|
Tag |
Size |
Fusion tag
location |
Tag type |
Comments |
|
His-tag |
6, 8, or 10 aa |
N-, C-, internal |
purification |
Most common purification tag used for immobilized metal affinity chromatography (IMAC) one-step purification [81]. Purification possible even under denaturing conditions [82]. Tag possibly influences crystallization |
|
T7-tag |
11 or 16 aa |
N-, internal |
purification, enhanced expression |
Monoclonal antibody-based purification (denaturing low pH elution needed). Leaves unnatural N-terminal amino acids on the recombinant protein. Possibly enhanced expression levels since the T7-tag is derived from the T7 gene 10 which is the naturally most abundant phage T7 gene product. |
|
S-tag |
15 aa |
N-, C-, internal |
Purification and detection |
S-protein (104 aa, Ribonuclease A minus S-tag peptide sequence) modified resin affinity purification. RNAse S assay possible for quantitative assay of expression levels. |
|
FLAG™ peptide
(DYKDDDDK) |
8 aa |
N-, C- |
Purification |
Ca2+-dependent monoclonal antibody affinity purification with EDTA elution. Tag cleavable with enterokinase [83]. |
|
thioredoxin |
109 aa
(11.7 kDa) |
N-,C-
|
Purification and enhanced expression
|
Affinity purification with phenylarsine oxide-modified (ThioBond) resin. |
|
His-patch thioredoxin |
109 aa
(11.7 kDa) |
N-,C- |
Purification and enhanced expression
|
Use of His-patch modified thioredoxin for IMAC affinity purification [84]. |
|
lacZ (β-Galactosidase) |
116 kDa |
N-,C- |
Purification |
Purification using p-amino-phenyl-b-D-thiogalactoside-modified sepharose. Classical tag used for protecting peptides from proteolytic degradation. However, fusion proteins with this tag have a high tendency to be insoluble. Active enzyme is a tetramer |
|
chloramphenicol acetyltransferase |
24 kDa |
N- |
Secretion, purification and detection |
Chloramphenicol-sepharose purification. Enzymatic assay possible for quantitation. |
|
trpE |
27 kDa |
N- |
Purification |
Often form insoluble precipitates. Hydrophobic interaction chromatographic purification. |
|
avidin/streptavidin/
Strep-tag |
|
|
Purification and secretion |
Biotin affinity purification and streptavidin affinity purification (Strep-tag) [85]. |
|
T7gene10 |
260 aa |
N- |
Purification and enhanced expression |
Produces insoluble fusion protein (potential enhanced expression for toxic clones).
|
|
staphylococcal protein A
|
14 kDa (or 31 kDa) |
N- |
Purification and Secretion
|
IgG antibody affinity purification possible (denaturing low pH elution needed). Fusion protein secretion due to protein A signal sequence [86]. |
|
streptococcal protein G |
28 kDa |
N-, C- |
Purification and Secretion |
Albumin affinity purification, low pH elution needed. Fusion protein secretion due to protein G signal sequence. |
|
glutathione-S-transferase (GST)
|
26 kDa |
N- |
Purification |
Glutathione affinity or GST antibody purification. Enzymatic activity assay possible for quantitative analysis. Fusion proteins form dimers. |
|
dihydrofolate reductase (DHFR)
|
25 kDa
|
N- |
Purification |
Methotrexate-linked agarose used for purification. |
|
cellulose binding domains (CBD's)
|
156 aa/
114 aa/
107 aa |
N-/
N-/
C-
|
Purification and secretion |
Cellulose-based resins used for affinity purification with water elution [87,88]. Different constructs available for cytoplasmic or periplasmic expression. Fusion proteins susceptible to proteolysis between the fusion partners [89]. |
|
maltose binding protein (MBP)
|
40 kDa |
N-, C- |
Purification and secretion |
Amylose affinity purification with maltose elution. |
|
galactose-binding protein
|
|
|
Purification |
Galactose-sepharose purification. |
|
calmodulin binding protein (CBP)
|
4 kDa |
N-, C- |
Purification and detection |
Calmodulin/Ca2+-affinity purification with EDTA elution. Can potentially assay expression levels with 32P-cAMP kinase. |
|
hemagglutinin influenza virus (HAI) |
|
|
Purification |
|
|
green fluorescent protein (GFP) |
220 aa |
N-, C- |
Detection |
Used as reporter gene fusion for detection purposes [90]. Used at one time for possible refolding tag. |
|
HSB-tag |
11 aa |
C- |
Purification |
Monoclonal antibody-based purification (denaturing low pH elution needed). |
|
B-tag (VP7 protein region of bluetongue virus) |
|
|
Purification |
Anti-BTag antibody purification. |
|
polyarginine |
5-15 aa |
C- |
Purification |
S-sepharose (cationic resin) purification. Fusion proteins potentially insoluble. |
|
polycysteine |
4 aa |
N- |
Purification |
Thiopropyl-sepharose purification. |
|
polyphenyalanine
|
11 aa |
N- |
Purification |
Phenyl-superose (hydrophobic interaction chromatography) purification. |
|
(Ala-Trp-Trp-Pro)n |
|
|
Purification |
|
|
polyaspartic acid
|
5-16 aa
|
C- |
Purification |
Anionic resin purification. |
|
KSI |
125 aa |
N- |
Enhanced expression |
High-level inclusion body production. |
|
c-myc |
|
|
Purification |
Anti-myc antibody purification. |
|
ompT
/ompA
/pelB
/DsbA
/DsbC |
22 aa /21 aa /20 aa /208 aa (21.8 kDa) /236 aa
|
N- |
Secretion |
Periplasmic leader sequences for potential protein export and folding [91], as well as potential disulfide bond formation and isomerization. |
|
chitin binding domain |
|
N-, C- |
Expression |
Used in the Impact™ system, with intein-based expression constructs |
|
NusA |
495 aa (54.8 kDa) |
N- |
Possible enhanced solubility |
Potentially improve solubility for proteins that are overexpressed. |
|
ubiquitin |
76 aa |
N- |
Possible enhanced solubility |
lac operator affinity purification |
