Carrot 'antifreeze' protein has an irregular ice-binding site that confers weak freezing point depression but strong inhibition of ice recrystallization
Carrot 'antifreeze' protein has an irregular ice-binding site that confers weak freezing point depression but strong inhibition of ice recrystallization
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胡萝卜“抗冻”蛋白具有不规则的冰结合位点，可较弱地降低冰点，但可强烈抑制冰的重结晶
DOI：
10.1042/bcj20200238
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发表时间：
2020
期刊：
影响因子：
--
通讯作者：
Peter L Davies
中科院分区：
文献类型：
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作者：
Yannan Wang;Laurie A. Graham;Zhifu Han;Robert Eves;Audrey K Gruneberg;Robert L Campbell;Heqiao Zhang;Peter L Davies
冰结合蛋白（IBP）存在于许多生物界中，它们作为防冻剂或冰重结晶抑制剂保护生物体免受冷冻损害。此处，来自胡萝卜 (Daucus carota) 的重组 IBP 的晶体结构已解析至 2.3 Å 的分辨率。正如预测的那样，该蛋白是植物多聚半乳糖醛酸酶抑制蛋白的结构同源物，形成具有富含亮氨酸重复基序的弯曲螺线管结构。出乎意料的是，仔细检查其表面并没有发现任何大片平坦、规则间隔的疏水残基区域，这些残基是抗冻鱼和昆虫的有效抗冻蛋白的冰结合位点（IBS）的特征。 IBS 是通过胡萝卜螺线管凸面上残基的定点诱变来定义的。这个不完美的位点让人想起草“抗冻”蛋白的不规则IBS。与草蛋白一样，胡萝卜 IBP 具有较弱的冰点降低活性，但在纳摩尔浓度下抑制冰重结晶的活性极高。在两种植物蛋白存在的情况下形成的冰晶在各个方向上缓慢且均匀地生长。我们认为这种缓慢、受控的冰生长对于耐冻性是有利的。事实上，两种植物 IBP 已经进化出非常不同的蛋白质结构，以相似的方式影响冰，这表明这种弱冰点降低和强冰重结晶抑制的模式有助于它们的宿主耐受冰冻而不是抵抗冰冻。
Ice-binding proteins (IBPs) are found in many biological kingdoms where they protect organisms from freezing damage as antifreeze agents or inhibitors of ice recrystallization. Here, the crystal structure of recombinant IBP from carrot (Daucus carota) has been solved to a resolution of 2.3 Å. As predicted, the protein is a structural homologue of a plant polygalacturonase-inhibiting protein forming a curved solenoid structure with a leucine-rich repeat motif. Unexpectedly, close examination of its surface did not reveal any large regions of flat, regularly spaced hydrophobic residues that characterize the ice-binding sites (IBSs) of potent antifreeze proteins from freeze-resistant fish and insects. An IBS was defined by site-directed mutagenesis of residues on the convex surface of the carrot solenoid. This imperfect site is reminiscent of the irregular IBS of grass 'antifreeze' protein. Like the grass protein, the carrot IBP has weak freezing point depression activity but is extremely active at nanomolar concentrations in inhibiting ice recrystallization. Ice crystals formed in the presence of both plant proteins grow slowly and evenly in all directions. We suggest that this slow, controlled ice growth is desirable for freeze tolerance. The fact that two plant IBPs have evolved very different protein structures to affect ice in a similar manner suggests this pattern of weak freezing point depression and strong ice recrystallization inhibition helps their host to tolerate freezing rather than to resist it.