Ice-binding proteins: a remarkable diversity of structures for stopping and starting ice growth

•Antifreeze proteins (AFPs) are a sub-set of ice-binding proteins (IBPs). •IBP functions include ice recrystallization inhibition and adhesion to ice. •IBPs have diverse structures but ice-binding sites with similar properties. •IBPs may organize ice-like waters on their surface to promote binding to ice. •Ice nucleating proteins might function in a similar way but on a larger scale. Antifreeze proteins (AFPs) were discovered in marine fishes that need protection from freezing. These ice-binding proteins (IBPs) are widespread across biological kingdoms, and their functions include freeze tolerance and ice adhesion. Consistent with recent independent evolution, AFPs have remarkably diverse folds that rely heavily on hydrogen- and disulfide-bonding. AFP ice-binding sites are typically flat, extensive, relatively hydrophobic, and are thought to organize water into an ice-like arrangement that merges and freezes with the quasi-liquid layer next to the ice lattice. In this article, the roles, properties, and structure–function interactions of IBPs are reviewed, and their relationship to ice nucleation proteins, which promote freezing at high subzero temperatures, is explored. Antifreeze proteins (AFPs) were discovered in marine fishes that need protection from freezing. These ice-binding proteins (IBPs) are widespread across biological kingdoms, and their functions include freeze tolerance and ice adhesion. Consistent with recent independent evolution, AFPs have remarkably diverse folds that rely heavily on hydrogen- and disulfide-bonding. AFP ice-binding sites are typically flat, extensive, relatively hydrophobic, and are thought to organize water into an ice-like arrangement that merges and freezes with the quasi-liquid layer next to the ice lattice. In this article, the roles, properties, and structure–function interactions of IBPs are reviewed, and their relationship to ice nucleation proteins, which promote freezing at high subzero temperatures, is explored. a proposed mechanism by which the adsorption of IBPs on the ice surface inhibits ice growth by the Kelvin effect. an IBP that protects an organism from freezing. solution properties (e.g., freezing point depression) caused by solute particles in proportion to their concentration. a cage. Used here to refer to a lattice-like arrangement of water molecules surrounding a hydrophobic group. a protein, found in organisms that live at subzero and near-zero temperatures, that binds to ice. Ice-binding proteins include AFPs and proteins that inhibit ice recrystallization, and might include proteins that can nucleate ice formation (INPs). the region of an IBP that binds to ice. a type of IBP, aggregates of which nucleate freezing at high subzero temperatures. a process that occurs readily at high subzero temperatures, in which large ice crystals grow at the expense of small ones. IR is associated with dehydration and structural damage to surrounding tissues. a protein that changes the physical structure of ice crystals. used here in reference to freezing point depression attributable to curvature of the ice surface. a numerical system for defining crystal facets. used here to mean the temperature difference between the melting point (elevated) and freezing point (depressed) of an ice crystal caused by adsorption of IBPs to the ice surface.