Whole-cell conversion of L-glutamic acid into γ-aminobutyric acid via an
engineered strain overexpressing glutamate decarboxylase from Priestia
flexa
Abstract
Gamma-aminobutyric acid (GABA) is widely applied in the food and
pharmaceutical industries, and glutamate decarboxylase (GAD) is the core
enzyme for the biosynthesis of GABA. GAD exhibits high activity but poor
stability under acidic conditions, and low activity under neutral
conditions. In this study, GAD from Priestia flexa (
PfGAD) with high activity was screened out and characterized, and
a variant with significantly improved stability was obtained through
molecular modification strategies. We constructed an engineered strain
that coexpressed PfGAD and a transporter protein for GABA and
L-glutamic acid. Furthermore, the consumption of GABA was suppressed by
knocking out the pepD gene, confirming a novel downstream
metabolic pathway of GABA in Escherichia coli. The continuous
accumulation of GABA in the engineered strain led to a yield of 154.7
g·L -1, with a conversation rate of 100%, meanwhile
the cell growth was remained normal. The problem of the trade-off
between cell growth and GABA accumulation was solved, which was one of
the urgent problems according to previous reports. Our study provides
important insights into the optimization of GABA production through
enzyme engineering and strain modification, which could have significant
implications for the industrial application of GABA.