Pandey Amit V, Babbarwal Vinod K, Okoyeh Jude N, Joshi Ratan M, Puri Sunil K, Singh Ram L, Chauhan Virander S
Department of Pediatrics, University of California San Francisco, San Francisco, CA 94143-0978, USA.
Biochem Biophys Res Commun. 2003 Sep 5;308(4):736-43. doi: 10.1016/s0006-291x(03)01465-7.
Major blood stage antimalarial drugs like chloroquine and artemisinin target the heme detoxification process of the malaria parasite. Hemozoin formation reactions in vitro using the Plasmodium falciparum histidine-rich protein-2 (Pfhrp-2), lipids, and auto-catalysis are slow and could not explain the speed of detoxification needed for parasite survival. Here, we show that malarial hemozoin formation is a coordinated two component process involving both lipids and histidine-rich proteins. Hemozoin formation efficiency in vitro is 1-2% with Pfhrp-2 and 0.25-0.5% with lipids. We added lipids after 9h in a 12h Pfhrp-2 mediated reaction that resulted in sixfold increase in hemozoin formation. However, a lipid mediated reaction in which Pfhrp-2 was added after 9h produced only twofold increase in hemozoin production compared to the reaction with Pfhrp-2 alone. Synthetic peptides corresponding to the Pfhrp-2 heme binding sequences, based on repeats of AHHAAD, neither alone nor in combination with lipids were able to generate hemozoin in vitro. These results indicate that hemozoin formation in malaria parasite involves both the lipids and the scaffolding proteins. Histidine-rich proteins might facilitate hemozoin formation by binding with a large number of heme molecules, and facilitating the dimer formation involving iron-carboxylate bond between two heme molecules, and lipids may then subsequently assist the mechanism of long chain formation, held together by hydrogen bonds or through extensive networking of hydrogen bonds.
像氯喹和青蒿素这样的主要血液阶段抗疟药物作用于疟原虫的血红素解毒过程。使用恶性疟原虫富含组氨酸的蛋白质-2（Pfhrp-2）、脂质和自催化在体外进行的疟色素形成反应很慢，无法解释疟原虫生存所需的解毒速度。在此，我们表明疟原虫的疟色素形成是一个涉及脂质和富含组氨酸蛋白质的协调双组分过程。在体外，使用Pfhrp-2时疟色素形成效率为1%-2%，使用脂质时为0.25%-0.5%。在由Pfhrp-2介导的12小时反应的9小时后添加脂质，导致疟色素形成增加了六倍。然而，在脂质介导的反应中，在9小时后添加Pfhrp-2，与仅使用Pfhrp-2的反应相比，疟色素产量仅增加了两倍。基于AHHAAD重复序列的与Pfhrp-2血红素结合序列相对应的合成肽，单独或与脂质组合都无法在体外产生疟色素。这些结果表明疟原虫中的疟色素形成涉及脂质和支架蛋白。富含组氨酸的蛋白质可能通过与大量血红素分子结合，并促进涉及两个血红素分子之间铁羧酸盐键的二聚体形成来促进疟色素形成，然后脂质可能随后协助由氢键或通过广泛的氢键网络维系的长链形成机制。
