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Publication Abstract from PubMed

The heptameric proteasome activator (PA) 28alphabeta is known to modulate class I antigen processing by docking onto 20S proteasome core particles (CPs). The exact stoichiometry and arrangement of its alpha and beta subunits, however, is still controversial. Here we analyzed murine PA28 complexes regarding structure and assembly. Strikingly, PA28alpha, PA28beta, and PA28alphabeta preparations form heptamers, but solely PA28alpha and PA28alphabeta associate with CPs. Co-expression of alpha and beta yields one unique PA28alphabeta species with an unchangeable subunit composition. Structural data on PA28alpha, PA28beta, and PA28alphabeta up to 2.9 A resolution reveal a PA28alpha4beta3 complex with an alternating subunit arrangement and a single alpha-alpha interface. Differential scanning fluorimetry experiments and activity assays classify PA28alpha4beta3 as most stable and most active, indicating that this assembly might represent the physiologically relevant species. Together, our data resolve subunit composition and arrangement of PA28alphabeta and clarify how an asymmetric heptamer can be assembled from two highly homologous subunits.

The Mammalian Proteasome Activator PA28 Forms an Asymmetric alpha4beta3 Complex.,Huber EM, Groll M Structure. 2017 Aug 22. pii: S0969-2126(17)30247-2. doi:, 10.1016/j.str.2017.07.013. PMID:28867616^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.