Migration of glutamate decarboxylase by cold treatment on whole-cell biocatalyst triggered activity for 4-aminobutyric acid production in engineering Escherichia coli

Glutamate decarboxylase B (GadB) from Escherichia coli, an intrinsic pyridoxal 5 '-phosphate (PLP)-dependent enzyme has been employed for 4-aminobutyric acid (GABA) biosynthesis, which involves the glutamate import and GABA export via a transporter located in the inner membrane as rate determined step of whole-cell (WC) biotransformation. Herein, GadB was cloned and overexpressed in E. coli under a constitutive promoter in a high copy number plasmid, and 46.9 g/L GABA was produced. It was observed that GadB migrated to the periplasm when the WC were subjected to -20 degrees C cold treatment for 24 h prior to the biotransformation. Kinetic studies indicated that the enzymatic turnover rate of WC increased 2-fold after cold treatment, which was correlated with the migration rate of GadB, and up to 88.6% of GadB. The export or possible migration of GadB mitigated the rate-limiting step of WC biotransformation, and a 100% conversion of substrate to GABA was obtained. Finally, we launched a promising strategy for GABA production of 850 g/L from cost-effective monosodium glutamate (MSG) by using WC biocatalysts with 10-times recycling.

Automated summary

By overexpressing GadB in Escherichia coli and subjecting it to cold treatment, the enzymatic turnover rate and migration rate of GadB increased, leading to improved GABA production in whole-cell biotransformation.