STUDIES OF STRUCTURE AND FUNCTION ON CEREBRAL GABA_B RECEPTOR

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The GTP-binding protein was purified from the bovine cerebral cortex and this preparation was found to contain the Gi protein but not Gs and Go proteins. It was reconstituted into the phospholipid vesicles with another two functional proteins, purified GABA_B receptor and purified adenylyl cyclase. These reconstitutionexperimentshave indicated that the GABA_B receptor directly inhibits the adenylyl cyclase activity through the Gi protein. On the other hand, a partial amino acid sequence of the GABA_B receptor was analyzed. It has been suggested a possibility that this sequence may be a part of G protein-coupled receptor. Therefore, the polymerase-chain-reaction (PCR) has been attempted using the transmembrane domains (TM), which have highly homologous sequences among various G protein-coupled receptors. A PCR product (278 bp) was obtained and its deduced amino acid sequences indicated that it might be a region from TM III to TM V.Furthermore, a cDNA library from the rat embryo brain was screened using this PCR product as a probe. As the results of these screenings, several positive clones which contained possible coding regions of a novel G protein-coupled receptor were obtained. The size of these cDNA was found to be 1.5-3.0kb.