Ice-nucleating proteins are activated by low temperatures to control the structure of interfacial water

Abstract

Ice-nucleation active (INA) bacteria can promote the growth of ice more effectively than any other known material. Using specialized ice-nucleating proteins (INPs), they obtain nutrients from plants by inducing frost damage and, when airborne in the atmosphere, they drive ice nucleation within clouds, which may affect global precipitation patterns. Despite their evident environmental importance, the molecular mechanisms behind INP-induced freezing have remained largely elusive. We investigate the structural basis for the interactions between water and the ice-nucleating protein InaZ from the INA bacterium Pseudomonas syringae. Using vibrational sum-frequency generation (SFG) and two-dimensional infrared spectroscopy, we demonstrate that the ice-active repeats of InaZ adopt a β-helical structure in solution and at water surfaces. In this configuration, interaction between INPs and water molecules imposes structural ordering on the adjacent water network. The observed order of water increases as the interface is cooled to temperatures close to the melting point of water. Experimental SFG data combined with molecular-dynamics simulations and spectral calculations show that InaZ reorients at lower temperatures. This reorientation can enhance water interactions, and thereby the effectiveness of ice nucleation.

Brachypodium Antifreeze Protein Gene Products Inhibit Ice Recrystallisation, Attenuate Ice Nucleation, and Reduce Immune Response

“…To experimentally test this INP model, ice nucleation assays were performed. Heating INPs at 37 °C for 24 h depressed the freezing point by 3.33 °C, suggesting that the proposed inter-strand interactions may not fully reform ( Figure S7 ), which is consistent with the requirement for low temperature activation [ 30 ]. The polyphenol, tannic acid (TA), destabilises tyrosine ladders such as those found in amyloid fibres [ 31 ], and thus INA assays were performed with TA as a further test of the modelled inter-strand binding.…”

Brachypodium antifreeze protein gene products inhibit ice recrystallization, attenuate ice nucleation, and reduce immune response

“…To experimentally test the INP model, ice nucleation assays were performed. Heating INP at 37 °C for 24 h depressed the freezing point (-3.33 °C), suggesting that proposed interstrand interactions may not fully reform again (Figure S7), consistent with the requirement for low temperature activation 29 . The polyphenol, tannic acid (TA), destabilises tyrosine ladders such as those found in amyloid fibres 30 , and thus INA assays were performed with TA as a further test of the modelled interstrand binding.…”

Prevalence and characterization of Ice Nucleation Active (INA) bacteria from rainwater in Indonesia

“…A recent study emphasizes the importance of low temperature (ca. 5 °C) to activate the INP in P. syringae [ 35 ]. Thus, environmental condition of Bandung might be more favorable for the INA bacteria to survive and subsequently promote the INA bacteria abundance in the region.…”