Department of Biological Sciences, Faculty of Science, National University of Singapore, Singapore.
J Biol Chem. 2012 Oct 5;287(41):34776-85. doi: 10.1074/jbc.M112.348730. Epub 2012 Aug 10.
Blo t 21 is a paralogue of the group 5 allergen, Blo t 5, a major allergen from the dust mite Blomia tropicalis. Blo t 21 has moderate sequence identity (40.7%) to Blo t 5 and low to moderate cross-reactivity to Blo t 5. In B. tropicalis, the most prevalent and allergenic allergens are in the order of Blo t 21, Blo t 5, and Blo t 7. Here, we determined the NMR solution structure of Blo t 21, which represents the first structure of the group 21 dust mite allergen. The structure of Blo t 21 closely resembles the structures of Blo t 5 and Der p 5, comprising three anti-parallel α-helices arranged in a helical bundle. Using site-directed mutagenesis and specific IgE binding ELISA, Blo t 21 was found to contain both conserved and unique charged IgE epitope residues at the L2 loop region and on helix α3. Cross-inhibition assays confirmed that Blo t 21 has a low to moderate cross-reactivity with Blo t 5 and Der p 5 and represents a novel group of major allergen in B. tropicalis. In addition to group 5 allergens, Blo t 21 has also a low to moderate cross-reactivity with group 21 allergens from Dermatophagoides mites, confirming that B. tropicalis is a major and distinct source of dust mite allergens.
Blo t 21 是花粉 5 组过敏原的旁系同源物，是主要过敏原 Blomia tropicalis 中的花粉 5。Blo t 21 与 Blo t 5 具有中度序列同一性（40.7%），与 Blo t 5 具有低到中度的交叉反应性。在 B. tropicalis 中，最普遍和最具致敏性的过敏原依次为 Blo t 21、Blo t 5 和 Blo t 7。在这里，我们确定了 Blo t 21 的 NMR 溶液结构，这代表了第 21 组尘螨过敏原的第一个结构。Blo t 21 的结构与 Blo t 5 和 Der p 5 的结构非常相似，由三个反平行的α-螺旋组成螺旋束。通过定点突变和特异性 IgE 结合 ELISA 发现，Blo t 21 在 L2 环区和α3 螺旋上既含有保守的也含有独特的带电荷的 IgE 表位残基。交叉抑制试验证实，Blo t 21 与 Blo t 5 和 Der p 5 具有低到中度的交叉反应性，代表了 B. tropicalis 中的一个新的主要过敏原组。除了花粉 5 组过敏原外，Blo t 21 与尘螨的第 21 组过敏原也具有低到中度的交叉反应性，这证实了 B. tropicalis 是尘螨过敏原的一个主要且独特的来源。
