Stromatoxin-1(ScTx-1) hasbeenisolatedfromthevenomoftheAfricantarentula Stromatopelmacalceata.Stromatoxin-1 isa34amino-acidlongpeptidethatbelongstothestructuralfamilyofinhibitorcystineknotpeptidesreticulatedbythreedisulfidebridges.IthasanamidatedC-terminusandbearsstronghomologywithhanatoxin1(83%).Stromatoxin-1 inhibitswithhighaffinitiesKv2.1andKv2.2,thatencodedelayedK+ channels(respectively,withIC50 of12and21nM).Theblockisvoltage-dependentandslowlyreversIBLe. Stromatoxin-1 isalsoaverysensitiveinhibitorofKv4.2,thatencodesatransientK+ current(IC50 of1.2nM).Herealso,theblockisvoltage-dependentindicatingthatScTx-1actsasagatingmodifierratherthanaporeblocker.ReversibilityisfasteronKv4.2channels.Incontrast,Stromatoxin-1 hasnoeffectonKv1.1,Kv1.2,Kv1.3,Kv1.4,Kv1.5,Kv1.6orKv3.4channels.Thetoxinhasalsonoeffectonvoltage-dependentNa+ andCa2+ channelsofcerebellargranulecells. Stromatoxin-1 wasfoundtoincreasethespontaneousphasiccontractionamplitude,muscleforceandtoneinisolatedraturinarybladdersmoothmuscle.Italsoenhancesmyogenicconstrictioninpressurizedarterialsegments.
Description:
AAsequence: Asp-Cys2-Thr-Arg-Met-Phe-Gly-Ala-Cys9-Arg-Arg-Asp-Ser-Asp-Cys15-Cys16-Pro-His-Leu-Gly-Cys21-Lys-Pro-Thr-Ser-Lys-Tyr-Cys28-Ala-Trp-Asp-Gly-Thr-Ile-NH2
Disulfidebonds:Cys2-Cys16,Cys9-Cys21 andCys15-Cys28
Length(aa):34
Formula:C156H237N49O48S7
MolecularWeight: 3791,3Da
Appearance:whitelyophilizedsolid
Solubility:waterorsalinebuffer
CASnumber:
Source:Synthetic
Purityrate:>98%
Reference:
Kv2dysfunctionafterperipheralaxotomyenhancessensoryneuronresponsivenesstosustainedinput
PeripheralnerveinjuriescausedbytraumaareassociatedwithincreasedsensoryneuronexcitABIlityanddebilitatingchronicpainsymptoms.Axotomy-inducedalterationsinthefunctionofionchannelsarethoughttolargelyunderliethepathophysiologyofthesephenotypes.Here,wecharacterisethemRNAdistributionofKv2familymembersinratdorsalrootganglia(DRG)anddescribealinkbetweenKv2functionandmodulationofsensoryneuronexcitability.Kv2.1andKv2.2wereamplyexpressedincellsofallsizes,beingparticularlyabundantinmedium-largeneuronsalsoimmunoreactiveforneurofilament-200.Peripheralaxotomyledtoarapid,robustandlong-lastingtranscriptionalKv2downregulationintheDRG,correlatedwiththeonsetofmechanicalandthermalhypersensitivity.TheconsequencesofKv2loss-of-functionweresubsequentlyinvestigatedinmyelinatedneuronsusingintracellularrecordingsonexvivoDRGpreparations.Innaïveneurons,pharmacologicalKv2.1/Kv2.2inhibitionbystromatoxin-1(ScTx)resultedinshorteningofactionpotential(AP)after-hyperpolarization(AHP).Incontrast,ScTxapplicationonaxotomizedneuronsdidnotalterAHPduration,consistentwiththeinjury-inducedKv2downregulation.InaccordancewithashortenedAHP,ScTxtreatmentalsoreducedtherefractoryperiodandimprovedAPconductiontothecellsomaduringhighfrequencystimulation.TheseresultssuggestthatKv2downregulationfollowingtraumaticnervelesionfacilitatesgreaterfidelityofrepetitivefiringduringprolongedinputandthusnormalKv2functionispostulatedtolimitneuronalexcitability.Insummary,wehaveprofiledKv2expressioninsensoryneuronsandprovideevidenceforthecontributionofKv2dysfunctioninthegenerationofhyperexcitablephenotypesencounteredinchronicpainstates.
