Interaction among the twelve-residue segment of antifreeze protein type I, or its mutants, water and a hexagonal ice crystal

The Antifreeze and Cryoprotective Activities of a Novel Antifreeze Peptide from Ctenopharyngodon idella Scales

The purpose of this study is to obtain new antifreeze peptides (AFPs) that are natural, safe, and high activity from Ctenopharyngodon idella scales. The optimal hydrolysis conditions were investigated, and chromatography-based isolation was conducted using thermal hysteresis activity (THA) as an index. Molecular dynamic simulation (MDs) was explored to reveal the antifreeze mechanism of the AFPs. The results showed that the optimal hydrolysis conditions were 4000 U/g papain enzyme for 60 °C at pH 5.0 and substrate concentration (1:10) for 3 h, as unveiled by single-factor experiment results. The AFPs documented a THA of 2.7 °C when the T_h was 1.3 °C. Hydrophilic peptide, named GCFSC-AFPs, with a THA of 5.09 °C when the T_h was 1.1 °C was obtained after a series isolation of gel filtration, ion exchange, and reversed-phase HPLC chromatography. The AFPs had a molecular weight of 1107.54~1554.72 Da with three main peptides in the amino acid sequence of VGPAGPSGPSGPQ, RGSPGERGESGPAGPSG, and VGPAGPSGPSGPQG, respectively. The survival rate of yeast with GCFSC-AFPs reached 84.4% following one week of exposure at −20 °C. MDs indicated that GCFSC-AFPs interfered with the ice-water interaction and thus inhibited the ice crystallization process. Our data suggested that the GCFSC-AFPs were a novel and potential antifreeze agent in the food industry.

Modelling of short synthetic antifreeze peptides: Insights into ice-pinning mechanism

Organisms living in icy environments produce antifreeze proteins to control ice growth and recrystallization. It has been proposed that these molecules pin the surface of ice crystals, thus inducing the formation of a curved surface that arrests crystal growth. Such proteins are very appealing for many potential applications in food industry, material science and cryoconservation of organs and tissues. Unfortunately, their structural complexity has seriously hampered their practical use, while efficient and accessible synthetic analogues are highly desirable. In this paper, we used molecular dynamics based techniques to model the interaction of three short antifreeze synthetic peptides with an ice surface. The employed protocols succeeded in reproducing the ice pinning action of antifreeze peptides and the consequent ice growth arrest, as well as in distinguishing between antifreeze and control peptides, for which no such effect was observed. Principal components analysis of peptides trajectories in different simulation settings permitted to highlight the main structural features associated to antifreeze activity. Modeling results are highly correlated with experimentally measured properties, and insights on ice-peptide interactions and on conformational patterns favoring antifreeze activity will prompt the design of new and improved antifreeze peptides.

Molecular Dynamics Analysis of Synergistic Effects of Ions and Winter Flounder Antifreeze Protein Adjacent to Ice-Solution Surfaces

The control of freezing saline water at the micrometer level has become very important in cryosurgery and cryopreservation of stem cells and foods. Adding antifreeze protein to saline water is a promising method for controlling the freezing because the protein produces a gap between the melting point and the freezing point. Furthermore, a synergistic effect of the solutes occurs in which the freezing point depression of a mixed solution is more noticeable than the sum of two freezing point depressions of single-solute solutions. However, the mechanism of this effect has not yet been clarified. Thus, we have carried out a molecular dynamics simulation on aqueous solutions of winter flounder antifreeze protein and sodium chloride or calcium chloride with an ice layer. The results show that the cations inhibit the hydrogen bond among water molecules not only in the salt solutions but also in the mixed solutions. This inhibition depends on the local number of ions and the valence of cations. The space for water molecules to form the hydrogen bonds becomes small in the case of the mixed solution of the protein and calcium chloride. These findings are consistent with the synergistic effect. In addition, it is found that the diffusion of ions near positively-charged residues is attenuated. This attenuation causes an increase in the possibility of water molecules staying near or inside the hydration shells of the ions. Furthermore, the first hydration shells of the cations become weak in the vicinity of the arginine, lysine and glutamic-acid residues. These factors can be considered to be possible mechanisms of the synergistic effect.