High-resolution structure of a potent, cyclic proteinase inhibitor from sunflower seeds

S. Luckett, R. Santiago Garcia, J. J. Barker, Al V. Konarev, P. R. Shewry, A. R. Clarke, R. L. Brady*

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)peer-review

293 Citations (Scopus)


Proteinaceous serine proteinase inhibitors are widespread throughout the plant kingdom where they play an important role in protection against pests and pathogens. Here, we describe the isolation and characterisation of a novel 14 amino acid residue cyclic peptide from sunflower seeds, which is a potent inhibitor of trypsin (K(i) = 100 pM). The crystal structure of this peptide in complex with bovine β-trypsin shows both sequence and conformational similarity with the trypsin-reactive loop of the Bowman-Birk family of serine proteinase inhibitors. This inhibitor, however, is unique in being monofunctional, cyclic and far shorter (14 amino acid residues) than inhibitors belonging to this family (typically 60-70 amino acid residues). The high potency of this peptide is likely to arise from the considerable structural rigidity achieved through its cyclic nature which is further stabilised by a single internal disulphide bond. This study helps delineate the minimal unit required for effective peptide inhibitors of serine proteinases, and will assist in the further design of inhibitors to this widespread class of enzymes.

Original languageEnglish
Pages (from-to)525-533
Number of pages9
JournalJournal of Molecular Biology
Issue number2
Publication statusPublished - 9 Jul 1999


  • Bowman-Birk inhibitor
  • Cyclic peptide
  • Sunflower seeds
  • Trypsin inhibitor
  • X-ray crystallography

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