title: Properties of the beta subunit of the proteasome activator PA28 (11S REG).
abstract: The proteasome activator PA28 (11S REG) is composed of two homologous subunits termed alpha and beta. The properties of the recombinant beta-subunit were explored and compared to the properties of the recombinant alpha-subunit. PA28beta produced in an Escherichia coli expression system migrates on a calibrated gel filtration column as an apparent heptamer (Mr = 250,000). Low concentrations of SDS (0.005%), dissociate the protein to a monomer (Mr = 33,000). PA28beta, has a complex effect on proteasome activity. At concentrations which favor oligomerization (> 2 microM), PA28beta is a strong proteasome activator although its affinity for the proteasome is about 10-fold less than recombinant PA28alpha. The catalytic properties of the PA28alpha and PA28beta-activated proteasome are similar. At low concentrations, PA28beta is a monomer and a potent allosteric proteasome inhibitor. These studies show that oligomerization of PA28beta is required for proteasome activation and that PA28beta monomers are potent proteasome inhibitors.
authors.affiliation: Department of Pharmacology, Mount Sinai School of Medicine, New York, New York 10029, USA. sherwin.wilk@mssm.edu
authors.forename: S
authors.initials: S
authors.lastname: Wilk
authors.forename: W E
authors.initials: WE
authors.lastname: Chen
authors.forename: R P
authors.initials: RP
authors.lastname: Magnusson
mesh_terms: D000494:Allosteric Regulation; D000818:Animals; D001704:Biopolymers / Q000378:metabolism; D002417:Cattle; D002918:Chymotrypsin / Q000737:chemistry; D003546:Cysteine Endopeptidases / Q000378:metabolism*; D010450:Endopeptidases / Q000378:metabolism; D004789:Enzyme Activation; D004926:Escherichia coli; D018841:HSP90 Heat-Shock Proteins / Q000494:pharmacology; D009097:Multienzyme Complexes / Q000037:antagonists & inhibitors / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex; D011506:Proteins / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology; D011994:Recombinant Proteins / Q000378:metabolism / Q000494:pharmacology
chemical_list: D001704:Biopolymers; D018841:HSP90 Heat-Shock Proteins; D009097:Multienzyme Complexes; D011506:Proteins; D011994:Recombinant Proteins; D010450:Endopeptidases; D002918:Chymotrypsin; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex; C114177:peptidylglutamylpeptide hydrolase