Photo‐Claisen Rearrangement in a Coumarin‐Caged Peptide Leads to a Surprising Enzyme Hyperactivation

Protein phosphatase-1 (PP1) is a ubiquitous enzyme that counteracts hundreds of kinases in cells. PP1 interacts with regulatory proteins via an RVxF peptide motif that binds to a hydrophobic groove on the enzyme. PP1-disrupting peptides (PDPs) compete with these regulatory proteins, leading to the release of the active PP1 subunit and promoting substrate dephosphorylation. Building on previous strategies employing the ortho-nitrobenzyl (o-Nb) group as a photocage to control PDP activity, we introduced coumarin derivatives into a PDP via an ether bond to explore their effects on PP1 activity. Surprisingly, our study revealed that the coumarin-caged peptides (PDP-DEACM and PDP-CM) underwent a photo-Claisen rearrangement, resulting in an unexpected hyperactivation of PP1. Our findings underscore the importance of linker design in controlling uncaging efficiency of photocages and highlight the need for comprehensive in vitro analysis before cellular experiments.