PDF(Pubmed)
Abstract：
The human malaria parasite Plasmodium falciparum requires exogenous fatty acids to support its growth during the pathogenic, asexual erythrocytic stage. Host serum lysophosphatidylcholine (LPC) is a significant fatty acid source, yet the metabolic processes responsible for the liberation of free fatty acids from exogenous LPC are unknown. Using an assay for LPC hydrolysis in P. falciparum-infected erythrocytes, we have identified small-molecule inhibitors of key in situ lysophospholipase activities. Competitive activity-based profiling and generation of a panel of single-to-quadruple knockout parasite lines revealed that two enzymes of the serine hydrolase superfamily, termed exported lipase (XL) 2 and exported lipase homolog (XLH) 4, constitute the dominant lysophospholipase activities in parasite-infected erythrocytes. The parasite ensures efficient exogenous LPC hydrolysis by directing these two enzymes to distinct locations: XL2 is exported to the erythrocyte, while XLH4 is retained within the parasite. While XL2 and XLH4 were individually dispensable with little effect on LPC hydrolysis in situ, loss of both enzymes resulted in a strong reduction in fatty acid scavenging from LPC, hyperproduction of phosphatidylcholine, and an enhanced sensitivity to LPC toxicity. Notably, growth of XL/XLH-deficient parasites was severely impaired when cultured in media containing LPC as the sole exogenous fatty acid source. Furthermore, when XL2 and XLH4 activities were ablated by genetic or pharmacologic means, parasites were unable to proliferate in human serum, a physiologically relevant fatty acid source, revealing the essentiality of LPC hydrolysis in the host environment and its potential as a target for anti-malarial therapy.
摘要：
人类疟原虫恶性疟原虫在致病过程中需要外源脂肪酸来支持其生长，无性红细胞期。宿主血清溶血磷脂酰胆碱(LPC)是一种重要的脂肪酸来源,然而，负责从外源LPC释放游离脂肪酸的代谢过程是未知的。在恶性疟原虫感染的红细胞中使用LPC水解测定法，我们已经确定了关键原位溶血磷脂酶活性的小分子抑制剂。基于竞争性活性的分析和一组单到四重敲除寄生虫系的产生表明，丝氨酸水解酶超家族的两种酶，称为出口脂肪酶（XL）2和出口脂肪酶同源物（XLH）4，构成了寄生虫感染的红细胞中主要的溶血磷脂酶活性。寄生虫通过将这两种酶引导到不同的位置来确保有效的外源LPC水解：XL2输出到红细胞，而XLH4保留在寄生虫内。虽然XL2和XLH4单独可有可无，对LPC原位水解影响很小，两种酶的丢失导致LPC中脂肪酸清除的强烈减少，磷脂酰胆碱的过度生产，和增强对LPC毒性的敏感性。值得注意的是,当在含有LPC作为唯一外源脂肪酸来源的培养基中培养时,XL/XLH缺陷型寄生虫的生长受到严重损害。此外，当XL2和XLH4活性通过遗传或药理学手段消融时，寄生虫不能在人血清中增殖,生理上相关的脂肪酸来源，揭示LPC水解在宿主环境中的重要性及其作为抗疟疾治疗靶标的潜力。
