Characterization of three glutamate decarboxylases from Bacillus spp. for efficient \u03b3-aminobutyric acid production

Lei Sun,Xiaoyun Su,Bin Yao,Jie Zhang,Yingguo Bai,Yuan Wang,Xiu Zhang,Cheng Zhou,Tao Tu,Huiying Luo

doi:10.1186/s12934-021-01646-8

Abstract

BackgroundGamma-aminobutyric acid (GABA) is an important bio-product used in pharmaceuticals and functional foods and as a precursor of the biodegradable plastic polyamide 4. Glutamate decarboxylase (GAD) converts l-glutamate (l-Glu) into GABA via decarboxylation. Compared with other methods, develop a bioconversion platform to produce GABA is of considerable interest for industrial use.ResultsThree GAD genes were identified from three Bacillus strains and heterologously expressed in Escherichia coli BL21 (DE3). The optimal reaction temperature and pH values for three enzymes were 40 °C and 5.0, respectively. Of the GADs, GADZ11 had the highest catalytic efficiency towards l-Glu (2.19 mM− 1 s− 1). The engineered E. coli strain that expressed GADZ11 was used as a whole-cell biocatalyst for the production of GABA. After repeated use 14 times, the cells produced GABA with an average molar conversion rate of 98.6% within 14 h.ConclusionsThree recombinant GADs from Bacillus strains have been conducted functional identification. The engineered E. coli strain heterologous expressing GADZ1, GADZ11, and GADZ20 could accomplish the biosynthesis of l-Glu to GABA in a buffer-free reaction at a high l-Glu concentration. The novel engineered E. coli strain has the potential to be a cost-effective biotransformation platform for the industrial production of GABA.

Highlights

Gamma-aminobutyric acid (GABA) is an important bio-product used in pharmaceuticals and functional foods and as a precursor of the biodegradable plastic polyamide 4
Using the amino acid sequences of GADZ1, GADZ11, and GADZ20 as query sequences, a total of 27 homologous sequences were identified in the NCBI database
The platform that we developed has the following merits: the E. coli strain engineered in this study may be used in industry for the commercial-scale production of GABA, and our results provide the preliminary data for the separation and purification of GABA from fermentation broth

Summary

Introduction

Gamma-aminobutyric acid (GABA) is an important bio-product used in pharmaceuticals and functional foods and as a precursor of the biodegradable plastic polyamide 4. Glutamate decarboxylase (GAD) converts l-glutamate (l-Glu) into GABA via decarboxylation. GABA can be converted into polyamide 4, known as GABA can be produced through the biocatalytic α-decarboxylation of l-Glu using glutamate decarboxylase (GAD, EC4.1.1.15) (Fig. 1) [10]. A variety of GADs are found in bacteria, actinomycetes, fungi, and plant, and they play a central role in the synthesis of GABA, Sun et al Microb Cell Fact (2021) 20:153. The genus Bacillus comprises gram-positive bacteria that are widely distributed on plant surfaces and in the soil and air. It produces many bioactive substances and various kinds of enzymes, such as amylases, proteases, and lipases [20]. We have, here, presented an efficient biosynthetic pathway for the industrial production of GABA

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Conclusion