Active-site directed probes are powerful in studies of enzymatic function. We report an active-site directed probe based on a warhead so far considered unreactive. By replacing the C-terminal carboxylate of ubiquitin (Ub) with an alkyne functionality, a selective reaction with the active-site cysteine residue of de-ubiquitinating enzymes was observed. The resulting product was shown to be a quaternary vinyl thioether, as determined by X-ray crystallography. Proteomic analysis of proteins bound to an immobilized Ub alkyne probe confirmed the selectivity toward de-ubiquitinating enzymes. The observed reactivity is not just restricted to propargylated Ub, as highlighted by the selective reaction between caspase-1 (interleukin converting enzyme) and a propargylated peptide derived from IL-1ß, a caspase-1 substrate.
Ekkebus, R., van Kasteren, S. I., Kulathu, Y., Scholten, A., Berlin, I., Geurink, P. P., de Jong, A., Goerdayal, S., Neefjes, J., Heck, A. J. R., Komander, D., & Ovaa, H. (2013). On terminal alkynes that can react with active-site cysteine nucleophiles in proteases. Journal of the American Chemical Society, 135(8), 2867-70. https://doi.org/10.1021/ja309802n