coli and are correctly processed. Dispase activates S. mobaraensis pro-TGase when incubated in a Tris–HCl buffer at pH 8 (Marx et al., 2007). To study the activation efficiency of pro-TGase in culture supernatants, the dispase solution was added directly to the culture supernatant of E. coli expressing pBB1-1010 or pBB1-1020. SDS-PAGE analysis showed that the pro-TGase secreted by E. coli expressing pBB1-1010 was rapidly transformed (within 30 min) into a smaller protein with a
molecular weight corresponding to that buy ICG-001 of the mature TGase (37.8 kDa), and TGase activity increased during the process (Fig. 2d,e). In addition, the intensity of the band corresponding to TGase and the TGase activity remained constant (approximately 4.5 U mL−1) in the later stages of activation (Fig. 2d,e). As expected, activation of the pro-TGase secreted by E. coli expressing pBB1-1020 showed a similar trend (data not shown). These results demonstrate that the secreted pro-TGase is directly activated by dispase and is not continuously degraded. It has been reported that the N-terminal pro-region of thermophilic subtilase greatly influences the secretion of its zymogen in E. coli (Fang et al., 2010). To elucidate the role of the TGase pro-region during pro-TGase secretion, N-terminal deletion mutants within the TGase pro-region were constructed. Each deletion was designed to remove a conserved part of
the pro-region of TGase as determined by the alignment of sequences from different Streptomyces strains (Fig. 1b). When the first six N-terminal amino acids of pro-TGase were removed, the secretion of the corresponding pro-TGase derivative decreased GSK2118436 datasheet (Fig. 3b), and intracellular accumulation of
the soluble pro-TGase derivative was observed PDK4 (Fig. 3c). After removal of the first 16 N-terminal amino acids of the pro-region, neither extracellular (Fig. 3b) nor intracellular soluble (Fig. 3c) pro-TGase derivatives were detected. However, an insoluble pro-TGase derivative was present (Fig. 3d). Further deletion of amino acids at the N-terminal of pro-TGase produced only insoluble pro-TGase derivatives (Fig. 3d). These results show that the pro-region of TGase is essential for TGase secretion and solubility in E. coli. Without disruption of cells, the efficient secretion of TGase in E. coli would undoubtedly simplify the recovery of the enzyme and the screening of mutants for directed evolution. In this study, S. hygroscopicus pro-TGase was efficiently secreted in E. coli using the TGase signal peptide or the pelB signal peptide. After activation in the culture supernatant, the yield of secreted TGase was 4.5 U mL−1, which is three times the amount of the TGase produced intracellularly (Marx et al., 2007). However, the S. mobaraensis pro-TGase that is fused to the pelB signal peptide failed to be secreted in E. coli (Marx et al., 2007; Yang et al., 2009). It has been reported that export of the glycolytic enzyme in E.