19. Determining the Ice-binding Face of an Antifreeze Protein from the Grass, Brachypodium distachyon

Abstract

At subzero temperatures extracellular ice growth can kill plants by dehydrating cells and rupturing their membranes. Some grasses can protect themselves from this damage by producing antifreeze proteins (AFPs). These AFPs irreversibly adsorb to growing ice crystals and prevent further gowth. This is measured by ice-recrystallization inhibition (IRI), whereby ice crystals remain small at high sub-zero temperatures. An AFP from Brachypodium distachyon, a temperate grass, has been structurally modelled as a left-handed beta helix with two flat ‘faces’ on either side of the molecule. I am trying to determine which ‘face’ is important for ice adsorption. I have made mutations in the sequence encoding the AFP so that a small, flat amino acid is replaced by a bulky residue, which will likely interfere with the “fit” of the protein to ice. A mutation on one of the flat ‘faces’ of the protein seems to retain all AFP activity, whereas mutations on the opposite ‘face’ appear to cause a loss in activity. Therefore, I believe that this latter ‘face’ is the one important for ice-binding. By understanding how proteins interact with ice, it may be possible to develop new technologies such as environmentally-friendly de-icing agents.