Characterizing and optimizing glutamate decarboxylase from Priestia flexa for efficient biosynthesis of γ-aminobutyric acid from l-glutamic acid powder.

Gamma-aminobutyric acid (GABA) is widely applied in the food and pharmaceutical industries, and is experiencing a continually growing market demand. Nevertheless, the efficient and stable production of GABA confronts challenges, especially the instability of its core enzyme, glutamate decarboxylase (GAD). GAD exhibits high activity under acidic conditions but very poor stability. This limitation severely restricts its application in large-scale industrial production. In this study, we identified and characterized a GAD from Priestia flexa (PfGAD) with high activity. We further developed a variant with significantly enhanced acidic st ability. The specific activity of the variant achieved 139.8 U/mg, and its residual activity remained approximately 90 % after overnight incubation in pH 3.0 buffer. Moreover, we engineered a strain by overexpressing a transporter protein for GABA and l-glutamic acid, while deleting the pepD gene. The yield of GABA led to 251.8 g L, accompanied by a conversation rate of 97.8 %, meanwhile the cell growth maintained normal. Our approach successfully addresses the challenge of balancing cell growth and GABA accumulation. Our findings offer valuable insights into acid resistance modification of the enzyme, and optimizing GABA production through strain modification, holding significant potential for the industrial application of GABA.