The Steric Fine Structure of Maurer's Cleft in “Unroofed” Plasmodium Falciparum-Infected Erythrocytes

Abstract

Plasmodium falciparum produces additional membrane systems, Maurer's cleft (MC) and tubulovesicular network (TVN), in the host erythrocytes. The parasites use these membrane compartments to transport proteins to the surface of erythrocytes. Previous studies reported the structure of MCs by transmission electron microscopy (TEM) using ultra-thin layer specimen and suggested physical connections between MCs and erythrocyte membrane via an extension of MC membrane. However, fine structures of MC including filamentous extensions smaller than the thickness of diamond knives were likely missing in the TEM images. To obtain intact structural information of MCs, we used unroofing/rip-off technique for both normal- and parasitized-erythrocytes and successfully captured accurate oval/global shape of MCs with elongated-fine filamentous extensions (diameters <10 nm). We also treated parasitized erythrocyte with aluminum tetrafluoride, which are known to inhibit intracellular vesicle transport, to clarify if the oval/global structures are MCs. In the presence of aluminum tetrafluoride, the vesicle was no longer observed in parasitized erythrocytes. This result was in agreement with the previous study (Trelka DP, et al., Mol Biochem Parasitol, 2000), demonstrating the oval/global structures are MCs which extends filaments to host erythrocyte membrane. Our EM images demonstrated that MCs in P. falciparum-infected erythrocyte involve fine filaments reaching erythrocyte membrane which may provide a direct transport pathway for their proteins to the surface of erythrocytes.