Site-specific nonenzymatic peptide S/O–glutamylation reveals the extent of substrate promiscuity in glutamate elimination domains

Formation of dehydroalanine and dehydrobutyrine residues via tRNA-dependent dehydration of serine and threonine is a key post-translational modification in the biosynthesis of lanthipeptides and thiopeptides. The dehydration process involves two reactions, wherein the O–glutamyl Ser/Thr intermediate, accessed by a dedicated enzyme utilizing Glu-tRNAGlu as the acyl donor, is recognized by the second enzyme, referred to as the glutamate elimination domain (ED), which catalyses the eponymous reaction yielding a dehydroamino acid. Here, we report two complementary strategies based on a thiol-thioester exchange reaction for direct, nonenzymatic access to diverse ED substrates. These chemistries enabled us to dissect the substrate recognition requirements of three known EDs. Our results establish that EDs are uniquely promiscuous enzymes capable of acting on substrates with arbitrary amino acid sequences, and performing retro-Michael reaction beyond the canonical glutamate elimination. To aid in the substrate recruitment process, EDs apparently engage in nonspecific hydrophobic interactions with their substrates.