Many plants produce compounds that serve as a defense against predators or pathogens. Some are also used by humans for a variety of beneficial purposes, such as in medicines. As recently as the early 1990s, a unique class of proteins previously unknown to science, the cyclotides, was discovered. First noted through African tribal use as a tea given to speed up delivery during childbirth, cyclotides have since been determined to serve as a powerful insecticidal and nematocidal defense in the plants that produce them, and they also have anti-HIV and antimicrobial properties, with obvious benefits for humans. However, scientists are still working on unlocking much of the basic science of these fascinating proteins, including how they work and where in the plant cell they are produced.
Among the scientists interested in cyclotides, as well as other immune proteins, is Marilyn Anderson of LaTrobe University, Australia.
"Cyclotides are small cyclic peptides of only 28-37 residues that most plant biologists may not have heard of, yet they form the largest family of cyclic proteins described to date in any organism," explains Anderson. "Cyclic cyclotides are widespread in members of the Rubiaceae, Violaceae, Cucurbitaceae and Fabaceae families, yet linear cyclotides are also produced by major monocots such as rice, corn and barley."
"The big question is what do they do?" she continues. "We have discovered that some are potent insecticidal and nematocidal molecules but it is likely that some have other functions as yet undescribed."
Indeed, cycolotides have a unique shape resulting from three disulfide bonds and a peptide backbone that twists in such as way as to produce a cystine knot. This cyclic configuration provides the protein with a very stable structure that is hard to break downwhich is how it maintains its bioactivity despite, for example, the high temperatures used to brew the tea used t
|Contact: Richard Hund|
American Journal of Botany