Point Mutation of the Ice-Binding Site in Antifreeze Protein Modify the Cold Tolerance in Caenorhabditis Elegans

Abstract

Antifreeze proteins (AFPs) inhibit the ice-crystal growth from the surface-bound waters that are spatially organized to bind to an ice crystal. The surface structure complementarity between AFP and the ice plane has been evaluated based on structural docking studies. The ice-binding properties are closely related to the freezing point depression activity of the AFP solution, which is evaluated as the difference between the melting and freezing temperatures (thermal hysteresis: TH). Although AFPs are thought to facilitate the survival of organisms living in cold environments, it is poorly understood that whether the exogenous expression of AFPs can improve the cold tolerance of animals. Moreover, it is also unclear whether TH activity is correlated with the survival ability of animals during cold shock. Here, we examined the functions of AFPs in vivo through behavioral and cellular observations of transgenic Caenorhabditis elegans expressing AFPs. We showed that the fungal AnpAFP improves the survival rate of worms and protects their cells from lethal cold shocks. The AnpAFP T156Y mutant exhibiting low TH resulted the reduced cold tolerance at the freezing temperature. The fungal TisAFP8 exhibiting high TH activity was observed to dramatically improve the survival rate and strongly protect muscle cells. Structural modification of the ice-binding site is crucial to regulate the ice-binding strength of AFPs. These results suggest that AFPs play a crucial role in the animal body, improving cold tolerance through the ice-binding mechanism. In this presentation, we will discuss the relationship between the ice-binding abilities of AFPs and their in vivo roles in cold tolerance and cellular protection in a living animal.