Breaking the ice: multiple origins of ice-binding/antifreeze proteins

Ice-binding proteins (IBPs) enable organisms to survive freezing environments by binding to ice and inhibiting crystal growth. Their remarkable structural, taxonomic, and evolutionary diversity makes them an exceptional system for studying protein evolution. This review examines the origins, structures, and distribution of IBPs across fishes, arthropods, plants, microorganisms, and other taxa. Comparative genomic analyses have revealed the progenitor genes of all known fish antifreeze proteins (AFPs), with the alanine-rich α-helical AFPs demonstrating repeated convergent evolution from diverse progenitors. β-solenoid IBPs have arisen repeatedly in arthropods, plants, fungi, and microorganisms. Although these proteins share the ability to bind ice, they can have different functions and their structures differ substantially in fold, architecture, and ice-binding surface composition. Horizontal gene transfer has also played a major role in IBP evolution, including transfer of type II AFP genes among fishes, DUF3494 IBPs among bacteria and numerous eukaryotes, and likely transfer of a hyperactive β-solenoid AFP between distantly related beetle lineages. The identification of IBPs presents significant experimental challenges, requiring rigorous verification through thermal hysteresis or ice recrystallization inhibition measurements together with recombinant expression. Nevertheless, advances in genome sequencing, transcriptomics, protein purification, and structural prediction are rapidly accelerating IBP discovery. Collectively, IBPs demonstrate the extraordinary diversity of evolutionary solutions to a common environmental challenge and provide a powerful model for investigating the mechanisms by which novel protein functions arise.