TsantoulasC., etal. (2014) Kv2dysfunctionafterperipheralaxotomyenhancessensoryneuronresponsivenesstosustainedinput. ExpNeurol. PMID:24252178
Voltage-gatedK+channelssensitivetostromatoxin-1regulatemyogenicandneurogeniccontractionsofraturinarybladdersmoothmuscle
Membersofthevoltage-gatedK(+)(K(V))channelfamilyaresuggestedtocontroltherestingmembranepotentialandtherepolarizationphaseoftheactionpotentialinurinarybladdersmoothmuscle(UBSM).Recentstudiesreportthatstromatoxin-1,apeptideisolatedfromtarantulas,selectivelyinhibitsK(V)2.1,K(V)2.2,K(V)4.2,andK(V)2.1/9.3channels.TheobjectiveofthisstudywastoinvestigatewhetherK(V)channelssensitivetostromatoxin-1participateintheregulationofratUBSMcontractilityandtoidentifytheirmolecularfingerprints.Stromatoxin-1(100nM)increasedthespontaneousphasiccontractionamplitude,muscleforce,andtoneinisolatedUBSMstrips.However,stromatoxin-1(100nM)hadnoeffectontheUBSMcontractionsinducedbydepolarizingagentssuchasKCl(20mM)orcarbachol(1microM).Thisindicatesthat,underconditionsofsustainedmembranedepolarization,theK(V)channelssensitivetostromatoxin-1havenofurthercontributiontothemembraneexcitabilityandcontractility.Stromatoxin-1(100nM)increasedtheamplitudeoftheelectricalfieldstimulation-inducedcontractions,suggestingalsoaroleforthesechannelsinneurogeniccontractions.RT-PCRexperimentsonfreshlyisolatedUBSMcellsshowedmRNAexpressionofK(V)2.1,K(V)2.2,andK(V)9.3,butnotK(V)4.2channelsubunits.ProteinexpressionofK(V)2.1andK(V)2.2channelswasdetectedusingWesternblotandwasfurtherconfirmedbyimmunocytochemicaldetectioninfreshlyisolatedUBSMcells.ThesenovelfindingsindicatethatK(V)2.1andK(V)2.2,butnotK(V)4.2,channelsubunitsareexpressedinratUBSMandplayakeyroleinopposingbothmyogenicandneurogenicUBSMcontractions.
ChenM., etal. (2013) Voltage-gatedK+ channelssensitivetostromatoxin-1regulatemyogenicandneurogeniccontractionsofraturinarybladdersmoothmuscle. AmJPhysiolRegulIntegrCompPhysiol. PMID:20393158
KV2.1andelectricallysilentKVchannelsubunitscontrolexcitabilityandcontractilityofguineapigdetrusorsmoothmuscle
Voltage-gatedK(+)(K(V))channelsareimplicatedindetrusorsmoothmuscle(DSM)function.However,littleisknownaboutthefunctionalroleoftheheterotetramericK(V)channelsinDSM.Inthisreport,weprovidemolecular,electrophysiological,andfunctionalevidenceforthepresenceofK(V)2.1andelectricallysilentK(V)channelsubunitsinguineapigDSM.Stromatoxin-1(ScTx1),aselectiveinhibitorofthehomotetramericK(V)2.1,K(V)2.2,andK(V)4.2aswellastheheterotetramericK(V)2.1/6.3andK(V)2.1/9.3channels,wasusedtoexaminetheroleoftheseK(V)channelsinDSMfunction.RT-PCRindicatedmRNAexpressionofK(V)2.1,K(V)6.2-6.3,K(V)8.2,andK(V)9.1-9.3subunitsinisolatedDSMcells.K(V)2.1proteinexpressionwasconfirmedbyWesternblotandimmunocytochemistry.Perforatedwholecellpatch-clampexperimentsrevealedthatScTx1(100nM)inhibitedtheamplitudeoftheK(V)currentinfreshlyisolatedDSMcells.ScTx1(100nM)didnotsignificantlychangethesteady-stateactivationandinactivationcurvesforK(V)current.However,ScTx1(100nM)decreasedtheactivationtime-constantoftheK(V)currentatpositivevoltages.Althoughourpatch-clampdatacouldnotexcludethepresenceofthehomotetramericK(V)2.1channels,thebiophysicalcharacteristicsoftheScTx1-sensitivecurrentwereconsistentwiththepresenceofheterotetramericK(V)2.1/silentK(V)channels.Current-clamprecordingsshowedthatScTx1(100nM)didnotchangetheDSMcellrestingmembranepotential.ScTx1(100nM)increasedthespontaneousphasiccontractionamplitude,muscleforce,andmuscletoneaswellastheamplitudeoftheelectricalfieldstimulation-inducedcontractionsofisolatedDSMstrips.Collectively,ourdatarevealedthatK(V)2.1-containingchannelsareimportantphysiologicalregulatorsofguineapigDSMexcitabilityandcontractility.
