Kaliotoxin-1(KTX1)hasbeenisolatedfromthevenomoftheScorpionAndroctonusmauretanicusmauretanicus.Kaliotoxin-1showsahighstructuralaffinitywithIberiotoxinandCharyBDotoxinthatinhibitKCa2+channelsactivity.Accordingtoseveralstudies,itappearsthatKaliotoxin-1hasaweakinhibitoryeffectonKCa2+channels,butitisapotentandselectiveinhibitorofvoltage-activatedpotassiumchannel(Kv1.1,Kv1.2,Kv1.3).Description:Productcode:N/A.Categories:Kvchannels,Potassiumchannels.Tags:kv,potassium.AAsequence:Gly-Val-Glu-Ile-Asn-Val-Lys-Cys8-Ser-Gly-Ser-Pro-Gln-Cys14-Leu-Lys-Pro-Cys18-Lys-Asp-Ala-Gly-Met-Arg-Phe-Gly-Lys-Cys28-Met-Asn-Arg-Lys-Cys33-His-Cys35-Thr-Pro-Lys-OH(DisulfidebondsbetweenCys8-Cys28,Cys14-Cys33andCys18-Cys35)Length(aa):38Formula:C171H283N55O49S6MolecularWeight:4149.89DaAppearance:WhitelyophilizedsolidSolubility:waterandsalinebufferCASnumber:Source:SyntheticPurityrate:>97%Reference:Neuropathophysiologicaleffectandimmuno-inflammatoryresponseinducedbykaliotoxinofandroctonusscorpionvenomKaliotoxin(KTX)isaneurotoxinpurifiedfromAndroctonusscorpionvenom.Purificationandpharmacologicalandimmunologicalcharacterizationofthisneurotoxinhasbeenextensivelystudied,butitsBIOLOGicaleffectshavenot.TheABIlityofKTXtoinduceneuropathophysiologicalandimmuno-inflammatoryeffectswasinvestigated.NMRImicewereinjectedwithasublethaldoseofKTX(20ng/20gofbodyweight)orsalinesolutionviatheintra-cerebro-ventricularroute.TissuedamageandimmunologicalbioMarkerssuchaseosinophilperoxidase(EPO),myeloperoxidase(MPO),andnitricoxide(NO)wereanalyzedinserum,brain,lung,andhearttissue.Proteinlevels,LDH,andCPKactivitieswerealsodeterminedinserum24hafterinjection.Inthisstudy,KTXinjectioninducedseverealterationsinthecerebralcortex,myocardium,andpulmonaryparenchyma.Tissuedamagewascorrelatedwithsericincreaseincreatinekinaseandlactatedehydrogenaseactivities.KTXalsoinducedanimmuno-inflammatoryresponsedistinguishedbycellinfiltrationcharacterizedbyasignificantincreaseinEPOandMPOactivitiesinthebrain,heart,andlungs.Thisinfiltrationwasalsoassociatedwithanincreaseinalbumin,α-,β-,andγ-globulinfractions,andNOrelease.KTXbindingtoitstargetsinCNS(Kv1.1andKv1.3channels)mayinduceseveremodificationsinthestructureandfunctionofvariousorgansassociatedwiththeactivationofimmuno-inflammatoryreactions.Ladjel-MendilA.,etal.(2013)Neuropathophysiologicaleffectandimmuno-inflammatoryresponseinducedbykaliotoxinofandroctonusscorpionvenom.Neuroimmunomodulation. PMID: 23295619HeterogeneouscompetitionofKv1channeltoxinswithkaliotoxinforbindinginratbrain:autorADIographicanalysisThealpha-subunitsofKv1channelsdisplaycharacteristicdistributionsandrestrictedco-assemblyinmammalianbrain.TheheterogeneouscompositionofKv1channelshasmadeitdifficulttousespecifictoxinstolabelbrainstructures.WeusedautoradiographytoanalysethecompetitivebehaviourofthreeKv1channeltoxins–alpha-dendrotoxin,kaliotoxin,andmastcelldegranulatingpeptide–forbindingtokaliotoxinbindingsitesinvariousbrainstructures.IC(50)variedconsiderablybetweenbrainregions(byuptothreeordersofmagnitude)foreachligand.alpha-dendrotoxinandkaliotoxincompetedequallyinsomeregionsandtodifferentextentsinothers,identifyingtwotypesofstructure.Mastcelldegranulatingpeptidecompetedwith(125)I-kaliotoxinlessefficientlythanalpha-dendrotoxinandkaliotoxin,inallregions.Thus,differencesinthecapacityofthesethreetoxinstobindtokaliotoxinbindingsitesprovideevidenceofmajordifferencesinthecompositionoftheKv1channelsconstitutingthekaliotoxinbindingsites.BessoneR.,etal.