Application of recombinant Bacillus subtilis γ-glutamyltranspeptidase to the production of l-theanine

• γ-GGT from B. subtilis 168 was expressed in E. coli with an activity of 80 U/mL.
• The properties of the recombinant GGT are suitable for l-theanine production.
• An effective method was established for large-scale production of l-theanine.
• Yield of l-theanine reached as high as 78%, 58% or 45% with 0.2 M, 0.5 M or 1 M Gln, respectively.

l-Theanine, which has seen increasing use in the functional food industry, can be prepared via enzymatic synthesis using γ-glutamyltranspeptidase (GGT; EC 2.3.2.2). In this study, the GGT from Bacillus subtilis 168 was cloned and expressed as a secreted protein using Escherichia coli BL21(DE3). The enzymatic properties of the GGT and the optimal conditions for the enzymatic synthesis of l-theanine were investigated in detail. The activity of the enzyme was optimal at pH 10; the optimal temperature was 50 °C. Desirable pH stability was observed between pH 5 and pH 12, and adequate thermostability was seen at 50 °C. In 5 h at 37 °C, the enzyme converted 200 mM l-glutamine and 2.2 M ethylamine to l-theanine with a final yield of 78%. Yields of l-theanine decreased to 58% when using 500 mM Gln and 45% when using 1 M Gln. The yield of l-theanine obtained at high substrate concentration provides the basis for the industrial-scale production of l-theanine.

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