A Diminished Role for Hydrogen Bonds in Antifreeze Protein Binding to Ice

• Published in: Biochemistry (Easton) Vol. 36; no. 47; pp. 14652 - 14660
• Main Authors: Chao, Heman, Houston, ME Jr, Hodges, R S, Kay, C M, Sykes, B D, Loewen, M C, Davies, P L, Soennichsen, F D
• Format: Journal Article
• Language: English
• Published: 01.11.1997
• Subjects: Pleuronectiformes
• ISSN: 0006-2960

The most abundant isoform (HPLC-6) of type I antifreeze protein (AFP super(1)) in winter flounder is a 37-amino-acid-long, alanine-rich, alpha -helical peptide, containing four Thr spaced 11 amino acids apart. It is generally assumed that HPLC-6 binds ice through a hydrogen-bonding match between the Thr and neighboring Asx residues to oxygens atoms on the {202 super(-)1} plane of the ice lattice. The result is a lowering of the nonequilibrium freezing point below the melting point (thermal hysteresis). HPLC-6, and two variants in which the central two Thr were replaced with either Ser or Val, were synthesized. The Ser variant was virtually inactive, while only a minor loss of activity was observed in the Val variant. CD, ultracentrifugation, and NMR studies indicated no significant structural changes or aggregation of the variants compared to HPLC-6. These results call into question the role of hydrogen bonds and suggest a much more significant role for entropic effects and van der Waals interactions in binding AFP to ice.