Electron microscopy and calorimetry of proteins in supercooled water

Abstract

Some of the best nucleating agents in nature are ice-nucleating proteins, which boost ice growth better than any other material. They can induce immersion freezing of supercooled water only a few degrees below 0 °C. An open question is whether this ability also extends to the deposition mode, i.e., to water vapor. In this work, we used three proteins, apoferritin, InaZ (ice nucleation active protein Z), and myoglobin, of which the first two are classified as ice-nucleating proteins for the immersion freezing mode. We studied the ice nucleation ability of these proteins by differential scanning calorimetry (immersion freezing) and by environmental scanning electron microscopy (deposition freezing). Our data show that InaZ crystallizes water directly from the vapor phase, while apoferritin first condenses water in the supercooled state, and subsequently crystallizes it, just as myoglobin, which is unable to nucleate ice.

Atomic-Level Insights into a Unique Semi-Clathrate Hydrate Formed in a Confined Environment of Porous Protein Crystal

“…The unique water network might be responsible for providing the interaction of ice with ferritin as reported previously. 25,26 If suitable alanine residues are placed within the confined environment, particularly at the interface of two helices, the resulting engineered protein could form a new semi-clathrate structure. Such studies are in progress.…”

“…Interactions of ferritin with ice nuclei have been studied by analytical methods such as dynamic light scattering and differential scanning calorimetry. 25,26 However, the presence of a semi-clathrate structure on the surface of ferritin has not been previously reported. Herein, we describe the structural details of a single semiclathrate in a crystal of ferritin that is formed over one specific alanine residue that is exposed to a large solvent channel (Figure 1) in an arrangement similar to the framework observed in Maxi.…”

In-situ Micro-thermography Reveals Inverse Relationship Between Ice Nucleation and Ice Growth in Frozen Foods

“…5C and 5D provide the opposite effect for potato and broccoli, respectively, as these samples froze at higher supercooling degrees (ΔT=9-20 ºC) than beef and zucchini (ΔT=5-13 ºC). The finding that ice nucleation rates are faster compared to the rest of the tested food products may be related to ice nucleation of ferritin 25,26 . Ferritin is a 28 kDa protein that assembles in the cell into 24 subunits with an outer diameter of 12 nm 25 and can carry 4500 iron atoms.…”

Hydration effects on thermal transitions and molecular mobility in Xanthan gum polysaccharides

“…Therefore, the properties of this so-called interfacial or hydration water may reveal specific features of water-polymer interactions. 15,[21][22][23][24][25] Among other issues, the non-freezing fraction of adsorbed water, 18,26,27 the confinement of water molecules 28,29 and the process of ice formation at sub-zero temperatures and the dynamics in partially crystallized water mixtures [30][31][32][33][34][35][36][37] are topics that provide insight into the properties of hydration water. Especially for polysaccharides, it is known that a small amount of water significantly affects the T g of the hydrated polysaccharide by disrupting inter-molecular hydrogen bonds.…”