第十七章-细胞连接、细胞黏着和细胞外基质-北大陈建国细胞生物学

Chapter19CellJunctions,CellAdhesion,andtheExtracellularMatrix细胞连接、细胞黏着和细胞外基质Figure19-1MolecularBiologyoftheCell(©GarlandScience2008)TwomainwaysinwhichanimalcellsareboundtogetherAsummaryofthevariouscelljunctionsfoundinavertebrateepithelialcell,classifiedaccordingtotheirprimaryfunctions17-1CellJunctionsFigure19-2dMolecularBiologyoftheCell(©GarlandScience2008)CELL–CELLJUNCTIONSTightJunctionsFormaSealBetweenCellsandaFenceBetweenPlasmaMembraneDomainsTheroleoftightjunctionsintranscellulartransportGlucoseleavesthecellthroughpassiveglucosetransportersinitsbasolateralmembrane.Theroleoftightjunctionsinallowingepitheliatoserveasbarrierstosolutediffusion.Figure19-26aMolecularBiologyoftheCell(©GarlandScience2008)Amodelofatightjunction.(A)Thesealingstrandsholdadjacentplasmamembranestogether.Thestrandsarecomposedoftransmembraneproteinsthatmakecontactacrosstheintercellularspaceandcreateaseal.Themolecularcompositionofasealingstrand.Themajorextracellularcomponentsofthetightjunctionaremembersofafamilyofproteinswithfourtransmembranedomains.Oneoftheseproteins,claudin,isthemostimportantfortheassemblyandstructureofthesealingstrands,whereastherelatedproteinoccludinhasthelesscriticalroleofdeterminingjunctionpermeability.Thetwoterminioftheseproteinsarebothonthecytoplasmicsideofthemembrane,wheretheyinteractwithlargescaffoldingproteinsthatorganizethesealingstrandsandlinkthetightjunctiontotheactincytoskeletonFigure19-27MolecularBiologyoftheCell(©GarlandScience2008)Figure19-28MolecularBiologyoftheCell(©GarlandScience2008)SeptateJunction(间壁连接）在无脊椎动物中的封闭连接Table19-2MolecularBiologyoftheCell(©GarlandScience2008)Desmosomes,hemidesmosomes,andtheintermediatefilamentnetwork.AdherensJunctionsFigure19-5MolecularBiologyoftheCell(©GarlandScience2008)Transmembraneadhesionproteinslinkthecytoskeletontoextracellularstructures.Theexternallinkagemaybeeithertoothercells(cell–celljunctions,mediatedtypicallybycadherins)ortoextracellularmatrix(cell–matrixjunctions,mediatedtypicallybyintegrins).Theinternallinkagetothecytoskeletonisgenerallyindirect,viaintracellularadaptorproteins.AdhesionbeltThefoldingofanepithelialsheettoformanepithelialtubeDesmosomes.(A)Thestructuralcomponentsofadesmosome.Onthecytoplasmicsurfaceofeachinteractingplasmamembraneisadenseplaquecomposedofamixtureofintracellularadaptorproteins.Abundleofkeratinintermediatefilamentsisattachedtothesurfaceofeachplaque.Transmembranenonclassicalcadherinsbindtotheplaquesandinteractthroughtheirextracellulardomainstoholdtheadjacentmembranestogether.(B)Someofthemolecularcomponentsofadesmosome.Desmogleinanddesmocollinarenonclassicalcadherins.Theircytoplasmictailsbindplakoglobin(γ-catenin)andplakophilin(adistantrelativeofp120-catenin),whichinturnbindtodesmoplakin.Desmoplakinbindstothesidesofintermediatefilaments,therebytyingthedesmosometothesefilaments.(C)Anelectronmicrographofdesmosomejunctionsbetweenthreeepidermalcellsintheskinofababymouse.(D)Partofthesametissueathighermagnification,showingasingledesmosome,withintermediatefilamentsattachedtoit.Figure19-18MolecularBiologyoftheCell(©GarlandScience2008)GapJunctionsCoupleCellsBothElectricallyandMetabolicallyDeterminingthesizeofagap-junctionchannelGapjunctions.