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Tag! Purifying Proteins with Affinity Chromatography
Affinitychromatography(withHIS-taggedproteins) ThisprotocolisdescribedinlessdetailinCopelandetal,Nature,379,162-165,1996. Affinitychromatographycanbeperformedusinganumberofdifferentproteintags.Inourlabwehavehadsuccessusingpoly-hisitidinetaggedproteinsforcreationofourproteinaffinitycolumns.Thehistidinetagisveryshort(10hisresidues)andshouldnotaltertheconformationofthetaggedprotein,norshoulditbeinvolvedinartifactualinteractions.Thepoly-histagbindstoanickelchelateresinforcreationofthecolumn.Weusetheresinaloneforthecontrolcolumns.Mostoften,wechallengeourcolumnswith35S-labeled,invitrotranslatedproteins,however,proteinsfromavarietyofsourcescanbeusedanddetectedappropriately. Theprotocolbelowdescribesourmethod.Theorderofthestepshasbeenoptimisedsothatboththeaffinitycolumnsandinvitrotranslatedproteinarereadyatthesametime. 1)BeginbygettingouttheDNAand35S-methioninefortheinvitrotranslationreactions. 2)Whilethesethaw,preparesolutionsforaffinitycolumns:ACBuffer:(10%glycerol,100mMNaCl,20mMTrispH7.6,0.5mMEDTA,0.1%Tween-20,ddH2O). NOTE:Youmaywishtoaddproteaseinhibitors(eg.TPCK),butusuallywedon"t;youmayalsochoosetofiltersterilizethebuffer,butagain,usuallywedon"t. 5%milkpowdersolution:10mLACBuffer+0.5gmilkpowder.Mixonashakerplatformuntildissolved. Storebothsolutionsonice. 4)Preparethenickelresin.50uL(settledvolume)ofresinisrequiredforeachexperimentalandcontrolcolumn.TransfertheappropriatevolumeofslurryintotwosiliconizedEppendorftubes,oneforthecontrolresin,onefortheproteincoupling.TheresinshouldbeallowedtosettleandthenwashedonceinwaterandtwiceinACbuffer.Ineachwashsteptheresincanbeallowedtosettlebygravityorbycentrifugingat1.5Kfor3minutesinabenchtopcentrifuge. 5)Betweenwashesoftheresinbegintosetuptheinvitrotranslationreactionsfortheproteinsthataretobetestedforbinding.Wefollowthestandardprotocolfora25uLreactionusingthePromegaTNTcoupledtranscription/translationkit. 6)Whilethereactionsareincubatingcoupleyourproteintotheresin.Weuse1mgofpureHis-taggedproteinpermLofresin.However,theoptimalratiomayvarydependingontheinteractionbeingpursued.Wetreatthecontrolresinwiththesamebufferthattheproteinisstoredin.Allowthecouplingtoproceedfor30minutesonice. 7)Preparespincolumnsforremovalofunicorporated35S-methioninefromthetranslationreaction.Thecolumnsaremadein1mLsyringesblockedwithglasswool.TheresinisG-25(BioRad)equilibratedinACbuffer.FollowtheManiatisprotocolforspincolumns. NOTE:inthefollowingsteps,youwanttoavoidfoamingandbubblesasmuchaspossIBLe,asthebubblescancontributetoproteindenaturation.So,alwaysmixgently. 8)Whiletheproteinisbeingcoupled,andbetweenspinsinthepreparationofspincolumns,begintosetupthehousingsfortheaffinitycolumns.Weuse200uLtipswithbevelledends(Diamed#230-1673-03K).Thetipshavetobeblockedwithglassbeadstopreventtheresinfromleakingout.UseSigmaAcidwashed212-300micronglassbeadsthathavebeenwashedinwater.Beadsshouldbeaddedtoalevelof7mmattheendofthetip.Afterthebeadshavebeentransferred,removeexcesswaterandthenadd100uLofACbuffer.Thisistopreventthecontactofproteinresindirectlywithwater. Atthistimethefractioncollectiontubescanalsobelabeled.Thecolumnsarerunstandingineppendorftubesonice,thecolumnsaremovedtonewtubesforeachfraction.7collectiontubeswillbeneededforeachcolumn:1flow-throughfraction,4washfractions,and2elutionfractions. 9)Whentheinvitrotranslationreactionsarefinishedpassthereactionoverthespincolumninavolumeof100uL. 10)Setupthecolumnloadsample.50uLinvitroreaction(halfthesampleafterthespincolumn),130uLACbuffer,and45uL5%milkpowder.Totalvolume=225uL 11)Washthenickelresin.Aftertheproteinhasbeenallowedtocoupletotheresinfor30minutesonice,washtheresintwicein1mLofACbuffertoremoveunboundproteinandtoequilibratetheresininACbuffer. 12)Setupthecolumns.Add50uLofsettledaffinityresintothepreparedtips.Allowtheresintosettleonice. 13)Loadthecolumns.Aftertheresinhassettled(5-10minutes)removeanybufferremainingontop.Carefullyload90uLoftheloadsampletothetopofeachcolumn(controlandexperimental).DONOTDISTURBTHESETTLEDRESIN.TheremainingportionoftheloadsampleshouldbesavedforSDS-PAGE. 14)Allowtheloadedproteintoflowintotheresin.Whenitreachesthebottomofthecolumn(youcanfollowitsprogressbecauseoftheredcoloroftheretic.lysate)transferthecolumnintotube#1.Allowtheremainingproteintoflowintothetube.Thiscomprisesthemajorityoftheflow-throughfraction.Whenthelastoftheloadhasflowedintothecolumntransferthecolumntotube#2. 15)Washthecolumnswith4x400uLofACbuffer.Eachwashfractionis400uL.Transferthecolumntoanewtubeaftereachwashstep. 16)Elutetheboundprotein.Afterthelastwashtransferthecolumnstotube#6atroomtemperature.Add30uLof2%SDS(thiswouldprecipitateonice).Allowthistoflow-in.Transferthecolumntotube#7.Add120uLof2%SDS.Allowthistorunthrough.Thisistheeluatefraction. 17)Forgels:LoadandFlowThroughwillhave9uLsample+3ul4XSDSgelloADIngbuffer Tocompensatefordilution,eluateloadedwillequal15ulsample+5uL4XSDS 18)Boilthesamples,storeinfreezeruntilreadyforSDS-PAGE.Afterelectrophoresis,drythegelandautoradiograph.Aninteractionisdetectedasdepletionofthelabeledproteinfromtheflow-throughandpresenceoftheproteinintheexperimentalcolumneluate. AffinitychromatographywithFTZ(1st3lanes)andcontrol(2nd3lanes)affinitycolumns.35S-labeledPRDandFTZ-F1bindtotheFTZcolumnsandcanthenbeeluted(E).(L=load,FT=flowthrough;Luc=luciferase,negativecontrol).
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