Abstract
Don't let go! The Co(3+)-mediated interaction between nitrilotriacetic acid (NTA) and the His6-tag is so stable and inert towards ligand exchange that it has a half-life of 7 days in the presence of imidazole and survives even under strongly chelating as well as reducing conditions, unlike the commonly used Ni(2+) or Co(2+) complexes. Possible applications include the separation of labeled proteins and the stable immobilization of proteins on surfaces.
Highlights
In the [NiIINTA(His6-tag)] complex, the Ni2+ ion is in an octahedral coordination environment, where four coordination sites are occupied by nitrilotriacetic acid (NTA) and two by the His6-tag
Enediaminetetraacetic acid) quickly disturb the complex. While this reversible character is favorable for applications such as protein purification, it is problematic if a permanent interaction is desired
Researchers have proposed the addition of multiple NTA groups to increase affinity[18,19,20] or forming covalent bonds through photo-chemical[21,22][23,24] reactions to achieve a permanent interaction, but these approaches typically require complex syntheses and are often unspecific
Summary
In the [NiIINTA(His6-tag)] complex, the Ni2+ ion is in an octahedral coordination environment, where four coordination sites are occupied by NTA and two by the His6-tag. Using Co3+ as the mediator ion between NTA and His6tagged proteins instead of the commonly used Co2+ and Ni2+ ions leads to the formation a complex that is drastically more stable in such a coordination environment and is inert to ligand-exchange reactions.
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