The tris-NTA/His-tag system comprises one of the smallest high-affinity recognition elements known to date. This interaction is based on the capacity of the histidine’s imidazole groups to form coordinative bonds with transition metal ions such as Ni(II). Chelators such as nitrilotriacetic acid (NTA) stably bind Ni(II) ions via three oxygen atoms and one nitrogen atom. The two remaining coordination sites of Ni(II) can each bind one histidine moiety of a His-tag, yielding a molecular binding affinity of ~10 μM. Tris-NTA is comprised of three NTA moieties coupled to a cyclic scaffold and thus can simultaneously bind six Histidine residues of a His₆-tag, yielding nanomolar binding affinity and a well-defined 1:1 stoichiometry.

peptide – small molecule interaction | His₆-tag | MO-P-059