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.

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Abstract
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 Escherichia coli, and a 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.