Close This Window

Please download official ILL logos here


For using on the web or on a screenFor printing in high resolutionWhite version, for dark backgrounds

Download PNG

Download AI

Download white PNG

Download JPG


Download white AI

How Arctic fish’s antifreeze proteins work

For any media request, please contact, or phone +33 4 76 20 71 07

Back to ILL Homepage
www > Press and news > Press room > Press releases > How Arctic fish’s antifreeze proteins work
English French Deutsch 

Press room

Neutron science explains mystery of how Arctic fish’s antifreeze proteins work. 7.04.2011

Neutron scientists have discovered for the first time how ‘antifreeze’ in arctic fish blood kicks in to keep them alive in subzero conditions. The results could provide benefits for areas as diverse as cryosurgery, food processing and agriculture.

Biological antifreeze proteins (AFPs) are unusual proteins in several ways. They safeguard organisms from freezing to death by binding to ice crystal nuclei as soon as they start to form in bodily fluids, and prevent them from growing into ice crystals. However, AFPs must not attach to liquid water otherwise the organism would dehydrate and die. New research using neutrons provides the first experimental data showing how type-III AFPs, found in arctic fish blood, recognise the ice crystal nuclei. It found that unusual hydrophobic regions on the protein surface fit into ‘holes’ in the ice crystal nuclei structure.

“AFPs are unusual proteins with a difficult job. We wanted to understand how they can work in an aqueous environment like blood but only interact with H2O molecules when they start to freeze. Neutron scattering provided essential information about how this happens. We found that the key is how the AFPs’ structure differs from typical proteins, and how the structure of ice compares with liquid water,” says Matthew Blakeley, an instrument scientist at ILL.
Biological proteins usually have hydrophobic amino acids in the core (away from water molecules in the solvent) and hydrophilic amino acids on the surface. Unusually, AFPs have many hydrophobic amino acids on their surface. These form part of the special binding surface that only sticks to ice nuclei, ie to solid but not liquid H2O. There have been a number of theories about how this works, but up till now no experimental observation of the molecular mechanism because hydrogen is almost ‘invisible’ to most imaging techniques.

“Neutrons ‘see’ hydrogen very well, so neutron scattering was the only way that we were able to locate the positions of H2O molecules at the protein’s binding surface. We identified an 'ice-type' tetrahedral cluster of waters at the binding surface. These mimic the arrangement of water molecules in ice, so we used these positions as the starting point to build up the rest of the ice crystal and model the ice-AFP interaction,” says Alberto Podjarny, from IGBMC in Strasbourg, who led the neutron research.

“The ice model has six rings of four H2O molecules, which leaves a gap, or hole, in the middle. The hydrophobic regions of the type-III AFPs fit into these holes and bind with the ice’s surface. These ‘holes’ are what distinguish the structure of ice crystal nuclei from water, and explain how AFPs can be present in a solvent without attaching to the water molecules until they start to freeze,” says Eduardo Howard from the Instituto de Física de Líquidos y Sistemas Biológicos (IFLYSIB) in Argentina. “This understanding has exciting implications for biomedical applications such as cryosurgery and tissue preservation.”

There are varied commercial applications for antifreeze proteins. These include:

  • Medicine – improving cryosurgery; enhancing preservation of tissues for transplant or transfusion
  • Food processing/production – lengthening the shelf life of frozen foods
    Unilever are using AFPs to improve the consistency and storage properties of ice cream
  • Agri/Aquaculture – increasing freeze tolerance of crop plants; improving farm fish production; extending the harvest season in cooler climates

Now the mechanism of recognition is understood, the next step is to investigate how AFP prevents the ice crystal nuclei growing into ice crystals.

Re.:    Journal of Molecular Recognition, 7 April 2011.

Contact: James Romero +44 845 680 1866

Notes to editors

1.    Type-III AFPs are found at high concentration in the blood of Arctic fish:
•    Temperature of surrounding sea is approx.   -1°C (salt water freezes at approximately -1.5°C)
•    The fish blood is less salty with freezing temperature of approximately -0.5°C
To avoid freezing to death, the fish must avoid ice crystals forming in the blood.

2.    Unusual protein-molecule interaction – Having hydrophobic amino acids at the surface explains another oddity about AFP: the binding force that governs its interaction with the ice nuclei. The research found that Van der Waals attractions (weak attractive/repulsive forces between molecules) are the governing force determining this interaction. Protein-molecule interactions are normally governed by hydrogen bonds. However, in this case it makes sense that hydrogen bonds aren’t the key interactions as otherwise the protein would also bind to liquid water.

3. This work was only possible due to the high flux available at the Laue diffractometer LADI-III, and the availability of perdeuterated single crystals from the Deuteration Lab.

4.    About IGBMC – the Institut de Génétique et de Biologie Moléculaire et Cellulaire is one of the leading European centres of biomedical research. IGBMC is a joint venture between CNRS, INSERM, and University of Strasbourg.

5.    About IFLYSIB – Instituto de Física de Líquidos y Sistemas Biológicos (the Institute of Physics of Fluids and Biological Systems) investigates the structure, function and properties of water and transport phenomena in biological systems, structure-function relationships in biomolecules.

The ocean pout