Improved structure and enhanced the insecticidal activity of Sip1Aa protein by adding disulfide bonds

Abstract Sip1Aa is an insecticidal protein of Bacillus thuringiensis at the secretory stage. It has a strong toxic effect on the members of order Coleoptera. To date, there are few available studies on Sip1Aa protein and the inclusion body problem is serious, and this raises the importance to conduct further studies on Sip1Aa protein. Disulfide bonds, as the only covalent bond on protein side chains, play an important role in the stability and function of the proteins. The tertiary structure of Sip1Aa protein was analyzed by homologous modeling and other bioinformatics methods to predict the conserved domain of Sip1Aa protein. Cysteine used to replace these amino acids by site-directed mutation. Consequently, we were able to successfully construct Sip149-251, Sip153-248, Sip158-243, and Sip178-314. These were exposed to ultraviolet radiation, and we found that Sip153-248 and Sip158-243 were the most stable, followed by Sip149-251 and Sip178-314 when compared with Sip1Aa. After the mutant strain was transferred into Escherichia coli BL21, sodium dodecyl sulfate-polyacrylamide gel electrophoresis was used to detect the inducible expression products. Approximately 37.6 kDa of proteins that were highly expressed in E. coli. We found no significant change in the insecticidal activity.