Das T, Alabi I, Colley M, Yan F, Griffith W, Bach S, Weintraub S T, Renthal R
Department of Biology, University of Texas at San Antonio, San Antonio, TX, USA.
Department of Chemistry, University of Texas at San Antonio, San Antonio, TX, USA.
Insect Mol Biol. 2018 Aug;27(4):505-511. doi: 10.1111/imb.12388. Epub 2018 Apr 15.
Proteins in the venom of the fire ant Solenopsis invicta have been suggested to function in pheromone binding. Venom from queens and workers contains different isoforms of these proteins, consistent with the differing pheromones they secrete, but questions remain about the venom protein composition and glandular source. We found that the queen venom contains a previously uncharacterized pheromone-binding protein paralogue known as Sol i 2X1. Using imaging mass spectrometry, we located the main venom proteins in the poison sac, implying that pheromones might have to compete with venom alkaloids for binding. Using the known structure of the worker venom protein Sol i 2w, we generated three-dimensional homology models of the worker venom protein Sol i 4.02, and of the two main venom proteins in queens and female alates, Sol i 2q and Sol i 2X1. Surprisingly, the models show that the proteins have relatively small internal hydrophobic binding pockets that are blocked by about 10 amino acids of the C-terminal region. For these proteins to function as carriers of hydrophobic ligands, a conformational change would be required to displace the C-terminal region, somewhat like the mechanism known to occur in the silk moth pheromone-binding protein.
火蚁（红火蚁）毒液中的蛋白质被认为具有信息素结合功能。蚁后和工蚁的毒液含有这些蛋白质的不同亚型，这与它们分泌的不同信息素相一致，但毒液蛋白质的组成和腺体来源仍存在疑问。我们发现蚁后毒液中含有一种以前未被鉴定的信息素结合蛋白旁系同源物，称为Sol i 2X1。利用成像质谱技术，我们确定了毒囊中主要的毒液蛋白，这意味着信息素可能必须与毒液生物碱竞争结合。利用已知的工蚁毒液蛋白Sol i 2w的结构，我们构建了工蚁毒液蛋白Sol i 4.02以及蚁后和雌性有翅蚁两种主要毒液蛋白Sol i 2q和Sol i 2X1的三维同源模型。令人惊讶的是，模型显示这些蛋白质具有相对较小的内部疏水结合口袋，这些口袋被C末端区域的大约10个氨基酸所阻断。为了使这些蛋白质作为疏水配体的载体发挥作用，需要发生构象变化以取代C末端区域，这有点类似于已知在蚕蛾信息素结合蛋白中发生的机制。
