Structural basis for antigenic peptide precursor processing by the endoplasmic reticulum aminopeptidase ERAP1

Endoplasmic reticulum aminopeptidase 1 (ERAP1) has a crucial role in antigen presentation because it trims peptide ligands to 8–10 residues so that they fit into the peptide-binding groove of MHC class I molecules. The structure of the ERAP1 in complex with bestatin, an aminopeptidase inhibitor, reveals how the enzyme´s catalytic center how the enzyme can preferentially process peptides 10–15 residues long while sparing shorter ones and provides the first evidence that substrate binding induces conformational changes.