Bacterial Ice Nucleation Proteins: Features, Structure, and Applications

Some bacteria commonly found on plants can catalyze the freezing of water at a higher temperature than others, at or near 0 °C. The freezing point of pure water is about -40 °C and is initiated by creating ice nucleations. However, when ice nucleation proteins (INPs) are present, ice nucleations form at temperatures close to or above 0 °C. INPs are often attached to the outer membrane by a phosphatidylinositol anchor and are sometimes secreted extracellularly. The monomers of INPs in Pseudomonas syringae are 120 to 180 kDa. INP has three domains, and the central domain is highly repetitive. The central domain consists of the consensus sequence of eight amino acid repeats. Eight amino acid repeats create a 16-residue fragment, and three 16-residue fragments form the 48-residue fragment. Studies have shown that INPs may have a β-helical fold and interact with water through the repetitive motif. Most ice nucleation bacteria are gram-negative, including P. syringae, Pseudomonas viridiflava, Pseudomonas fluorescens, Xanthomonas compestris, Erwinia ananas, and Erwinia herbicola. For optimum protein activity, the presence of the complete bacterial cell is essential. INPs are influential in different aspects, including snowmaking, agriculture, freeze-concentration in the food industry, signal transduction, atmospheric applications as cloud condensation nuclei, and surface display (expression of a foreign protein on the cell surface for biotechnological purposes). This study provides a brief overview of ice nucleation proteins and their applications since ice nucleation is an important phenomenon that affects various aspects, from climate to biological systems.