title: Lysine-rich Cyclotides: A New Subclass of Circular Knotted Proteins from Violaceae.
abstract: Cyclotides are macrocyclic proteins produced by plants for host defense. Although they occur sparsely in other plant families, cyclotides have been detected in every Violaceae plant species so far screened. Many of the Violaceae species examined until now have been from closely related geographical regions or habitats. To test the hypothesis that cyclotides are ubiquitous in this family, two geographically isolated (and critically endangered) species of Australasian Violaceae, namely Melicytus chathamicus and M. latifolius, were examined. Surprisingly, we discovered a suite of cyclotides possessing novel sequence features, including a lysine-rich nature, distinguishing them from "conventional" cyclotides and suggesting that they might have different physiological activities in plants to those reported to date. The newly discovered cyclotides were found to bind to lipid membranes and were cytotoxic against cancer cell lines but had low toxicity against red blood cells, which is advantageous for potential therapeutic applications. This suite of novel Lys-rich cyclotides emphasizes the broad diversity of cyclotides in Violaceae species.
authors: Institute for Molecular Bioscience, The University of Queensland , Brisbane, Queensland 4072, Australia.
authors: Anjaneya S
authors: AS
authors: Ravipati
authors: Institute for Molecular Bioscience, The University of Queensland , Brisbane, Queensland 4072, Australia.
authors: Sónia Troeira
authors: ST
authors: Henriques
authors: Institute for Molecular Bioscience, The University of Queensland , Brisbane, Queensland 4072, Australia.
authors: Aaron G
authors: AG
authors: Poth
authors: Institute for Molecular Bioscience, The University of Queensland , Brisbane, Queensland 4072, Australia.
authors: Quentin
authors: Q
authors: Kaas
authors: Institute for Molecular Bioscience, The University of Queensland , Brisbane, Queensland 4072, Australia.
authors: Conan K
authors: CK
authors: Wang
authors: Commonwealth Scientific and Industrial Research Organization , Agriculture Flagship, St. Lucia, Queensland 4067, Australia.
authors: Michelle L
authors: ML
authors: Colgrave
authors: Institute for Molecular Bioscience, The University of Queensland , Brisbane, Queensland 4072, Australia.
authors: David J
authors: DJ
authors: Craik
mesh_terms: D000595:Amino Acid Sequence; D002478:Cells, Cultured; D047169:Cyclotides / Q000737:chemistry* / Q000494:pharmacology; D047168:Cystine Knot Motifs; D004912:Erythrocytes / Q000187:drug effects; D006801:Humans; D008239:Lysine / Q000737:chemistry* / Q000494:pharmacology; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D010455:Peptides / Q000737:chemistry / Q000235:genetics; D011485:Protein Binding; D021241:Spectrometry, Mass, Electrospray Ionization; D029649:Violaceae / Q000737:chemistry*
chemical_list: D047169:Cyclotides; D010455:Peptides; D008239:Lysine