Biocatalytic cyclization of small macrolactams by a penicillin-binding protein-type thioesterase

Macrocyclic peptides represent promising scaffolds for chemical tools and potential therapeutics. Synthetic methods for peptide macrocyclization are often hampered by C-terminal epimerization and oligomerization, leading to difficult scalability. While chemical strategies to circumvent this issue exist, they often require specific amino acids to be present in the peptide sequence. Herein, we report the characterization of Ulm16, a peptide cyclase belonging to the penicillin-binding protein-type class of thioesterases that catalyze head-to-tail macrolactamization of nonribosmal peptides. Ulm16 efficiently cyclizes various nonnative peptides ranging from 4 to 6 amino acids with catalytic efficiencies of up to 3 x 106 M-1 s-1. Unlike many previously described homologs, Ulm16 tolerates a variety of C- and N-terminal amino acids. The crystal structure of Ulm16, along with modeling of its substrates and site-directed mutagenesis, allows for rationalization of this wide substrate scope. Overall, Ulm16 represents a promising tool for the biocatalytic production of macrocyclic peptides. Macrocyclic peptides are promising scaffolds for chemical tools and potential therapeutics, but their synthesis is currently difficult. Here, the authors report the characterization of Ulm16, a peptide cyclase of the penicillin-binding protein (PBP)-type class of thioesterases, that catalyzes head-to-tail macrolactamization of nonribosmal peptides of 4-6 amino acids in length.

Automated summary

Macrocyclic peptides show great potential as chemical tools and potential therapeutics. However, their synthesis is currently challenging. In this study, Ulm16, a peptide cyclase belonging to the penicillin-binding protein-type class of thioesterases, is characterized for its ability to catalyze head-to-tail macrolactamization of nonribosomal peptides of 4-6 amino acids in length.