Protein tag

Protein tags are peptide sequences genetically grafted onto a

Chromatography tags are used to alter chromatographic properties of the protein to afford different resolution across a particular separation technique. Often, these consist of polyanionic amino acids, such as FLAG-tag or polyglutamate tag.^[3]

Fluorescence tags are used to give visual readout on a protein. Green fluorescent protein (GFP) and its variants are the most commonly used fluorescence tags.^[4] More advanced applications of GFP include using it as a folding reporter (fluorescent if folded, colorless if not).

Protein tags may allow specific enzymatic modification (such as

List of protein tags

(See Proteinogenic amino acid#Chemical properties for the A-Z amino-acid codes)

Peptide tags

• ALFA-tag, a de novo designed helical peptide tag (SRLEEELRRRLTE) for biochemical and microscopy applications. The tag is recognized by a repertoire of single-domain antibodies ^[5]
• AviTag, a peptide allowing biotinylation by the enzyme BirA and so the protein can be isolated by streptavidin (GLNDIFEAQKIEWHE)
• C-tag, a peptide that binds to a single-domain camelid antibody developed through phage display (EPEA)^[6][7]
• Calmodulin-tag, a peptide bound by the protein calmodulin (KRRWKKNFIAVSAANRFKKISSSGAL)
• iCapTag™ (intein Capture Tag), a self-removing peptide-based tag (MIKIATRKYLGKQNVYGIGVERDHNFALKNGFIAHN). The iCapTag™ is controlled by pH change (typically pH 8.5 to pH 6.2). Therefore, this technology can be adapted to a wide range of buffers adjusted to the target pH values of 8.5 and 6.2. The expected purity of target proteins or peptides is between 95-99%. The iCapTag™ contains patented component derived from
  mAbs^[8][9][10]
• polyglutamate tag, a peptide binding efficiently to anion-exchange resin such as Mono-Q (EEEEEE) [3]
• polyarginine tag, a peptide binding efficiently to cation-exchange resin (from 5 to 9 consecutive R)
• E-tag, a peptide recognized by an antibody (GAPVPYPDPLEPR)
• FLAG-tag, a peptide recognized by an antibody (DYKDDDDK)^[11]
• HA-tag, a peptide from hemagglutinin recognized by an antibody (YPYDVPDYA)^[12]
• His-tag, 5-10 histidines bound by a nickel or cobalt chelate (HHHHHH)
  • Gly-His-tags are N-terminal His-Tag variants (e.g. GHHHH, or GHHHHHH, or GSSHHHHHH) that still bind to immobilised metal cations but can also be activated via azidogluconoylation to enable click-chemistry applications^[13]
• Myc-tag, a peptide derived from c-myc recognized by an antibody (EQKLISEEDL)
• NE-tag, an 18-amino-acid synthetic peptide (TKENPRSNQEESYDDNES) recognized by a monoclonal IgG1 antibody, which is useful in a wide spectrum of applications including Western blotting, ELISA, flow cytometry, immunocytochemistry, immunoprecipitation, and affinity purification of recombinant proteins ^[14]
• Rho1D4-tag, refers to the last 9 amino acids of the intracellular C-terminus of bovine rhodopsin (TETSQVAPA). It is a very specific tag that can be used for purification of membrane proteins.
• S-tag, a peptide derived from Ribonuclease A (KETAAAKFERQHMDS)
• SBP-tag, a peptide which binds to streptavidin (MDEKTTGWRGGHVVEGLAGELEQLRARLEHHPQGQREP)^{[15][16][self-published source?]}
• Softag 1, for mammalian expression (SLAELLNAGLGGS)
• Softag 3, for prokaryotic expression (TQDPSRVG)
• nanobody
  (PDRVRAVSHWSS) for immunoprecipitation, affinity purification, immunofluorescence and super resolution microscopy
• Strep-tag, a peptide which binds to streptavidin or the modified streptavidin called streptactin (Strep-tag II: WSHPQFEK)^[2]
• affinity purification Mainly used ^[17]
• TC tag, a tetracysteine tag that is recognized by FlAsH and ReAsH biarsenical compounds (CCPGCC)
• Ty tag (EVHTNQDPLD)
• V5 tag, a peptide recognized by an antibody (GKPIPNPLLGLDST)^[18]
• VSV-tag, a peptide recognized by an antibody (YTDIEMNRLGK)
• Xpress tag (DLYDDDDK), a peptide recognized by an antibody