Digestive vacuole membrane in Plasmodium falciparum-infected erythrocytes: relevance to templated nucleation of hemozoin.
Crystallization of the malaria pigment hemozoin sequesters the toxic heme byproduct of hemoglobin digestion in Plasmodium -infected red blood cells (RBCs). Recently, we applied electron and X-ray imaging and diffraction methods to elucidate this process. We observed crystals oriented with their {100} faces at the inner membrane surface of the digestive vacuole (DV) of Plasmodium falciparum in parasitized RBCs. Modeling of the soft X-ray tomographic (SXT) images of a trophozoite-stage parasite indicated a 4-16 nm DV membrane thickness, suggesting a possible role for lipid multilayers. Here, we reanalyzed the trophozoite SXT images quantitatively via X-ray absorption to map the DV membrane thickness. Making use of the chemical structure and crystal density of the lipid, we found, predominantly, a bilayer 4.2 nm thick, and the remainder was interpreted as patches ∼8 nm thick. Image analysis of electron micrographs also yielded a 4-5 nm DV membrane thickness. The DV lipid membrane is thus mainly a bilayer, so induced hemozoin nucleation occurs primarily via the inner of the membrane's two leaflets. We argue that such a leaflet embodying mono- and di-acyl lipids with appropriate OH or NH bearing head groups may catalyse hemozoin nucleation by stereochemical and lattice match to the {100} crystal face, involving a two-dimensional nucleation aggregate of ∼100 molecules.
Department of Materials and Interfaces, Weizmann Institute of Science , Rehovot 76100, Israel.
Sergey
S
Kapishnikov
Allon
A
Weiner
Eyal
E
Shimoni
Gerd
G
Schneider
Michael
M
Elbaum
Leslie
L
Leiserowitz
D004912:Erythrocytes / Q000378:metabolism* / Q000382:microbiology; D006420:Hemeproteins / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D007425:Intracellular Membranes / Q000737:chemistry / Q000378:metabolism* / Q000382:microbiology; D010963:Plasmodium falciparum / Q000378:metabolism*; D014617:Vacuoles / Q000737:chemistry / Q000378:metabolism* / Q000382:microbiology
D006420:Hemeproteins; C020753:hemozoin