Over-expression, secretion, biochemical characterisation, and structure analysis of Bacillus subtilis aminopeptidase

Background: Aminopeptidases have great application in the food industry. Current research on the expression of aminopeptidases mainly focuses on the Escherichia coli expression system. However, the application of recombinant E. coli in the food industry is restricted due to its pathogenicity and low secretory efficiency, which should be concerned in the industrial production of aminopeptidases.

Results: The gene of aminopeptidase from Bacillus subtilis Zj016 (BSAP) was identified. Over-expression and secretion of BSAP were achieved in a B. subtilis expression system with the signal peptide of itself. The yield researched 52 ± 1.9 U mL(-1) , which was 18 times that of the wild-type microbe. The purified enzyme was stable at pH 7.5-9.0 and below 60°C, and was inhibited by several metal ions except appropriate Co(2+) . BSAP was most active toward p-nitroaniline derivatives of Leu, Arg and Lys. Homology modelling and structure analysis showed that there was a flexible protease-associated domain in the predicted structure of BSAP.

Conclusions: The study presented a simple procedure for over-expression and purification of BSAP. The substrate specificity and structure information were indicated based on the characterisation and homology modelling. This will be useful for further research of aminopeptidases not only from an academic standpoint but also from an applied point of view.