Cloning and expression of cDNA for human diazepam binding inhibitor, a natural ligand of an allosteric regulatory site of the gamma-aminobutyric acid type A receptor.

Diazepam binding inhibitor (DBI) is a protein that displaces ligands bound to the beta-carboline/benzodiazepine recognition site, an allosteric modulatory site of the type A gamma-aminobutyric acid receptor complex. An incomplete rat cDNA clone coding for DBI was isolated. This rat sequence was utilized to identify a cDNA clone that encoded the entire 104 residues of human DBI. This sequence was engineered for expression in E. coli, and recombinant DBI exhibits identical biochemical and antigenic characteristics of natural human DBI. DBI is encoded by a multigene family of at least five members, but a single gene appears to account for the majority of DBI expression. DBI is expressed in a tissue-specific manner. Expression is found in central nervous system tissues and appears to extend to peripheral tissues rich in the peripheral type of high-affinity benzodiazepine recognition sites. The role of these sites and DBI in adrenal gland, testis, and kidney remains to be determined.