Water is critical for life and is considered the universal solvent because of its unique properties. When temperatures drop below the freezing point of water, however, ice crystals form and can be lethal to cells. Cold-blooded organisms that live in cold climates have evolved mechanisms to cope with freezing temperatures, one of which is the synthesis of antifreeze proteins that block ice crystal growth. The larval antifreeze protein contains multiple stretches of 12 amino acids that repeat the sequence threonine–cysteine–threonine. The placement of the threonines in the repeating amino acid sequence positions their hydroxyl groups at precisely the spacing needed to maximize hydrogen bond formation with the water molecules at the leading edge of the ice crystal, thereby blocking further growth of the crystal lattice.
Everyday BioChem 