title: Alanine scanning mutagenesis of the prototypic cyclotide reveals a cluster of residues essential for bioactivity.
abstract: The cyclotides are stable plant-derived mini-proteins with a topologically circular peptide backbone and a knotted arrangement of three disulfide bonds that form a cyclic cystine knot structural framework. They display a wide range of pharmaceutically important bioactivities, but their natural function is in plant defense as insecticidal agents. To determine the influence of individual residues on structure and activity in the prototypic cyclotide kalata B1, all 23 non-cysteine residues were successively replaced with alanine. The structure was generally tolerant of modification, indicating that the framework is a viable candidate for the stabilization of bioactive peptide epitopes. Remarkably, insecticidal and hemolytic activities were both dependent on a common, well defined cluster of hydrophilic residues on one face of the cyclotide. Interestingly, this cluster is separate from the membrane binding face of the cyclotides. Overall, the mutagenesis data provide an important insight into cyclotide biological activity and suggest that specific self-association, in combination with membrane binding mediates cyclotide bioactivities.
authors.affiliation: Institute for Molecular Bioscience, University of Queensland, St. Lucia, Brisbane, Queensland 4072, Australia.
authors.forename: Shane M
authors.initials: SM
authors.lastname: Simonsen
authors.forename: Lillian
authors.initials: L
authors.lastname: Sando
authors.forename: K Johan
authors.initials: KJ
authors.lastname: Rosengren
authors.forename: Conan K
authors.initials: CK
authors.lastname: Wang
authors.forename: Michelle L
authors.initials: ML
authors.lastname: Colgrave
authors.forename: Norelle L
authors.initials: NL
authors.lastname: Daly
authors.forename: David J
authors.initials: DJ
authors.lastname: Craik
mesh_terms: D000818:Animals; D047169:Cyclotides / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D047168:Cystine Knot Motifs / Q000502:physiology; D004331:Drosophila melanogaster; D000939:Epitopes / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D007306:Insecticides / Q000737:chemistry* / Q000378:metabolism; D016297:Mutagenesis, Site-Directed; D010449:Peptide Mapping; D010940:Plant Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D013329:Structure-Activity Relationship
chemical_list: D047169:Cyclotides; D000939:Epitopes; D007306:Insecticides; D010940:Plant Proteins