细胞质膜与细胞表面讲义_Cell_Membrane_and_Cell_Surface.ppt

CellMembraneandCellSurface,I.CellMembraneII.CellJunctionsIII.CellAdhesionIV.ExtracellularMatrix,I.Biomembranes:TheirStructure,ChemistryandFunctions,Learningobjectives:AbriefhistoryofstudiesonthestructrureoftheplasmamembraneModelofmembranestructure:anexperimentalperspectiveThechemicalcompositionofmembranesCharacteristicsofbiomembraneAnoverviewofthefunctionsofbiomembranes,1.Abriefhistoryofstudiesonthestructrureoftheplasmicmembrane,A.Conception:Plasmamembrane(cellmembrane),Intracellularmembrane,Biomembrane.B.ThehistoryofstudyOverton(1890s):LipidnatureofPM;,J.D.Robertson(1959):TheTEMshowing:thetrilaminarappearanceofPM;Unitmembranemodel;S.J.SingerandG.Nicolson(1972):fluid-mosaicmodel;K.Simonsetal(1997):lipidraftsmodel;FunctionalraftsinCellmembranes.Nature387:569-572,2.SingerandNicolsonsModelofmembranestructure:Thefluid-mosaicmodelisthe“centraldogma”ofmembranebiology.,Thecorelipidbilayerexistsinafluidstate,capableofdynamicmovement.Membraneproteinsformamosaicofparticlespenetratingthelipidtovaryingdegrees.,TheFluidMosaicModel,proposedin1972bySingerandNicolson,hadtwokeyfeatures,bothimpliedinitsname.,3.Thechemicalcompositionofmembranes,A.MembraneLipids:TheFluidPartoftheModel,Phospholipids:PhosphoglycerideandsphingolipidsGlycolipidsSterols(isonlyfoundinanimals),Membranelipidsareamphipathic.Therearethreemajorclassesoflipids:,Figure10-2.Thepartsofaphospholipidmolecule.Phosphatidylcholine,representedschematically(A),informula(B),asaspace-fillingmodel(C),andasasymbol(D).Thekinkduetothecis-doublebondisexaggeratedinthesedrawingsforemphasis.,Figure10-3.Alipidmicelleandalipidbilayerseenincross-section.Lipidmoleculesformsuchstructuresspontaneouslyinwater.Theshapeofthelipidmoleculedetermineswhichofthesestructuresisformed.Wedge-shapedlipidmolecules(above)formmicelles,whereascylinder-shapedphospholipidmolecules(below)formbilayers.,Figure10-4.Liposomes.(A)Anelectronmicrographofunfixed,unstainedphospholipidvesicles(liposomes)inwater.Thebilayerstructureofthevesiclesisreadilyapparent.(B)Adrawingofasmallsphericalliposomeseenincross-section.Liposomesarecommonlyusedasmodelmembranesinexperimentalstudies.(A,courtesyofJeanLepault.),Figure10-5.Across-sectionalviewofasyntheticlipidbilayer,calledablackmembrane.Thisplanarbilayerisformedacrossasmallholeinapartitionseparatingtwoaqueouscompartments.Blackmembranesareusedtomeasurethepermeabilitypropertiesofsyntheticmembranes.,Figure10-6.Phospholipidmobility.Thetypesofmovementpossibleforphospholipidmoleculesinalipidbilayer.,Figure10-7.Influenceofcis-doublebondsinhydrocarbonchains.Thedoublebondsmakeitmoredifficulttopackthechainstogetherandthereforemakethelipidbilayermoredifficulttofreeze.,Figure10-8.Thestructureofcholesterol.Cholesterolisrepresentedbyaformulain(A),byaschematicdrawingin(B),andasaspace-fillingmodelin(C).,Figure10-9.Cholesterolinalipidbilayer.Schematicdrawingofacholesterolmoleculeinteractingwithtwophospholipidmoleculesinoneleafletofalipidbilayer.,Figure10-10.Fourmajorphospholipidsinmammalianplasmamembranes.Notethatdifferentheadgroupsarerepresentedbydifferentsymbolsinthisfigureandthenext.Allofthelipidmoleculesshownarederivedfromglycerolexceptforsphingomyelin,whichisderivedfromserine.,Figure10-11.Theasymmetricaldistributionofphospholipidsandglycolipidsinthelipidbilayerofhumanredbloodcells.ThesymbolsusedforthephospholipidsarethoseintroducedinFigure10-10.Inaddition,glycolipidsaredrawnwithhexagonalpolarheadgroups(blue).Cholesterol(notshown)isthoughttobedistributedaboutequallyinbothmonolayers.,Figure10-12.Glycolipidmolecules.Galactocerebroside(A)iscalledaneutralglycolipidbecausethesugarthatformsitsheadgroupisuncharged.Aganglioside(B)alwayscontainsoneormorenegativelychargedsialicacidresidues(alsocalledN-acetylneuraminicacid,orNANA),whosestructureisshownin(C).Whereasinbacteriaandplantsalmostallglycolipidsarederivedfromglycerol,asaremostphospholipids,inanimalcellstheyarealmostalwaysproducedfromsphingosine,anaminoalcoholderivedfromserine,asisthecaseforthephospholipidsphingomyelin.Gal=galactose;Glc=glucose,GalNAc=N-acetylgalactos-amine;thesethreesugarsareuncharged.,Figure10-13.Sixwaysinwhichmembraneproteinsassociatewiththelipidbilayer.Mosttrans-membraneproteinsarethoughttoextendacrossthebilayerasasingleahelix(1)orasmultipleahelices(2);someofthesesingle-passandmultipassproteinshaveacovalentlyattachedfattyacidchaininsertedinthecytoplasmicmonolayer(1).Othermembraneproteinsareattachedtothebilayersolelybyacovalentlyattachedlipid-eitherafattyacidchainorprenylgroup-inthecytoplasmicmonolayer(3)or,lessoften,viaanoligosaccharide,toaminorphospholipid,phosphatidylinositol,inthenoncytoplasmicmonolayer(4).Finally,manyproteinsareattachedtothemembraneonlybynoncovalentinteractionswithothermembraneproteins(5)and(6).Howthestructurein(3)isformedisillustratedinFigure10-14.,Membraneproteins,Figure10-14.Thecovalentattachmentofeitheroftwotypesoflipidgroupscanhelplocalizeawater-solubleproteintoamembraneafteritssynthesisinthecytosol.(A)Afattyacidchain(eithermyristicorpalmiticacid)isattachedviaanamidelinkagetoanamino-terminalglycine.(B)Aprenylgroup(eitherfarnesyloralongergeranylgeranylgroup-bothrelatedtocholesterol)isattachedviaathioetherlinkagetoacysteineresiduethatisfourresiduesfromthecarboxylterminus.Followingthisprenylation,theterminalthreeaminoacidsarecleavedoffandthenewcarboxylterminusismethylatedbeforeinsertionintothemembrane.Thestructuresoftwolipidanchorsareshownunderneath:(C)amyristylanchor(a14-carbonsaturatedfattyacidchain),and(D)afarnesylanchor(a15-carbonunsaturatedhydrocarbonchain).,Figure10-15.Asegmentofatransmembranepolypeptidechaincrossingthelipidbilayerasanahelix.Onlythea-carbonbackboneofthepolypeptidechainisshown,withthehydrophobicaminoacidsingreenandyellow.(J.Deisenhoferetal.,Nature318:618-624andH.Micheletal.,EMBOJ.5:1149-1158),Figure10-17.Atypicalsingle-passtransmembraneprotein.Notethatthepolypeptidechaintraversesthelipidbilayerasaright-handedahelixandthattheoligosaccharidechainsanddisulfidebondsareallonthenoncytosolicsurfaceofthemembrane.Disulfidebondsdonotformbetweenthesulfhydrylgroupsinthecytoplasmicdomainoftheproteinbecausethereducingenvironmentinthecytosolmaintainsthesegroupsintheirreduced(-SH)form.,Figure10-18.Adetergentmicelleinwater,shownincross-section.Becausetheyhavebothpolarandnonpolarends,detergentmoleculesareamphipathic.,Figure10-19.Solubilizingmembraneproteinswithamilddetergent.Thedetergentdisruptsthelipidbilayerandbringstheproteinsintosolutionasprotein-lipid-detergentcomplexes.Thephospholipidsinthemembranearealsosolubilizedbythedetergent.,Figure10-20.Thestructuresoftwocommonlyuseddetergents.Sodiumdodecylsulfate(SDS)isananionicdetergent,andTritonX-100isanonionicdetergent.Thehydrophobicportionofeachdetergentisshowningreen,andthehydrophilicportionisshowninblue.NotethatthebracketedportionofTritonX-100isrepeatedabouteighttimes.,Figure10-21.Theuseofmilddetergentsforsolubilizing,purifying,andreconstitutingfunctionalmembraneproteinsystems.InthisexamplefunctionalNa+-K+ATPasemoleculesarepurifiedandincorporatedintophospholipidvesicles.TheNa+-K+ATPaseisanionpumpthatispresentintheplasmamembraneofmostanimalcells;itusestheenergyofATPhydrolysistopumpNa+outofthecellandK+in,asdiscussedinChapter11.,Figure10-22.Ascanningelectronmicrographofhumanredbloodcells.Thecellshaveabiconcaveshapeandlacknuclei.