title: Cycloviolacin H4, a hydrophobic cyclotide from Viola hederaceae.
abstract: Cycloviolacin H4, a new macrocyclic miniprotein comprising 30 amino acid residues, was isolated from the underground parts of the Australian native violet Viola hederaceae. Its sequence, cyclo-(CAESCVWIPCTVTALLGCSCSNNVCYNGIP), was determined by nanospray tandem mass spectrometry and quantitative amino acid analysis. A knotted disulfide arrangement, which was designated as a cyclic cystine knot motif and characteristic to all known cyclotides, is proposed for stabilizing the molecular structure and folding. The cyclotide is classified in the bracelet subfamily of cyclotides due to the absence of a cis-Pro peptide bond in the circular peptide backbone. A model of its three-dimensional structure was derived based on the template of the homologous cyclotide vhr1 (Trabi et al. Plant Cell 2004, 16, 2204-2216). Cycloviolacin H4 exhibits the most potent hemolytic activity in cyclotides reported so far, and this activity correlates with the size of a surface-exposed hydrophobic patch. This work has thus provided insight into the factors that modulate the cytotoxic properties of cyclotides.
authors.affiliation: Institute for Molecular Bioscience, Australian Research Council Special Research Centre for Functional and Applied Genomics, University of Queensland, Brisbane, QLD 4072, Australia.
authors.forename: Bin
authors.initials: B
authors.lastname: Chen
authors.forename: Michelle L
authors.initials: ML
authors.lastname: Colgrave
authors.forename: Conan
authors.initials: C
authors.lastname: Wang
authors.forename: David J
authors.initials: DJ
authors.lastname: Craik
mesh_terms: D000595:Amino Acid Sequence; D000596:Amino Acids / Q000032:analysis; D001315:Australia; D047169:Cyclotides / Q000737:chemistry* / Q000302:isolation & purification* / Q000494:pharmacology; D004912:Erythrocytes / Q000187:drug effects; D006461:Hemolysis; D006801:Humans; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011487:Protein Conformation; D016415:Sequence Alignment; D032413:Viola / Q000737:chemistry*
chemical_list: D000596:Amino Acids; D047169:Cyclotides; C508326:cycloviolacin H4