Kaliotoxin-1(KTX1)hasbeenisolatedfromthevenomoftheScorpionAndroctonusmauretanicusmauretanicus.Kaliotoxin-1showsahighstructuralaffinitywithIberiotoxinandCharyBDotoxinthatinhibitKCa2+channelsactivity.Accordingtoseveralstudies,itappearsthatKaliotoxin-1hasaweakinhibitoryeffectonKCa2+channels,butitisapotentandselectiveinhibitorofvoltage-activatedpotassiumchannel(Kv1.1,Kv1.2,Kv1.3).
Description:
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):38
Formula:C171H283N55O49S6
MolecularWeight:4149.89Da
Appearance:Whitelyophilizedsolid
Solubility:waterandsalinebuffer
CASnumber:
Source:Synthetic
Purityrate:>97%
Reference:
Neuropathophysiologicaleffectandimmuno-inflammatoryresponseinducedbykaliotoxinofandroctonusscorpionvenom
Kaliotoxin(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.
HeterogeneouscompetitionofKv1channeltoxinswithkaliotoxinforbindinginratbrain:autorADIographicanalysis
Kaliotoxin,aKv1.1andKv1.3channelblocker,improvesassociativelearninginrats
Selectiveblockingofvoltage-gatedK+channelsimprovesexperimentalautoimmuneencephalomyelitisandinhibitsTcellactivation
Distributioninratbrainofbindingsitesofkaliotoxin,ablockerofKv1.1andKv1.3alpha-subunits
3Dstructureofkaliotoxin:isresidue34akeyforchannelselectivity?
Tcellactivationisregulatedbyvoltage-dependentandcalcium-activatedpotassiumchannels
Membranepotential(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: 8568243
Effectsofchannelmodulatorsonclonedlarge-conductancecalcium-activatedpotassiumchannels
Throughexpressionoftheclonedmouse(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: 8700114
PharmacologicalpropertiesofCa2+activatedK+currentsoframifiedmurinebrainmacrophages
Usingthewhole-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: 9272730
Kaliotoxin,anovelpeptidylinhibitorofneuronalBK-typeCa(2+)-activatedK+channelscharacterizedfromAndroctonusmauretanicusmauretanicusvenom
ApeptidylinhibitorofthehighconductanceCa(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