第2章蛋白质化学-jht(修改版)

第二章

蛋白质化学CHEMISTRYOFPROTEINS第一节蛋白质在生命活动中的重要生理功能IMPORTANTROLESOFPROTEINSINLIFE第二节蛋白质的分子组成MOLECULARCOMPOSITIONOFPROTEINS第三节蛋白质的分子结构MOLECULARSTRUCTUREOFPROTEINS第四节蛋白质结构与功能的关系RELATIONSHIPBETWEENFUNCTIONANDSTRUCTURE第五节蛋白质的理化性质PHYSICO-CHEMICALPROPERTIESOFPROTEINS第一节蛋白质在生命活动中的重要功能IMPORTANTROLESOFPROTEINSINLIFE●PROTEINCONTENSOFHUMANBODY

（人体蛋白质的含量）Carbohydrates（糖类）,Lipids（脂类）,Proteins（蛋白质）,NucleicAcids（核酸）,Water（水）,Middle/Smallorganic&inorganicMolecules（中小分子有机化合物及无机物分子）

15~20%expressedinwholebody（全重/湿重）~45%expressedindryweight（干重）Proteome(蛋白质组):ThecompletesetofproteinsinacellProteomics(蛋白质组学):Thecatalogingandanalysisofproteinstodeterminewhenaproteinisexpressed,howmuchismade,andwithwhatotherproteinstheproteinmayinteract●PROTEINMULTIFUNCTIONS（蛋白质的多功能）●EssentialCompositionofTissuesorCells

（组织或细胞的基本组成成分）

●MaintainingGrowth,RenewandRepair

（维持生长、更新和修复）●SpecificRoles（特殊功能）

Catalysis(催化):i.e.,enzymes(酶)Regulation(调节):e.g.,hormones(激素);regulatoryproteins(调节蛋白/转录因子)Transport(运输)：Hb,Apoprotein(载脂蛋白),Albumin(清蛋白)Motion/Mobile(运动、移动)：Actin(肌动蛋白),Myosin(肌球蛋白),Tubulin(微管蛋白)

Signaling(信号转导)：Gproteins,ATM/ATRStorage(储存)：Ferritin(铁蛋白)

Defence(防御/保护)：Immuniglobins(Igs)……●

OxidativeDegradationforProvidingEnergy（氧化降解供能）第二节蛋白质的分子组成MOLECULARCOMPOSITIONOFPROTEINS●MOLECULARCOMPOSITIONOFPROTEINS——ChemicalElements(化学元素)

C(50~55%),H(6~8%),O(19~24%),N(13~19%,average16%),

S(0.0~4.0%),Metal/non-metalZn、Fe、Mg、Cu…,P、IProteincontentin100gsample=

Ncontentpergram×6.25×100●STRUCTURALUNIT——AMINOACIDSA.AminoAcids(氨基酸)

L-α-aminoacidB.20AminoAcidsandIts’Structure(P.16-174)L-AlanineD-Alanine(SH)(H)R●PHYSICO-CHEMICALPROPERTIESOFAMINOACIDS(氨基酸的理化性质)DipolarStateofAminoAcids(氨基酸的两性解离):Zwitterion(兼性离子)；Isoelectricpoint(pI)(等电点)B.UVAbsorption(紫外吸收):aromaticaminoacidsW,Y,F

at280nmC.ColourReaction(呈色反应):D.NinhydrinReaction(茚三酮反应):

blue-violet,570nm;yellowP440nm;brownNE.PeptideFormation(成肽反应):residues(残基)H3N+—HC—COO-RH3N+—HC—COO-R+—→H3N+—H

OC—

CR—N—HC—COO-R|H–H2OGlutathione(GSH)第三节蛋白质的分子结构MOLECULARSTRUCTUREOFPROTEINSAminoAcidSequencesinPeptides(NtoC)●PEPTIDEBOND（肽键），PEPTIDEPLANE（肽平面）ANDPOLYPEPTIDE（多肽）●PRIMARYSTRUCTURE（一级结构）

