20S Immunoproteasome: ProductsThe 20S Immunoproteasome is a modified form of the constitutively active 20S Proteasome core particle and is the catalytic subunit of the multi-complex Immunoproteasome. The structure of the 20S Immunoproteasome is similar to the 20S Proteasome, which is composed of 28 non-identical subunits arranged into four stacked rings. However, during 20S Immunoproteasome assembly, the three catalytic beta subunits, beta 1, 2, and 5, in the two interior rings of the 20S Proteasome are replaced by three IFN-gamma-inducible catalytic subunits: beta 1i/LMP2, beta 2i/LMP7, and beta 5i/MECL-1. The 20S Immunoproteasome is commonly associated with the 19S, PA28 alpha/beta, or the PA28 gamma regulatory complexes. 20S Immunoproteasome expression is enriched in antigen presenting cells of the immune system where the 20S Immunoproteasome selectively degrades intracellular proteins in a manner that optimizes the generation of peptides for MHC class I antigen presentation.