(CourtesyofBernadetteChailley.),Figure10-24.SDSpolyacrylamide-gelelectrophoresispatternoftheproteinsinthehumanredbloodcellmembrane.Thegelin(A)isstainedwithCoomassieblue.Thepositionsofsomeofthemajorproteinsinthegelareindicatedinthedrawingin(B);glycophorinisshowninredtodistinguishitfromband3.Otherbandsinthegelareomittedfromthedrawing.Thelargeamountofcarbohydrateinglycophorinmoleculesslowstheirmigrationsothattheyrunalmostasslowlyasthemuchlargerband3molecules.(A,courtesyofTedSteck.),Figure10-25.Spectrinmoleculesfromhumanredbloodcells.Theproteinisshownschematicallyin(A)andinelectronmicrographsin(B).Eachspectrinheterodimerconsistsoftwoantiparallel,looselyintertwined,flexiblepolypeptidechainscalledaandbtheseareattachednoncovalentlytoeachotheratmultiplepoints,includingbothends.Thephosphorylatedheadend,wheretwodimersassociatetoformatetramer,isontheleft.Boththeaandbchainsarecomposedlargelyofrepeatingdomains106aminoacidslong.In(B)thespectrinmoleculeshavebeenshadowedwithplatinum.(D.W.SpeicherandV.T.Marchesi,Nature311:177-180;B,D.M.Shottonetal.,J.Mol.Biol.131:303-329),Figure10-26.Thespectrin-basedcytoskeletononthecytoplasmicsideofthehumanredbloodcellmembrane.Thestructureisshownschematicallyin(A)andinanelectronmicrographin(B).Thearrangementshownin(A)hasbeendeducedmainlyfromstudiesontheinteractionsofpurifiedproteinsinvitro.Spectrindimersassociatehead-to-headtoformtetramersthatarelinkedtogetherintoanetlikemeshworkbyjunctionalcomplexescomposedofshortactinfilaments(containing13actinmonomers),tropomyosin,whichprobablydeterminesthelengthoftheactinfilaments,band4.1,andadducin.Thecytoskeletonislinkedtothemembranebytheindirectbindingofspectrintetramerstosomeband3proteinsviaankyrinmolecules,aswellasbythebindingofband4.1proteinstobothband3andglycophorin(notshown).Theelectronmicrographin(B)showsthecytoskeletononthecytoplasmicsideofaredbloodcellmembraneafterfixationandnegativestaining.(B,courtesyofT.ByersandD.Branton,PNSA.82:6153-6157),Figure10-31.Thethree-dimensionalstructureofabacteriorhodopsinmolecule.Thepolypeptidechaincrossesthelipidbilayerassevenahelices.Thelocationofthechromophoreandtheprobablepathwaytakenbyprotonsduringthelight-activatedpumpingcycleareshown.Whenactivatedbyaphoton,thechromophoreisthoughttopassanH+tothesidechainofasparticacid85.Subsequently,threeotherH+transfersarethoughttocompletethecyclefromasparticacid85totheextra-cellularspace,fromasparticacid96tothechromophore,andfromthecytosoltoasparticacid96.(R.Hendersonetal.J.Mol.Biol.213:899-929),Figure10-32.Thethree-dimensionalstructureofaporintrimerofRhodobactercapsulatusdeterminedbyx-raycrystallography.(A)Eachmonomerconsistsofa16-strandedantiparallelbbarrelthatformsatransmembranewater-filledchannel.(B)Themonomerstightlyassociatetoformtrimers,whichhavethreeseparatechannelsforthediffusionofsmallsolutesthroughthebacterialoutermembrane.Alongloopofpolypeptidechain(showninred),whichconnectstwobstrands,protrudesintothelumenofeachchannel,narrowingittoacross-sectionof0.6x1nm.(AdaptedfromM.S.Weissetal.,FEBSLett.280:379-382),Figure10-33.Thethree-dimensionalstructureofthephotosyntheticreactioncenterofthebacteriumRhodopseudomonasviridis.Thestructurewasdeterminedbyx-raydiffractionanalysisofcrystalsofthistransmembraneproteincomplex.Thecomplexconsistsoffoursubunits,L,M,H,andacytochrome.TheLandMsubunitsformthecoreofthereactioncenter,andeachcontainsfiveahelicesthatspanthelipidbilayer.Thelocationsofthevariouselectroncarriercoenzymesareshowninblack.