Details
PA28 (also called the 11S regulatory complex) is another activator of the 20S proteasome, which assembles on either one or both ends of the 20S proteasome in an ATP-independent manner. PA28 can greatly enhance the peptidase activities of the 20S proteasome, but not for degradation of ubiquitinated proteins. The PA28 activator is a complex of two alternating homologous subunits, PA28α and PA28β, which assembles as a hexameric ring with an α3β3 stoichiometry. PA28α and PA28β are induced by interferon. Functionally, PA28 enhances the generation of class I peptides for antigen presentation. The third subunit, PA28γ, was recently identified in the nucleus. Recombinant PA28α and PA28β form a heptomeric ring; whereas PA28γ forms a hexameric ring. All of them can stimulate the peptidase activities of the 20S proteasome.
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Coomassie-stained SDS-PAGE
Lane 1: Molecular weight markers
Lane 2: 5 µg purified 6xHis-PA28gamma
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Activation of 5 nM 20S proteasome (Cat. # A1400) by 25 nM PA28γ (Cat. # A2300), the proteasome activity was assayed by using 50 µM Suc-LLVY-AMC (Cat. # G1100) as the substrate. The AMC fluorescence was monitored by a plate reader with excitation and emission filters of 360±40 nm and 460±30 nm, respectively.
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