Journal
CHEMISTRY & BIOLOGY
Volume 22, Issue 5, Pages 571-582Publisher
CELL PRESS
DOI: 10.1016/j.chembiol.2015.04.010
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Funding
- USDA IFAFS program
- NSF Plant Genome Program
- Australian Research Council [FT120100013, FT110100242, CE14010008, DP12103369]
- Australian Research Council [FT110100242, FT120100013] Funding Source: Australian Research Council
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Proteases usually cleave peptides, but under some conditions, they can ligate them. Seeds of the common sunflower contain the 14-residue, backbone-macrocyclic peptide sunflower trypsin inhibitor 1 (SFTI-1) whose maturation from its precursor has a genetic requirement for asparaginyl endopeptidase (AEP). To provide more direct evidence, we developed an in situ assay and used O-18-water to demonstrate that SFTI-1 is excised and simultaneously macrocyclized from its linear precursor. The reaction is inefficient in situ, but a newfound breakdown pathway can mask this inefficiency by reducing the internal disulfide bridge of any acyclic-SFTI to thiols before degrading it. To confirm AEP can directly perform the excision/ligation, we produced several recombinant plant AEPs in E. coli, and one from jack bean could catalyze both a typical cleavage reaction and cleavage-dependent, intramolecular transpeptidation to create SFTI-1. We propose that the evolution of ligating endoproteases enables plants like sunflower and jack bean to stabilize bioactive peptides.
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