Concerted antigen processing of a short viral antigen by human caspase-5 and -10.

The generation of peptides presented by MHC class I molecules requires the proteolytic activity of the proteasome and/or other peptidases. The processing of a short vaccinia virus-encoded antigen can take place by a proteasome-independent pathway involving initiator caspase-5 and -10, which generate antigenic peptides recognized by CD8(+) T lymphocytes. In the present study, comparing single versus double enzyme digestions by mass spectrometry analysis, both qualitative and quantitative differences in the products obtained were identified. These in vitro data suggest that each enzyme can use the degradation products of the other as substrate for new cleavages, indicating concerted endoproteolytic activity of caspase-5 and -10.