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Gamma-aminobutyric acid production using immobilized glutamate decarboxylase followed by downstream processing with cation exchange chromatography.

ABSTRACT: We have developed a gamma-aminobutyric acid (GABA) production technique using his-tag mediated immobilization of Escherichia coli-derived glutamate decarboxylase (GAD), an enzyme that catalyzes the conversion of glutamate to GABA. The GAD was obtained at 1.43 g/L from GAD-overexpressed E. coli fermentation and consisted of 59.7% monomer, 29.2% dimer and 2.3% tetramer with a 97.6% soluble form of the total GAD. The harvested GAD was immobilized to metal affinity gel with an immobilization yield of 92%. Based on an investigation of specific enzyme activity and reaction characteristics, glutamic acid (GA) was chosen over monosodium glutamate (MSG) as a substrate for immobilized GAD, resulting in conversion of 2.17 M GABA in a 1 L reactor within 100 min. The immobilized enzymes retained 58.1% of their initial activities after ten consecutive uses. By using cation exchange chromatography followed by enzymatic conversion, GABA was separated from the residual substrate and leached GAD. As a consequence, the glutamic acid was mostly removed with no detectable GAD, while 91.2% of GABA was yielded in the purification step.

SUBMITTER: Lee S

PROVIDER: S-EPMC3565344 | biostudies-literature | 2013

REPOSITORIES: biostudies-literature

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Gamma-aminobutyric acid production using immobilized glutamate decarboxylase followed by downstream processing with cation exchange chromatography.

Lee Seungwoon S Ahn Jungoh J Kim Yeon-Gu YG Jung Joon-Ki JK Lee Hongweon H Lee Eun Gyo EG

International journal of molecular sciences 20130115 1

We have developed a gamma-aminobutyric acid (GABA) production technique using his-tag mediated immobilization of Escherichia coli-derived glutamate decarboxylase (GAD), an enzyme that catalyzes the conversion of glutamate to GABA. The GAD was obtained at 1.43 g/L from GAD-overexpressed E. coli fermentation and consisted of 59.7% monomer, 29.2% dimer and 2.3% tetramer with a 97.6% soluble form of the total GAD. The harvested GAD was immobilized to metal affinity gel with an immobilization yield o ...[more]

PMID: 23322022

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Project description:BACKGROUND:Gamma-aminobutyric acid (GABA) is a non-protein amino acid present in all living things. GABA is mainly synthesized from glutamate by glutamate decarboxylase (GAD). In plants the enzymatic activity of GAD is activated by Ca2+/calmodulin binding (CaMBD) at the C-terminus in response to various stresses, allowing rapid GABA accumulation in cells. GABA plays a central role in not only stress responses but also many aspects of plant growth and development as a signaling molecules. Furthermore, it is known to be a health-promoting functional substance that exerts improvements in life-style related diseases such as hypertension, diabetes, hyperlipidemia, and so on. Previous reports indicated that CaMBD found plant GADs possess an autoinhibitory function because truncation of GAD resulted in extreme GABA accumulation in plant cells. Therefore, we attempted a genetic modification of rice GAD via genome editing technology to increase GABA levels in the edible part of rice. RESULTS:In this study, we focused on GAD3, one of five GAD genes present in the rice genome, because GAD3 is the predominantly expressed in seeds, as reported previously. We confirmed that GAD3 has an authentic Ca2+/CaMBD that functions as an autoinhibitory domain. CRISPR/Cas9-mediated genome editing was performed to trim the coding region of CaMBD off from the OsGAD3 gene, then introducing this transgene into rice scutellum-derived calli using an all-in-one vector harboring guide RNAs and CRISPR/Cas9 via Agrobacterium to regenerate rice plants. Out of 24 transformed rice (T1), a genome-edited rice line (#8_8) derived from two independent cleavages and ligations in the N-terminal position encoding OsGAD3-CaMBD and 40 bp downstream of the termination codon, respectively, displayed a AKNQDAAD peptide in the C-terminal region of the putative OsGAD3 in place of its intact CaMBD (bold indicates the trace of the N-terminal dipeptides of the authentic CaMBD). A very similar rice line (#8_1) carrying AKNRSSRRSGR in OsGAD3 was obtained from one base pair deletion in the N-terminal coding region of the CaMBD. Free amino acid analysis of the seeds (T2) indicated that the former line contained seven-fold higher levels of GABA than wild-type, whereas the latter line had similar levels to the wild-type, although in vitro enzyme activities of recombinant GAD proteins based on the GAD3 amino acid sequence elucidated from these two lines in the absence of Ca2+/bovine CaM were both higher than wild-type counterpart. In addition to high level of GABA in #8_8, the average seed weight per grain and protein content were superior to wild-type and #8_1. CONCLUSIONS:We have successfully established GABA-fortified rice by using CRISPR/Cas9 genome editing technology. Modified rice contained seven-fold higher GABA content and furthermore displayed significantly higher grain weight and protein content than wild-type brown rice. This is the first report of the production of GABA-enriched rice via a genome editing.

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Gamma-aminobutyric acid production using immobilized glutamate decarboxylase followed by downstream processing with cation exchange chromatography.

Publications

Gamma-aminobutyric acid production using immobilized glutamate decarboxylase followed by downstream processing with cation exchange chromatography.

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