title: Identification of a 14 kDa FK-506/rapamycin binding immunophilin from calf thymus.
abstract: Specific binding proteins (immunophilins, 12-17 kDa) have been described in the cytosol for the immunosuppressant drugs cyclosporine, FK-506, and rapamycin. We describe the identification of a low abundant minor immunophilin (14 kDa) from calf thymus. Saturation experiments using dihydro[3H]-FK-506 gave a Kd of 2 nM and the Bmax of 72 nmol/mg protein. At saturation, 71.3 nmol of FK-506 is bound per mg of the 14 kDa protein (71 nmol) giving a drug/protein ratio of 1.0. Competition experiments using 3H-dihydro FK-506 and rapamycin showed displacement of rapamycin, with Kd in the range of 40 nM. The 14 kDa immunophilin does not have peptidyl-prolyl cis-trans isomerase activity with any of the four substrates investigated. Initial amino acid analysis and protein sequencing data indicate that the immunophilin is different from both the 12 kDa FK-506 binding protein and any other known protein.
authors.affiliation: Department of Laboratory Medicine, Children's National Medical Center, Washington, DC 20010.
authors.forename: J N
authors.initials: JN
authors.lastname: Murthy
authors.forename: Y
authors.initials: Y
authors.lastname: Chen
authors.forename: S J
authors.initials: SJ
authors.lastname: Soldin
mesh_terms: D000591:Amino Acid Isomerases / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D001667:Binding, Competitive; D002352:Carrier Proteins / Q000737:chemistry / Q000302:isolation & purification*; D002417:Cattle; D002852:Chromatography, Ion Exchange; D003600:Cytosol / Q000737:chemistry; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000302:isolation & purification*; D006360:Heat-Shock Proteins / Q000737:chemistry / Q000302:isolation & purification*; D007525:Isoelectric Focusing; D008969:Molecular Sequence Data; D008970:Molecular Weight; D010446:Peptide Fragments / Q000737:chemistry; D011090:Polyenes / Q000302:isolation & purification*; D011869:Radioligand Assay; D020123:Sirolimus; D016559:Tacrolimus / Q000302:isolation & purification*; D022021:Tacrolimus Binding Proteins; D013950:Thymus Gland / Q000737:chemistry*
chemical_list: D002352:Carrier Proteins; D004268:DNA-Binding Proteins; D006360:Heat-Shock Proteins; D010446:Peptide Fragments; D011090:Polyenes; D000591:Amino Acid Isomerases; D022021:Tacrolimus Binding Proteins; D020123:Sirolimus; D016559:Tacrolimus