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Chemists redesign natural antifreeze

Jessica Gorman

Chemists have created a family of synthetic compounds akin to proteins that keep Arctic and Antarctic fish from freezing stiff. If the new molecules can work as well as the fish proteins do, they could offer a new route to protecting frozen foods and chilled transplant organs from destructive ice buildup.

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Natural antifreeze keeps the Antarctic mackerel icefish supple.

K. Hoefling

Researchers discovered these so-called antifreeze proteins in the 1960s (SN: 4/19/97, p. 237). Scientists believe that the compounds bind to tiny ice crystals and make it harder for them to grow. Researchers have shown that the antifreeze proteins can thwart ice-crystal formation when added to food.

Yet, researchers haven't revealed molecular details of how the proteins work. Also, harvesting the proteins from fish is costly and time-consuming, says chemist Robert N. Ben of the State University of New York at Binghamton.

In the September-October Bioconjugate Chemistry, Ben and his colleagues report a new method for chemically synthesizing molecules that resemble sugar-containing antifreeze proteins called antifreeze glycoproteins.

The new chemical strategy creates a whole family of compounds, each one a variation on natural antifreeze glycoproteins, the team reports. Structural differences among the variants might help reveal the molecular motifs underlying the natural antifreeze proteins. Also, the variants might be more or less suited for specific anti-ice jobs, Ben says.

With an eye on commercial possibilities, the Binghamton team strengthened each of its molecules by creating a strong carbon-carbon bond in the location where the natural glycoproteins contain a weaker carbon-oxygen bond. With this added muscle, the synthetic molecules remain intact under certain chemical and biological conditions that destroy the natural glycoproteins, Ben says. That could make the new chemicals promising for ice-thwarting coatings, additives, or sprays for aircraft, concrete, or crops, he suggests.

Although the new molecules differ from the natural ones, Ben says preliminary evidence suggests his compounds bind to ice and inhibit crystal growth.

Chi-Hing C. Cheng, a biologist at the University of Illinois at Urbana-Champaign, calls the report "a gallant attempt" at synthesizing antifreezes. However, she adds, Ben's group must show that the molecules' anti-ice powers rival those of the natural glycoproteins or are better.

"Nature evolves a particular compound for a purpose," Cheng says. The added carbon-carbon bonds might make the new molecules more stable, but the proteins might need the carbon-oxygen bonds for good antifreeze activity, she says.

If the new molecules do prove as effective as natural agents, then the new synthesis techniques Ben's team developed might suggest a route to commercially viable antifreeze products, comments biochemist Robert E. Feeney of the University of California, Davis. A specific application would be to prevent the buildup of gritty ice granules in ice cream, he says.

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References:

Eniade, A., K.D. Williams, and R.N. Ben. 2001. Solid phase synthesis of C-linked antifreeze glycoprotein analogs and in vitro assessment of antifreeze protein-specific activity. 222nd National Meeting of the American Chemical Society. August 30. Chicago.

Eniade, A., … and R.N. Ben. 2001. A general synthesis of structurally diverse building blocks for preparing analogues of C-linked antifreeze glycoproteins. Bioconjugate Chemistry 12(September/October).

Further Readings:

1992. Something fishy about frozen livers. Science News 141(March 21):189.

Ben, R.N. 2001. Antifreeze glycoproteins—preventing the growth of ice. ChemBioChem 2(March):161–166.

Eniade, A., and R.N. Ben. 2001. Fully convergent solid phase synthesis of antifreeze glycoprotein analogues. Biomacromolecules 2(June):557–561.

Mlot, C. 1997. Evolutionary origins of fish antifreeze. Science News 151(April 19):237.

Peterson, I. 1986. A biological antifreeze. Science News 130(Nov. 22):330.

Wu, C. 1998. Fish enzyme flexes to adapt to the cold. Science News 154(Sept. 19):183.

______. 1997. Protein shells out guidance to crystals. Science News 152(Nov. 22):327.

______. 1997. Freeze! Insect proteins halt ice growth. Science News 152(Aug. 30):135. Available at Science News.

Sources:

Robert N. Ben
Department of Chemistry
State University of New York, Binghamton
Binghamton, NY 13902

Chi-Hing Christina Cheng
University of Illinois, Urbana-Champaign
Department of Animal Biology
515 Morrill Hall
505 South Goodwin Avenue
Urbana, IL 61801

Robert Feeney
Department of Food Science and Technology
104 IMR Building
University of California, Davis
Davis, CA 95616-8598


From Science News, Volume 160, No. 8, August 25, 2001, p. 119.