Asparaginyl endopeptidases (AEPs) catalyze the key backbone cyclization step during the biosynthesis of plant-derived cyclic peptides. Here, we report the identification of two AEPs from Momordica cochinchinensis and biochemically characterize MCoAEP2 that catalyzes the maturation of trypsin inhibitor cyclotides. Recombinantly produced MCoAEP2 catalyzes the backbone cyclization of a linear cyclotide precursor (MCoTI-II-NAL) with a k cat /K m of 620 mM −1 s −1 , making it one of the fastest cyclases reported to date. We show that MCoAEP2 can mediate both the N-terminal excision and C-terminal cyclization of cyclotide precursors in vitro. The rate of cyclization/hydrolysis is primarily influenced by varying pH, which could potentially control the succession of AEP-mediated processing events in vivo. Furthermore, MCoAEP2 efficiently catalyzes the backbone cyclization of an engineered MCoTI-II analog with anti-angiogenic activity. MCoAEP2 provides enhanced synthetic access to structures previously inaccessible by direct chemistry approaches and enables the wider application of trypsin inhibitor cyclotides in biotechnology applications.

Cyclotides are ultra-stable peptides derived from plants. They are around 30 amino acids in size and are characterized by their head-to-tail cyclic backbone and cystine knot. Their exceptional stability and tolerance to sequence substitutions has led to their use as frameworks in drug design. This article describes recent developments in this field, particularly developments over the last two years relating to the grafting of bioactive peptide sequences into the cyclic cystine knot framework of cyclotides to stabilize the sequences. Grafted cyclotides have now been developed that interact with protein or enzyme targets, both extracellular and intracellular, as well as with cell surface receptors and membranes.

An environmentally sustainable production platform for a variety of correctly folded cyclic disulfide-rich peptides with enhanced yields.