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Insecticidal compounds in plants

Several members of three plants families – the Rubiaceae, Violaceae and Cucurbitaceae– produce cyclotides, cyclic mini-peptides made up of 28-37 amino acids arranged in a circular configuration. These compounds are very stable and have attracted the attention of pharmaceutical companies. Because these peptides lack free amino and carboxyl ends, they cannot be broken down by proteases. The compounds helicoverpa_size.jpgappear to act primarily as insecticides. In an article published in the January 29 issue of PNAS, Barbara Barbeta and colleagues investigated the role of these compounds on the larvae of lepidopterans (butterflies and moths). The compounds damaged the cells of the midgut of Helicoverpa armigera larvae, which severely stunted their growth (image from Wikipedia; see license details).

Barbeta, B.L., Marshall, A.T., Gillon, A.D., Craik, D.J., and Anderson, M.A. 2008. Plant cyclotides disrupt epithelial cells in the midgut of lepidopteran larvae. Proceedings of the National Academy of Sciences USA 105(4):1221-1225 DOI:10.1073/pnas.0710338104

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6 Responses

  1. Very reminiscent of a number of fungal toxins, particularly those made by the Amanitas and a few related genera.

  2. I’m fascinated by the idea of circular peptides. I’d never heard of anything of the sort before. Very devious.

  3. Oh, VERY devious.

    The major toxins of the Amanitas are cyclic and bicyclic peptides. Alpha amanitin is a particularly nasty one; it binds only to RNA polymerase that’s actively involved in transcription, so it’s technically a non-competitive inhibitor. It essentially rams itself through the “back” of the polymerase, since the active site of the enzyme is already busy. Phalloidin, another Amanita toxin, locks actin into a polymerized state, so it freezes cells in their tracks.

    There’s a quick and dirty overview here and a paper on how the Amanitas make their toxic peptides here.

  4. […] studies conducted in Australia, China, Spain and the United States focusing on six pest species: Helicoverpa armigera, H. zea, Heliothis virescens, Ostrinia nubilalis, Pectinophora gossypiella and Sesamia […]

  5. […] studies conducted in Australia, China, Spain and the United States focusing on six pest species: Helicoverpa armigera, H. zea, Heliothis virescens, Ostrinia nubilalis, Pectinophora gossypiella and Sesamia […]

  6. I read your blog for quite a long time and must tell that your posts are always valuable to readers.

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