Table 3 Important peptide- and protein-tags for fluorescently chemical labeling applied on living cells

Lumio™-tag

tetracysteine/biarsenical system

tetracysteine motif: CCXXCC

size: 6–20 aa

biarsenical dyes, e.g.:

CHoXAsH (blue)

FlAsH (green)

ReAsH (red)

membrane-permeable

non-fluorescent until binding

[80, 81, 93]

His-tag

oligo-histidine/nickel-complex system

oligo-histidine sequence: (H)_n, n = 6

size: 6–10 aa

nickel-nitrilotriacetic acid (NTA-Ni²⁺) dyes, e.g.:

NTA-FITC-Ni²⁺ (green)

NTA-QSY-Ni²⁺ (red)

NTA-DCF-Ni²⁺ (green)

[82, 83]

SNAP™-tag

mutated human O⁶-alkylguanine alkyltransferase (hAGT)

size: 182 aa

fluorescent benzylguanine (BG) derivatives, e.g.:

BG-505 (green)

BG-TMR-Star (red)

cell-permeable or cell-impermeable

[80, 84, 85]

ACP/PCP-tag

acyl carrier/peptide carrier protein tag labeled via phosphopatheine transferase (PPTase)

size: 80 aa

fluorescent coenzyme A conjugates, e.g.:

CoA-fluorescein (blue)

CoA-Cy3 (green)

CoA-Cy5 (red)

cell-impermeable

[86, 87]

HaloTag™

mutated prokaryotic dehalogenase

size: 297 aa

fluorescent haloalkane ligand, e.g.:

HaloTag 488 ligand (green)

HaloTag TMR ligand (red)

cell-permeable or cell-impermeable

[88, 89]

AP-tag

biotin acceptor peptide labeled via E. coli biotin ligase BirA

size: 15 aa

fluorescent streptavidin, e.g.:

streptavidin-Alexa568 (red)

[90]