Ice recrystallization is strongly inhibited when antifreeze proteins bind to multiple ice planes

Ice recrystallization is a phenomenon observed as the increase in ice crystal size within an already frozen material. Antifreeze proteins (AFPs), a class of proteins capable of arresting ice crystal growth, are known to inhibit this phenomenon even at sub milli-molar concentrations. A tremendous range in the possible applications of AFPs is hence expected in both medical and industrial fields, while a key determinant of the ice recrystallization inhibition (IRI) is hardly understood. Here, IRI efficiency and ice plane affinity were examined for the wild-type AFPI-III, a defective AFPIII isoform, and a fungal AFP isoform. To simplify the IRI analysis using the formal representation of Ostwald-ripening (r(3) = r(0)(3) + kt), we monitored specific ice grains exhibiting only uniform growth, for which maximum Feret diameter was measured. The cube of an ice grain's radius (r(3)) increased proportionately with time (t), and its slope gave the recrystallization rate (k). There was a significant difference in the IRI efficiency between the samples, and the fungal AFP possessing the activity with the smallest amount (0.27 mu M) exhibited an affinity to multiple ice planes. These results suggest that the IRI efficiency is maximized when AFPs bind to a whole set of ice planes.