Enzymatic synthesis of γ-glutamylmethylamide from glutamic acid γ-methyl ester and methylamine catalyzed by Escherichia coli having γ-glutamyltranspeptidase activity

Effects of pH and NaCl on hydrolysis and transpeptidation activities of a salt-tolerant γ-glutamyltranspeptidase from Bacillus amyloliquefaciens S0904

Bacillus amyloliquefaciens S0904 was selected as a hyperproducer of a glutamine-hydrolyzing enzyme which was identified as a γ-glutamyltranspeptidase catalyzing both hydrolysis and transpeptidation of glutamyl substrates. The signal peptide-truncated recombinant enzyme (rBAGGT) showed two-fold enhanced specific activity for hydrolysis and optimum pH shift to pH 7 from pH 6 compared with the wild type. The hydrolysis activity of rBAGGT was tolerant against NaCl up to 2.5 M, whereas the transpeptidation activity decreased by NaCl. At pH 6, the addition of 1.5 M NaCl not only enhanced the hydrolysis activity but also inhibited the transpeptidation activity to be ignorable. By contrast, at pH 9 in the absence of NaCl, the alkaline pH-favored transpeptidation activity was 99% of the maximum with only 15% of the maximum hydrolysis activity. In conclusion, the hydrolysis and transpeptidation activities of the recombinant BAGGT is controllable by changing pH and whether or not to add NaCl.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10068-021-00928-6.

Ultrasound enhanced biosynthesis of L-theanine from L-glutamine and ethylamine by recombinant γ-glutamyltranspeptidase

A mutant library of the key amino acid residue site E387 in γ-glutamyltranspeptidase was constructed to screen the mutant enzymes with significantly improved thermal stability (E387Q). The reaction temperature of the mutant enzyme (E387Q) was 10℃ higher than that of the parent enzyme. Ultrasound-assisted synthesis of L-theanine by γ-glutamyltranspeptidase was investigated. The effects of ultrasonic power, reaction pH and substrate concentration on the enzymatic synthesis of L-theanine were studied by the response surface method. The results showed that the optimal process conditions are ultrasonic power of 100 W, reaction pH of 9, substrate L-glutamine concentration of 120 mmol/L, reaction temperature of 45℃, and L-theanine yield of 89.1%. The yield of L-theanine is 2.61 times higher than that obtained without ultrasound. Ultrasound can significantly promote the synthesis of L-theanine by γ-glutamyltranspeptidase.