This review provides a comprehensive update of the advances in discovery, biosynthesis, and engineering of ribosomally-synthesized and post-translationally modified peptides (RiPPs).

Lanthipeptides are ribosomally synthesized and post-translationally modified peptides (RiPPs) that display a wide variety of biological activities, from antimicrobial to antiallodynic. Lanthipeptides that display antimicrobial activity are called lantibiotics. The post-translational modification reactions of lanthipeptides include dehydration of Ser and Thr residues to dehydroalanine and dehydrobutyrine, a transformation that is carried out in three unique ways in different classes of lanthipeptides. In a cyclization process, Cys residues then attack the dehydrated residues to generate the lanthionine and methyllanthionine thioether cross-linked amino acids from which lanthipeptides derive their name. The resulting polycyclic peptides have constrained conformations that confer their biological activities. After installation of the characteristic thioether cross-links, tailoring enzymes introduce additional post-translational modifications that are unique to each lanthipeptide and that fine-tune their activities and/or stability. This review focuses on studies published over the past decade that have provided much insight into the mechanisms of the enzymes that carry out the post-translational modifications.

Structural and biochemical studies show that the biosynthesis of the food preservative nisin involves the tRNA-dependent glutamylation of serine and threonine. Nisin, a member of the lantibiotic family of thioether-bridge containing antibiotics, has been used widely in the food industry for more than 40 years without substantial development of resistance. This property has become of particular interest in light of the emergence of resistance to many clinically used antibiotics. Wilfred van der Donk and colleagues present the X-ray structure of the lantibiotic dehydratase NisB, an enzyme involved in nisin biosynthesis, and use biochemical data to show that NisB utilizes glutamyl-tRNAGlu in the critical activation of Ser/Thr residues. These findings provide a basis for the functional characterization of the many lantibiotic-like dehydratases involved in the biosynthesis of other classes of natural products. Lantibiotics are a class of peptide antibiotics that contain one or more thioether bonds. The lantibiotic nisin is an antimicrobial peptide that is widely used as a food preservative to combat food-borne pathogens1. Nisin contains dehydroalanine and dehydrobutyrine residues that are formed by the dehydration of Ser/Thr by the lantibiotic dehydratase NisB (ref. 2). Recent biochemical studies revealed that NisB glutamylates Ser/Thr side chains as part of the dehydration process3. However, the molecular mechanism by which NisB uses glutamate to catalyse dehydration remains unresolved. Here we show that this process involves glutamyl-tRNAGlu to activate Ser/Thr residues. In addition, the 2.9-Å crystal structure of NisB in complex with its substrate peptide NisA reveals the presence of two separate domains that catalyse the Ser/Thr glutamylation and glutamate elimination steps. The co-crystal structure also provides insights into substrate recognition by lantibiotic dehydratases. Our findings demonstrate an unexpected role for aminoacyl-tRNA in the formation of dehydroamino acids in lantibiotics, and serve as a basis for the functional characterization of the many lantibiotic-like dehydratases involved in the biosynthesis of other classes of natural products.

Nisin is a posttranslationally modified antimicrobial peptide that is widely used as a food preservative. It contains five cyclic thioethers of varying sizes that are installed by a single enzyme, NisC. Reported here are the in vitro reconstitution of the cyclization process and the x-ray crystal structure of the NisC enzyme. The structure reveals similarities in fold and substrate activation with mammalian farnesyl transferases, suggesting that human homologs of NisC posttranslationally modify a cysteine of a protein substrate.