TRYPTOPHAN METABOLISM IN MOSQUITOES

蚊子是重要的疾病媒介，传播许多病毒、细菌和寄生虫病，如疟疾、登革热、黄热病和丝虫病。疟疾由感染疟原虫引起，是一种毁灭性的疾病，全世界有多达5亿人受到影响，每年有多达200万人死亡。抗药性寄生虫和抗药性蚊子媒介的发展迫切需要开发新的、创新的蚊子或寄生虫控制策略。破坏蚊子或疟疾寄生虫正常发育所必需的必要的生理生化过程是控制疟疾的一种方法。在埃及伊蚊体内发现了一种新的转氨酶，它特异性地将色氨酸氧化过程中形成的具有化学活性和潜在毒性的3-羟基犬尿氨酸转氨为稳定的黄原酸，这种酶在幼虫和成年雌性蚊子中受到严格调控，在吸血后活性很高。我们最近的数据显示，黄原酸还能刺激疟原虫的配子发生，提示这一途径可能在启动蚊媒中的疟原虫发育过程中发挥关键作用。这项研究的长期目标是全面了解蚊媒中该酶的调控途径和机制。本研究的具体目的是：(1)利用多种生化技术对蚊虫3-羟基犬尿氨酸转氨酶进行纯化和鉴定；(2)利用多种分子生物学技术对蚊虫发育过程中3-羟基犬尿氨酸转氨酶的遗传调控进行研究，包括构建蚊虫幼虫基因文库，从文库中分离3-羟基犬尿氨酸转氨酶基因，研究3-羟基犬尿氨酸转氨酶在蚊体发育过程中的基因表达；(3)研究3-羟基犬尿氨酸转氨酶在按蚊体内转化为黄原酸的途径。我们的假设是，这种转氨途径对蚊子的正常发育至关重要，也可能在刺激疟原虫发育方面发挥关键作用；因此，了解其调控机制可能会对未来通过创新的蚊子控制策略负面干扰媒介发展的努力产生重大影响，也可能为开发通过干扰蚊媒中疟原虫配子发生来控制疟疾寄生虫的新工具提供洞察力。

Mosquitoes are important disease vectors, responsible for transmission of numerous viral, bacterial and parasitic diseases, such as malaria, dengue fever, yellow fever, and filariasis. Malaria, caused by infection with species of Plasmodium, is a devastating, disease which affects up to 500 million people world-wide, killing as many as 2 million a year. The development of drug resistant parasites, and insecticide resistant mosquito vectors urgently demands that new and innovative mosquito or parasite control strategies be developed. Disruption of the required physio-biochemical processes that are necessary for the normal development of either mosquitoes or malaria parasites is one approach for malaria control. A novel transaminase that is specific for the transamination of a chemically reactive and potentially toxic 3-hydroxykynurenine, formed during tryptophan oxidation, to stable xanthurenic acid is identified in Aedes aegypti mosquitoes, and this enzyme is tightly regulated with high activity in larvae and adult females after a bloodmeal. Our recent data show that xanthurenic acid also stimulates gametogenesis of Plasmodium parasites, suggesting this pathway may play critical role in initiating Plasmodium development in mosquito vectors. The long term goal of this research is to achieve a full understanding of the pathways and mechanisms governing the regulation of this enzyme in mosquito vectors. The specific aims of the proposed research are (I) to purify and characterize the 3-hydroxykynurenine transaminase from mosquitoes by various biochemical techniques, (II) to initiate studies concerning the genetic regulation of this transaminase in mosquitoes during development with various molecular techniques, which includes preparation of a cDNA library from mosquito larvae, isolation of 3-hydroxykynurenine transaminase cDNA from the library, and study of gene expression of the 3-hydroxykynurenine transaminase in mosquitoes during development, and (III) to study the transamination pathway of 3-hydroxykynurenine to xanthurenic acid in Anopheles mosquitoes. Our hypotheses are that this transamination pathway is critical for the normal development of mosquitoes and also may play a critical role in stimulating Plasmodium development; consequently, understanding the mechanism controlling its regulation could have a significant impact on future efforts to negatively interfere with vector development through innovative mosquito control strategies and also may provide insight into developing novel tools for the control of malaria parasites by interrupting gametogenesis of Plasmodium in mosquito vectors.