中山大学生物化学PPT课件

liguofu,.,1,4ProteinFunction,4.1Generalfeatures4.2Oxygen-bindingproteins4.3Immunoglobulins4.4Musclecontraction,liguofu,.,2,4.1Generalfeatures,VersatileinfunctionBeinghardtostudyFunctionviainteraction,Theinteractionwithothermolecule(ligand)isreversible.Theinterfacebetweenthebindingsiteiscomplementaryinstructure,makingsuchinteractionhighlyspecific.Structuredynamicnessofaproteinisusuallyessentialforsuchinteractions.,liguofu,.,3,4.1Generalfeatures4.2Oxygen-bindingproteins4.3Immunoglobulins4.4Musclecontraction,4ProteinFunction,liguofu,.,4,Quantitativedescriptionofinteraction(1),Protein+nLigandPLn,liguofu,.,5,Quantitativedescriptionofinteraction(2),Ifkdisconstant,liguofu,.,6,Quantitativedescriptionofinteraction(3),Ifkdisnotconstant,liguofu,.,7,Quantitativedescriptionofinteraction(4),liguofu,.,8,Quantitativedescriptionofinteraction(5),liguofu,.,9,Theiron-porphyrininhemoglobinaccountsfortheredcolorofblood,thecopper-porphyrininhemocyaninforbluecolorofblood,andthemagnesium-porphyrininchlorophyllisresponsibleforthegreenofplants.,liguofu,.,10,StructureofPorphyrin,Pyrrolering,Methenebridge,liguofu,.,11,Oxygencanbeboundtoaheme(1),Heme=ProtoporphyrinIX+Fe2+,NoneoftheaasidechainsinproteinsissuitedforreversiblebindingO2,Hemeprostheticgroup,Transitionmetals,Fethefirsttobeassociatedwithaspecificphysiologicalfunction(around1875);oneofthefirstproteinstohaveitsmolecularweightdeterminedcorrectly(64,500);thefirsteukaryoticmessenger(mRNA)tobeisolatedandsubsequentlysequenced.thefirsteukaryoticproteintobesynthesizedinacell-freesysteminvitro;thesecondproteinhavingits3-Dstructuredetermined(1969).,liguofu,.,19,The“redcoloringmatter”(hemoglobin)ofanimalbloodcouldbebroughttocrystallization,withcrystalformscharacteristicoftheirbiologicalorigins(1840s-1860s).Reversibleinterconversionofoxyhemoglobinanddeoxyhemoglobinwasrevealedbyusingspectroscope(1860s).Treatmentofhemoglobinwithacidgaveacolorlessalbuminoidconstituent(globin)andarediron-containingmaterial(by1870).Thestructureofhemewaselucidatedtobeatetrapyrrol(porphyrin)derivativebychemicalsynthesis(HansFischer,1929).Similartetrapyrrolderivativesarealsousedasprostheticgroupsofotherproteins(e.g.,thecytochromesthatfunctioninbiologicaloxidationandphotosynthesis!,liguofu,.,20,Hbhasfoursubunits,Mr=64,500,141residues,146residues,liguofu,.,21,Hbsubunitsarestructurallysimilartomyoglobin,subunitlackstheshortDhelix,Dhelix,liguofu,.,22,conservedinallknownglobins,conserved,27positionsareidentical,18%,82,143,liguofu,.,23,30residues,Interactionsinthefoursubunits,19residues,19residues,HydrophobicinteractionsHbondsSaltbonds,liguofu,.,24,ThisiscalledTensestate(deoxyHb),Someionpairsarenotshownhere,Ionpairsatthe1/2and2/1interface(1),liguofu,.,25,Ionpairsatthe1/2and2/1interface(2),IonpairsstabilizetheTstateofdeoxyHb,liguofu,.,26,QuantitativedescriptionofHbbindingO2（1）,liguofu,.,27,Hillplot,nH:hillcoefficient,QuantitativedescriptionofHbbindingO2（3）,liguofu,.,28,HbundergoesastructuralchangeonbindingO2(1),TensestateismorestableandthusthepredominantconformationofdeoxyHb,RelaxedstateisthepredominantconformationofhigheraffinitytoO2,BindingO2,ValE11,liguofu,.,29,IntheTstate,theporphyrinisslightlypuckered,causingthehemeirontoprotrudesomewhatontheproximalHis(HisF8)side.ThebindingofO2causesthehemetoassumeamoreplanarconformation,shiftingthepositionofHisF8andFhelix.,HbundergoesastructuralchangeonbindingO2(2),liguofu,.,30,Allostericproteinisoneinwhichthebindingofaligandtoonesiteaffectsthebindingpropertiesofanothersiteonthesameprotein.Modulatorisamoleculethatbindstoanallostericproteinandaffectsitsbindingproperties.Homotropic:thenormalligandandmodulatorareidentical.Heterotropic:thenormalligandandmodulatorarenotidentical.Someproteinshavetwoormoremodulatorsandthereforecanhavebothhomotropicandheterotropicinteractions.,Hemoglobinbindsoxygencooperatively,liguofu,.,31,Twomodelforcooperativebinding,ConcertedModelMWCModel,SequentialModel,liguofu,.,32,HemoglobintransportsCO2,carbonicanhydrase,15%to20%,80%to85%,liguofu,.,33,HemoglobinalsotransportsH+,Bohreffect,H+bindsto:NHofHis146inb4N-terminalNH2Others:Arg,Lys,liguofu,.,34,O2bindingtoHbisregulatedbyBPG(1),liguofu,.,35,O2bindingtoHbisregulatedbyBPG(2),liguofu,.,36,BindingofBPGtodeoxy-HbstabilizestheT-state,thuslowerstheO2affinityofHb.,OnlyoneBPGbindstoeachdeoxy-Hbtetramer,liguofu,.,37,TheBPGbindingpocketexistsintheT-state,butdisappearsintheR-stateofHb.,T-state(deoxy-Hb),R-state(oxy-Hb),PositivelychargedgroupsthatBPGinteractswith,Infetushemoglobin(a2g2),theconversionofb-His143tog-ser143resultsinthedecreaseoftheaffinityofBPG,liguofu,.,38,MutantHbsprovidedauniqueopportunitytostudystructure-functionrelationshipsinproteins,Many(500)Hbgeneticvariants,mostly(95%)withasingleaminoaciddifference,havebeenidentifiedinthehumanpopulation.Mostofsuchvariationhaveaveryminoreffectontheproteinstructureandfunction.Somedocausedebilitatingdiseases(e.g.,thosefromsicklecellanemia.)Deleteriousmutationsaremostlyclusteredaboutthehemepocketsandinthevicinityofthea-bcontactregionthatisimportantintheallosterictransition.,liguofu,.,39,Distributionofmutationsinhumanhemoglobin,GluVal,Sicklecellanemia,liguofu,.,40,liguofu,.,41,Sicklecellanemiaiscausedbyasingleaminoacidreplacementonthebsubunit:Glu6Val,liguofu,.,42,GluVal,liguofu,.,43,liguofu,.,44,Electronmicrographofdeoxy-HbSfibersspillingoutofarupturederythrocyte.,Thesickledcellsarefragile.Theirbreakdownleadstoananemiathatleavesthevictimsusceptibletoinfectionsanddiseases.,liguofu,.,45,Theelongatedcellstendtoblockcapillaries,causinginflammationandconsiderablepain,liguofu,.,46,ByLinusPaulingin1949.,1903,1987,Normal,Trait,Patient,(Normal),(defective),liguofu,.,47,TheHbSalleleconfersasmallbutsignificantresistancetomalariainheterozygousindividuals,TheHbSallele(i.e.,sicklecelltrait)wasfoundcommonincertainpartsofAfrica.Plasmodium(aprotozoancausingmalaria)increasestheacidityoferythrocyte,favoringtheformationofdeoxy-HbS(theBohreffect),thusprobablyallowingthespleentopreferentiallyremovetheinfectedredcells.,liguofu,.,48,4.1Generalfeatures4.2Oxygen-bindingproteins4.3Immunoglobulins4.4Musclecontraction,4ProteinFunction,liguofu,.,49,liguofu,.,50,Structureofimmunoglobulin(1),liguofu,.,51,Structureofimmunoglobulin(2),H=HeavychainL=LightchainC=ConstantV=VariableCHO=carbohydrate,liguofu,.,52,Structureofimmunoglobulin(3),liguofu,.,53,StructureofVariableRegion(1),LightChain,HeavyChain,CDRs:complementarity-determiningregionsHypervariableloops,liguofu,.,54,StructureofVariableRegion(2),HeavyChain,liguofu,.,55,Antibodybindtightly&specificallytoantigen(1),Smallantigen,liguofu,.,56,Smallantigen,Antibodybindtightly&specificallytoantigen(2),Largeantigen:lysozyme,AntibodyI,AntibodyII,V,C1,liguofu,.,57,liguofu,.,58,Fiveclassesofimmunoglobulins(1),liguofu,.,59,liguofu,.,60,抗体的作用：例,liguofu,.,61,Polyclonal/Monoclonalantibody,liguofu,.,62,liguofu,.,63,4.1Generalfeatures4.2Oxygen-bindingproteins4.3Immuneproteins4.4Musclecontraction,4ProteinFunction,liguofu,.,64,Musclestructure,liguofu,.,65,Musclestructure,liguofu,.,66,Musclecontraction,liguofu,.,67,Musclecontraction,liguofu,.,68,Actinmolecules,Tropomyosinmolecules,Troponinmolecules,Crossbridges(headgroupsofmyosinmolecules),Actin,Tropomyosin,Troponin,Myosinmolecule,headgroups,Splitbypapain,Thinfilament,Thinfilament,Thickfilament,liguofu,.,69,Myosin(1),325nm,liguofu,.,70,Myosin(2),liguofu,.,71,Myosin(3)：S1structure,liguofu,.,72,Myosin(3)：S1structure,liguofu,.,73,GactinFactin(1),liguofu,.,74,GactinFactin(2),liguofu,.,75,GactinFactin(3),liguofu,.,76,InteractionbetweenmyosinandF-actin,liguofu,.,77,Step1,Step2,The“powerst