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Nat Chem Biol. 2008 Sep;4(9):557-63. doi: 10.1038/nchembio.104. Epub 2008 Jul 27.

Beta-lactone probes identify a papain-like peptide ligase in Arabidopsis thaliana.

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Plant Chemetics Lab, Max Planck Institute for Plant Breeding Research, Carl-von-Linne Weg 10, 50829 Cologne, Germany.


New activity-based probes are essential for expanding studies on the hundreds of serine and cysteine proteases encoded by the genome of Arabidopsis thaliana. To monitor protease activities in plant extracts, we generated biotinylated peptides containing a beta-lactone reactive group. These probes cause strong labeling in leaf proteomes. Unexpectedly, labeling was detected at the N terminus of PsbP, nonproteolytic protein of photosystem II. Inhibitor studies and reverse genetics led to the discovery that this unusual modification is mediated by a single plant-specific, papain-like protease called RD21. In cellular extracts, RD21 accepts both beta-lactone probes and peptides as donor molecules and ligates them, probably through a thioester intermediate, to unmodified N termini of acceptor proteins.

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