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Hyperactive Antifreeze Proteins |
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Written by xScience.Info
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Wednesday, 14 March 2007 |
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Hyperactive antifreeze proteins naturally secreted by an insect
known as the spruce budworm, prevent it from freezing to death
during winters in North American forests. Ohio University's Ido
Braslavsky and his colleagues
presented studies of these potent yet nontoxic proteins at this
week’s APS Meeting.
 Ice crystals decorated by fluorescent antifreeze proteins. Left: AFP type III (orange) and sbwAFP (green) mix, right: AFP type I (red) and sbwAFP (green) mix. Images: I. Braslavsky
Found in several other species such as snow
fleas, the hyperactive proteins bind to ice, modify its crystalline
shape, and prevent ice from growing further, effectively reducing
the freezing point of ice for an organism that excretes them. These
nontoxic substances have more recently been renamed "ice structuring
proteins" (ISPs) to distinguish them from the toxic antifreeze
products for automobiles.
Extracting ISPs from biological sources
has many potential applications, such as preserving organs and blood
products, protecting against agricultural frost damage, and even
preventing frostbite. These natural proteins are currently used in
some "light" ice cream products to improve their texture, but those
ISPs, derived from fish, are much less potent.
 Ice crystals decorated by fluorescent antifreeze proteins. Images: Pertaya et al, Biophysical Journal 2007, in press; Publish Online at BioFast 26 Feb 2007
How the hyperactive versions inhibit ice from growing is a topic of
interest to Braslavsky's group and their collaborators, such as
Peter Davies from Queen's University. The
researchers attached fluorescent molecules, derived from jellyfish,
to the protein.
Through a microscope, they watched how the
fluorescing ISPs inhibited ice crystals from growing. They observed
that the ISPs prevent ice crystals from expanding in their normal
disk-shaped form. Instead, they inhibit ice growth in certain
directions and cause the crystals to grow in altered shapes.
While a
fish ISP promotes the growth of a "bipyramidal" ice-crystal form
that looks like two pyramids whose bases are attached to each other,
the spruce budworm ISP blocks growth in the preferred direction of
the pyramid's apexes. Using the fluorescence microscopy they watched
the proteins attached to the ice blocking growth in this direction.
For more
information, see http://www.phy.ohiou.edu/~braslavs/APS2007/
Source: API
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