title: Multiple actions of phi-LITX-Lw1a on ryanodine receptors reveal a functional link between scorpion DDH and ICK toxins.
abstract: We recently reported the isolation of a scorpion toxin named U1-liotoxin-Lw1a (U1-LITX-Lw1a) that adopts an unusual 3D fold termed the disulfide-directed hairpin (DDH) motif, which is the proposed evolutionary structural precursor of the three-disulfide-containing inhibitor cystine knot (ICK) motif found widely in animals and plants. Here we reveal that U1-LITX-Lw1a targets and activates the mammalian ryanodine receptor intracellular calcium release channel (RyR) with high (fM) potency and provides a functional link between DDH and ICK scorpion toxins. Moreover, U1-LITX-Lw1a, now described as ϕ-liotoxin-Lw1a (ϕ-LITX-Lw1a), has a similar mode of action on RyRs as scorpion calcines, although with significantly greater potency, inducing full channel openings at lower (fM) toxin concentrations whereas at higher pM concentrations increasing the frequency and duration of channel openings to a submaximal state. In addition, we show that the C-terminal residue of ϕ-LITX-Lw1a is crucial for the increase in full receptor openings but not for the increase in receptor subconductance opening, thereby supporting the two-binding-site hypothesis of scorpion toxins on RyRs. ϕ-LITX-Lw1a has potential both as a pharmacological tool and as a lead molecule for the treatment of human diseases that involve RyRs, such as malignant hyperthermia and polymorphic ventricular tachycardia.
authors.affiliation: Chemical and Structural Biology, Institute for Molecular Biosciences, University of Queensland, St. Lucia, QLD 4072, Australia.
authors.forename: Jennifer J
authors.initials: JJ
authors.lastname: Smith
authors.forename: Irina
authors.initials: I
authors.lastname: Vetter
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Lewis
authors.forename: Steve
authors.initials: S
authors.lastname: Peigneur
authors.forename: Jan
authors.initials: J
authors.lastname: Tytgat
authors.forename: Alexander
authors.initials: A
authors.lastname: Lam
authors.forename: Esther M
authors.initials: EM
authors.lastname: Gallant
authors.forename: Nicole A
authors.initials: NA
authors.lastname: Beard
authors.forename: Paul F
authors.initials: PF
authors.lastname: Alewood
authors.forename: Angela F
authors.initials: AF
authors.lastname: Dulhunty
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D020746:Calcium Channels, L-Type / Q000737:chemistry / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid; D004220:Disulfides / Q000737:chemistry; D055724:Electrophysiological Phenomena / Q000502:physiology; D005727:Ganglia, Spinal / Q000166:cytology; D006801:Humans; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D008969:Molecular Sequence Data; D020125:Mutation, Missense / Q000235:genetics; D009474:Neurons / Q000378:metabolism*; D009865:Oocytes / Q000378:metabolism; D017510:Protein Folding; D011817:Rabbits; D051381:Rats; D019837:Ryanodine Receptor Calcium Release Channel / Q000378:metabolism*; D012604:Scorpion Venoms / Q000138:chemical synthesis / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D016415:Sequence Alignment; D060327:Solid-Phase Synthesis Techniques / Q000379:methods; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D014316:Tritium; D014982:Xenopus laevis
chemical_list: D020746:Calcium Channels, L-Type; D004220:Disulfides; D019837:Ryanodine Receptor Calcium Release Channel; D012604:Scorpion Venoms; D014316:Tritium