(2004)HeterogeneouscompetitionofKv1channeltoxinswithkaliotoxinforbindinginratbrain:autoradiographicanalysis.NeuRochemInt. PMID: 15337303Kaliotoxin,aKv1.1andKv1.3channelblocker,improvesassociativelearninginratsOlfactoryassociativelearningwasusedtoinvestigatetheinvolvementofKvchannelscontainingKv1.1andKv1.3alpha-subunitsinlearningandmemory.Kaliotoxin(KTX),aspecificinhibitoroftheseKvchannels,wasinjectedintracerebroventricularlyintheratbrain,atadoseof10ngthatdidnotdisturbtherats’locomotoractivityordrinkingbehaviour.Inthefirstparadigm(odour-rewardtraining),KTXimprovedlearningbutnotinformationconsolidation.Moreover,KTXincreasedthelong-termretrievalofanodour-rewardassociationtestedbyareversaltest1monthaftertheodour-rewardtraining.Thesecondparadigm(successiveodour-pairtraining)testedreferencememory.Thefirstsessionwasanacquisitionsessionwheretheratslearnedanewodour-discriminationproblemwiththesameprocedure.Thesecondwasaretentionsessionheld24hlatertotestretrievalofthelearnedinformation.KTXinjectedbeforetheacquisitionorretentionsessionimprovedperformance,butnoeffectwasfoundwhenKTXwasinjectedimmediatelyafteracquisition.WeshowedthattheseeffectswerenotduetotheactionofKTXonattentionprocesses.Thus,theseresultssuggestthattheblockageofKv1.1orKv1.3channelsbyKTXfacilitatescognitiveprocessesaslearning,inparticularinareferencerepresentation.KourrichS.,etal. (2001)Kaliotoxin,aKv1.1andKv1.3channelblocker,improvesassociativelearninginrats.BehavBrainRes. PMID: 11173083Selectiveblockingofvoltage-gatedK+channelsimprovesexperimentalautoimmuneencephalomyelitisandinhibitsTcellactivationKaliotoxin(KTX),ablockerofvoltage-gatedpotassiumchannels(Kv),ishighlyselectiveforKv1.1andKv1.3.First,Kv1.3isexpressedbyTlymphocytes.BlockersofKv1.3inhibitTlymphocyteactivation.Second,Kv1.1isfoundinparanodalregionsofaxonsinthecentralnervoussystem.Kvblockersimprovetheimpairedneuronalconductionofdemyelinatedaxonsinvitroandpotentiatethesynaptictransmission.Therefore,weinvestigatedthetherapeuticpropertiesofKTXviaitsimmunosuppressiveandsymptomaticneurologicaleffects,usingexperimentalautoimmuneencephalomyelitis(EAE),ananimalmodelformultiplesclerosis.TheTlinecellsusedtoinduceadoptiveEAEweremyelinbasicprotein(MBP)-specific,constitutivelycontainedmRNAforKv1.3.andexpressedKv1.3.ThesechannelswereshowntobeblockedbyKTX.ActivationisacrucialstepforMBPTcellstobecomeencephalitogenic.TheadditionofKTXduringAg-TcellactivationledtoagreatreductionintheMBPTcellproliferativeresponse,intheproductionofIL-2andTNF,andinCa(2+)influx.FurThermore,theadditionofKTXduringTcellactivationinvitroledadecreasedencephalitogenicityofMBPTcells.Moreover,KTXinjectedintoLewisratsimpairedTcellfunctionsuchasthedelayed-typehypersensitivity.Lastly,theadmiNISTrationofthisblockerofneuronalandlymphocytechannelstoLewisratsimprovedthesymptomsofEAE.WeconcludethatKTXisapotentimmunosuppressiveagentwithbeneficialeffectsontheneurologicalsymptomsofEAE.BeetonC.,etal.