ASIC3selectiveinhibitorAPETx2 isatoxinthatwasoriginallyisolatedfromAnthopleuraelegantissima(Seaanemone).APETx2 selectivelyblockstheH(+)-gatedsodiumchannelASIC3(ACCN3).TheblockageisrapidandreversIBLe.ThistoxindoesnotblockisoformASIC1a(unlike Psalmotoxin1)andisoformASIC1bofASIC1(ACCN2),norASIC2(ACCN1).ItalsoinhibitstheheteromericASIC2b-ASIC3channel,and haslessaffinityforASIC1b-ASIC3,ASIC1a-ASIC3,andnoeffectontheASIC2a-ASIC3channels.IC50 is63nMonASIC3channel.IC50 is117nMonASIC2b-ASIC3heteromericchannel.IC50 is0.9µMonASIC1b-ASIC3heteromericchannel.IC50 is2µMonASIC1a-ASIC3heteromericchannel.Interestingly,recentstudiesdemonstratedthat APETx2also inhibitsNav1.8currents withanIC50 ofaround2µM.Fig1: Dose-responsecurveoftheeffectofsyntheticAPETx2#07APE002onratASIC3currentrecordedinXenopusoocytes.Inthissystem,anIC50of80.5nMwasdeterminedforAPETx2(N=5).Description:Productcode:07APE002.Category:ASICchannels.Tags:ASIC,pain.AAsequence: H-Gly-Thr-Ala-Cys4-Ser-Cys6-Gly-Asn-Ser-Lys-Gly-Ile-Tyr-Trp-Phe-Tyr-Arg-Pro-Ser-Cys20-Pro-Thr-Asp-Arg-Gly-Tyr-Thr-Gly-Ser-Cys30-Arg-Tyr-Phe-Leu-Gly-Thr-Cys37-Cys38-Thr-Pro-Ala-Asp-OH(DisulfidebondsbetweenCys4-Cys37,Cys6-Cys30 andCys20-Cys38)Length(aa): 42Formula: C196H280N54O61S6MolecularWeight: 4561.13DaAppearance:WhitelyophilizedsolidSolubility: waterandsalinebufferCASnumber: notavailableSource: SyntheticPurityrate: >98%Reference:CitationsPeigneurS, etal.(2012)Anaturalpointmutationchangesbothtargetselectivityandmechanismofactionofseaanemonetoxins. FASEBJ. PubMedlinkBlanchardMG,RashLD,KellenbergerS.(2011)Inhibitionofvoltage-gatedNa(+)currentsinsensoryneuronsbytheseaanemonetoxinAPETx2. BrJPharmacol. PubMedlinkTsuchimochiH,YamauchiK,McCordJL,KaufmanMP.(2011)BlockadeofAcidSensingIonChannelsAttenuatestheAugmentedExercisePressorReflexinRatswithChronicFemoralArteryOcclusion. JPhysiol. PubMedlinkHumanASIC3channeldynamicallyadaptsitsactivitytosensetheextracellularpHinbothacidicandalkalinedirections.Inrodentsensoryneurons,acid-sensingionchannel3(ASIC3)hasrecentlyemergedasaparticularlyimportantsensorofnonadaptivepainassociatedwithtissueacidosis.However,littleisknownaboutthehumanASIC3channel,whichincludesthreesplicevariantsdifferingintheirC-terminaldomain(hASIC3a,hASIC3b,andhASIC3c).hASIC3atranscriptsrepresentthemainmRNAsexpressedinbothperipheralandcentralneuronaltissues(dorsalrootganglia[DRG],spinalcord,andbrain),whereasmallproportionofhASIC3ctranscriptsisalsodetected.WeshowthathASIC3channels(hASIC3a,hASIC3b,orhASIC3c)areabletodirectlysenseextracellularpHchangesnotonlyduringacidification(uptopH5.0),butalsoduringalkalization(uptopH8.0),anoriginalandinduciblepropertyyetunknown.WhentheexternalpHdecreases,hASIC3displayatransientacidmodewithbriefactivationthatisrelevanttotheclassicalASICcurrents,aspreviouslydescribed.Ontheotherhand,anexternalpHincreaseactivatesasustainedalkalinemodeleADIngtoaconstitutiveactivityatrestingpH.BothmodesareinhibitedbytheAPETx2toxin,anASIC3-typechannelinhibitor.ThealkalinesensitivityofhASIC3isanintrinsicpropertyofthechannel,whichissupportedbytheextracellularloopandinvolvestwoarginines(R68andR83)onlypresentinthehumanclone.hASIC3isthusabletosensetheextracellularpHinbothdirectionsandthereforetodynamicallyadaptitsactivitybetweenpH5.0and8.0,apropertylikelytoparticipateinthefinetuningofneuronalmembranepotentialandtoneuronsensitizationinvariouspHenvironments.DelaunayA.,etal.