Table 3.

Properties and applications of commonly used fusion tags sorted by class of use in alphabetical order.

Tag (Reference(s))	Size*	Organism	Tag placement	Use	Used in membrane protein expression in [expression system]?
Calmodulin binding domain (Vaillancourt et al. 2000)	26 aa	Mammalian	N- or C-terminal	Purification	Yes (Pestov and Rydstrom 2007) [E. coli]
Cellulose binding module (Tomme et al. 1998)	4–20 kDa	Synthetic	N- or C-terminal	Purification	Yes (Maurice et al. 2003) [fish]
c-Myc (Ellison and Hochstrasser 1991)	11 aa	H. sapien	N- or C-terminal	Purification	Yes (Sarramegna et al. 2002) [yeast]
Dock (dockerin domain) (Kamezaki et al. 2010)	22 aa	C. josui	N-or C-terminal	Purification	No
FLAG (Munro and Pelham 1984)	8 aa	Synthetic	N- or C-terminal	Purification	Yes (Quick and Wright 2002) [E. coli]
HA (hemagglutinin) (Field et al. 1988)	9 aa	Influenza Virus	N- or C-terminal	Purification	Yes (Gao et al. 2015) [insect]
IMPACTTM (intein-mediated purification with chitin binding domain) (Chong et al. 1997)	51 aa	B. ciruculans, Pyrococcus sp., S. cerevisiae	N- or C-terminal	Purification†	No
Poly-His (Hochuli et al. 1988; Kohno et al. 1998)	6–12 aa	Synthetic	N or C-terminal	Purification	Yes (Park et al. 2012a) [E. coli]
S (S protein of RNase A) (Kim and Raines 1993)	15 aa	Mammalian	N- or C-terminal	Purification	No
Strep II (Schmidt et al. 1996)	8 aa	S. avidinii	N or C-terminal	Purification	Yes (Rahman et al. 2007) [E. coli]
Fh8 (Fasciolahepatica 8-kDa antigen) (Costa et al. 2013a; Costa et al. 2013b)	69 aa	F. hepatica	N-terminal	Purification & solubility	No
GST (glutathione S-transferase) (Smith and Johnson 1988)	211 aa	S. japonicum	N-terminal	Purification & solubility	Yes (Park et al. 2012a) [E. coli]
HaloTag (Mutated dehalogenase) (Ohana et al. 2009)	~300 aa	Rhodococcus sp.	N-terminal	Purification & solubility	Yes (Suzuki et al. 2013) [mammlian]
MBP (maltose binding protein) (di Guana et al. 1988; Pryor and Leiting 1997)	396 aa	E. coli	N- or C-terminal	Purification & solubility	Yes (Chaudhary et al. 2011) [E. coli]
T7 gene10 (Olins et al. 1988)	260 aa	Bacteriophage T7	N-terminal	Purification & solubility	No
Ubiquitin (Kohno et al. 1998)	76 aa	S. cerevisiae	N-terminal	Purification & solubility	Yes (Bird et al. 2015) [E. coli]
Acidic proteins (MsyB and YjgD) (Zou et al. 2008)	124, 138 aa	E. coli	N-terminal	Solubility	No
AK (adenylate kinase) (Liu et al. 2015)	362 aa	E. coli	N-terminal	Solubility	Yes (Londesborough et al. 2014) [yeast]
ArsC (Stress-responsive arsenate reductase) (Song et al. 2011)	141 aa	E. coli	N-terminal	Solubility	No
CaBP (Calcium-binding protein) (Reddi et al. 2002)	134 aa	E. histolya	N-terminal	Solubility	No
Crr (glucose-specific phosphotransferase enzyme IIA component) (Han et al. 2007a)	169 aa	E. coli	N-terminal	Solubility	No
CysQ (3′-phosphoadenosine-5′-phosphatase) (Lee et al. 2014)	266 aa	E. coli	N-terminal	Solubility	No
EDA (KDPG aldolase) (Kang et al. 2015)	213 aa	E. coli	N-terminal	Solubility	No
EspA (E. coli secreted protein A) (Cheng et al. 2010)	192 aa	E. coli	N-terminal	Solubility	No
GB1 (IgG domain of B1 of protein G) (Huth et al. 1997; Kumar et al. 2012; Zhou et al. 2001)	56 aa	Streptococcus sp.	N-terminal	Solubility	Yes (Kumar et al. 2012) [E. coli]
IF2-domain I (N-terminal fragment of translation initiation factor IF2) (Sørensen et al. 2003)	158 aa	E. coli	N-terminal	Solubility	No
