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Protein tags are peptide sequences genetically grafted onto a
recombinant protein Recombinant DNA (rDNA) molecules are DNA molecules formed by laboratory methods of genetic recombination (such as molecular cloning) that bring together genetic material from multiple sources, creating DNA sequence, sequences that would not othe ...
. Tags are attached to proteins for various purposes. They can be added to either end of the target protein, so they are either C-terminus or N-terminus specific or are both C-terminus and N-terminus specific. Some tags are also inserted at sites within the protein of interest; they are known as internal tags. Affinity tags are appended to proteins so that they can be purified from their crude biological source using an affinity technique. Affinity tags include chitin binding protein (CBP),
maltose binding protein Maltose-binding protein (MBP) is a part of the maltose/maltodextrin system of ''Escherichia coli'', which is responsible for the uptake and efficient catabolism of maltodextrins. It is a complex regulatory and transport system involving many pro ...
(MBP), Strep-tag and
glutathione-S-transferase Glutathione ''S''-transferases (GSTs), previously known as ligandins, are a family of eukaryotic and prokaryotic phase II metabolic isozymes best known for their ability to catalyze the conjugation of the reduced form of glutathione (GSH) to x ...
(GST). The poly(His) tag is a widely used protein tag, which binds to matrices bearing immobilized metal ions. Solubilization tags are used, especially for recombinant proteins expressed in species such as '' E. coli'', to assist in the proper folding in proteins and keep them from aggregating in inclusion bodies. These tags include
thioredoxin Thioredoxin is a class of small redox proteins known to be present in all organisms. It plays a role in many important biological processes, including redox signaling. In humans, thioredoxins are encoded by ''TXN'' and '' TXN2'' genes. Loss-of-fu ...
(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 FLAG-tag, or FLAG octapeptide, or FLAG epitope, is a peptide protein tag that can be added to a protein using recombinant DNA technology, having the sequence DYKDDDDK (where D= aspartic acid, Y=tyrosine, and K= lysine). It is one of the most specifi ...
or polyglutamate tag.
Epitope An epitope, also known as antigenic determinant, is the part of an antigen that is recognized by the immune system, specifically by antibodies, B cells, or T cells. The epitope is the specific piece of the antigen to which an antibody binds. The p ...
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 ALFA-tag, V5-tag,
Myc-tag A myc tag is a polypeptide protein tag derived from the c-myc gene product that can be added to a protein using recombinant DNA technology. It can be used for affinity chromatography, then used to separate recombinant, overexpressed protein from wil ...
,
HA-tag Human influenza hemagglutinin (HA) is a surface glycoprotein required for the infectivity of the human influenza virus. The HA-tag is derived from the HA-molecule corresponding to amino acids 98-106. HA-tag has been extensively used as a general ...
, Spot-tag, T7-tag and NE-tag. These tags are particularly useful for
western blotting The western blot (sometimes called the protein immunoblot), or western blotting, is a widely used analytical technique in molecular biology and immunogenetics to detect specific proteins in a sample of tissue homogenate or extract. Besides detect ...
, immunofluorescence and immunoprecipitation experiments, although they also find use in antibody purification. 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. 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
biotinylation In biochemistry, biotinylation is the process of covalently attaching biotin to a protein, nucleic acid or other molecule. Biotinylation is rapid, specific and is unlikely to disturb the natural function of the molecule due to the small size of bi ...
by biotin ligase) or chemical modification (such as coupling to other proteins through SpyCatcher or reaction with
FlAsH-EDT2 FlAsH-EDT2 is an organoarsenic compound with molecular formula C24H18As2O5S4. Its structure is based around a fluorescein core with two 1,3,2-dithiarsolane substituents. It is used in bioanalytical research as a fluorescent label for visualisi ...
for fluorescence imaging). Often tags are combined, in order to connect proteins to multiple other components. However, with the addition of each tag comes the risk that the native function of the protein may be compromised by interactions with the tag. Therefore, after purification, tags are sometimes removed by specific proteolysis (e.g. by TEV protease,
Thrombin Thrombin (, ''fibrinogenase'', ''thrombase'', ''thrombofort'', ''topical'', ''thrombin-C'', ''tropostasin'', ''activated blood-coagulation factor II'', ''blood-coagulation factor IIa'', ''factor IIa'', ''E thrombin'', ''beta-thrombin'', ''gamma- ...
,
Factor Xa Factor X, also known by the eponym Stuart–Prower factor, is an enzyme () of the coagulation cascade. It is a serine endopeptidase (protease group S1, PA clan). Factor X is synthesized in the liver and requires vitamin K for its synthesis. Fa ...
or
Enteropeptidase Enteropeptidase (also called enterokinase) is an enzyme produced by cells of the duodenum and is involved in digestion in humans and other animals. Enteropeptidase converts trypsinogen (a zymogen) into its active form trypsin, resulting in the ...
) or intein splicing.