(A)Adrawingoftheinteractingplasmamembranesoftwoadjacentcellsconnectedbygapjunctions.Eachlipidbilayerisshownasapairofredsheets.Proteinassembliescalledconnexons(green),eachofwhichisformedbysixconnexinsubunits,penetratetheapposedlipidbilayers.Twoconnexonsjoinacrosstheintercellulargaptoformacontinuousaqueouschannelconnectingthetwocells.(C)Thehigh-resolutionstructureofahomomericgap-junctionchannel,determinedbyx-raycrystallographyofhumanconnexin26.Inthisview,wearelookingdownonthepore,formedfromsixconnexinsubunits.Thestructureillustratesthegeneralfeaturesofthechannelandsuggestsaporesizeofabout1.4nm,aspredictedfromstudiesofgap-junctionpermeabilitywithmoleculesofvarioussizes(B)Theorganizationofconnexinsintoconnexons,andconnexonsintointercellularchannels.Theconnexonscanbehomomericorheteromeric,andtheintercellularchannelscanbehomotypicorheterotypic.Gapjunctionsasseenintheelectronmicroscope.(A)Thinsectionand(B)freeze-fractureelectronmicrographsofalargeandasmallgapjunctionplaquebetweenfibroblastsinculture.In(B),eachgapjunctionisseenasaclusterofhomogeneousintramembraneparticles.Eachintramembraneparticlecorrespondstoaconnexon(seeFigure19–25).Figure19-36MolecularBiologyoftheCell(©GarlandScience2008)Connexinturnoveratagapjunction.Cellsweretransfectedwithaslightlymodifiedconnexingene,codingforaconnexinwithashortaminoacidtagcontainingfourcysteinesinthesequenceCys-Cys-X-XCys-Cys(whereXdenotesanarbitraryaminoacid).Thistetracysteinetagcanbindstronglytocertainsmallfluorescentdyemolecules,whichcanbeaddedtotheculturemediumandwillreadilyentercellsbydiffusingacrosstheplasmamembrane.Intheexperimentshown,agreendyewasaddedfirsttolabelalltheconnexinmoleculesinthecells,andthecellswerethenwashedandincubatedfor4or8hours.Attheendofthistime,areddyewasaddedtothemediumandthecellswerewashedagainandfixed.Connexinmoleculesalreadypresentatthebeginningoftheexperimentarelabeledgreen(andtakeupnoreddyebecausetheirtetracysteinetagsarealreadysaturatedwithgreendye),whileconnexinssynthesizedsubsequently,duringthe4-or8-hourincubation,arelabeledred.Thefluorescenceimagesshowgapjunctionsbetweenpairsofcellstreatedinthisway.Thecentralpartofthegap-junctionplaqueisgreen,indicatingthatitconsistsofoldconnexinmolecules,whiletheperipheryisred,indicatingthatitconsistsofconnexinssynthesizedduringtheprevious4or8hours.Thelongerthetimeofincubation,thesmallerthegreencentralpatchofoldmolecules,andthelargertheperipheralringofnewmoleculesthathavebeenrecruitedtoreplacetheoldones.将荧光黄注射兔子视网膜神经元，A.向周围神经元扩散.B.巴比妥阻碍荧光素的扩散。InPlants,PlasmodesmataPerformManyoftheSameFunctionsasGapJunctionsPlasmodesmataFigure19-38cMolecularBiologyoftheCell(©GarlandScience2008)Figure19-38dMolecularBiologyoftheCell(©GarlandScience2008)Figure19-22aMolecularBiologyoftheCell(©GarlandScience2008)Figure19-22bMolecularBiologyoftheCell(©GarlandScience2008)Figure19-22cMolecularBiologyoftheCell(©GarlandScience2008)17-2CellAdhesionMolecule,CAM37CadherinsMediateCa2+DependentCell-CellAdhesioninAllAnimals38Figure19-6MolecularBiologyoftheCell(©GarlandScience2008)Cadherindiversityinthecentralnercoussystem39Thecadherinsuperfamilar40CadherinStructureandFunctionTheextracellularregionofaclassicalcadherincontainsfivecopiesoftheextracellularcadherindomainseparatedbyflexiblehingeregions.Ca2+ions(reddots)bindintheneighborhoodofeachhinge,preventingitfromflexing.Asaresult,theextracellularregionformsarigid,curvedstructureasshownhere.Togeneratecell–celladhesion,thecadherindomainattheN-terminaltipofonecadherinmoleculebindstheN-terminaldomainfromacadherinmoleculeonanothercell.Thestructurewasdeterminedbyx-raydiffractionofthecrystallizedC-cadherinextracellularregion.4142(B)IntheabsenceofCa2+,increasedflexibilityinthehingeregionsresultsinafloppiermoleculethatisnolongerorientedcorrectlytointeractwithacadherinonanothercell—andadhesionfails.(C)Atatypicalcell–celljunction,anorganizedarrayofcadherinmoleculesfunctionslikeVelcrotoholdcellstogether.Cadherinsonthesamecellarethoughttobecoupledbyside-to-sideinteractionsbetweentheirN-terminalheadregions,resultinginalineararraylikethealternatinggreenandlightgreencadherinsonthelowercellshownhere.Thesearraysarethoughttointeractwithsimilarlineararraysonanadjacentcell(bluecadherinmolecules,topcell).Thelineararraysononecellareperpendiculartothoseontheothercell,asindicatedbytheredarrows.Multipleperpendiculararraysonbothcellsinteracttoformatight-knitmatofcadherinproteins.Figure19-10MolecularBiologyoftheCell(©GarlandScience2008)SortingOut.43Figure19-12a,bMolecularBiologyoftheCell(©GarlandScience2008)ChangingPatternsofCadherinexpressionduringconstructionofthenervoussystemE-cadherinN-cadherin44Figure19-12cMolecularBiologyoftheCell(©GarlandScience2008)Asthepatternsofgeneexpressionchangethedifferentgroupofcellssegregatefromoneanotheraccordingtothecadherinstheyexpress.45Figure19-13MolecularBiologyoftheCell(©GarlandScience2008)Cadherin-dependentcellsorting.46Figure19-14MolecularBiologyoftheCell(©GarlandScience2008)Thelinkageofclassicalcadherinstoactinfilaments47Thecadherinsarecoupledindirectlytoactinfilamentsthroughanadaptorproteincomplexcontainingp120-catenin,β-catenin,andα-catenin.Otherproteins,includingvinculin,associatewithα-cateninandhelpprovidethelinkagetoactin.β-Cateninhasasecond,andveryimportant,functioninintracellularsignaling,aswediscussinChapter15(seeFigure15–60).Forclarity,thisdiagramdoesnotshowthecadherinoftheadjacentcellinthejunction.Assemblyofanadherensjunction.(A)Assemblybeginswhentwounattachedepithelialcellprecursorsexploretheirsurroundingswithmembraneprotrusions,generatedbylocalnucleationofactinnetworks.Whenthecellsmakecontact,smallcadherinandcateninclusterstakeshapeatthecontactsitesandassociatewithactin,leadingtoactivationofthesmallmonomericGTPaseRac(notshown),animportantactinregulator(seeFigure16–85).(B)Racpromotesadditionalactinprotrusionsinthevicinity,expandingthesizeofthecontactzoneandtherebypromotingfurtherrecruitmentofcadherinsandtheirassociatedcateninproteins.(C)Eventually,RacisinactivatedandreplacedbytherelatedGTPaseRho(notshown),whichshiftsactinremodelingtowardtheassemblyoflinear,contractilefilamentbundles.RhoalsopromotestheassemblyofmyosinIIfilamentsthatassociatewithbundlesofactinfilamentstogeneratecontractileactivity.Thiscontractileactivitygeneratestensionthatstimulatesfurtheractinrecruitmentandexpansionofthejunction,inpartthroughthemechanismsillustratedinFigure19–12.TengJ.,NatureCellBiology49SelectinsMediateTransientCell–CellAdhesionsintheBloodstreamThestructureandfunctionofselectins.L-selectinonlymphocytes,

