Production and characterization of the 13C/15N single‐labeled insecticidal protein Cry1Ab/Ac using recombinant Escherichia coli

Synthetic Cry1Ab/Ac proteins expressed by genetically modified (GM) crops have a high potential to control insect pests without utilizing large amounts of chemical insecticides. Before these crops are used in agriculture, the environmental fate and interactions in the soil must be understood. Stable isotope‐labeled Cry1Ab/Ac protein is a highly useful tool for collecting such data. We developed a protocol to produce 13C/15N single‐labeled Cry proteins. The artificially synthesized gene Cry1Ab/Ac of Bt rice Huahui No. 1, which has been certified by the Chinese government to be safe for human consumption, was subcloned into pUC57, and the expression vector pET‐28a‐CryAb/Ac was constructed and transformed into Escherichia coli BL21 (DE3) competent cells. Next, 0.2 mM isopropyl thiogalactoside (IPTG) was added to these cells and cultured at 37°C for 4 h to induce the synthesis and formation of inclusion bodies in M9 growth media containing either [U‐13C] glucose (5% 13C‐enriched) or [15N] ammonium chloride (5% 15N‐enriched). Then, Cry inclusion bodies were dissolved in urea and purified by affinity chromatography under denaturing conditions, renatured by dialysis, and further detected by sodium dodecyl sulfate–polyacrylamide gel electrophoresis (SDS‐PAGE) and Western blotting. The purities of 13C/15N‐labeled Cry proteins reached 99% with amounts of 12.6 mg/L and 8.8 mg/L, respectively. The δ 13C and ä 15N values of 13C‐labeled Cry protein and 15N‐labeled Cry protein were 3,269‰ and 2,854‰, respectively. A bioassay test revealed that the labeled Cry1Ab/Ac proteins had strong insecticidal activity. The stable isotope‐labeled insecticidal Cry proteins produced for the first time in this study will provide an experimental basis for future metabolic studies on Cry proteins in soil and the characteristics of nitrogen (N) and carbon (C) transformations. Our findings may also be employed as a reference for elucidating the environmental behavior and ecological effects of BT plants and expressed products. We established in this study a method to produce 13C/15N single‐labeled insecticidal protein Cry1Ab/Ac using a recombinant Escherichia coli strain. A stable isotope‐labeled Cry protein existing in the form of inclusion bodies was solubilized, purified, and refolded successfully, revealing strong insecticidal activity. Our results lay a foundation for the further study of the metabolic fate, biological function, and safety evaluation of Cry proteins.