Membrane-bound component of the endocytic receptor formed by AMN and CUBN. Required for normal CUBN glycosylation and trafficking to the cell surface (PubMed:15342463). The complex formed by AMN and CUBN is required for efficient absorption of vitamin B12 (By similarity). Required for normal CUBN-mediated protein transport in the kidney (PubMed:15342463). Interacts (via extracellular region) with CUBN/cubilin (PubMed:15342463). This gives rise to a huge complex containing one AMN chain and three CUBN chains (By similarity). Expressed in polarized epithelial cells which are specialized in resorption or transport, specifically kidney proximal tubules and intestinal epithelium. Detected in primitive endoderm at 4.5 dpc, and on the apical surface of the visceral endoderm from 5.5 dpc to 8.5 dpc. Expressed in mesonephric tubules at 11.5-12.5 dpc and in the metanephric kidney beginning at 14.5 dpc. Expressed in the intestine from 16.5 dpc. 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. Full embryonic lethality at about 10.5 dpc with failure of primitive middle streak assembly and absence of trunk mesoderm formation. 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.