The Two-step Biosynthesis of Cyclic Peptides from Linear Precursors in a Member of the Plant Family Caryophyllaceae Involves Cyclization by a Serine Protease-like Enzyme

• Published in: The Journal of biological chemistry Vol. 288; no. 18; pp. 12500 - 12510
• Main Authors: Barber, Carla J.S., Pujara, Pareshkumar T., Reed, Darwin W., Chiwocha, Shiela, Zhang, Haixia, Covello, Patrick S.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 03.05.2013; American Society for Biochemistry and Molecular Biology
• Subjects: Amino Acid Sequence; Caryophyllaceae; Cloning, Molecular; Cyclic Peptide; DNA, Complementary - genetics; Enzymology; Molecular Sequence Data; Peptidases; Peptide Biosynthesis; Peptide Biosynthesis, Nucleic Acid-Independent - physiology; Peptide Cyclase; Peptides, Cyclic - biosynthesis; Peptides, Cyclic - genetics; Plant Biochemistry; Plant Molecular Biology; Plant Proteins - genetics; Plant Proteins - metabolism; Protease; Saponaria - enzymology; Saponaria - genetics; Saponaria vaccaria; Seeds - enzymology; Seeds - genetics; Serine Proteases - genetics; Serine Proteases - metabolism; Peptidases; Plant Biochemistry; Peptide Cyclase; Peptide Biosynthesis; Protease; Saponaria vaccaria; Cyclic Peptide; Plant Molecular Biology; Caryophyllaceae
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M112.437947

Caryophyllaceae-type cyclic peptides (CPs) of 5–12 proteinogenic amino acids occur in 10 plant families. In Saponaria vaccaria (Caryophyllaceae), they have been shown to be formed from linear peptide precursors derived from ribosomal translation. There is also evidence for such precursors in other members of the Caryophyllaceae, Rutaceae, and Linaceae families. The biosynthesis of CP in the developing seeds of S. vaccaria was investigated with respect to the enzymes involved in precursor processing. Through biochemical assays with seed extracts and synthetic peptides, an enzyme named oligopeptidase 1 (OLP1) was found that catalyzes the cleavage of intermediates at the N terminus of the incipient CP. A second enzyme, peptide cyclase 1 (PCY1), which was separated chromatographically from OLP1, was found to act on the product of OLP1, giving rise to a cyclic peptide and concomitant removal of a C-terminal flanking sequence. PCY1 was partially purified, and using the methods of proteomics, a full-length cDNA clone encoding an enzyme matching the properties of PCY1 was obtained. The substrate specificity of purified recombinant PCY1, believed to be the first cloned plant enzyme whose function is peptide cyclization, was tested with synthetic peptides. The results are discussed in the light of CP biosynthetic systems of other organisms. Background: In the Caryophyllaceae, cyclic peptides (CP) are biosynthesized from linear precursors via an unknown pathway. Results: Two protease-like enzymes are involved in precursor processing. Conclusion: A serine protease-like enzyme was recruited for the cyclization step in CP biosynthesis. Significance: This represents a very significant advance in our understanding of the mode and evolution of CP biosynthesis in plants.