中山大学生物化学课件.ppt

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1、§4ProteinFunction§4.1Generalfeatures§4.2Oxygen-bindingproteins§4.3Immunoglobulins§4.4Musclecontractionliguofu§4.1GeneralfeaturesVersatileinfunctionBeinghardtostudyFunctionviainteractionTheinteractionwithothermolecule(ligand)isreversible.Theinterfacebetweenthebindingsiteiscomplementaryinstr

2、ucture,makingsuchinteractionhighlyspecific.Structuredynamicnessofaproteinisusuallyessentialforsuchinteractions.liguofu§4.1Generalfeatures§4.2Oxygen-bindingproteins§4.3Immunoglobulins§4.4Musclecontraction§4ProteinFunctionliguofuQuantitativedescriptionofinteraction(1)Protein+nLigandPLnliguo

3、fuQuantitativedescriptionofinteraction(2)IfkdisconstantliguofuQuantitativedescriptionofinteraction(3)IfkdisnotconstantKdliguofuQuantitativedescriptionofinteraction(4)liguofuQuantitativedescriptionofinteraction(5)liguofuTheiron-porphyrininhemoglobinaccountsfortheredcolorofblood,thecopper-po

4、rphyrininhemocyaninforbluecolorofblood,andthemagnesium-porphyrininchlorophyllisresponsibleforthegreenofplants.liguofuStructureofPorphyrinPyrroleringMethenebridgeliguofuOxygencanbeboundtoaheme(1)Heme=ProtoporphyrinIX+Fe2+NoneoftheaasidechainsinproteinsissuitedforreversiblebindingO2Hemeprost

5、heticgroupTransitionmetals,Fe&Cu,haveastrongtendencytobindO2needmorecommonlyliguofuOxygencanbeboundtoaheme(2)Heme=ProtoporphyrinIX+Fe2+FreeIronpromotestheformationofhighlyreactiveoxygenspeciessuchashydroxylradicals.CoordinatedNatomshelppreventtheconversionofFe2+toFe3+liguofuMbhasasinglebin

6、dingsiteforoxygenMyoglobin:153residues,16700DaHis93/F8His64/E7liguofuOxygencanbeboundtoaheme(3)Infreehememolecules,reactionofoxygenatoneofthetwo“open”coordinationbondsofironcanresultinirreversibleconversionofFe2+toFe3+Inheme-containingproteins,thisreactionispreventedbysequesteringthehemede

7、epwithinaproteinstructurewhereacesstothetwo“open”coordinationbondsisrestricted.Oneofthesetwocoordinationbondsisoccupiedbyaside-chainNofaHisresidue.NOCOAlsoliguofuQuantitativedescriptionofMbbindingO2liguofuProteinstructureaffectsligandsbind(1)InfreehemeorInmyog