Protein tag
Protein tags are peptide sequences genetically grafted onto a
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),
Solubilization tags are used, especially for recombinant proteins expressed in species such as
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
- 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
Covalent peptide tags
- Isopeptag, a peptide which binds covalently to pilin-C protein (TDKDMTITFTNKKDAE)[19]
- SpyTag, a peptide which binds covalently to SpyCatcher protein (AHIVMVDAYKPTK)[20]
- SnoopTag, a peptide which binds covalently to SnoopCatcher protein (KLGDIEFIKVNK).[21] A second generation, SnoopTagJr, was also developed to bind to either SnoopCatcher or DogTag (mediated by SnoopLigase) (KLGSIEFIKVNK)[22]
- DogTag, a peptide which covalently binds to DogCatcher (DIPATYEFTDGKHYITNEPIPPK),[23] and can also covalently bind to SnoopTagJr, mediated by SnoopLigase [22]
- SdyTag, a peptide which binds covalently to SdyCatcher protein (DPIVMIDNDKPIT).[24] 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
- BromoTag, a "bump-and-hole" mutated version of the second PROTAC degrader AGB1 to form a ternary complex between the "BromoTagged" protein and the E3 ligase VHL, leading to ubiquitination of the tagged protein and its subsequent rapid and effective proteasomal degradation in cells.[25]
- FAST (Fluorescence-Activating and absorption-Shifting Tag), a mutated photoactive yellow protein (PYP) that reversibly binds cognate fluorogenic ligands
- CL7-tag, an engineered variant of Colicin E7 that has a strong binding affinity and specificity for immobilized Immunity Protein 7 (Im7). [26]
- Glutathione-S-transferase-tag, a protein which binds to immobilized glutathione
- Green fluorescent protein-tag,[4] a protein which is spontaneously fluorescent and can be bound by nanobodies
- HaloTag, a mutated bacterial haloalkane dehalogenase that covalently attaches to haloalkane substrates
- SNAP-tag, a mutated eukaryotic DNA methyltransferase that covalently attaches to benzylguanine derivatives
- CLIP-tag, a mutated eukaryotic DNA methyltransferase that covalently attaches to benzylcytosinederivatives
- HUH-tag, a sequence-specific single-stranded DNA binding protein that covalently binds to its target sequence
- Maltose binding protein-tag, a protein which binds to amylose agarose[27]
- 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,..)[28]
- Carbohydrate Recognition Domain or CRDSAT-tag, a protein which binds to lactose agarose or Sepharose[29]
Others
HiBiT-tag was developed by Scientists at 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.[30] Its small size leads to a rapid knock-in of this tag with other proteins through CRISPR/Cas9 technology.[30]
Applications
- Affinity purification
- Protein array
- TimeSTAMP protein labelling
- Western blotting
References
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