title: Oxytocic plant cyclotides as templates for peptide G protein-coupled receptor ligand design.
abstract: Cyclotides are plant peptides comprising a circular backbone and three conserved disulfide bonds that confer them with exceptional stability. They were originally discovered in Oldenlandia affinis based on their use in traditional African medicine to accelerate labor. Recently, cyclotides have been identified in numerous plant species of the coffee, violet, cucurbit, pea, potato, and grass families. Their unique structural topology, high stability, and tolerance to sequence variation make them promising templates for the development of peptide-based pharmaceuticals. However, the mechanisms underlying their biological activities remain largely unknown; specifically, a receptor for a native cyclotide has not been reported hitherto. Using bioactivity-guided fractionation of an herbal peptide extract known to indigenous healers as "kalata-kalata," the cyclotide kalata B7 was found to induce strong contractility on human uterine smooth muscle cells. Radioligand displacement and second messenger-based reporter assays confirmed the oxytocin and vasopressin V1a receptors, members of the G protein-coupled receptor family, as molecular targets for this cyclotide. Furthermore, we show that cyclotides can serve as templates for the design of selective G protein-coupled receptor ligands by generating an oxytocin-like peptide with nanomolar affinity. This nonapeptide elicited dose-dependent contractions on human myometrium. These observations provide a proof of concept for the development of cyclotide-based peptide ligands.
authors.affiliation: Center for Physiology and Pharmacology, Medical University of Vienna, 1090 Vienna, Austria.
authors.forename: Johannes
authors.initials: J
authors.lastname: Koehbach
authors.forename: Margaret
authors.initials: M
authors.lastname: O'Brien
authors.forename: Markus
authors.initials: M
authors.lastname: Muttenthaler
authors.forename: Marion
authors.initials: M
authors.lastname: Miazzo
authors.forename: Muharrem
authors.initials: M
authors.lastname: Akcan
authors.forename: Alysha G
authors.initials: AG
authors.lastname: Elliott
authors.forename: Norelle L
authors.initials: NL
authors.lastname: Daly
authors.forename: Peta J
authors.initials: PJ
authors.lastname: Harvey
authors.forename: Sarah
authors.initials: S
authors.lastname: Arrowsmith
authors.forename: Sunithi
authors.initials: S
authors.lastname: Gunasekera
authors.forename: Terry J
authors.initials: TJ
authors.lastname: Smith
authors.forename: Susan
authors.initials: S
authors.lastname: Wray
authors.forename: Ulf
authors.initials: U
authors.lastname: Göransson
authors.forename: Philip E
authors.initials: PE
authors.lastname: Dawson
authors.forename: David J
authors.initials: DJ
authors.lastname: Craik
authors.forename: Michael
authors.initials: M
authors.lastname: Freissmuth
authors.forename: Christian W
authors.initials: CW
authors.lastname: Gruber
mesh_terms: D000704:Analysis of Variance; D002851:Chromatography, High Pressure Liquid; D003001:Cloning, Molecular; D003094:Collagen / Q000187:drug effects; D047169:Cyclotides / Q000032:analysis / Q000378:metabolism* / Q000494:pharmacology; D015195:Drug Design; D005260:Female; D006801:Humans; D008024:Ligands; D009682:Magnetic Resonance Spectroscopy; D032067:Oldenlandia / Q000737:chemistry*; D009842:Oligopeptides / Q000096:biosynthesis*; D010120:Oxytocics / Q000032:analysis / Q000378:metabolism* / Q000494:pharmacology; D011869:Radioligand Assay; D043562:Receptors, G-Protein-Coupled / Q000378:metabolism*; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D014590:Uterine Contraction / Q000187:drug effects
chemical_list: D047169:Cyclotides; D008024:Ligands; D009842:Oligopeptides; D010120:Oxytocics; D043562:Receptors, G-Protein-Coupled; D003094:Collagen
keywords: chemical pharmacology; circular plant peptide; peptide drugs; peptide ligand design; uterotonic