Generation, intracellular transport and loading of peptides associated with MHC class I molecules

MHC class I molecules present antigenic peptides that are mostly derived from endogenous cytosolic proteins. Recent studies addressing the function of the proteasome and its activator complexes have advanced our understanding of the cytosolic processing of peptides. Transporters associated with antigen processing (TAPs) translocate these peptides to the endoplasmic reticulum where MHC class I molecules, which are retained in transient complexes with chaperones and TAPs, await them for binding. The sequence specificity and the peptide length preference of TAPs roughly meet the requirements of class I molecules in a range of different species, suggesting evolutionary shaping of the specificity of TAPs.