(AdaptedfromadrawingbyJ.RichardsonbasedondatafromJ.Deisenhoferetal.,Nature318:618-624),4.Characteristicsofbiomembrane,A.Dynamicnatureofbiomembrane,Fluidityofmembranelipid.Itgivemembranestheabilitytofuse,formnetworks,andseparatecharge;Motilityofmembraneprotein.,ThelateraldiffusionofmembranelipidscandemonstratedexperimentallybyatechniquecalledFluorescenceRecoveryAfterPhotobleaching(FRAP).,Figure10-34.Experimentdemonstratingthemixingofplasmamembraneproteinsonmouse-humanhybridcells.Themouseandhumanproteinsareinitiallyconfinedtotheirownhalvesofthenewlyformedheterocaryonplasmamembrane,buttheyintermixwithtime.Thetwoantibodiesusedtovisualizetheproteinscanbedistinguishedinafluorescencemicroscopebecausefluoresceinisgreenwhereasrhodamineisred.(BasedonobservationsofL.D.FryeandM.Edidin,J.CellSci.7:319-335),Figure10-35.Antibody-inducedpatchingandcappingofacell-surfaceproteinonawhitebloodcell.Thebivalentantibodiescross-linktheproteinmoleculestowhichtheybind.Thiscausesthemtoclusterintolargepatches,whichareactivelyswepttothetailendofthecelltoformacap.Thecentrosome,whichgovernsthehead-tailpolarityofthecell,isshowninorange.,Figure10-37.Diagramofanepithelialcellshowinghowaplasmamembraneproteinisrestrictedtoaparticulardomainofthemembrane.ProteinA(intheapicalmembrane)andproteinB(inthebasalandlateralmembranes)candiffuselaterallyintheirowndomainsbutarepreventedfromenteringtheotherdomain,atleastpartlybythespecializedcelljunctioncalledatightjunction.Lipidmoleculesintheouter(noncytoplasmic)monolayeroftheplasmamembranearelikewiseunabletodiffusebetweenthetwodomains;lipidsintheinner(cytoplasmic)monolayer,however,areabletodoso.,Figure10-38.Threedomainsintheplasmamembraneofguineapigspermdefinedwithmonoclonalantibodies.Aguineapigspermisshownschematicallyin(A),whileeachofthethreepairsofmicrographsshownin(B),(C),and(D)showscell-surfaceimmunofluorescencestainingwithadifferentmonoclonalantibody(ontheright)nexttoaphase-contrastmicrograph(ontheleft)ofthesamecell.Theantibodyshownin(B)labelsonlytheanteriorhead,thatin(C)onlytheposteriorhead,whereasthatin(D)labelsonlythetail.(CourtesyofSelenaCarrollandDianaMyles.),Figure10-39.Fourwaysinwhichthelateralmobilityofspecificplasmamembraneproteinscanberestricted.Theproteinscanself-assembleintolargeaggregates(suchasbacteriorhodopsininthepurplemembraneofHalobacterium)(A);theycanbetetheredbyinteractionswithassembliesofmacromoleculesoutside(B)orinside(C)thecell;ortheycaninteractwithproteinsonthesurfaceofanothercell(D).,Figure10-41.Simplifieddiagramofthecellcoat(glycocalyx).Thecellcoatismadeupoftheoligosaccharidesidechainsofglycolipidsandintegralmembraneglycoproteinsandthepolysaccharidechainsonintegralmembraneproteoglycans.Inaddition,adsorbedglycoproteinsandadsorbedproteoglycans(notshown)contributetotheglycocalyxinmanycells.Notethatallofthecarbohydrateisonthenoncytoplasmicsurfaceofthemembrane.,cellcoat,Figure10-42.Theprotein-carbohydrateinteractionthatinitiatesthetransientadhesionofneutrophilstoendothelialcellsatsitesofinflammation.(A)ThelectindomainofP-selectinbindstothespecificoligosaccharideshownin(B),whichispresentonbothcell-surfaceglycoproteinandglycolipidmolecules.Thelectindomainoftheselectinsishomologoustolectindomainsfoundonmanyothercarbohydrate-bindingproteinsinanimals;becausethebindingtotheirspecificsugarligandrequiresextracellularCa2+,theyarecalledC-typelectins.Athree-dimensionalstructureofoneoftheselectindomains,determinedbyx-raycrystallography,isshownin(C);itsboundsugariscoloredblue.Gal=galactose;GlcNAc=N-acetylglucosamine;Fuc=fucose;NANA=sialicacid.,5.AnOverviewofmembranefunctions,1.Definetheboundariesofthecellanditsorganelles.