Physicochemical properties of antifreeze proteins

Abstract

Proteins’ physicochemical properties is a broad term, and cover more than has been investigated for antifreeze proteins. In this chapter the investigations of antifreeze proteins (AFPs) are confined to weight, activity, solubility, hydrophobicity, and stability of the proteins. The weight and activity are presented together and compared, as much research suggests a positive correlation between these properties. This correlation applies for both fish AFPs and hyperactive arthropod AFPs, when comparing activity measurements within each AFP type. Not much research has focused on the solubility of AFPs, most likely due to their high solubility, which has not been inflicting with the main objective of the investigations. The AFPs are generally amphiphilic, having a relatively hydrophobic surface at the flat ice-binding region of the protein, while the rest of the proteins’ solvent-exposed surface is regarded as relatively hydrophilic. The hydrophobicity of the ice-binding site is regarded to be a key feature to bind to ice, explained by the anchored clathrate mechanism. The AFPs are generally stable in a broad pH range. The temperature stability shows no particular pattern, as both very heat-labile and heat-stable AFPs are found. However, several AFPs have the ability to refold into an active/native form after having been unfolded due to heat exposure. Not surprisingly, the diverse group of AFPs has just as diverse physicochemical properties, with the ability to interact with ice as the only common denominator.