FlAsH-EDT2

in TFA; Step 2: AsCl3, followed by Pd(OAc)2 and DIEA; Step 3: H2EDT in aqueous acetone. FlAsH-EDT2 can be prepared in three steps from fluorescein (see figure). ==Formation of FlAsH-TC adduct==

: Many studies show that trivalent arsenic compounds bind to pairs of cysteine residues. This binding is responsible for the toxicity of many arsenic compounds. Binding is reversed by 1,2-ethanedithiol, which binds tightly to arsenic compounds, as shown by the stability of FlAsH-EDT2. Such strong sulfur-arsenic bond can be, again, regulated by designing a peptide domain that exhibits higher affinity toward the arsenic, such as tetracysteine motif. By modulating the distance between the two pairs of cysteine residues and the space between the arsenic centers of FlAsH-EDT2, a cooperative and entropically favored dithiol arsenic bond could be achieved. The binding of FlAsH-EDT2 is thus subject to equilibration. The FlAsH-peptide adduct formation can be favored in low concentration of EDT (below 10 μM) and be reversed in high concentration of EDT (above 1  mM). ==Properties==

FlAsH becomes fluorescent upon the binding of tetracysteine motif. It is excited at 508 nm and emits 528 nm, a green-yellow, of free fluorescein. The quantum yield is 0.49 for 250 nM FlAsH is bound to a model tetracysteine-containing peptide in a phosphate-buffered saline at pH 7.4. ==Application==

FlAsH-EDT2 enables less toxic and more specific fluorescent labeling that is membrane permeable. The modification of the fluorescein moiety also allows multicolor analysis. It has been proven to be a good alternative to green fluorescent proteins (GFP) with the advantage that FlAsH-EDT2 is much smaller (molar mass 2 has been widely used to study a number of in vivo cellular events and subcellular structures in animal cells, Ebola virus matrix protein, and protein misfolding. With the electron microscopic imaging, FlAsH-EDT2 is also used to study the processes of protein trafficking in situ. More recently, it was used in an extended study of plant cells like Arabidopsis and tobacco. ==References==