Fatty Acid Biosynthesis in Cryptosporidium parvum

描述（由申请人提供）：小隐孢子虫是一种单细胞病原体，可引起人类和动物严重的水样腹泻。这种病原体可引起艾滋病患者的一种机会性感染，目前尚无完全有效的治疗方法。隐孢子虫也是一种重要的水和食源性病原体，在美国国立卫生研究院生物防御研究计划中被列为B类优先病原体之一。抗隐孢子虫病化疗进展缓慢主要是由于对这种寄生虫的基本代谢途径了解不足。在其他顶复合体中发现的许多明确的或有希望的药物靶点在小梭菌中要么不存在，要么高度分化。因此，需要对其独特的代谢途径进行详细的分子和功能研究，以了解和控制这种寄生虫。脂肪酸是所有细胞的基本成分之一。我们率先开展了小弧菌脂肪酸合成的研究。我们目前的数据显示，细小C. parvum与其他顶复合体的不同之处是缺乏II型FAS及其相关的顶质体，并依赖于三种不同的途径（即I型模块化脂肪酸合成酶（CpFAS1），聚酮合成酶（CpPKS1）和长链脂肪酸酰基延长酶（CpLCE1））来延长脂肪酸。此外，我们已经确定了推定的主要成分，构成高度流线型脂肪酸代谢在小弧菌。这些进展现在使我们能够合理地详细剖析小弧菌脂肪酸代谢的功能。我们的长期目标是描述构成小弧菌脂肪酸代谢的主要成分的功能，并探索这一途径作为合理的药物靶点。我们的假设是，参与小弧菌脂肪酸代谢的主要酶在结构和功能水平上与人类和动物的对应酶不同，可能是合理的药物靶点。在本研究中，我们将通过以下三个具体目标来研究不同机制控制的脂肪酸延伸和激活：1)通过CpFAS1， CpPKS1和膜相关脂肪酸延伸酶的功能分析来描述控制寄生虫脂肪酸合成的分子机制。2)通过对酰基辅酶a合成酶和脂肪酰基辅酶a结合蛋白的功能分析，阐明脂肪酸活化和转运的分子机制。3)通过发现选择性抑制隐孢子虫脂肪酸代谢酶的抑制剂，验证脂肪酸代谢酶可能作为隐孢子虫的合理药物靶点。

DESCRIPTION (provided by applicant): Cryptosporidium parvum is a unicellular pathogen that can cause severe watery diarrhea in humans and animals. This pathogen can cause one of the opportunistic infections in AIDS patients for which no complete effective treatment is yet available. Cryptosporidium is also a significant water- and food-borne pathogen, and listed as one of the Category B priority pathogens in the NIH biodefense research program. The slow development of anti-cryptosporidiosis chemotherapy is primarily due to the poor understanding on the basic metabolic pathways in this parasite. Many well-defined or promising drug targets found in other apicomplexans are either absent or highly divergent in C. parvum. Therefore, detailed molecular and functional studies on the unique C. parvum metabolic pathways are needed for the understanding and control of this parasite. Fatty acids are one of the essential components in all cells. We have pioneered the research on the fatty acid synthesis in C. parvum. Our current data have revealed that C. parvum differs from other apicomplexans by lacking Type II FAS and its associated apicoplast, and relying on three distinct pathway for elongating fatty acids (i.e. a Type I modular fatty acid synthase (CpFAS1), a polyketide synthase (CpPKS1), and a long chain fatty acyl elongase (CpLCE1). In addition, we have identified putative major components that constitute the highly streamlined fatty acid metabolism in C. parvum. These advances now allow us to rationally dissect the function of C. parvum fatty acid metabolism in detail. Our long-term goal is to delineate the function(s) of major components constituting the fatty acid metabolism in C. parvum and to explore this pathway as a rational drug target. Our hypothesis is that major enzymes involved in the C. parvum fatty acid metabolism differ from their counterparts in humans and animals at both structural and functional levels, and may serve as rational drug targets. In this proposal, we will focus on studying different mechanisms governing fatty acid elongation and activation in C. parvum by achieving the following three specific aims: 1) To delineate the molecular machineries governing the fatty acid synthesis in the parasite by functional analyses of CpFAS1, CpPKS1 and a membrane-associated fatty acid elongase. 2) To elucidate the molecular mechanisms involved in the activation and transporting of fatty acids by functional analyses of acyl-CoA synthases and fatty acyl-CoA binding protein. 3) To validate that fatty acid metabolic enzymes may serve as rational drug target in Cryptosporidium by discovering inhibitors selectively against, parasite fatty acid metabolic enzymes.