(2001)Selectiveblockingofvoltage-gatedK+channelsimprovesexperimentalautoimmuneencephalomyelitisandinhibitsTcellactivation.JImmunol. PMID: 11145670Distributioninratbrainofbindingsitesofkaliotoxin,ablockerofKv1.1andKv1.3alpha-subunitsThedistributionofthebindingsitesforkaliotoxin(KTX),ablockerofvoltage-dependentK(+)channels,wasstudiedwithquantitativeautoradiographyinadultratbrainandduringpostnatalbrainmaturation.IodinatedKTXboundspecificallytotissuesectionswithahighaffinity(K(d)=82pM)andamaximalbindingcapacityof13.4fmol/mgprotein.ThedistributionofKTXbindingsiteswithinthecentralnervoussystemwasheterogeneous.Thehighestdensitieswerefoundintheneocortex,hypothalamus,dentategyrus,bednucleusofthestriaterminalis,andparabrachialnuclei.Thelowestlevelwasobservedinthewhitematter.Frompostnatalday5onward,KTXbindingsitesweredetectableonlyinthehindbrain.ThedensityofKTXbindingsitesinwholebraindrasticallyincreasedafterpostnatalday15toachieveadultlevelsatpostnatalday60inthewholebrain.BathapplicationofKTXtoXenopuslaevisoocytesblockedrecombinantKv1.3andKv1.1channelspotentlyandKv1.2channelslesspotently,withrespectiveK(d)valuesof0.1,1.5,and25nM.KTXaffinitiesforeachofthesechannelsexpressedinmammaliancellswereabout10-foldlower.AcomparisonofthedistributionofKTXbindingsiteswiththatofKv1channelpolypeptides,togetherwiththepharmacologyofKTXblock,suggeststhattheprincipaltargetsforKTXinratbrainareK(+)channelscontainingKv1.1andKv1.3alpha-subunits.MourreC,etal.(1999)Distributioninratbrainofbindingsitesofkaliotoxin,ablockerofKv1.1andKv1.3alpha-subunits.JPharmacolExpTher. PMID: 105658093Dstructureofkaliotoxin:isresidue34akeyforchannelselectivity?Kaliotoxin(KTX)isanaturalpeptideblockerofvoltage-dependentK+channels.The3DstructureofatruncatedanalogueofKTX(Fernandezetal.(1994)Biochemistry33,14256-14263)wasdeterminedbyNMRspectroscopyandshowedsignificantdifferencesfromstructuresestablishedforotherrelatedscorpiontoxins.Arecentpublicationwiththestructureofthecompletetoxin(Aiyaretal.(1995)Neuron15,1169-1181)didnotconfirmthesedifferences.InthiscommunicationwereportNMRdataforKTXatpH3.0,5.5and7.2andthe3DstructureobtainedfromdataatpH=5.5.CompleteKTXdisplaysafoldingsimilartothatofothertoxinswithanalpha-helixandabeta-sheetlinkedbytwodisulphidebonds.ThepKaofHis34isanomalouslylow(4.7-5.2dependingonthebuffer)owingtoitsinteractionwithtwoLysresidues(includingtheessentialLys27),thechargedN-terminusandthesidechainofMet29.Chargedresiduesareplacedsymmetricallywithrespecttoanaxisthatapproximatelycoincideswithoneoftheprincipalcomponentsofthemomentofinertiaofthetoxin.His34,whichoccupiesawell-definedpositionbetweentwoconservedCys,islocatedonthecentreofalayerofchargedgroups.Positivelyandnegativelychargedresiduesarefoundatthesamepositioninrelatedtoxins.ItissuggestedthatelectrostaticeffectsmodulatethedistancesbetweenpositivechargesinflexIBLesidechains,contributingtothefinetuningoftheselectivitytowarddifferentchannelsubclassesandthattheapproximatecoincidencebetweenthemomentofinertiaandthechargeaxisfacilitatetheapproachofthetoxintothechannel.TheverylowpKaofHis34impliesthatitwillbecompletelyunprotonatedatphysiologicalpH.GairíM,etal.3Dstructureofkaliotoxin:isresidue34akeyforchannelselectivity?JPeptSci. PMID: 