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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.

Author information

1
†FOM-Institute for Atomic and Molecular Physics AMOLF, Science Park 104, 1098 XG Amsterdam, The Netherlands.
2
‡Laboratory of Macromolecular and Organic Chemistry and Institute for Complex Molecular Systems, Eindhoven University of Technology, Postbus 513, 5600 MB Eindhoven, The Netherlands.
3
§Department of Animal Biology, University of Illinois at Urbana-Champaign, 515 Morrill Hall, Urbana, Illinois 61801, United States.
4
∥Department of Biological Sciences, University of Notre Dame, 100 Galvin Life Sciences Center, Notre Dame, Indiana 46556, United States.

Abstract

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.

KEYWORDS:

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

PMID:
26262966
DOI:
10.1021/acs.jpclett.5b00281
[Indexed for MEDLINE]

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