How Butterfly Peas Became the Ultimate Cyclotide Factory

The butterfly pea legume (Clitoria ternatea) is native to South America and tropical regions of Asia and was introduced to Queensland, Australia in 1991. The legume is best known for its decorative flower with brilliant blue petals. When used as a tea it infuses the water with a bright blue hue, which turns purple following the addition of an acid, such as lemon. Our researchers at the Institute for Molecular Bioscience, The University of Queensland, have been investigating the butterfly pea to understand its potential as a green and sustainable bio-factory for the mass production of cyclotide peptides. 

 Cyclotides are unique macrocyclic peptides with interlocking loops, known as cyclic cystine knots. These peptides have shown potent medicinal properties for humans and an increased ability to bind to targets. Plants commonly produce cyclotides as defence agents to combat pests and pathogens. Most legumes evolved to express linear album-1 peptides, whilst the butterfly pea legume has been discovered to express cyclotides instead. The mystery behind this evolution has remained unsolved until now. Our Centre Investigators from The University of Queensland and The University of Sydney, Professor David Craik, Professor Kathy Belov, Professor Carolyn Hogg, Research Fellows Dr Edward Gilding, Dr Mark Jackson, Dr Katherine Farquharson, along with their PhD students have worked diligently to unveil this mystery. 

 They discovered that in the butterfly pea legume a mutation occurred in the genes that once produced the linear album-1. The genes were reprogrammed for cyclotide synthesis through a series of evolutionary steps. First, an amino acid was added to the end of the protein chain, then the original asparaginyl endopeptidase (AEP), which had weak activity, was duplicated and specialized for cyclotide formation. Finally, the genes responsible for cyclotides were copied and diversified to take on various roles. 

 Understanding the evolutionary mechanisms behind the mysteries of cyclotide formation in butterfly pea will enable protein engineers to learn from nature and to potentially adopt this finding to identify new plants with similar bioactivity, as well as optimize the biosynthesis of cyclotides in plants to develop tools in agricultural and conservation, or next-generation therapies using more sustainable methods. 

Citation:  Gilding, E.K., Jackson, M.A., Nguyen, L.T.T. et al. Hijacking of N-fixing legume albumin-1 genes enables the cyclization and stabilization of defense peptides. 2024 Nat. Commun. 15, 6565.  

 Doi: 10.1038/s41467-024-50742-x 

 CIPPS contributors: David Craik, Katherine Belov, Carolyn Hogg, Edward Gilding, Mark Jackson, Katherine Farquharson, Linh Nguyen, Wing Ho, Kuok Yap