Direct visualization of spruce budworm antifreeze protein interacting with ice crystals: basal plane affinity confers hyperactivity
Natalya Pertaya 1, Christopher B. Marshall 2, Yeliz Celik 1, Peter L. Davies 3 and Ido Braslavsky 1*
1 Department of Physics and Astronomy, Ohio University
2 Ontario Cancer Institute
3 Department of Biochemistry, Queen's University
* To whom correspondence should be addressed. E-mail: braslavs{at}ohio.edu.
Submitted on November 20, 2007
Revised on January 15, 2008
Accepted on 28 February 2008
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Abstract |
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Antifreeze proteins (AFPs) protect certain organisms from freezing by adhering to ice crystals, thereby preventing their growth. All AFPs depress the non-equilibrium freezing temperature below the melting point; however AFPs from overwintering insects, such as the spruce budworm (sbw) are 10 to 100 times more effective than most fish AFPs. It has been proposed that the exceptional activity of these AFPs depends on their ability to prevent ice growth at the basal plane. To test the hypothesis that the hyperactivity of sbwAFP results from direct affinity to the basal plane, we fluorescently tagged sbwAFP and visualized it on the surface of ice crystals using fluorescence microscopy. SbwAFP accumulated at the six prism plane corners and the two basal planes of hexagonal ice crystals. In contrast, fluorescently tagged fish type III AFP did not adhere to the basal planes of a single-crystal ice hemisphere. When ice crystals were grown in the presence of a mixture of type III AFP and sbwAFP, a hybrid crystal shape was produced with sbwAFP bound to the basal planes of truncated bipyramidal crystals. These observations are consistent with the blockage of c-axial growth of ice as a result of direct interaction of sbwAFP with the basal planes.
Key Words:
Antifreeze proteins, basal plane affinity, crystal growth, fluorescence microscopy, ice binding