P-selectinonbloodplatelets,andonendothelialcellsthathavebeenlocallyactivatedbyaninflammatoryresponse,E-selectinonactivatedendothelialcellsMembersoftheImmunoglobulinSuperfamilyMediateCa2+-IndependentCell–CellAdhesionneuralcelladhesionmolecule(NCAM),intercellularcelladhesionmolecules(ICAMs)vascularcelladhesionmolecules(VCAMs).NCAM–NCAMFAS3–FAS3(神经-肌肉）ICAM–IntegrinTable19-5MolecularBiologyoftheCell(©GarlandScience2008)Figure19-53MolecularBiologyoftheCell(©GarlandScience2008)THEEXTRACELLULARMATRIXOFANIMALSTheextracellularmatrixisconstructedfromthreemajorclassesofmacromolecules:glycosaminoglycans(GAGs，葡萄糖胺聚糖),whicharelargeandhighlychargedpolysaccharidesthatareusuallycovalentlylinkedtoproteinintheformofproteoglycans;Fibrousproteins,whichareprimarilymembersofthecollagenfamily;Alargeclassofnoncollagenglycoproteins,whichcarryconventionalasparagine-linkedoligosaccharides.Figure19-41MolecularBiologyoftheCell(©GarlandScience2008)Fibroblastsinconnectivetissue.Thisscanningelectronmicrographshowstissuefromthecorneaofarat.Theextracellularmatrixsurroundingthefibroblastsisherecomposedlargelyofcollagenfibrils.Theglycoproteins,hyaluronan,andproteoglycans,whichnormallyformahydratedgelfillingtheintersticesofthefibrousnetwork,havebeenremovedbyenzymeandacidtreatment.(CourtesyofT.Nishida.)TheExtracellularMatrixIsMadeandOrientedbytheCellsWithinItGlycosaminoglycan(GAG)ChainsOccupyLargeAmountsofSpaceandFormHydratedGels乙酰葡萄糖胺葡萄糖醛酸Therepeatingdisaccharidesequenceofaheparansulfate(硫酸乙酰肝素)glycosaminoglycan(GAG)chainFourmaingroupsofGAGs

aredistinguishedbytheirsugars,thetypeoflinkagebetweenthesugars,andthenumberandlocationofsulfategroups:hyaluronan,透明质素chondroitinsulfate硫酸软骨素anddermatansulfate硫酸皮肤素,heparansulfate,硫酸肝素类keratansulfate.硫酸角质素Therepeatingdisaccharidesequenceinhyaluronan,arelativelysimpleGAG.Thisubiquitousmoleculeinvertebratesconsistsofasinglelongchainofupto25,000sugarmonomers.Notetheabsenceofsulfategroups.HyaluronanActsasaSpaceFillerDuringTissueMorphogenesisandRepairThelinkagebetweenaGAGchainanditscoreproteininaproteoglycanmolecule.Aspecificlinktetrasaccharideisfirstassembledonaserinesidechain.TherestoftheGAGchain,consistingmainlyofarepeatingdisaccharideunit,isthensynthesized,withonesugarbeingaddedatatime.Inchondroitinsulfate,thedisaccharideiscomposedofD-glucuronicacidandN-acetyl-D-galactosamine;inheparansulfate,itiseitherD-glucuronicacidorL-iduronicacidandN-acetyl-Dglucosamine;inkeratansulfate,itisD-galactoseandN-acetyl-D-glucosamine.ProteoglycansAreComposedofGAGChainsCovalentlyLinkedtoaCoreProtein核心蛋白多糖聚集蛋白聚糖[来自软骨]核糖核酸酶Examplesofasmall(decorin)andalarge(aggrecan)proteoglycanfoundintheextracellularmatrixAnaggrecanaggregatefromfetalbovinecartilage.角质素硫酸软骨素Figure19-61MolecularBiologyoftheCell(©GarlandScience2008)ProteoglycansintheextracellularmatrixofratcartilageCollagensAretheMajorProteinsoftheExtracellularMatrixThestructureofatypicalcollagenmolecule.(A)Amodelofpartofasinglecollagenαchain.Thechainisabout1000aminoacidslong.Itisarrangedasalefthandedhelix,withthreeaminoacidsperturnandwithglycineaseverythirdaminoacid.Therefore,anαchainiscomposedofaseriesoftripletGly-X-Ysequences.