Transaminase encoded by NCgl2515 gene of Corynebacterium glutamicum ATCC13032 is involved in 7-aminobutyric acid decomposition

摘要

Corynebacterium glutamicum that expresses an exogenous L-glutamate decarboxylase (GAD) gene can synthesize gamma-aminobutyric acid (GABA). GABA is decomposed to succinic semialdehyde (SSA) by GABA transaminase (GABA-T) and to succinate thereafter by SSA dehydrogenase (SSADH). However, deletion of the gabT gene encoding GABA-T could not prevent GABA from decomposing at neutral pH. In this study, an additional transaminase gene, NCgl2515, was deleted in a gabT-deleted GAD strain, and GABA fermentation in this gabT NCgl2515-deleted GAD strain was investigated. GABA concentration remained at 22.5-24.0 g/L when pH was maintained at 7.5-8.0, demonstrating that GABA decomposition was reduced. Activity assay indicated that unlike GabT, which exhibits high GABA-T activity (1.34 +/- 0.06 U/mg) and utilizes only alpha-ketoglutarate as amino acceptor, the purified NCgl2515 protein exhibits very low GABA-T activity (approximately 0.03 U/mg) only when coupled with the SSADH, GabD, but can utilize both alpha-ketoglutarate and pyruvate as amino acceptor. The optimum pH for coupled NCgl2515-GabD was 8.0, similar to that of GabT (7.8). Therefore, NCg12515 has weak GABA-T activity and is involved in GABA decomposition in C. glutamicum. Deletion of gabT and NCgl2515 could effectively reduce GABA decomposition at neutral pH. (C) 2017 Elsevier Ltd. All rights reserved.