HristovKL., etal. (2012) KV2.1andelectricallysilentKVchannelsubunitscontrolexcitabilityandcontractilityofguineapigdetrusorsmoothmuscle. AmJPhysiolCellPhysiol.PMID:21998137
MechanismofestrADIol-inducedblockofvoltage-gatedK+currentsinratmedialpreopticneurons
Thepresentstudywasconductedtocharacterizepossiblerapideffectsof17-β-estradiolonvoltage-gatedK(+)channelsinpreopticneuronsand,inparticular,toidentifythemechanismsbywhich17-β-estradiolaffectstheK(+)channels.Whole-cellcurrentsfromdissociatedratpreopticneuronswerestudiedbyperforated-patchrecording.17-β-Estradiolrapidly(withinseconds)andreversiblyreducedtheK(+)currents,showinganEC(50)valueof9.7µM.Theeffectwasslightlyvoltagedependent,butindependentofexternalCa(2+),andnotsensitivetoanestrogen-receptorblocker.Although17-α-estradiolalsosignificantlyreducedtheK(+)currents,membrane-impermeantformsofestradioldidnotreducetheK(+)currentsandotherestrogens,testosteroneandcholesterolwereconsiderablylesseffective.ThereductioninducedbyestradiolwasoverlappingwiththatoftheK(V)-2-channelblockerr-stromatoxin-1.ThetimecourseofK(+)currentin17-β-estradiol,withatime-dependentinhibitionandaslightdependenceonexternalK(+),suggestedanopen-channelblockmechanism.Thepropertiesofblockwerepredictedfromacomputationalmodelwhere17-β-estradiolbindstoopenK(+)channels.Itwasconcludedthat17-β-estradiolrapidlyreducesvoltage-gatedK(+)currentsinawayconsistentwithanopen-channelblockmechanism.Thissuggestsanewmechanismforsteroidactiononionchannels.
DruzinM., etal. (2011) Mechanismofestradiol-inducedblockofvoltage-gatedK+currentsinratmedialpreopticneurons. PLoSOne. PMID:21625454
PostnataldevelopmentofA-typeandKv1-andKv2-mediatedpotassiumchannelcurrentsinneocorticalpyramidalneurons
Potassiumchannelsregulatenumerousaspectsofneuronalexcitability,andseveralvoltage-gatedK(+)channelsubunitshavebeenidentifiedinpyramidalneuronsofratneocortex.Previousstudieshaveeitherconsideredthedevelopmentofoutwardcurrentasawholeordividedcurrentsintotransient,A-typeandpersistent,delayedrectifiercomponentsbutdidnotdifferentiatebetweencurrentcomponentsdefinedbyα-subunittype.TofacilitatecomparisonsofstudiesreportingK(+)currentsfromanimalsofdifferentagesandtounderstandthefunctionalrolesofspecificcurrentcomponents,wecharacterizedthepostnataldevelopmentofidentifiedKvchannel-mediatedcurrentsinpyramidalneuronsfromlayersII/IIIfromratsomatosensorycortex.Boththepersistent/slowlyinactivatingandtransientcomponentsofthetotalK(+)currentincreasedindensitywithpostnatalage.WeusedspecificpharmacologicalagentstotesttherelativecontributionsofputativeKv1-andKv2-mediatedcurrents(100nMα-dendrotoxinand600nMstromatoxin,respectively).Acombinationofvoltageprotocol,pharmacology,andcurvefittingwasusedtoisolatetherapidlyinactivatingA-typecurrent.Wefoundthatthedensityofallidentifiedcurrentcomponentsincreasedwithpostnatalage,approachingaplateauat3-5wk.Wefoundnosignificantchangesintherelativeproportionsorkineticsofanycomponentbetweenpostnatalweeks1and5,exceptthattheactivationtimeconstantforA-typecurrentwaslongerat1wk.TheputativeKv2-mediatedcomponentwasthelargestatallages.ImmunocytochemistryindicatedthatproteinexpressionforKv4.2,Kv4.3,Kv1.4,andKv2.1increasedbetween1wkand4-5wkofage.
