Peptidase M1 family containing Aminopeptidase NThis family contains bacterial and eukaryotic aminopeptidase N (APN; CD13; Alanyl aminopeptidase; EC 220.127.116.11), a Type II integral membrane protease belonging to the M1 gluzincin family. APN consists of a small N-terminal cytoplasmic domain, a single transmembrane domain and a large extracellular ectodomain that contains the active site. It preferentially cleaves neutral amino acids from the N-terminus of oligopeptides and, in higher eukaryotes, is present in a variety of human tissues and cell types (leukocyte, fibroblast, endothelial and epithelial cells). APN expression is dysregulated in inflammatory diseases such as chronic pain, rheumatoid arthritis, multiple sclerosis, systemic sclerosis, systemic lupus erythematosus, polymyositis/dermatomyosytis and pulmonary sarcoidosis, and is enhanced in tumor cells such as melanoma, renal, prostate, pancreas, colon, gastric and thyroid cancers. It is predominantly expressed on stem cells and on cells of the granulocytic and monocytic lineages at distinct stages of differentiation, thus considered a marker of differentiation. Thus, APN inhibition may lead to the development of anti-cancer and anti-inflammatory drugs. APNs are also present in many pathogenic bacteria and represent potential drug targets, Some APNs have been used commercially, such as one from Lactococcus lactis used in the food industry. APN also serves as a receptor for coronaviruses, although the virus receptor interaction site seems to be distinct from the enzymatic site and aminopeptidase activity is not necessary for viral infection. APNs have also been extensively studied as putative Cry toxin receptors. Cry1 proteins are pore-forming toxins that bind to the midgut epithelial cell membrane of susceptible insect larvae, causing extensive damage. Several different toxins, including Cry1Aa, Cry1Ab, Cry1Ac, Cry1Ba, Cry1Ca and Cry1Fa, have been shown to bind to APNs; however, a direct role of APN in cytotoxicity has been yet to be firmly established.