Taman Amira, Ribeiro Paula
Institute of Parasitology, McGill University, Macdonald Campus, 21,111 Lakeshore Road, Sainte Anne de Bellevue, Quebec, Canada H9X 3V9.
Mol Biochem Parasitol. 2011 Mar;176(1):42-50. doi: 10.1016/j.molbiopara.2010.12.001. Epub 2010 Dec 14.
l-Glutamate is a major neurotransmitter of both vertebrates and invertebrates. Earlier studies have shown that glutamate stimulates neuromuscular activity in the bloodfluke, Schistosoma mansoni, but its mode of action is unknown. Here we describe a novel glutamate receptor in S. mansoni (SmGluR), the first of its kind to be identified in a parasitic flatworm. SmGluR belongs to the G protein-coupled receptor (GPCR) superfamily and is distantly related to metabotropic glutamate receptors from other species. The full-length receptor cDNA was cloned, stably expressed in HEK-293 cells and shown to be activated by glutamate, whereas aspartate and the glutamate derivative, gamma-aminobutyric acid (GABA) had no significant effect. Among the classical (mammalian) agonists and antagonists tested, only LY341495 was able to interact with the schistosome receptor, suggesting that the pharmacological profile of SmGluR is substantially different from that of receptors in the host. The presence of SmGluR in the parasite was verified by immunoprecipitation and Western blot analyses, using a specific peptide antibody. Confocal immunolocalization studies revealed that SmGluR is strongly expressed in the nervous system of adult worms and larvae. In the adults, the receptor was detected in the longitudinal nerve cords and cerebral commissures, as well as the peripheral nerve fibers and plexuses innervating the acetabulum and the somatic musculature. Outside the nervous system, SmGluR was detected along the length of the female reproductive system, including the oviduct, ootype and the uterus. A comparative expression analysis at the RNA level revealed that SmGluR is expressed at about the same level in cercaria and adult stages, as determined by quantitative reverse-transcription PCR. The results identify SmGluR as an important neuronal receptor and provide the first molecular evidence for a glutamate signaling system in schistosomes.
L-谷氨酸是脊椎动物和无脊椎动物的主要神经递质。早期研究表明，谷氨酸能刺激曼氏血吸虫的神经肌肉活动，但其作用方式尚不清楚。在此，我们描述了一种曼氏血吸虫中的新型谷氨酸受体（SmGluR），这是在寄生扁形虫中首次鉴定出的此类受体。SmGluR属于G蛋白偶联受体（GPCR）超家族，与其他物种的代谢型谷氨酸受体亲缘关系较远。全长受体cDNA被克隆出来，在HEK-293细胞中稳定表达，并显示能被谷氨酸激活，而天冬氨酸和谷氨酸衍生物γ-氨基丁酸（GABA）则无显著影响。在所测试的经典（哺乳动物）激动剂和拮抗剂中，只有LY341495能够与血吸虫受体相互作用，这表明SmGluR的药理学特征与宿主中的受体有很大不同。利用特异性肽抗体通过免疫沉淀和蛋白质印迹分析验证了寄生虫中SmGluR的存在。共聚焦免疫定位研究表明，SmGluR在成虫和幼虫的神经系统中强烈表达。在成虫中，该受体在纵神经索和脑连合中被检测到，以及支配吸盘和体壁肌肉的外周神经纤维和神经丛中也有。在神经系统之外，沿着雌性生殖系统的长度，包括输卵管、卵模和子宫，都检测到了SmGluR。在RNA水平上的比较表达分析表明，通过定量逆转录PCR测定，SmGluR在尾蚴和成虫阶段的表达水平大致相同。这些结果确定SmGluR为一种重要的神经元受体，并为血吸虫中的谷氨酸信号系统提供了首个分子证据。
