Yang Cheng, Sharp Kim A
The Johnson Research Foundation, Department of Biochemistry and Biophysics, University of Pennsylvania, Philadelphia, PA 19104, USA.
Biophys Chem. 2004 Apr 1;109(1):137-48. doi: 10.1016/j.bpc.2003.10.024.
The random network model of water quantitatively describes the different hydration heat capacities of polar and apolar solutes in terms of differential distortions of the water-water hydrogen bonding angle in the first hydration shell. This method of hydration analysis is applied here to study the hydration of the wild type III thermal hysteresis protein from eel pout and three mutations at residue 16. Wild type and one mutant have full activity, the other two mutants have little or no anti-freeze (thermal hysteresis) activity. The analysis reveals significant differences in the hydration structure of the ice-binding site (centered on residue 16) among four proteins. For the A16T and A16Y mutants with reduced activity, polar groups have a typical polar-like hydration. For the wild type and mutant A16C with 100% of the wild type activity, polar groups have unusual, very apolar-like hydration. In the latter case, hydrating water molecules form a more ice-like pattern of hydrogen bonding on the ice-binding face, while in the former case water-water H-bonds are more distorted and more heterogenous. Overall, the binding surface of active protein strongly enhances the water tetrahedral structure, i.e. promotes ice-like hydration. It is concluded that the specific shape, residue size and clustering of both polar/apolar groups are essential for the binding surface to recognize, and preferentially interact with nascent ice crystals forming in liquid water.
水的随机网络模型从第一水化层中水分子间氢键角的差异畸变角度，定量描述了极性和非极性溶质不同的水化热容量。这里应用这种水化分析方法来研究鳗鲡野生型III型热滞蛋白及其16位残基处的三个突变体的水化情况。野生型和一个突变体具有完全活性，另外两个突变体几乎没有或完全没有抗冻（热滞）活性。分析揭示了这四种蛋白质在冰结合位点（以16位残基为中心）的水化结构存在显著差异。对于活性降低的A16T和A16Y突变体，极性基团具有典型的类似极性的水化。对于具有100%野生型活性的野生型和A16C突变体，极性基团具有不寻常的、非常类似非极性的水化。在后一种情况下，水化水分子在冰结合面上形成更类似冰的氢键模式，而在前一种情况下，水分子间的氢键更扭曲且更不均匀。总体而言，活性蛋白的结合表面强烈增强了水的四面体结构，即促进了类似冰的水化。得出的结论是，极性/非极性基团的特定形状、残基大小和聚集对于结合表面识别并优先与液态水中形成的新生冰晶相互作用至关重要。
