Reversible Protein Labeling via Genetically Encoded Dithiolane-Containing Amino Acid and Organoarsenic Probes

Conventional protein labeling techniques often rely on irreversible covalent bonds, limiting dynamic control over protein modifications. Here, we present a reversible protein labeling strategy using genetically encoded dithiolane-containing amino acid (dtF) and organoarsenic conjugation chemistry. Using dithiarsolane dicarboxylic acid probe A2, we achieved near-quantitative labeling and ethanedithiol-mediated removal within 1 h at room temperature. A2 exhibited reduced toxicity with a 7-fold higher IC₅₀ compared to arsenoxide, and its fluorescent derivative A2-FB showed no cytotoxicity up to 100 μM, enabling live-cell applications. This is the first demonstration of dithiol-arsenic chemistry at a single amino acid residue, providing a structural alternative to dicysteine motifs. Reversible labeling was validated in purified proteins (sfGFP-Y151dtF and MYO-K99dtF) and live <i>Escherichia coli</i>, offering a versatile tool for dynamic protein modifications and molecular tracking in biological systems.