The cyclic peptide sunflower trypsin inhibitor 1 (SFTI-1) blocks trypsin and is a promising target for blocking other proteins associated with cancer. However, SFTI and its analogues have not been broadly adopted by drug designers because of the expense of producing them using traditional, synthetic manufacturing methods.

Joshua Mylne, David Craik and co-workers, University of Queensland, Australia, have shown that the enzyme used to process and mature sunflower seed storage proteins is commandeered by SFTI-1. SFTI-1 is buried in precursors for seed storage protein albumins. The albumins are matured by asparaginyl endopeptidase, which also liberates both ends of SFTI-1, freeing it from the albumin precursor by the action of albumin’s own processing enzyme.

Pharmaceutical-producing seeds are cheap to grow and there are established systems for their production, harvest, storage and transportation, making them a very low-cost drug delivery system.

• Albumins and their processing machinery are hijacked for cyclic peptides in sunflower
  J. S. Mylne, M. L. Colgrave, N. L. Daly, A. H. Chanson, A. G. Elliott, E. J. McCallum, A. Jones, D. J. Craik,
  Nat. Chem. Biol. 2011.
  DOI: 10.1038/nchembio.542