Cobalt exhibits a more specific interaction with histidine tags, resulting in less nonspecific interaction than nickel. For this reason, cobalt is the preferred divalent cation for purifying His-tagged proteins when high purity is a primary concern.

I read this last week, and I'm wondering, why is cobalt like that? What about it causes that?

(Source of quote: https://www.lifetechnologies.com/us/en/home/life-science/protein-biology/protein-biology-learning-center/protein-biology-resource-library/pierce-protein-methods/his-tagged-proteins-production-purification.html)

  • $\begingroup$ Could you edit your question to include a link to or at least a reference to where you read this? It's a very good question you ask, and I think experts here will want as much background info as possible to construct answers that are helpful for you. $\endgroup$ – Curt F. Apr 13 '15 at 20:15

Your question is about immobilized metal affinity chromatography (IMAC), often used to separate a protein expressed in the E. coli bacterium from other proteins made by it. The protein of interest is expressed with a histidine-containing affinity tag which binds to immobilized nickel or cobalt at neutral or basic pH. Immobilization is achieved by complexing to NTA (nitrilotriacetic acid) or IDA (iminodiacetic acid). For a discussion of the two ligands, see e.g. here.

There are a few proteins from E. coli (listed in this paper) that are known to bind along with the protein of interest. According to a post written by Damien Soghoian in 2004, nickel-NTA tends to bind stronger to histidine-tags while cobalt-NTA tends to bind more weakly, but this does not affect specificity (e.g. it would be across the board, not making the separation easier or harder).

| improve this answer | |

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.