Altered secretary efficiency of Streptomyces hygroscopicus transglutaminase in Escherichia coli by the pro-peptide modification

• The N-terminal α-helix12–30 is essential for the pro-TGase folding and secretion by disruption of the hydrogen bonds.
• The α-helix37–42 has negative influence in TGase activity.
• The accumulation of pro-TGase in supernatant secreted by the mutant without loop43–52 increased by 70%.

Streptomyces transglutaminase (TGase) is naturally synthesized as a zymogen (pro-TGase), which is then processed to produce the active enzyme through removal of its pro-peptide. In this study, we investigated the effect of the pro-peptide on the secretion of Streptomyces hygroscopicus TGase in Escherichia coli by modifying its pro-peptide. Four N-terminal amino acid residues (Tyr12, Asn27, Asn30, and Arg32) in the pro-peptide predicted to interact with TGase region through hydrogen bonds. When the four amino acid residues were mutated into Ala, the secretion of TGase was partially or completely inhibited. Furthermore, deletion of the C-terminal α-helix37–42 in the pro-peptide concomitantly decreased the secretion of TGase. However, deletion of the C-terminal loop43–52 of the pro-peptide, resulted in increased secretion of TGase by approximately 70% as compared with the control native pro-peptide. These findings indicate that modification of the pro-peptide has a significant impact on the secretory efficiency of TGase in E. coli.