免疫球蛋白的结构与功能的关系课件

ImmunoglobulinStructure-FunctionRelationship

免疫球蛋白的结构与功能的关系SignallingantigenreceptorsonBcells-bifunctionalantigen-binding secretedmolecules（B细胞表面受体和分泌的抗体）Structuralconservationandinfinitevariability-domainstructure（结构上不仅保守而且无限可变的）.TheImmunoglobulinGeneSuperfamily（免疫球蛋白的超家族）Theimmunoglobulinfold（免疫球蛋白的折叠）Frameworkandcomplementaritydeterminingregions-hypervariable loops（框架结构和可变区）Modesofinteractionswithantigens（与抗原相互作用的模型）Effectormechanismsandisotype–roleoftheFc.（Fc区的作用）MultimericantibodiesandmultimerisationCharacteristicsandpropertiesofeachIgisotypeIgreceptorsandtheirfunctionsImmunoglobulinStructure-FunctionRelationshipCellsurfaceantigenreceptoronBcellsB细胞表面受体和分泌的抗体AllowsBcellstosensetheirantigenicenvironmentConnectsextracellularspacewithintracellularsignallingmachinerySecretedantibody（抗体）

Neutralisation（中和作用） Arming/recruitingeffectorcells（激活或者诱导功能细胞） Complementfixation（帮助机体对抗原的清除）ImmunoglobulinStructure-FunctionRelationshipStructuralconservationandacapacityforinfinitevariabilityina singlemoleculeisprovidedbyaDOMAIN

structure.（结构上不仅保守而且无限可变的-抗体结构域）Igdomainsarederivedfromasingleancestralgenethathas duplicated,diversifiedandbeenmodifiedtoendowan assortmentoffunctionalqualitiesonacommonbasicstructure（Ig结构域源于一个原始基因，复制，多元化，修饰等）Igdomainsarenotrestrictedtoimmunoglobulins（Ig结构域不仅仅局限于免疫球蛋白）.ThemoststrikingcharacteristicoftheIgdomainisadisulphide bond-linkedstructureof110aminoacidslong（Ig结构域最明显的特点是其双硫键，连接了110个氨基酸）.ImmunoglobulindomainsThegenesencodingIgdomainsarenotrestrictedtoIggenes.Althoughfirstdiscoveredinimmunoglobulins,theyarefoundinasuperfamilyofrelatedgenes,particularlythoseencodingproteinscrucialtocell-cellinteractionsandmolecularrecognitionsystems.IgSFmoleculesarefoundinmostcelltypesandarepresentacrosstaxonomicboundariesIggenesuperfamily-IgSFAntibodiesareProteinsthatRecognizeSpecificAntigens

