The26Sproteasomeisanapproximately2.5mDalargecomplexcomposedofthe20Sproteasomeandthe19Sregulatoryparticle(alsocalledPA700inmammals).The20Sproteasomehas28subunitsthatformabarrel–shapedstructurearrangedasfourheptomericringofαββα.Threeβsubunitshavepeptidaseactivitiesthathydrolyzeproteins.Eitheroneorbothendsofthe20SproteasomecanassociatewithPA700toformthe26Sproteasome.PA700contains19differentproteinsthathavethe
ABIlitytobind,deubiquitinateandunfoldpolyubiquitinatedproteinswiththeconsumptionofATPhydrolysis.The26Sproteasomedegradespolyubiquitinatedproteins,whichplaysessentialrolesinregulatingvariouscellulareventsincludingproteinqualitycontrol,genetranscriptionandsignaltransduction.