%0 Journal Article
%T Bacterial Ice Crystal Controlling Proteins
%A Janet S. H. Lorv
%A David R. Rose
%A Bernard R. Glick
%J Scientifica
%D 2014
%I Hindawi Publishing Corporation
%R 10.1155/2014/976895
%X Across the world, many ice active bacteria utilize ice crystal controlling proteins for aid in freezing tolerance at subzero temperatures. Ice crystal controlling proteins include both antifreeze and ice nucleation proteins. Antifreeze proteins minimize freezing damage by inhibiting growth of large ice crystals, while ice nucleation proteins induce formation of embryonic ice crystals. Although both protein classes have differing functions, these proteins use the same ice binding mechanisms. Rather than direct binding, it is probable that these protein classes create an ice surface prior to ice crystal surface adsorption. Function is differentiated by molecular size of the protein. This paper reviews the similar and different aspects of bacterial antifreeze and ice nucleation proteins, the role of these proteins in freezing tolerance, prevalence of these proteins in psychrophiles, and current mechanisms of protein-ice interactions. 1. Introduction Throughout the planet, environmental temperatures can reach low to freezing levels. Organisms indigenous to these habitats are presented with potential desiccation, which can lead to potentially detrimental challenges such as decreased enzymatic rates, freezing, and aggregation of endogenous proteins [1, 2]. Besides hindering cellular processes, subzero temperatures induce ice formation, which can lead to cell death [3]. In some cases, intracellular ice crystals can rupture cells either physically or through osmotic pressure changes [4]. The temperature at which water freezes varies based on solution homogeneity [1]. Pure water was reported to freeze at £¿40¡ãC. On the other hand, a heterogeneous water solution can contain additional molecules, such as dust particles and ice active bacteria, that act as seeds for ice nucleation [1, 5]. In these situations, a solution can freeze at high subzero temperatures, up to £¿2¡ãC. Cellular cryodamage incurred from freezing is dependent on freezing rate and ice crystal location [1]. For intracellular ice, a flash freezing rate (e.g., £¿100¡ãC/min) minimizes potential damage while a slow rate is more detrimental [3]. Furthermore, with a slow rate of freezing, the internal ice acts as a solute drawing water into cells until they rupture. On the other hand, extracellular ice can cause membrane fracturing or shifting in osmotic pressures [6]. During external freezing, water solidification into ice removes available liquid water and concentrates extracellular solutes. This change simulates a high saline environment, drawing out internal water that is needed for cellular processes.
%U http://www.hindawi.com/journals/scientifica/2014/976895/