The fusion of a small protein or peptide (tag) to the protein of interest is a commonly used method to aid purification of recombinant proteins.

Fusion tags can improve protein expression, stability, resistance to proteolytic degradation and solubility. A wide range of fusion tags are available from small peptides to relatively large proteins, each with its own unique characteristics. Many solubility tags are engineered for use in bacterial expression systems to overcome poor protein solubility.

Fusion Tag Function Size (kDa) Description
Polyhistidine (e.g. 6xHis, 10xHis) Affinity 1-2 The most commonly used affinity tag, binds to metal ions
Strep-tag II Affinity 1 High affinity for engineered streptavidin
Thioredoxin (Trx) Solubility 12 Aids in refolding proteins that require a reducing environment
Small Ubiquitin-like Modifier (SUMO) Solubility 12 Contains a native cleavage sequence enabling tag removal with SUMO protease
Glutathione S-transferase (GST) Solubility, affinity 26 High affinity for glutathione, often needs to be removed due to large size
Maltose Binding Protein (MBP) Solubility, affinity 41 Binds to maltose, often needs to be removed due to large size