Glutamate Decarboxylase from Lactic Acid Bacteria-A Key Enzyme in GABA Synthesis.

Ida Bagus Agung Yogeswara,Suppasil Maneerat,Dietmar Haltrich

doi:10.3390/microorganisms8121923

Abstract

Glutamate decarboxylase (l-glutamate-1-carboxylase, GAD; EC 4.1.1.15) is a pyridoxal-5’-phosphate-dependent enzyme that catalyzes the irreversible α-decarboxylation of l-glutamic acid to γ-aminobutyric acid (GABA) and CO2. The enzyme is widely distributed in eukaryotes as well as prokaryotes, where it—together with its reaction product GABA—fulfils very different physiological functions. The occurrence of gad genes encoding GAD has been shown for many microorganisms, and GABA-producing lactic acid bacteria (LAB) have been a focus of research during recent years. A wide range of traditional foods produced by fermentation based on LAB offer the potential of providing new functional food products enriched with GABA that may offer certain health-benefits. Different GAD enzymes and genes from several strains of LAB have been isolated and characterized recently. GABA-producing LAB, the biochemical properties of their GAD enzymes, and possible applications are reviewed here.

Highlights

Lactic acid bacteria (LAB) are Gram-positive, acid-tolerant, non-spore forming bacteria, with a morphology of either cocci or rods that share common physiological and metabolic characteristics
The occurrence of gad genes encoding glutamate decarboxylase (GAD) has been shown for many microorganisms, and glutamic acid to γ-aminobutyric acid (GABA)-producing lactic acid bacteria (LAB) have been a focus of research during recent years
GABA biosynthesis can be achieved by using whole cell reactions, recombinant bacteria, and purified GAD (Table 3). gad genes from various sources of LAB have been overexpressed in different hosts including E. coli [86], L. sakei [87], L. plantarum [88], Corynebacterium glutamicum [89], and Bacillus subtilis [90]

Summary

Introduction

Lactic acid bacteria (LAB) are Gram-positive, acid-tolerant, non-spore forming bacteria, with a morphology of either cocci or rods that share common physiological and metabolic characteristics. LAB are among the most important organisms when it comes to the fermentation of various food raw materials They efficiently and rapidly convert sugars into lactic acid as their main metabolic product (or one of their main products), and contribute to the preservation of these fermented foods. Many of these raw materials or foods contain glutamate in significant amounts, which can be utilized by LAB to increase their tolerance against acidic conditions. A number of GABA-producing LAB have been isolated from a wide range of fermented foods including cheese, kimchi, paocai, fermented Thai sausage nham, or various fermented Asian fish products [2,13,25,26,30] (Table 1). 30 ◦C, 72 h 30 ◦C, 24 h pH 6.5, 37 ◦C, 48 h 30 ◦C, 96 h pH 5.25, 37 ◦C, 48 h 37 ◦C, 108 h

Improvement of GAD Activities and GABA Production

Findings

Future Trends and Conclusions