Antifreeze proteins (AFPs) are characterized by their ability to adsorb to the surface of ice crystals and prevent any further crystal growth. AFPs have independently evolved for this purpose in a variety of organisms that encounter the threat of freezing, including many species of polar fish, insects, plants and microorganisms. Despite their diverse origins and structures, it has been suggested that all AFPs can organize ice-like water patterns on one side of the protein (the ice-binding site) that helps bind the AFP to ice. Here, to test this hypothesis, we have solved the crystal structure at 2.05 Å resolution of an AFP from the longhorn beetle, Rhagium mordax with five molecules in the unit cell. This AFP is hyperactive, and its crystal structure resembles that of the R. inquisitor ortholog in having a β-solenoid fold with a wide, flat ice-binding surface formed by four parallel rows of mainly Thr residues. The key difference between these structures is that the R. inquisitor AFP crystallized with its ice-binding site (IBS) making protein–protein contacts that limited the surface water patterns. Whereas the R. mordax AFP crystallized with the IBSs exposed to solvent enabling two layers of unrestricted ordered surface waters to be seen. These crystal waters make close matches to ice lattice waters on the basal and primary prism planes.

中文翻译：

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昆虫防冻蛋白的晶体结构揭示了冰结合表面上有序的水。

抗冻蛋白（AFP）的特征是能够吸附到冰晶表面并防止任何进一步的晶体生长。为此，AFP已在遇到冰冻威胁的各种生物体中独立进化，包括许多极地鱼类，昆虫，植物和微生物。尽管它们的起源和结构各不相同，但已表明所有AFP都可以在蛋白质的一侧（冰结合位点）组织类似于冰的水样，从而帮助AFP与冰结合。在这里，为了检验该假设，我们解决了长角甲虫Rhodium mordax的AFP的晶体结构，其分辨率为2.05Å，在单位晶胞中具有五个分子。该AFP具有高活性，其晶体结构类似于R. inquisitor直系同源物的晶体结构，具有β-类电磁体折叠，宽，由四列主要是Thr残渣的平行行形成的平坦冰层表面。这些结构之间的主要区别在于，R。inquisitor AFP的冰结合位点（IBS）结晶，形成蛋白质-蛋白质接触，从而限制了地表水的分布。而R. mordax AFP在IBS暴露于溶剂的条件下结晶，因此可以看到两层不受限制的有序地表水。这些结晶水与基础和主棱柱面上的冰晶格水非常匹配。将IBS暴露在溶剂中使mordax AFP结晶，从而可以看到两层不受限制的有序地表水。这些结晶水与基础和主棱柱面上的冰晶格水非常匹配。将IBS暴露在溶剂中使mordax AFP结晶，从而可以看到两层不受限制的有序地表水。这些结晶水与基础和主棱柱面上的冰晶格水非常匹配。