GuanD., etal. (2011) PostnataldevelopmentofA-typeandKv1-andKv2-mediatedpotassiumchannelcurrentsinneocorticalpyramidalneurons. JNeurophysiol.PMID:21451062
Stromatoxin-sensitive,heteromultimericKv2.1/Kv9.3channelscontributetomyogeniccontrolofcerebralarterialdiameter
Cerebralvascularsmoothmusclecontractilityplaysacrucialroleincontrollingarterialdiameterand,thereby,bloodflowregulationinthebrain.AnumberofK(+)channelshavebeensuggestedtocontributetotheregulationofdiameterbycontrollingsmoothmusclemembranepotential(E(m))andCa(2+)influx.Previousstudiesindicatethatstromatoxin(ScTx1)-sensitive,Kv2-containingchannelscontributetothecontrolofcerebralarterialdiameterat80mmHg,buttheirpreciseroleandmolecularcompositionwerenotdetermined.Here,wetestedifKv2subunitsassociatewith‘silent’subunitsfromtheKv5,Kv6,Kv8orKv9subfamiliestoformheterotetramericchannelsthatcontributetocontrolofdiameterofratmiddlecerebralarteries(RMCAs)overarangeofintraluminalpressurefrom10to100mmHg.ThepredominantmRNAsexpressedbyRMCAsencodeKv2.1andKv9.3subunits.Co-localizationofKv2.1andKv9.3proteinsattheplasmamembraneofdissociatedsingleRMCAmyocyteswasdetectedbyproximityligationassay.ScTx1-sensitivenativecurrentofRMCAmyocytesandKv2.1/Kv9.3currentsexhibitedfunctionalidentitybasedonthesimilarityoftheirdeactivationkineticsandvoltagedependenceofactivationthatweredistinctfromthoseofhomomultimericKv2.1channels.ScTx1treatmentenhancedthemyogenicresponseofpressurizedRMCAsbetween40and100mmHg,butthistoxinalsocausedconstrictionbetween10and40mmHgthatwasnotpreviouslyobservedfollowinginhibitionoflargeconductanceCa(2+)-activatedK(+)(BK(Ca))andKv1channels.Takentogether,thisstudydefinesthemolecularbasisofKv2-containingchannelsandcontributestoourunderstandingofthefunctionalsignificanceoftheirexpressionincerebralvasculature.Specifically,ourfindingsprovidethefirstevidenceofheteromultimericKv2.1/Kv9.3channelexpressioninRMCAmyocytesandtheirdistinctcontributiontocontrolofcerebralarterialdiameteroverawiderrangeofE(m)andtransmuralpressurethanKv1orBK(Ca)channelsowingtotheirnegativerangeofvoltage-dependentactivation.
