CHARACTERIZATION AND TISSUE DISTRIBUTION OF OPIOID-BINDING CELL-ADHESION MOLECULE (OBCAM) USING MONOCLONAL-ANTIBODIES

Monoclonal antibodies to opioid-binding cell adhesion molecule (OBCAM) were produced against a synthetic OBCAM peptide. Immunoblotting analy sis revealed that the antibodies reacted with 58 and/or 51 kDa protein s in P2 membranes from bovine, rat, mouse, guinea pig and rabbit brain s. In bovine brain, the 58 and 51 kDa proteins were present in the str iatum and cerebral cortex at high levels, but not in the pituitary. OB CAM was also detected in the cerebellum mainly in the 51 kDa form. In other tissues, the proteins were found in the spleen at very low level s, but not at all in the liver or kidney of the rat. OBCAM was effecti vely solubilized from bovine P2 membranes by bacterial phosphatidylino sitol specific-phospholipase C (PI-PLC), indicating that OBCAM is a gl ycosylphosphatidylinositol (GPI)-anchored protein. PI-PLC treatment, h owever, had little effect on the opioid binding activity of the residu al P2 membranes. The molecular weight of the proteins (58 and 51 kDa) was reduced to 36 kDa following treatment with N-glycanase but not fur ther reduced after subsequent treatment with neuraminidase and O-glyca nase, suggesting that OBCAM has N-glycosylated carbohydrate chains and that its two isoforms are different, at least, in the degree of N-gly cosylation. Taken together, these results suggest that OBCAM consists of 58/51 kDa GPI-anchored glycoproteins which are highly N-glycosylate d and are expressed mainly in the nervous system. (C) 1996 Elsevier Sc ience Ltd.