Relative Functions of the α and β Subunits of the Proteasome Activator, PA28

摘要: Abstract PA28 is a 180,000-dalton protein that activates hydrolysis of small nonubiquitinated peptides by the 20 S proteasome. composed two homologous subunits, α and β, arranged in alternating positions ring-shaped oligomer with likely stoichiometry (αβ)3. Our previous work demonstrated carboxyl terminus subunit was necessary for to bind activate The goals this were define exact structural basis effect determine relative roles β subunits proteasome activation. Each various mutants expressed Escherichia coli purified. PA28α stimulated proteasome, but had much greaterK act than native heteromeric PA28. In contrast, PA28β unable stimulate Mutants which carboxyl-terminal tyrosine residue deleted or substituted charged amino acids could neither nor However, substitution other resulted proteins extents. Tryptophan as well did PA28, whereas serine phenylalanine poorer wild type PA28α. Deletion “KEKE” motif, 28-amino acid domain near PA28α, no on stimulatory activity. Hetero-oligomeric reconstituted from isolated mutant subunits. functional properties indistinguishable those hetero-oligomeric protein. molecules inactive remained inactive. suboptimally active same activity These results indicate modulates activity, perhaps influencing affinity