ZhongXZ., etal. (2010) Stromatoxin-sensitive,heteromultimericKv2.1/Kv9.3channelscontributetomyogeniccontrolofcerebralarterialdiameter. JPhysiol. PMID:20876197
ParticipationofKCNQ(Kv7)potassiumchannelsinmyogeniccontrolofcerebralarterialdiameter
KCNQgeneexpressionwaspreviouslyshowninvariousrodentbloodvessels,wheretheproductsofKCNQ4andKCNQ5,Kv7.4andKv7.5potassiumchannelsubunits,respectively,haveaninfluenceonvascularreactivity.TheaimofthisstudywastodetermineifsmallcerebralresistancearteriesoftheratexpressKCNQgenesandwhetherKv7channelsparticipateintheregulationofmyogeniccontrolofdiameter.Quantitativereversetranscriptionpolymerasechainreaction(QPCR)wasundertakenusingRNAisolatedfromratmiddlecerebralarteries(RMCAs)andimmunocytochemistrywasperformedusingKv7subunit-specificantibodiesandfreshlyisolatedRMCAmyocytes.KCNQ4messagewasmoreabundantthanKCNQ5=KCNQ1,butKCNQ2andKCNQ3messagelevelswerenegligible.Kv7.1,Kv7.4andKv7.5immunoreactivitywaspresentatthesarcolemmaoffreshlyisolatedRMCAmyocytes.Linopirdine(1microm)partiallydepressed,whereastheKv7activatorS-1(3and/or20microm)enhancedwhole-cellKv7.4(inHEK293cells),aswellasnativeRMCAmyocyteKvcurrentamplitude.TheeffectsofS-1werevoltage-dependent,withprogressivelossofstimulationatpotentialsof>15mV.AttheconcentrationsemployedlinopirdineandS-1didnotaltercurrentsduetorecombinantKv1.2/Kv1.5orKv2.1/Kv9.3channels(inHEK293cells)thatarealsoexpressedbyRMCAmyocytes.Incontrast,anotherwidelyusedKv7blocker,XE991(10microm),significantlyattenuatednativeKvcurrentandalsoreducedKv1.2/Kv1.5andKv2.1/Kv9.3currents.PressurizedarterialmyographywasperformedusingRMCAsexposedtointravascularpressuresof10-100mmHg.Linopirdine(1microm)enhancedthemyogenicresponseat20mmHg,whereastheactivationofKv7channelswithS-1(20microm)inhibitedmyogenicconstrictionat>20mmHgandreversedtheincreasedmyogenicresponseproducedbysuppressionofKv2-containingchannelswith30nmstromatoxin(ScTx1).ThesedatarevealanovelcontributionofKCNQgeneproductstotheregulationofmyogeniccontrolofcerebralarterialdiameterandsuggestthatKv7channelactivatingdrugsmaybeappropriatecandidatesforthedevelopmentofaneffectivetherapytoamelioratecerebralvasospasm.
ZhongXZ.,etal.(2010) ParticipationofKCNQ(Kv7)potassiumchannelsinmyogeniccontrolofcerebralarterialdiameter.JPhysiol.PMID:20624791
Membranepotential-dependentinactivationofvoltage-gatedionchannelsinalpha-cellsinhibitsglucagonsecretionfromhumanislets
OBJECTIVE:
Todocumentthepropertiesofthevoltage-gatedionchannelsinhumanpancreaticalpha-cellsandtheirroleinglucagonrelease.
RESEARCHDESIGNANDMETHODS:
Glucagonreleasewasmeasuredfromintactislets.[Ca(2+)](i)wasrecordedincellsshowingspontaneousactivityat1mmol/lglucose.Membranecurrentsandpotentialweremeasuredbywhole-cellpatch-clampinginisolatedalpha-cellsidentifiedbyimmunocytochemistry.
RESULT:
Glucoseinhibitedglucagonsecretionfromhumanislets;maximalinhibitionwasobservedat6mmol/lglucose.Glucagonsecretionat1mmol/lglucosewasinhibitedbyinsulinbutnotbyZnCl(2).GlucoseremainedinhibitoryinthepresenceofZnCl(2)andafterblockadeoftype-2somatostatinreceptors.Humanalpha-cellsareelectricallyactiveat1mmol/lglucose.InhibitionofK(ATP)-channelswithtolbutamidedepolarizedalpha-cellsby10mVandreducedtheactionpotentialamplitude.Humanalpha-cellscontainheteropodatoxin-sensitiveA-typeK(+)-channels,stromatoxin-sensitivedelayedrectifyingK(+)-channels,tetrodotoxin-sensitiveNa(+)-currents,andlow-thresholdT-type,isradipine-sensitiveL-type,andomega-agatoxin-sensitiveP/Q-typeCa(2+)-channels.Glucagonsecretionat1mmol/lglucosewasinhibitedby40-70%bytetrodotoxin,heteropodatoxin-2,stromatoxin,omega-agatoxin,andisradipine.The[Ca(2+)](i)oscillationsdependprincipallyonCa(2+)-influxviaL-typeCa(2+)-channels.Capacitancemeasurementsrevealedarapid(<50ms)componentofexocytosis.Exocytosiswasnegligibleatvoltagesbelow-20mVandpeakedat0mV.BlockingP/Q-typeCa(2+)-currentsabolisheddepolarization-evokedexocytosis.
