Molecular cloning and characterization of glutamate decarboxylase cDNA from the giant-embryo Oryza sativa

A full-length cDNA encoding glutamate decarboxylase (designated as OsGAD3), which catalyzes the conversion of glutamate to gamma-aminobutyric acid (GABA), was isolated from the GABA-rich giant-embryo Oryza sativa (Shangshi Jing 315). The full-length cDNA of OsGAD3 (SSJ315) has a 1479 bp open reading frame (ORF) encoding a protein of 492 amino acid residues. The deduced protein had an isoelectric point (pI) of 5.72 and a calculated molecular weight of 56.1 kD. Sequence comparison showed that OsGAD3 (SSJ315) matches the glutamate decarboxylases of other plant species reported previously. Analysis of the structural features of the C-terminal portions of plant GADs revealed that OsGAD3 (SSJ315) has the typical CaM-binding domain (CaMBD) in the C-terminal region as most other plant GADs. Evolution analysis showed that plant GADs are conserved in the process of evolution. The cloning and characterization of the OsGAD3 (SSJ315) gene will enable us to use OsGAD3 to enhance GABA production in O. sativa (SSJ315) by metabolic engineering in the near future.