Epitope tagging is a technique that employs genetic engineering to fuse a known epitope, called an affinity tag, to either the C or N terminus of a recombinant protein to facilitate affinity purification and detection. This approach enables high selective capture and circumvents the multistep purification processes that limit throughput during R&D.

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The ideal affinity tag should be small in size and as inert as possible to limit any potential interaction with the recombinant protein or proteins that might be present in culture media.

CaptureSelect C-tagXL Affinity Tag System

CaptureSelect C-tagXL is a novel affinity tag system offering unique selectivity for a small four amino acid peptide tag: E-P-E-A (glutamic acid–proline–glutamic acid–alanine), which enables simple purification of C-tagged proteins.

C-tag benefits

  • Smallest affinity tag available comprised of four residues: E-P-E-A
  • Limited effect on protein functionality unlike larger tags (GST, HIS6)
  • High selectivity and binding affinity for recombinant protein purification
  • Enabling high target yield and purity from complex mixtures (compared to HIS6-tag)

CaptureSelect C-tagXL Resin

  • High binding affinity when E-P-E-A tag displayed at C-terminus of protein
  • Binding under both physiological and denaturing conditions (up to 8 M urea)
  • Crude feed stock can be applied
  • Mild elution, protecting the protein of interest
  • Robust and reusable affinity matrix
Product Characteristics
CaptureSelect C-tagXL Affinity Matrix

Unique selectivity for a small four amino acid peptide tag (E-P-E-A). Purifies C-terminal tagged proteins with high affinity and selectivity from complex mixtures like cell culture harvests and periplasmatic fractions in a one-step process.

CaptureSelect C-tagXL Affinity Matrix (pre-packed)
1 mL and 5 mL columns pre-packed with the CaptureSelect C-tagXL affinity matrix

CaptureSelect C-tag Affinity Matrix

Binds the short C-tag sequence E-P-E-A (glutamic acid - proline - glutamic acid – alanine) when this affinity tag is fused at the C-terminus of a target protein
CaptureSelect Biotin Anti-C-tag Conjugate Binds the short C-tag sequence E-P-E-A (glutamic acid - proline - glutamic acid – alanine) when this affinity tag is fused at the C-terminus of a target protein

Purification of a C-tagged protein


Figure 1. Coomassie Brilliant Blue (CBB) stained SDS-PAGE analysis of a C-tagged antibody fragment spiked in CHO cell culture harvest.

M. Molecular weight marker
1. CHO cell culture harvest
2. Flow through fraction
3. Wash fraction
4. Elution fraction


Additional reading

Application note

Reinventing Affinity Tags


Accelerating the clinical development of protein-based vaccines for malaria by efficient purification using a four amino acid C-terminal ‘C-tag’

The Biotechnological Applications of Recombinant Single-Domain Antibodies are Optimized by the C-Terminal Fusion to the EPEA Sequence (C Tag)

Discovery of C-tag: Structure and properties of a complex of α-synuclein and a single-domain camelid antibody


Anti-C-tag affinity ligand

In addition to the CaptureSelect C-tag affinity resin, the anti-C-tag affinity ligand is also available as conjugated ligand (conjugated to Biotin). This facilitates easy detection and or quantitation of EPEA C-tagged proteins using techniques such as ELISA, Western blot, and label-free platforms (Biacore™ and Octet®).


 For Research Use or Further Manufacturing. Not for diagnostic use or direct administration into humans or animals.