Abstract
γ-amino butyric acid (GABA) is a non-protein amino acid, considered a potent bioactive compound. This study focused on biosynthesis of food-grade GABA by immobilized glutamate decarboxylase (GAD) from Lactobacillus plantarum in the rice vinegar and monosodium glutamate (MSG) reaction system. The gene encoding glutamate decarboxylase (GadB) from L.plantarum has been heterologously expressed in Lactococcus lactis and biochemically characterized. Recombinant GadB existed as a homodimer, and displayed maximal activity at 40°C and pH 5.0. The Km value and catalytic efficiency (kcat/Km) of GadB for L-Glu was 22.33mM and 62.4 mM-1min-1, respectively, with a specific activity of 24.97 U/mg protein. Then, purified GadB was encapsulated in gellan gum beads. Compared to the free enzyme, immobilized GadB showed higheroperationalandstoragestability. Finally, 9.82 to 21.48g/L of GABA have been acquired by regulating the amounts of catalyst microspheres ranging from 0.5 to 0.8g (wet weight) in 0.8mL of the designed rice vinegar and MSG reaction system. The method of production GABA by immobilized GadB microspheres mixed in the rice vinegar and MSG reaction system is introduced herein for the first time. Especially, the results obtained here meet the increased interest in the harnessing of biocatalyst to synthesize food-grade GABA.
Highlights
Introduction γAminobutyrate (GABA), a major inhibitory neurotransmitter in the mammalian central nervous system, has been reported to possess various important biological properties, such as antidiuretic, anti-hypertension, anti-oxidant, anti-fatigue, tranquilizing, and growthpromoting effects (Ngo and Vo 2019)
The gene encoding GadB from L. plantarum has been heterologously expressed in Lactococcus lactis and biochemically characterized
9.82 to 21.48 g/L of GABA have been acquired by regulating the amounts of catalyst microspheres ranging from 0.5 to 0.8 g in 0.8 mL of the designed rice vinegar and monosodium glutamate (MSG) reaction system
Summary
Introduction γAminobutyrate (GABA), a major inhibitory neurotransmitter in the mammalian central nervous system, has been reported to possess various important biological properties, such as antidiuretic, anti-hypertension, anti-oxidant, anti-fatigue, tranquilizing, and growthpromoting effects (Ngo and Vo 2019). Development of efficient approaches for the low-cost production of food-grade GABA becomes an important issue to meet its increasing commercial demand (Lyu et al 2017; Lyu et al 2020). GABA can be biosynthesized through reversible α-decarboxylation of L-glutamate (L-Glu) by glutamate decarboxylase (GAD, EC 4.1.1.15). A number of methods for the production of GABA by the microbes with high GAD activities or purified native and recombinant GADs have been developed (Lyu et al 2018; Pandey and Mishra 2021; Park et al 2021; Yogeswara et al 2020). Despite some achievements in whole cell microbial transformation, the enzymatic conversion cou ld be attractive in terms of the higher GABA yield and its purity (Cui et al 2020). The immobilized GADs are roughly limited in E. coli one or heterologously expressed in E. coli (Lammens et al 2009; Lee and Jeon 2014; Matsuura et al 2021)
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