Histidine (His, H) is an amino acid. It is encoded by the codons CAU and CAC.

A string of  6-14 histidines is often called polyhistidine or His-tag.

The imidazole side chains of a His-tag can bind to certain transition metal ions (Ni, Co, Zn, Mg) whereas Nickle ion shows the highest affinity.


His-tag is used to drive nanoparticles to surfaces.

The imidazole side-chain/group/ring

The classic His-tag has six consecutive histidines. Due to their hydrophilic and flexible nature, His-tags can increase the solubility of target molecules.

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