||Liu Q, Cheng H, Ma X, Xu N, Liu J, Ma Y
||Expression, characterization and mutagenesis of a novel glutamate decarboxylase from Bacillus megaterium
|| Bacillus megaterium; Gamma-aminobutyric acid (GABA); Glutamate decarboxylase (GAD); Mutagenesis
To search for a novel glutamate decarboxylase (GAD) with an optimum pH towards near-neutrality in order to improve production of gamma-aminobutyric acid (GABA) in recombinant hosts.
A novel glutamate decarboxylase, BmGAD, from Bacillus megaterium was overexpressed and purified. BmGAD was approximately 53 kDa by SDS-PAGE analysis. Its optimum activity was at pH 5 and 50 °C. BmGAD had a specific activity of 59 ± 5.2 U mg(-1) at pH 6, which is the highest value reported so far. The apparent Km and Vmax values of BmGAD were 8 ± 0.5 mM and 150 ± 4.7 U mg(-1), respectively. Through site-directed mutagenesis, two BmGAD mutants (E294R and H467A) showed higher Vmax values than that of wild-type, with the values of 210 ± 6.9 and 180 ± 4.1 U mg(-1) at pH 5 and 50 °C, respectively.
The unusual high activity of BmGAD at pH 6 makes it an attractive GABA-producing candidate in industrial application.