Enzyme‐Primed Native Chemical Ligation Produces Autoinducing Cyclopeptides in Clostridia

Abstract

Clostridia coordinate many important processes such as toxin production, infection, and survival by density‐dependent communication (quorum sensing) using autoinducing peptides (AIPs). Although clostridial AIPs have been proposed to be (thio)lactone‐containing peptides, their true structures have remained elusive. Here, we report the genome‐guided discovery of a cyclic AIP (cAIP) that controls endospore formation in Ruminiclostridium cellulolyticum . Through a combination of chemical synthesis and chemical complementation assays with mutant strain, we reveal that a homodetic cyclopeptide is the genuine chemical mediator. Kinetic analyses indicate that the mature cAIP is produced via a cryptic thiolactone intermediate that undergoes a rapid S → N shift, in a manner similar to intramolecular native chemical ligation (NCL). Finally, by implementing a chemical probe in a targeted screen, we show that this novel enzyme‐primed, intramolecular NCL is a widespread feature of clostridial cAIPs.