Properties of the Beta Subunit of the Proteasome Activator PA28 (11S REG)

• Published in: Archives of biochemistry and biophysics Vol. 384; no. 1; pp. 174 - 180
• Main Authors: Wilk, Sherwin, Chen, Wei-Er, Magnusson, Ronald P.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.12.2000
• Subjects: 11S regulator; Allosteric Regulation; Animals; Biopolymers - metabolism; Cattle; Chymotrypsin - chemistry; Cysteine Endopeptidases - metabolism; Endopeptidases - metabolism; Enzyme Activation; Escherichia coli; HSP90 Heat-Shock Proteins - pharmacology; multicatalytic proteinase complex; Multienzyme Complexes - antagonists & inhibitors; Multienzyme Complexes - metabolism; PA28; proteasome; proteasome activator; Proteasome Endopeptidase Complex; proteasome inhibitor; Proteins - genetics; Proteins - metabolism; Proteins - pharmacology; Recombinant Proteins - metabolism; Recombinant Proteins - pharmacology; proteasome; PA28; proteasome inhibitor; 11S regulator; multicatalytic proteinase complex; proteasome activator
• ISSN: 0003-9861; 1096-0384
• DOI: 10.1006/abbi.2000.2112

The proteasome activator PA28 (11S REG) is composed of two homologous subunits termed α and β. The properties of the recombinant β-subunit were explored and compared to the properties of the recombinant α-subunit. PA28β 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). PA28β has a complex effect on proteasome activity. At concentrations which favor oligomerization (> 2 μM), PA28β is a strong proteasome activator although its affinity for the proteasome is about 10-fold less than recombinant PA28α. The catalytic properties of the PA28α and PA28β-activated proteasome are similar. At low concentrations, PA28β is a monomer and a potent allosteric proteasome inhibitor. These studies show that oligomerization of PA28β is required for proteasome activation and that PA28β monomers are potent proteasome inhibitors.