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Polyhistidine-tag

A polyhistidine-tag is an amino acid motif in proteins that consists of at least six histidine residues, often at the N- or C-terminus of the protein. It is also known as hexa histidine-tag, 6xHis-tag, His6 tag and by the trademarked name His-tag. The tag was invented by Roche, although the use of histidines and its vectors are distributed by Qiagen. Various purification kits for histidine-tagged proteins are available from Qiagen, Sigma, Thermo Scientific, GE Healthcare, Macherey-Nagel, Clontech, Bio-Rad, and others. The use of the tag for academic users is unrestricted; however, commercial users must pay royalties to Roche. The original patent expired on 11 Feb 2003, and thus should be 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; for example, MK(HQ)6 may be used for enhanced expression in E. coli and tag removal. The total number of histidine residues may vary in the tag. The his-tag may also be followed by a suitable amino acid sequence that facilitates a removal of the polyhistidine-tag using endopeptidases. This extra sequence is not necessary if exopeptidases are used to remove N-terminal His-tags. 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. This video is targeted to blind users. Attribution: Article text available under CC-BY-SA Creative Commons image source in video