(2012)HumanASIC3channeldynamicallyadaptsitsactivitytosensetheextracellularpHinbothacidicandalkalinedirections.PNAS.PMID:22829666SolutionstructureofAPETx2,aspecificpeptideinhibitorofASIC3proton-gatedchannels.Acid-sensingionchannels(ASIC)areproton-gatedsodiumchannelsthathavebeenimplicatedinpaintransductionassociatedwithacidosisininflamedorischemictissues.APETx2,apeptidetoxineffectorofASIC3,hasbeenpurifiedfromanextractoftheseaanemoneAnthopleuraelegantissima.APETx2isa42-amino-acidpeptidecross-linkedbythreedisulfidebridges.Itsthree-dimensionalstructure,asdeterminedbyconventionaltwo-dimensional1H-NMR,consistsofacompactdisulfide-bondedcorecomposedofafour-strandedbeta-sheet.Itbelongstothedisulfide-richall-betastructuralfamilyencompassingpeptidetoxinscommonlyfoundinanimalvenoms.ThestructuralcharacteristicsofAPETx2arecomparedwiththatofPcTx1,anothereffectorofASICchannelsbutspecifictotheASIC1asubtypeandtoAPETx1,atoxinstructurallyrelatedtoAPETx2,whichtargetstheHERGpotassiumchannel.Structuralcomparisons,coupledwiththeanalysisoftheelectrostaticcharacteristicsofthesevariousionchanneleffectors,ledustosuggestaputativechannelinteractionsurfaceforAPETx2,encompassingitsNterminustogetherwiththetypeI-betaturnconnectingbeta-strandsIIIandIV.Thisbasicsurface(R31andR17)isalsorichinaromaticresidues(Y16,F15,Y32,andF33).AnadditionalregionmadeofthetypeII’-betaturnconnectingbeta-strandsIandIIcouldalsoplayaroleinthespecificityobservedforthesedifferentioneffectors.ChagotB.,etal.(2005)SolutionstructureofAPETx2,aspecificpeptideinhibitorofASIC3proton-gatedchannels,ProteinSci.PMID:15987885Anewseaanemonepeptide,APETx2,inhibitsASIC3,amajoracid-sensitivechannelinsensoryneurons.Fromasystematicscreeningofanimalvenoms,weisolatedanewtoxin(APETx2)fromtheseaanemoneAnthopleuraelegantissima,whichinhibitsASIC3homomericchannelsandASIC3-containingheteromericchannelsbothinheterologousexpressionsystemsandinprimaryculturesofratsensoryneurons.APETx2isa42amino-acidpeptidecrosslinkedbythreedisulfidebridges,withastructuralorganizationsimilartothatofotherseaanemonetoxinsthatinhibitvoltage-sensitiveNa+andK+channels.APETx2reversiblyinhibitsratASIC3(IC50=63nM),withoutanyeffectonASIC1a,ASIC1b,andASIC2a.APETx2directlyinhibitstheASIC3channelbyactingatitsexternalside,anditdoesnotmodifythechannelunitaryconductance.APETx2alsoinhibitsheteromericASIC2b+3current(IC50=117nM),whileithaslessaffinityforASIC1b+3(IC50=0.9microM),ASIC1a+3(IC50=2microM),andnoeffectontheASIC2a+3current.TheASIC3-likecurrentinprimaryculturedsensoryneuronsispartlyandreversiblyinhibitedbyAPETx2withanIC50of216nM,probablyduetothemixedinhibitionsofvariousco-expressedASIC3-containingchannels.DiochotS.,etal.(2004)Anewseaanemonepeptide,APETx2,inhibitsASIC3,amajoracid-sensitivechannelinsensoryneurons.EMBOJ.PMID:15044953