title: Holocyclotoxin-1, a cystine knot toxin from Ixodes holocyclus.
abstract: In the past 100 years minimal venom research has focused on ticks despite several species possessing a highly paralytic and lethal venom cocktail of proteinaceous molecules. The saliva of the Australian paralysis tick, Ixodes holocyclus, has been responsible for 20 human fatalities from 1900 to 1945, and up to 100,000 domestic animal fatalities annually. In the last 50 years, research on this tick has focused on identifying the neurotoxins present in the saliva and in the last ten years the sequence of a potential neurotoxin, HT-1, has been determined. In this study we chemically synthesised HT-1 using Boc-chemistry in combination with native chemical ligation. Following successful oxidative folding, we determined the three-dimensional structure of HT-1 by NMR spectroscopy and found a novel structural fold with three of the four disulfide bonds comprising the inhibitory cystine knot (ICK) motif. The fourth disulfide bond connects the second loop to the N-terminal, which decreases the flexibility of the structure.
authors.affiliation: Institute for Molecular Bioscience, The University of Queensland, Brisbane, Australia.
authors.forename: Simone
authors.initials: S
authors.lastname: Vink
authors.affiliation: Institute for Molecular Bioscience, The University of Queensland, Brisbane, Australia; AITHM and Centre for Biodiscovery and Molecular Development of Therapeutics, James Cook University, Cairns, Australia.
authors.forename: Norelle L
authors.initials: NL
authors.lastname: Daly
authors.affiliation: Institute for Molecular Bioscience, The University of Queensland, Brisbane, Australia.
authors.forename: Natalie
authors.initials: N
authors.lastname: Steen
authors.affiliation: Institute for Molecular Bioscience, The University of Queensland, Brisbane, Australia.
authors.forename: David J
authors.initials: DJ
authors.lastname: Craik
authors.affiliation: Institute for Molecular Bioscience, The University of Queensland, Brisbane, Australia. Electronic address: p.alewood@imb.uq.edu.au.
authors.forename: Paul F
authors.initials: PF
authors.lastname: Alewood
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001180:Arthropod Venoms / Q000737:chemistry / Q000302:isolation & purification* / Q000633:toxicity; D002851:Chromatography, High Pressure Liquid; D003545:Cysteine / Q000737:chemistry*; D018884:Ixodes / Q000737:chemistry*; D008969:Molecular Sequence Data; D019906:Nuclear Magnetic Resonance, Biomolecular; D053719:Tandem Mass Spectrometry
chemical_list: D001180:Arthropod Venoms; C038423:holocyclotoxin; D003545:Cysteine
keywords: Holocyclotoxin-1; ICK motif; Ixodes holocyclus; Native chemical ligation; Paralysis tick; SPPS