A fluorescent probe for cysteine depalmitoylation reveals dynamic APT signaling

The development of small-molecule fluorescent probes through addition of a lipidated cysteine residue next to a caged fluorophore enables detection of endogenous cysteine depalmitoylation by acyl–protein thioesterases in vitro and in live cells. Hundreds of human proteins are modified by reversible palmitoylation of cysteine residues (S-palmitoylation), but the regulation of depalmitoylation is poorly understood. Here, we develop 'depalmitoylation probes' (DPPs), small-molecule fluorophores, to monitor the endogenous activity levels of 'erasers' of S-palmitoylation, acylprotein thioesterases (APTs). Live-cell analysis with DPPs reveals rapid growth-factor-mediated inhibition of the depalmitoylation activity of APTs, exposing a novel regulatory mechanism of dynamic lipid signaling.