φψ●SECONDARYSTRUCTURE（二级结构）Secondarystructurereferstoalocallyspatialarrangementofacertainpeptidesegmentbyhydrogenbondingbetweenpeptidebonds（基于氢键所导致的肽段在局部空间的排列形式）,i.e.,therelativepositionsofbackboneatomsofthispeptidesegment（肽段骨架原子的相对位置）.Hydrogenbondsareresponsibleforstabilizingthesecondarystructure.Therearefourcommontypesofsecondarystructure:

-helix（

-螺旋）,β-pleatedsheet（β-折叠/β-片层）,-turn(

-bend)（β-转角）,Ω-loop(Ω-环)andrandomcoil（随机卷曲）.The

-helix

structuredependsonintramolecular

hydrogenbondingbetweenthe-NHand–COgroupsofpeptidebonds.Alongtheaxisofan

-helix,theriseperaminoacidresidueis1.5Å,andthereare3.6residuesperturn,whichmakesthepitchofeachturn5.4Å.Most

-helicesofknownpolypeptidesareright­-handed.Some(e.g.,myoglobin,Hb)haveahighpercentageof

-helicalstructures;others(chymotrypsinandCytc)havealowpercentage.Theaminoacidsequenceinfluencethedegreeofhelicalstructureinagivenpolypeptide.Theβ-pleatedsheetstructuredependsoninter­molecular(interchain)

hydrogenbonding.Oneofthesestructuresistheantiparallel

β-pleatedsheet,inwhichtheindividualpolypeptidechainisextendedandismaximallybondedtotwoneighboringpolypeptides.Inanantiparallelstructure,theneighboringpolypeptidesarealignedinanoppositeN-to-Cterminusdirection.Ifinaβ-pleatedstructure,thehydrogen-bondedneighboringpolypeptidesarealignedinthesameN-to-Cdirection,thestructureisparallelβ-pleated.SUPERSECONDARYSTRUCTURE（超二级结构）:Adistinctfoldingpatternforelementsofsecondarystructure,observedinoneormoreproteins;alsocalledamotiforfold.(局部肽段中相连的几个二级结构单元在空间的折叠形式，即超二级结构，又称基序或模体)CD4consistsoffoursimilardomainsDOMAIN(域结构):Adistinctstructuralunitofapeptide（肽链中不同的结构单位即结构域，或域结构）;domainsmayhaveseparatefunctionsandmayfoldasindependent,compactunits●TERTIARYSTRUCTURE（三级结构）HydrogenBonding,SaltingBond,HydrophobicInteraction,DisulfidebondVanderWaal’sForce●QUATERNARYSTRUCTURE（四级结构）Subunits（亚基）ProstheticGroup/Co-factor（辅助基团/辅助因子）

第四节蛋白质结构与功能的关系PROTEINFUNCTIONISRELATEDTOITSSTRUCTURE●PRIMARYSTRUCTUREISTHEBASEOFHIGHSTRUCTUREANDFUNCTION(一级结构是高级结构、功能的基础)

A.ProteinswithSimilarStructuresHaveSimilarFunctionsB.ProteinswithDifferentStructuresHaveDifferentFunctionsC.PrimaryStructureDetermines2nd/3rd/4thStructureD.PrimaryStructureDeterminesFunctionsE.Moleculardiseases（分子病）C-Y-I-Q-N-C-P-L-G-NH2SSC-Y-F-Q-N-C-P-R-G-NH2SSADH加压素Oxytocin催产素●PROTEINFUNCTIONRELATESTOITSCONFORMATION(蛋白质构象表现功能）A.AllostericEffect&AllostericRegulation（别位效应与别为调节）

B.Denaturation/Renaturation&Function（变性、复性与功能）C.ActivationofZymogen（酶原的激活）D.ConformationalDiseases（构象病）activeinactiveactiveO2O2O2O2O2第五节蛋白质的理化性质PHYSICO-CHEMICAL