Transformation And Conformational Changes Of Bt Protein On Mineral Surface

With the large-scale promotion and application of commercialization of transgenic Bt crops,its potential harm to farmland ecosystems has attracted more and more attention.A large number of studies in China and abroad have shown that the Bt proteins expressed in transgenic Bt crops are released into the soil in different ways and remain in the soil for a long time,affecting the soil ecosystem.In this paper,the adsorption and desorption behaviors of transgenic Bt crop virulence proteins on soil minerals,including toxic proteins and conformational changes after adsorption and desorption reactions,were analyzed by FTIR,fluorescence and CD spectroscopy.The adsorption and desorption mechanism of Cry1 Ac protein and the relationship of protein conformation was discussed,which provided a reference for the ecological risk assessment of soil environment by Bt crops.It was found that Cry1 Ac protein was adsorbed on the surface of soil minerals by electrostatic interaction at some sites.The change of pH could affect the interaction between them,which affected the adsorption state of Cry1 Ac protein on soil mineral surface.Among different soil minerals,the optimum pH value of Cry1 Ac protein adsorption is different,and it is more favorable for the adsorption of toxin protein under neutral and alkaline conditions.When the pH reached 7.6,the adsorption capacity and adsorption strength of Cry1 Ac protein on the surface of soil minerals increased significantly.The increase in temperature and the decrease in buffer concentration are not conducive to the adsorption of Bt protein on the surface of kaolinite and montmorillonite minerals.Infrared spectra of Cry1 Ac protein and different soil minerals showed that there was no obvious protein absorption peak due to the low concentration of added protein,and no other characteristic peaks were observed.It could not explain the Cry1 Ac protein conformation during the adsorption process.Fluorescence spectroscopy showed that after adding three different RL to desorp the Cry1 Ac protein,the fluorescence peak of the protein molecule was red-shifted,indicating that the environmental polarity of the amino acid residue was enhanced.After the addition of the surfactant CTAB desorption,the red shift phenomenon in the kaolinite system is more obvious,but the protein fluorescence intensity is weakened.It can be seen from the fluorescence spectrum after desorption of SDS that the emission peaks of kaolinite and montmorillonite have a weak blue shift phenomenon,and the fluorescence intensity is stronger than that of the free protein after adsorption.It can be seen that the conformation of the protein changes after the addition of different surfactants.Circular dichroism spectroscopy shows that the interaction of different surfactants with soil minerals after adsorption of proteins leads to changes in the secondary structure of the protein(?-helix,?-sheet,?-turn,free curl).In the kaolinite system,the ?-helix content increases and the ?-sheet decreases,while the ?-sheet structure is hydrophobic,and the decrease of the ?-sheet content causes a large decrease in the hydrophobic region in the system,thereby obtaining a decrease in the fluorescence intensity in the fluorescence spectrum due to the surface.The addition of the active agent concluded that the hydrophobicity of the Cry1 Ac protein was reduced.The experimental results lay a scientific basis for the environmental behavior regulation of protein pollutants in the soil medium environment,and provide reference for the ecological risk assessment of soil environment by Bt crops.