2.Svidemechanismsforcell-to-cellcontact,communicationandadhesion,LearningObjectives:1.IntegratingCellsintoTissues2.Celljunctons:Cell-celladhensionandcommunication;3.Cell-Matrixadhension;4.Extracellularmatrix:ComponentsandFunctions;5.CellWalls,II.Celljunction,CelladhensionExtracellularmatrix,Figure19-1Simplifieddrawingofacross-sectionthroughpartofthewalloftheintestine.Thislong,tubelikeorganisconstructedfromepithelialtissues(red),connectivetissues(green),andmuscletissues(yellow).Eachtissueisanorganizedassemblyofcellsheldtogetherbycell-celladhesions,extracellularmatrix,orboth.,Figure19-2Theroleoftightjunctionsintranscellulartransport.Transportproteinsareconfinedtodifferentregionsoftheplasmamembraneinepithelialcellsofthesmallintestine.Thissegregationpermitsavectorialtransferofnutrientsacrosstheepithelialsheetfromthegutlumentotheblood.Intheexampleshown,glucoseisactivelytransportedintothecellbyNa+-drivenglucosesymportsattheapicalsurface,anditdiffusesoutofthecellbyfacilitateddiffusionmediatedbyglucosecarriersinthebasolateralmembrane.Tightjunctionsarethoughttoconfinethetransportproteinstotheirappropriatemembranedomainsbyactingasdiffusionbarrierswithinthelipidbilayeroftheplasmamembrane;thesejunctionsalsoblockthebackflowofglucosefromthebasalsideoftheepitheliumintothegutlumen.,Tightjunctions,Figure19-3Tightjunctionsallowcellsheetstoserveasbarrierstosolutediffusion.(A)Schematicdrawingshowinghowasmallextracellulartracermoleculeaddedononesideofanepithelialcellsheetcannottraversethetightjunctionsthatsealadjacentcellstogether.(B)Electronmicrographsofcellsinanepitheliumwhereasmall,extracellular,electron-densetracermoleculehasbeenaddedtoeithertheapicalside(ontheleft)orthebasolateralside(ontheright);inbothcasesthetracerisstoppedbythetightjunction.(B,courtesyofDanielFriend.),Figure19-4Structureofatightjunctionbetweenepithelialcellsofthesmallintestine.Thejunctionsareshownschematicallyin(A)andinfreeze-fracture(B)andconventional(C)electronmicrographs.Notethatthecellsareorientedwiththeirapicalendsdown.In(B)theplaneofthemicrographisparalleltotheplaneofthemembrane,andthetightjunctionappearsasabeltlikebandofanastomosingsealingstrandsthatencircleeachcellinthesheet.Thesealingstrandsareseenasridgesofintramembraneparticlesonthecytoplasmicfracturefaceofthemembrane(thePface)orascomplementarygroovesontheexternalfaceofthemembrane(theEface)(seeFigure19-5).In(C)thejunctionisseenasaseriesoffocalconnectionsbetweentheouterleafletsofthetwointeractingplasmamembranes,eachconnectioncorrespondingtoasealingstrandincross-section.(BandC,fromN.B.Gilula,inCellCommunicationR.P.Cox,ed.,pp.1-29),Figure19-5Acurrentmodelofatightjunction.Itispostulatedthatthesealingstrandsthatholdadjacentplasmamembranestogetherareformedbycontinuousstrandsoftransmembranejunctionalproteins,whichmakecontactacrosstheintercellularspaceandcreateaseal.Inthisschematicthecytoplasmichalfofonemembranehasbeenpeeledbackbytheartisttoexposetheproteinstrands.Twoperipheralproteinsassociatedwiththecytoplasmicsideoftightjunctionshavebeencharacterized,buttheputativetransmembraneproteinhasnotyetbeenidentified.Infreeze-fractureelectronmicroscopythetight-junctionproteinswouldremainwiththecytoplasmic(Pface)halfofthelipidbilayertogivethepatternofintramembraneparticlesseeninFigure19-4B,insteadofstayingintheotherhalfasshownhere.,Anchoringjunctions,Figure19-7Constructionofananchoringjunction.Highlyschematizeddrawingshowingthetwoclassesofproteinsthatconstitutesuchajunction:intracellularattachmentproteinsandtransmembranelinkerproteins.,Figure19-8Adhesionbeltsbetweenepithelialcellsinthesmallintestine.Thisbeltlikeanc