Aminopeptidase that plays a central role in peptide trimming, a step required for the generation of most HLA class I-binding peptides. Peptide trimming is essential to customize longer precursor peptides to fit them to the correct length required for presentation on MHC class I molecules. Preferentially hydrolyzes the basic residues Arg and Lys. Binds 1 zinc ion per subunit. Heterodimer with ERAP1. Ubiquitously expressed. Highly expressed in spleen and leukocytes. By IFNG/IFN-gamma. N-glycosylated. Defects in the expression of this gene may cause improper antigen processing, possibly leading to favor tumor escape from the immune surveillance. Belongs to the peptidase M1 family.