Discovering secrets of 'natural antifreeze'

For 50 years researchers have been baffled by the enigma of natural antifreeze production in animals and plants living in cold climates. The natural antifreeze proteins (AFP) serve as a survival mechanism and prevent organic fluids from crystallizing and forming ice.

However, a team of Israeli, American and Canadian scientists that investigated this process believe that it has found an explanation and recently published their work in the American journal PNAS (Proceedings of the National Academy of Sciences).

Working on unraveling the AFP enigma were Dr. Ido Braslavsky of the Hebrew University and Ohio University, in collaboration with Prof. Peter Davies of Queens University in Ontario and Prof. Alex Groisman of the University of California in San Diego.

The significance of the scientists’ findings offer important insight on a scientific and practical level. For example, low-fat ice cream already uses fish AFPs to prevent ice recrystallization, allowing it to maintain its soft and creamy texture. These proteins can also be used in other frozen foods for maintaining the desired texture without additional fats, researchers said.

In medicine, AFPs can be used to improve the quality of sperm, ovules and embryos stored in a frozen state. Additionally, it can improve the cyropreservation of organs for transplantation. They can also be used for cryosurgery and agriculture purposes.

Other studies on AFPs focus on preparation of recombinant plants and fish with improved survival rates in cold climates and conditions that lead to dehydration.

Researchers believe such recombinant crops may improve food dispersion over the world.

The production of antifreeze proteins in living things is one of the major evolutionary routes taken by a variety of organisms. These include fish, insects, bacteria, plants and fungi. To understand how this mechanism works is significant not only in itself, but also has important implications for improving food and medicine production around the world, the researchers wrote.

Members of the academic community continue to this day to discuss and debate on the chemistry and physics behind the interactions of AFPs and ice.

In particular, there is an ongoing argument over whether the binding of certain proteins to ice is reversible. Additionally, opinions vary on whether the continued presence of these proteins in a solution prevents ice growth.

The challenge in unraveling these questions is finding viable solutions to produce an experiment in a controlled setting. The growth and tracking of tiny ice crystals in an environment that mimics the surroundings of the antifreeze proteins in nature give rise to a host of technical problems.

To circumvent such problems, Israeli and North American researchers studied the antifreeze protein of the yellow mealworm. This protein is a hyperactive AFP with a potency to arrest ice growth hundreds of times greater than the potency of those present in fish and plants.

A fluorescent marker version of the AFP was biochemically created in order to allow for direct observation under a microscopic lens.

The protein was then injected into custom-designed microfluidic devices with minute diameter channels.

The microfluidic devices were then placed in cooling units engineered with a temperature control at the level of a few thousandth of a degree, so that ice crystals of 20 to 50 micrometers could be grown and melted controllably, all under microscopic observation.

Using this specialized system, researchers were able to show that the ice grown and incubated in an antifreeze solution remains coated with protein and thus, protected.

It was then shown that the AFPs bind ice directly and strongly enough so as to prevent the ice from growth even after there is no longer any further presence of protein in the solution.