Molecular Characterization of a Novel Gamma-Glutamyl Transpeptidase Homologue Found in Rat Brain1.

A cDNA clone for a novel homologue to -γ-glutamyl transpeptidase (γ-GTP), termed GTPH, was isolated from a rat brain expression cDNA library using antisera against total brain synaptosomal fractions. The cloned GTPH consists of 641 amino acid residues (78 kDa) and exhibits structural similarity with a conventional type of γ-GTP that is predominantly expressed in the liver: They share significant amino acid homology (33% identity, 73% similarity) spanning over the entire sequence. RNA analyses revealed that GTPH mRNA expression is found only in the nervous system, including all brain regions, eyes and peripheral ganglia, and increases during development. Endogenous GTPH protein is a membrane-bound glycoenzyme and migrates as 90-100 kDa in poly-acrylamide gels. Taken together, GTPH is a novel form of a γ-GTP-like molecule expressed exclusively in the nervous system. [ABSTRACT FROM AUTHOR]