K48-polyubiquitinated substrate precursor peptide fragment (>16 aa) oligopeptide fragment (8-16aa) Proteasomal cleavage of substrate Authored: Garapati, P V, 2010-10-29 Edited: Garapati, P V, 2010-10-29 Pubmed11350924 Pubmed14734113 Pubmed15224091 Pubmed15224092 Pubmed15571818 Pubmed9380723 Reactome Database ID Release 43983150 Reactome, http://www.reactome.org ReactomeREACT_75871 Reviewed: Elliott, T, 2011-02-10 The 26S proteasome complex consists of the 20S catalytic core particle which harbours the proteolytically active sites and the regulatory 19S particle which is responsible for substrate interaction. This process generates a vast number (perhaps hundreds) of different peptides, depending on the length and sequence of the substrate protein. Only a small fraction of these peptides (nearly 10%) form the exact length to be presented by class I MHC; most (approximately 70%) are too short to bind. The remaining proteasome products (10-20%) are N-terminally extended precursors that require additional cleavage by cytosolic aminopeptidases for presentation by MHC class I molecules. ubiquitin L-Amino Acids