title: The intrinsic factor (IF)-cobalamin receptor binding site is located in the amino-terminal portion of IF.
abstract: Intrinsic factor has two binding sites, one each for cobalamin and for the ileal receptor recognizing the intrinsic factor-cobalamin complex. To obtain initial functional mapping of these domains, cDNAs encoding intact rat and human intrinsic factor or fragments thereof were expressed transiently in COS-1 cells or in an in vitro transcription/translation system. Deletion of as little as 12% of the amino acids from the carboxyl terminus resulted in loss of cobalamin binding activity. On the other hand, the receptor binding region of intrinsic factor appears localized to a restricted region in the amino-terminal portion of the protein. Only those transcription/translation fragments of rat or human intrinsic factor tested that contained amino acid residues 25 to 62 (out of 399) showed calcium-dependent binding to isolated kidney brush borders, the shortest sequence corresponding with 20 consecutive amino acids. In contrast, a 232-amino acid carboxyl-terminal fragment of rat intrinsic factor and 243- and 338-amino acid carboxyl-terminal fragments of human intrinsic factor showed no receptor binding activity.
authors.affiliation: Washington University Medical School, St. Louis, Missouri 63110.
authors.forename: L H
authors.initials: LH
authors.lastname: Tang
authors.forename: H
authors.initials: H
authors.lastname: Chokshi
authors.forename: C B
authors.initials: CB
authors.lastname: Hu
authors.forename: M M
authors.initials: MM
authors.lastname: Gordon
authors.forename: D H
authors.initials: DH
authors.lastname: Alpers
mesh_terms: D000818:Animals; D001665:Binding Sites; D002460:Cell Line; D003001:Cloning, Molecular; D006801:Humans; D007437:Intrinsic Factor / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D014176:Protein Biosynthesis; D051381:Rats; D011956:Receptors, Cell Surface / Q000378:metabolism*; D011994:Recombinant Proteins / Q000302:isolation & purification / Q000378:metabolism; D015183:Restriction Mapping; D014158:Transcription, Genetic; D014162:Transfection
chemical_list: D011956:Receptors, Cell Surface; D011994:Recombinant Proteins; C029486:intrinsic factor-cobalamin receptor; D007437:Intrinsic Factor