抗体能够特异性的识别抗原ConsequencesofAntibodyBinding

抗体结合效应CLVLSSSSSSSSCH3CH2CH1VHFcFabF(ab)2Domainsarefolded,compact,proteaseresistantstructuresDomainStructureofImmunoglobulins免疫球蛋白的结构域Pepsincleavagesites-1x(Fab)2&1xFcPapaincleavagesites-2xFab1xFcLightchainCdomainskorlHeavychainCdomainsa,d,e,g,ormCH3CH3CH2CH1CH3CH2CH1VH1CH3CH2CH1VH1VLCH3CH2CH1VH1CLVLHingeCH3CH2CH1VH1VLCLElbowCH3CH2FbFvFvFvFbFvHingeElbowCH3CH2FbFvFlexibilityandmotionofimmunoglobulinsTheImmunoglobulinFoldThecharacteristicstructuralmotifofallIgdomainsBarrelunderconstructionAbarrelmadeofasheetofstavesarrangedinafoldedoversheetAbbarrelof7(CL)or8(VL)polypeptidestrandsconnectedbyloopsandarrangedtoencloseahydrophobicinteriorSingleVLdomainUnfoldedVLregionshowing8antiparallelb-pleatedsheetsconnectedbyloops.NH2COOHSSTheImmunoglobulinFoldImmunoglobulinsmustinteractwithafinitenumberof specialisedmolecules-EasilyexplainedbyacommonFcregionirrespectiveofspecificity-whilstsimultaneouslyrecognisinganinfinitearrayof antigenicdeterminants.Inimmunoglobulins,whatisthestructuralbasisfortheinfinitediversityneededtomatchtheantigenicuniverse?ImmunoglobulinsareBifunctionalProteinsFR1FR2FR3FR4CDR2CDR3CDR1Distinctregionsofhighvariabilityandconservationledtotheconcept ofaFRAMEWORK(FR),onwhichhypervariableregionswere suspended.FrameworkandHypervariableregionsAminoacidNo.Variability8010060402020406080100120Mosthypervariableregionscoincidedwithantigencontactpoints- theCOMPLEMENTARITYDETERMININGREGIONS(CDRs)HypervariableregionsHypervariableCDRsarelocatedonloopsattheendoftheFvregionsAntigensvaryinsizeandcomplexityProtein:InfluenzahaemagglutininHapten:5-(para-nitrophenylphosphonate)-pentanoicacid.AntibodiesinteractwithantigensinavarietyofwaysAntigeninsertsintoapocketintheantibodyAntigeninteractswithanextendedantibodysurfaceoragrooveintheantibodysurfaceCH3CH2FbFvFvFvFbFvHingeElbowCH3CH2FbFvFlexibilityandmotionofimmunoglobulins30stronglyneutralisingMcAb60stronglyneutralisingMcAbFabregions60weaklyneutralisingMcAbFabregionsHumanRhinovirus14-acommoncoldvirus30nmModelsofHumanRhinovirus14neutralisedbymonoclonalantibodiesElectronmicrographsofAntibodiesandcomplementopsonisingEpsteinBarrVirus(EBV)NegativelystainedEBVEBVcoatedwithacoronaofanti-EBVantibodiesEBVcoatedwithantibodiesandactivatedcomplementcomponentsAntibody+complement-mediateddamagetoE.coliHealthyE.coliElectronmicrographsoftheeffectofantibodiesandcomplementuponbacteriaNon-covalentforcesinantibody-antigeninteractionsElectrostaticforces AttractionbetweenoppositechargesHydrogenbonds HydrogenssharedbetweenelectronegativeatomsVanderWaal’sforces Fluctuationsinelectroncloudsaroundmolecules oppositelypolariseneighbouringatomsHydrophobicforces Hydrophobicgroupspacktogethertoexclude water(involvesVanderWaal’sforces)WhydoantibodiesneedanFcregion?DetectantigenPrecipitateantigenBlocktheactivesitesoftoxinsorpathogen-associated moleculesBlockinteractionsbetweenhostandpathogen-associated moleculesThe(Fab)2fragmentcan-InflammatoryandeffectorfunctionsassociatedwithcellsInflammatoryandeffectorfunctionsofcomplementThetraffickingofantigensintotheantigenprocessing pathwaysbutcannotactivateStructureandfunctionoftheFcregionCH3CH2IgAIgDIgGCH4CH3CH2IgEIgMThehingeregionisreplacedbyanadditionalIgdomainFcstructureiscommontoallspecificitiesofantibodywithinanISOTYPE(althoughthereareallotypes)ThestructureactsasareceptorforcomplementproteinsandaligandforcellularbindingsitesMonomericIgMIgMonlyexistsasamonomeronthesurfaceofBcellsCm4containsthetransmembraneandcytoplasmicregions.TheseareremovedbyRNAsplicingtoproducesecretedIgMMonomericIgMhasaverylowaffinityforantigenCm4Cm3Cm2Cm1N.B.OnlyconstantheavychaindomainsareshownCm3bindsC1qtoinitiateactivationoftheclassicalcomplementpathwayCm1bindsC3btofacilitateuptakeofopsonisedantigensbymacrophagesCm4mediatesmultimerisation(Cm3mayalsobeinvolved)Cm4Cm3Cm2Cm1N.B.OnlyconstantheavychaindomainsareshownPolymericIgMIgMformspentamersandhexamersCCCCCCMultimerisationofIgMCm4Cm3Cm2CCCm4Cm3Cm2CCCm4Cm3Cm2CCCm4Cm3Cm2CCCm4Cm3Cm2CCssssssCCss1.TwoIgMmonomersintheER (Fcregionsonlyshown)2.CysteinesintheJchainformdisulphidebondswithcysteinesfromeachmonomertoformadimer3.AJchaindetachesleavingthedimerdisulphidebonded.4.AJchaincapturesanotherIgMmonomerandjoinsittothedimer.5.Thecycleisrepeatedtwicemore6.TheJchainremainsattachedtotheIgMpentamer.Antigen-inducedconformationalchangesinIgMPlanaror‘Starfish’conformationfoundinsolution.DoesnotfixcomplementStapleor‘crab’conformationofIgMConformationchangeinducedbybindingtoantigen.EfficientatfixingcomplementIgMfactsandfiguresHeavychain:

m-MuHalf-life:

5to10days%ofIginserum: 10Serumlevel(mgml-1):

0.25-3.1Complementactivation:

++++byclassicalpathwayInteractionswithcells:

PhagocytesviaC3breceptors

EpithelialcellsviapolymericIgreceptorTransplacentaltransfer:

