Education Ministry Key Laboratory of Integrated Management of Crop Diseases and Pests, College of Plant Protection, Nanjing Agricultural University, Nanjing 210095, China.
J Insect Physiol. 2013 Mar;59(3):263-72. doi: 10.1016/j.jinsphys.2012.12.004. Epub 2013 Jan 4.
Odorant-binding proteins (OBPs), widely and abundantly expressed in insect olfactory organs, are important for insect olfaction. In this study, two novel Minus-C OBP genes (HarmOBP17 and HarmOBP18) were characterized from the cotton bollworm, Helicoverpa armigera, one of the most important pests in cotton and other crops. Quantitative RT-PCR results indicate that the expression levels of the two genes differed greatly in regard to developmental stages, tissues, and genders. Binding properties of the two OBPs with plant volatiles were investigated at different pH levels using a competitive binding assay. Both OBPs displayed the highest binding affinities (Ki<13 μM) with Beta-ionone among the 85 tested compounds. Surprisingly, the two OBPs (HarmOBP17 in particular) displayed higher binding at pH 5.0 than at pH 7.4 and 10.0. This is the first reported Lepidopteran OBPs showing a contrary pH-dependent ligand binding behavior to other OBPs, implying a different mechanism of ligand binding and release. In addition, binding assays of the mutant OBPs (with the C-terminus eliminated) showed that the C-terminus was important for the ligand binding, but this importance varied with different ligands and OBPs, suggesting that their binding properties depend on the specific interactions between OBP and ligand.
气味结合蛋白（OBPs）广泛而丰富地表达于昆虫嗅觉器官中，对于昆虫嗅觉具有重要作用。本研究从棉花蕾铃虫（Helicoverpa armigera）中鉴定了两个新的 Minus-C OBP 基因（HarmOBP17 和 HarmOBP18），该基因是棉花和其他作物上最重要的害虫之一。定量 RT-PCR 结果表明，这两个基因在发育阶段、组织和性别上的表达水平存在显著差异。采用竞争结合测定法，在不同 pH 值条件下研究了这两个 OBP 与植物挥发物的结合特性。在 85 种测试化合物中，两种 OBP 与β-紫罗兰酮均表现出最高的结合亲和力（Ki<13 μM）。令人惊讶的是，与 pH 值为 7.4 和 10.0 相比，两种 OBP（特别是 HarmOBP17）在 pH 值为 5.0 时表现出更高的结合能力。这是首次报道鳞翅目昆虫 OBP 表现出与其他 OBP 相反的 pH 依赖性配体结合行为，这意味着配体结合和释放的机制不同。此外，突变 OBP（去除 C 末端）的结合测定表明 C 末端对于配体结合很重要，但这种重要性因不同的配体和 OBP 而异，表明它们的结合特性取决于 OBP 和配体之间的特定相互作用。
