Membrane-bound component of the endocytic receptor formed by AMN and CUBN (PubMed:14576052, PubMed:30523278, PubMed:29402915). Required for normal CUBN glycosylation and trafficking to the cell surface (PubMed:14576052, PubMed:29402915). The complex formed by AMN and CUBN is required for efficient absorption of vitamin B12 (PubMed:12590260, PubMed:14576052, PubMed:26040326). Required for normal CUBN-mediated protein transport in the kidney (Probable). Interacts (via extracellular region) with CUBN/cubilin, giving rise to a huge complex containing one AMN chain and three CUBN chains. At least 5 isoforms, 1, 2, 3, 4 and 5, are produced. Detected in proximal tubules in the kidney cortex (at protein level) (PubMed:14576052, PubMed:29402915). Long isoforms are highly expressed in small intestine, colon and kidney (renal proximal tubule epithelial cells). Shorter isoforms are detected at lower levels in testis, thymus and peripheral blood leukocytes. The complex formed by AMN and CUBN is composed of a 400 Angstrom long stem and a globular crown region. The stem region is probably formed by AMN and the CUBN N-terminal region, including the EGF-like domains. The crown is probably formed by the CUBN CUB domains. N-glycosylated. A soluble form arises by proteolytic removal of the membrane anchor. The disease is caused by variants affecting the gene represented in this entry. The role of Amn in embryonic development seems to be species specific. In mice, null mutations lead to embryonic lethality. Human mutations give rise to much milder symptoms.