9262650Tcellactivationisregulatedbyvoltage-dependentandcalcium-activatedpotassiumchannelsMembranepotential(Vm)istightlycontrolledinTcellsthroughtheregulatedfluxofionsacrosstheplasmamembrane.Toinvestigatethefunctionalroleofvoltage-dependent(Kv)andcalcium-activated(KCa)potassiumchannelsinTcellactivation,wecomparedtheeffectsoftwoK+channelblockers,namelykaliotoxin(KTX)andcharybdotoxin(CHTX),onVm,calciuminflux,andcellproliferation.KTXpotentlyinhibitedKv(ID50=3nM)butnotKCa(ID50=5microM)currentsinTcells.RestingTcellsexposedtoKTX(300nM)depolarizedfrom-56mVto-50mV.KTXhadnoeffectonthetransientmembranehyperpolarizationthatcharacteristicallyfollowsreceptor-mediatedTcellstimulation.However,TcellsstimulatedinthepresenceofKTXsubsequentlydepolarizedto-40mV.KTXalsoreducedthesteadystateintracellularfreecalciumconcentration([Ca2+]i)instimulatedcellsby19%andinhibitedTcellproliferationby35%.CHTXpotentlyinhibitedbothKvandKCacurrents(ID50=approximately1nM).CHTX(300nM)depolarizedrestingTcellsto-48mV,equivalenttotheeffectobservedforKTX.InstimulatedTcells,300nMCHTXcompletelyblockedtheinducedhyperpolarizationandsubsequentlydepolarizedthecellsto-21mV.Theseeffectswereassociatedwitha45%reductioninpeak[Ca2+]i,a60%decreaseinsteadystate[Ca2+]i,and63%inhibitionofTcellproliferation.TheseresultssuggestthatbothKvandKCaconductancescontributetotheunderlyingmechanismsofTcellactivation.RaderRK,etal.(1997)Tcellactivationisregulatedbyvoltage-dependentandcalcium-activatedpotassiumchannels.JImmunol. PMID: 8568243Effectsofchannelmodulatorsonclonedlarge-conductancecalcium-activatedpotassiumchannelsThroughexpressionoftheclonedmouse(mSlo)orhuman(hSlo)large-conductance(BK)Ca(2+)-activatedK+channelinXenopuslaevisoocytesandHEK293cells,wecharacterizedtheeffectsofreportedblockersandopenersofBKchannelstoinitiatethestudyofthemoleculardeterminantsofBKchannelmodulation.Inoocytes,iberiotoxinandcharybdotoxin,peptidylscorpiontoxins,werebothequallyeffectiveblockersofBKcurrent,althoughiberiotoxinwassignificantlymorepotentthancharybdotoxin.ThestructurallyrelatedpeptidekaliotoxinwasnotapotentblockerofBKcurrent.Paxilline,afungaltremorgenicalkaloid,wasaneffectivebutcomplexblockerofBKcurrent.Tetrandrine,aputativeblockeroftypeIIBKchannels,andketaminewererelativelyineffective.TheputativeBKopenersNS004andNS1619,phloretin,niflumicacid,flufenamicacid,and5-nitro-2-(3-phenylpropylamino)benzoicacid(NPPB)increasedBKcurrentinoocytesatmicroMconcentrations;manyoftheseproducedbiphasicconcentration-responserelationships.Coapplicationofrepresentativeblockersandopenersrevealedseveralpatternsofinteraction,includingcompetitiveandnoncompetitiveantagonism.NS1619,niflumicacid,andphloretinweretestedbyusingexcisedinside-outmembranepatchesfromHEK293cellsandwerefoundtoincreasetheactivityofhSloBKchannelsandproducealeftwardshiftintheG/Gmax-versus-voltagerelationshipofthesechannels.TheseresultsrepresentthefirstcomprehensiveexaminationofthemolecularpharmacologyofBKchannels.GribkoffVK.1996)Effectsofchannelmodulatorsonclonedlarge-conductancecalcium-activatedpotassiumchannels.MolPharmacol. PMID: 