Rating antifreeze proteins: Not a breeze

Antifreeze proteins (AFPs) are an interesting class of biomolecules that hinder macroscopic freezing by binding to small ice crystals and blocking their further growth. They were first discovered in the 1960s in arctic fish (1) and have since been observed in a wide range of other organisms, e.g., bacteria (2), fungi (3), plants (4), insects (5), and vertebrates (1, 6), that live in low-temperature environments. AFPs are also of considerable practical interest due to their potential applications in cryopreservation (7), food processing (8), and hydrate inhibition (9). The most widely used metric for characterizing the antifreeze activity of an AFP is a quantity known as thermal hysteresis (TH) activity, which is typically determined from nanoliter cryoscopy experiments. In PNAS, Olijve et al. (10) demonstrate that the notion of the antifreeze potency of an AFP is complex and process-dependent, and using a single quantity such as TH activity measured from a particular assay is inadequate in predicting the performance of an AFP under different temperature regimes and processing conditions.