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 * AviTag, a peptide allowing
biotinylation In biochemistry, biotinylation is the process of covalently attaching biotin to a protein, nucleic acid or other molecule. Biotinylation is rapid, specific and is unlikely to disturb the natural function of the molecule due to the small size of bi ...
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) * Calmodulin-tag, a peptide bound by the protein calmodulin (KRRWKKNFIAVSAANRFKKISSSGAL) * ''i''CapTag™ (''intein'' Capture Tag), peptide-based a self-removing tag controlled by pH change (MIKIATRKYLGKQNVYGIGVERDHNFALKNGFIAHN). Its patented component derived from ''
Nostoc punctiforme ''Nostoc punctiforme'' is a species of filamentous cyanobacterium. Under non-limiting nutritional environmental conditions, its filaments are composed of photosynthetic vegetative cells; upon nutrient limitation, some of these cells undergo dif ...
'' (Npu) intein. This tag is used for protein purification o
recombinant proteins
and its fragments. It can be used in research labs and it is intended for large-scale purification during downstream manufacturing process as well. The ''i''CapTag™-target protein complex can be expressed in a wide range of expression hosts (''e.g.'' CHO and ''
E.coli ''Escherichia coli'' (),Wells, J. C. (2000) Longman Pronunciation Dictionary. Harlow ngland Pearson Education Ltd. also known as ''E. coli'' (), is a Gram-negative, facultative anaerobic, rod-shaped, coliform bacterium of the genus ''Esche ...
'' cells). It is not intended for fully expressed mAbs or membrane proteins * polyglutamate tag, a peptide binding efficiently to anion-exchange resin such as Mono-Q (EEEEEE) * 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 FLAG-tag, or FLAG octapeptide, or FLAG epitope, is a peptide protein tag that can be added to a protein using recombinant DNA technology, having the sequence DYKDDDDK (where D= aspartic acid, Y=tyrosine, and K= lysine). It is one of the most specifi ...
, a peptide recognized by an antibody (DYKDDDDK) *
HA-tag Human influenza hemagglutinin (HA) is a surface glycoprotein required for the infectivity of the human influenza virus. The HA-tag is derived from the HA-molecule corresponding to amino acids 98-106. HA-tag has been extensively used as a general ...
, a peptide from
hemagglutinin In molecular biology, hemagglutinins (or ''haemagglutinin'' in British English) (from the Greek , 'blood' + Latin , 'glue') are receptor-binding membrane fusion glycoproteins produced by viruses in the '' Paramyxoviridae'' family. Hemagglutinins a ...
recognized by an antibody (YPYDVPDYA) *
His-tag A polyhistidine-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 hexa histidine-tag, 6xHis-tag, His6 tag, by the US tra ...
, 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 *
Myc-tag A myc tag is a polypeptide protein tag derived from the c-myc gene product that can be added to a protein using recombinant DNA technology. It can be used for affinity chromatography, then used to separate recombinant, overexpressed protein from wil ...
, a peptide derived from c-
myc ''Myc'' is a family of regulator genes and proto-oncogenes that code for transcription factors. The ''Myc'' family consists of three related human genes: ''c-myc'' (MYC), ''l-myc'' ( MYCL), and ''n-myc'' (MYCN). ''c-myc'' (also sometimes refe ...
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
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 protein Membrane proteins are common proteins that are part of, or interact with, biological membranes. Membrane proteins fall into several broad categories depending on their location. Integral membrane proteins are a permanent part of a cell membrane ...
s. * S-tag, a peptide derived from Ribonuclease A (KETAAAKFERQHMDS) *
SBP-tag The Streptavidin-Binding Peptide (SBP)-Tag is a 38-amino acid sequence that may be engineered into recombinant proteins. Recombinant proteins containing the SBP-Tag bind to streptavidin and this property may be utilized in specific purification, ...
, a peptide which binds to streptavidin (MDEKTTGWRGGHVVEGLAGELEQLRARLEHHPQGQREP) * Softag 1, for mammalian expression (SLAELLNAGLGGS) * Softag 3, for prokaryotic expression (TQDPSRVG) * Spot-tag, a peptide recognized by a
nanobody A single-domain antibody (sdAb), also known as a nanobody, is an antibody fragment consisting of a single monomeric Variable region, variable antibody domain. Like a whole antibody, it is able to bind selectively to a specific antigen. With a mol ...
(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) * T7-tag, an epitope tag derived from the T7 major capsid protein of the T7 gene (MASMTGGQQMG). Used in different immunoassays as well as
affinity purification Affinity chromatography is a method of separating a biomolecule from a mixture, based on a highly specific macromolecular binding interaction between the biomolecule and another substance. The specific type of binding interaction depends on the ...
Mainly used * 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) * VSV-tag, a peptide recognized by an antibody (YTDIEMNRLGK) * Xpress tag (DLYDDDDK), a peptide recognized by an antibody


Covalent peptide tags

* Isopeptag, a peptide which binds covalently to pilin-C protein (TDKDMTITFTNKKDAE) * SpyTag, a peptide which binds covalently to SpyCatcher protein (AHIVMVDAYKPTK) * SnoopTag, a peptide which binds covalently to SnoopCatcher protein (KLGDIEFIKVNK). A second generation, SnoopTagJr, was also developed to bind to either SnoopCatcher or DogTag (mediated by SnoopLigase) (KLGSIEFIKVNK) * DogTag, a peptide which covalently binds to DogCatcher (DIPATYEFTDGKHYITNEPIPPK), and can also covalently bind to SnoopTagJr, mediated by SnoopLigase * SdyTag, a peptide which binds covalently to SdyCatcher protein (DPIVMIDNDKPIT). SdyTag/SdyCatcher has a kinetic-dependent cross-reactivity with SpyTag/SpyCatcher.


