Many Antarctic and Arctic fish contain antifreeze proteins (AFPs) and glycoproteins (AFGPs) which prevent ice crystal growth down to -1.9 °C thus allowing the fish to survive in sub-zero waters. These biological antifreezes have tremendous medical and industrial applications where low temperature storage is required and ice crystallization is damaging e.g., including improved protection of blood platelets and human organs at low temperatures, and in improving the smooth texture of frozen foods.
(a) Synthesis of AF(G)Ps and Mimics
One of the major limitations that has prevented commercial applications of natural AFGPs, is that the compounds must be harvested from fish from Polar oceans. Furthermore the natural products contain mixtures of oligomers with structural variations depending on the exact species of fish. In collaboration with Dr Richard Payne and Professor Kate Jolliffe (University of Sydney) we have used chemical ligation strategies to produce AFGP mimics, that can be routinely and conveniently prepared as pure glycoforms. We are currently designing mimics that can be more easily prepared in the lab using different scaffolds.
(b) How do AF(G)Ps protect cells from damage by ice crystals?
AF(G)Ps also share the ability to protect mammalian cells and tissues from hypothermic damage and are also able to stabilize or disrupt membranes to leakage during low temperature and freezing stress. Hence these molecules have enormous potential as cryoprotective agents in medicine and biotechnology. Preliminary studies have shown promising results in applications including the enhanced storage of blood, sperm, embryos and other biological samples at reduced temperatures however the mechanism whereby they exert these effects is unknown, and the lack of understanding of both the antifreeze and cryoprotectant properties has not permitted the tailoring of AF(G)Ps for specific applications.
In collaboration with Professor Frances Separovic (University of Melbourne) and James Hook (UNSW Analytical Centre) we have recently used solid-state NMR spectroscopy to study how the type I helical AFPS and the AFGPS interact with phospholipid membranes. Our results show that the interaction of AF(G)Ps is highly dependent on the lipid structure and exact composition of the membrane. In the long term, these results have the potential insight into which compounds will protect and which will damage a particular membrane during chilling or freezing, and assist in the design of synthetic compounds tailored for interaction with specific membranes.