Topic summary
FlAsH-EDT2
FlAsH-EDT2 is an organoarsenic compound with molecular formula C24H18As2O5S4. Its structure is based around a fluorescein core with two substituents. It is used in bioanalytical research as a fluorescent label for visualising proteins in living cells. FlAsH-EDT2 is an abbreviation for fluorescin arsenical hairpin binder-, and is a pale yellow or pinkish fluorogenic solid. It has a semi-structural formula (C2H4AsS2)2-(C13H5O3)-C6H4COOH, representing the dithiarsolane substituents bound to the hydroxyxanthone core, attached to an o-substitutedmolecule of benzoic acid.
FlAsH-EDT2 is used for site-specific labelling, selectively binding to proteins containing the tetracysteine (TC) motif Cys-Cys-Xxx-Xxx-Cys-Cys and becoming fluorescent when bound. It displays non-specific binding to endogenous cysteine-rich proteins, meaning it binds to sites other than the one of interest (CCXXCC). Further optimization of the TC motif has revealed improved FlAsH binding affinity for a CCPGCC motif, and higher quantum yield when the tetracysteine motif is flanked with specific residues (HRWCCPGCCKTF or FLNCCPGCCMEP).