Homingin:mechanismsofsubstratetargetingbyproteinkinasesChadJ.MillerandBenjaminE.Turk*DepartmentofPharmacology,YaleSchoolofMedicine,NewHaven,CT06520,USAAbstractProteinphosphorylationisthemostcommonreversibleposttranslationalmodificationineukaryotes.Humanshaveover500proteinkinases,ofwhichmorethanadozenareestablishedtargetsforanti-cancerdrugs.Allkinasesshareastructurallysimilarcatalyticdomain,yeteachoneisuniquelypositionedwithinsignalingnetworkscontrollingessentiallyallaspectsofcellbehavior.Kinasesaredistinguishedfromoneanotherbasedontheirmodesofregulationandtheirsubstraterepertoires.Couplingspecificinputstothepropersignalingoutputsrequiresthatkinasesphosphorylatealimitednumberofsitestotheexclusionofhundredsofthousandsofoff-targetphosphorylationsites.Here,wereviewrecentprogressinunderstandingmechanismsofkinasesubstratespecificityandhowtheyfunctiontoshapecellularsignalingnetworks.KeywordsProteinkinase;proteinphosphorylation;enzymespecificity;linearsequencemotif;proteininteractionsPrinciplesofproteinkinasesubstratespecificityProteinkinasesselectivelytargetspecificsubstratesthroughseveraltypesofphysicalinteractions(Figure1)[1,2].Forexample,itisself-evidentthatthephosphorylatedaminoacidresiduemustinteractatleasttransientlywiththeactivesiteofthekinase.Eukaryoticproteinkinasesaregenerallysubdividedintotyrosinekinases(TyrKs),serine-threoninekinases(STKs)anddual-specificitykinasesbasedontheirfavoredsubstratephosphoacceptorresidues,whicharedeterminedbyconservedfeaturesofthekinaseactivesiteuniquetoeachclass[3].Aswithotherprotein-modifyingenzymes,kinaseshavebroadcatalyticcleftsthataccommodatemultipleresiduesflankingthesiteofphosphorylation,leadingtospecificityatthelevelofphosphorylationsitesequence[4,5].However,asarule,catalyticsiteinteractionsaloneareinsufficienttomediateselectionofproteinsubstrates.Kinaserecognitionmotifstypicallyconsistofonlyonetothreeresiduesthatarecriticalforefficientphosphorylation(Table1).Asaconsequence,essentiallyallproteinswillharbor*Correspondence:be...
