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分子生物物理学.ppt

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MolecularBiophysics分子水平Biopolymers:Nucleicacid(DNARNA)ProteinPROTEINSTRUCTURESecondaryStructureChiralzwitterionClassificatoryofaminoacidbasedsidechains(Rgroups)?ProteinPrimaryStructurePeptidebondphi(F)psi(Y)andomega(W)H-bonddefinitionH-bondlocationO….H-XProteinSecondaryStructureHelicesrepetitivesecondarystructurea-helixintroductiona-heliceshave3.6aminoacidresiduesperturni.e.ahelix36aminoacidslongwouldform10turns.thephiandpsianglesofthealphahelixlieinthecenterofanallowedminimumenergyregionoftheRamachandran(phipsi)map.thedipolesofhydrogenbondingbackboneatomsareinnearperfectalignment.theradius(2.3angstrom)ofthehelixallowsforfavorablevanderWaalsinteractionsacrossthehelicalaxisCOgrouptowardcarboxylterminusNHgrouptowardamideterminusH-bondi-(i+4)Sidechain:i-(i+3);i-(i+4)interactionsbetweeniandi+4stabilizehelixDistortionsofa-helices310helixintroductionStandard310helixProlinehelixp-helicesintroductionthephiandpsianglesofthepurepihelix(-57.1-69.7)lieattheveryedgeofanallowedminimumenergyregionoftheRamachandran(phipsi)map.thepihelixrequiresthattheangletau(N-Ca-C')belarger(114.9)thanthestandardtetrahedralangleof109.5degrees.thelargeradiusofthepihelixmeansthepolypeptidebackboneisnolongerinvanderWaalscontactacrossthehelicalaxisforminganaxialholetoosmallforsolventwatertofill.sidechainsaremorestaggeredthantheideal3.10helixbutnotaswellasthealphahelix.H-bond:1-5alpha-helixsurfaceofproteinbarrieramphiphilicproteindesignprojectsbyDegradoUSAHelixdipoleSheet-139and+135ParallelsheetTwistsParallelsheetsarelesstwistedthananti-parallelandarealwaysburied.BulgesTurnGamma-turnTypeIandI’turnThebackbonedihedralanglesofresidueare(-60120)and(800)ofresiduesi+1andi+2respectivel