CONTRIBUTION OF PROTEASOME-MEDIATED PROTEOLYSIS TO THE HIERARCHY OF EPITOPES PRESENTED BY MAJOR HISTOCOMPATIBILITY COMPLEX CLASS-1 MOLECULES

Major histocompatibility complex (MHC) class 1-restricted cytotoxic T lymphocytes (CTL) recognize peptide epitopes of protein antigens in a hierarchical fashion, We investigated whether proteolytic cleavage, in particular by proteasomes, is important in determining epitope hierar chy. Using highly purified 20S proteasomes, we find preferred cleavage sites directly adjacent to the N- and C-terminal ends of the immunodo minant epitope of chicken ovalbumin, Ova257-264, while most of the sub dominant epitope, Ova55-62, is destroyed by a major cleavage site loca ted within this epitope. Moreover, we shaw that variations in amino ac id sequences flanking these epitopes influence proteasomal cleavage pa tterns in parallel with the efficacy of their presentation, The result s suggest that proteasomal cleavage within and adjacent to class 1-res tricted epitopes contributes to their level of presentation.