Table 3.

Characteristics of Commonly used Fusion Tags

Tag	Protein	Amino acids	Size (kDa)	Source organism	Purification aid	Affinity matrix	Comments
Tags with solubility‐enhancing properties
GST	Glutathione S‐transferase	243	28.1	Schistosoma japonicum	Yes	Glutathione agarose	Forms dimer in solution
MBP	Maltose binding protein	390	43.0	Escherichia coli	Yes	Amylose resin	Strong solubility‐enhancer
DsbA	Disulfide oxidoreductase	228	25.4	Escherichia coli	No		Aids periplasmic disulfide‐bond formation
NusA	N‐utilizing substance A protein	535	59.3	Escherichia coli	No		Strong solubility‐enhancer
Trx	Thioredoxin	135	14.7	Escherichia coli	No		Aids cytosolic disulfide‐bond formation
Z‐domaina	Protein A IgG ZZ repeat domain	91	10.6	Staphylococcus aureus	Yes	Protein A‐sepharose
GB1b	Protein G β1 domain	85	9.7	Streptococcus sp.	Yes	IgG‐resins	Used often with proteins for NMR
SUMO	Small ubiquitin‐like modifier	99	11.1	Homo sapiens	No
SET	Solubility‐enhancing tags	<40		T7 phage gene 10B; synthetic	No		Small, highly acidic peptide tags that limit protein aggregation
HaloTag‐7c	Catalytically‐inactive derivative of DhaA	296	34.0	Rhodococcus sp.	Yes	HaloLink resin	Strong solubility‐enhancer
Tags without solubility‐enhancing properties
His6	Hexahistadine	6	0.8	Synthetic	Yes	Immobilized metal resin	Often combined with solubility‐enhancing tags
Inteind	Protein splicing element	128‐1650		Variable	Yes	Chitin resin	Remove from resin by induced self‐cleavage

^aSee Nilsson et al., 1987; Zhao et al., 2005.

^bSee Bao et al., 2006.

^cSee Ohana et al., 2009.

^dSee Chong et al., 1998; Singleton et al., 2002.

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