| Comment |
A 20-S protein composed of 28 subunits arranged in four rings of
seven. The outer rings are composed of alpha subunits, but the beta
subunits forming the inner rings are responsible for peptidase
activity. In eukaryotic organisms there are up to seven different
types of beta subunits, three of which may carry the N-terminal
threonine residues that are the nucleophiles in catalysis, and show
different specificities. The molecule is barrel-shaped, and the
active sites are on the inner surfaces. Terminal apertures restrict
access of substrates to the active sites. There is evidence that
catalytic subunits are replaced by others under some conditions so
as to alter the specificity of proteolysis, perhaps optimizing it
for the formation of antigenic peptides. A complex of the 20-S
proteasome endopeptidase complex with a 19-S regulatory unit is the
26-S proteasome that degrades ubiquitin-protein conjugates. Type
example of peptidase family T1. |
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Reference
Authors
Title
Journal
Organism
|
4 [PMID:9748229]
Dick TP, Nussbaum AK, Deeg M, Heinemeyer W, Groll M, Schirle M,
Keilholz W, Stevanovic S, Wolf DH, Huber R, Rammensee HG, Schild H.
Contribution of proteasomal beta-subunits to the cleavage of peptide
substrates analyzed with yeast mutants.
J. Biol. Chem. 273 (1998) 25637-46.
Homo sapiens [GN:hsa], Saccharomyces cerevisiae [GN:sce] |
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