Improved Productivity of Streptomyces mobaraensis Transglutaminase by Regulating Zymogen Activation

Streptomyces mobaraensis transglutaminase (TGase) is extracellularly expressed as a zymogen and then activated by TGase-activating protease (TAP). In this study, we reported the strategy for improving TGase production via the regulation of TAP activity in S. mobaraensis. First, we analyzed the effects of three inorganic nitrogen sources on TGase production. With 30 mM nitrogen content, the time to the peak of TGase activity induced by (NH₄)₂SO₄ or NH₄Cl was 72 h, 12 h earlier than that of the fermentation without adding NH₄ ⁺. SDS-PAGE analysis indicated that NH₄ ⁺ accelerated the TGase activation in S. mobaraensis. Then, we examined the effect of NH₄ ⁺ on TAP biosynthesis using a TGase-deficient S. mobaraensis strain. It showed that NH₄ ⁺ enhanced the TAP activity at the early stage of the fermentation, which was dependent on the concentration and time of NH₄ ⁺ addition. Last, the yield and productivity of S. mobaraensis TGase were increased by 1.18-fold and 2.1-fold, respectively, when optimal NH₄ ⁺ addition (60 mM and 12 h) was used. The fermentation period was shortened from 84 to 48 h. The NH₄ ⁺ addition also increased the storage stability of crude enzyme at room temperature. These findings will benefit the TGase production and its activation mechanism in S. mobaraensis.