| Modification Notes |
The 20S proteasome is a protease complex that is responsible for cytosolic protein degradation and generation of peptide ligands for major histocompatabilty complex (MHC) class I molecules, either in their final form or in the form of amino-terminally extended precursors (1,2). Upon IFN-gamma stimulation of cells, three constitutively expressed subunits of the 20S proteasome are replaced by inducible subunits LMP2 (low-molecular mass polypeptide 2), LMP7, and MECL-1 (multicatalytic endopeptidase complex-like-1, LMP10)(1,3). LMP2, LMP7, and MECL-1 subunits form immunoproteasomes, which are associated with more efficient class I antigen processing and presentation (1,2). Independent assortment of LMP-2, LMP-7, and MECL-1 into different proteasome complexes can lead to 36 unique proteasome subsets, which may mediate differences in the cleavage specificities/cleavage motifs of proteins subject to constitutive- and immuno-proteasomes (4,5). |