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. 2021 Mar 31;22(13):2219–2236. doi: 10.1002/cbic.202000882

Figure 2.

Figure 2

Labelling molecules and fluorogenic dyes. a) Relative sizes of an antibody (PDB ID: 5DK3[169]), green fluorescent protein (PDB ID: 3K1K[170]), a SNAP‐tag (PDB ID: 3kzz) and Silicon Rhodamine (SiR) dye (modelled) are shown for comparison. b) The logic of fluorogenicity. A molecule can be in two isomeric states, a non‐fluorescent form and a fluorescent one, where only the latter shows emission upon application of excitation wavelength. The fluorogenic molecule silicon rhodamine is shown linked to the actin binder jasplakinolide. It exists in its unbound, nonfluorescent and closed spirolactone form, which is converted to an open, zwitterionic form that turns on fluorescence upon binding to actin (PDB ID: 6T23[171]).