Endocytic receptor which plays a role in lipoprotein, vitamin and iron metabolism by facilitating their uptake (PubMed:10371504, PubMed:11606717, PubMed:11717447, PubMed:14576052, PubMed:9572993). 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 (PubMed:14576052, PubMed:9572993). 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 (PubMed:9572993). 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. {ECO:0000269|PubMed:10371504, ECO:0000269|PubMed:11606717, ECO:0000269|PubMed:11717447, ECO:0000269|PubMed:14576052, ECO:0000269|PubMed:9572993}. This is the function of CUBN (cubilin, ENSG00000107611).