Photolabeled tryptic degradation products of benzodiazepine-binding proteins are glycopeptides Implications for localization of cleavage sites

• Published in: FEBS letters 1989-02, Vol.244 (2), p.433-438
• Main Authors: Schmitz, Elke, Reichelt, Ralf, Möhler, Hanns, Hebebrand, Johannes
• Format: Article
• Language: English
• Subjects: Aminobutyric acid receptor, γ; Animals; Benzodiazepine receptor; Cattle; Cerebral Cortex - metabolism; Columbidae; Deglycosylation; Flunitrazepam - metabolism; Glycopeptides - isolation & purification; Glycoproteins - metabolism; Immunoblotting; Molecular Weight; Peptide Fragments - isolation & purification; Photoaffinity labeling; Receptors, GABA-A - metabolism; Swine; Synaptic Membranes - metabolism; Telencephalon - metabolism; Transmembrane topology; Trypsin; Tryptic degradation
• ISSN: 0014-5793; 1873-3468
• DOI: 10.1016/0014-5793(89)80578-2

Crude synaptic membranes of avian and mammalian brain tissue were photolabeled with the benzodiazepine-receptor ligand [ 3H]flunitrazepam and subsequently treated extensively with trypsin followed by incubation with endoglycosidase F. SDS-polyacrylamide gel electrophoresis and fluorography revealed that the final tryptic degradation product of 25 kDa in both pigeon and calf brain is deglycosylated in two steps. These results were confirmed by immunoblots of similarly pretreated membranes of pig brain using the α-subunit-specific monoclonal antibody bd-24. Benzodiazepine-receptor binding and its enhancement by GABA are largely retained after trypsinization. Based on the proposed transmembrane topology for the α-subunits of the GABA/benzodiazepine receptor, we suggest that the large N-terminal domain of benzodiazepine-binding proteins is protected against tryptic cleavage.