Cloning, sequencing and expression of a novel glutamate decarboxylase gene from a newly isolated lactic acid bacterium, Lactobacillus brevis OPK-3

Lactobacillus brevis OPK-3, having 84.292 mg/L/h of gamma-aminobutyric acid (GABA) productivity, was isolated from Kimchi, a traditional fermented food in Korea. A core fragment of glutamate decarboxylase (GAD) DNA was isolated from the L. brevis OPK-3, using primers based on two highly conserved regions of GAD. A full-length GAD (LbGAD) clone was subsequently isolated through rapid amplification of cDNA ends (RACE) PCR. Nucleotide sequence analysis revealed that the open reading frame (ORF) consisted of 1401 bases and encoded a protein of 467 amino acid residues with a calculated molecular weight of 53.4 kDa and a pI of 5.65. The amino acid sequence deduced from LbGAD ORF showed 83%, 71%, and 60% identity to the Lactobacillus plantarum GAD, Lactococcus lactis GAD, and Listeria monocytogenes GAD sequences, respectively. The LbGAD gene was expressed in Escherichia coli strain UT481, and the extract of transformed E. coli UT481 contained an induced 53.4 kDa protein and had significantly enhanced GAD activity.