Crystal structure of the dog allergen Can f 6 and structure-based implications of its cross-reactivity with the cat allergen Fel d 4
Crystal structure of the dog allergen Can f 6 and structure-based implications of its cross-reactivity with the cat allergen Fel d 4
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DOI：
10.1038/s41598-018-38134-w
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发表时间：
2019-02
影响因子：
4.6
通讯作者：
Kenji Yamamoto;O. Ishibashi;K. Sugiura;Miki Ubatani;Masaya Sakaguchi;Masatoshi Nakatsuji;S. Shimamoto-S.-Shim
中科院分区：
文献类型：
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作者：
Kenji Yamamoto;O. Ishibashi;K. Sugiura;Miki Ubatani;Masaya Sakaguchi;Masatoshi Nakatsuji;S. Shimamoto-S.-Shim
在世界范围内，一些狗的过敏原会引起人类的过敏反应。到目前为止，已经确定了七种不同的狗过敏原，命名为犬类过敏原1至7 （Can f1 - Can f1）。Can f6分别与猫和马的主要过敏原Fel d1和Equ c1具有较高的序列相似性和交叉反应性。本研究基于Can f6的结构特征对其致敏表位进行了研究。我们证明38例狗致敏患者中有18例（47%）的血清对重组Can f6蛋白（rCan f6）有反应。然后，我们通过x射线晶体学确定了rcanf6的晶体结构，其表现出在脂钙蛋白家族蛋白中发现的保守的三级结构结构。基于三级结构和与Fel d1和Equ c1序列的相似性，我们预测了三个可能参与交叉反应的ige识别位点。在这些位点上用三个连续的氨基酸代替三个丙氨酸可以降低IgE对过敏原的反应性。然而，IgE反应性的降低程度在很大程度上取决于突变位点和使用的血清，这表明Can f6是一种含有多个表位的多价过敏原，Can f6反应性血清含有不同数量的IgE识别单个Can f6表位，包括本研究预测的那些表位。我们还证明了预测的表位部分参与了IgE对Fel d1的交叉反应。有趣的是，突变的影响取决于蛋白质是结构化的还是变性的，这表明Can f6的真正三级结构在确定其IgE表位方面是必不可少的。
Several dog allergens cause allergic reactions in humans worldwide. Seven distinct dog allergens, designatedCanis familiarisallergen 1 to 7 (Can f 1–Can f 7), have been identified thus far. Can f 6 shows high sequence similarity and cross-reactivity with Fel d 4 and Equ c 1, major cat and horse allergens, respectively. This study was conducted on the allergenic epitopes of Can f 6 based on its structural characterization. We demonstrated that sera from 18 out of 38 (47%) dog-sensitized patients reacted to recombinant Can f 6 protein (rCan f 6). We then determined the crystal structure of rCan f 6 by X-ray crystallography, which exhibited a conserved tertiary structural architecture found in lipocalin family proteins. Based on the tertiary structure and sequence similarities with Fel d 4 and Equ c 1, we predicted three IgE-recognizing sites that are possibly involved in cross-reactivity. Substituting three successive amino acids in these sites to triple alanine decreased IgE reactivity to the allergen. However, the degree of reduction in IgE reactivity largely depended on the site mutated and the serum used, suggesting that Can f 6 is a polyvalent allergen containing multiple epitopes and Can f 6-reactive sera contain varied amounts of IgE recognising individual Can f 6 epitopes including those predicted in this study. We also demonstrated that the predicted epitopes are partly involved in IgE cross-reactivity to Fel d 4. Interestingly, the effect of the mutation depended on whether the protein was structured or denatured, indicating that the bona fide tertiary structure of Can f 6 is essential in determining its IgE epitopes.