Abstract:

Ice binding proteins (IBPs) are proteins that interfere with ice growth. Some IBPs disturb and prevent the growth of ice, and are thus called antifreeze proteins (AFPs). Others promote nucleation of ice and are thus called ice nucleation proteins (INPs). IBPs protect organisms from freezing injury and have many potential applications in medicine and agriculture. Such proteins could potentially serve as a platform for future biotechnology applications in which crystal growth is manipulated by specific additives. Controlling ice formation is essential for life in cold environments and may therefore play an important role in the search for extraterrestrial life by astrobiologists. Although the first AFP was found 40 years ago, the way in which these proteins function is still not completely resolved. To resolve some of the key issues regarding the interactions between IBPs and ice, we developed a new approach for investigating the activity of IBPs that relies on fluorescence microscopy and dynamic control of the solvent around ice crystals with the aid of microfluidic devices. One of the interesting questions in this field is why certain AFPs are "hyperactive". AFPs can be classified into two groups: moderate ones that can depress the freezing point by ~1.0 C⁰ and hyperactive ones that can depress the freezing point by several degrees Celsius even when present at low concentrations. I will present experimental results based on fluorescence microscopy of AFP-bound ice crystals that highlight the differences between moderate and hyperactive AFPs. These include direct evidence for the basal plane affinity of hyperactive AFPs , the effects of AFPs on the growth-melt behavior of ice , the dynamics of their interaction with ice , the nature of the bonding between AFPs and ice , and the ability of AFPs to inhibit melting of ice under superheated conditions .