Protein tags

* BCCP (Biotin Carboxyl Carrier Protein), a protein domain biotinylated by BirA enabling recognition by streptavidin *
Glutathione-S-transferase Glutathione ''S''-transferases (GSTs), previously known as ligandins, are a family of eukaryotic and prokaryotic phase II metabolic isozymes best known for their ability to catalyze the conjugation of the reduced form of glutathione (GSH) to x ...
-tag, a protein which binds to immobilized glutathione * Green fluorescent protein-tag, a protein which is spontaneously fluorescent and can be bound by nanobodies *
HaloTag HaloTag is a self-labeling protein tag. It is a 297 residue protein (33 kDa) derived from a bacterial enzyme, designed to covalently bind to a synthetic ligand. The bacterial enzyme can be fused to various proteins of interest. The synthetic ligand ...
, a mutated bacterial
haloalkane dehalogenase In enzymology, a haloalkane dehalogenase () is an enzyme that catalyzes the chemical reaction :1-haloalkane + H2O \rightleftharpoons a primary alcohol + halide Thus, the two substrates of this enzyme are 1-haloalkane and H2O, whereas its two ...
that covalently attaches to haloalkane substrates *
SNAP-tag SNAP-tag® is a self-labeling protein tag commercially available in various expression vectors. SNAP-tag is a 182 residues polypeptide (19.4 kDa) that can be fused to any protein of interest and further specifically and covalently tagged with a sui ...
, a mutated eukaryotic
DNA methyltransferase In biochemistry, the DNA methyltransferase (DNA MTase, DNMT) family of enzymes catalyze the transfer of a methyl group to DNA. DNA methylation serves a wide variety of biological functions. All the known DNA methyltransferases use S-adenosyl m ...
that covalently attaches to benzylguanine derivatives *
CLIP-tag SNAP-tag® is a self-labeling protein tag commercially available in various expression vectors. SNAP-tag is a 182 residues polypeptide (19.4 kDa) that can be fused to any protein of interest and further specifically and covalently tagged with a sui ...
, a mutated eukaryotic
DNA methyltransferase In biochemistry, the DNA methyltransferase (DNA MTase, DNMT) family of enzymes catalyze the transfer of a methyl group to DNA. DNA methylation serves a wide variety of biological functions. All the known DNA methyltransferases use S-adenosyl m ...
that covalently attaches to benzylcytosine derivatives *
HUH-tag HUH endonucleases (HUH-tags) are sequence-specific single-stranded DNA (ssDNA) binding proteins originating from numerous species of bacteria and viruses. Viral HUH endonucleases are involved in initiating rolling circle replication while ones o ...
, a sequence-specific single-stranded DNA binding protein that covalently binds to its target sequence *
Maltose binding protein Maltose-binding protein (MBP) is a part of the maltose/maltodextrin system of ''Escherichia coli'', which is responsible for the uptake and efficient catabolism of maltodextrins. It is a complex regulatory and transport system involving many pro ...
-tag, a protein which binds to amylose agarose * Nus-tag *
Thioredoxin Thioredoxin is a class of small redox proteins known to be present in all organisms. It plays a role in many important biological processes, including redox signaling. In humans, thioredoxins are encoded by ''TXN'' and '' TXN2'' genes. Loss-of-fu ...
-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,..) * Carbohydrate Recognition Domain or CRDSAT-tag, a protein which binds to lactose agarose or Sepharose


Others

HiBiT-tag was developed by Scientists a
Promega.
It is an 11-amino-acid peptide tag, and it can be fused to the N- or C-terminus or internal locations of proteins. Its small size leads to a rapid knock-in of this tag with other proteins through CRISPR/Cas9 technology.


Applications

*
Affinity purification Affinity chromatography is a method of separating a biomolecule from a mixture, based on a highly specific macromolecular binding interaction between the biomolecule and another substance. The specific type of binding interaction depends on the ...
*
Protein array A protein microarray (or protein chip) is a high-throughput method used to track the interactions and activities of proteins, and to determine their function, and determining function on a large scale. Its main advantage lies in the fact that larg ...
* TimeSTAMP protein labelling *
Western blotting The western blot (sometimes called the protein immunoblot), or western blotting, is a widely used analytical technique in molecular biology and immunogenetics to detect specific proteins in a sample of tissue homogenate or extract. Besides detect ...


References

{{DEFAULTSORT:Protein Tag Biochemical separation processes Biochemistry detection methods Laboratory techniques Molecular biology techniques Peptide sequences Protein methods