Graether S P, Jia Z
Department of Biochemistry, Queen's University, Kingston, Ontario K7L 3N6, Canada.
Biophys J. 2001 Mar;80(3):1169-73. doi: 10.1016/S0006-3495(01)76093-6.
Antifreeze proteins (AFPs) inhibit the growth of ice, whereas ice-nucleation proteins (INPs) promote its formation. Although the structures of several AFPs are known, the structure of INP has been modeled thus far because of the difficulty in determining membrane protein structures. Here, we present a novel model of an INP structure from Pseudomonas syringae based on comparison with two newly determined insect AFP structures. The results suggest that both this class of AFPs and INPs may have a similar beta-helical fold and that they could interact with water through the repetitive TXT motif. By theoretical arguments, we show that the distinguishing feature between an ice inhibitor and an ice nucleator lies in the size of the ice-interacting surface. For INPs, the larger surface area acts as a template that is larger than the critical ice embryo surface area required for growth. In contrast, AFPs are small enough so that they bind to ice and inhibit further growth without acting as a nucleator.
抗冻蛋白（AFPs）抑制冰的生长，而成核蛋白（INPs）则促进冰的形成。尽管几种抗冻蛋白的结构已为人所知，但由于确定膜蛋白结构存在困难，成核蛋白的结构迄今仍为模型结构。在此，我们基于与两种新确定的昆虫抗冻蛋白结构的比较，提出了一种来自丁香假单胞菌的成核蛋白结构的新模型。结果表明，这类抗冻蛋白和成核蛋白可能都具有相似的β-螺旋折叠，并且它们可以通过重复的TXT基序与水相互作用。通过理论论证，我们表明冰抑制剂和冰成核剂之间的区别特征在于与冰相互作用的表面大小。对于成核蛋白，较大的表面积充当模板，其大于生长所需的临界冰胚表面积。相比之下，抗冻蛋白足够小，以至于它们与冰结合并抑制进一步生长而不充当成核剂。
