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Ice-binding proteins: from antifreeze mechanism to resistant soft materials

Periodic Reporting for period 3 - PRISM (Ice-binding proteins: from antifreeze mechanism to resistant soft materials)

Reporting period: 2018-05-01 to 2019-10-31

Crystallization of water into ice is lethal to most organisms and detrimental to many soft materials. Freeze-tolerant fish living in polar seas evolved to tackle this problem with an unusual coping strategy. They produce ‘antifreeze’ proteins that block the growth of nascent ice crystals within a narrow temperature range known as the ‘thermal hysteresis gap’ enabling survival under extreme conditions. Encoding this functionality into synthetic polymers would open up new avenues in biomedicine, agrifood and materials science for e.g. cryopreservation, crop hardiness, ice-templating, dispersion stability, and advanced coatings. Progress requires a profound understanding of the mechanism of non-colligative freezing point depression at the molecular level and allows for efficient strategies for the design and preparation of powerful macromolecular antifreezes.
Quantitative data analysis methods for the critical evaluation of ice recrystallization inhibition (IRI) of natural and synthetic antifreezes based on the sandwich assay of IRI activity have been developed. The thermal hysteresis (TH) and IRI activities of a range of IBP classes have been determined precisely and compared quantitatively. This study revealed that the activities are uncorrelated, and furthermore, TH activity determined by two distinct assays (cryoscopy and sonocrystallization) differ dramatically. These differences are tentatively attributed to differential affinities of the IBP clasess for fast and slow growing ice crystal planes and differences in growth conditions between the three assays. A synthetic route towards polyvinyl alcohol (PVA) bottlebrushes has been developed aiming to prepare highly IRI effective PVA-based synthetic antifreezes. The IRI activity of these PVA bottlebrushes has been compared to the activity of linear PVA polymers. The impact of chain architecture on the IRI activity of polyvinyl alcohol based synthetic antifreezes was found negligible as the effective inhibitory concentration Ci of the bottlebrush and linear PVA were found to be comparable. Two reviews on ice-binding proteins and analogues thereof have been published. The structure has been elucidated of a bacterial adhesion from the Antarctic bacterium Marinomonas primoryensis and the mechanical stability of its extender domain probed by single molecule force spectroscopy experiments. The stability and growth mechanism of nanotubes (NT) of putative antifreeze cyclic peptides (AFCP) have been studied by Molecular Dynamics simulations.
In the upcoming reporting period the team will focus on ensemble and single-molecule experiments to elucidate the mechanistic underpinning of the activity of native ice-binding proteins and their bio-inspired mimics. Furthermore, novel routes for the preparation of bio-inspired mimics in high yield and purity with record performance will be developed.