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Macrocyclic, disulfide-rich peptides have found widespread applications in drug design and development. Current peptide production strategies rely heavily on solid phase peptide synthesis (SPPS) requiring large amounts of hazardous/toxic reagents and solvents which have negative environmental impacts. A possible solution is to develop a sustainable hybrid production platform incorporating recombinant production of cyclic peptide precursors in yeast followed by enzymatic maturation of these precursors into cyclic peptides using asparaginyl endopeptidases in vitro. Harnessing the efficient secretory pathway of Pichia pastoris, peptide precursors, cloned downstream of the α-mating factor secretion signal, were purified from culture supernatant mitigating the need for complex purification. To demonstrate the broad utility of the platform, three distinct classes of cyclic peptides were produced; two were structurally validated by NMR and shown to be functionally equivalent to their synthetically produced versions. Furthermore, using this platform we report the first recombinant production of any α-conotoxin in its native "globular" conformation. Using scale-up production in bioreactors, cyclic peptide yields of 85–97 mg L−1 of culture were achieved, far exceeding the highest yields so far achieved for cyclic disulfide-rich peptides in any recombinant process. This platform can potentially unlock production and facilitate applications of cyclic disulfide-rich peptides previously inaccessible through large-scale chemical synthesis and reduce their environmental burden. [ABSTRACT FROM AUTHOR]

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 kcat/Km 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. Asparaginyl endopeptidases (AEPs) catalyze the cyclization step during the biosynthesis of cyclic peptides in plants. Here, the authors report a recombinantly produced AEP that catalyzes the backbone cyclization of a linear cyclotide precursor and an engineered analog with high efficiency and in a pH-dependent manner. [ABSTRACT FROM AUTHOR]

Cyclotides are cyclic peptides from plants in the Violaceae, Rubiaceae, Fabaceae, Cucurbitaceae, and Solanaceae families. They are sparsely distributed in most of these families, but appear to be ubiquitous in the Violaceae, having been found in every plant so far screened from this family. However, not all geographic regions have been examined and here we report the discovery of cyclotides from a Viola species from South-East Asia. Two novel cyclotides (Visu 1 and Visu 2) and two known cyclotides (kalata S and kalata B1) were identified in V. sumatrana. NMR studies revealed that kalata S and kalata B1 had similar secondary structures. Their biological activities were determined in cytotoxicity assays; both had similar cytotoxic activity and were more toxic to U87 cells compared with other cell lines. Overall, the study strongly supports the ubiquity of cyclotides in the Violaceae and adds to our understanding of their distribution and cytotoxic activity. [ABSTRACT FROM AUTHOR]

Abstract: Cyclotides are a large family of plant peptides characterized by a macrocyclic backbone and knotted arrangement of three disulfide bonds. This unique structure renders cyclotides exceptionally stable to thermal, chemical and enzymatic treatments. They exhibit a variety of bioactivities, including uterotonic, anti-HIV, cytotoxic and hemolytic activity and it is these properties that make cyclotides an interesting peptide scaffold for drug design. In this study, eight new cyclotides (Viphi A–H), along with eight known cyclotides, were isolated from Viola philippica, a plant from the Violaceae family. In addition, Viba 17 and Mram 8 were isolated for the first time as peptides. The sequences of these cyclotides were elucidated primarily by using a strategy involving reduction, enzymatic digestion and tandem mass spectroscopy sequencing. Several of the cyclotides showed cytotoxic activities against the cancer cell lines MM96L, HeLa and BGC-823. The novel cyclotides reported here: (1) enhance the known sequence variation observed for cyclotides; (2) extend the number of species known to contain cyclotides; (3) provide interesting structure–activity relationships that delineate residues important for cytotoxic activity. In addition, this study provides insights into the potential active ingredients of traditional Chinese medicines. [Copyright &y& Elsevier]