Inhibition of endogenous α-amylase and protease of Aspergillus flavus by trypsin inhibitor from cultivated and wild-type soybean

Abstract

The anti-Aspergillus flavus activity of trypsin inhibitor (TI) from cultivated and wild-type soybean (SBTI and WBTI) was investigated in order to confirm its ability to reduce the activity of endogenous α-amylase, protease enzymes and production of aflatoxin B1 secreted by A. flavus. In the current study, it was demonstrated that purified SBTI/WBTI belonged to the family of Bowman-Birk TI, based on evidence from amino acid composition, the presence of two independent binding sites for trypsin and chymotrypsin, and a lysine residue as the active site for trypsin inhibition. Studying the inhibition of A. flavus showed that the effect of SBTI/SBTI on A. flavus α-amylase activity and aflatoxin B1 production depended on TI concentration. However, no inhibitory effect was observed when sufficient exogenous α-amylase (EC 3.2.1.1, from Bacillus subtilis) was added. The resistance to A. flavus infection was partially due to the ability of SBTI/WBTI to inhibit α-amylase activity, thereby limiting the availability of hydrolyzed reducing sugar for fungal growth and further suppressing aflatoxin B1 biosynthesis. In addition, the relationship between SBTI/WBTI levels and fungal protease expression revealed that A. flavus released a certain quantity of endogenous proteases into the culture medium, and the decreased activity of protease and production of aflatoxin B1 suggested that the inhibition activity might also be mediated by SBTI/WBTI as A. flavus protease inhibitor activity.