His-tag

A simple gravity flow column for Ni2+-affinity chromatography. The sample and subsequent buffers are manually poured into the column and collected at the bottom end after flowing through the resin bed (in light blue at the base of the column).

A polyhistidine-tag, best known by the trademarked name His-tag, is an amino acid motif in proteins that typically consists of at least six histidine (His) residues, often at the N- or C-terminus of the protein. It is also known as a hexa histidine-tag, 6xHis-tag, or His6 tag. The tag was invented by Roche,[1] although the use of histidines and its vectors are distributed by Qiagen. Various purification kits for histidine-tagged proteins are commercially available from multiple companies.[2]

The total number of histidine residues may vary in the tag from as low as two, to as high as 10 or more His residues. N- or C-terminal His-tags may also be followed or preceded, respectively, by a suitable amino acid sequence that facilitates removal of the polyhistidine-tag using endopeptidases. This extra sequence is not necessary if exopeptidases are used to remove N-terminal His-tags (e.g., Qiagen TAGZyme). Furthermore, exopeptidase cleavage may solve the unspecific cleavage observed when using endoprotease-based tag removal. Polyhistidine-tags are often used for affinity purification of genetically modified proteins.

  1. ^ Hochuli E, Bannwarth W, Döbeli H, Gentz R, Stüber D (1988). "Genetic Approach to Facilitate Purification of Recombinant Proteins with a Novel Metal Chelate Adsorbent". Bio/Technology. 6 (11): 1321–5. doi:10.1038/nbt1188-1321. S2CID 9518666. INIST 7229670.
  2. ^ The use of the tag for academic users was unrestricted; however, commercial users had to pay royalties to Roche. The original patent expired on 11 Feb 2003, and is now public property; current claims to royalties are based on a much narrower set of more recent patents. Suitable tag sequences are available free for commercial use.