Endocytic receptor which plays a role in lipoprotein, vitamin and iron metabolism by facilitating their uptake. Acts together with LRP2 to mediate endocytosis of high-density lipoproteins, GC, hemoglobin, ALB, TF and SCGB1A1. Acts together with AMN to mediate endocytosis of the CBLIF-cobalamin complex. Binds to ALB, MB, Kappa and lambda-light chains, TF, hemoglobin, GC, SCGB1A1, APOA1, high density lipoprotein, and the CBLIF-cobalamin complex. Ligand binding requires calcium. Serves as important transporter in several absorptive epithelia, including intestine, renal proximal tubules and embryonic yolk sac. May play an important role in the development of the peri-implantation embryo through internalization of APOA1 and cholesterol. Binds to LGALS3 at the maternal-fetal interface. Interacts with AMN. Component of the cubam complex composed of one CUBN trimer and one AMN chain (By similarity). The cubam complex can dimerize (By similarity). Interacts with LRP2 in a dual-receptor complex in a calcium-dependent manner. Found in a complex with PID1/PCLI1, LRP1 and CUBNI. Interacts with LRP1 and PID1/PCLI1 (By similarity). Lacks a transmembrane domain and depends on interaction with AMN for location at the plasma membrane (By similarity). Colocalizes with AMN and LRP2 in the endocytotic apparatus of epithelial cells (By similarity). Expressed in kidney, thymus, ileum, placenta, small intestine and yolk sac. In kidney expressed on the apical brush border surface of proximal tubular cells, in particular in endosomes and recycling membranes vesicles, so-called dense apical tubules, which carry internalized receptors back to the cell surface. Expressed in fetal membranes of yolk sac, placenta of pregnant females. Detected in yolk sac endoderm as early as day 6 and is present at the apical surface of those cells throughout the remainder of pregnancy. Apical expression is pronounced in the extraembryonic visceral endoderm (VE) of 6-9.5 dpc. Expressed by a subpopulation of cells dispersed within the 7.5 dpc embryonic endoderm and having a migratory morphology. First detected at the eight-cell stage. At the 32-cell stage expressed in all outer cells which are at the origin of the trophectoderm (TE). During the blastocyst stage, expression is predominant at the apical membrane of the TE cells. The CUB domains 5 to 8 mediate binding to CBLIF and ALB. CUB domains 1 and 2 mediate interaction with LRP2. The cubam complex 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. The precursor is cleaved by a trans-Golgi proteinase furin, removing a propeptide. N-glycosylated.