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.