HRP2 Mediated Hemozoin Formation in P.falciparum

描述(申请人提供)：疟疾寄生虫恶性疟原虫能降解宿主细胞的血红蛋白，作为其中间代谢的一部分。在血红蛋白的蛋白质分解过程中释放出的细胞毒性游离的血红素被聚合成一种不溶的结晶物质，称为血球蛋白。血球蛋白的形成被认为是由富含组氨酸的蛋白2(PfHRP2)介导的，PfHRP2是一种30 kDa的蛋白质，由几个HHAHHAADA重复序列组成，这两个重复序列都存在于恶性疟原虫的食物液泡(发生血红素蛋白分解的地方)中，并被认为与游离的血红素结合。然而，PfHRP2如何有助于血红素聚合的分子细节仍不清楚。最近的研究表明，PfHRP2能够与大量的血红素分子结合，提示与血红素结合后，PfHRP2可能形成具有3(10)-螺旋二级结构的二聚体。为了进一步研究PfHRP2介导的血红素聚合模型，将用C(α)-甲基取代氨基酸合成PfHRP2的重复序列，这将迫使多肽形成3(10)-螺旋构象。我们将使用核磁共振、红外和圆二色谱研究该模型PfHRP2多肽的结构，然后使用电子吸收光谱、共振拉曼光谱、电子顺磁共振和停流光谱研究其与血红素的结合特性。这些研究提供了一个有趣的蛋白质靶点，可能为血球蛋白的形成机制和PfHRP2在这一过程中的作用提供分子线索。疟疾病理学方面的这些经验教训应该对合理设计新的抗疟疾药物具有重要意义。

DESCRIPTION (provided by applicant): The malaria parasite Plasmodium falciparum degrades host cell hemoglobin as a part of its intermediary metabolism. The cytotoxic free heme liberated during proteolysis of hemoglobin is polymerized into an insoluble crystalline material termed hemozoin. Hemozoin formation is proposed to be mediated by histidine-rich protein 2 (PfHRP2), a 30 kDa protein made up of several HHAHHAADA repeats that has both been found inside P. falciparum's food vacuole (where proteolysis of heme takes place) and is known to bind free heme. The molecular details of how PfHRP2 may aid in heme polymerization remain unknown, however. Recent studies have revealed that PfHRP2 is capable of binding an extraordinary number of heme molecules and it is suggested that upon heme binding, PfHRP2 may form dimers with 3(10)-helical secondary structure. To investigate this PfHRP2-mediated heme polymerization model further, the repeat sequence of PfHRP2 will be synthesized using C(alpha)-methyl substituted amino acids, which should force the peptide into a 3(10)-helical conformation. The structure of this model PfHRP2 peptide will be studied using NMR, IR, and CD spectroscopies and the heme binding properties will then be studied using electronic absorption spectroscopy, resonance Raman, EPR, and stopped-flow spectroscopies. These studies provide an interesting protein target that may lend molecular clues to the mechanism of hemozoin formation and the role of PfHRP2 in this process. These lessons in the pathology of malaria ought to have important implications in the rational design of novel antimalarial drugs.