Department of Molecular and Cellular Biology, University of California, Davis Davis, CA, USA.
Front Physiol. 2015 Feb 27;6:56. doi: 10.3389/fphys.2015.00056. eCollection 2015.
As opposed to humans, insects rely heavily on an acute olfactory system for survival and reproduction. Two major types of olfactory proteins, namely, odorant-binding proteins (OBPs) and odorant receptors (ORs), may contribute to the selectivity and sensitivity of the insects' olfactory system. Here, we aimed at addressing the question whether OBPs highly enriched in the antennae of the southern house mosquito, Culex quinquefasciatus, contribute at least in part to the selective reception of physiologically relevant compounds. Using a fluorescence reporter and a panel of 34 compounds, including oviposition attractants, human-derived attractants, and repellents, we measured binding affinities of CquiOBP1, CquiOBP2, and CquiOBP5. Based on dissociation constants, we surmised that CquiOBP2 is a carrier for the oviposition attractant skatole, whereas CquiOBP1 and CquiOBP5 might transport the oviposition pheromone MOP, a human-derived attractant nonanal, and the insect repellent picardin. Binding of these three ligands to CquiOBP1 was further analyzed by examining the influence of pH on apparent affinity as well as by docking these three ligands into CquiOBP1. Our findings suggest that CquiOBP1 might discriminate MOP from nonanal/picaridin on the basis of the midpoint transition of a pH-dependence conformational change, and that MOP is better accommodated in the binding cavity than the other two ligands. These findings, along with previous experimental evidence suggesting that CquiOBP1 does not detect nonanal in vivo, suggest that OBP selectivity may not be clearly manifested in their dissociation constants.
与人类不同，昆虫在生存和繁殖过程中严重依赖于灵敏的嗅觉系统。两种主要的嗅觉蛋白，即气味结合蛋白（OBP）和气味受体（OR），可能有助于昆虫嗅觉系统的选择性和敏感性。在这里，我们旨在探讨以下问题：在南方家蚊（Culex quinquefasciatus）的触角中高度富集的 OBPs 是否至少部分有助于对生理相关化合物的选择性接收。使用荧光报告基因和包含产卵引诱剂、人类来源引诱剂和驱避剂的 34 种化合物的面板，我们测量了 CquiOBP1、CquiOBP2 和 CquiOBP5 的结合亲和力。根据解离常数，我们推测 CquiOBP2 是产卵引诱剂 skatole 的载体，而 CquiOBP1 和 CquiOBP5 可能运输产卵信息素 MOP、人类来源引诱剂壬醛和昆虫驱避剂 picardin。通过检查 pH 值对表观亲和力的影响以及将这三种配体对接入 CquiOBP1，进一步分析了这三种配体与 CquiOBP1 的结合。我们的研究结果表明，CquiOBP1 可能基于 pH 依赖性构象变化的中点转变来区分 MOP 与非醛/picaridin，并且 MOP 比其他两种配体更好地适应结合腔。这些发现，以及先前的实验证据表明 CquiOBP1 在体内无法检测到非醛，表明 OBP 的选择性可能不会在其解离常数中明显体现。
