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J Phys Chem Lett. 2015 Apr 2;6(7):1162-7. doi: 10.1021/acs.jpclett.5b00281. Epub 2015 Mar 18.

Investigation of the Ice-Binding Site of an Insect Antifreeze Protein Using Sum-Frequency Generation Spectroscopy.

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†FOM-Institute for Atomic and Molecular Physics AMOLF, Science Park 104, 1098 XG Amsterdam, The Netherlands.
‡Laboratory of Macromolecular and Organic Chemistry and Institute for Complex Molecular Systems, Eindhoven University of Technology, Postbus 513, 5600 MB Eindhoven, The Netherlands.
§Department of Animal Biology, University of Illinois at Urbana-Champaign, 515 Morrill Hall, Urbana, Illinois 61801, United States.
∥Department of Biological Sciences, University of Notre Dame, 100 Galvin Life Sciences Center, Notre Dame, Indiana 46556, United States.


We study the ice-binding site (IBS) of a hyperactive antifreeze protein from the beetle Dendroides canadensis (DAFP-1) using vibrational sum-frequency generation spectroscopy. We find that DAFP-1 accumulates at the air-water interface due to the hydrophobic character of its threonine-rich IBS while retaining its highly regular β-helical fold. We observe a narrow band at 3485 cm(-1) that we assign to the O-H stretch vibration of threonine hydroxyl groups of the IBS. The narrow character of the 3485 cm(-1) band suggests that the hydrogen bonds between the threonine residues at the IBS and adjacent water molecules are quite similar in strength, indicating that the IBS of DAFP-1 is extremely well-ordered, with the threonine side chains showing identical rotameric confirmations. The hydrogen-bonded water molecules do not form an ordered ice-like layer, as was recently observed for the moderate antifreeze protein type III. It thus appears that the antifreeze action of DAFP-1 does not require the presence of ordered water but likely results from the direct binding of its highly ordered array of threonine residues to the ice surface.


air−water interface; antifreeze proteins; chiral sum-frequency generation spectroscopy; phase-sensitive sum-frequency generation; protein−water interface

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