Article

Cloning and expression of a pharmacologically unique bovine peripheral-type benzodiazepine receptor isoquinoline binding protein.

Department of Pharmacology and Toxicology, College of Pharmacy, University of Arizona, Tucson 85721.
Journal of Biological Chemistry (Impact Factor: 4.65). 08/1991; 266(21):14082-7.
Source: PubMed

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.

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