Identification and Characterization of an Isoform Antifreeze Protein from the Antarctic Marine Diatom, Chaetoceros neogracile and Suggestion of the Core Region

Antifreeze Proteins: A Tale of Evolution From Origin to Energy Applications

Icing and formation of ice crystals is a major obstacle against applications ranging from energy systems to transportation and aviation. Icing not only introduces excess thermal resistance, but it also reduces the safety in operating systems. Many organisms living under harsh climate and subzero temperature conditions have developed extraordinary survival strategies to avoid or delay ice crystal formation. There are several types of antifreeze glycoproteins with ice-binding ability to hamper ice growth, ice nucleation, and recrystallization. Scientists adopted similar approaches to utilize a new generation of engineered antifreeze and ice-binding proteins as bio cryoprotective agents for preservation and industrial applications. There are numerous types of antifreeze proteins (AFPs) categorized according to their structures and functions. The main challenge in employing such biomolecules on industrial surfaces is the stabilization/coating with high efficiency. In this review, we discuss various classes of antifreeze proteins. Our particular focus is on the elaboration of potential industrial applications of anti-freeze polypeptides.

Characterization of Ice-Binding Proteins from Sea-Ice Microalgae

Several species of polar microalgae are able to live and thrive in the extreme environment found within sea ice, where ice crystals may reduce the organisms' living space and cause mechanical damage to the cells. Among the strategies adopted by these organisms to cope with the harsh conditions in their environment, ice-binding proteins (IBPs) seem to play a key role and possibly contribute to the success of microalgae in sea ice. Indeed, IBPs from microalgae predominantly belong to the so-called "DUF 3494-IBP" family, which today represents the most widespread IBP family. Since IBPs have the ability to control ice crystal growth, their mechanism of function is of interest for many potential applications. Here, we describe methods for a classical determination of the IBP activity (thermal hysteresis, recrystallization inhibition) and further methods for protein activity characterization (ice pitting assay, determination of the nucleating temperature).

Suppression of droplets freezing on glass surfaces on which antifreeze polypeptides are adhered by a silane coupling agent

The development of ice-phobic, glass-substrate surfaces is important for many reasons such as poor visibility through the ice-covered windshields of vehicles. The present authors have developed new glass surfaces coated with a silane coupling agent and polypeptides whose amino-acid sequence is identical to a partial sequence of winter flounder antifreeze protein. We have conducted experiments on the freezing of sessile water droplets on the glass surfaces, and measured the droplet temperature, contact angle, contact area and surface roughness. The results show that the supercooling temperature decreased noticeably in the case where a higher concentration solution of polypeptide was used for the coating. The adhesion strength of frozen droplets was lowest in the same case. In addition, we observed many nanoscale humps on the coated surface, which were formed by polypeptide aggregates in the solution. We argue that the combination of the hydrophilic humps and the hydrophobic base surfaces causes water molecules adjacent to the surfaces to have a variety of orientations in that plane, even after the ice layer started to grow. This then induces a misfit of water-molecule spacing in the ice layers and consequent formation of fragile polycrystalline structure. This explains the lower values of ice adhesion strength and supercooling enhancement in the cases of the polypeptide-coated glass plates.

Growth suppression of ice crystal basal face in the presence of a moderate ice-binding protein does not confer hyperactivity

Ice-binding proteins (IBPs) affect ice crystal growth by attaching to crystal faces. We present the effects on the growth of an ice single crystal caused by an ice-binding protein from the sea ice microalga Fragilariopsis cylindrus (fcIBP) that is characterized by the widespread domain of unknown function 3494 (DUF3494) and known to cause a moderate freezing point depression (below 1 °C). By the application of interferometry, bright-field microscopy, and fluorescence microscopy, we observed that the fcIBP attaches to the basal faces of ice crystals, thereby inhibiting their growth in the c direction and resulting in an increase in the effective supercooling with increasing fcIBP concentration. In addition, we observed that the fcIBP attaches to prism faces and inhibits their growth. In the event that the effective supercooling is small and crystals are faceted, this process causes an emergence of prism faces and suppresses crystal growth in the a direction. When the effective supercooling is large and ice crystals have developed into a dendritic shape, the suppression of prism face growth results in thinner dendrite branches, and growth in the a direction is accelerated due to enhanced latent heat dissipation. Our observations clearly indicate that the fcIBP occupies a separate position in the classification of IBPs due to the fact that it suppresses the growth of basal faces, despite its moderate freezing point depression.