(B)Amodelofpartofacollagenmolecule,inwhichthreeαchains,eachshowninadifferentcolor,arewrappedaroundoneanothertoformatriple-strandedhelicalrod.Glycineistheonlyaminoacidsmallenoughtooccupythecrowdedinteriorofthetriplehelix.Onlyashortlengthofthemoleculeisshown;theentiremoleculeis300nmlong.Afibroblastsurroundedbycollagenfibrilsintheconnectivetissueofembryonicchickskin.Table19-7MolecularBiologyoftheCell(©GarlandScience2008)Cross-linksformedbetweenmodifiedlysinesidechainswithinacollagenfibrilCollagenfibrilsinthetadpoleskin.Thiselectronmicrographshowstheplywoodlikearrangementofthefibrils:successivelayersoffibrilsarelaiddownnearlyatrightanglestoeachother.ThisorganizationisalsofoundinmatureboneandinthecorneaTypeIXcollagen.(A)TypeIXcollagenmoleculesbindinginaperiodicpatterntothesurfaceofafibrilcontainingtypeIIcollagen.(B)Electronmicrographofarotary-shadowedtype-II-collagen-containingfibrilincartilage,decoratedbytypeIXcollagenmolecules.(C)AnindividualtypeIXcollagenmolecule.TheshapingoftheextracellularmatrixbycellsElasticfibers.Thesescanningelectronmicrographsshow(A)alow-powerviewofasegmentofadog’saortaand(B)ahigh-powerviewofthedensenetworkoflongitudinallyorientedelasticfibersintheouterlayerofthesamebloodvessel.Alltheothercomponentshavebeendigestedawaywithenzymesandformicacid.ElastinGivesTissuesTheirElasticityStretchinganetworkofelastinmolecules.Themoleculesarejoinedtogetherbycovalentbonds(red)togenerateacross-linkednetwork.Inthismodel,eachelastinmoleculeinthenetworkcanextendandcontractinamannerresemblingarandomcoil,sothattheentireassemblycanstretchandrecoillikearubberband.Theelastincoreiscoveredwithasheathofmicrofibrilswhicharecomposedofanumberofdistinctglycoproteins,includingthelargeglycoproteinfibrillin,whichbindstoelastinandisessentialfortheintegrityofelasticfibers.MutationsinthefibrillingeneresultinMarfan’ssyndrome,arelativelycommonhumandisorder.ComplexglycoproteinsoftheextracellularmatrixFibronectinandOtherMultidomainGlycoproteinsHelpOrganizetheMatrixThestructureofafibronectindimer.Tension-sensingbyfibronectin.SometypeIIIfibronectinrepeatsarethoughttounfoldwhenfibronectinisstretched.TheunfoldingexposescrypticbindingsitesthatinteractwithotherfibronectinmoleculesresultingintheformationoffibronectinfilamentslikethoseshowninFigure19–49.(FromV.VogelandM.Sheetz,Nat.Rev.Mol.CellBiol.7:265–275,2006.)Organizationoffibronectinintofibrilsatthecellsurface.Thisfluorescencemicrographshowsthefrontendofamigratingmousefibroblast.Extracellularfibronectinisstainedgreenandintracellularactinfilamentsarestainedred.Thefibronectinisinitiallypresentassmalldotlikeaggregatesneartheleadingedgeofthecell.Itaccumulatesatfocaladhesionsandbecomesorganizedintofibrilsparalleltotheactinfilaments.Integrinmoleculesspanningthecellmembranelinkthefibronectinoutsidethecelltotheactinfilamentsinside.Tensionexertedonthefibronectinmoleculesthroughthislinkageisthoughttostretchthem,exposingbindingsitesthatpromotefibrilformation.TensionExertedbyCellsRegulatestheAssemblyofFibronectinFibrilsSummaryofcalumeninandfibulin-1.Extracellularly,calumeninformscomplexwithfibulin-1,andinhibitsMMP-13-mediateddegradationoffibulin-TheBasa