组蛋白的泛素化与去泛素化

Histoneubquitination&deubquitinationThestructureofnucleosome组蛋白是一种11-15KDa的碱性蛋白，与DNA相互作用构成核小体。核心组蛋白的尾巴伸出来，受到广泛的修饰。Ubquitin泛素(ubiquitin，Ub)是高度保守的、含76个氨基酸的蛋白质，分子量为8.5kDa，在真核生物体内广泛存在。泛素分子氨基端1-72位点的氨基酸残基形成一个紧密球状结构，紧靠羧基端的4个氨基酸残基是随机盘绕的（random-coiled）。Ubiquitination&Deubiquitination泛素化修饰就是底物的赖氨酸残基位点与泛素分子的羧基末端相互结合的过程。由于泛素本身的7个赖氨酸位点,也可与另一个泛素相结合,因此单泛素化的底物蛋白,可作为Seed，结合多个泛素，形成了多泛素化修饰。GENES&DEVELOPMENT17:2733–2740.2003byColdSpringHarborLaboratoryPressHistoneUbiquitinationHistoneubiquitination•Primarymonoubiquitination•reversible，regulatedbyubiquitinaseanddeubquitinase•Histonemodificationscrosstalk•Involvedinmultiplecellularevents---geneexpressionregulation、DNAdamageresponseandrepair、femaleXchromosomeinactiveandsoon除了单泛素化，H2A/H2AX在DNA损伤时可发生K63位的多泛素化负责H2A/H2B泛素化与去泛素化的酶H2A-specificCommontoH2A/H2BH2B-specificHistoneubiquitinaseOneE1(activating),mutipleE2(conjugating),substrate-specificE3(ligase)SchematicdepictionofhistoneubiquitinationMethods.2011Jul;54(3):315–325.E3主要有两大类:HECT(homologoustotheE6-APcarboxylterminus)结构域家族，通过与泛素形成催化作用所必需的硫酯键发挥作用RING(reallyinterestingnewgene)结构域家族，为E2和底物提供居留位点从而使E2催化泛素转移到底物上Histonedeubiquitinatingenzyme（DUBs）H2AdeubiquitinationUSP16：HOXgenesilencing,DNAdamagerepairXchromosomeinactivation,cellcycleprogression2A-DUB：interactswithPCAFUSP21：regulatorofliverregenerationBAP1：C-terminalhydrolase,repressionofHOXgenesH2BdeubiquitinationUbp8：residewithinSAGA，TranscriptionUbp10（Dot4）：Sir-mediatedtelomericandrDNAsilencingFunctionofHistoneUbiquitination•Transcriptionregulation•DNAdamageresponse•inactiveXchromosome：H2Aub•chromatinboundaryintegrity：H2Bub•stemcellmaintenanceanddifferentiationHistoneUbiquitinationandDeubiquitinationinTranscription,DNADamageResponse,andCancer.FrontOncol,2(26),CaoJ&YanQ,2012Regulationofcellcycleprogression—chromosomesegregationduringmitosis•Ubp-M(USP16)candeubiqutinateH2A.•Duringthecellcycle,Ubp-Missequentiallyphosphorylatedanddephosphorylated,potentiallybythecdc-2/cyclinBcomplex.•Ubp-MisessentialforSer-10H3phosphorylationmediatedbytheAuroraBkinaseandisrequiredforchromosomesegregationduringmitosis.CellReports,Volume10,Issue2,2015,226-238:ataxiatelangiectasiamutatedDSB:DNAdouble-strandbreakRNF:Ringfingerligase（E3）DDR:DNAdamageresponse53BPI：p53bindingprotein1Transcriptionregulation•H2A与H2B的单泛素化与转录调节有关:H2Aub与基因沉默有关,H2Bub与基因活化有关【CHIP-on-chip实验证明ubH2A在卫星区，ubH2B在转录活化基因的主体】•H2A/H2B泛素化机制：co-transcriptionmechanism•H2B的泛素化与去泛素化的循环与转录起始及延伸有密切关系ubH2A&silence•H2A-specificE3：Ring1B，2A-HUB，与转录沉默有关•Ring1B存在于3种不同的转录抑制复合物PRC1,BCoR及E2F6.com-1中•2A-HUB与N-CoR/HDAC1/3complex联系，定位于chemokinegenes的启动子处，阻断FACT的招募a.HistoneH2AMonoubiquitinationRepressesTranscriptionby•H3K4methylationisessentialforpreinitiationcomplex(PIC)formation.•UbiquitylationofH2Adoesinhibitpreinitiationcomplexformation,notinadirectwaybutindirectlybypreventingH3K4methylation.•DeubiquitylationofhistoneH2AbyUSP21activatestranscriptionalinitiationviatrans-histonecrosstalkwithH3K4di-andtri-methylation.Fig.1–Modeloftranscriptionalinitiationfromchromatintemplate.InhibitingPICformationb.HistoneH2AMonoubiquitinationRepressesTranscriptionby•2A-HUB:aH2A–specificubiquitinligase,catalyzesmonoubiquitinationofH2AatK119•H2AmonoubiquitinationactstopreventFACTrecruitmentatthetranscriptionalpromoterregion,blockingRNApolymeraseIIreleaseattheearlystageofelongation.MolecularCell,MGRosenfeld,1(29),2008InhibitingRNAPIITranscriptionalElongationFACT:facilitateschromatintranscription二聚体，包括SPT16和SSRP1，能从核小体中置换出H2A/H2B二聚体，进而促使染色体介导的转录延伸抑制得到释放Fig.1.ThediverseactivitiesofH2Bub1.H2Bmonoubiquitylationanddeubiquitylationcandirectlymodulatethechromatinstatebyalteringnucleosomestability,promotingpartialnucleosomedisassemblyandreassembly,andregulatingchromatinhigher-orderstructure.modulatechromatinindirectlythroughthebindingorrepulsionofspecificreaders,whichcallintoactionaplethoraofproteinsandproteincomplexeswithdiversebiochemicalactivities.ThedirectandindirectmechanismsarenotmutuallyexclusiveE.g.relaxationofhigher-orderchromatinstructureisexpectedtofacilitatetheaccessofH2Bub1readers注：H2Bub1即对K120进行泛素化G.Fuchs,M.Oren/BiochimicaetBiophysicaActa1839(2014)694–701H2BH2BUbiquitinationRequiresEarlyStepsinTranscriptionElongation(Co-Transcription)1.酸性激活蛋白GAL4招募H2B特异的泛素酶复合物到启动子区2.在与PAF、BUR（对Rad6的Ser120磷酸化）、延伸形式的RNAP2（其CTD的Ser5被Kin28磷酸化）的作用下，泛素酶复合物对H2B的K120位进行泛素化（co-transcription）ModelfortheregulationofchromatindynamicsbyH2Bubiquitinationanddeubiquitinationduringtranscriptionelongation.Rad6andBre1associatewiththePaf1complexandtravelwiththeelongatingformofRNAPol(iandii)Rad6/Bre1-mediatedH2Bub1stabilizesthenucleosomeinfrontofthepolymerasetocounteractanytorsionalstressandmightactsasa“checkpoint”tocoordinatetranscription-coupledevents,suchas,allowingthebindingofSpt16/FACTandrestrictingCtk1bindingtochromatin.泛素化稳定(B)In(i),Ubp8,acomponentoftheSAGAsub-complexthattravelswithRNAPolII,removestheconjugatedubiquitintodestabilizethenucleosome.(ii)ThisfacilitatesnucleosomedisassemblybySpt16/FACT.(iii)DeubiquitinationbyUbp8all