NoAffinityforantigen:

MonomericIgM-lowaffinity-valencyof2

PentamericIgM-highavidity-valencyof10IgDfactsandfiguresIgDisco-expressedwithIgMonBcellsduetodifferentialRNAsplicingLevelofexpressionexceedsIgMonnaïveBcellsIgDplasmacellsarefoundinthenasalmucosa-howeverthefunctionofIgDinhostdefenceisunknown-knockoutmiceinconclusiveLigationofIgDwithantigencanactivate,deleteoranergiseBcellsExtendedhingeregionconferssusceptibilitytoproteolyticdegradationHeavychain:

d-DeltaHalf-life:

2to8days%ofIginserum: 0.2Serumlevel(mgml-1):

0.03-0.4Complementactivation:

NoInteractionswithcells:

TcellsvialectinlikeIgDreceptorTransplacentaltransfer:

NoIgAdimerisationandsecretionIgAisthemajorisotypeofantibodysecretedatmucosalsufacesExistsinserumasamonomer,butmoreusuallyasaJchain-linkeddimer,thatisformedinasimilarmannertoIgMpentamers.JCCSSSSCCSSSSCCssIgAexistsintwosubclassesIgA1ismostlyfoundinserumandmadebybonemarrowBcellsIgA2ismostlyfoundinmucosalsecretions,colostrumandmilkandismadebyBcellslocatedinthemucosaeEpithelialcellJCCSSSSCCSSSSCCssSecretoryIgAandtranscytosisBJCCSSSSCCSSSSCCssJCCSSSSCCSSSSCCssJCCSSSSCCSSSSCCsspIgR&IgAareinternalised‘Stalk’ofthepIgRisdegradedtoreleaseIgAcontainingpartofthepIgR-thesecretorycomponentJCCSSSSCCSSSSCCssIgAandpIgRaretransportedtotheapicalsurfaceinvesiclesBcellslocatedinthesubmucosaproducedimericIgAPolymericIgreceptorsareexpressedonthebasolateralsurfaceofepithelialcellstocaptureIgAproducedinthemucosaIgAfactsandfiguresHeavychains:

a1

ora2-Alpha1or2Half-life:

IgA15-7days

IgA24-6daysSerumlevels(mgml-1):

IgA11.4-4.2

IgA20.2-0.5%ofIginserum: IgA111-14

IgA21-4Complementactivation:

IgA1-byalternativeandlectinpathway

IgA2-NoInteractionswithcells:

EpithelialcellsbypIgR

PhagocytesbyIgAreceptorTransplacentaltransfer:

NoToreducevulnerabilitytomicrobialproteasesthehingeregionofIgA2istruncated,andinIgA1thehingeisheavilyglycosylated.IgAisinefficientatcausinginflammationandelicitsprotectionbyexcluding,binding,cross-linkingmicroorganismsandfacilitatingphagocytosisIgEfactsandfiguresIgEappearslateinevolutioninaccordancewithitsroleinprotectingagainstparasiteinfectionsMostIgEisabsorbedontothehighaffinityIgEreceptorsofeffectorcellsIgEisalsocloselylinkedwithallergicdiseasesHeavychain: e-EpsilonHalf-life:

1-5daysSerumlevel(mgml-1):

0.0001-0.0002%ofIginserum: 0.004Complementactivation:

NoInteractionswithcells:

ViahighaffinityIgEreceptorsexpressed bymastcells,eosinophils,basophils andLangerhanscells

VialowaffinityIgEreceptoronBcells andmonocytesTransplacentaltransfer:

NoThehighaffinityIgEreceptor(FceRI)achainbchaing2SSSSSSCe1Ce1Ce2Ce2Ce3Ce3Ce4Ce4Ce1Ce1Ce2Ce2Ce3Ce3Ce4Ce4TheIgE-FceRIinteractionisthehighestaffinityofanyFcreceptorwithanextremelylowdissociationrate.BindingofIgEtoFceRIincreasesthehalflifeofIgECe3ofIgEinteractswiththeachainofFceRIcausingaconformationalchange.IgGfactsandfiguresHeavychains:

g1g2g3g4-Gamma1-4Half-life:

IgG1 21-24days IgG2 21-24days

IgG3 7-8days IgG4 21-24daysSerumlevel(mgml-1):

IgG1 5-12 IgG2 2-6

IgG3 0.5-1 IgG4 0.2-1%ofIginserum: IgG1 45-53 IgG2 11-15

IgG3 3-6 IgG4 1-4Complementactivation:

IgG1 +++ IgG2 + IgG3 ++++ IgG4 NoInteractionswithcells:

AllsubclassesviaIgGreceptorsonm