Mocr (Monomeric bacteriophage T7 0.3 protein) (DelProposto et al. 2009)	117 aa	Bacteriophage T7	N-terminal	Solubility	No
NusA (N-utilization substance) (Davis et al. 1999)	495 aa	E. coli	N-terminal	Solubility	Yes (Goehring et al. 2014) [mammalian]
PotD (spermidine/putrescine-binding periplasmic protein) (Han et al. 2007a)	348 aa	E. coli	N-terminal	Solubility	No
RpoA, S, D (RNA polymerase subunits) (Ahn et al. 2007; Zou et al. 2008)	329, 330, 613 aa	E. coli	N-terminal	Solubility	No
Skp (Seventeen kDa protein) (Chatterjee and Esposito 2006)	161 aa	E. coli	N-terminal	Solubility	No
SlyD (FKBP-type peptidyl-prolyl cis-trans isomerase) (Han et al. 2007b)	196 aa	E. coli	N-terminal	Solubility	No
SNUT (Solubility enhancing ubiquitous tag) (Caswell et al. 2010)	147 aa	S. aureus	N-terminal	Solubility	No
SUMO (small ubiquitin modified protein) (Zuo et al. 2005a)	100 aa	H. sapiens	N-terminal	Solubility	Yes (Zuo et al. 2005b) [E. coli]
T7PK (Phage T7 protein kinase) (Chatterjee and Esposito 2006)	~240 aa	Bacteriophage T7	N-terminal	Solubility	No
Trx (Thioredoxin) (LaVallie et al. 1993)	109 aa	E. coli	N- or C-terminal	Solubility	Yes (Yeliseev et al. 2007) [E. coli]
Tsf (elongation factor Ts) (Han et al. 2007b)	283 aa	E. coli	N-terminal	Solubility	No
GlpF (the glycerol-conducting channel protein) (Neophytou et al. 2007)	281 aa	E. coli	N-terminal	Inner membrane insertion	Yes (Neophytou et al. 2007) [E. coli]
OmpA signal sequence (Tiralongo and Maggioni 2011)	21 aa	E. coli	N-terminal	Inner membrane insertion	Yes (Tiralongo and Maggioni 2011) [E. coli]
S. cerevisiae α-factor signal sequence (Weiss et al. 1995)	89 aa	S. cerevisiae	N-terminal	Plasma membrane insertion	Yes (Weiss et al. 1995)[yeast]
Yeast STE2 receptor signal sequence (King et al. 1990; LaVallie et al. 1993)	24 aa	S. cerevisiae	N-terminal	Plasma membrane insertion	Yes (Ficca et al. 1995; King et al. 1990; Sander et al. 1994a)[yeast]
Lpp-OmpA (Lpp signal peptide + OmpA) (Francisco et al. 1992)	142 aa	E. coli	N-terminal	Outer membrane display	Yes# [E. coli]
Ice nucleation protein (Inp) (Jung et al. 1998)	114 kDa	P. syringae	N-terminal	Outer membrane display/insertion	Yes# (Yim et al. 2010)
Ecotin (E. coli trypsin inhibitor) (Malik et al. 2006)	162 aa	E. coli	N-terminal	Solubility & periplasm/media secretion	No
ZZ (IgG repeat domain ZZ of Protein A) (Löwenadler et al. 1987; Rondahl et al. 1992)	116 aa	S. aureus	N- and C-terminal	Solubility & periplasm/media secretion	Yes (Nizard et al. 2001) [mammalian]
Cell-CD (cellulase catalytic domain) (Gao et al. 2015)	20, 375 aa	Bacillus sp.	N-terminal	Periplasm/media secretion	No
Cex (exoglucanase) (Hasenwinkle et al. 1997)	41 aa	C. fimi	N-terminal (signal sequence)	Periplasm/media secretion	No
DsbA (disulfide oxidoreductase A) (Soares et al. 2003)	19 aa	E. coli	N-terminal (signal sequence)	Periplasm/media secretion	Yes (Jappelli et al. 2014) [E. coli]
Exl/Enx (endoxylanase) (Jeong and Lee 2000, 2001)	12, or 28 aa	Bacillus sp.	N-terminal (signal sequence)	Periplasm/media secretion	No
LamB (λ receptor protein) (Pratap and Dikshit 1998)	25 aa	E. coli	N-terminal (signal sequence)	Periplasm/media secretion	Yes#
LTB (heat-labile enterotoxin subunit B) (Sanchez et al. 1988)	21 aa	E. coli	N-terminal (signal sequence)	Periplasm/media secretion	No
Outer membrane protein (OmpC, F) (Becker and Hsiung 1986)	21, 22 aa	E. coli	N-terminal (signal sequence)	Periplasm/media secretion	Yes# [E. coli]