8700114PharmacologicalpropertiesofCa2+activatedK+currentsoframifiedmurinebrainmacrophagesUsingthewhole-cellconfigurationofthepatchclamptechnique,calcium-activatedpotassiumcurrents(I(K,Ca))wereinvestigatedinramifiedmurinebrainmacrophages.InordertoinduceI(K,Ca)theintracellularconcentrationofnominalfreeCa2+wasadjustedto1microM.TheCa2+-activatedK+currentofbrainmacrophagesdidnotshowanyvoltagedependenceattestpotentialsbetween-120and+30mV.AtenfoldchangeinextracellularK+concentrationshiftedthereversalpotentialofI(K,Ca)by51mV.Thebeevenomtoxinapaminappliedatconcentrationsofupto1microMdidnotaffectI(K,Ca).Ca2+-activatedK+currentsoframifiedbrainmacrophageswerehighlysensitivetoextracellularlyappliedcharybdotoxin(CTX).Thehalf-maximaleffectiveconcentrationofCTXwascalculatedtobe4.3nM.IncontrasttoCTX,thescorpiontoxinkaliotoxindidnotinhibitI(K,Ca)atconcentrationsbetween1and50nM.Tetraethylammonium(TEA)blocked8.0%ofI(K,Ca)ataconcentrationof1mM,whereas31.4%ofcurrentwasblockedby10mMTEA.Severalinorganicpolyvalentcationsweretestedataconcentrationof2mMfortheirabilitytoblockI(K,Ca).La3+reducedI(K,Ca)by72.8%,whereasCd2+decreasedI(K,Ca)by17.4%;incontrast,Ni2+didnothaveanyeffectonI(K,Ca).Ba2+appliedataconcentrationof1mMreducedI(K,Ca)voltage-dependentlyathyperpolarizingpotentials.EderC.(1997)PharmacologicalpropertiesofCa2+activatedK+currentsoframifiedmurinebrainmacrophages.NaunynSchmiedebergsArchPharmacol. PMID: 9272730Kaliotoxin,anovelpeptidylinhibitorofneuronalBK-typeCa(2+)-activatedK+channelscharacterizedfromAndroctonusmauretanicusmauretanicusvenomApeptidylinhibitorofthehighconductanceCa(2+)-activatedK+channels(KCa)hasbeenpurifiedtohomogeneityfromthevenomofthescorpionAndroctonusmauretanicusmauretanicus.Thepeptidehasbeennamedkaliotoxin(KTX).Itisasingle4-kDapolypeptidechain.Itscompleteaminoacidsequencehasbeendetermined.KTXdisplayssequencehomologywithotherscorpion-derivedinhibitorsofCa(2+)-activatedorvoltage-gatedK+channels:44%homologywithcharybdotoxin(CTX),52%withnoxiustoxin(NTX),and44%withiberiotoxin(IbTX).ElectrophysiologicalexperimentsperformedinidentifiednervecellsfromthemolluscHelixpomatiashowedthatKTXspecificallysuppressedthewholecellCa(2+)-activatedK+current.KTXhadnodetectableeffectsonvoltage-gatedK+current(delayedrectifierandfasttransientAcurrent)oronL-typeCa2+currents.KTXinteractsinaone-to-onewaywithKCachannelswithaKdof20nM.SinglechannelexperimentswereperformedonhighconductanceKCachannelsexcisedfromtheaboveHelixneuronsandfromrabbitcoeliacgangliasympatheticneurons.KTXactedexclusivelyattheouterfaceofthechannel.KTXappliedonexcisedoutside-outKCachannelsinducedatransientperiodoffast-flickerblockfollowedbyapersistentchannelblockade.TheKTX-inducedblockwasnotvoltage-dependentwhichsuggestsdifferencesintheblockadeofKCachannelsbyKTXandbyCTX.ComparisonofKTXandCTXsequencesleadstotheidentificationofashortaminoacidsequence(26-33)whichmaybeimplicatedinthetoxin-channelinteraction.KTXthereforeappearstobeausefultoolforelucidatingthemolecularpharmacologyofthehighconductanceCa(2+)-activatedK+channel.CrestM.,etal.(1992)Kaliotoxin,anovelpeptidylinhibitorofneuronalBK-typeCa(2+)-activatedK+channelscharacterizedfromAndroctonusmauretanicusmauretanicusvenom.JBC. PMID: 1730708