Scientists put 'antifreeze' protein under the microscope

Scientists studying the natural "antifreeze" proteins that allow fish to swim in Arctic waters and insect larvae to withstand harsh winters have developed a new tool for witnessing the proteins in action, one they hope will aid in the design of molecules able to keep organs alive and resist damage from freezing.

Antifreeze proteins also called ice-structuring proteins or ISPs to disassociate them from the toxic coolant used in automobiles attach to the surface of ice crystals and act as a barrier between the crystals and water.

This inhibits the growth of the crystals and allows some animals, plants, fungi and bacteria to stay alive at temperatures where their tissue would normally freeze.

But scientists have long been confused as to how exactly the protein bonds withan ice crystal and why some of these proteins including those found in many insects have developed to withstand far colder temperatures than others. The proteins found in certain species of fish, for example, are generally weaker at preventing ice crystallization.

To betterexamine the process, Ohio University professor Ido Braslavsky working in conjunction with Queen's University biochemistry professor Peter Davies combined the ISPs with fluorescent proteins derived from jellyfish, allowing researchers to see for the first time under a microscope the bonding of the proteins to ice crystals.

Braslavsky and Davies wrote a paper describing the process using weaker ISPs found in fish in the March issue of the Biophysical Journal.

"It's the first time we've seen the antifreeze protein bond on the ice," said Davies, the Canada Research Chair in protein engineering in an interview with CBC News Online. "We used to have to look at the change in shape of the ice crystals or look at the residue and try and derive what had happened."

Braslavsky and Davies also looked at the far more active ISP of the spruce budworm, an insect familiar to Canadians for its destructive effects on northern forests, which iscapable of withstanding temperatures as low as 30 C when in its larval stage. Braslavsky presented these findings at the March meeting of the American Physical Society.

What they found was thatthe much stronger ISP of the spruce budworm bonded to the ice crystal on its broadest face, restricting growth far more efficiently than weaker proteins, which tended to attach only to the edges of the crystals.

The results are the first step in understanding how these proteins work, said Davies, and could be usefulin engineering more efficient proteins capable of withstanding even greater temperatures.

Ice cream manufacturers already use ISPsin some of their products to improve the texture of low-fat ice cream, and researchers believe they could be cultivated to preserve organs and tissues for medical applications such as transplants.