Malaria is a potentially fatal infectious disease caused by the obligate intracellular parasite Plasmodium falciparum. The parasite infects human red blood cells (RBC) and derives nutrition by catabolism of hemoglobin. As amino acids are assimilated from the protein component, the toxic heme is released. Molecular heme is detoxified by rapid sequestration to physiologically insoluble hemozoin crystals within the parasite's digestive vacuole (DV). Common antimalarial drugs interfere with this crystallization process, leaving the parasites vulnerable to the by-product of their own metabolism. A fundamental debate with important implications on drug mechanism regards the chemical environment of crystallization in situ, whether aqueous or lipid. This issue had been addressed previously by cryogenic soft X-ray tomography. We employ cryo-scanning transmission electron tomography (CSTET) to probe parasite cells throughout the life cycle in a fully hydrated, vitrified state at higher resolution. During the acquisition of CSTET data, Bragg diffraction from the hemozoin provides a uniquely clear view of the crystal boundary at nanometer resolution. No intermediate medium, such as a lipid coating or shroud, could be detected surrounding the crystals. The present study describes a unique application of CSTET in the study of malaria. The findings can be extended to evaluate new drug candidates affecting hemozoin crystal growth.
Bibliographical noteFunding Information:
DM acknowledges the kind assistance of members of the NRR lab, particularly Anna Rivkin, Yifat Ofir-Birin, and Paula Abou Karam, for assistance with parasite culture and handling. Panels of Fig. 1, 2 and contents entry graphics were created using BioRender.com. This work was supported in part by research grants from the Minerva Research Foundation, the Israel Science Foundation (grant no. 1696/18), and the Estate of David Levinson. Participation of RD was supported by Israel Science Foundation grant no. 1523/18, the Ministry of Science and Technology grant no. 103240 and by the United States-Israel Binational Science Foundation (BSF) grant no. 2019236. RD is also supported by the Dr Louis M. Leland and Ruth M. Leland Chair in Infectious Diseases. ME is the Head of the Irving and Cherna Moskowitz Center for Nano and Bionano Imaging and incumbent of the Sam and Ayala Zacks Professorial Chair in Chemistry.
© 2022 The Royal Society of Chemistry.