HRP2 Mediated Hemozoin Formation in P.falciparum

描述（由申请人提供）：疟疾寄生虫恶性疟原虫（Plasmodium falciparum）降解宿主细胞血红蛋白作为其中间代谢的一部分。在血红蛋白蛋白水解过程中释放的细胞毒性游离血红素被聚合成一种称为血色素的不溶性结晶物质。血红素的形成被认为是由富组氨酸蛋白2 （PfHRP2）介导的，这是一种30 kDa的蛋白，由几个HHAHHAADA重复序列组成，都存在于恶性疟原虫的食物液泡中（发生血红素蛋白水解的地方），并且已知能结合游离血红素。然而，PfHRP2如何帮助血红素聚合的分子细节仍然未知。最近的研究表明，PfHRP2能够结合大量的血红素分子，并提示在与血红素结合后，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，将使用C(α)-甲基取代氨基酸合成PfHRP2的重复序列，这将迫使肽形成3(10)-螺旋构象。该模型PfHRP2肽的结构将使用核磁共振、红外和CD光谱进行研究，然后使用电子吸收光谱、共振拉曼光谱、EPR和停流光谱研究血红素结合特性。这些研究提供了一个有趣的蛋白靶点，可能为血色素蛋白形成机制和PfHRP2在这一过程中的作用提供分子线索。疟疾病理学的这些经验教训应该对合理设计新型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.