资源环境科技发展态势分析平台

Ice nucleation active bacteria have attracted particular attention due to their unique ability to produce specific ice nucleation proteins (INpros), which are the most efficient ice nuclei known as they induce nucleation at temperatures close to 0 degrees C. Our model bacterium Pseudomonas syringae strain R10.79 produced INpros containing 67 tandem repeats, forming the proposed ice-binding surface. To understand the role of the INpro repeats as well as the role of intermolecular interactions between INpros for their ice nucleation behavior, we produced a truncated version of the protein with only 16 tandem repeats (INpro(16R)). The purified INpro(16R) produced oligomers of varying sizes. Immersion freezing ice nucleation behavior of purified INpro(16R) was characterized by droplet-freezing assays and in the Leipzig Aerosol Cloud Interaction Simulator. Predominant INpro(16R) oligomers introduced into Leipzig Aerosol Cloud Interaction Simulator as single particles with diameters of 50nm or 70nm were ice nucleation active at temperatures of -26 degrees C and -24 degrees C, respectively. These are much lower temperatures compared to that of intact INpros (-12 degrees C). The data clearly indicated that the number of repeats determines the ice nucleation temperature. In addition, ice nucleation between -9 degrees C and -10 degrees C, comparable to the activity of intact INpro, was caused by higher-order INpro(16R) oligomers. This supported previous observations that INpro oligomerization increases the ice-binding surface, thereby affecting ice nucleation activity. In conclusion, both repeat number and oligomerization contribute in a seemingly independent manner to the nucleation mechanism of INpros.