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.
Subcellular locations: Endoplasmic reticulum membrane
Ubiquitously expressed. Highly expressed in spleen and leukocytes.