The proteasome (or macropain) (EC 18.104.22.168) [1,2,3,4,5,6] is a multicatalytic
proteinase complex that seems to be involved in an ATP/ubiquitin-dependent
nonlysosomal proteolytic pathway. The core of this 2.5 MDa enzyme complex is
formed by the 20S proteasome, a barrel-shaped protease of about 700 KDa that
associates with one or two 19S regulatory complexes. The 20S proteasome is
ubiquitous in archaea and in eukaryotes. In bacteria, the 20S has been found
only in actinomycetes.
The main difference between prokaryotic and eukaryotic proteasomes is one of
complexity. Prokaryotic 20S proteasomes contain mostly only to different but
related subunits, α and β (see <PDOC00668>), while eukaryotic
proteasomes contain seven paralogous α-type and seven paralogous β-type
subunits. Subunits that belong to the α-type group are proteins of from
210 to 290 amino acids that share a number of conserved sequence regions.
Some subunits that are known to belong to this family are listed below:
- Vertebrate subunits C2 (nu), C3, C8, C9, iota and zeta.
- Drosophila PROS-25, PROS-28.1, PROS-29 and PROS-35.
- Yeast C1 (PRS1), C5 (PRS3), C7-α (Y8) (PRS2), Y7, Y13, PRE5, PRE6 and
- Arabidopsis thaliana subunits α and PSM30.
- Thermoplasma acidophilum α-subunit. In this archaebacteria the
proteasome is composed of only two different subunits.
- Rhodococcus erythropolis 20S proteasome α subunit 1 (PrcA 1) and 2
The core of the α subunit is a sandwich of two five-stranded antiparallel
β-sheets. The β sandwich is flanked by the α helices H3, H4, and H5
on top and by H1 and H2 at the bottom (see <PDB:1PMA>) .
As a signature pattern for proteasome A-type subunits we selected the best
conserved region, which is located in the N-terminal part of these proteins.
We also have developed a profile which covers the whole conserved region.
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