Growth Habit Modification of Ice Crystals Using Antifreeze Glycoprotein (AFGP) Analogues

• Published in: Crystal Growth & Design
• Main Authors: Peltier, R, Evans, CW, DeVries, AL, Brimble, MA, Dingley, AJ, Williams, DE
• Format: Article in Journal/Newspaper
• Language: English
• Published: American Chemical Society 2010
• Subjects: POINT-DEPRESSING GLYCOPROTEINS; NUCLEAR MAGNETIC-RESONANCE; ANTARCTIC FISH; POLAR FISH; THERMAL HYSTERESIS; MOLECULAR-WEIGHT; PROTEIN-ACTIVITY; CIRCULAR-DICHROISM; HOFMEISTER SERIES; WATER; Antarctic; Antarc*
• Online Access: http://hdl.handle.net/2292/7977; https://doi.org/10.1021/cg1005083

The research reported here considers the modification of ice crystal growth habit using analogues of antifreeze glycoproteins: compounds that control the growth of ice crystals in the blood of Antarctic fishes. A range of analogues of the smallest antifreeze glycoprotein (AFGP8: Ala-Ala-Thr-Ala-Ala-Thr-Pro-Ala-Thr-Ala-Ala-Thr-Pro-Ala) were synthesized, all of which have either N-acetyl-galactosamine or galactose moieties attached to their threonines instead of the native galactose-Nacetyl-galactosamine disaccharide. We also synthesized analogues in which the prolines were substituted with alanines in the protein sequence. The analogues were systematically studied for their effects on ice crystal shape and their effects when combined with a range of salts chosen across the Hofmeister series. A simple 1 H NMR freezing experiment was used to detect adsorption onto ice and indicate differences in water proton hydrogen bonding. CD spectroscopy highlighted the role of the terminal galactose, the proline residues, and the N-acetylamine group in modifying the solution conformation. The results illustrate a delicate balance between the effects of hydrophobic and hydrophilic groups on the glycoprotein and the interactions between the glycoprotein, a developing ice crystal, and water. We demonstrate three ways of modulating the ice crystal shape: by changing the adsorbent concentration, by changing the adsorbent structure, or by altering the interaction of the glycoprotein with liquid water through the use of simple solution additives. We show a continuum of behavior between no shape modification and no thermal hysteresis to a strong shape modification and a significant thermal hysteresis, and we relate the results to kinetic models for antifreeze activity.