Structure and Protein-Protein Interactions of Ice Nucleation Proteins Drive Their Activity.

Microbially-produced ice nucleating proteins (INpro) are unique molecular structures with the highest known catalytic efficiency for ice formation. Airborne microorganisms utilize these proteins to enhance their survival by reducing their atmospheric residence times. INpro also have critical environmental effects including impacts on the atmospheric water cycle, through their role in cloud and precipitation formation, as well as frost damage on crops.

Stochastic nucleation processes and substrate abundance explain time-dependent freezing in supercooled droplets.

Atmospheric immersion freezing (IF), a heterogeneous ice nucleation process where an ice nucleating particle (INP) is immersed in supercooled water, is a dominant ice formation pathway impacting the hydrological cycle and climate. Implementation of IF derived from field and laboratory data in cloud and climate models is difficult due to the high variability in spatio-temporal scales, INP composition, and morphological complexity. We demonstrate that IF can be consistently described by a stochastic nucleation process accounting for uncertainties in the INP surface area.

Contrasting Behavior of Antifreeze Proteins: Ice Growth Inhibitors and Ice Nucleation Promoters.

Several types of natural molecules interact specifically with ice crystals. Small antifreeze proteins (AFPs) adsorb to particular facets of ice crystals, thus inhibiting their growth, whereas larger ice-nucleating proteins (INPs) can trigger the formation of new ice crystals at temperatures much higher than the homogeneous ice nucleation temperature of pure water. It has been proposed that both types of proteins interact similarly with ice and that, in principle, they may be able to exhibit both functions.