Papain-like cysteine proteases prepare plant cyclic peptide precursors for cyclization

Abstract

Significance Ribosomally synthesized and post-translationally modified peptides are natural products that hold great promise for a range of medical and biotechnological applications. However, the cost-effective heterologous production of these peptides is hampered by a poor understanding of their biosynthesis. Cyclotides, plant-derived, disulfide-knotted, head-to-tail cyclic peptides, exhibit exceptional stability and great amenability for amino acid substitutions and insertions. Although much effort has been invested toward understanding cyclotide biosynthesis, details of the key proteolytic step before cyclization remained elusive for two decades. We used an activity-guided approach to discover the enzymes involved. Our characterization of these enzymes will enable efficient approaches for heterologous cyclotide production.