Aminopeptidases hydrolyze N-terminal amino acids of proteins or peptide substrates. Major histocompatibility complex (MHC) class I molecules rely on aminopeptidases such as ERAP1 (MIM 606832) and LRAP to trim precursors to antigenic peptides in the endoplasmic reticulum (ER) following cleavage in the cytoplasm by tripeptidyl peptidase II (TPP2; MIM 190470) (Tanioka et al., 2003 [PubMed 12799365]).
