The Human Intrinsic Factor-Vitamin B12 Receptor,Cubilin: Molecular Characterization and Chromosomal Mapping of the Gene to 10p Within the Autosomal Recessive Megaloblastic Anemia (MGA1) Region

Abstract

Uptake of vitamin B12 (cyanocobalamin) is facilitated by the cobalamin-binder gastric intrinsic factor (IF), which recognizes a 460-kD receptor, cubilin, present in the epithelium of intestine and kidney. Surface plasmon resonance analysis of ligand-affinity-purified human cubilin demonstrated a high-affinity calcium- and cobalamin-dependent binding of IF-cobalamin. Complete cDNA cloning of the human receptor showed a 3597 amino acid peripheral membrane protein with 69% identity to rat cubilin. Amino-terminal sequencing of the receptor indicates that the cDNA sequence encodes a precursor protein undergoing proteolytic processing due to cleavage at a recognition site (Arg7-Glu8-Lys9-Arg10) for the trans-Golgi proteinase furin. Using fluorescence in situ hybridization, radiation hybrid mapping, and screening of YAC clones, the human cubilin gene was mapped between the markers D10S1661 and WI-5445 on the short arm of chromosome 10. This is within the autosomal recessive megaloblastic anemia (MGA1) 6-cM region harboring the unknown recessive-gene locus of juvenile megaloblastic anemia caused by intestinal malabsorption of cobalamin (Imerslund-Gräsbeck's disease). In conclusion, the present molecular and genetic information on human cubilin now provides circumstantial evidence that an impaired synthesis, processing, or ligand binding of cubilin is the molecular background of this hereditary form of megaloblastic anemia.

Megalin and cubilin in proximal tubule protein reabsorption: from experimental models to human disease

“…[27][28][29][30] The N-terminal part of cubilin consists of 8 epidermal growth factor repeats and a 110-amino acid stretch. 25,26 Cubilin is an extracellular protein and interacts with other membrane proteins for membrane localization and endocytosis. In the proximal tubule it is believed to interact with megalin, forming a multireceptor complex with megalin driving internalization of the complex and bound ligands ( Figure 1).…”

Megalin and cubilin: synergistic endocytic receptors in renal proximal tubule

“…1). The complete DNA sequences of rat (65), human (52), and canine (96) cubilin have been identified, showing a nonglycosylated molecular mass of 400 kDa. It has little structural homology with other known endocytic receptors.…”

“…The posttranslational processing of cubilin may involve furin-mediated cleavage in the trans-Golgi network, as suggested by the finding that affinity-purified human cubilin appears to be truncated at a recognition cleavage site for furin in the NH 2 -terminal region (52). Furthermore, pulse-chase studies have suggested an unusual processing of cubilin in yolk sac cells, involving the expression of newly synthesized, endoglycosidase H-sensitive cubilin at the plasma membrane although the majority of cubilin is endoglycosidase H resistant (4).…”

Inborn errors of cobalamin absorption and metabolism

“…Cubam is composed of two proteins, cubilin and amnionless [He et al, 2005]. The former is a large extracellular protein of approximately 400 kDa containing 8 EGF repeats and 27 contiguous 110‐amino acid CUB domains [Kozyraki et al, 1998]. Binding of IF‐Cbl to cubam is mediated by CUB domains 5–8 of cubilin [Andersen et al, 2010].…”