CONCLUSIONS:
Humanalpha-cellsareelectricallyexcitable,andblockadeofanyionchannelinvolvedinactionpotentialdepolarizationorrepolarizationresultsininhibitionofglucagonsecretion.Weproposethatvoltage-dependentinactivationofthesechannelsunderliestheinhibitionofglucagonsecretionbytolbutamideandglucose.
RamracheyaR.,etal.(2010) Membranepotential-dependentinactivationofvoltage-gatedionchannelsinalpha-cellsinhibitsglucagonsecretionfromhumanislets.Diabetes.PMID:20547976
Voltage-gatedionchannelsinhumanpancreaticbeta-cells:electrophysiologicalcharacterizationandroleininsulinsecretion
OBJECTIVE:
Tocharacterizethevoltage-gatedionchannelsinhumanbeta-cellsfromnondiabeticdonorsandtheirroleinglucose-stimulatedinsulinrelease.
RESEARCHDESIGNANDMETHODS:
Insulinreleasewasmeasuredfromintactislets.Whole-cellpatch-clampexperimentsandmeasurementsofcellcapacitancewereperformedonisolatedbeta-cells.TheionchannelcomplementwasdeterminedbyquantitativePCR.
RESULTS:
Humanbeta-cellsexpresstwotypesofvoltage-gatedK(+)currentsthatflowthroughdelayedrectifying(K(V)2.1/2.2)andlarge-conductanceCa(2+)-activatedK(+)(BK)channels.BlockadeofBKchannels(usingiberiotoxin)increasedactionpotentialamplitudeandenhancedinsulinsecretionby70%,whereasinhibitionofK(V)2.1/2.2(withstromatoxin)waswithoutstimulatoryeffectonelectricalactivityandsecretion.Voltage-gatedtetrodotoxin(TTX)-sensitiveNa(+)currents(Na(V)1.6/1.7)contributetotheupstrokeofactionpotentials.InhibitionofNa(+)currentswithTTXreducedglucose-stimulated(6-20mmol/l)insulinsecretionby55-70%.Humanbeta-cellsareequippedwithL-(Ca(V)1.3),P/Q-(Ca(V)2.1),andT-(Ca(V)3.2),butnotN-orR-typeCa(2+)channels.BlockadeofL-typechannelsabolishedglucose-stimulatedinsulinrelease,whileinhibitionofT-andP/Q-typeCa(2+)channelsreducedglucose-induced(6mmol/l)secretionby60-70%.MembranepotentialrecordingssuggestthatL-andT-typeCa(2+)channelsparticipateinactionpotentialgeneration.BlockadeofP/Q-typeCa(2+)channelssuppressedexocytosis(measuredasanincreaseincellcapacitance)by>80%,whereasinhibitionofL-typeCa(2+)channelsonlyhadaminoreffect.
CONCLUSIONS:
Voltage-gatedT-typeandL-typeCa(2+)channelsaswellasNa(+)channelsparticipateinglucose-stimulatedelectricalactivityandinsulinsecretion.Ca(2+)-activatedBKchannelsarerequiredforrapidmembranerepolarization.Exocytosisofinsulin-containinggranulesisprincipallytriggeredbyCa(2+)influxthroughP/Q-typeCa(2+)channels.
