Other protective measures of antifreeze proteins

Abstract

The primary function of antifreeze proteins is without doubt the inhibition of ice crystal growth in the body fluids and the inhibition of ice recrystallization in various organisms. Modification of the structure of the frozen environment by ice algae has also been reported but also this is a mechanism related to ice. However, other properties, not related to ice but still related to cold, of antifreeze proteins have been observed. These properties include interaction with cell membranes and anti-virulence properties in both animals and plants. In this chapter we present evidence that AFPs interact with both biological and model membrane systems and that these interactions rely both on the type of antifreeze protein as well as the saturation/unsaturation of the membrane lipids in question. Anti-virulence of an antifreeze glycoprotein has been shown in the context of a single species of insect and for a large number of plants. In the first case it is an AFGP and a derivative of this, from the tick Ixodes scapularis (IAFGP), which is shown to influence the formation of bacterial biofilm conferring increased resistance to various pathogens in both transgenic invertebrates and transgenic vertebrates. In the second case, plant antifreeze proteins are similar to pathogenesis-related proteins in plants and confer antifungal properties to the plants whereby increased survival of plants subjected to psychrophilic pathogens is achieved. The adaptational and evolutionary aspects of the above properties are also discussed in this chapter.