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Protein Expression & Purification


Products >  Protein_Expression_and_Purification >  His-Tagged_Protein_Purification >  Cobalt_Resin-Batch

Batch or Gravity Flow Purification of His-Tagged Proteins—TALON Metal Affinity Resin

TALON His-Tag Purification Resin lets you prepare exceptionally pure his-tagged proteins from bacterial, mammalian, yeast, and baculovirus-infected cells, under native or denaturing conditions. TALON is an immobilized metal affinity chromatography (IMAC) resin charged with cobalt, which binds to his-tagged proteins with higher specificity than nickel-charged resins. As a result, TALON resin delivers his-tagged proteins of the highest purity. In addition, each cobalt ion is bound to the resin at four sites, resulting in low metal ion leakage.

Reactive Core Contains Cobalt for Highest Purity

TALON Metal Affinity Resin is complexed with cobalt ions that make it highly selective for his-tagged proteins. TALON’s cobalt-containing reactive core has strict spatial requirements—only proteins containing adjacent histidines or specially positioned, neighboring histidines are able to bind. The spatial requirements for nickel-based resins (e.g., Ni-NTA) are less strict—these resins have a much higher affinity for randomly positioned (i.e., non-his-tag) histidines. As a result, TALON resin binds more specifically to his-tagged proteins.

Uniform Matrix Guarantees Less Contamination

Cobalt-based resins have a more uniform structure than nickel-based resins. TALON resin contains negatively charged reactive sites that form three-dimensional pockets. Each pocket contains three carboxyl groups and one nitrogen atom that collectively bind a single, positively charged cobalt ion—an arrangement that allows the cobalt ion to bind to two adjacent histidine residues. In this configuration, cobalt is bound very tightly and does not leach out of the resin. Nickel-based resins are less homogeneous in structure because nickel ions can form two different coordination complexes: one of which forms a three-dimensional pocket similar to that of the TALON ligand, and a second that forms a planar (flat) structure. In the distorted, planar structure, each nickel ion binds to only two carboxyl groups and one nitrogen atom. As a result, the planar structure binds the nickel ions less tightly, allowing them to leach from the resin. TALON Metal Affinity Resin, with its uniform matrix, provides high affinity binding under a variety of purification conditions, ensuring optimal protein purification.

Choice of Native or Denaturing Purification Conditions

TALON Resin retains its protein binding specificity and yield under a variety of purification conditions. It is stable under both denaturing and native (nondenaturing) conditions (see flow chart). Deciding whether to use native or denaturing purification conditions depends on protein location, solubility, accessibility of the his tag, downstream applications, and preservation of biological activity.

  • Native Conditions

    Purifying a protein under native conditions (see example) is the most efficient way to preserve its biological activity, but requires that the protein be soluble. Advantages include:

    • Eliminating the renaturation step at the end of the purification, saving time, and preventing significant loss of activity
    • Retaining the ability to copurify enzyme subunits, cofactors, and associated proteins
  • Denaturing Conditions

    Because proteins that are overexpressed in prokaryotic systems sometimes form insoluble aggregates called inclusion bodies, you may need to purify proteins under denaturing conditions (see example)—using strong denaturants such as 6 M guanidinium or 8 M urea to enhance protein solubility. Advantages include:

    • Complete solubilization of inclusion bodies and his-tagged proteins
    • Improved binding to the matrix and reduced nonspecific binding, due to full exposure of the his tag

His-tagged proteins purified under denaturing conditions can be used directly in subsequent applications, or may need to be renatured and refolded. Protein renaturation and refolding can be performed prior to elution from the column. However, yields of recombinant proteins will be lower than under native conditions, because urea and guanidinium molecules compete with histidines for binding to metal.

Use of Reducing Agents

Purification with TALON Resin may be carried out in the presence of β-mercaptoethanol (see example), but not DTT or DTE, to preserve reduced sulfhydryl (-SH) groups that are important for the biological activity and structure of a given protein. TALON provides higher yields than Ni-NTA (see example) in the presence of β-mercaptoethanol.

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Features

  • Exhibits high affinity for his-tagged proteins
  • No copurification of proteins
  • Resists metal leakage
  • Performs well under a wide range of purification conditions

Applications

Purified recombinant his-tagged proteins can be used for:

  • Crystallography
  • Functional assays
  • Structural investigations
  • Other applications

Reagents Compatible with TALON Resin

Reagent Acceptable Concentration
Beta-mercaptoethanola 10 mM (with caution)
CHAPSb 1% (with caution)
Ethanolc 30%
Ethylene glycol 30%
HEPES 50 mM
Glycerol 20%
Guanidiniuma 6 mM
Imidazoled 200 mM at pH 7.0–8.0, for elution
KCl 500 mM
MES 20 mM
MOPS 50 mM
NaCl 1.0 M
NP-40 1%
SDSb 1% with caution
TRISe 50 mM
Triton-X 100 <1%
Urea 8 M

a Use resin immediately after equilibrating with buffers containing these reagents. Otherwise, the resin will change color. Do not store resin in buffers containing these reagents.
b Ionic detergents like CHAPS (3-[(3-Cholamidopropyl)-dimethylammonio]-1-propane-sulfonate), SDS (sodium dodecyl sulfate), and sarkosyl are compatible up to 1%. However, due to their charged nature, you should anticipate interference with binding.
c Ethanol may precipitate proteins, causing low yields and column clogging.
d Imidazole cannot be used at concentrations higher than 5–10 mM for loading his-tagged proteins, because it competes with the histidine side chains (imidazole groups) for binding to the immobilized metal ions.
e TRIS coordinates weakly with metal ions, causing a decrease in capacity.

Reagents Incompatible with TALON Resin

These reagents are incompatible at any concentration:

  • DTT (dithiothreitol) and DTE (dithioerythritol)
    NOTE: Using strong reducing agents will interfere with cobalt metal ion binding to the resin.

  • EDTA (ethylenediaminetetraacetic acid), EGTA (ethylene glycol-bis([β-amino-ethyl ether]), and PEI
    NOTE: Although you can use EDTA at indicated points, it must be removed from the sample by gel filtration prior to applying the sample to TALON Resins.

 
 
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