THE HUMAN INTRINSIC FACTOR VITAMIN-B-12-RECEPTOR, CUBILIN - MOLECULARCHARACTERIZATION AND CHROMOSOMAL MAPPING OF THE GENE TO 10P WITHIN THE AUTOSOMAL RECESSIVE MEGALOBLASTIC-ANEMIA (MGA1) REGION

Uptake of vitamin B-12 (cyanocobalamin) is facilitated by the cobalami n-binder gastric intrinsic factor (IF), which recognizes a 460-kD rece ptor, cubilin, present in the epithelium of intestine and kidney. Surf ace plasmon resonance analysis of ligand-affinity-purified human cubil in demonstrated a high-affinity calcium-and cobalamin-dependent bindin g 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 proc essing due to cleavage at a recognition site (Arg(7)-Glu(8)-Lys(9)-Arg (10)) 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 unknow n recessive-gene locus of juvenile megaloblastic anemia caused by inte stinal malabsorption of cobalamin (Imerslund-Grasbeck's disease). In c onclusion, the present molecular and genetic information on human cubi lin now provides circumstantial evidence that an impaired synthesis, p rocessing, or ligand binding of cubilin is the molecular background of this hereditary form of megaloblastic anemia. (C) 1998 by The America n Society of Hematology.