Loveridge Kade M, Sigala Paul A
Department of Biochemistry, University of Utah School of Medicine, Salt Lake City, UT, United States.
bioRxiv. 2024 Jun 10:2024.05.10.587216. doi: 10.1101/2024.05.10.587216.
malaria parasites invade and multiply inside red blood cells (RBCs), the most iron-rich compartment in humans. Like all cells, requires nutritional iron to support essential metabolic pathways, but the critical mechanisms of iron acquisition and trafficking during RBC infection have remained obscure. Parasites internalize and liberate massive amounts of heme during large-scale digestion of RBC hemoglobin within an acidic food vacuole (FV) but lack a heme oxygenase to release porphyrin-bound iron. Although most FV heme is sequestered into inert hemozoin crystals, prior studies indicate that trace heme escapes biomineralization and is susceptible to non-enzymatic degradation within the oxidizing FV environment to release labile iron. Parasites retain a homolog of divalent metal transporter 1 (DMT1), a known mammalian iron transporter, but its role in iron acquisition has not been tested. Our phylogenetic studies indicate that DMT1 (PfDMT1) retains conserved molecular features critical for metal transport. We localized this protein to the FV membrane and defined its orientation in an export-competent topology. Conditional knockdown of PfDMT1 expression is lethal to parasites, which display broad cellular defects in iron-dependent functions, including impaired apicoplast biogenesis and mitochondrial polarization. Parasites are selectively rescued from partial PfDMT1 knockdown by supplementation with exogenous iron, but not other metals. These results support a cellular paradigm whereby PfDMT1 is the molecular gatekeeper to essential iron acquisition by blood-stage malaria parasites and suggest that therapeutic targeting of PfDMT1 may be a potent antimalarial strategy.
疟原虫在红细胞（RBCs）内侵入并繁殖，红细胞是人体中铁含量最丰富的区室。与所有细胞一样，疟原虫需要营养性铁来支持基本的代谢途径，但在红细胞感染期间铁获取和运输的关键机制仍不清楚。疟原虫在酸性食物泡（FV）内大规模消化红细胞血红蛋白的过程中内化并释放大量血红素，但缺乏血红素加氧酶来释放与卟啉结合的铁。尽管大多数食物泡血红素被隔离成惰性疟色素晶体，但先前的研究表明，微量血红素会逃避生物矿化，并且在氧化性食物泡环境中易受非酶降解，从而释放不稳定的铁。疟原虫保留了二价金属转运蛋白1（DMT1）的同源物，DMT1是一种已知的哺乳动物铁转运蛋白，但其在疟原虫铁获取中的作用尚未得到验证。我们的系统发育研究表明，疟原虫DMT1（PfDMT1）保留了对金属转运至关重要的保守分子特征。我们将该蛋白定位到食物泡膜，并确定了其在具有输出能力的拓扑结构中的方向。有条件地敲低PfDMT1的表达对疟原虫是致命的，疟原虫在铁依赖性功能中表现出广泛的细胞缺陷，包括顶质体生物发生受损和线粒体极化。通过补充外源性铁而不是其他金属，可以选择性地挽救部分PfDMT1敲低的疟原虫。这些结果支持了一种细胞模式，即PfDMT1是血液期疟原虫获取必需铁的分子守门人，并表明对PfDMT1进行治疗靶向可能是一种有效的抗疟策略。
