title: Cloning and expression of a pharmacologically unique bovine peripheral-type benzodiazepine receptor isoquinoline binding protein.
abstract: High affinity binding of isoquinolines, such as PK 11195, is a conserved feature of peripheral-type benzodiazepine receptors (PBR) across species. However, species differences in PBR ligand binding have been described based on the affinity for N1-alkyl-1,4-benzodiazepines, such as Ro5-4864. Ro5-4864 binds with high affinity to the rat receptor but has low affinity for the bovine PBR. Photolabeling with an isoquinoline ligand, [3H]PK 14105, identifies a 17-kDa protein, the PBR isoquinoline binding protein (PBR/IBP), in both species. To further elucidate the role of the PBR/IBP in determining PBR benzodiazepine and isoquinoline binding characteristics, the bovine PBR/IBP was cloned and expressed. Using a cDNA encoding a rat PBR/IBP to screen a fetal bovine adrenal cDNA library, a bovine cDNA encoding a polypeptide of 169 residues was cloned. The bovine and rat PBR/IBPs had similar hydropathy profiles exhibiting five potential transmembrane domains. Transfecting the cloned bovine PBR/IBP cDNA into COS-7 cells resulted in an 11-fold increase in the density of high affinity [3H]PK 11195 binding sites which had only low affinity for Ro5-4864. Expression of the bovine PBR/IBP yields a receptor which is pharmacologically distinct from both endogenous COS-7 PBR and the rat PBR based on the affinity for several N1-alkyl-1,4-benzodiazepine ligands. These results suggest the PBR/IBP is the minimal functional component required for PBR ligand binding characteristics and the different protein sequences account for the species differences in PBR benzodiazepine ligand binding.
authors.affiliation: Department of Pharmacology and Toxicology, College of Pharmacy, University of Arizona, Tucson 85721.
authors.forename: A L
authors.initials: AL
authors.lastname: Parola
authors.forename: D G
authors.initials: DG
authors.lastname: Stump
authors.forename: D J
authors.initials: DJ
authors.lastname: Pepperl
authors.forename: K E
authors.initials: KE
authors.lastname: Krueger
authors.forename: J W
authors.initials: JW
authors.lastname: Regan
authors.forename: H E
authors.initials: HE
authors.lastname: Laird
mesh_terms: D000345:Affinity Labels; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D015152:Blotting, Northern; D015139:Blotting, Southern; D002352:Carrier Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D002417:Cattle; D002522:Chlorocebus aethiops; D003001:Cloning, Molecular; D004247:DNA / Q000235:genetics; D015870:Gene Expression; D066298:In Vitro Techniques; D007546:Isoquinolines / Q000378:metabolism; D008969:Molecular Sequence Data; D012333:RNA, Messenger / Q000235:genetics; D011963:Receptors, GABA-A / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D012995:Solubility; D014162:Transfection
chemical_list: D000345:Affinity Labels; D002352:Carrier Proteins; D007546:Isoquinolines; D012333:RNA, Messenger; D011963:Receptors, GABA-A; C069997:Tspo protein, rat; D004247:DNA; C037850:PK 11195