity of such peptides towards immobilized Cu(II) ions than the chelator groups (iminodiacetate) which are covalently bound to the gel matrix.

Amino acid side chain interaction with chelate-liganded crosslinked dextran, agarose and TSK gel. A mini review of recent work

Protein adsorption and retention data collected from recent chromatographic studies on hydrophilic gels substituted with chelate-bonded metal ions are discussed. Attempts are made to interpret the adsorption behavior in terms of molecular events caused by the affinity for the immobilized metal ions.

Immobilization and affinity purification of recombinant proteins using histidine peptide fusions

A gene fusion approach to simplify protein immobilization and purification is described. A gene encoding the protein of interest is fused to a gene fragment encoding the affinity peptide Ala-His-Gly-His-Arg-Pro. The expressed fusion proteins can be purified using immobilized metal affinity chromatography. A vector, designed to ensure obligate head-to-tail polymerization of oligonucleotide linkers was constructed by in vitro mutagenesis. A linker encoding the affinity peptide, was synthesized and polymerized to two, four and eight copies. These linkers were fused to the 3' end of a structural gene encoding a two-domain protein A molecule, ZZ, and to the 5' end of a gene encoding beta-galactosidase. Fusion proteins, of both types, with zero or two copies of the linker showed little or no binding to immobilized Zn2+, while a relatively strong interaction could be observed for the fusions based on four or eight copies of the linker. Using a pH gradient, the ZZ fusions were found to be eluted from the resin at different pHs depending on the number of the affinity peptide. These results demonstrate that genetic engineering can be used to facilitate purification and immobilization of proteins to immobilized Zn2+ and that the multiplicity of the affinity peptide is an important factor determining the binding characteristics.

Evaluation of the interaction of peptides with Cu(II), Ni(II), and Zn(II) by high-performance immobilized metal ion affinity chromatography

High-performance immobilized metal ion affinity chromatography was utilized to evaluate the adsorption properties of 67 synthetic, biologically active, peptides ranging in size from 5 to 42 residues. The metal ions, Cu(II), Ni(II) and Zn(II), were immobilized by iminodiacetic acid (IDA) coupled to TSK gel 5PW (10 microns). Two types of gradient elution (imidazole and pH) were used to evaluate peptide retention by the metal ions. A decreasing pH gradient and an increasing imidazole gradient eluted the peptides in similar order. IDA-Cu(II) and IDA-Zn(II) showed very similar selectivities for the peptides analyzed; however, IDA-Zn(II) displayed a weaker affinity for the peptides. IDA-Ni(II) showed a slightly different pattern of selectivity. Peptide adsorption effects contributed by the metal-free gel matrix were found to be relatively minor. The concentration and type of salt included in the mobile phase could affect the relative affinities of the peptides for the immobilized metal ions. Retention coefficients were assigned to individual amino acid residues by multiple linear regression analysis. Histidine showed the largest positive correlation with retention, followed by aromatic amino acid residues. Modified N-terminal residues resulted in negative contributions to retention. Analyses of peptide amino acid composition alone allowed prediction of peptide retention behavior on immobilized metal ion affinity columns.

Cell surface interactions with metal chelates

We have explored immobilized metal ion affinity adsorption as a means of discrimination between cells and to assess partially the types of interaction that might contribute to the adsorption of cells on the such adsorbents. Erythrocytes from different sources were adsorbed on immobilized iminodiacetic acid charged with Cu2+, Ni2+ or Zn2+. The affinity of the human erythrocytes for the immobilized metal ions follows the order Cu2+ greater than Ni2+ greater than Zn2+. The adsorption capacity of the rat erythrocytes decreased in the following order: Zn2+ greater than Ni2+ greater than Cu2+. Pre-saturation of the columns with imidazole lead to the recovery of over 90% of the cells applied on the columns. Enzymic removal of sialic acid residues from the surface of erythrocytes has no effect on the adsorption-elution profiles of these cells on affinity adsorbents. These findings suggest that histidine residues localized on the cell surface are involved in the cell binding to the adsorbent. This new separation principle could be expanded to other types of cell. It could be used as a diagnostic tool and for separation, as well as for probing cell surfaces.

High-performance immobilized-metal-ion affinity chromatography of peptides and proteins

The present status of the undeveloped branch of high-performance immobilized-metal-ion affinity chromatography (HPIMAC) is reviewed. As demonstrated, high resolution of peptides and protein mixtures can be obtained. Under specified conditions, more than 1000 runs can be made repeatedly on a single column without much change in pattern or recovery. Occasionally, 10(3)- to 10(4)-fold purification of a protein can be obtained in a single chromatographic run.

Purification strategies for Sendai virus membrane proteins

Viral membrane proteins extracted from Sendai virions with the non-ionic detergents decylpolyethyleneglycol-300 and Triton X-100 were used as a model mixture of hydrophobic membrane proteins. The detergent extract contained the fusion protein (F) and the tetrameric and dimeric forms of the hemagglutinin-neuraminidase protein (HN). These proteins were purified by size-exclusion high-performance liquid chromatography (HPLC) in the presence of 0.1% sodium dodecyl sulphate, by ion-exchange and metal chelate affinity HPLC in the presence of 0.1% decylpolyethyleneglycol, and by reversed-phase HPLC without prior removal of the detergent. The tetramer of HN and F could be purified by size-exclusion HPLC after dissociation of a micellar aggregate containing tetrameric HN and multimeric F. The F and HN proteins could be purified by ion-exchange HPLC. Pure F protein could be obtained after metal chelate affinity HPLC. The F protein and the dimer and tetramer of HN could be eluted from a large-pore (100 nm) reversed-phase column, but they were eluted as broad, overlapping peaks. Only after reduction of the virion extract, the relatively small (13-15 kilodaltons) F2 protein could be obtained in pure form.

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.

Salt-promoted adsorption: recent developments

Efficient fractionation of human serum proteins is accomplished by use of a series of tandem-coupled beds of group-affinity adsorbents. The general fractionation strategy for group fractionation of a complex protein mixture is discussed.