BraunM.,etal.(2008) Voltage-gatedionchannelsinhumanpancreaticbeta-cells:electrophysiologicalcharacterizationandroleininsulinsecretion.Diabetes.PMID:18390794
Structuralbasisofbindingandinhibitionofnoveltarantulatoxinsinmammalianvoltage-dependentpotassiumchannels
Voltage-dependentpotassiumchannelKv2.1iswidelyexpressedinmammalianneuronsandwassuggestedresponsibleformediatingthedelayedrectifier(I(K))currents.Furtherinvestigationofthecentralroleofthischannelrequiresthedevelopmentofspecificpharmacology,forinstance,theutilizationofspidervenomtoxins.Mostofthesetoxinsbelongtothesamestructuralfamilywithashortpeptidereticulatedbydisulfidebridgesandshareasimilarmodeofaction.Hanatoxin1(HaTx1)fromaChileantarantulawasoneoftheearliestdiscussedtoolsregardingthisandhasbeenintensivelyappliedtocharacterizethechannelblockingnotthroughtheporedomain.Recently,morerelatednoveltoxinsfromAfricantarantulassuchasheteroscordratoxins(HmTx)andstromatoxin1(ScTx1)wereisolatedandshowntoactasgatingmodifierssuchasHaTxonKv2.1channelswithelectrophysiologicalrecordings.However,furtherinteractiondetailsareunavailableduetothelackofhigh-resolutionstructuresofvoltage-sensingdomainsinsuchmammalianKvchannels.Therefore,inthepresentstudy,weexploredstructuralobservationviamoleculardockingsimulationbetweentoxinsandKv2.1channelsbaseduponthesolutionstructuresofHaTx1andatheoreticalbasisofanindividualS3(C)helicalchannelfragmentincombinationwithhomologymodelingforothernoveltoxins.Ourresultsprovideprecisechemicaldetailsfortheinteractionsbetweenthesetarantulatoxinsandchannel,reasonablycorrelatingthepreviouslyreportedpharmacologicalpropertiestothethree-dimensionalstructuralinterpretation.Inaddition,itissuggestedthatcertainsubtlestructuralvariationsontheinteractionsurfaceoftoxinsmaydiscriminatebetweentherelatedtoxinswithdifferentaffinitiesforKvchannels.Evolutionarylinksbetweenspiderpeptidetoxinsanda“voltagesensorpaddles”mechanismmostrecentlyfoundinthecrystalstructureofanarchaebacterialK(+)channel,KvAP,arealsodelineatedinthispaper.
SchiauYS., etal. (2003) Structuralbasisofbindingandinhibitionofnoveltarantulatoxinsinmammalianvoltage-dependentpotassiumchannels. ChemResToxicol.PMID:14565763
NovelTarantulaToxinsforSubtypesofVoltage-DependentPotassiumChannelsintheKv2andKv4Subfamilies
Threenovelpeptideswiththeabilitytoinhibitvoltage-dependentpotassiumchannelsintheshab(Kv2)andshal(Kv4)subfamilieswereidentifiedfromthevenomoftheAfricantarantulasStromatopelmacalceata(ScTx1)andHeteroscodramaculata(HmTx1,HmTx2).Thethreetoxinsare34-to38-aminoacidpeptidesthatbelongtothestructuralfamilyofinhibitorcystineknotspiderpeptidesreticulatedbythreedisulfidebridges.ElectrophysiologicalrecordingsinCOScellsshowthatthesetoxinsactasgatingmodifierofvoltage-dependentK+channels.ScTx1isthefirsthigh-affinityinhibitoroftheKv2.2channelsubtype(IC50,21.4nM)tobedescribed.ScTx1alsoinhibitstheKv2.1channels,withanIC50of12.7nM,andKv2.1/Kv9.3heteromultimersthathavebeenproposedtobeinvolvedinO2sensinginpulmonaryarterymyocytes.Inaddition,itisthemosteffectiveinhibitorofKv4.2channelsdescribedthusfar,withanIC50of1.2nM.HmTxtoxinssharesequencesimilaritieswithboththepotassiumchannelblockertoxins(HmTx1)andthecalciumchannelblockertoxinomega-GsTxSIA(HmTx2).TheyinhibitpotassiumcurrentassociatedwithKv2subtypesinthe100to300nMconcentrationrange.HmTx2seemstobeaspecificinhibitorofKv2channels,whereasHmTx1alsoinhibitsKv4channels,includingKv4.1,withthesamepotency.HmTx1isthefirstdescribedpeptideeffectoroftheKv4.1subtype.Thosenoveltoxinsarenewtoolsfortheinvestigationofthephysiologicalroleofthedifferentpotassiumchannelsubunitsincellularphysiology.
EscoubasP.,etal.(2002) NovelTarantulaToxinsforSubtypesofVoltage-DependentPotassiumChannelsintheKv2andKv4Subfamilies.MolPharm.PMID:12065754