OmpT (protease VII) (Kurokawa et al. 2001)	20 aa	E. coli	N-terminal (signal sequence)	Periplasm/media secretion	Yes# [E. coli]
PhoA (alkaline phosphatase) (Xu et al. 2002)	21 aa	E. coli	N-terminal (signal sequence)	Periplasm/media secretion	Yes (Kaderbhai and Kaderbhai 1996) [E. coli]
PelB (pectate lyase B) (Better et al. 1993)	22 aa	E. carotov	N-terminal (signal sequence)	Periplasm/media secretion	Yes (Jappelli et al. 2014) [E. coli]
SpA (S. aureus Protein A) (Abrahmsén et al. 1986)	280	S. aureus	N-terminal (signal sequence)	Purification& periplasm/media secretion	Yes (Hansson et al. 1995) [E. coli]
SthII (heat stable enterotoxin II) (Qiu et al. 1998)	23 aa	E. coli	N-terminal (signal sequence)	Periplasm/media secretion	No
AT rich gene tags (PS, T7, AT, SER, H, G, R) (Haberstock et al. 2012; Pandey et al. 2014)	8, 11, 6, 6, 6, 6, 6 aa	Derived from various species	5′-end of mRNA	Expression enhancement	Yes (Haberstock et al. 2012; Pandey et al. 2014) [E. coli]
HmBRI/D94N (mutated bacteriorhodopsin (BR) (Hsu et al. 2013)	250 aa	H. marismortui	N-terminal	Expression enhancement	Yes (Hsu et al. 2013) [E. coli]
Mistic (Kefala et al. 2007; Marino et al. 2015)	110 aa	B. subtilis	N-terminal	Expression enhancement	Yes (Kefala et al. 2007; Marino et al. 2015) [E. coli]
YaiN (regulator of frmRAB operon) (Leviatan et al. 2010)	98 aa	E. coli	N- or C-terminal	Expression enhancement	Yes (Leviatan et al. 2010) [E. coli]
YbeL (Leviatan et al. 2010)	120 aa	E. coli	N- or C-terminal	Expression enhancement	Yes (Leviatan et al. 2010) [E. coli]
EDDIE (N-terminal autoprotease NPRO) (Achmuller et al. 2007)	168 aa	Classical swine fever virus	N-terminal	Inclusion body targeting	No
KSI (ketosteroid isomerase) (Kuliopulos and Walsh 1994)	14 kDa	P. testosteroni	N-terminal	Inclusion body targeting	Yes (Chun et al. 2012) [E. coli]
Outer membrane protein FΔSP (OmpF missing signal peptide)	142 aa	E. coli	N-terminal	Inclusion body targeting	Yes (Su et al. 2013) [E. coli]
PagPΔSP (palmitoyltransferase missing the signal peptide) (Hwang et al. 2012)	161 aa	E. coli	N-terminal	Inclusion body targeting	No
PaP3.30 (ORF 30) (Rao et al. 2004)	162 aa	P. aeruginosa bacteriophage Pap3	N-terminal	Inclusion body targeting	No
PurF (N-terminal of polypeptide F4) (Lee et al. 2000)	152 aa	E. coli	N-terminal	Inclusion body targeting	No
TAF12 HFD (histone folding domain of human transcription factor) (Vidovic et al. 2009)	72 kDa	H. sapiens	N-terminal	Inclusion body targeting	No
TrpΔLE (deletion of a part of TrpL from TrpE operon) (Cook et al. 2011)	17 aa	E. coli	N-terminal	Inclusion body targeting	Yes (Cook et al. 2011) [E. coli]
BRIL (thermostabilized apocytochrome b562) (Chun et al. 2012)	10.9 kDa	H. sapiens	Intermolecular	Stabilization & crystallization	Yes (Chun et al. 2012) [insect]
T4 lysozyme (Engel et al. 2002)	15.9 kDa	Bacteriophage T4	Intermolecular	Stabilization & crystallization	Yes (Engel et al. 2002) [E. coli] & (Cherezov et al. 2007; Chun et al. 2012; Granier et al. 2012; Kruse et al. 2012) [insect]

^*aa: amino acids

^†intein-mediated removal of chitin binding domain (single step purification, no protease-mediated removal of tag)

^#Given that the tags are derived from membrane proteins, they have inherently been used for membrane protein expression

Note: tags may not function as specified depending on the effect of POI on the fusion protein.