Heterologous signal peptides-directing secretion of Streptomyces mobaraensis transglutaminase by Bacillus subtilis

Microbial transglutaminase (MTG) from Streptomyces mobaraensis has been widely used for crosslinking proteins in order to acquire products with improved properties. To improve the yield and enable a facile and efficient purification process, recombinant vectors, harboring various heterologous signal peptide-encoding fragments fused to the mtg gene, were constructed in Escherichia coli and then expressed in Bacillus subtilis. Signal peptides of both WapA and AmyQ (SP (wapA) and SP (amyQ) ) were able to direct the secretion of pre-pro-MTG into the medium. A constitutive promoter (P (hpaII) ) was used for the expression of SP (wapA) -mtg, while an inducible promoter (P (lac) ) was used for SP (amyQ) -mtg. After purification from the supernatant of the culture by immobilized metal affinity chromatography and proteolysis by trypsin, 63.0 +/- 0.6 mg/L mature MTG was released, demonstrated to have 29.6 +/- 0.9 U/mg enzymatic activity and shown to crosslink soy protein properly. This is the first report on secretion of S. mobaraensis MTG from B. subtilis, with similar enzymatic activities and yields to that produced from Escherichia coli, but enabling a much easier purification process.