A disrupted transsulphuration pathway results in accumulation of redox metabolites and induction of gametocytogenesis in malaria
A disrupted transsulphuration pathway results in accumulation of redox metabolites and induction of gametocytogenesis in malaria
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DOI：
10.1038/srep40213
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发表时间：
2017-01-16
影响因子：
4.6
通讯作者：
Tatu, Utpal
中科院分区：
文献类型：
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作者：
Beri, Divya;Balan, Balu;Tatu, Utpal
已知疟疾寄生虫在红细胞内的生长会引起氧化还原应激。除了产生活性氧物种(ROS)的血红素降解外，这种寄生虫还被认为可以外流氧化还原活性的同型半胱氨酸。为了了解同型半胱氨酸积累的基础，我们研究了寄生虫中的反硫化(TS)途径，该途径在高等真核生物中将同型半胱氨酸转化为半胱氨酸。我们的生物信息学分析表明，寄生虫中缺乏半胱氨酸生物合成的关键酶，即胱硫醚-β-合成酶和胱硫醚-伽马裂解酶。利用质谱仪，我们证实了同型半胱氨酸的酶促转化所形成的胱硫氨酸的缺失，从而证实了TS途径的截断。我们还定量了感染红细胞及其废液中谷胱甘肽和同型半胱氨酸的水平。我们的结果显示这些代谢物在细胞内和培养上清液中的水平增加。我们的结果为已知的疟疾高同型半胱氨酸血症的发生提供了机制基础。最重要的是，我们发现同型半胱氨酸诱导参与配子体发生的转录因子，即AP2-G，从而触发有性阶段的转换。我们在体外用恶性疟原虫培养证实了这一观察结果，并在疟疾小鼠模型中证实了这一点。我们的研究表明，同型半胱氨酸是配子体发生的潜在生理触发因素。
Intra-erythrocytic growth of malaria parasite is known to induce redox stress. In addition to haem degradation which generates reactive oxygen species (ROS), the parasite is also thought to efflux redox active homocysteine. To understand the basis underlying accumulation of homocysteine, we have examined the transsulphuration (TS) pathway in the parasite, which is known to convert homocysteine to cysteine in higher eukaryotes. Our bioinformatic analysis revealed absence of key enzymes in the biosynthesis of cysteine namely cystathionine-beta-synthase and cystathionine-gamma-lyase in the parasite. Using mass spectrometry, we confirmed the absence of cystathionine, which is formed by enzymatic conversion of homocysteine thereby confirming truncation of TS pathway. We also quantitated levels of glutathione and homocysteine in infected erythrocytes and its spent medium. Our results showed increase in levels of these metabolites intracellularly and in culture supernatants. Our results provide a mechanistic basis for the long-known occurrence of hyperhomocysteinemia in malaria. Most importantly we find that homocysteine induces the transcription factor implicated in gametocytogenesis namely AP2-G and consequently triggers sexual stage conversion. We confirmed this observation both in vitro using Plasmodium falciparum cultures, and in vivo in the mouse model of malaria. Our study implicates homocysteine as a potential physiological trigger of gametocytogenesis.