Mimicry of ice structure by surface hydroxyls and water of a β-helix antifreeze protein

• Published in: Nature (London) 2000-07, Vol.406 (6793), p.322-324
• Main Authors: Davies, Peter L, Liou, Yih-Cherng, Tocilj, Ante, Jia, Zongchao
• Format: Article
• Language: English
• Subjects: Animals; Antifreeze Proteins; Antifreeze solutions; Crystallography; Crystallography, X-Ray; Freezing; Freezing point; Glycoproteins - chemistry; Humanities and Social Sciences; Hydrolysis; Ice; Insects; letter; Models, Molecular; Molecular Mimicry; multidisciplinary; Protein Structure, Secondary; Proteins; Recombinant Proteins - chemistry; Science; Science (multidisciplinary); Surface Properties; Tenebrio; Tenebrio molitor; Water - chemistry
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/35018604

Insect antifreeze proteins (AFP) are much more effective than fish AFPs at depressing solution freezing points by ice-growth inhibition. AFP from the beetle Tenebrio molitor is a small protein (8.4 kDa) composed of tandem 12-residue repeats (TCTxSxxCxxAx). Here we report its 1.4- resolution crystal structure, showing that this repetitive sequence translates into an exceptionally regular β-helix. Not only are the 12-amino-acid loops almost identical in the backbone, but also the conserved side chains are positioned in essentially identical orientations, making this AFP perhaps the most regular protein structure yet observed. The protein has almost no hydrophobic core but is stabilized by numerous disulphide and hydrogen bonds. On the conserved side of the protein, threonine-cysteine-threonine motifs are arrayed to form a flat β-sheet, the putative ice-binding surface. The threonine side chains have exactly the same rotameric conformation and the spacing between OH groups is a near-perfect match to the ice lattice. Together with tightly bound co-planar external water, three ranks of oxygen atoms form a two-dimensional array, mimicking an ice section.