The human proteasomal subunit HsC8 induces ring formation of other α-type subunits

WLH Gerards, WW de Jong, H Bloemendal… - Journal of Molecular …, 1998 - Elsevier
WLH Gerards, WW de Jong, H Bloemendal, W Boelens
Journal of Molecular Biology, 1998Elsevier
The eukaryotic 20 S proteasome is a barrel-shaped protease complex, made up of four
seven-membered rings. The outer and inner rings contain seven different α and β-type
subunits, respectively, each subunit located at a defined position. Recently, we have
reported that the recombinant human α-type subunit C8 (HsC8) assembles into a
heptameric ring-like structure by itself. In the present study we show that the two naturally
neighboring α-type subunits of HsC8, HsPROS30 and HsPROS27, do not form ring-like …
The eukaryotic 20 S proteasome is a barrel-shaped protease complex, made up of four seven-membered rings. The outer and inner rings contain seven different α and β-type subunits, respectively, each subunit located at a defined position. Recently, we have reported that the recombinant human α-type subunit C8 (HsC8) assembles into a heptameric ring-like structure by itself. In the present study we show that the two naturally neighboring α-type subunits of HsC8, HsPROS30 and HsPROS27, do not form ring-like complexes by themselves, but only dimers. This indicates that the propensity to form homo-oligomeric rings is not a general feature among human α-type subunits. However, coexpression of HsC8 and either of these neighbor α-type subunits results in the formation of hetero-oligomeric ring complexes, resembling the HsC8 ringlike structure. The ratio between the two types of subunits in the mixed complexes is surprisingly heterogeneous, varying from very high to very low HsC8 content. The three tested α-type subunits thus apparently lack binding sites that selectively interact with a specific neighboring subunit. This suggests that the correct positioning of the different α-type subunits in the eukaryotic 20 S proteasome is not dictated by the α-type subunits themselves, but rather by the interaction with specific β-type subunits.
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