Expression and identification of truncation Lactobacillus casei invertase based on rational design

In this study, a invertase-producing strain was screened and identified from soil samples of Qiandao Lake.The Lactobacillus casei invertase gene (LevH1) was amplified from L.casei complementary deoxyribonucleic acid (cDNA), and the recombinant L.casei invertase LEVH1-LC was obtained by constructing Escherichia coli.On the basis of rational design of enzyme, four invertase truncates LevH1-LC-N, LevH1-LC-C, LevH1-LC-NC and LevH1-LC-M were obtained by gene truncation technique, and their enzymatic properties were studied.The results showed that an excellent invertase-producing strain LC23 was obtained, which was identified as L.casei with enzyme activity of 0.06 U/ml.The LevH1-LC enzyme activity of recombinant L.casei invertase was 8.37 U/ml, which was 138 times higher than that of natural invertase.Compared with recombinant L.casei invertase LevH1-LC, the enzyme activities of truncates LevH1-LC-N and LevH1-LC-NC were increased 4.1 times and 6.6 times, respectively, and the enzyme activity was increased 568.5 times and 923.7 times compared with natural invertase.The results of enzyme kinetic analysis showed that the catalytic efficiency of truncate LevH1-LC-NC was the highest, which was 29.7 times that of recombinant L.casei invertase LevH1-LC.The optimum reaction temperature and pH were 50 ℃ and 6.0, respectively, indicating good thermal stability and pH stability.Therefore, the truncate LevH1-LC-NC was a superior invertase mutant.