Protein tag

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Protein tags are peptide sequences genetically grafted onto a recombinant protein. Often these tags are removable by chemical agents or by enzymatic means, such as proteolysis or intein splicing. Tags are attached to proteins for various purposes.

Affinity tags are appended to proteins so that they can be purified from their crude biological source using an affinity technique. These include chitin binding protein (CBP), maltose binding protein (MBP), and glutathione-S-transferase (GST). The poly(His) tag is a widely used protein tag; it binds to metal matrices.

Solubilization tags are used, especially for recombinant proteins expressed in chaperone-deficient species such as E. coli, to assist in the proper folding in proteins and keep them from precipitating. These include thioredoxin (TRX) and poly(NANP). Some affinity tags have a dual role as a solubilization agent, such as MBP, and GST.

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.

Epitope tags are short peptide sequences which are chosen because high-affinity antibodies can be reliably produced in many different species. These are usually derived from viral genes, which explain their high immunoreactivity. Epitope tags include V5-tag, Myc-tag, and HA-tag. These tags are particularly useful for western blotting, immunofluorescence and immunoprecipitation experiments, although they also find use in antibody purification.

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

Protein tags find many other usages, such as specific enzymatic modification (such as biotin ligase tags) and chemical modification (FlAsH) tag. Often tags are combined to produce multifunctional modifications of the protein. However, with the addition of each tag comes the risk that the native function of the protein may be abolished or compromised by interactions with the tag. Therefore, after purification, tags are commonly removed by specific proteolysis (e.g. by TEV protease, Thrombin, Factor Xa or Enteropeptidase)

List of protein tags[edit]

(See Proteinogenic_amino_acid#Chemical_properties for the A-Z amino-acid codes)

Peptide tags[edit]

  • AviTag, a peptide allowing biotinylation by the enzyme BirA and so the protein can be isolated by streptavidin (GLNDIFEAQKIEWHE)
  • Calmodulin-tag, a peptide bound by the protein calmodulin (KRRWKKNFIAVSAANRFKKISSSGAL)
  • polyglutamate tag, a peptide binding efficiently to anion-exchange resin such as Mono-Q (EEEEEE)
  • E-tag, a peptide recognized by an antibody (GAPVPYPDPLEPR)
  • FLAG-tag, a peptide recognized by an antibody (DYKDDDDK)[1]
  • HA-tag, a peptide from hemagglutinin recognized by an antibody (YPYDVPDYA)[2]
  • His-tag, 5-10 histidines bound by a nickel or cobalt chelate (HHHHHH)
  • Myc-tag, a peptide derived from c-myc recognized by an antibody (EQKLISEEDL)
  • S-tag, a peptide derived from Ribonuclease A (KETAAAKFERQHMDS)
  • SBP-tag, a peptide which binds to streptavidin (MDEKTTGWRGGHVVEGLAGELEQLRARLEHHPQGQREP)[3][4]
  • Softag 1, for mammalian expression (SLAELLNAGLGGS)
  • Softag 3, for prokaryotic expression (TQDPSRVG)
  • Strep-tag, a peptide which binds to streptavidin or the modified streptavidin called streptactin (Strep-tag II: WSHPQFEK)[5]
  • TC tag, a tetracysteine tag that is recognized by FlAsH and ReAsH biarsenical compounds (CCPGCC)
  • V5 tag, a peptide recognized by an antibody (GKPIPNPLLGLDST)[6]
  • VSV-tag, a peptide recognized by an antibody (YTDIEMNRLGK)
  • Xpress tag (DLYDDDDK)

Covalent peptide tags[edit]

  • Isopeptag, a peptide which binds covalently to pilin-C protein (TDKDMTITFTNKKDAE)[7]
  • SpyTag, a peptide which binds covalently to SpyCatcher protein (AHIVMVDAYKPTK)[8]

Protein tags[edit]

  • BCCP (Biotin Carboxyl Carrier Protein), a protein domain biotinylated by BirA enabling recognition by streptavidin
  • Glutathione-S-transferase-tag, a protein which binds to immobilized glutathione
  • Green fluorescent protein-tag, a protein which is spontaneously fluorescent and can be bound by nanobodies
  • Halo-tag, a mutated hydrolase that covalently attaches to the HaloLink™ Resin (Promega)
  • Maltose binding protein-tag, a protein which binds to amylose agarose
  • Nus-tag
  • Thioredoxin-tag
  • Fc-tag, derived from immunoglobulin Fc domain, allow dimerization and solubilization. Can be used for purification on Protein-A Sepharose
  • Designed Intrinsically Disordered tags containing disorder promoting amino acids (P,E,S,T,A,Q,G,..)[9]




  1. ^ Einhauer, A.; Jungbauer, A. (2001). "The FLAG™ peptide, a versatile fusion tag for the purification of recombinant proteins". Journal of Biochemical and Biophysical Methods 49 (1–3): 455–65. doi:10.1016/S0165-022X(01)00213-5. PMID 11694294. 
  2. ^ Prakriya, Murali; Feske, Stefan; Gwack, Yousang; Srikanth, Sonal; Rao, Anjana; Hogan, Patrick G. (2006). "Orai1 is an essential pore subunit of the CRAC channel". Nature 443 (7108): 230–3. Bibcode:2006Natur.443..230P. doi:10.1038/nature05122. PMID 16921383. 
  3. ^ Keefe, Anthony D.; Wilson, David S.; Seelig, Burckhard; Szostak, Jack W. (2001). "One-Step Purification of Recombinant Proteins Using a Nanomolar-Affinity Streptavidin-Binding Peptide, the SBP-Tag". Protein Expression and Purification 23 (3): 440–6. doi:10.1006/prep.2001.1515. PMID 11722181. 
  4. ^ Gelerter, Bruce (June 11, 2014). "PEMF For Treatment Of Corneal Disorders And Injuries". [self-published source?]
  5. ^ Schmidt, Thomas G.M.; Koepke, Jürgen; Frank, Ronald; Skerra, Arne (1996). "Molecular Interaction Between the Strep-tag Affinity Peptide and its Cognate Target, Streptavidin". Journal of Molecular Biology 255 (5): 753–66. doi:10.1006/jmbi.1996.0061. PMID 8636976. 
  6. ^ McNutt, Markey C.; Lagace, Thomas A.; Horton, Jay D. (2007). "Catalytic Activity is Not Required for Secreted PCSK9 to Reduce Low Density Lipoprotein Receptors in HepG2 Cells". Journal of Biological Chemistry 282 (29): 20799–803. doi:10.1074/jbc.C70009520. PMID 17537735. 
  7. ^ Zakeri, Bijan; Howarth, Mark (2010). "Spontaneous Intermolecular Amide Bond Formation between Side Chains for Irreversible Peptide Targeting". Journal of the American Chemical Society 132 (13): 4526–7. doi:10.1021/ja910795a. PMID 20235501. 
  8. ^ Zakeri, Bijan; Fierer, Jacob O.; Celik, Emrah; Chittock, Emily C.; Schwarz-Linek, Ulrich; Moy, Vincent T.; Howarth, Mark (2012). "Peptide tag forming a rapid covalent bond to a protein, through engineering a bacterial adhesin". Proceedings of the National Academy of Sciences 109 (12): E690–7. Bibcode:2012PNAS..109E.690Z. doi:10.1073/pnas.1115485109. PMC 3311370. PMID 22366317. 
  9. ^ Minde, David P; Halff, Els F; Tans, Sander (2013). "Designing disorder: Tales of the unexpected tails". Intrinsically Disordered Proteins 1: 5–15. doi:10.4161/idp.26790.