Specific bacteria, such as Pseudomonas syringae,  attack plants by using ice-nucleating proteins anchored to their outer cell surfaces. Ice nucleating proteins promote the massive crystallization of ice at temperatures that would otherwise not allow ice formation. The frost damage caused by ice crystals then facilitates bacterial invasion of the affected plants. Ice nucleating proteins not only play an important role for agriculture, but are also very important for atmospheric processes: airborne ice-nucleating proteins have been shown to be among the most effective promoters of ice particle formation in the atmosphere. A recent NASA survey of bacteria in the troposphere has discovered large emissions of biogenic ice nucleators from large forest areas like the amazon, which likely change precipitation patterns and may affect the global climate. To understand biogenic ice formation, a detailed molecular level picture of the mechanism by which ice-nucleating proteins interact with water molecules is important. Sum frequency generation (SFG) spectroscopy � owing to its inherent interface sensitivity � is ideally suited to determine the structure and dynamics of water molecules at interfaces. Here, we report on the interaction a layer of the ice-nucleating protein inaZ with water using static and time-resolved SFG spectroscopy. When cooling the sample from room temperature to near-freezing temperatures (~5�C for D2O), inaZ significantly increases the structural order of water molecules in contact with inaZ proteins. This effect was not observed for liquid water surfaces without the protein or for protein monolayers which are not ice nucleators. The data indicates the activation of a specific binding mechanism at lower temperatures. Femtosecond, time- resolved 2-dimensional SFG spectroscopy was used to quantify the energy transfer from intrfacial water towards the protein contacts.

Molecular perspective on water structure and motion at the surface of climate-active ice nucleating proteins

247th National Meeting (2014)

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