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Epitope Tag Antibodies

Epitope tag antibodies recognize and bind epitope tags, the short peptide sequences that are typically added to the N- or C- termini of proteins through genetic engineering to facilitate detection and isolation. They offer many advantages for scientific research, including the ability to study protein targets for which specific antibodies are not available.

Our high-quality, in-house produced epitope tag antibodies are supplied either unconjugated or labeled with biotin, fluorescein (FITC), horseradish peroxidase (HRP), alkaline phosphatase (AP), R-phycoerythrin (PE), Sepharose® (agarose), and Alexa Fluor® dyes. Validated applications include ELISA, flow cytometry, and western blot, as well as immunocytochemistry, immunoprecipitation, and purification.

Frequently Asked Questions

An epitope tag is a well-characterized antigenic determinant that can be attached to a protein of interest through genetic engineering, thus enabling that protein to be recognized by an epitope tag antibody. Although the term epitope tag is commonly used to describe a short peptide, it also encompasses a multitude of larger protein molecules. Choosing between the different tags that are available depends on the intended downstream application.

Epitope tags are mainly used to facilitate protein detection and isolation. For detection purposes, routine immunoassays such as western blot and ELISA use epitope tag antibodies for either direct or indirect detection. Protein isolation is achieved by immobilizing epitope tag antibodies onto a bead or chromatographic resin to extract the epitope tagged protein from solution.

A major benefit of using epitope tags is that they allow for studying proteins to which specific antibodies are not available, such as newly discovered targets or proteins that are poorly immunogenic. Epitope tags also increase accessibility to antibodies that have been validated for a particular application. In addition, epitope tags can improve the detection or isolation of proteins that have low abundance in endogenous conditions. Notably, epitope tag antibodies may represent a more cost-effective option than using target-specific antibodies.

Epitope tags can be broadly categorized as peptide tags, protein tags, and fluorescent protein reporters. The following are some of the most widely used examples:

Peptide tags

  • His-tag

A His-tag, also known as a polyhistidine tag, comprises a series of 6 to 10 histidine residues. The 6 residue format (6-His), which has a molecular weight of just 0.8 kDa, is used most often. An advantage of His-tags is that they allow for affinity purification using inexpensive and readily available nickel or cobalt resins.

  • S-tag

The S-tag consists of the N-terminal 15 amino acid residues of pancreatic RNase A (KETAAAKFERQHMDS) and has a molecular weight of 1.8 kDa. It binds with high affinity to the S-protein, which comprises residues 21-124 of the same RNase enzyme.

  • DYKDDDDK-tag

The DYKDDDDK-tag, also known as the FLAG®-tag, is a hydrophilic epitope tag with a molecular weight of 1 kDa. It can be added singly, in tandem, or in triplicate, with the most commonly used triplicate motif being DYKDHDG-DYKDHDI-DYKDDDDK. The DYKDDDDK-tag is easily removed with enterokinase, which cleaves after the lysine (DDDDK^X).

  • Myc

The Myc tag is a 10 amino acid peptide (EQKLISEEDL) with a molecular weight of 1.2kDa that is derived from the Myc proto-oncogene. It is frequently used for immunoassays such as western blot and flow cytometry, but less often for purification since elution requires low pH, which risks damaging the tagged protein.

Protein tags

  • Glutathione S-Transferase (GST)

GST is a 26 kDa protein, derived from the parasite Schistosoma japonicum, that binds with strong affinity to its substrate, glutathione. It is useful for increasing the solubility of recombinant proteins, especially those expressed in bacteria. However, the large size of GST can interfere with some protein functions and often necessitates its removal by protease cleavage.

  • Maltose-Binding Protein (MBP)

MBP is a 43 kDa protein, encoded by the malE gene of Escherichia coli, that allows for affinity purification using amylose resins. It is one of the most common crystallization chaperones and, like GST, can improve the solubility of recombinant proteins expressed in bacteria.

  • Small Ubiquitin-like Modifier (SUMO)

SUMO is a 12 kDa protein that regulates protein function by serving as a post-translational modification. It has been shown to improve the stability and solubility of recombinant proteins and is easily removed using SUMO-specific proteases.

Fluorescent protein reporters

  • Green Fluorescent Protein (GFP)

Originally derived from the jellyfish Aequorea victoria, GFP is one of the longest established fluorescent proteins for scientific research. It has a molecular weight of 27 kDa and is widely used for immunofluorescence, flow cytometry, and fluorescence resonance energy transfer (FRET), as well as for live-cell imaging studies.

  • DsRed

DsRed, a 30 kDa protein isolated from Discosoma sp., was the first red fluorescent protein (RFP) to be discovered. A main advantage of DsRed, and RFPs generally, is that the red-shifted wavelength spectrum avoids damaging cells and tissues by excitation light, as well as is distinct from autofluorescence.

  • mCherry

mCherry is a second-generation RFP that was developed via the directed mutagenesis of DsRed. It has a molecular weight of 27 kDa and benefits from good photostability, rapid maturation (assembly), and low acid sensitivity.