Peptide generation in the major histocompatibility complex class I antigenprocessing and presentation pathway

The bulk of antigens that are presented by major histocompatibility complex (MHC) class I molecules are processed in the cytosol. Therefore, the cellu lar protein degradation machinery is thought to play a major role in antige n processing. For example, there is clear evidence that the ubiquitin-prote asome pathway, the major proteolytic pathway in the cytosol, plays a role i n the processing of class I-associated antigens. In addition, peptide chape rones must exist to properly target peptides to the transporter associated with antigen processing. Here, the author reviews some of the more importan t advances over the past year that further define the pathways of antigen b reakdown in the cytosol. This includes a took at the distinctive roles of p roteasomes versus immunoproteasomes, the isolation of peptide processing in termediates in the cytosol, and the role of defective ribosomal products. T hese findings highlight the importance of understanding basic cellular prot ein degradation pathways in antigen processing. (C) 2001 Lippincott William s & Wilkins, Inc.