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. Author manuscript; available in PMC: 2022 Jan 28.
Published in final edited form as: ACS Chem Biol. 2020 Aug 17;15(9):2433–2443. doi: 10.1021/acschembio.0c00419

Figure 1.

Figure 1.

Graphical outline of FAP–DAPA system and reagents utilized. (A) Interactions of FAP and HaloTag receptors with DAPA dye showing how (a) the distribution of receptors bound is dictated by differential in KD(FAP/fluorogen) and kon(HT/HexCl), and concentration of DAPA. At sub KD concentrations of DAPA, the DAPA HexCl ligand will first bind to the HaloTag (b, c), and then DAPA Malachite Green (MG) ligand will bind to FAP if the distance D is less than ~20 nm (c). (B) Structure of dimerized L5**-MG complex (PDB: 4K3H) with MG highlighted in green. (C) Structure of the HaloTag protein (PDB: 5UXZ) with estimated HexCl ligand extension. (D) Synthesis of DAPA dye, MG-PEG3500-HexCl using a fluorogenic alkyne for Cu-“click” cycloaddition to the azide terminus and MG-NHS ester for reaction with amino-terminal end of the NH2–PEG3500-N3 polymer.