CHARACTERIZATION OF PEPTIDE CYCLASE 1 (PCY1), A SERINE PROTEASE-LIKE ENZYME INVOLVED IN CYCLIC PEPTIDE BIOSYNTHESIS IN PLANTS
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Plants within the Caryophyllaceae, and certain other families, produce cyclic peptides (CPs) which generally consist of 5–12 proteinogenic amino acids. Until recently, very little was known about the biosynthesis of CPs in the Caryophyllaceae. Recently, in the Covello lab, two enzymes in Saponaria vaccaria were found to be involved in the processing of ribosome-derived linear precursors, giving rise to cyclic peptides. Thus, oligopeptidase 1 (OLP1) and peptide cyclase 1 (PCY1) are involved in the biosynthesis of segetalin A (a six-membered CP) from a 32 amino acid linear peptide precursor called presegetalin A1. PCY1 carries out the unusual cyclization reaction to form mature segetalin A from a linear intermediate. The purified recombinant PCY1, the first cloned plant enzyme whose function is peptide cyclization, was identified as a homologue of a prolyl-oligopeptidase from the S9 serine protease family. In principle, PCY1 performs an intra-molecular transpeptidation reaction to produce a CP. A homology-based structural model of PCY1 suggests that it has two domains, a catalytic α/β hydrolase domain and an unusual β- propeller domain. In an effort to define the substrate specificity of PCY1, a wide variety of synthetic peptide precursors were tested in assays and the results are discussed.
DegreeMaster of Science (M.Sc.)
SupervisorCovello, Patrick S.
CommitteeLee, Jeremy; Loewen, Michele; Geyer, Ron
Copyright DateNovember 2013