The ER aminopeptidase ERAP1 enhances or limits antigen presentation by trimming epitopes to 8–9 residues.

Endoplasmic reticulum (ER) aminopeptidase I (ERAPI) appears to be specialized to produce peptides presented on class I major histocompatibility complex molecules. We found that purified ERAPI trimmed peptides that were ten residues or longer, but spared eight-residue peptides. In vivo, ERAPI enhanced production of an eight-residue ovalbumin epitope from precursors extended on the NH[sub 2] terminus that were generated either in the ER or cytosol. Purified ERAPI also trimmed nearly half the nine-residue peptides tested. By destroying such nine-residue peptides in normal human cells, ERAPI reduced the overall supply of antigenic peptides. However, after interferon-γ treatment, which causes proteasomes to produce more NH[sub 2]-extended antigenic precursors, ERAPI increased the supply of peptides for MHC class I antigen presentation. [ABSTRACT FROM AUTHOR]

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